Ask the Crew: STS-98

From: Marcie Butcher from Marion, Ind., age 47
To: Commander Kenneth Cockrell

Question: I understand Flight Dynamics 101, but I want to know the actual process that takes place when the orbiter does the ˝ roll after clearing the tower during the launch. What all has to take place for this event to take place?

Cockrell: First of all, the reason for the roll is because we use the Apollo launch pads for shuttle operations. And because of the way the Apollo launch pads were constructed, the space shuttle has to be on the launch pad with the back of it basically facing south. And because we fly uphill inverted, we have to roll around to get the back of the vehicle pointed in the direction we want to go for ascent. The actual process that happens is the flight control computers, or the flight control portion of the computers, commands the roll and the roll is caused by the gimbaling of the solid rocket motor nozzles as well as the shuttle main engine nozzles. They move very slightly on their gimbals and create the rolling moment force that is used to roll the vehicle around. It is quite a fantastic feeling inside because besides rolling it gives you a yawing feeling because we are above the axis of roll in the cockpit. So it gives you a good swing around. And then when the roll is complete it usually over shoots a little bit and comes back and so it sort of feels like you are on the end of a rope being swung around and it is a lot of fun.

From: Howard Leeming from Poulsbo, Wash., age: 37
To: Commander Kenneth Cockrell

Question: Why switch to manual control of the shuttle on descent for the landing? Why not use the computers to handle the task? It is done on commercial airliners and military planes, and it removes any chance of human error.

Cockrell: We get asked this question quite often. There is quite a bit difference between a space shuttle landing and that of an airplane, whether it's commercial or military. Airplanes have the ability for the pilot to take over, and make a misapproach if anything goes wrong or if they see any equipment malfunctions on the autoland systems. In fact I have flown quite a few automatic landings to aircraft carriers and it is true the automatic landing systems usually make very precise landings. However it is also true that sometimes they don't. Some little thing may go wrong or some sensor may provide an input to the system that gives you a little bit of a scary ride. And it is nice to be able to take over disconnect the autopilot portion, add power and go around. That is something that we can't do on the shuttle. In fact during testing of the autoland system using our shuttle airplanes which model the behavior of the shuttle, we found that there are some fairly large dispersions between the planned touch down air speed and the touch down air speed the autoland actually accomplishes and because we are landing very close to the limit speed for our main gear tires we really can't handle those kinds of dispersions. So, over the years the program has come to the decision that it's best to let the pilots actually make the landing for two reasons. One is we can't make a go around if there is a system problem with the autoland. And the second one being that we actually can do a slightly better job at controlling the touch down air speed, which is important for the main tires. So for the foreseeable future or at least with the current autoland system we plan to land it manually. That happens to be good news for the pilots because we enjoy doing that.

From: Carron Schweiger from De Pere, Wis., age: 20
To: Commander Kenneth Cockrell

Question: I am in the elementary/middle school education program at St. Norbert College, De Pere, Wis. Our project for this semester is to teach a 10-week unit on the space station/space travel to a group of sixth-graders. One of the questions our group has is how do the shuttles get back to the Earth? For example, when they lift off, there is fuel and whatever else to get them started. But how do they get that boost or whatever is needed to get back here?

Cockrell: We do have a lot more fuel when we lift off, fuel that provides power to the main engines and also the boosters are filled with solid rocket fuel. But on board the shuttle there is quite a bit of fuel that we use for maneuvering in orbit, including raising and lowering our orbit. Returning to Earth is simply a matter of reducing your speed. You don't have to reduce it very much either. Something around the order of about 180 to 200 miles per hour reduction of speed, is enough to make you lower the orbit to the point where it'll descend into the upper reaches of the atmosphere and then the drag from the atmosphere allows us to slow down and also change our path and move from left and right to aim directly at the landing site, and we can control ourselves with the atmosphere. But, the answer to the question is that we just use some of the fuel that we saved for the end of the mission to reduce the orbit speed just a slight amount and that causes us to drop out of orbit and into the Earth's atmosphere.

From: Mike from Smyrna, Del., age: 14
To: Pilot Mark Polansky

Question: My class just did a little report on what it would be like to be part of the crew for a space shuttle or space station, and I figured I would ask the experts. What is it like to work in a gravity free environment?

Polansky: Being a new guy I will say it is just utterly fantastic, and there are some differences of course. You float around a lot and the new fliers sometimes go a little bit too fast, maybe you bump off a wall or two. So you need to go slowly and you need to hold onto things and use your hands and feet to sort of keep you in place while you are doing work. On the other hand it's a lot easier to work in space because you can get into lots of places you can't get on the ground because you can work in any orientation whether it is right side up, upside down or sideways. And so that makes our task of building the space station and working inside the lab a lot easier as we are trying to get tools in place. So there are pluses and minuses about being in zero g for work but as far as the experience it's just wonderful.

From: Zack from Atlanta, Ga., age: 5
To: Commander Kenneth Cockrell

Question: I got a blue "flight suit" at Kennedy Space Center. Do astronauts wear flight suits like mine? Do they get a new patch for every flight?

Cockrell: Well, first of all we do wear flight suits similar to the one you purchased. We wear them to fly in the T-38 airplanes which we use to keep us proficient as pilots and as crewmembers in between our space flights. And, yes, we do get a new patch for every flight. In fact, the crew has a hand in designing the patch, and we put pictures and emblems on the patch that are significant to what we will be doing on that flight, and usually the patch carries our names on it. And we're usually very proud of the patches that we design, and we wear them on our blue flight suits when we go flying in T-38s, and we also have a copy of the patch on most of our flight data file, our checklist, and the patch is there also on our space suits that we go space walking in, and also the orange suits that we use for take off and landing in the shuttle.

From: Greggory Blunt from Memphis, Tenn., age: 30
To: Commander Kenneth Cockrell

Question: Congratulations on a model launch of Space Shuttle Atlantis. It was a sight to see. Can you say how soon Destiny will be fully operational?

Cockrell: As you probably know, Greg, we brought up just the minimum number of racks needed to provide environmental control and also attitude control in Destiny. And the next two flights will bring a total of 11 more racks, bringing the number to 16 that will be installed in Destiny. The laboratory holds 23 racks. There are slots for 24 but one of the spaces has a window in it so we're not going to put a rack there. And as each flight comes up, there will be a greater capability installed in Destiny. By Flight 6A, we'll be running the Space Station robot arm from inside the lab at what's called the Robotics Workstation, and then also science will have begun and the medical facility will have been installed by that flight, and subsequent flights will bring more and more science. The concept of Destiny is one of adaptability and change, and you'll see racks being traded out and maybe not always the full complement of racks aboard. It just depends on what research is scheduled at which time and what missions they can be fit on, so you'll see the science complement of Destiny changing, and the type of research that's done on board the laboratory changing.

From: Alex Miller from Moss Beach, Calif., age: 13
To: Mission Specialist Tom Jones

Question: Tom Jones, you met my father when we were living in Baltimore. His name is John Miller, who used to be the former baseball broadcaster for the Baltimore Orioles. I am extremely interested in pretty much anything at all about space, and in the future, I am greatly hoping to become an astronaut myself. The question that I want to know is what sensations do you feel when you exit the space shuttle or space station for an EVA? Do you feel a sensation of vertigo, a sensation of awe looking back at the beautiful sight of Earth, or frightened at the reality that you are floating in the vacuum of space?

Jones: I didn't feel a sense of vertigo when I went outside on our EVA. But, I did sometimes feel after working in someplace for a few minutes that I had a sensation of disorientation. Not knowing which way was port or starboard, or which way was back to the orbiter hatch, which way was to the front of the space station. That's just because you get turned around while working and especially when it is dark it is hard to locate yourself. So, you have to take a moment to look around and reorient. You do have a stupendous view of the Earth, it is much better out of the helmet than inside the orbiter, just because the window frames are not in view and your helmet permits you to see almost a full 180 degrees from side to side. And, I wasn't frightened at being in the vacuum because the spacesuit is a superb little spaceship in itself. And it protects you from micrometeoroids and extremes in temperature outside and of course keeps the pressure next to your body so that you can breath and maintain the workload that you're keeping up with outside. Thanks.

From: Jacco van Schaik from Almere, The Netherlands, age: 35
To: Commander Kenneth Cockrell

Question: I have a couple of questions about the re-entry procedure. How far ahead of the landing site do you start the retros? How long do you burn them? What's the delta-v resulting from the burn?

Cockrell: Actually, we don't have separate engines called retros; we use sort of multi-purpose engines known as the orbital maneuvering system engines. They're used for everything from a little bit of assist during ascent to the rendezvous burns that we conduct to adjust our orbit to enable us to rendezvous with another space craft such as International Space Station. And we use them also for deorbit. The only difference is that we turn around and face backwards and fire them in reverse. The burn usually lasts about three minutes, somewhere between two minutes and 50 seconds and three minutes and 20 seconds or so, and the change in velocity is very small compared to our 17,500 miles per hour. We probably change our speed…the number is usually on the order of 300 to 330 or so feet per second, which is maybe 250 miles per hour or about 350 kilometers per hour. So it's not a very big change in velocity at all; it's just a slight amount that causes us to drop a little bit lower in the orbit and for the atmosphere to capture us and bring us down to Earth.

From: Remy Autz from White Bear Lake, Minn., age: 32
To: Mission Specialist Tom Jones

Question: How long do the astronauts usually wait to go on a space walk to prevent getting sick in their space suits?

Jones: We usually wait on the basis of our experience till the third day of a flight to conduct the space walk. It's not because of nausea because we have medicines that can take care of that, but your head is usually somewhat congested for the first few days after launch. As the fluid in your lower body, your legs, shifts to your chest and head and that makes your sinuses clog and that can present a problem when you repressurize to cabin pressure after a space walk. The lower pressure in the spacesuit comes up to cabin pressure, and it can cause some ear pain or sinus pain if you don't have good breathing passages and sinus passages. And that is why we wait for the third day of a mission to conduct our space walk, at least.

From: Jake Davenport from Des Plaines, Ill., age: 28
To: Mission Specialist Robert Curbeam

Question: I have wondered about this for the past 15 years and have yet to find an answer anywhere: What is the effect of lighting a match in zero gravity? My assumption is that it would form a "ball" of flame. Is this true, and why or why not?

Curbeam: Well, Jake, I have never lit a match in zero gravity because that's not allowed here. But, I can tell you what happens when you light a fire, because on my last flight we had a fire, a controlled fire, on one of our experiments, and what happened is it does form a ball of flame. But, because convection depends on gravity it burns for a very short time and it burns very, very hot and burns up all the oxygen around it very quickly and then goes out.