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Jerry from London (UK): Why does the shuttle rotate through its axis immediately after take off and how is it achieved?
Ask The Mission Team - Question and Answer Session
Leinbach: Well, we need to rotate the shuttle through its axis to get on the proper azimuth for the launch inclination itself. If you look at the launch pad out by the Atlantic Ocean, it's in a due north/south orientation. So if we didn't roll right after lift-off, the orbiter would be going due east. We don't like that. We need to align the orbiter with the International Space Station inclination. So, after lift off we have to roll to achieve that heading as the orbiter continues through ascent. It's achieved by gimbling the main engines itself – the three SSME – the main engines – and also by gimbling the two solid rocket booster nozzles to achieve that roll profile.
Jennifer from Green Bay, WI: The camera views of the shuttle going up on STS-121 were fantastic!! Will those same cameras be installed on the shuttle Atlantis to see what's going on during ascent? Will these installations be normal procedure for all future missions for safety reasons?
Leinbach: Well, I can tell you those views were fantastic to the launch team, too. They were just spectacular and the short answer is, yes -- they are going to be on all future missions including the upcoming one next week. We use those for a variety of reasons. Principally, the extra cameras were put on to see any debris that may be coming off the external tank, but as you watch them you can see other aspects of the vehicle system during ascent. You can see the slight adjustments to the trajectory with those cameras. So, they are really providing outstanding engineering data as well as a lot of really neat pictures for all of us on the ground.
Ann from Sun Prairie: Can you go into some detail concerning the way the shuttle system is supported on the launch platform? I understand there are four bolts that support each of the SRBs. Do these bolts support the entire stack? What means of support is in place for the orbiter? The engineering involved just in getting the stack safely from the VAB to the launch pad is mind boggling! Thanks!
Leinbach: That's a good question, too. The questioner is exactly right. Each solid rocket booster is supported with four bolts to the mobile launch platform. They're very, very large bolts. They're about four inch diameter each. They hold up the solid rocket boosters. In between the solid rocket boosters is the external tank. It's connected to the booster with other large bolts and then the orbiter is connected to the side of the external tank with large bolts and pyrotechnics to separate it and that type of thing. So, the whole stack is held to the mobile launch platform with eight bolts and they are detonated at T minus 0 seconds -- right at liftoff. We send electrical charges that fire pyrotechnics inside the hold-down posts itself and split those nuts into two pieces and release the tension there and allow the shuttle to fly away.
Arun from Cupertino: Would you have to put more fuel into the space shuttle since it's carrying the 35,000 lb P3/P4 segment?
Leinbach: No, we don't load any extra fuel for a mission. What we do is compensate other weight consideration onboard the shuttle based on the payload's pretty high weight. This time we are only going to be flying six crew members. Each crew member accounts for about 500 pounds when we do the bookkeeping - the weight of the astronaut himself or herself along with the food and clothing and all the support that goes into flying an astronaut in space. So, we do other weight adjustments. Inside the orbiter we can fly ballast to keep the center of gravity just right. We will adjust and have adjusted the ballast for Atlantis for this mission. We have the payload properly situated in the payload bay for balance considerations. We really don't load any extra fuel for a mission -- we compensate for it in other ways.
Francois from Namur (Belgium): Why is the external tank emptied after a launch delay. Can't the fuel be used for a new launch attempt?
Leinbach: This is a great question and something we've struggled with as a team for quite some time. There are folks that believe we could leave the external tank loaded and go for the next launch attempt the next day. The fuel is reused. We drain back from the external tank into the large spheres that you see out at the launch pad. So, we do recover the fuel. Some of it is lost in boiling off during the attempt, but never-the-less we do reuse about 90% of the fuel. We do it really for one major reason: If we have to enter the launch pad after a scrub, it's a lot more safe for ground crews to do so with the external tank empty than it is full. So, that's the principle reason we drain the tank. There are other considerations. One being the fatigue of our engineers in the control room who would have to monitor the tank continuously if it were to remain full. The principle reason is the safety of the ground crews that we always send out to the pad after a scrub. That's really why we drain back.
Stan from Cincinnati: If the tank is covered with foam, and we are not looking at bare metal, then why is it orange?
Leinbach: Another good question. The orange color is essentially… the foam itself is a very pale orange, but over time it ages in contact with the atmosphere and it turns that dark orange that you see. In fact, if you look closely at the external tank where we have done the modifications to remove the various pieces of foam on the tank that we don't want to come off again, you will see the foam that has been exposed is a much lighter color. That's the true color of the foam and then over the years it turns that darker orange. The tank we're flying this mission is on the order of four to four and a half years old and so it's had that long to age. That's just a natural color change that occurs over time. It is not bare metal, I assure you. The whole tank is covered with foam to keep ice from forming on launch day.
Steve from Lymington (UK): During launch is any heat damage caused to the pad (RSS, Payload change-out room, and particularly the White room, which is very close by) due to the brief, but terrifically hot, contact with the thrust from three main engines and two SRBs? Many thanks and best wishes for STS-115 and beyond.
Leinbach: We do occasionally get damage to the launch pad from the launch itself. Things that typically occur are the elevator doors get blown off their tracks or hinges. We can get cracking to the deck of the mobile launcher platform. You'll see that about T minus 16 seconds or so we turn on a lot of water to quench to deck of the mobile launcher, but even with that we can occasionally get cracking to the steel plate of the mobile launch platform. The white room is retracted as far as we can get it away from the launch itself, so we get some rather good vibrations in the white room. Occasionally we'll get phones that are damaged. We'll get cable tray covers that are blown off. We can get bricks that are down inside of the flame trench come loose and get thrown miles away from the pad. So, it's a very dynamic situation at the pad during a launch. We do all we can to protect the ground support equipment so that the turn-around to the next flight is as brief as it can be. We've learned a lot over the years trying to minimize our damage, but there will be damage after every launch. It's just a question of how severe. Thankfully, we've never had a really severe set of damage after a launch.
Nik from Urbana, IL: Just before ignition there seems to be sparks flying at the perimeter of the nozzles. What are those? Thanks.
Leinbach: Those sparks are called our hydrogen burn-off igniters and they are intended to burn free hydrogen. When we start up the engines, there is a little bit of hydrogen that comes out that hasn't ignited yet when combined with the oxygen in the system. Also, if we do have an on-pad engine shutdown after we've started the engines and have to turn them off for some reason, we shut down fuel rich as well meaning that the last bit of fuel that comes out of the engines will be hydrogen. So, those sparklers, that we like to call them, will burn off free hydrogen in the atmosphere rather than let it ignite on its own as it travels up the side of the ship. That's a safety consideration. It burns hydrogen before it causes us any trouble.
JOHNNY (Age 9) from Beacher: Do you get nervous when you launch?
Leinbach: Nervous when we launch -- I'm nervous before we launch. When we get inside of T minus 9 minutes, I can tell you the mood inside the control room is so intense and so focused that nerves really aren't part of it. It's more of an intense feeling of making sure you are watching the right vehicle systems and the temperatures and the pressures and when the main engines start we make sure that they stay on the 6.6 seconds before lift off and if we have an engine shutdown that occurs within those last 6.6 seconds. Nervousness? No. Intensity? Absolutely. It's dead quiet in the control room. No one is talking. Everyone is concentrating on their data. Nerves after nine and counting - no. Before that, you look around the control room and you see a lot of people in there. The TV cameras, I know, are on. The astronauts are on board. A lot of visitors to the Kennedy Space Center -- No nervousness there -- a lot of pride at that point. So, nerves? No. Intensity? -- absolutely.
Brian from Peoria: What is the rate of fuel consumption of the shuttle at takeoff?
Leinbach: This is another good question. The external tank really is made up of two tanks: one for hydrogen and another smaller tank for oxygen. In the hydrogen tank we have 383,000 gallons of liquid hydrogen and the liquid oxygen tank contains 143,000 gallons of liquid oxygen. After we start the main engines, they burn for the full eight and half minutes until we reach main engine cutoff on orbit. So, if you run the numbers that equates to burning 45,000 gallons of hydrogen per minute and 17,000 gallons of liquid oxygen per minute during ascent. The solid rocket boosters each have 1,000,000 pounds of solid rocket propellant inside of them. They burn for two minutes. So, that equates to 1,000,000 pounds of solid rocket propellant per minute being expended.
Megan McKenna from Beecher, IL: After the shuttle launches, how fast is the vehicle going when the command is given to "throttle up," and how long (in seconds) does it take to reach 17,000 mph?
Leinbach: Another good question. The "go" at throttle up command is interesting because as we ascend through the atmosphere in the early stages of ascent, we go through a regime that's called the maximum dynamic pressure. The maximum dynamic pressure is a combination of the speed of the vehicle and the density of the atmosphere we are flying through. So, shortly after T zero, shortly after lift off, we throttle the main engines back down to around 64% rated power to keep that dynamic pressure on the vehicle to a minimum. If we didn't throttle down, the loads on the external tank and the solid rocket boosters and the orbiter would be too high because we'd be flying faster through this regime in the atmosphere called the maximum dynamic pressure. Once we get through that area, then it's safe to throttle back up and go for the maximum acceleration of the vehicle. That occurs when the vehicle is about 35,000 feet high. At that point in time, the vehicle is going 1,636 miles per hour when we are "go" for throttle up. Then the engines stay at the maximum power rated level all the way through ascent. We do throttle them back down slightly as we get really close to orbit to maintain no more than three G's on the astronauts and on the orbiter itself, but that is late in the ascent - maybe around eight minutes or so during the eight and half minute flight. So, the throttle up is to bring the main engines back up to speed, the full rated speed, once we get though that maximum dynamic pressure.
Mark McKenna from Hickory Hills: Launch Pads 39A and 39B are historic places in NASA history. Great space adventures and missions have begun at both these sites. Is there any NASA plan for a new launch site?
Leinbach: You're right on the money that they are great places in NASA history and really in the history of American manned spaceflight. I can remember the Apollo launches off of pads 39A and 39B. I was a youngster, but nevertheless I remember the launches - watching them on TV. Right now there are no new plans to build new launch pads. You'll see in the newspapers and on TV that we are designing in the next generation, a launch vehicle after the shuttle retires after the year 2010. As we are designing the new vehicle, we will be modifying launch pad 39B. We expect that this STS-115 mission and one more mission in December will be the last shuttle missions off of pad B -- that's STS-116 mission currently scheduled for December 14th. After we fly off at pad B in December, we will give pad B to the new program and let them modify it for their needs. In the meantime, we're finishing up modifications to launch pad 39A -- the twin pad a little bit further south on the beach. We will fly out the remainder of the shuttle program -- all flights will go off of 39A as the Constellation program prepares 39B for their needs.
Bryan from Cork, Ireland:
How does the shuttle communicate with mission control during launch, mission and landing?
Leinbach: Well, another good question about communications. On the ground, first of all, we communicate back through the control room to our Merritt Island Launch Area set-up which is a communications facility that we have here on Merritt Island near the Kennedy Space Center. On orbit, the S-band communications, which is the voice and the data communications, goes to our TDRS satellite -- the tracking data relay satellite -- that's a NASA satellite. We have three of them in orbit so we can maintain almost continuous communications with the astronauts. So, that S-band data goes to TDRS and then down to the White Sands Space Harbor out in Mexico where it's received on the ground and then distributed to the Johnson Space and the Kennedy Space Center. In addition, we have a KU-band antenna. That's a high gain antenna for TV pictures, or other uses that have a wider bandwidth when more data needs to be transmitted, we use the KU-band. Likewise, that goes to the tracking data relay satellite from on orbit -- from the orbiter to the TDRS satellite to White Sands to Johnson to Kennedy. So, it's kind of a cumbersome loop, but it works really, really well. We maintain virtually continuous communications with the astronauts now.
Tom from Avon: How is the load balanced for ascent (I would think the center of mass would be critical)? How is the load balanced for landing (sounds like it is loaded up with everything - hard to know mass beforehand and how to distribute)?
Leinbach: Weights and balances are very, very critical for ascent and landing as the questioner rightly points out. When the orbiter gets ready to roll out of the orbiter processing facility, we put it on a transporter for its short trip over to the vehicle assembly building. On the transporter we do a very, very detailed calculation of the weight of the orbiter and where the center of gravity is. So, we know exactly where that is before we take the orbiter out of the OPF. The center of gravity and the weight of the solid rocket booster and the external tank really doesn't change mission to mission, so we already have that pre-calculated. We add on the orbiter and the smart guys can do a calculation on where the whole center gravity and the weight of the whole stack is. When we roll out to the launch pad, we do another weight calculation on top of the crawler transporter with the mobile launch platform. So, that's actually weighing the whole assembly as it goes out to the pad, but that's another weight check. On orbit, before the mission even starts, mission control and the flight planners do a very, very detailed set of calculations on what we know we are going to be bringing back from on orbit. We have a contingency plan that says that if we don't get to deploy the P3/P4 solar array element for any reason we can bring it back down with us. We know that contingency case. We also know all of the trash and other supplies, other pieces of equipment we'll be bringing back down on the shuttle. It's all pre-thought out. We know what we are bringing back. We know where we are going to put it inside the orbiter. So, it's all pre-calculated. It may look like a Chinese fire drill as the astronauts are stowing stuff on orbit to come home, but it's all pre-thought out and we know exactly where it's going to go.
Mark McKenna from Hickory Hills:
Are there more landing sites besides Kennedy or Edwards if the orbiter requires it at any point?
Leinbach: Well there sure are. In fact, on launch day, we have three of what we call our TAL sites: trans-oceanic abort landing sites. These are necessary. Two of them are in Spain and one is in France. These are necessary if the main engines of the shuttle terminate early during ascent, we can reach one of these landing sites in either Spain or France. But after we go through a certain point in the ascent, then we are going so fast that if we had an engine go out we can't get to the TAL site. We essentially would abort to orbit which would mean that maybe two engines are only burning, but we can still get to a perfectly fine and safe orbit. So, we have the three sites on launch day -- the TAL sites. In addition, if we get some really wild contingency scenario, we have probably 25 or 30 emergency landing sites around the world that the orbiter can land at. We've never been to one of these sites. We've never been to a TAL site with the orbiter. We have folks over there waiting for the orbiter in case we get into that on launch day. But at the emergency landing sites, we don't have anybody pre-positioned there because of the unlikelihood of actually going there. There is a series of airports up the east coast of the United States that the orbiter can land at if we have to. We have those plans and processes in place with all of those airports if we call up an emergency site early in the ascent, we notify them, they clear their air space and the orbiter can land at one of those sites. Again, there is a couple of dozen of those around the globe in case we get into a situation where we just can't wait to land at Kennedy or Edwards, we have to land somewhere, there is some vehicle issue that's going on that says we need to get the astronauts down now, we don't care where the orbiter lands, we just want it on the ground safely with our astronauts.
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