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STS-111 Space Shuttle
Question and Answer Board

Jim from Blue Springs, Missouri
When a launch has to be canceled within a few minutes of lift-off, what procedures have to be done to ready the shuttle for the next launch date?
There are a lot of things we have to go do. But the primary thing, and the one you most often hear about, is generally speaking for a short-duration launch scrub that we've had the main thing we go do is fix any little problems we may have had or what caused the launch scrub. We'll actually go fix a large technical problem. If the delay is of a larger magnitude, two, three, four days maybe, we'll go and reload what's part of our Power Reactant System. This is the thing that generates electricity for the orbiter when it's up in space. And that process takes at least two days so we need at least a three-day scrub in order to go do that sort of thing. It all depends on how long your scrub is for and for what reasons.
Debra from West Palm Beach
Where does the crew stay during a launch delay?
During the launch delay they stay in the same place they were staying prior to the launch. We have a crew quarters area located in one of our buildings around here, and the crew just goes back to their little hotel rooms that they have here on the Center, where they're kept nice and safe and isolated from everyone else because they are under a kind of quarantine. But that's exactly where they stay, where they were before.
Dan Andrews from West Islip, New York
How come planes can fly in the rain but something as advanced as a shuttle can't?
I can understand why you would ask that question. The shuttle cannot fly in the rain because those tiny little water droplets of rain when they hit a tile and the shuttle is traveling at say 300, 400, Mach 2, at those kinds of speeds, it acts almost like a bullet hitting that tile. The tiles are very brittle and fragile on their outside, so they can't stand to hit raindrops going at high speeds. So I can understand why you'd be confused about this very high-tech thing that can't do something as simple as fly through the rain. But that's why we can't do it.
Leonardo from Laredo
What does STS mean? For example, STS-111.
It stands for, very simply, Space Transportation System. When they were originally designing the shuttle, that was the official name that everybody gave it. So, when we fly a mission, we are flying Space Transportation System mission 111. That's where it comes from and what it means.
Steve from Mt. Dora, Florida
During launch the solid rocket boosters provide the lift. What help do the main engines on the shuttle provide?
Well see, they are also providing some of the lift. Each one of those main engines generates about 400,000 pounds of thrust, so you're getting close to 1.2 million pounds of thrust in addition to the six million pounds of thrust you're getting from the solid rocket boosters. Overall the shuttle is generating seven million pounds of thrust at T-0 so you get some idea there that the main engines are doing a lot of the work, they're not just along for the ride at that point.
Taylor from Colorado Springs
Jon - can you tell me why the space shuttle's engine nozzles appear to "wobble" during liftoff? Does this truly happen or do I just need a new TV?
No, you don't need a new TV set. They really are wobbling. When those main engines ignite, the initial flame and explosions going on inside the engine bell are not evenly distributed as they are when the engine is up at full throttle and running. So what you have is it ovals, then goes back to circular, then ovals in the other direction, sometimes there'll be an explosion on this side, so they really do move quite a bit, that's not your imagination. And you may have noticed before the engines start they do an engine gimbal as well. Well as soon as those hydraulics lock into place, as soon as you get the engines up to full power and there's no more uneven distribution of the loads in the engine, then you see them settle out. Yeah -- your TV's doing fine.
Mark from Albuquerque
How to mission managers keep track of who fixes a specific part when needed? The team that fixed the valve on the launch pad seemed to complete the work in a timely manner and no delays were caused. Can you give us an idea of how many people are involved in keeping the program successful?
Depending upon where the problem is, that would determine who's going to go fix it, or what the problem was. We have, the last number I heard, was about 17,000 people who work in the shuttle program to keep these things flying safely. And that all comes down to at one point if you have for example the valve failure that we had last week there is a team of engineers who work on the Orbital Maneuvering System, we know who they are, we also have technicians who are better at working that sort of thing than they are working on other systems on the orbiter, so whenever we have a malfunction or a breakdown, we call upon these people who are the experts, if you will, in that area. And that doesn't just include experts here at the Kennedy Space Center. There are experts at Johnson Space Center in Houston Texas as well as in California. And these folks are consulted on the right way to go do the fixes. It's a very large team effort, but when it comes right down to it, here at Kennedy Space Center it's the technicians we have here that go and do the work.
Seth from Seattle
When the orbiter returns from space, are the main engines on or is the entire return maneuver that of a glider?
It is indeed that of a glider, in fact the astronauts sometimes refer to it as a "brick with wings," once you fire those Orbital Maneuvering System engines, usually one hour before landing, and sometimes over Australia, to give you an idea of how far away it is, then the orbiter turns around and begins that glide, usually at an altitude of about 400,000 feet we begin what's called entry interface, that's when they can begin to feel the effects of the Earth's atmosphere, they also use, once they get into the dense enough part of the atmosphere, they can use the aerosurfaces like the elevons, the body flap, and the rudder speed brake, to help control the orbiter. Between the time they fire the Orbital Maneuvering System and when they begin to feel the effects of the Earth's atmosphere, they do use the reaction control jets, but they're not for boosting, or allowing you to glide. Once the orbiter is in the Earth's atmosphere, the rocket engines of the Reaction Control System are no longer used, and the orbiter really is just a brick with wings and they only have one shot and landing, there is no way to pull up and go around if they missed the runway by any measure.
Dave from Ft. Leonard Woo
Heat tile loss from the shuttle used to be a problem early on in the shuttle program. Has tile loss been solved completely? How many tiles (average) come off each shuttle mission?
Very few of the tiles actually come off anymore. The reason we usually replace tiles now is because they've been damaged slightly, or maybe they've gotten a little old and look a little bit worn and crusty perhaps. But we have solved 99.9% of our tile problems that we had, you remember way back in the early part of the program, when they were indeed just falling off, but we've fixed that problem, and there's very few to replace, I'd say the worst mission I think I've heard lately they had to replace 12 tiles. And most of the tiles we replace are damaged when we're coming in for landing, and the main gear touchdown, and that throws up a little bit of rubber perhaps, or debris, from the landing surface, and that's what causes it to damage tile, right behind the landing gear.
Aaron from Sydney
Is it possible for the shuttle to make a return trip to Mars? If not, what are the limiting factors?
No, it is not possible for the orbiter to go to Mars. It is not possible for the orbiter even to go back to the moon. The reason being we don't have enough of a propulsion system to allow them to get that extra bit of miles per hour that they need. When they're orbiting the Earth they're going about 17,000 miles per hour. If you're going to go to the moon, or even on to Mars, you've got to get to at least 25,000 miles per hour, and the Orbital Maneuvering System engines are designed to do only a job in low Earth orbit, to boost us a tiny bit or to slow us down enough to reenter the Earth's atmosphere there is no way that we could get enough fuel on board to get us enough "oomph" to get us out to the moon or Mars. I'm sorry, because I would love to go to Mars in the space shuttle, it would be a lot of fun.
Douglas from Elizabeth City
How much fuel does the space shuttle use per flight?
The space shuttle uses, believe it or not, half a million gallons of hydrogen and oxygen on every flight. During the initial part of the liftoff, it's using a thousand gallons per second. Now if we were to take the pumps on board the orbiter that are pumping the hydrogen and the oxygen, and we were to pump water instead, we could drain an average-sized swimming pool in about 25 seconds. So that gives you some idea of how much fuel and oxidizer we're using here at NASA.
Jeff from Binghamton
From one of my 6th grade students, Adam. My question is how does the shuttle know how to enter the atmosphere so it lands at that tiny runway? How hot does it get slowing from 17,000 mph?
I kind of started answering that one a little earlier. The orbiter does know, it's got onboard Initial Measurement Units that tell it where it is in relationship to everything, but the main reason is we know when to do the deorbit burn, when we're going to have entry interface, how the handling characteristics of the orbiter are once we're in the Earth's atmosphere. Once you begin to feel the atmospheric drag at 400,000 feet, the orbiter is flying at a fairly steep angle, about 40 degrees is the angle of attack. And so it's putting that blunt surface into the atmosphere and slowing it down, and it's also doing a series of what we call S turns, where it's bleeding off energy, it's going from 17,500 miles per hour, which is Mach 25, at entry interface, down to a touchdown speed of about 220 miles per hour. So, the pilots are just good to begin with, they weren't selected to be astronauts if they weren't good pilots, and plus we have this special aircraft called the Shuttle Training Aircraft, that's a modified Gulfstream, which mimics the behavior of the orbiter very closely, and so before they ever do a landing in a real orbiter, they've done one a few hundred times in the Shuttle Training Aircraft. So they get the exact feel of what it's going to look like, what the sensations are. The only time the commander takes control and flies it is during the last couple of minutes of the flight. The rest of the time, it's the orbiter's guidance computers that are handling it, guiding it through those S turns.
David from West Palm Beach
Why doesn't the space shuttle go directly to the ISS instead of spending a day before linking up?
I like that question, Dave, because it makes a lot of sense to ask that. The reason is, there's two reasons really. The first thing is, we need to get up into orbit and verify that everything is working, from the Shuttle's robot arm to all the other mechanisms on board the orbiter, make sure they come through the launch A-OK and nothing is troubling the orbiter. The other reason is, if you're going to get space sick, it usually happens in the first 24 hours. And the last thing we want is nauseous, ill-feeling astronauts trying to do a very critical maneuver like coming in and just barely docking with the International Space Station. It has to be done very very precisely, and if you're not feeling well, you're nauseous from getting space sick -- and close to half the astronauts do get space sick - we don't want you doing that. So we launch, we take our time, we check the orbiter out, we make sure the astronauts are all checked out and they're A-OK too.
Ian from Burbank
Why does Endeavour have a 'u' in it? Did Webster miss this one? Author, harbor and color, to name a few, don't have a 'u'.
Well, Ian, you've been looking at the wrong book. You shouldn't have been looking at your dictionary, you should have been looking at your English history book. Endeavour is named after one of the exploration ships of Capt. James Cook of the English Navy. He did his exploring back around the time of the American revolution, in fact he discovered New Zealand, and also the Hawaiian Islands, in fact he was killed when he discovered Hawaii. Had a problem with the natives there. So it's named after the English ship Endeavour. And by the way Capt. Cook also had another ship, in one of his previous times, that was called Discovery. So that's where two of the names of our orbiters come from.
Don from Waycross
Why is liquid hydrogen allowed to escape from the main fuel tank?
We have to do that. The reason is, the hydrogen is very very cold and boiling off. And if we don't let it boil off, we can't keep it sealed in that container and eventually that container, called the liquid hydrogen tank, will explode. So we have to allow that gas to escape so we have the hydrogen vent arm, the HVA we call it around here, that allows that gas to escape. We want to keep a certain amount of pressure inside the tank, but we don't want it to build up too much. And if you're thinking perhaps, say, just filling the tank up a little bit, and let it boil off, well then you wouldn't have enough liquid. You've got to have enough liquid and it's got to be filled up to nearly the 100 percent point, and at the very very top there's a small amount of hydrogen gas we call our ullage pressure and we're letting our ullage gas bleed off to keep the tank at the right pressure.
Tiffani from Beverly Hills
What sort of weather is required for launch? Under what circumstances do you have to cancel, and why?
Good question. I was out in Beverly Hills last week, where you always have good weather. There's an awful lot of things that can cause you not to launch. Today you may have seen, if you watched the launch, we did have a lot of cloudiness in the area, but it was high, thin clouds. Those are OK. If the clouds are maybe a little bit lower, or maybe if the clouds are a little bit thicker, I think somewhere around 4,500 feet -- there's a number that was being thrown around today -- if they're that thick, you can't fly through clouds that are that thick. You have to look at what temperature is freezing inside the clouds. And things like that. You have to look at winds, last week we had a big concern that the anvil clouds, if you've ever seen a thunderstorm, at the top of it you might see the very top of the thunderstorm shearing off in one direction, well those can actually cause hail and can trigger lightning, so even though the thunderstorm is 20 miles away, if the anvil is being blown over the launch pad, we can have adverse weather. We also have to worry about landing weather because we can do what's called a Return to Launch Site. So you have to verify that the winds at the Shuttle Landing Facility here at the Cape are not out of limits. We can't have too much crosswind or even too much headwind. It'd be pretty hard for us to get too much headwind or tailwind but the crosswind is something that the orbiter is only certified to a certain landing speed, and that's another reason we'd have to scrub the launch and not go for it that day. But the Launch Commit Criteria for weather is, I'm not kidding, probably about two inches thick. It's an awful lot to take into consideration.
Noah from Weatheford, Oklahoma
How long does it take for the shuttle to reach supersonic speeds?
Just to give you a couple of cute little things here, the orbiter goes from zero to 60 in about two seconds, but it's acheive supersonic speed in about 45 seconds. So the orbiter is accelerating straight up faster than the fastest stock car you can buy anywhere. Corvette, you name it, Ferrari, it's accelerating faster straight up than those cars could. It's quite a ride, if you're up on the flight deck!
Earl from Hirst
Why do most space shuttles go to the East and not the West?
Earl, they never go West. They only go East. The reason being, now they'll go North, they'll go fairly far North, but they will never ever go so far North that they're going west. The reason being, that's part of our launch area, we don't want to launch over populated areas. The folks down in Miami or the folks up in Cape Hatteras, North Carolina, have not volunteered to be part of the Great Shuttle Experiment. So we make sure that when we do these launches we're not passing over populated areas and we have launch limit lines which if the shuttle deviates out of that, then we have a situation where the Range Safety Officer has to take control. But that's never happened, and that's why we have those limits there.
Chorkler from Tatiyatka
Is it possible to launch the shuttle from California?
In fact, that was my very first job when I got out of college, I was working on a launch pad that we were building in California. but that was scrapped for a whole bunch of reasons one of which was the Challenger accident, so no, we cannot launch out of California, only because there's not a launch pad there, otherwise we could and there were a lot of good reasons to pursue it at that time, but not anymore, so no, sorry, we can't launch out of California, I love to go there and just like I was telling Tiffani, I would love to go there and launch shuttles if we could.
Scott from Cape Canaveral
Why are there no shuttle launches on Saturday or Sunday?
Well there are sometimes, but we don't usually plan them on Saturday or Sunday, the reason being the countdown is a four-day-long process, and so to keep from having people working on the weekend, we try to schedule it so we can start the countdown on Monday. It's a four-day countdown, math's pretty simple, that launches you on Thursday. Now if for some reason we have a scrub, and like this last scrub we had it put us into working over the weekend, if it just so happens it's a 48-hour delay from a Thursday launch, we're going to launch on Saturday, that's the way it's going to be. But if we have a nominal countdown, we will always start on Monday and we will always launch on Thursday. That's how we do it.
Karen from Punta Gorda
Why schedule a launch between 4 and 8 during the rainy season in Florida, when the morning weather is likely to be more favorable?
NASA's John F. Kennedy Space Center