Sunday, December 13, 2009

Your typical Space Shuttle Mission Part 4: Getting back home (AKA Deorbit, Reentry, TAEM and Landing)

So, the shuttle blasts off, reaches orbit, and does its mission, be it working on a satellite, or going to the ISS to deliver parts, either for spare storage or for making the station bigger and more efficient, and to exchange crewmembers. Actually, to date, the last remaining shuttle missions will go to the ISS to resupply it and complete it. There will be no more crew rotations by the shuttle. Crew rotation is now the sole responsibility of the Russian Space Agency and their Soyuz spacecrafts.

So, finally, after a successful mission and the orbiter’s heat shield is cleared for reentry, the mission enters its deorbit preparations phase. Typically, this takes a day, done the day before scheduled deorbit. The astronauts check the flight control system, and makes a hot-fire test of the RCS thrusters, which are critical in controlling the shuttle’s attitude during most of reentry, at least before the airstream is thick enough to be able to use the aerosurfaces. Also, the RMS arm and the OBSS boom is stowed for landing, and the KU band antenna, responsible for high speed data transmissions between the ground, shuttle and station, is deactivated and stowed. Only the regular antennas are used for communications and telemetry.

Remember that NASA has 2 main landing sites and a backup landing site. The first main landing site, and the primary main landing site, is the Shuttle Landing Facility at Kennedy Space Center, Florida. The second, ‘backup’ main landing site is Edwards Air Force Base at California. The actual backup landing site, only used once in all of the space shuttle program, is the White Sands Testing Range in New Mexico.

Finally, the day has arrived. The crew wakes up and immediately jump into action for the return home. Let’s assume, as always, that the shuttle in question is Discovery, and that landing is possible at Kennedy.

DEORBIT PREPARATIONS

The start of the Deorbit Burn, in terms of the countdown to it, is called “Time of Ignition”, or TIG. With that in mind, we start our journey back home.

TIG-4 hours. Final Deorbit preparations start here.

The crew has been briefed about the weather conditions at the landing site, this time at Kennedy Space Center’s Shuttle Landing Facility. The crew executes an alignment of the Inertial Measurement Units used for guidance of the orbiter. They also activate systems that aren’t in use during the mission that support entry and landing operations.

Now, the commander’s and pilot’s seats cannot be removed, but the mission specialist seats, both in the flight deck and the mid-deck, are stowed to increase space within the orbiter (it gets kinda cramped with 6-7 people). At this time, the seats are installed back into their positions.

TIG-3 hours.

“Discovery, you have a Go for Payload Bay Door Closing.”

This means the crew can now close the payload bay doors. Now, the radiators on the doors were stowed before this. They were used to maintain correct thermal conditions for the orbiter’s systems during its mission. Well, how does it maintain it now that the doors will be closed?

Flash Evaporation, that’s what.

During launch, right around the point of SRB separation, the Flash Evaporator System activates and rejects heat from the coolant system by means of water boiling, all the way until the Payload Bay Doors are opened and the radiators are deployed, which take over. From radiator stowage until less than 100,000 feet in altitude, the Flash Evaporator System takes over once again. However, under 100,000 feet, water loses its efficiency to reject heat with this method. The Flash Evaporator switches to ammonia boiling to maintain temperatures until the shuttle lands and the ground cooling system is hooked up to it.

The crew had stowed the radiators, and checked that the flash evaporator system is working correctly, before Mission Control gives a Go for Payload Bay Doors closing. The crew does so, and the doors are closed.

TIG-2 1/2 hours. Roughly around this timeframe, another call is given from Houston.

“Discovery, Houston. You are Go for OPS-3".

The crew starts to set up the shuttle’s GPCs for the deorbit, entry and landing program, called OPS 3. Remember that OPS 1 controlled launch, ascent and stabilization of the orbit, and OPS 2 controlled everything during orbit? OPS 3 will bring them home. Since on-orbit operations isn’t as dynamic as a launch and a landing is, the backup computer, GPC 5, and normally one of the 4 main GPCs, is shut down. At this point, both are re-enabled and configured for OPS 3, and the program is loaded. Now, all GPCs are running on Major Mode OPS 301, the ‘coast to deorbit’ portion of the software. Shortly after, the Star Trackers, used for navigation, two small doors on the front of the orbiter, are closed and deactivated.

TIG-1 hour, 30 minutes. Starting with the Commander and Pilot, the crew begins to put on their bright orange Launch and Entry Suits, actually called the Advanced Crew Escape System. These suits provide them with their own pressurized oxygen supply in the event of cabin pressure loss, and are equipped with survival tools in case of a bailout, including, of course, a parachute and a life raft.

TIG-1 hour. Everyone is ready to get strapped into their seats. A call from Houston confirms that deorbit looks realistic.

“Discovery, Houston. You are go for fluid loading.”

This means that the crew must consume large amounts of liquid and salt tablets. This helps them to adapt better to gravity once they land. The liquids can be water or any kind of drink.

TIG-20 minutes.

The crew is strapped into their seats, and the landing team polls are made. The weather has been assessed, and everything looks great.

“Discovery, Houston. You are go for the deorbit burn.”

This call tells the crew that their trip home is sealed. The pilot and commander transition the GPCs to OPS 302, the “deorbit burn” mode, load the deorbit burn targets and execute the attitude adjustment. The shuttle then changes its attitude so that at the point of deorbit, the shuttle’s engines are aiming at the direction of travel, for the retrograde (backward firing) deorbit burn. The pilot executes the APU (auxiliary power unit) Prestart procedure, putting all 3 APUs ready to start. The APUs are critical to landing, since they will power the hydraulics needed to move the aerosurfaces needed for control of the shuttle in the atmosphere, and for lowering the landing gear for landing.

TIG-3 minutes. The pilot activates one of the 3 APUs needed for landing. Before actually committing the shuttle to reentering the atmosphere, it must be checked that at least one APU works and operates correctly. Only 1 APU is needed for a safe landing. The APU checks out perfectly. The OMS engines are armed, and Mission Control confirms that the shuttle has the correct configuration for the burn. The minutes become seconds, and…

3….2….1…

TIG. OMS Engine Ignition.

DEORBIT AND ENTRY INTERFACE

The deorbit burn commences, and the shuttle begins to slow down from its stable orbital speed as the twin OMS engines fire against the direction of travel. This burn is executed half a world away from the landing site, so that the perigee (lowest point of the orbit) is precisely there. The perigee is dropped all the way to ZERO miles during this burn, and even after that, the burn continues. The burn typically lasts around 3 minutes, depending on the orbit’s height. The commander and pilot see the displays as the burn timer ticks down to zero. After chopping off at least 200MPH off their ~17,500MPH speed, the OMS engines cut off, and they disable the OMS engines for good, as this was their very last job in the mission.

Discovery is now on a decaying orbit, its altitude slowly dropping. It is now committed to land, officially one hour away from landing, and roughly half an hour away from the Entry Interface, the next milestone in landing. Before hitting the atmosphere, the commander and pilot transition the computer to OPS 303, the “coast to EI” mode. At this point, they manually maneuver the shuttle to its correct reentry angle, where it will enter the atmosphere with the nose pitched 40 degrees upwards, the reentry angle of attack. It is done like this so the thermal protection system, the heat tiles, are the ones aiming at the airstream, and to bleed off its tremendous orbital speed by increasing drag.

Moments after they maneuver the shuttle to the correct attitude, the pilot activates the other APUs, and all 3 APUs are running. After that, they do a check of the aerosurfaces, mainly to prime them, to run warm hydraulic fluid through them. The engine nozzles are gimbaled (aimed) to prevent damage to them during reentry. Also, ALL of the Forward RCS fuel is dumped. This is done to prevent pollution of the air when the shuttle lands. The forward RCS jets, as you may have guessed, are not needed for reentry.

5 minutes before Entry Interface, the computers are transitioned to OPS 304, the “entry interface” mode. The shuttle is ready for reentry, and the GPCs assume automatic control of the descent.

Entry Interface begins roughly half an hour away from landing. As Discovery drops below 400,000 feet, it encounters the airstream, a bit at first, then slowly but steadily thickening. Soon, a halo of plasma covers the entire shuttle as friction of the shuttle against the thickening airstream increases. The shuttle is essentially a fireball at this point, streaking down and across the sky like a meteor. Temperatures from the friction can increase up to 2000 degrees Farenheit on the nosecap and wing leading edges at the point of Maximum Heating. The Thermal Protection System is designed to dissipate this tremendous heat and protect the shuttle from burning up.

Of course, Discovery is encountering the thickening airstream. It’s become a fireball. Thanks to the plasma generated by the superheated air coming off the shuttle’s belly from the effects of friction, there are no communications. Only NASA’s Deep Space Network, powered by their Tracking Data and Relay Satellites (TDRS), is still tracking Discovery. But something important is happening. The atmosphere is slowing Discovery down!! As the atmosphere thickens, it creates more and more of a stopping force for Discovery, braking it even further. The speed drops from 17,000MPH… to 16,000… to 14,000…. to 12,000….

However, the GPCs onboard Discovery know that if they maintain this course and angle of attack, by the time they reach a stable flying speed and altitude suitable for landing, they would have overshot the landing site by too many miles. You’re asking yourself, why did they deorbit so late then? This is done to allow a great margin of error to be able to reach the landing site with sufficient “energy” to land. If they deorbit too soon, they run the risk of running out of “energy” before reaching the landing site, and having the shuttle crash-land. They prefer to have the GPCs correct for this, rather than have no alternatives at all.

So, a few minutes into EI, the GPCs command the aft RCS yaw jets to force the shuttle into roughly an 80-degree bank to either left or right, depending on the trajectory. This is the first of 4 steep banks, and the first is known simply as a “roll”. For now, let’s say it did a left roll. By doing this steep bank, Discovery increases the drag effect, slowing down even further, getting rid of the excess “energy”.

Oh, the term “energy” is how fast and how high the shuttle is going. Of course, at launch, that energy is acquired as the shuttle reaches its orbital speed and altitude. So now it must get rid of this energy, and get rid of it just enough to be able to have the correct amount of “energy” at the point of reaching the landing site in order to land.

A few minutes after this first steep bank, the GPCs see that it is veering off course. Of course, banking to the left would have an effect sooner or later since the speed is steadily decreasing and the atmosphere is steadily thickening as it drops in altitude. So, the GPCs command the second steep bank, in the opposite direction of the first one. This is know as a “roll reversal”, since it is reversing itself from that previous roll. This allows the same drag effect as the first steep bank, but it is more of a course correction maneuver. When you see the ground track zoomed way out to thousands of miles, you notice that the track is a mega-stretched S due to these banks. It executes 2 more of these roll reversals later on during Entry Interface.

The plasma eventually gives way as the shuttle descends and slows down. Communications are regained and it is confirmed that the crew is doing well. The shuttle keeps doing its roll reversals to bleed off speed and altitude, aligning itself with the landing site. Soon it reaches Florida airspace, and comes within range of the Merrit Island Launch Area (MILA) tracking station (Merrit Island is the name of the island where Cape Canaveral and Kennedy Space Center are located).

As the shuttle slows down below 3 times the speed of sound, the commander deploys the air data probes. Two small doors open on each side of the orbiter, revealing air probes. These probes relay wind speed and direction to the commander and pilot during the landing phase.

By the time Discovery’s roughly 85 thousand feet high, and slowed down to MACH 2.5, which is 2 1/2 times the speed of sound, the pilot sets up for HAC interception and landing. At the landing site, they have what is called a “Microwave Beam Landing System”, or MBLS. This beams information to the shuttle about its position with relation to the runway, and helps guide the shuttle to the Heading Alignment Cylinder (cylinder, circle, whatever, those terms are used and are correct), and subsequently towards the runway. As soon as the shuttle comes within range of MILA’s MBLS, the crew engages the landing system.

And the shuttle keeps slowing down, this time with the aid of the speed brake in its tail. And finally, it reaches MACH 1 and goes under that.

TAEM, HAC, FINAL APPROACH AND LANDING

Several things occur when the shuttle hits MACH 1 as it slows down.

At this point, throughout Central Florida, especially at the Kennedy Space Center, 2 sonic booms sound in rapid succession. These sonic booms are the announcement that Discovery has arrived at the landing site. They’re pretty strong, especially if the proximity to the landing site is nearer. I’ve read somewhere that you hear 2 sonic booms instead of 1 because of the length of the orbiter as it breaks the sound barrier as it slows below the speed of sound, being considerably longer than those supersonic fighter jets.

Also, reaching MACH 1 automatically transitions the GPCs to mode OPS 305, the “TAEM” portion of OPS 3. The RCS jets that were still active at this point are finally cut off, as control passes completely to the aerosurfaces, now fully active. The commander switches from automatic control over to manual control, and begins piloting the shuttle. Discovery is, at this point, a heavy, unpowered, hi-tech glider. Some refer to the shuttle as a ‘brick’ at this point, as this is what it feels like to pilots to land it. The commander calls it out.

“Houston, Discovery. On Energy, approaching the HAC.”

“Copy. You’re Go for nominal chute deploy.”

Usually that call from Mission Control comes accompanied with a last-minute weather update concerning winds at the landing site, which the commander has to compensate for in the case of a crosswind. “Nominal chute deploy” means that they have to pop the drag chute upon MAIN GEAR touchdown, that is, the back tires. If the call had asked for a “late chute deploy”, the chute would be popped after NOSE GEAR touchdown

Also, when they say on energy, remember what I said about energy, about how high and fast they’re going? Now they have to manage it correctly in order to make it to the final approach with the correct altitude and speed. This is something commanders and pilots train for YEARS: landing the shuttle successfully in their first try… because that’s the only try they’ll ever get. Remember, the shuttle’s engines are useless, and the OMS engines only provide adequate thrust when in orbit (they take 3 minutes to change the shuttle’s speed by 200 MPH. Sports cars do better than that, and they’re on the ground), but are otherwise useless under the full influence of Earth’s gravity, much less the RCS jets. This is a one-shot deal. Fly in too low, and the shuttle crashlands before the runway. Fly in too high and too fast and you overshoot it and, of course, crashland. This is also one of the reasons why the runway at KSC is wider and longer than most regular airplane runways. So far, all 127 missions that have successfully completed their mission have landed successfully (STS-3 was a bit of a scare… maybe that’s why they created the drag chute? Search YouTube for the STS-3 landing). There have been 129 missions, but remember, 1 of them never even reached space (STS-51L Challenger), and the second didn’t even reach Kennedy (STS-107 Columbia)…

Thanks to the MBLS, GPSs onboard the shuttle, and the air probes, the commander and pilot have all the info they need right on their GPC displays and HUD (Heads Up Display, like them fighter jets). The GPC displays show their position with relation to the Heading Alignment Cylinder and the runway, range, direction of travel, and so forth. and the HUD, an even more important, if not the most important piece of equipment used for landing, shows altitude, speed, and most importantly, and thanks to the MBLS, a small diamond representing where the shuttle must be aiming at to successfully land with the correct amount of energy (speed, altitude).

The commander (and in a brief period of time, the pilot) guides the shuttle to the HAC. Once it reaches it, the shuttle begins its slow, wide, final turn into the final approach to the runway, still losing speed and altitude. Usually the turns are long. Let’s assume this is a 230 degree turn. It begins the turn, and the degree counter decreases. When it is just 180 degrees from facing the runway, Houston calls it.

“Discovery, on at the 180.”

They might accompany that with remarks to their speed and/or altitude. Another call comes up when there are just 90 degrees left in the turn.

“Discovery, on at the 90.”

And the turn progresses, and they still lose altitude, keeping speed stable, until…

“Houston, field in sight.”

The commander and pilot see the runway dead ahead as the come out of the turn, seeing the graphical overlay of the runway generated by the HUD (thanks to the MBLS down there) overlapping the actual runway, with a point generated roughly a mile in front and before the runway’s start. This is it.

The shuttle comes out of the HAC and into the final approach glideslope as it hits 10 thousand feet, at around 460MPH, its wings level and centered on the runway line. It’s called the final approach “glideslope” because, obviously, the shuttle is an unpowered glider and most importantly, the shuttle goes into an apparent dive here, as if going down a steep slope. It pitches its nose down to around 20 degrees, which, by airline standards, is a damn STEEP dive of an approach. Nearly 7 times steeper than the angle of an airliner approaching the runway, the commander pilots Discovery into this steep dive, aiming at the point generated by the HUD overlay. Discovery divebombs closer, dropping quickly in altitude and approaching the runway, as the pilot primes the landing gear. It is done like this to have the correct energy for landing, that is, the speed and the correct sink rate, or the rate in which the altitude drops at the moment of touchdown. Almost like seconds, the altitude goes 9000’… 8000’…. 7000’… 6… 5… …4… …3…

Discovery hits 2000’, roughly 400MPH. The commander pulls on the stick and the shuttle straightens up from the steep dive and raises the nose to 1.5 degrees, in what is called a “pre-flare” maneuver. This slows down the shuttle’s rate of descent and speed, converting all that accumulated energy from the dive into rising force with reduced speed, and just the right amount to carry Discovery over to the runway threshold. At this point, the shuttle hits 600’ in altitude, and the landing gear is commanded to lower. Doors below the left and right wing and the nose open up, and wheels come out, all 3 locking down in place in a matter of seconds.

As the shuttle reaches the runway threshold, hitting 600’ in altitude, the commander pulls more on the stick, performing what is called the “final flare”, increasing the shuttle’s rising force and further decreasing the speed. The orbiter’s sink rate is slowed down to a safe touch-down sink rate as the shuttle finally passes the runway threshold. If the speed is too high, the speed brake is used to compensate.

The landing gear lowers slowly… 50 feet… 40… 30… 20… 10…. 5…

The 2 wheels under the wings are the first to touchdown on the runway, at 230MPH. These are the “Main Gear”, which, of course, is why that is called “main gear touchdown”. As soon as that is confirmed, the pilot presses a couple of buttons which pop a door off on the back of the shuttle, at the base of its tail. This carries a drag chute that aids in braking Discovery to a halt into its open position, pulling back on Discovery and braking it. The nose of the shuttle slowly comes down until it also touches down on the runway, know as both WoW (weight on nose wheel… not world of warcraft) and “nose gear touchdown”. The shuttle keeps rolling on the runway, steering provided by the nose gear in case it needs to be centered. As soon as it slows to 70 MPH, the chute is released, as it loses its braking effectiveness, and also to avoid having it tangle up with the engine nozzles. By then, the commander and pilot are braking Discovery with actual brakes in the wheels. Soon, the speed is reduced to 0 and the shuttle comes to a complete stop. The commander calls it immediately.

“Houston, Discovery. Wheels stop.”

This marks the end of the mission. After this, the crew commences shutdown and safing of the shuttle. Meanwhile, outside, the landing convoy begins operation. Two men with an air probe are sent in pressure suits to detect any poisonous chemicals in the air around Discovery, before giving the go ahead for the convoy to move in and get the crew out of the shuttle. After the crew are given quick medical checks, they walk around the shuttle, a tradition in NASA, and they leave for their crew quarters to meet with their family. The ground crew assumes control of the shuttle, and they take it to the OPF.

And the cycle repeats. At least, in Atlantis’s case, as of this date, the turnover process it’s undergoing for mission STS-132 will be its last, as STS-132 is Atlantis’s last mission before it is to be decommissioned.

Now that you’ve read all this, look at the following video:

This was STS-128, Discovery, with a landing at Edwards AFB. This one called a late chute deploy.

Sunday, November 29, 2009

STS-129: IMHO Pretty much the coolest mission so far

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I have got to say, STS-129 went by so fast, so flawlessly, and so greatly. Several interesting things happened during the mission. And the crew was pretty funny too! And the most amazing thing is, there were no scrubs nor delays!!! Everything went right off on the first try!!!

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The two guys in front holding helmets are Commander Charlie “Scorch” Hobaugh to the left, and pilot Barry “Butch” Wilmore to the right. The 4 on the back, from left to right, is Mission Specialist #1 Leland Melvin (Astro_Flow on Twitter), Mission Specialist #3 Mike Foreman, Mission Specialist #4 Dr. Robert “Bobby” Satcher, and Mission Specialise #2 Randy “Komrade” Bresnik.

Here’s the full launch. Remember that it takes 8 minutes and 29 seconds from SRB ignition (T-0 seconds) for it to reach initial orbit and main engine cutoff. Once again, this is the first launch attempt, and they DID launch!

After MECO, the crew went to work, and after setting up the shuttle for on-orbit operations, went to sleep. On flight day 2, they begun some rendezvous burns to start catching up to the ISS, and in the meantime, checked out the Thermal Protection System with the OBSS. On flight day 3, they catched up to the ISS and performed their routine RPM, or rendezvous pitch maneuver. I found this video which sped up the RPM for our benefit (the backflip alone takes 9 whole minutes), and cuts to docking (after the RPM, the shuttle then travels forward and pitches up, getting in front of the station, its payload bay and docking port looking AT the station. That’s when docking starts).

(For those ppl not yet fully familiarized with the english (french?) vernacular, “rendezvous” is to meet, to catch up with someone or something. It’s used in NASA to point out that vehicle 1 is catching up to vehicle 2, and the point where the two finally meet is the rendezvous point. English pronunciation would be like “run, day, voo” all together. Spanish is like “rondeivu”.)

(for those people that seriously asked me what is vernacular… http://www.answers.com/topic/vernacular)

After 2 hours of leak checks to see if the docking system had a good airtight seal, hatches were opened and the crews greeted themselves like long lost friends.

After that, all 3 spacewalks and transfers went by like it was meant to be done perfectly. I won’t bore you with the details, but, MAN!

And the whole thing was done with the STS-129 crew cracking jokes at every possible moment, ever since launch day, up until landing. I laughed my head off several times. I was like, OMG he did not just say that during <extremely serious maneuver/procedure/etc>!!! :P

The only issue was an alarm going off in the ISS. Apparently it was a false alarm. And there was a problem with one of the spacewalkers’ drinking tube (they have a small tube close to their lips that they bite and suck fresh water from it while they’re outside of the station and in their spacesuits. remember they can be out there for 5 to 8 hours. one does get hungry and thirsty, but at least the thirsty part can be covered) which did delay them an hour. But in all 3 spacewalks, they were HOURS ahead of schedule!!! (which kinda negated that delay). They got a heck of a lot of get-ahead tasks. I think they even did something a future space shuttle crew had to do later on! Talk about efficiency!!! And for Satcher and Bresnik, it was their first spacewalk. Could have fooled me!!!

Randy Bresnik was supervising another launch of sorts from the ISS: his baby daughter Abigail Mae Bresnik was due to be born around the timeframe where he would be at the ISS. NASA went to great lengths to get private conferencing between him and his wife while he was up there. After the event, Bresnik thanked NASA for helping him with that, and a celebration was done in the ISS’s Harmony node, with Bresnik handing out pink cigars to every crewmember of ISS-21 and STS-129, sporting a black tee with the pink words “it’s a girl!”, and proudly displaying a pink onezie with the STS-129 patch on it.

Also, an actual ISS change of command was made while a shuttle crew, the STS-129 crew, was there (a first for the program), and they stood (floated) witness to the ceremony. Frank De Winne of the European Space Agency (ESA), Commander of Expedition 21 and first ISS commander from the ESA, handed over control of the ISS to Jeff Williams of NASA, now Commander of Expedition 22. Frank, Roman Romanenko of the Russian Federal Space Agency (RSA) and Bob Thirsk of the Canadian Space Agency (CSA) will soon leave the ISS as 3 other crew members, Oleg Kotov (RSA), Souichi Noguchi (Japanese Space Agency, JAXA), and Timothy Creamer (NASA). Also, Jeff Williams awarded Nicole Stott her gold Astronaut Wings. Let me remind you that Nicole Stott is the last ISS crewmember to be rotated in a space shuttle. They did this before Atlantis left so they could close the expedition with Nicole present, as a closure for her. When she leaves, crew rotations will be the sole responsibility of RSA until further notice.

After that, the crews said their goodbyes, “transferred” the final piece of cargo known as Nicole Stott to Atlantis and the crews closed hatches. Nicole Stott now is about to be on her way home.

And the day after… Atlantis undocks fro the ISS and pilot Barry “Butch” Wilmore executes the flyaround around the ISS, a maneuver known in NASA jargon as TORF (Twice Orbital Rate Flyaround).

After that, Atlantis burned its OMS engines for a few seconds, initiating the separation of Atlantis and the ISS. The STS-129 crew then made a final inspection of their TPS before calling it a day.

The day after, the crew did several preparations and checkouts prior to reentry. All these checks were successful, so Atlantis was cleared for reentry. The day after, everything went by flawlessly. The final preparations. The deorbit burn (the first attempt to Kennedy was a go!). The entry interface, the roll/roll reversals, and finally… TAEM, as depicted in the video below.

Hobaugh: Couldn’t have picked a clearer day!

Twin sonic booms were heard at 3:48 in the video, signaling the arrival of Atlantis at Kennedy. Slightly low on the Heading Alignment Cylinder turn, but all in all a perfect landing.

Man, I loved this mission! :P It was all to carry a new antenna assembly and 2 external logistics carriers (massive things) to support continued operation of the ISS after the shuttle retires. And of course to bring Nicole Stott back home, where she can finally have her Coke in a Styrofoam cup and a slice of New York style pizza. :P And a nice hot shower where water will actually go DOWN. :P

Oh, didn’t you know? Astronauts take sponge baths. There are no showers in space. Which is especially why a long duration (2 to 6 month stay) ISS crew member considers a hot shower “A LUXURY”.

LOL.

Great mission, fellas!

Computer problems :P

Actually, it was more of an upgrade, but I consider it a problem in that I forgot to backup what I had of my “reentry” blog entry. …oh well.. *starts to type again* It’ll just take a bit more.

Wednesday, October 14, 2009

Space Shuttle Abort Modes quickly explained

There are 2 categories of abort scenarios in the beginning of a shuttle flight, a pad abort, and an ascent abort.

PAD ABORT

A pad abort is precisely that, a launch abort that occurs while the shuttle is still firmly bolted down to the pad and SRB ignition hasn’t taken place. In any point of the countdown, an abort may occur, be it because of weather conditions or systems malfunction scrubbing the launch, or because the GLS (during the last 9 minutes of the count up until 31 seconds remaining) detected a fault and paused the countdown (or was commanded by a flight controller to do so), or because the RSLS gave a cutoff to the launch in between T-31 seconds and T-0.001 seconds (not kidding. These computers are precise!). Many missions have been scrubbed in many points in the countdown, particularly when tanking is about to occur, or during the Launch Status Check (go/nogo for launch) during the final 9-minute hold. But only 5 missions have had these aborts, and 4 of those have taken the crown for being the most stressful of all aborts: right between main engine start (T-6.6 seconds) and SRB ignition (T-0). Below is a video of all 5.

In most cases, the Redundant Set Launch Sequencer program on the shuttle’s onboard GPCs, gave the cutoff because one or two of the three main engines did not ignite. In other cases, it might have detected a leak within the engines, or a fault on a critical system. When the RSLS gives the cutoff, it is known as an RSLS abort. This abort is most stressful when the engines actually fired, be it one or 2 or all three and then it gets cut off. The shuttle starts to sway with the sudden thrust, and keeps swaying for a couple of minutes until all motion stops. The astronauts onboard know it is only 8 explosive bolts holding down all 4,400,000 pounds of the shuttle in its upright position via its SRBs. It is not a pretty scenario for them when suddenly the shuttle sways forward and back for a few minutes, straining against those bolts. Luckily, no one was hurt in these 5 aborts. Well, the first 4. The fifth never even got to fire the engines (cutoff was at T-7.5 seconds), so no swaying occurred. These missions were attempted later, and succeeded.

ASCENT ABORTS

From T-0 to MECO, there are different abort scenarios that can occur depending on the kind of failure and the altitude/speed/position of the shuttle. In this category, there are 2 subcategories, intact aborts and contingency aborts. In order to select an abort, when called to do so, the commander selects the abort mode in a rotary switch and presses the ABORT button to execute the selected abort. The shuttle then does a pre-programmed set of commands that will put it in the right path and configuration to that specific abort (accelerating remaining engines to max, dumping unnecessary fuel, reorienting the shuttle, releasing the external tank, etc.). This usually happens when an engine, or 2, or all 3 are lost, or a critical system malfunction occurs (life support, APUs, Fuel Cells, etc) during ascent. I will name them from most desirable to least desirable.

ATO: Abort To Orbit. This mode isn’t a real abort, as it actually makes the shuttle reach a lower than planned, but safe orbit, thus requiring just an OMS burn or 2 to raise the orbit to the right one so the mission can start. The moment when this abort becomes available is when CapCom says “Press to ATO”. (no, not the company that makes Street Fighter or Mega Man. This is the CAPsule COMmunicator, the guy whose job is to relay orders and info to the astronauts and receive replies by them. He is the only one who ever talks to the shuttle, and anything that must be told to the astronauts has to go through him. It’s usually an astronaut, because they believe an astronaut would convey info/orders in a way that the crew would understand, being an astronaut himself.)

AOA: Abort Once Around. This abort mode makes the shuttle make one complete orbit before reentering the atmosphere. There’s a short margin in which this abort is possible, right before ATO is possible. However, a (not so critical but meaningful) emergency might cause them to execute this abort anyways. This abort is available also after MECO (Main Engine Cut Off) when needed. It can land on Kennedy Space Center, Florida, Edwards Air Force Base, California or White Sands Missile Range, New Mexico (not preferred since the sand can damage the orbiter, as seen on STS-3, however, the facility’s been upgraded to permit a landing with the least amount of complications should the need for it arise.). Theoretically it can land on any runway, considering it’s long and wide enough, should the emergency arise. This applies to all intact abort modes, except RTLS.

TAL: Trans-Atlantic Abort. This abort mode is selected when ATO is unreachable, and RTLS is either not needed or already unavailable (“Negative Return”). The shuttle has a ballistic trajectory that has it crossing the Atlantic Ocean for a landing in Europe/Africa friendly bases.The ones being selected for TAL sites right now are Moron and Zaragoza Air Force Bases in Spain and Istres Air Force Base in France.

RTLS: Return To Launch Site. This is the fastest, and most dangerous intact abort mode. If an engine failure before TAL capability is reached, or an extreme emergency requiring immediate landing occurs (such as cabin leak), RTLS is activated. If the SRBs are still latched onto the shuttle, it waits till the SRBs are detached and clear, then it executes the abort. If the SRBs are already clear, it immediately executes it. It pitches the shuttle around to aim back at Kennedy Space Center and burns the remaining engines, OMS engines, and RCS thrusters into the flight path until downrange speed is killed. It then accelerates back to Kennedy, releases the tank so it still falls into the ocean, and glides back to Kennedy Space Center as if it were a normal descent and landing. The danger comes with the pitch around of the shuttle while still burning its main engines, resulting in a lot of gravitational stress to the crew AND orbiter, not to mention aerodynamic forces still present at those altitudes, although NASA says it’s already at a sufficient altitude for those aerodynamic stresses to be a non-issue.

The aforementioned aborts are the “intact” abort scenarios, where both orbiter and crew are safely recovered, well, intact. However, if a catastrophic malfunction occurs (all-engine malfunction, multiple APU/fuel cell malfunction, etc), which leaves the orbiter incapable of reaching a suitable landing site, a contingency abort is made. It simply consists of attempting to put the shuttle into a stable glide, aiming at open ocean, until it reaches the survivable altitude and speed limit. There, the crew pops the side hatch, slide a pole out, and bails out of the orbiter, the pole clearing them from the shuttle (they have parachutes latched onto their orange launch and entry suits. Their suits are called the Advanced Crew Escape Suit). There, they parachute down to the ocean. Their backpack also contains survival gear, including a personal life raft. There they wait until search and recovery forces pull them out of the water. As for the orbiter, it is ditched into the ocean.

The same thing can happen if this failure occurs during/after entry interface. Of course, the same survivable speed and altitude limit criteria must be met before bailout is possible, unlike STS-107 Columbia’s case, where the speed and altitude were too great for bailout to be survivable (and, consequently, had their unfortunate deaths for granted, as they could only sit and wait until the crew module broke up) when the orbiter breakup began. Popping that hatch open would have instantly killed the astronauts because of the plasma generated by the high speed reentry into the atmosphere, EVEN with their suits on and sealed. In fact, they found melted pieces of the suits. PIECES. And the body parts supposed to be inside the pieces miles away from said suit pieces, and in several degrees of heat/dismembering damage (a woman heard a noise on that day and went out to find her dog chewing happily on a charred body part. This is no joke. Look it up.) A suit designed to keep your body at a stable temperature even under severe temperatures, MELTED. And they were still being protected by a significant portion of the crew cabin as it broke up. Think about how bad the day was for the person INSIDE the suit when the heat went through the suit. Even worse when the crew cabin broke up and what was left was exposed to the limb-severing, flesh-ripping airstream of 12,500 MPH. And its associated flash-burning due to the friction. IF somehow the suit would have held together, it still didn’t solve the fact that they were still flying at over 200,000 feet, and because of their immensely reduced weight (230,000 pounds of the orbiter to a measly 200 pound guy), their dropping speed would be at an all-time low, and their oxygen reserve would run out before they reach breathable air. May I remind you that the guys who climbed all 29,029 feet of Mount Everest, Earth’s tallest mountain, needed OXYGEN MASKS/TANKS to stay there. 200,000 feet is like vacuum in comparison. May I also remind you that altitudes in excess of 26,250 feet is called “The Death Zone”, since a person slowly suffocates to death, no matter how used he or she is to low air pressure. The body has its limits on how far it can adapt before it gives up, as stated in this article: http://en.wikipedia.org/wiki/Death_zone, and I quote, “Finally, in the "death zone" at 7,000 to 8,000 m (23,000 to 26,200 ft) and higher, no human body can acclimatize. The body uses up its store of oxygen faster than it can be replenished. An extended stay in the zone without supplementary oxygen will result in deterioration of body functions, loss of consciousness and, ultimately, death.” That’s at 26,250 feet. 200,000 feet is like holding your breath and never breathing again until your brain stops. Or being hanged by the neck. Same result. Death by suffocation. (And somehow, there is still a sufficient airstream to rip you apart at 12,500MPH. Nature is clinically bat-shit insane. But so are we for messin’ with it xD)

So, popping the hatch and bailing out at insane speeds and altitude is a big no-no.

And on that note, for my next blog… …REENTRY. …and landing.

…fricken tiles.

Tuesday, October 13, 2009

Orbital Mechanics Extremely Simplified

After reading this, you’ll understand how is it that something stays up there and doesn’t come crashing down unexpectedly.

An orbit is, as taken from a dictionary, “the path of a celestial body or an artificial satellite as it revolves around another body”. IT is exactly what it means. Something just going in circles around something. No, not your kids when they attempt to burn you at a makeshift stake. A CELESTIAL body or an artificial satellite. An example of a celestial body is… our very own planet Earth!

Why? Because it’s going in circles around the sun. It’s a 365.25 day long circle, but a circle nonetheless. An easier example is the moon, going around the Earth.

An example of an artificial satellite is, well, one of many satellites you might be using to watch your favorite TV channel. When a shuttle launches and performs its mission in orbit, it is, well, IN orbit, so it’s considered an artificial satellite at that point. The International Space Station, or ISS, is also a perfect example of an artificial satellite. The ISS typically has a roughly 90-minute orbit, meaning it can do 16 laps around the Earth in a day. They have 16 sunrises and 16 sunsets per day. Talk about a ‘fast-paced environment’!

So how does it stay up there? Is it because there’s no gravity?

NO. Even at 200 miles above the Earth, there’s 80% gravity. So, how come the space shuttle, satellites and ISS stay up there without using any engines to stay up?

Two words. Permanent freefall.

Grab a transparent plastic cup. Put 2 or 3 colored paper clips. Cover the cup. Now throw it up, but not too hard. You’ll notice that when it reaches the top part of the climb, when it drops down again, the clips inside seem to float before flying towards the top of the cup. It all happens extremely fast, but you should notice that. In that micro-instant, the clips were floating as their falling speed matched the cup’s. That instant is known as free-fall, or as others would recognize the term, the feeling of weightlessness.

When astronauts go up to space, they have already experienced weightlessness so they know what they’re dealing with, but how do you recreate that feeling on Earth? Simple. Grab a plane, go up real high, then let the plane drop. Anyone inside the plane will immediately feel weightless, and everyone inside will float… until the plane runs out of altitude to keep dropping from, so it’ll have to pull up to avoid crashing into the ground, and immediately, everyone will feel heavy and drop down. NASA has a contract with a company called Zero Gravity Corp that does exactly this. They also give shorter rides to paying customers for around $5000 a ride (go http://www.gozerog.com if interested). They’re shorter because the sensation of going weightless and going back to weighting a lot again will cause nausea to people with queasy stomachs (hence, the airplane’s name, the Vomit Comet). Astronauts are trained to bear this so their training rides are longer.

Now, we threw the cup straight up. The same can be achieved if you throw it up at an angle, which would be similar to a shuttle blasting off into orbit. The harder you throw it, the more time gravity takes to pull it down to the ground. Even harder, and gravity takes even longer. Do you notice a pattern?

…eventually, throw an object hard enough, and gravity will take from almost forever to forever to pull it down, and this object is considered being in orbit around the Earth. This is how the shuttle achieves orbit. It accelerates to insane speeds, speeds where gravity will never be able to pull it down, but still has a sufficient hold on it to keep it going around the Earth. Thanks to the upwards of 17,000 MPH speeds acting against the 80% pull of gravity, the shuttle remains in orbit, and doesn’t slingshot away from the Earth. Higher speeds will result in higher, longer orbits, until you reach what is called “escape velocity”, in which you’re going so fast, the Earth’s gravity can no longer pull you back and you just keep going into space. We don’t want that to happen, so they stay within 17,250~17,500 MPH.

A quick note. If the shuttle can stay up without engines if travelling fast enough, why does it have to be at such a high altitude?

Atmospheric drag and friction.

Run a car to 65MPH. Crank the window down and put your hand out, the palm of your hand aiming at the airstream. You will feel that the air is pulling your hand backwards. The air, when one is going fast enough, actually acts as a braking force. At higher Mach (faster than sound) speeds, the air then causes heating due to friction of the air particles running through the object. The shuttle would be a fireball if it were travelling at such speeds at a low altitude. Not good. That’s why it must ascend (climb) to where there are no air particles whatsoever: above 400,000 feet. THEN it can accelerate undeterred AND stay in orbit.

Alright, so now we know how the shuttle stays up there. Quick notes on 2 orbit terms. There are usually some variations in the orbit altitude, and these are identified as “apogee” and “perigee”. Very simple terms. The apogee is the point in orbit where the altitude is highest. The perigee, always on the opposite side of the orbit, is the lowest point. Quick example, an orbiter reaches its apogee at 150 miles above the Earth. It then slowly decreases altitude until it reaches perigee on the other side of the planet, at around 135 miles above the planet. It then increases altitude until it again reached apogee, again on the other side, once again at 150 miles above the Earth, and the cycle repeats.

So, how does it change its orbit? Just accelerate and that’s it?

No. A simple rule applies. If you want to change an orbit, you must increase or decrease your speed precisely at either the apogee and/or perigee. Changing your speed in perigee will affect the apogee’s altitude. The other way around is also true. Changing speeds at apogee will change the perigee altitude. Increasing speeds will increase the other point’s altitude, and decreasing speed decreases the altitude at the other point. There might be irregular burns done at a point other than perigee or apogee, but these are rare, thanks to NASA programming their launches in a way that taking off at one point will identically match the orbit they’re trying to get to, meaning they only need to make certain adjustments to altitude in order to catch up to what they’re trying to reach (thus, saving fuel). The changes in speeds are measured in feet per second, since the changes in speed are subtle, but it affects the altitude greatly.

There’s another rule applied here when trying to catch an object in orbit. It’s called Kepler’s Law, actually, the third law. Basically, and as an example, an object travelling at 17,250 miles per hour at an altitude of 125~150 will actually travel faster than an object going at 17,300 MPH, but at an altitude of 225~230 miles. In other words, higher orbit means longer orbit, lower orbit means faster orbit.

To view this, it’s simple. Draw a small circle, and draw a bigger circle, and then an even bigger circle. You’ll end up with 3 circles, one inside the other. The smallest one is the Earth, and the bigger one is orbit 1, and the largest one, orbit 2. Then, trace with your finger at a slow speed, so you take 10 seconds to make a lap on orbit 1. Now, using that same speed, trace your finger around orbit 2. You’ll notice it took you longer than 10 seconds to make a lap.

That’s Kepler’s Law in effect. Assuming both objects on both orbits are going at roughly the same speed, give or take a few hundred miles, the wider the circle (the higher the orbit), the more time it will take to go around the Earth.

A ground example of this is a race. There are 5 tracks on a racetrack, and the racetrack has curves. However, the ones running on the inner tracks have a starting position that is behind the ones who are on the outer tracks. This is done because the ones on the inner track have less of a curve to go around than the outer track, so they clear these curves faster. The race coordinators calculated how far back each of the inner track racers need to start so if they all run at the same speed, when they come out of the final curve, everyone will be evenly matched.

This is used as an advantage to NASA to catch up to satellites or the ISS. The ISS is in an orbit of roughly 225 miles, give or take a few miles. When the launch window opens for the shuttle, it takes off, MATCHING the ISS’s ground track. Therefore, it only needs to go a bit faster to catch up to the ISS if it’s too far ahead. So the shuttle remains at a lower orbit, going slightly “faster” than the ISS in relation to the Earth, until it catches up. At this point, the shuttle changes its altitude, in a series of burns designed to roughly match the shuttle’s altitude with the ISS, precisely at the point where the ISS is very close to the shuttle, around 40,000 feet away. The shuttle then uses its RCS thrusters to close the distance and fine-tune and match its speed with the ISS, before it docks with it.

In orbit, the shuttle has several dimensions of movement that are unavailable/impossible for us who are at gravity’s mercy. It can roll, it can pitch, and it can yaw, and it can translate up, down, left, right, forward or back. Those movements are divided into 2 categories, Rotation and Translation.

For rotation, grab a tennis ball. Roll it forward or backwards. Now imagine it doing that while staying at the same place. Now imagine the shuttle doing that. That’s the pitch up and pitch down. Now, same exercise, but make the ball roll left or right. That is the roll of the shuttle. Once more, but this time, SPIN the ball to the left or right. This is the yaw of the shuttle. The rotation controls of the shuttle affect the attitude of the shuttle.

For translation, use the same tennis ball, only now, imagine the shuttle remaining in the same direction it’s pointing at, and that it’s simply drifting to the directions given. The shuttle can move forward, it can back up, or move backwards, just like a car. The difference is that it can also move left and right, unlike a car which can only go forward or back. And of course, it can move upwards and downwards like an elevator. The translation controls affect the position of the shuttle.

Rotation and Translation are combined to affect the attitude and position of the orbiter, and it can get to places like that. Usually, when docking to the ISS, it must maintain a precise attitude so the docking adapter can latch into the mating adapter of the ISS precisely and without any angles. And of course, it must be positioned exactly so that the mating adapter is centered with the orbiter’s docking adapter, before slowly closing in to dock.

Well, I guess that’s it. For my next blog, I’ll explain the abort modes available during ascent of the shuttle, and after that, descent and landing. I need to finish this before STS-129 Atlantis takes off in November…

Friday, September 25, 2009

Your typical Space Shuttle Mission Part 3: Getting to space (AKA Countdown, Launch, Ascent and Orbit Insertion)

After reading all I wrote, now you know how a space shuttle roughly works, and all the people involved. A quick note, a shuttle crew, the astronauts, are usually a minimum of 2: The Commander (CDR on the radio) and the Pilot (PLT). If a mission requires extra hands, Mission Specialists are also included in the crew (MS1, MS2, and so forth). Up to now, the maximum number of crewmembers to ever have flown on the space shuttle is 7 (The CDR, The PLT, MS1, MS2, MS3, MS4 and MS5). The commander pilots the shuttle and speaks for the entire crew, while the pilot assists in piloting. To understand this, in normal flying, the CDR is the pilot, and the PLT is the co-pilot.

On to actual launch procedures!!!

top.discovery.launchpad.ap

COUNTDOWN

3 days before actual launch. Shuttle Discovery is in the pad, covered by the rotating service structure, protecting it from the weather. Countdown-wise, at T-43 hours (yet, 3 days before… remember, the holds), the countdown clock is started, and everyone is called to their stations. The Shuttle Test Team, the Launch team and the Mission Management Team start to work 24/7 to make sure the shuttle and crew are ready to launch, and that the systems and weather conditions allow for it, beggining with final checkouts to the shuttle and launchpad, and software loading into the shuttle’s computers.

The first built-in hold is at T-27 hours, and lasts 4 hours. During this hold, the pad is cleared of all non-essential personnel and the shuttle’s power reactant storage and distribution system is filled with cryogenic (read: uber cold) propellants. When the hold releases and it counts down again, the fuel cells’ storage tanks are filled with said cryogenic propellants.

The countdown holds again at T-19 hours, another 4-hour hold, unless the distribution system needs time to do an offload. They cut off the umbilical to the orbiter, clean and vacuum the crew cabin, and some other tasks.

The hold releases from T-19 hours. Now the 3 Main Engines are prepared for the fuel tanking and actual flight, the closing out of the orbiter and launchpad continues, and the Sound Suppression System tank is filled with water.

(A side-note: The SSS (sound suppress system) is composed of a 300,000 gallon water tank several meters away from the launchpad. This tank is connected via tubes and pumps to the launcher platform, which has several jets of water, some of them for quick-flooding the space below the launcher platform, and some that suppress fire from the launch as soon as the vehicle clears. The REAL purpose is flooding the compartments below the launcher platform, so the sound shockwave generated by the engines and boosters is dampened by the water, and doesn’t harm the orbiter on the rebound. The entire system, on peak maximum pumping, shoots a whooping 900,000 gallons of water per minute (meaning it’ll be over in less than half a minute, considering there’s only 300,000 gallons). This is the sudden rush of water you see flowing from below the platform at 16 seconds prior to liftoff. Watch a Youtube video of a launch to see what I mean)

The hold once again hold at T-11 hours. This is the LOOOOOOOOOONGEST hold, lasting 13 or 14 hours. This is where the rotating service structure opens up to reveal the shuttle, and sets itself on the ready launch park position, as pictured below.

space-shuttle-discovery-launch-pad

Now, weather and engineering briefings occur during this hold, and the pad and surrounding area is checked for debris. The late flight crew equipment is stowed at this point, the IMUs (inertial measurement units, for the shuttle’s position) and the communication systems are activated, and the shuttle’s switches are put in the correct initial position for startup and launch.

Finally, the countdown resumes, and the orbiter’s fuel cells are finally activated. The blast area is cleared of all nonessential personnel for the duration of the count, and the orbiter purges its air to clean it.

We reach the T-6 hour hold, which lasts 2 hours, or one, if the launch was scrubbed and this is another next-day attempt. This is an important hold, where the Mission Management and Launch teams receive weather briefings. Launch team verifies that everything is ok for launch before ordering the External Tank fueling (called Tanking). Once everything is ok, the pad is cleared of all personnel, the go for tanking is given, and the fuel lines are chilled down to the temperatures of the liquid hydrogen and oxygen, and finally, tanking starts, where hydrogen and oxygen are pumped slowly, then quick. Usually, when tanking starts, the hold is released, and the countdown reaches T-3 hours, where another hold occurs.

At the T-3 hour hold, the tanking process finally reaches “Stable Replenish” mode. This is because a bit of the liquid hydrogen and oxygen will evaporate and escape the tank via exhaust lines. The fuel pumps keep pumping just a small stream of the liquids to replace whatever gets evaporated. All in all, the tanking is complete.

The IMUs are calibrated, and the Merritt Island Launch Area (MILA) tracking antennas are aligned. The final inspection team arrives at the pad and checks for possible ice damage (read: uber-cold liquid hydrogen and oxygen) and other issues. Finally, the Closeout Crew goes to the pad and prepares the orbiter for the astronauts’ entry (ingress).

The hold releases, and the astronauts depart to the launchpad, and they go up to the crew access arm and reach the “white room”, a small room at the end of the crew access arm that is put against the orbiter’s hatch. It has air conditioning for the comfort of the astronauts and closeout crew and it has a hose that blasts cool, clean air inside the orbiter. One by one, the astronauts are helped inside the orbiter, seated and harnessed into their seats. Once seated, they perform a basic voice check with both the NASA Test Director and Mission Control. All communications are in this format: the callsign of the one you’re calling, your callsign, and the situation, if any. This is an example of the commander’s voice check:

Mission Commander: “NTD, CDR, Comm check.”
NASA Test Director: “CDR, NTD, Loud and clear. Good afternoon!”
Mission Commander: “NTD, CDR, loud and clear. Glad to be here.”

After a brief pause, the commander checks communications with Mission Control, AKA “Houston”.

Mission Commander: “Houston, CDR, Comm check.”
Mission Control Center: “CDR, Houston, Loud and clear. Good day, and good luck.”
Mission Commander: “Houston, CDR, thanks!”

The Pilot, whose callsign is PLT, and the mission specialists, MS1, MS2, etc, also conduct their voicechecks. This is to ensure communications are possible to the ground, and that their mike lines are properly connected.

Once all astronauts are seated, the Closeout crew closes the orbiter hatch, latches and seals it for flight, and pressurizes the cabin, finally checking for leaks, before closing out the white room and leaving the pad. The astronauts perform several checks and configurations during this time.

Finally, we reach the second to last hold, at T-20 minutes, only lasting 10 minutes. The NTD makes a final launch team briefing during this hold, and the orbiter’s IMU alignment is complete.

The countdown timer resumes, and the crew is given the go to transition all GPCs to OPS 101, the terminal countdown phase of the OPS 1 (launch ops on the GPCs, remember?), and the cabin vent valves of the crew cabin are closed for flight.

And we finally reached the T-9 minute hold!! This hold typically lasts 45 minutes, but the time is adjusted to the launch window at this point (the precise moment when the shuttle must launch to reach a certain point in orbit by using the least amount of fuel possible, usually nowadays to catch up to the ISS). In this hold, the flight recorders (black boxes?) are activated. And the final flight readiness polls are done independently of all 3 teams. In the final 7 to 5 minutes of the hold, the official, final flight readiness poll is conducted as follows, assuming everything is ok for launch (transcript from STS-123 Endeavour launch poll, with names removed):

NTD: “Attention on the net, this is the NTD, conducting the Launch Status Check. All stations verify ready to resume count and go for launch. OTC?”
OTC: “OTC is Go.”
NTD: “TBC?”
TBC: “TBC is Go.”
NTD: “PTC?”
PTC: “PTC is Go.”
NTD: “LPS?”
LPS: “LPS Go.”
NTD: “Houston Flight?”
Houston: “Houston Flight is Go.”
NTD: “MILA?”
MILA: “MILA’s Go.”
NTD: “STM?”
STM: “STM is go.”
NTD: “Safety Console?”
Safety Console: “Safety is Go.”
NTD: “SPE?”
SPE: “SPE’s Go.”
NTD: “LRD?”
LRD: “LRD is Go.”
NTD: “SRO?”
SRO: “SRO is Go, you have a range clear to launch.”
NTD: “…and CDR?”
Mission Commander: “CDR is Go.”
(At this point, the Shuttle Test Team is Go, and will report to the Launch Director immediately confirming the CDR’s Go for launch. Launch will then poll his team.)
NTD: “Launch Director, NTD.”
Launch: “Launch Director.”
NTD: “Launch Team is ready to proceed.”
Launch: “Ok, I copy, thank you. Chief Processing Engineer, verify no constrains for launch.”
CPE: “No constrains, we’re ready.”
Launch: “Ok, thanks. KSC Safety Mission Assurance?”
KSMA: “KSC Safety Mission Assurance is ready to go.”
Launch: “Thank you. Payload Launch Manager?”
Payload: “The <insert whatever important cargo is hauled to space and the teams overseeing the operations> is ready to proceed.”
Launch: “Thank you. Range Weather?”
Weather Officer: “Weather has no constrains for launch.”
Launch: “Thank you. And OPS Manager?”
(The OPS Manager reports the readiness of the Mission Management Team)
OpsMan: “Ops Manager, Launch Director, the MMT is working no issues, you are go for launch.”
Launch: “Thank you, sir. Endeavour, Launch Director.”
Mission Commander aboard Endeavour: “Go ahead, Launch Director.”
Launch: <Insert praises to team, crew and weather, and gives the go for launch>
Mission Commander: <Thanks Launch Director, etc etc.>
Launch: “And NTD, you are clear to launch Endeavour.”
NTD: “Copy, clear to launch, thank you.”

And with this, the shuttle has been given the green light, the Go for Launch. The countdown usually resumes 2 to 4 minutes following the end of the Launch Status Check.

NTD: “Countdown will resume on my mark… 3…. 2…. 1… mark.”

T-9 minutes and counting.

This is the point where everything gets very dynamic, fast, and tense. Several things happen at the point of the hold releasing the 9-minute countdown. First of all, duh, the countdown timer starts to tick the final countdown to launch. Second, everyone is now checking their systems VERY CLOSELY for any problems. And third, and most importantly, all control of the countdown and all shuttle and pad systems have been transferred to the Ground Launch Sequencer Computer, or GLS. From T-9 minutes to T-31 seconds, the GLS can hold the countdown if requested by any launch controller or if it detects a problem. After that, only a cutoff and a launch scrub is possible, because the GLS gives control to the 5 GPCs aboard the orbiter.

At T-9 minutes, GLS Auto Sequence is initiated and it starts to check all systems, and perform several duties. The GLS console operator is monitoring and calling out anything the GLS reports to him.

T-7 minutes, 30 seconds. The tension rises.

“GLS is go for retract orbiter access arm.”

The crew access arm, complete with white room, slowly swings out of the way, leaving the astronauts truly confined to the orbiter. Within 30 seconds, the arm is out of the way.

T-6 minutes, 15 seconds. The pilot is given an instruction.

OTC: “PLT, OTC. Go for APU Pre-Start.”
PLT: “PLT, in work.” (a few seconds later after working on the corresponding switches on his panel) “APU Prestart complete.”

The countdown keeps rolling. Steadily it makes it to 5 minutes.

T-5 minutes.

GLS: “GLS is go for APU Start.”
OTC: “PLT, OTC. Start APU.”
PLT: “PLT in work.” (some seconds later) “APU Start complete.”

The Auxiliary power units are enabled. The shuttle’s aerosurfaces become active.

T-4 minutes, 55 seconds.

The GLS does two simultaneous checks. One is to check if the SRB’s ignition is armed and ready, and the other, which we hope never to use, is the SRB Range Safety System. This, in case the shuttle strays off course into a populated area while latched onto the SRBs, an army officer will have no choice but to activate the Range Safety System, which will detonate the SRBs and the External Tank, destroying everything, which of course results in the loss of the orbiter and the crew. Like they say, we’d rather lose 7 astronauts than hundreds or thousands of civilians.

The GLS also terminates the Liquid Oxygen Stable Replenish mode and shuts down the pump.

T-3 minutes, 55 seconds.

The GLS commands the shuttle to begin a series of programmed motions of its aerosurfaces to test them, and for warm hydraulic fluid to course through them.

T-3 minutes, 30 seconds.

With the aerosurface profile test done, the 3 main engines are gimballed (Moved around in place. The nozzles can be aimed if you didn’t know) in a preset motion pattern.

T-3:03. The gimbal check is complete, and the 3 engines are spread wide apart to avoid colliding with each other at ignition. The body flap under the engines is verified to be in launch position.

T-2:55. The GLS commands the External Tank to begin pressurization of the liquid oxygen. 5 seconds later, the cap on top of the ET, that removed whatever evaporated oxygen came out and drawed it out of the way, is removed, and moved out of the way of the shuttle.

T-2:35. The cryogenic reactant distribution system no longer fuels the fuel cells, and the fuel cells begin to take their reactants off their internal orbiter tanks to generate its own power.

T-2:00.

OTC: “OTC, crew. Close and Lock Visors.”

That means that the crew must close and lock their helmet visors for their suits to become pressurized, in the unlikely event of cabin depressurization.

T-1:57. Liquid hydrogen stable replenish terminated, all tank valves closed.

T-1:46. The External Tank begins Liquid Hydrogen pre-pressurization.

T-50 seconds. Ground power is cut from the shuttle, letting it use its internal power.

And this is the moment of truth. T-31 seconds.

“GLS is go for Auto-Sequence Start.”

From this point on, GLS arms the Cut-off command, the only command available from this point to T-0. It also initiates the Redundant Set Launch Sequencer, which will monitor that everything goes smoothly with the last 4 commands to be given by the shuttle’s computers, otherwise it’ll force a cut-off to the GLS. The countdown control is transferred to the shuttle’s computers as well, which continue the final countdown, the Auto-Sequence for launch.

T-28. The SRB APUs are started, which control the nozzles of the SRBs. 7 seconds later, the SRBs do a quick gimbal test.

atlantis-sss

T-16. The Sound Suppression System activates. A loud whistling is heard as 300,000 gallons of water are quickly pumped into the SRB and SSME’s trenches under the Mobile Launcher Platform, to mitigate the sound shockwave from the engines’ roar and lessen damage to the orbiter. From afar, a torrent of water is seen blasting down from under the platform, as you can appreciate in the picture.

T-10 Seconds.

hyd burn off

Sparks begin to fly. But not yet from the engines. A system called the Free Hydrogen Burn Off System ignites, aiming hundreds of sparks at the engine nozzles, burning off any residual hydrogen that may be in its vicinity. It’s done like this so the ignition of the engines is controlled, and no errant explosions occur that may crack or break the engine nozzles. At the same time, the GLS gives its green light to the GPCs onboard the shuttle to start its engines.

“GLS is go for Main Engine Start.”

Everyone is on the edge of their seats. Will the engines ignite? The RSLS system monitors for the successful ignitions of all 3 engines. Everyone holds their breath.

T-6.6 seconds. The GPC sends Main Engine #3 the start command.
T-6.48 seconds. Main Engine #2 is ordered to start.
T-6.36 seconds. Main Engine #1 is last.

ssmestart

Almost instantly, a loud whoosh and rumble comes out of the launchpad as red hot flames shoot out of the 3 main engines. The instant incredible heat hits the water in the trench, which is divided into 2 sections. A massive cloud of water vapor shoots out of the front of the pad as the water from the SSS is flash-evaporated. At first, the flames look out of control. But just as quickly they settle into a normal down-blasting direction, and the flame blast is almost invisible, save for the white halo core ‘inside’ the flame blast. The engines have ignited!! The entire stack makes a motion, a small nod. If you look at the top part of the ET, you see it lurches forward a bit, then settles back up straight in time for T-0. The movement is completely imperceptible from a moderate range.

Everyone still holds their breath, though. The engines have to reach 100% power within 3 seconds, or the RSLS will cut off the launch. It has happened 5 times in NASA’s shuttle flight record. Everyone silently prays this isn’t a 6th time. 6….5….4…3…

The engines reached 100%. RSLS is standing by for the final command. …2…1…

The point of no return is here.

T-0 seconds. Booster ignition.

LAUNCH

Simultaneously, the SRBs are given the ignite command. Almost instantly, a mass of white-hot flames shoot out of each of the SRBs’ nozzle, flash-evaporating the water on their side of the trench, shooting a massive cloud to the back of the platform. And at the same time, the bolts holding down the entire shuttle stack are detonated, releasing the entire shuttle. Since the SRBs have a powerful thrust, the shuttle literally leaps up and out of the launchpad.

…and LIFTOFF!!!!

discovery_liftoff_2009_nyreblog_com_

ASCENT

The countdown is no more. It is now the mission elapsed time counter. The count is now read as “x days, x hours, x minutes, x seconds into the flight”.

Now begins the ascent part of the flight. As soon as the shuttle clears the launchpad, Kennedy Space Center instantly surrenders all responsibility, communications and monitoring of the shuttle to Mission Control Center at Johnson Space Center, Houston, Texas.

All functions from this point to MECO (Main Engine Cut-off) are controlled by the shuttle’s onboard GPCs, and is fully automatic, unless there’s an emergency. Different milestones occur during ascent. Let’s assume Discovery’s the one lifting off.

NOTE: All times from this point on are estimates based on a real mission. It will vary from mission to mission.

T+0. The GPCs are transitioned into OPS102, the “First Stage Ascent” Phase of OPS1. Discovery lifts off thanks to the combined power of both SRBs and the 3 Main Engines.

T+6.5 Seconds. Discovery clears the tower around this timeframe. Instantly, Mission Control Center at Houston, Texas assumes control of the mission.

T+11 seconds. Discovery does a roll and pitch maneuver. Basically, the engine nozzles move so that the shuttle turns until the top side of Discovery is aiming at the desired flight path. Then it begins to pull its nose up, aiming the nose at the flight path, which is up and away from the pad. It seems like a backflip, because Discovery ends flying upside down. It remains like this for almost all of the ascent. Once the roll maneuver is underway, Discovery’s CDR calls it out.

Discovery: “Houston, Discovery. Roll Program.”
Houston: “Roger Roll, Discovery.” (it seriously almost sounds like rock and roll…. look up STS-119 launch on Youtube and you’ll see… er, hear what I mean, immediately after CDR Lee Archambault’s callout of the roll program.)

T+30 seconds. Discovery’s already flying at 365MPH, 1 mile in altitude, and 7 miles downrange (meaning away) from KSC.

T+45 seconds. Discovery begins to go past the speed of sound, and the main engines are commanded to drop to 60% power to reduce the stress the strong aerodynamic pressure is causing on the orbiter. If you are viewing the launch, at this point, you’ll see the indication of the shuttle breaking the sound barrier because of the vapor-shockwave-like cloud forming around it, usually when something goes past the speed of sound. Later on, the atmosphere is already thinning out, and the stresses are no more.

T+1:05. Discovery’s engines are commanded to throttle up to 104%, its maximum power.

Houston: “Discovery, Go at throttle up.”
Discovery: “Discovery copies. Go at throttle up.”

At this point, the shuttle travels at a speed that makes the atmosphere cause the highest amount of aerodynamic pressure on Discovery. This region, which is quickly passed as the atmosphere keeps thinning out, is called Max Q.

All systems are in good shape. The engines are still going, the fuel cells are healthy and the APUs are working perfectly.

T+1:16. A little over a minute, and Discovery’s already at 1800MPH, 10 miles high and almost 12 miles away from KSC.

T+2:05. The SRBs have burned all of their useful propellant. At this point, explosive bolts are blown that cut off the SRBs from the External Tank. They go up for a bit due to the speed they were going, before dropping down to the ocean, where the SRB Salvage Ships, the Liberty Star and the Freedom Star, are waiting. The GPCs onboard Discovery transition to OPS 103, “Second Stage Ascent”. Now, several abort options are called out, the one available at this point being the “Return To Launch Site” abort, or RTLS abort, if one or 2 engines fail. I’ll explain the abort options on the next post. But note that if in any moment of the ascent, until when the shuttle’s path is permanently increasing in altitude and the shuttle goes past 300,000 feet, all 3 engines fail, the only option is to ditch the orbiter into the ocean

At this point, Discovery is now flying under the power of its 3 main engines. The flight path goes up, remains level, then seems to drop, but then, it goes level, then shoots up in altitude. This is because the 3 main engines don’t have that much power to keep Discovery climbing at first, and the climb decreases until it begins to fall back to Earth. However, since it’s wasted so much propellant at that point, and it keeps wasting it, Discovery begins to get extremely lighter, until the main engines are more than enough to propel Discovery clear out of the atmosphere. It stops dropping, and again starts to climb at an ever increasing rate. Either way, it keeps developing horizontal speed, which is very important. It needs to reach over 17,000 MPH by the end of the ascent.

A few seconds later after the SRBs are released, the OMS engines (remember, the 2 small engines on either side of the back used for orbit maneuvers) fire for a few minutes, providing an assist boost to the 3 Main Engines.

T+2:15. Thanks to the assistance of the SRBs, Discovery’s at 3600MPH, 32 miles high and 43 miles away from KSC, and now accelerating quickly.

T+2 minutes, 39 seconds.

Houston: “Discovery, 2-engine Moron.”
Discovery: “2-engine Moron.”

No, Houston didn’t just insult Discovery’s engines. This is a call to Discovery indicating that they are sufficiently high and fast to make it to a Transatlantic abort landing site if just one of the engine fails. Still, if 2 engines fail, it’s an RTLS abort. If all 3 fail, I already told you. There are several transatlantic landing bases, which are checked before launch and selected due to weather. The two sites usually chosen are Zaragoza and Moron Air Force Bases in Spain. Right now, for this flight path, Moron AFB is chosen. However, all 3 engines are still doing great.

T+3:05. Discovery’s speed is 4,300MPH, 48 miles high and 83 miles away from KSC.

T+3:42. Discovery’s at 5000MPH, 56 miles high and 127 miles away from KSC.

T+3 minutes, 55 seconds.

Houston: “Discovery, Negative Return.”
Discovery: “Discovery copies, Negative Return.”

The first major milestone in the second stage ascent has been reached. Discovery is too high and too fast to be able to do an RTLS abort. Tensions rise, because in this period, 2 engine failures would be catastrophic, but Moron AFB can be reached if just one fails. However, the engines are still burning and at 104%.

T+4:18. Discovery’s at 6000MPH, 62 miles high, 177 miles downrange.

T+4:55. Discovery’s at 7000MPH, 65 miles in altitude, and 235 miles downrange.

T+5 minutes, 17 seconds.

Houston: “Discovery, Press to ATO.”
Discovery: “Discovery. Press to ATO.”

Finally, the shuttle is flying sufficiently fast and high to reach a safe lower orbit than planned if an engine fails. Then it’s just a matter of adjusting the orbit with the OMS engines and the mission goes as planned. But, all engines are still good. To date, only one mission suffered an ATO abort. Tensions rise again, because once again, a 2-engine failure would be catastrophic.

T+5 minutes, 39 seconds.

Houston: “Discovery, Single Engine OPS 3.”
Discovery: “Single Engine OPS 3.”

A welcome sound. At this point, an engine burnout would still initiate an ATO abort (which, when you come to think of it, isn’t really an abort, just a plan to reach a lower orbit and continue the mission), but if 2 fail, the crew has a failsafe. Now a Transatlantic abort to Moron AFB is possible.

T+5 minutes, 50 seconds.

Discovery’s zooming along at 9000MPH. The GPCs command the engines to swivel and cause the entire shuttle to roll to a heads-up position, or right side up again. By 6:15, the roll is complete. This is done to have a better signal and use the NASA TDRS Network, way high above the Earth, for tracking.

T+6 minutes, 3 seconds.

Houston: “Discovery, Single Engine Zaragoza, 104.”
Discovery: “Single Engine Zaragoza, 104.”

The Transatlantic Abort site has been switched to Zaragoza AFB, and can be reached on one engine. If just one of the 3 engines fail, it still triggers an ATO. This will change in a few seconds…

T+6 minutes, 20 seconds.

Houston: “Discovery, Press to MECO.”
Discovery: “Press to MECO.”

Most would breathe a slight sigh of relief at this point. The ATO option is discarded. Discovery is well on its way to orbit, and has a little over a minute to go until Main Engine Cut Off. If an engine should fail at this point, the MECO point can still be reached. If 2 fail, Zaragoza is standing ready.

T+6:40. Discovery’s at 11,000MPH, 66 miles in altitude. Some callouts are done around this point for the MECO plan.

Houston: "Your shutdown plan is nominal. You are GO for the Plus X, GO for the Pitch."

Discovery: "Nominal Shutdown, Go plus X, Go Pitch."

T+7 minutes.

Houston: “Discovery, Single Engine Press 104, good readback.”
Discovery: “Single Engine Press 104.”

An even bigger sigh of relief from everyone. All the scary abort modes are gone, and now, even if 2 of the 3 engines fail, the correct MECO altitude and speed can be reached. The ‘good readback’ remark was to indicate that Discovery read the previous instructions correctly (the MECO plan).

T+7:35. As the ET gets lighter because the 3 main engines have eaten up almost all of the liquid hydrogen and oxygen, the shuttle begins to climb excessively, and accelerates faster than it was doing. The acceleration becomes uncomfortable as the astronauts are pressed like pancakes to their seats. The shuttle also has some structural limits that can easily be overshot if the engines remain at 104%. This is why, at this point, the engines are commanded to throttle down until the GPCs see that the acceleration stress is just under 3gs, that is, they’re feeling they’re just under 3 times heavier than usual. Go to your bathroom scale, and multiply that number by 3, and think about what that means for you.

Astronauts are effin’ hardcore.

T+7:43. Discovery’s massive acceleration boost has it now at 14,800MPH, 64 miles high (over 337 thousand feet, well above the thick part of the atmosphere), and 700 miles downrange.

T+8:30. Discovery’s engines are commanded to start throttling down even more, in preparation for MECO, 8 seconds later.

T+8 minutes, 38 seconds.

The GPCs send the shutdown command to the 3 engines, and cuts off the hydrogen and oxygen flow to them. The engines instantly die out, and the acceleration ceases. In a particular Youtube video, which I will post below, show the several milestones. However, at 10:09 they call the throttle down, and at 10:12, you see the seats slowly bend forward as the engines’ power is lessened. At 10:18, the seats bend all the way to an upright position because they reached MECO, and the acceleration is now 0. It’s fun to hear them whoop as they finally reach initial orbit. Who says they don’t have fun? Apparently this guy doesn’t know that orbiter is spelled orbiter, not orbitor…

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Houston: “Discovery. Nominal MECO on schedule. OMS 1 not required.”
Discovery: “Copy Houston. Nominal MECO, OMS 1 not required.”
Houston: “Good copy.”

The callout confirms that MECO has occurred perfectly and on time. The ‘OMS 1 not required’ call means that Discovery doesn’t have to do an initial orbit adjustment, since launch and ascent went superbly, and it put them in the correct altitude and flight path.

A bit of history. Initially, the shuttles had to do both an OMS 1 and an OMS 2 burn to stabilize the orbit, until NASA explored the possibility of a ‘direct insertion’ launch, coordinating the time of the launch, and the assistance of the OMS engines shortly after SRBs are separated from the shuttle. Almost all flights from there onwards use this launch method, and ultimately saves propellant. An OMS1 burn can still be done if needed. I’ll explain more about orbital maneuvers and how they work at a later post.

MECO

ET Tank sep

T+8:55. The External Tank is released from the orbiter, and the orbiter does a small upward thrust using its RCS thrusters, separating the orbiter from the tank. The tank tumbles downward, and will continue on a ballistic trajectory, meaning up, then down. It’ll burn up over the Indian Ocean. And believe it or not, Discovery will suffer the same fate… but before it does, it will execute its OMS2 burn to stabilize and ‘circulize’ the orbit.

ORBIT INSERTION

And here we are. Discovery is travelling at roughly 17,250MPH, over 400 thousand feet, or slightly 76 miles above the planet. It’s well above the atmosphere, and the guys are weightless. Or are they? More on that on a later post.

Since OMS 1 burn wasn’t required, the crew has time to set up they various orbiter systems in preparation for their stay in orbit, be it thermal control systems (in space… no one can hear you scream “ITS HOT—NO, COLD OMGWTFHAX!!!111” Considering that in the shade, temperatures drop to finger-snapping-off minus 100 degrees Farenheit, and in direct sunlight, a nice, boiling, cancer-causing 200 degrees Farenheit. The orbiter acts as a gigantic Thermos, shielding the crew from said temperature changes), attitude control systems (RCS, vernier thrusters), and the like. In the meantime, the GPCs are transitioned to OPS 105, the final orbit insertion burn phase of OPS 1. OPS 105 executes the OMS 2 burn. (We skipped OPS 104 because OMS 1 isn’t required.)

Right now, the orbiter’s apogee, or the highest point of the orbit, must be at 150 or 200 miles, or something in between. However, the perigee, or lowest point, is still passing under the atmosphere. That has to be changed in order for Discovery to remain in space. Which is where the OMS 2 burn comes in. By accelerating for a few minutes, the perigee of the orbit changes until it is either safely above 400,000 feet, at the same altitude as the apogee, or higher (thus, becoming the apogee), depending on the mission needs. The OMS 2 burn is automatic, and only needs to be commanded to be done via the right keypad on the front of the orbiter. After that, it’s waiting until the orbiter reaches apogee, roughly 45 minutes after it reaches orbit, or, on the opposite side of the planet from where KSC is (at orbital speed, the shuttle goes around the planet once every roughly 90 minutes.) Once it does, the OMS engines fire until the perigee is at the desired altitude, then stops. The GPCs are then transitioned to OPS 106, the final checkout phase of OPS 1 before heading over to in-orbit OPS 2. After the shuttle is checked out, the GPCs are transitioned to OPS 2, and the mission officially is underway.

And that, my friends, is how a shuttle takes off and reaches space. My fingers are bleeding.

On the next post (because I’m a masochist, and because I can), I’ll explain about the abort modes, and later, about the orbit maneuvering and mechanics… which is a bit of geometry in itself.