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RichO from Elk Grove, IL: What modifications were done to the external tank for STS-121 compared to the last shuttle launch?
OK. Well, NASA's taken on quite a few modifications to the external tank following our STS-114 mission last July. In particular, we had one large piece of foam shed off of the tank. It was called the protuberance airload ramp, which is an aerodynamic feature of the external tank to keep the loads on the cable tray and the pressurization lines that go up the side of the external tank to a minimum. And we did see a piece of that foam break off during ascent last time, and so the modification we've made to the tank for this mission and all future missions is to simply remove that entire ramp -- it's a sprayed-on foam feature. We just simply removed that entire feature off of the tank for all future external tanks.
We also had an issue at the bipod region of the external tank where the forward end of the orbiter connects to the tank. We had some wires that protruded from the external tank underneath of the foam, and there was some condensation accumulated in that area, and during ascent that condensation expanded as you would expect, became vapor and popped a little bit of the foam off that area, as well.
And so we've modified that closeout area on those wires, as they come out of the intertank of the external tank, to preclude that condensation underneath of the foam itself. And then there were a few other minor modifications to the external tank that we made.
In fact, we work on the external tank and all elements of the flight vehicle -- the orbiter, solid rocket boosters and the external tank -- virtually continuously, although some modifications are more major than others. For instance, the protuberance airload ramp removal for the external tank this time was a major modification for us. But we typically modify all flight elements somewhat after each flight, because it is a learning vehicle. We are a test flight program, and so we do learn from each vehicle, each mission and tend to make minor modifications continuously in our program.
RichO from Elk Grove, IL and Philip from Swansea, Wales: If it were necessary to stay at the ISS, how long could the shuttle crew stay there? And when would Atlantis be ready to launch as the rescue shuttle?
Currently, in the Space Shuttle Program, we have a requirement to provide a rescue vehicle for a particular mission should it become necessary to go up and get the crew (if the orbiter is damaged during ascent). The way this plays out would be that the astronauts would stay onboard the International Space Station, really for quite some time as we do final preparations and launch of the next vehicle, which is Atlantis, and then go up and rescue the crew that has been staying on the International Space Station. The space station has quite a bit of capability.
We would have seven astronauts join the existing two astronauts that are continuously onboard the station, and so that full complement of nine astronauts could remain on the station for upwards of 75 to 80 days, during which time we would be finishing our preparations in launch of Atlantis to bring the seven folks back down that needed to be rescued. Because the assumption is that Discovery was damaged beyond the point of wanting to use it as a return vehicle. Very, very unlikely scenario, but nevertheless, we do have that capability and will have that capability to rescue astronauts off of the space station for the remainder of the shuttle program.
Francois from Namur (Belgium): How is the exact shuttle launch time determined and why is the launch window very short for the mission to the ISS?
It's a very complicated set of equations and determinations that go into an exact launch window, and of course for a mission to the International Space Station, which all of our missions will be for the remainder of the program. With the possible exception of a return trip to the Hubble Space Telescope, all missions will be going to the International Space Station and rendezvousing with the space station.
The station itself is in an orbit 230 nautical miles above the Earth, give or take, and it's in an inclination far above the latitude of the Kennedy Space Center. And so we have to launch at a particular time in order to catch up to the space station from below, as the space station is orbiting overhead of us.
So it's kind of like throwing a ball towards a speeding train and hoping to land the ball on the train. So we have to launch at a particular time to rendezvous with the station in orbit, and that set of equations says we really only have about a 10-minute period of time during which, on any particular day, we could launch and make it to the station.
There are many, many, many other factors that go into a launch decision. Right now, in the shuttle program, we have to launch during daylight hours so that we have good photography of the ascent to see if there's any foam being shed from the tank or any other ascent issues that we're going to photograph. We also have a requirement to separate the external tank from the orbiter in lit conditions on orbit, so that further limits our capability, our possibilities for launch times.
So it's a multi-faceted question. It's a great question. It's very difficult to answer, but again, it's like trying to hit a very, very fast-moving object from an object that starts out at zero miles per hour. It's extremely difficult. When you see the astronauts do it, they make it look easy, but it's a very, very tough thing to do.
Mark from Chicago, IL: After solid rocket booster separation, where will the boosters splashdown in the ocean?
The solid rocket boosters provide most of the thrust for our first stage of ascent performance. That's a solid rocket fuel system, and they ignite at T-0 and liftoff of the space shuttle system. The solid rocket fuel burns for 2 minutes and 5 seconds, after which they begin to burn out and tail off, and separation of the boosters from the external tank occurs 2 minutes and 7 seconds into flight.
At that time, the shuttle is going extremely fast. The main engines of the space shuttle are still burning, and will burn for another 6-1/2 minutes or so. But nevertheless, the solids have done their job providing the vast majority of the initial thrust for the system. So they separate from the external tank and fall back down to Earth in the Atlantic Ocean, approximately 140 miles northeast of the Kennedy Space Center. Out in the ocean, we have two recovery vessels that rendezvous with the boosters in the ocean, get them in tow and bring them back to the port and eventually to the Kennedy Space Center for refurbishment, back at our processing facility out at Brigham City, Utah.
Junichi Maki from Niihama-City: How many cameras are watching the external tank both from the ground and from the orbiter?
As you recall, during the ascent of STS-107, Columbia's final mission, a piece of the external tank's foam broke off and damaged the orbiter to the point that caused the breakup of the orbiter during reentry, and the loss of her seven brave astronauts. Since that mission, we have expanded the number of cameras on the ground and on the flight vehicle itself, to give a better idea of what the system performance is like during ascent.
Prior to STS-107, we had five long-range camera sites on the ground; we have doubled those to 10 sites. At each site are two cameras for redundancy purposes. So there are 20 cameras from as near to the pad as approximately 3 miles to as far away as 20 miles. Of course, we also have quite a few cameras within the pad fence itself, looking at the first portions of the ascent. Also onboard the vehicle, we have new cameras on the solid rocket boosters, two on each booster -- one looking down from the forward assembly and one on the aft end of the booster, looking up as we're ascending through the atmosphere. Two on each booster. We also have a camera on the external tank that we also had for the previous mission, STS-114, that's looking down between the orbiter and the external tank itself. And on the orbiter itself, where the orbiter connects to the external tank, there's a series of three cameras inside that well area that photograph the external tank immediately after separation from the orbiter.
So we have quite a few cameras looking at all aspects of the ascent, especially to make sure that the foam on the external tank is behaving as we expect it to.
Brandon from Orlando: How long does it take to get the shuttle into space?
It takes the shuttle approximately 8-1/2 minutes to get to orbit. And if you think about it, we're accelerating a 4-1/2 million pound system from zero miles per hour to its orbital velocity of 17,500 miles per hour in those 8-1/2 minutes. So it's a heck of a ride for the astronauts. They typically experience about three times the force of gravity during most of the ascent, and once we reach orbit, when the main engines cut off, they go from that three-G acceleration to zero acceleration virtually instantaneously, and that's when they become weightless on orbit.
Tom from Avon: How far away do ground personnel have to be from the launch platform?
Well, our ground personnel on launch day have to remain far away from the launch pad in case we do have a contingency on the pad. We have some forward observers, they're actually fire rescue folks that we could send in to the launch pad if we needed to, to help the astronauts get out of the vehicle. And they're about a mile and a half from the launch pad. At liftoff, the fire rescue folks position themselves inside of an armored personnel carrier in the unlikely event that we do have a contingency on the launch pad.
Unprotected observers are limited to 3-1/2 miles from the pad, and in fact, you see most folks standing just outside the launch control center, which is at that 3-1/2 mile radius from the pad. So protected observers, and that's about seven or eight folks, a little closer. But for the unprotected observer, 3-1/2 miles from the pad.
Shyla from Sioux City: If the 121 mission is successful and the shuttle keeps to the projected schedule, will the crew members for the ISS ride the shuttle or continue to launch from Russia?
The International Space Station currently is continuously manned by only two astronauts. That will go up to three-man capability with this mission of the space shuttle, when Thomas Reiter will stay onboard the station after his ride to the ISS on the shuttle.
So with three men permanent capability onboard the station, that says that manned crew rotation is best accomplished by the Soyuz capsules. And so, for most of the missions, virtually all the missions, we expect that the Russian space system, the Soyuz, will be the return capability for the astronauts and also the ride to the space station for the astronauts.
Sometime further in the future, when the station is manned by six men, which is late in this decade, we will have to reevaluate whether the Soyuz system can handle that, because the Soyuz really only carries three people up and down, and so it may make more sense, rather than have two Soyuzes for crew return, just to have one shuttle for crew up and crew down. That's a decision that's yet in front of us, so the near term crew rotation would be performed by our Russian counterparts.
Abigail from Pembroke Pines: I've heard that during a launch countdown the "T" in T minus does not stand for "Time." If so, what does the "T" really mean?
You hear us talk in the Launch Control Center about T-9 minutes, T-20 minutes, etcetera. And so the assumption is that T stands for time. I joined the space program about 20 years ago and I asked this question of my elders in the program when I did join, and it turns out that T stands for test. Because it's not always related to time. And so, in the early days of the space program, back in the Mercury and Gemini days and, indeed, Apollo, T stood for test. Because again, not all tests are based on time. It could be the start of a particular test in our Orbiter Processing Facility that is independent of the time of day. And so, the T actually stands for test. Good question. It took me awhile to figure that out myself, but it's a good question.
Junichi Maki from Niihama-City: What is the tile gap-filler made of and what purpose does it serve?
Well, the tile gap filler, of course, made a lot of news during the STS-114 mission when Steve Robinson had to go out on an EVA, extra-vehicular activity, to pull out two gap fillers that had protruded from between two tiles on the belly of the orbiter. So it made a lot of news and it was an interesting EVA to watch, and he performed it flawlessly. The gap fillers are made of a felt material. It's relatively hard felt, and its purpose is to keep tiles from chattering against each other during ascent and entry.
The tiles typically are about 4-1/2 inches square and need to be that small because the vehicle flexes during ascent and entry. And it also shrinks and expands as it goes up in the atmosphere during ascent, the vehicle tends to shrink as it becomes cooler, and when we come back down, it tends to warm up and expand slightly, and so the tiles need to move with the skin of the orbiter. So that's the reason the tiles are relatively small, and again, the gap fillers are really meant to keep the chattering between tiles to a minimum since the tile material is so brittle that we don't want the tiles rubbing against another tile for fear of chipping off the tiny edges of the tiles. And so we put the gap filler material in there, essentially as a shock absorber between tiles.
Philip from Swansea, Wales: Has Discovery undergone any further modifications to its framework since her last Orbiter Maintenance Down Period?
The answer really is no. We've done quite a few inspections, as you can imagine, after her flight last summer. But major modifications to the framework, no. The framework is in great shape. We inspect it very, very closely after each mission. But the structural members of the orbiter are behaving fine after all these years, so really, major modifications are not required of its airframe.
We do inspect every portion of the vehicle after each mission, and one thing we're currently wrestling quite a bit with are the windows and the very, very minor imperfections that we see in the windows after each mission. So we have changed out all the windows on Discovery since the STS-114 mission and plan to change out the windows again after this mission, take the old windows off of Discovery, take them to our shops and our labs, and figure out what's going on with the windows -- whether it's ascent debris that's causing the minor imperfections or whether it's imperfections we get on orbit, or whether it's imperfections we see as we're coming back on landing day.
So we'll change out the windows again and try to understand this phenomenon that is perfectly safe, but it causes a little bit of distortion for the astronauts as they look out the windows, as you can imagine. So we like to have the best windows possible for them on orbit.
Jennifer from Green Bay, WI: Will the shuttle do the same flip maneuver as it approaches the International Space Station to see if the orbiter was damaged during liftoff?
You'll recall on STS-114, Eileen Collins, our commander on that mission, did this flip maneuver for the first time in the history of the program. We did it in order to inspect the belly of the orbiter and other surfaces, but in particular the belly, to see if there's any damage to the tiles that we had incurred during ascent. And so that is baseline for every mission now in the shuttle program. As we approach the space station, we will do this reverse pitch maneuver, it's called, and do a flip and photograph the orbiter from the International Space Station in very, very fine detail to see if there are any areas on the belly of the orbiter that we want the astronauts to go out and inspect themselves. And so, as a precaution, it's data collection, and this is indeed how we saw the two gap fillers protruding from the belly of Discovery last mission. So it's a very, very prudent thing to do, and we do plan to do it on every mission from here on out.
Jennifer from Green Bay, WI: Are the WB-57 aircraft going to be taking images of the shuttle's ascent like in the first return-to-flight mission?
This question is aimed again at photography of the shuttle during ascent. This particular question gets to the use of our WB-57 aircraft that we had airborne for STS-114 at approximately 60,000 feet northeast of the launch pad. This time, we will have one WB-57 aircraft doing the same job that two aircraft did last time, and so, yes, we will have an aircraft up there -- the purpose, of course, being to get as good imagery of the belly of the orbiter and other surfaces of the orbiter. Later, in ascent, then our ground assets can photograph the orbiter. So we will have that airborne platform taking pictures of the orbiter this time, and we expect to have this particular asset for most missions in the future, as well.
Jennifer from Green Bay, WI: What improvements and modifications have been made to the shuttle and the tiles to make them safer for launch and will these changes be made to all the other shuttles?
OK. This is another good question about the shuttle and her tiles, and this question is aimed at is there any way to make the tiles more durable in the future. And indeed, the answer is yes. We have a new shuttle tile system that's been developed. The surface coating of the tile is 78 percent tougher than the tile coating that we've used in the past, but as you can imagine, to be tougher it's more dense and therefore more heavy, and so we use this relatively sparingly. We will use it at the perimeters, the perimeter tile of the main landing gear door and the nose landing gear door. We'll also use it around the external tank doors that need to close after we separate from the ET.
So there is a better tile out there. We will not be able to replace all the tiles on the orbiter, both from a weight perspective and a time-to-replace-the-tile perspective. You can imagine it would take a heck of a long time to replace the 20,000 tiles onboard the shuttle, and so we will put them again in selected areas where we need the improved toughness, and leave the original tiles where they are, which is virtually the whole belly of the orbiter, with the exception of those areas that I mentioned.
Lisa from Clinton Twp: What type of fuel is used and how much is used for the space shuttle?
OK, the fuel onboard the shuttle. Most of the fuel is in the external tank. The external tank is actually two tanks in one. We have a liquid hydrogen tank, which contains 383,000 gallons of hydrogen, and we have a liquid oxygen tank at the top of the external tank, that holds 143,000 gallons of liquid oxygen. Those fuels combine in the shuttle main engines to provide the thrust from the SSMEs (space shuttle main engines).
There are several other fuels onboard the shuttle, in particular for our reaction control system, we have monomethyl hydrazine and nitrogen tetroxide as the two components of that fuel system. Those are hypergolic fuels that ignite when they combine and are very, very good fuels for the reaction control system that steers the orbiter when it's on orbit.
So most of the fuel is spent during the first 8-1/2 minutes of ascent from the external tank. We also have the hypergolic fuels that I mentioned for the reaction control system. Those same fuels are used for our orbital maneuvering system pods that fire the main engines for the orbital maneuvering system to slow the orbiter down so it can fall out of orbit.
Jennifer from Green Bay, WI: Will we get to see what is going on inside the shuttle when the crew is getting ready for liftoff and also when in space?
On launch day, as the astronauts are boarding the shuttle, we will have a special camera inside the crew module that's put in there by the astronaut closeout team. The closeout crew is our ground support folks who help the astronauts board the orbiter, get their lap belts all fully tight, get their comm (communications) hooked up, get their oxygen hooked up to their suits, etcetera, and during that process, we will have a camera or two inside the crew module as the astronauts are getting strapped in, doing comm checks with my launch team, etcetera.
That camera, unfortunately, has to come out. It is not a flight worthy camera. So just prior to closing the hatch, that particular camera will be removed from the crew module, so we won't see any more camera, any more views of the astronauts during liftoff. But of course, once we get into orbit, there are several cameras that the astronauts set up, so we'll see quite a bit of activity during our whole flight.
John from Ronkonkoma (Long Island, NY): What ever happened to Space Shuttles Atlantis and Endeavour and will they be flying in any future shuttle missions after STS-121?
Let me assure you, Atlantis and Endeavour are great vehicles and they will very much fly again. In fact, Atlantis is going through her final preparation in the Orbiter Processing Facility for the second mission of return to flight. That mission is scheduled for August the 28th of this year. Endeavour is going through its orbiter maintenance down period, which is when we go in and look more deeply at the various systems and structural components of the orbiter and make sure she's ready to fly again. That's a relatively long process, so Endeavour's next mission is not scheduled until STS-118, currently scheduled for June 11 of 2007.
So while last summer's flight of Discovery and this week's flight of Discovery are both of Discovery, Atlantis and Endeavour are very much part of our fleet and we're looking forward to getting them back flying again.
Johnny (8) from Beecher, IL: How soon after liftoff does the commander or the pilot have control of the orbiter?
Well, the question is about the commander and the pilot actually flying the orbiter during liftoff. It's funny, the entire shuttle system is computer controlled from liftoff until we make it into orbit, so it's really like autopilot for the commander and the pilot. There are certain procedures, certain abort procedures that the crew could get into which would require the astronauts to take over flight control the vehicle, which we have never done in the history of the program. But there are those possibilities, and so there is a remote chance that the commander might have to fly the shuttle during ascent and emergency return to Earth.
But for the most part, it's all fully automated, and the commander and the pilot, while watching all systems very, very closely for good performance, essentially are hands off in letting the autopilot fly the orbiter into orbit. So on launch day, the commander and the pilot are essentially riders going along for a very exciting ride onboard the shuttle. Landing day is different.
Landing day is a bit different. It's mostly auto-pilot from our de-orbit burn of the orbiter maneuvering system engines, where we slow the orbiter down to allow it to fall out of orbit. And it's mostly autopilot until the orbiter reaches the Florida area. Once overtop of the Shuttle Landing Facility, the commander does take control of the orbiter and flies it in for its final approach and touchdown. So about the last minute or so, the commander is actually flying the vehicle and landing the orbiter itself.
Pawan from Sharjah: Have the astronauts undergone training to repair the space shuttle tiles?
That is a great question about repairing shuttle tiles on orbit. You may recall that during the STS-114 mission, we had a special test set up for the astronauts where they went out into the payload bay and performed some, some shuttle repair techniques on tiles and the reinforced carbon-carbon panels that are used, the leading edges of the wings. That proved out to be pretty good. We're going to repeat that test this time onboard STS-121 with a slightly different application of the tile-repair technique, but all aimed at providing some amount of repair capability for the tires and the panels of the leading edges of the wings.
This is not a certified system yet; this would be a best-case effort. It's really part of our test flight program to prove to the ground controllers that we have the capability to repair tiles if we had one that's damaged to the point that we'd want to repair it before we bring the orbiter back home.
Mike Vestergaar from Fredericia, DK: How much time in advance do you normally put a shuttle stack out on the pad and is the TCDT always performed 2 weeks ahead of launch day?
Well, the shuttle normally rolls out to the launch pad approximately one month before its scheduled liftoff. There are several tests that we have to perform on the orbiter that can only be done at the launch pad for either safety reasons or from a time perspective. Things like the loading of our hypergolic propellants can only be done at the launch pad; the installation and connection of our ordnance that separates the orbiter from the tank and the tank from the boosters, etcetera, that ordnance can only be done at the launch pad for safety reasons.
And there are several other tests we have to do out at the launch pad that cannot be done anywhere else at the Kennedy Space Center. One of those tests is the Terminal Countdown Demonstration Test, where the astronauts come to town and interact with the launch team and practice the launch countdown in their fully suited flight suits, get onboard the orbiter, get strapped in just like they're going to do on launch day, and that's typically done about two weeks prior to flight. So again, the vehicle goes out about a month before liftoff. We're watching continuously that we don't have any bad weather in the area that may force a rollback of the shuttle back to the Vehicle Assembly Building. So we have the capability of rolling back, should we need to if there's a hurricane or some other system threatening the east coast of Florida.
David from Oviedo, Spain: Will the external tank re-entry be recorded in any way through on-board cameras or directly by the astronauts?
The external tank separates from the orbiter about 8-1/2 minutes after liftoff. We have cameras in the belly of the orbiter that take pictures of the tank as it's falling away from the orbiter. We also ask the astronauts to perform a roll maneuver of the shuttle itself so that the astronauts can take pictures of the tank from the crew module windows as the tank is falling away from them. And so we take photographs from the belly of the orbiter, the wells of the orbiter where the tank and the orbiter connect, those are automatically taken at separation, and then the astronauts also photograph the tank after separation.
But once it gets several hundred or a thousand feet away, the photography gets really pretty poor. We photograph as much as we can, but the final stages of the external tank's reentry into the atmosphere is so far away from the orbiter that no photography really can pick it up. So we don't actually capture the breakup of the tank as it's entering the atmosphere.
David from Oviedo, Spain: How long will it take before Discovery flies again after STS-121?
Well, Discovery will fly two times this year -- for STS-121 of course, on July 1, and her second flight this year is currently scheduled for Dec. 14. So after she lands, hopefully back here at the Kennedy Space Center, we'll take Discovery back to the Orbiter Processing Facility to begin her about three-month turnaround in the Orbiter Processing Facility, after which we take her to the Vehicle Assembly Building and mate her up with the external tank and solid rocket boosters for her next mission. So we typically can fly any particular orbiter about three times a year, and we expect to get Discovery on orbit twice this year.
Francois from Namur (Belgium) and Mike Rubenick from Thunder Bay: What happens to the external tank after being jettisoned - is it totally destroyed by atmospheric reentry or is there a chance that big pieces might fall to Earth? Is there any possible use for the external tank or parts of it that can be saved?
Well, this is a great question about what happens to the external tank after it's done doing its job. You'll recall that the first 8-1/2 minutes of the shuttle ascent, the fuel from the external tank is a source for the main engines onboard the shuttle, providing the thrust for the shuttle itself. So after those 8-1/2 minutes when the fuel's expended out of the external tank, the tank and the orbiter separate and the external tank -- not having achieved orbital velocity -- does indeed fall back to the Earth. It falls in a region of the Pacific Ocean southwest of Hawaii, and there are some pieces onboard the external tank that are so large and are so massive that they do make it through the orbital breakup and do fall to Earth.
In particular, there's a beam that goes through the intertank of the external tank that essentially connects the two solid rocket boosters at their forward location to the external tank itself. That's a very massive beam, it's 4 feet deep, and that beam makes it back down to the Earth and falls in the ocean as I described. There are other pieces of the external tank that make it back to the ocean too. Some of the valves make it back down, probably some pieces of the skin make it back down, but a lot of it is burned up in the atmosphere during reentry. And even though these pieces fall back down to Earth, they do fall in the ocean. They're not recovered. And in fact, even if we could recover them, they would have seen atmospheric reentry and probably would be non-reusable for any future mission.
Abigail from Pembroke Pines, FL: How fast does the space shuttle and ISS move in orbit? Does it feel like they are going that fast?
Well, the question is about how fast do the space shuttle and International Space Station travel in orbit. They go 17,500 miles per hour. That velocity is necessary in order to stay in orbit and not fall out and return to Earth. There's really very little sensation of the astronauts going that fast. The best indication is when they look out the window and see the Earth moving by so quickly below them. But they are at about 230 miles high, so even that sensation -- the Earth going by below them -- is a relatively slow thing to look at. So they're going very, very fast. It probably doesn't feel like they're going that fast to the astronauts themselves.
Joe from jacksboro: Can you explain why the shuttle breaks the sound barrier on the return to Earth when it is already traveling faster than the speed of sound?
Well, the space shuttle on its return to Earth breaks the sound barrier when it drops below about 750 miles per hour. Any time you break the sound barrier, whether it's, whether it's increasing speed or decreasing speed, you're still breaking that barrier, and therefore you get the sonic booms that I think the questioner is referring to. There are two booms that come off the shuttle during landing. One comes off of the nose of the orbiter when it breaks the sound barrier as it's decelerating, and the second one comes off of the tail of the orbiter at, for the same reason slightly later, maybe a second or so later. So a spacecraft will break the sound barrier during ascent. It also breaks it during descent.
Jennifer from Green Bay, Wi: How big is the living quarters on board Discovery?
Well, the living quarters onboard of a shuttle are relatively small. I like to compare it to the size of a typical walk-in closet you may have at home. But on orbit, as the astronauts are weightless, they have that full volume to move around in. And so, while on Earth we only walk around in two dimensions, on orbit the astronauts have the full three dimensions and so it feels much bigger to them, although it's really not much bigger than the closet, as I described.
For this mission, they will also have a multi-purpose logistics module that they can float into, and of course, after they dock to the International Space Station, they have that space to get into, as well. So I'm sure once docking is achieved to the space station, they'll feel really good, because they have that much more room to move around in.
Junichi Maki from Niihama-City: How long is shuttle's robotic arm and what is the length of the CanadaArm on the ISS?
Onboard the shuttle currently, we have two arms. We have the original shuttle arm, which is about 50 feet long and that's on the left-hand side of the payload bay. Since the Columbia accident, when we needed to inspect the belly of the orbiter, we developed a second arm which is on the right-hand side of the ship. It is also approximately 50 feet long. And so we can connect those two arms together on orbit and make a capability of about 100 feet to reach the belly of the orbiter to inspect for tile damage.
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