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STS-110 Space Shuttle
Question and Answer Board

Andreas from Magdeburg
Is it possible to distinguish each space shuttle orbiter from the other by any markings other than their name on the hull?
Well let's see, Andreas -- yeah, you can. There's not a whole lot of difference. The one that stands out the most is of course Columbia, and the way you can tell Columbia is it has a large, almost looks like a missile on its vertical tail and it's called silk pod. And that's for scanning infrared lee side temperature sensing. What it was designed to do was look down over the top of the orbiter during reentry. And would look this way and that way and see what the temperatures were when it was coming in. The other thing is you can look on the wing-gloves, these are the areas just behind the crew module and those areas will be black, instead of white as they are on the other orbiters. The other orbiters have significant differences internally; some have more structure than others. Columbia is the heaviest, as it was the first one built and therefore they beefed up the structure. We learned a lot of stuff during the developmental flights on Columbia and we took some of the structure out on each succeeding orbiter until finally, Endeavour is the lightest of the orbiters, and that is something you couldn't see from the outside. Yes, there are a lot of differences but very little you could notice from the outside.
Allan from Derry
The shuttle heat shield comes into play only on reentry. On lift off the shuttle goes from 0 to 17,500 mph. On the return, 17,500 to 0 mph. Could you explain the interaction between speed, altitude and atmospheric density as it relates to the heat build up on reentry and why it is not a concern going up into orbit?
All right, first of all you notice when we first lift off you are going straight up and you are going to try to get out of the densest part of the atmosphere very quickly, because that is where a lot of heating could occur. And of course, during lift off, that is when you are going the slowest, as you start that initial ascent. Once we get up above the majority of the dense part of the atmosphere that would cause a lot of atmospheric heating, we finally begin that turn and finally have to build up some speed. We want to get a lot of altitude initially, then we have to build up speed to get us into orbit and get that 17,500 miles an hour you were talking about. During reentry, we have a point at about 400,000 feet that we call entry interface, and that is where you first begin to feel the affects of the earth’s atmosphere and feel that drag and some minor heating. The real heating doesn’t occur until you’re about 100,000 feet or more below that. But as I said, when you lift off you’re going straight up through all the dense part of the atmosphere, and when you are coming back in you are sloughing through most of the dense part of the atmosphere. So that is why you see a lot of heating during reentry and you don’t see a whole lot during launch and ascent.
Liz from Davis
How many hours of EVA simulation underwater do the astronauts practice?
Let's see -- it used to be that they practiced about ten hours in the water for every hour they spent doing an EVA. I believe that number has been reduced to just about seven to one in recent years. I'm going to go with seven hours in the tank for every hour they will spend outside.
Greg from San Rafael
Who selects the wake-up music played for the crew while the shuttle is in orbit? How long has that been a tradition?
Well, let's see...the music is selected by the wake-up CAPCOM. That's usually the person on the planning shift while the astronauts are asleep. He also gets to be the one to wake the astronauts up. And what he does is, he knows the astronauts, he deals with them and has kind of gotten some feel for them and occasionally the astronauts will give him some ideas. He tries to keep the wake-up music a little bit of a secret. It's kind of a morale thing to wake them up with some interesting music that pertains to something going on that day, or maybe pertains to one of the astronauts up there. That's how it's done!
Nikita from Round Rock
How fast does the spacecraft travel?
Gee, that's an easy one! The shuttle or anything in low earth orbit has to travel about 17,500 miles per hour, and that is roughly ten times the speed of a rifle bullet. If you think a rifle bullet is moving fast -- just imagine the orbiter. It's moving about ten times that speed. So that should give you some idea.
Nick from Melbourne, Australia
Once the countdown for shuttle launch has begun, at what point can the launch no longer be canceled? Or can it be canceled at any point during the countdown?
It can be canceled at just about any point. There does come a point when we finally have to send the command to the blow the bolts, which hold the whole vehicle to the ground. At that point you are pretty much committed. And by the way, we are so confident that the boosters are going to ignite that we send the command that blows the bolts first, then we send the command to ignite the SRBs. So once you get to that point, from T minus 6.6 seconds until very very near T zero, when we send that bolt command, we can stop the launch and shut down the main engines and save everything.
Charlie from London U.K.
How many gallons of water are sprayed onto the launch pad during the launch of a shuttle?
That's a relatively easy one. There are about 300,000 gallons of water. And if you look at the launch pad, or at some of the pictures we have of the launch pad. Just to the northeast you will see this huge water tower and in that water tower and in the huge piping that comes down from it, we have about 300,000 gallons of water. And at T minus 16 seconds we begin to flow the water underneath the launch pad. That's sound suppression water, in order to stop the echo of the engine ignition and going down and hitting the bottom of the pad then bouncing back and knocking tiles off the orbiter. So about 300,000 gallons of water will flow in 30 seconds. As the orbiter begins to lift off you may have seen in some slow-motion photos right at the pad deck there are these huge stand pipes. We call them rainbirds, and they begin to spray water all over the pad surface to cool and also to deaden the noise there as well.
Grant from Colorado Springs
How long does it take for the shuttle to reach orbit (from the launch pad to orbit)?
Today it was 8 minutes and 24 seconds. It varies from mission to mission. Depending upon whether or not you are going into a higher orbit, what inclination you are going into, the performance, and the weight of the payload. All of these things are taken into account. We generally say that in 8 minutes and 30 seconds after T zero you are going to be in orbit, just about every time.
Zoe from Santa Cruz
The shuttle stack goes into a roll program at approximately +12 sec, why? I have never heard a good explanation.
At about T plus 12, you will see the whole shuttle stack begin to do that rotation. The reason being is when the pads were built in order to make it easy for the mobile launch platform and the crawler to get to the pad area. You come in from the south so the whole vehicle is oriented and the wings are going east-west and the external tank north-south. We could have done it another way, but that would of cost millions of dollars to reorient the track, the crawlerway, the MLP and the tower. So we saved some money by making that vehicle roll. Now part of that roll is to get the right orientation depending on what orbit it is going into. If it is going into a low inclination orbit, say 28.5 degrees, it will only do about a 90 degree roll. If it is going up to the International Space Station into a high inclination, 51.6, then it's got to roll a little more than 90 degrees. The main reason we do that is for stability. The vehicle is more stable with the orbiter on the bottom. If you tie a weight on a broomstick, you will find it a lot easier to hold broomstick with the weight on the bottom than trying to balance with it on top. The other reason is it allows the astronauts to look out their window and they have a better view of the curvature of the Earth in the event of some kind of crisis or problem they have some orientation, some visual cue, as to where they are. And that's why we do it. Boy, I sure hope that was a good answer.
Roxana from Saratoga, CA
How does the numbering system for shuttle missions work? I know this is STS-110, but have heard it is only the 109th shuttle flight.
That is a common question, and I understand why because when I first came here I thought the same thing. When the flights are originally laid out -- years in advance -- they are sequential, 110, 111, 112, and so forth. What happens is one launch will need to slip because the payload is not ready or the orbiter is not ready, or something happens and we have to move them around. There's a whole lot of paper work associated with every single mission and to go back and change all the paperwork that designates STS-110 as STS-110 to a sequential number after that would be an incredible headache. That is why we don't do it. We leave it the way it is and I'm sorry if it adds a little confusion to everybody. But for our business it makes the paper work easier and once again saves a little money.
Jeff from Wichita Falls
Since there usually is no such thing as greater than 100 percent how can the shuttle's main engines withstand 104 percent power up just before SRB separation? Doesn't this cause undue stress to the engines? What would be the difference if they were powered up to only 100 percent? Especially considering the density of the air at that altitude.
That's a pretty good question. The engines were originally rated for a certain power level, a certain amount of thrust. Over the years we've done some upgrades and improvements. And now they can perform at -- surprise -- a 104 percent of their original design value. And that sounds pretty good when you say that you can do something at 104 percent so we just leave the number there. If we were to use them at their regular rate of 100 percent level, we would not get the performance we are looking for out of the engines and therefore we would have to burn the engines longer or rate them up again, which is what we do. So that is why we do that. It is 104 percent but was originally 100 percent.
Oliver from Vero Beach
How do you drink water in space?
This is one of those cute questions. You can do it in a lot of ways. What they tend to do is have a bagged drink and put your straw in there so nothing can leak past it and drink it out of the sipper you have. Another way you can do it, and I've seen it done. When they get into a playful mood, the astronauts will get enough water and make a big globular of water and it will float like a sphere, and that is what water will tend to do up in space in the absence of any acceleration and it will just float there and you will see it moving and they will take a straw and stick in it the middle of that big old sphere of water and drink it that way. I've seen it done; there are videos of it. It's kind of cute.
David from Austin
Is it possible to launch and orbit to east to west and why is it that the shuttle and station orbit cross north to south rather than just always heading east?
I love this question! You go from east to west because it's the direction that the Earth rotates in and you want to take advantage of the spin of the Earth. If you tried to go in the other direction you are going to have to fight. At our latitude, I think is somewhere around 500 miles per hour, is the speed we are moving as we go around the center of the Earth. That is 500 mph you already have towards Earth's orbit. If you have to go the other way, first you have to negate that 500 mph and then you have to add that 500 back and that is going to cost you 1,000 mph to try to go west instead of east. The other thing is for range safety. When you go out you don't want to pass over a populated area. There are people in Orlando and Miami who have not volunteered to be part of the shuttle program and if we were to have an accident we don't want to be dropping stuff on them. That's why we go over unpopulated area and that is what we head east, over the ocean. That's why we do it.
Terje from Oslo
What kind of weather conditions can prevent taking, and why?
Tanking -- how can you have bad weather just to fill up the external tank? Well, the external tank has liquid hydrogen and liquid oxygen and inside it is very very cold. And if there is a lot of humidity out there and the temperatures are just right, that humidity will come out of solution, out of the air and will bond to the external tank and form ice and frost. Now frost generally isn't too bad but if the frost continues to build up you will get ice. And the reason ice is bad, is because during a launch, vibrations during ascent could cause the ice to chunk off and knock a tile off the orbiter, which isn't a problem until reentry day when the tiles aren't there to do their job. If you have relative humidity, air temperature and wind speed -- if you get a lot of wind speed that will help dissipate and prevent the ice from forming. If you don't have much wind speed and you high humidity and low temperature it is a bad combination. That is why weather can prevent from tanking.
Mahesh from Phopal, India
How do the shuttle engines start -- pyro-electric fuse on oxygen plus hydrogen jet or like internal combustion engines?
Certainly not like an internal combustion engine, it's a multi-stage start-up. We have oxidizer pre-burners, fuel pre-burners, and oxidizer valve, high-pressure turbo valves. It's very complex and without a course in thermal dynamics and heat and mass transfer it'll be kind of tough to really explain it to you, but I'll do the best I can. What happens is we'll open the main fuel valve, this will allow the liquid hydrogen to begin to flow towards the engine. At that point we begin to open the pre-burner valves, before everything goes into the main combustion chamber, the oxygen and hydrogen are burned a little bit first to start generating some turbine speed. The turbine speed is then used to drive the high-pressure fuel turbo pump. and the high-pressure oxidizer turbo pump. Once that happens you can start feeding that stuff really quickly and then it begins to flow into the combustion chamber, and there is the big plate where they have hundreds of tubes welded to it and you begin to inject the hydrogen and oxygen into there. And you get the main combustion chamber to spark and from the point you get 6,000 degrees Fahrenheit the very high press OK there.
Charles from Oklahoma City
Why does the shuttle always orbit the earth upside down?
Ah -- good question. The reason we go in upside down is the payload bay doors. The insides of those are a giant freon-filled radiator and there is a lot of heat being generated inside the crew module. There are hundreds of electronic boxes, and the astronauts -- the human body -- is generating heat all the time. And that heat must be dissipated, and so you have water that flows into the crew module and cools it. You have radiators in there, and fans blowing across and that cools everything and that water flows back out to the payload bay. Then there is freon out there, the freon cools the water. The freon has to get rid of the heat that it just picked up from the water. It does that by flowing through the radiators. Your best place to reject the heat is to point toward deep space all the time. But when you are on the Sun side of the Earth that is hard to do. So you just turn towards the Earth and that is cooler than facing towards the sun. And instead of using a whole bunch of fuel to keep the orbiter rotating every time we go from sunlight into darkness, which is once every 45 minutes, we just stay oriented towards the Earth. There have been times when we really needed to cool the orbiter and while we were on dark side we'd point to deep space and reject more heat. But that's why we do it.
NASA's John F. Kennedy Space Center