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STS-111
Shuttle Q & A
Before
the KSC Direct! webcast of the STS-111 launch, space enthusiasts from
all over the world submitted questions for our Shuttle expert, Jon Cowart.
The questions were answered during the show. In case you missed the webcast,
or would like to review each of the questions and answers, we have provided
the STS-111 Shuttle Q&A in its entirety below.
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Jim
from Blue Springs, MO
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 ny
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, FL
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 6 million pounds of thrust you're getting from the solid
rocket boosters. Overall the Shuttle is generating 7 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 Colo 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's 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 spacesick, 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 spacesick
- and close to half the astronauts do get spacesick - 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 coulds 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. |
Noal
from Weatherford, OK
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? |
| Once
again, a very, very good question. Probably a lot of you are
sitting out there saying, "Well, why do they do that? They
know it's going to rain, why would NASA be so dumb as to go
do that?" Well, we're not. What we're doing is we're waiting
for the appropriate launch time. We're having to go rendezvous
with this thing that's already in orbit, the International Space
Station, so what we have to wait for is the Earth's rotation
to bring us underneath the orbital path of the International
Space Station. If that orbital path does not pass over us, we
have a couple hundred miles to either side of that, so that's
why the launch window is fairly short. Because the Earth is
moving from west to east, and so we will pass underneath the
orbital path of the Space Station. Once we get within 500 miles
of it, that's when the window opens. Once we get 500 miles past
it, that's when the launch window closes. When it's set right
over the top of us, that's when we're in the exact correct plane,
we don't have to do any corrections, when we're doing the launch
ascent or maybe once we get on orbit. But we are determined
the only time we can do it is when we launch northeast, and
that's why we do it from 4 and 8 p.m. right now. Six months
from now we may have to launch between 1 and 5 a.m. in order
to wait for that orbital path. Now I'm sorry, we know it's a
bad time to go launch in afternoons around here, but that's
when the orbital science says it's time to go do it. |
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