|Ask The Mission Team - Question and Answer Session|
Jeremy from Tuscaloosa: When the main engines are fired at T-minus 6.6 seconds why does the shuttle look like it goes up and back down before the SRBs are ignited?
Leinbach: Well, the shuttle doesn't actually go up and down after the main engines are ignited, but it does rock back and forth. With the orbiter on the side of the external tank and the, and the main engines of the shuttle at a slight angle to the vehicle itself, when the engines are fired, it tends to push the whole stack a little bit to the north. And so, if you look at the top of the external tank, the very tippy top does go back and forth, it goes, it goes north and then back down towards the south, and when the top of the tank reaches a perfectly vertical position that corresponds to RT-0 and the SRBs are ignited and the vehicle takes off.
Jeremy from Tuscaloosa: If the weather turns from green to red between the T-minus 10 liftoff stage, what makes the shuttle not lift off? Who has the call for the abort liftoff?
Leinbach: Well, the weather call comes to me, the launch director, from our launch weather officer, Kathy Winters, who works for the department of Air Force, and she gives me weather forecasts throughout the countdown, and gives a final "go/no go" based on her weather criteria during the hold at T-9 minutes. And so, assuming I get the green light from Kathy that we're go and we've met all of our launch weather criteria, if for some reason the weather turns bad on us in that remaining 15 minutes or so, that call would come to me and I would hold the clock. That would be a manual hold. I would instruct the NASA test director to insert a hold. We would talk about the weather and see if, indeed, the weather criteria were violated or they might be just on the edge of acceptable, and then we would have about five more minutes to talk about the weather before we'd either have to scrub for the day or lift off. So it's a manual call after we pick up the clock at T-9 minutes and it's never happened. Usually, the forecasts are good enough so we get a forecast that's acceptable for the next 30 minutes or so.
Justin from Tuscaloosa: Why does the shuttle have to go through Roll Program during liftoff? Is it because of the positioning of the ISS and the back flip to dock with the ISS?
Leinbach: Well, that's a great question, and it does very much have to do with the position of the International Space Station -- not so much the back flip when we get to the station, but in order to get the liftoff and the ascent to the right trajectory, the orbiter has to go through its roll program to align with the heading that's necessary to get to the International Space Station on orbit. So we come off of the pad and roll to a 51.6-degree inclination and press on with the ascent from there. Once we get on orbit, the back flip that you see on orbit, we've already rendezvoused, we're about to dock with the station, that back flip is in order to take pictures of the belly of the orbiter to assess the health of the thermal protection system. So by the time we get there and do that back flip, that's well after the roll program, of course, so that's a vehicle inspection maneuver, not a maneuver to get to the station itself.
Jeremy from Tuscaloosa: What will happen if the shuttle gets damaged during liftoff, and it can not get fixed in space and how will the damaged shuttle get back home?
Leinbach: Well, in the unlikely event that we do have a damaged orbiter during ascent, or if we suffer damage on orbit, the astronauts would go aboard the International Space Station and stay there until the next orbiter would come up to rescue them. We always have a second orbiter ready to go. It would launch within about 60 days or so, which is plenty of time for the on-orbit stay on the International Space Station. So the second orbiter would go up and rescue the astronauts, bring them back down, and then we would have to determine what we would do with the orbiter that suffered the damage.
And onboard the International Space Station, it is possible to have two shuttles docked to the station at the same time, obviously docking to different ports. But that's a capability that the International Space Station has and we would use if we had to.
Jeremy from Tuscaloosa: And how will the damaged shuttle get back home?
Leinbach: And for the rescue mission, our plan would have four astronauts onboard the orbiter, rather than the normal seven astronauts we put up per mission. So the four on the rescue orbiter would go up, they'd perform the rendezvous and docking maneuvers. They'd also assist getting the astronauts from the station over to the rescue orbiter, and so then on the return trip, there would be 11 folks onboard the orbiter, and we've looked at that very, very closely, and while that would be kind of cramped for them coming home, it's a perfectly safe scenario and we'd be able to land the second orbiter with all 11 astronauts onboard.
Nick from Brisbane: I am amazed how the shuttle sits on the launch pad and my question is what holds it in its place? Every time I look at it I wonder how it stays there and not fall off.
Leinbach: Well, the space shuttle system is attached to the mobile launch platform with very large bolts at the bottom end of the solid rocket boosters. Each of the two solid rocket boosters has four bolts that hold it to the mobile launch platform. They're about 4-inch-diameter bolts. They're very, very highly torqued, and they have an explosive charge attached to the nut on those bolts that releases the orbiter right at T-0. So it is bolted down, although it doesn't look like it from a, from a distance because these bolts are within containment systems within the back end of the solid rocket boosters.
Dario from Milan, Italy: In the days immediately preceding the launch, if during the night any problems on the shuttle systems are found and the launch need to be scrubbed, who makes this decision if the launch director is not on duty in that moment? Thanks! You are doing a great job there and I wish you great missions ahead!
Leinbach: We would continue on with the countdown. The point in the countdown you don't want to pass if you think you have a constraint to launch is the loading of the external tank, which is about 10 hours prior to launch. And so we get together as a launch team and as a Space Shuttle Program team and decide if, if there are any issues that we're working on that may be a constraint to launch prior to fueling the external tank. So we have the ability to monitor problems during the full three-day launch countdown and hold the clock if we need to, but scrubbing prior to external tank load usually doesn't happen.
Lynn from Hopedale: Why has Discovery been used for three out of the last four missions? When will Endeavour fly again?
Leinbach: Well, I like the question about Endeavour flying again, and she absolutely will. Endeavour is set to fly in June of 2007, STS-118. She's been going through a major modification over the last couple or three years or so, and that's why you haven't seen Endeavour in the fleet. But that's a process we put all orbiters through about every three years or so. But she's just about done with that. Final preparations for her launch will begin in the springtime and, again, a liftoff STS-118 in June of 2007. And so that means we had to use Discovery and Atlantis for all the missions since the Columbia accident, and you look at things like the weight of the payload, the capabilities of the robot arms, those types of things, in deciding which orbiter to use. And so, while the orbiters look similar, almost identical from the outside, their weights are slightly different, the capabilities are slightly different, and we try to align an orbiter with a particular payload, and that's why we've flown Discovery three out of the last four missions. In particular, the last mission with the P3/P4 truss, that was such a very heavy payload, that Discovery had to fly that mission. Atlantis weighs a little bit more than Discovery, and so we had to use Discovery for that mission. But again, you'll be seeing Endeavour fly again before too long, and then we'll have all three orbiters remaining in the fleet for the rest of the shuttle program.
Ryan from Houston: What is the feeling or mood around the Kennedy Space Center and Mission Control when the words "launch is scrubbed" are heard?
Leinbach: Well, "launch is scrubbed" are words we don't like to hear, but it's part of our business. We have so many criteria we have to meet as a team both here at the Kennedy Space Center, at the Johnson Space Center in order to have a successful and safe mission that whenever we get a problem that violates our criteria, we have no choice but to scrub the mission and try to fix that problem and come back, hopefully the next day or whenever the problem is fixed. And so "launch is scrubbed" is something we don't like to hear, but again it's part of our business. We deal with it; a little bit of disappointment, as you can imagine, in the control room, both here and at Johnson Space Center, but the team knows that we will not lift off, we will not put the astronauts in any type of jeopardy if we haven't met all the criteria. And so scrubbing is just part of the business. It's something we don't like to do it but it's a necessary part if we can't meet our criteria.
Corey from Edmonton: Why is the external tank not reused but the solid rocket boosters are?
Leinbach: Well, the external tank cannot be reused because after its mission is complete, 8-1/2 minutes into the flight, it's jettisoned and falls back to Earth and burns up in the atmosphere. It is, of course, the fuel supply for the main engines on the shuttle, and has to be with the shuttle for its full 8-1/2 minute ride to space. And by that time, you have reached your orbital altitude and the external tank, after separation, re-enters the atmosphere, burns up and falls into the Pacific Ocean.
Corey from Edmonton: What is meant by "Inclination/Orbit Altitude?"
Leinbach: Well, the inclination is the trajectory we need to put the shuttle on in order to rendezvous with the International Space Station. The space station is at an inclination of 51.6 degrees to the equator, and so, when we launch, we have to go through a roll program and align the ascent of the orbiter to reach that 51.6-degree inclination.
When we first make it to orbit, we're at about 142 miles high, and then, after external tank separation, we'll fire the OMS pods, the orbital maneuvering system engines, in order to circularize that orbit. And then, over the next couple, three days, in preparation for docking with the International Space Station, we fire the thrusters onboard the orbiter to gain more altitude to our final rendezvous altitude of 218 miles.
Dario from Milan, Italy: If the mission needs to be aborted during the ascent phase when the shuttle is not yet on a stable orbit, I guess that the decision is to be made in a few seconds. Who is responsible to make that decision -- the shuttle commander or the flight director at the MCC?
Leinbach: OK, well this is a great question and it has to do with the abort capability of the shuttle system. As we ascend through our mission profile, if we have a main engine onboard the shuttle fail, or for some other reason we can't make a stable orbit altitude, that would drive us to an abort condition.
The flight director at the Johnson Space Center has control of the orbiter from T-0 all the way through wheels stop after a successful mission. And so the flight director at the Johnson Space Center makes that abort call, and depending where in the 8-1/2 minutes of ascent to a normal altitude of orbit the failure occurs, drives which abort we would actually be in.
If the failure of an engine, for instance, occurs early in the ascent, we have the ability to abort and come back to the Kennedy Space Center, land back here at the Kennedy Space Center. If it's later in the ascent but yet not far enough in the ascent to get to a stable orbit, we would abort to one of the landing sites overseas, either in Spain or France. So it all depends on when the failure occurs, and those calls are made by Mission Control, the flight director at the Johnson Space Center.
Jennifer from Green Bay, WI: With this being a night launch, are you worried that during launch, you will not see something that could cause harm to the shuttle?
Leinbach: Well, as you well know, this is our first night launch since the Columbia accident. And after the accident, of course with the foam coming off the external tank and the video we had of that foam hitting the orbiter -- wasn't very good video, but nevertheless we were able to see what happened -- we levied a requirement on ourselves to launch only during the daytime so that we could see the ascent as best as possible and as long as possible, to see how the external tank was behaving, the modifications to the external tank.
The missions we've had since Columbia have all been very successful. The last two, in particular, have had extremely low amounts of foam coming off the external tank, well within the acceptable criteria. And so we feel, as a program, that it's OK now to go back to night launches.
And part of your question has to do with not being able to see the orbiter during its full ascent and any type of debris that may be coming off the external tank. That's going to be true for this night launch, but again, our test of the health of the orbiter is after we've reached orbit. We do that full inspection of the belly of the orbiter and the leading edges of the wings, and really all surfaces of the orbiter, using the new boom system and using the pitch maneuver right prior to docking with the International Space Station. And so, while we may not see the source of the damage if we see one on orbit, the proof that the orbiter is healthy enough to come home, that the TPS system hasn't been damaged to the point that we couldn't reenter the atmosphere, those tests are done on orbit regardless of the time of day of launch.
And so, again, we may not see where the piece of foam came off of the external tank if it's late in the ascent, but we will know if the orbiter is safe enough for the astronauts to ride back down to Earth or not.
Nitin from Hyderabad: What is Debris Verification Review? Why is it done before the launch?
Leinbach: Well, that's a great question about debris, and how do we deal with debris, and how do we try to understand what types of debris may be coming off the external tank or any other systems onboard the orbiter or the solid rocket boosters.
The debris verification review itself is a culmination of many months' worth of work by many, many engineers and technicians across the program to try to calculate, to try to analyze how much debris may be coming off the external tank and, likewise, what sort of debris impacts on the orbiter itself are acceptable.
As you might imagine, there are tiny pieces of foam that come off the external tank every launch, but they're so small that even if they did hit the orbiter, it's really not a problem to us.
And so the debris verification review, is a review of the calculations of what we expect to come off the external tank and what damage criteria the orbiter, damage tolerance the orbiter has against that expected debris.
And so it's not a review of what happened during ascent for a particular mission; it's a calculation of what we expect to happen this mission. And then, after we go through a mission, of course we go back and validate the models, we validate the calculations, and we try to match up if our assumptions on what was coming off the external tank is, indeed, what happened during ascent. And then we plug that back into the calculations for the next mission.
So it's really a comparison of allowable-sized debris that can hit the orbiter versus expected debris coming off the external tank. It's those two factors that go into the whole calculation of is it acceptable to launch or not.
Matt from Laurel: I noticed in pictures of Atlantis and Discovery, that there are "dimples" on the top and left of the nose of the shuttle (behind the RCS, in front of the cabin). I was curious what purpose they serve.
Leinbach: Well, Matt, you have great eyes to see those dimples on top of the orbiter, and indeed there are dimples there. There are dimple-like features. What they are are indentations in the thermal protection system where we have doors that open to allow the star trackers to perform their function on orbit. Once the orbiter is on orbit and the astronauts need to calculate where the system is in space, these doors open up and there are optical pointing devices that pick out certain stars to help guide the orbiter through its mission. And so the doors open, they are open the entire time the orbiter is on its mission, and they close before we reenter the atmosphere.
Francois from Namur (Belgium): I noticed that during the launch of STS-115, the orbital maneuvering system engines were used to provide additional thrust. Is it done for each launch or was it explained by the high weight of the P3/P4 truss?
Leinbach: Well, this is a really good question about the orbital maneuvering system. The OMS system is there to help circularize the orbit once the shuttle gets on orbit. During the 8-1/2 minute ride to orbit, of course all the thrust is provided by the main engines of the space shuttle after separation from the solid rocket boosters, but once the main engines shut down, the orbit is, is highly elliptical. We, we've reached an altitude but we haven't circularized that orbit around the Earth yet.
And so after we separate the external tank, we do fire the orbital maneuvering system engines at the proper time to circularize that orbit, and then we use them again to help boost the orbit slightly to get to the International Space Station. And of course, one of their main functions is to slow the orbiter down for landing, we turn the orbiter around, point it in the reverse direction of the travel and fire the OMS engines to slow the orbiter down slightly so it can fall out of orbit.
Paul from West Palm Beach: Why does the shuttle always go Northeast after a launch? Do shuttles ever go on a Southeastern heading?
Leinbach: The space shuttle always goes to the northeast after launch, and we do that in order to line up with the International Space Station to achieve that rendezvous on orbit. If we ever did try to roll the shuttle so much that we end up going on a southeastern direction, it would use up so much of the performance, so much of the fuel that we probably couldn't get to a proper orbit. And so we have just enough fuel to get to a good orbit. It's always going to go to the northeast. It's going to go to the 51.6-degree inclination of the International Space Station, and so you always see it roll on its back right after launch to get on that northeastern trajectory.
David from Colorado Spring: At launch to T+20, what speed is the shuttle traveling at?
Leinbach: Well, the speed of the orbiter, of course, starts at zero. Right at T-0, we lift off and we gain speed continuously through ascent, get up to a condition that's about three times the force of gravity at about 6-1/2 minutes during the ascent. The main engines of the shuttle are on for 8-1/2 minutes. And after that 8-1/2 minutes, we have reached our orbital speed of 17,500 miles per hour. We shut the main engines of the shuttle down and the shuttle stays at that speed throughout its entire mission. And so we go from zero to 17,500 miles per hour in 8-1/2 minutes.
Tucker from Powell, TN: Since the STS 107 Columbia tragedy, all the missions have launched from Launch Pad 39B. When will a shuttle be launched again off of Launch Pad 39A?
Leinbach: Well, the next launch off of 39A is expected to be STS-117 in March of 2007. Pad A has been going through a modification period. We need to upgrade its systems periodically. We need to do corrosion prevention and paint structures, etc., and that work is now winding down. And so, while it's not available for this mission, we do expect to launch STS-117 off pad A early next year.
Nhat Lam from Vietnam: I'm a student. Are you nervous before the launch?
Leinbach: Am I nervous before launch? No, I'm not nervous. The feeling I tell everybody is that it's an intense feeling. We have so many criteria we have to meet. It's a feeling of excitement, it's a feeling of intensity, it's a feeling of immense pride when we do liftoff. Our training is so good that we don't have time to get nervous. We know the system so well that if we experience failures, we're able to deal with them. So nervous is not the right word; intensity, pride, excitement I think are better.
Tucker White from Powell, TN: I recall back in my college days from the first four shuttle missions that the external tanks were painted white. Why doesn't NASA still paint them white?
Leinbach: Well, that's a good question about the first four missions of the space shuttle system. The tanks back then were painted white, and we decided back then we didn't need to paint them any longer. And by not painting them, we saved 600 pounds of ascent performance. It took 600 pounds of white paint to paint the external tank, and so it's simply a weight savings and is no longer necessary.
Jeremy from Tuscaloosa: What tracks the shuttle when it comes in to land? Are there tracking stations located at the runway? Do the deploy air data probes give the crew the positioning to land the shuttle?
Leinbach: OK, well, Jeremy, this is a great question about landing and the different systems we have to guide the orbiter back to Earth safely. There are four different landing aids that we use principally on landing day to make sure that the orbiter makes it back to the Kennedy Space Center, and they essentially pick up at different phases of the landing.
After we've fired the OMS pod engines, the orbital maneuvering system engines to slow the orbiter down and she starts to fall out of orbit, once it passes through the atmosphere itself, when we lose contact with the orbiter and we've broken out of that "no comm." area, at about a minute or so after that, we will turn on our TACANS, or tactical air navigation system. That's a system that's used worldwide, both in commercial aviation and defense applications. It's a long-range, air navigation system that picks up on beacons on the ground from the Kennedy Space Center up to the orbiter, and it helps align the orbiter from several thousand miles away to about 100 miles away.
Once we get about 100 miles out, we turn on the microwave scanning beam landing system, the MSBLS system. It's a similar type of system. It a little bit more fined-data tuning, I guess you could say. It guides the orbiter from a couple hundred miles out to within about five miles of the runway or so. Actually, we use it all the way down but there are other systems that come on later in the descent. Once we get just above the runway itself, there's another system onboard the orbiter, the radar altimeter.
That's a very, very fine-detail altitude detection system that tells the commander and the general-purpose computers inside the orbiter how high the orbiter is above the runway. There are landing aids on the runway itself, for ball-bar and PAPI lights, or precision path approach indicator lights, that help the commander line the vehicle up and make sure they're at the right heading.
All these systems tie together. They tie into the general-purpose computers where our flight control system software is guiding the vehicle. After the commander takes manual control of the orbiter about two minutes from landing, he uses these data also, in particular the ball-bar and the PAPI lights to help land the orbiter.
The air-data probes, themselves, that you mentioned, they deploy at about five minutes or so from landing, and it's a system that deploys from the orbiter itself and it sticks out into the airstreams and calculates the density of the air, and that data is fed to the general-purpose computers as well, to help guide the orbiter and help steer the, the rudder speed brake and the elevons for a safe landing.
So there are quite a few landing aids that come into play. They play both with the general-purpose computers that help guide the orbiter and also feed the data to the commander who needs that data to land the orbiter itself.
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