- BACK
- What is a launch window?
- The launch window is simply the time of day that a rocket can be launched
that will support all of the mission objectives. Things that are considered
when determining the launch window for a Space Shuttle launch are: whether
the landing sites for an abort will be in daylight, if the normal landing
site in Florida will be in daylight, any special payload requirements such
as being over a certain portion of the Earth at a certain time of day,
the weather predictions at the launch site for the time of year, or a rendezvous
with another orbiting body.
All Mir and International Space Station missions will have a much smaller
launch window than the 2.5-hour window usually seen on Spacelab-type missions.
The smaller launch window will be on the order of 5 to 10 minutes based
on the position of Mir relative to the launch site at KSC, available launch
performance, upper level winds, external tank loading, etc. BACK
- What does "launch inclination" mean?
- Once a space ship is launched into earth orbit, it travels in a circle
that is basically fixed with respect to the earth. The "inclination"
of this circle (the orbital plane) is the angle it makes with the equator.
Another way to look at inclination is how far north and south of the equator
will a spacecraft go during its orbit. BACK
- Why does the shuttle launch at different inclinations
on different missions?
- The launch inclination chosen for a specific flight depends on the
mission's objectives. BACK
- Could the crew launch the shuttle without the use
of computers?
- Five computers run automatically during the Ascent phase. This is necessary
since reaction times on the order of microseconds which the astronauts
could not hope to effect are needed to steer the vehicle through specific
parts of the atmosphere. The computers have automatic fault logic that
detects any abnormality in any of the computers operations and they vote
against each other. The computer synchronization required for this feat
is unique to the space shuttle and has not been duplicated anywhere else
in any vehicle. BACK
- How are the engines started prior to liftoff?
- The three SSMEs are started by the Orbiter’s onboard computers at approximately
6.6 seconds prior to liftoff. The Orbiter’s computers tell the SSME controllers
(additional computers in control of each SSME) to start a very complex
ignition sequence. The controllers open several liquid propellant valves
to allow propellant to 'fall' into internal combustion chambers. The controller
than turns on several spark ignitors (spark plugs) in each engine which
ignite the propellant mixtures in internal combustion chambers. These combustion
gases then drive propellant pumps (turbopumps) which continue to feed the
overall combustion process. Additional combustion occurs in the 'main'
combustion chamber and then the gases escape from the nozzle producing
the thrust. It is a very convoluted process with lots of feedback paths
for liquid and gaseous propellants. The hard part to believe is that it
is just as complicated and delicate a process to get the SSME’s shut down
safely at the end of their 8 1/2 minute burn time. BACK
- What is the final escape velocity obtained by the
shuttle during liftoff?
- At Main Engine Cutoff (MECO), the shuttle is at an altitude of approximately
70 miles, traveling 24927 ft/sec (about 17,000 mi/hr) relative to the earth.
At that point, the Shuttle is still not yet "in orbit". If we
did nothing else, it would come back to earth somewhere in the South Pacific
ocean. In fact, the External Tank does fall there. In order to achieve
a safe orbit, the Shuttle must coast to the highest point in its trajectory
(somewhere over Europe) and add another 90 ft/sec with its Orbit Maneuvering
Engines in order to raise the low end of the orbit to a minimum altitude.
BACK
- From a pilot's perspective, what are the differences between a night
launch and a day launch?
- Any launch is a great launch when you make it to orbit with a crew
that you enjoy spending time with. And the preparation for a night launch
versus a day launch was that we had to practice landings more at night
because of the possibility of a Return-to-Launch-Site abort. Other than
that the training is pretty much the same. The only difference I noticed
during a night launch was that the beach was lit up bright as day and things
I didn't notice during a day launch I noticed at night because they were
illuminated primarily by the SRBs instead of the sunlight.BACK
- Why isn't there a sonic boom when the shuttle reaches the speed
of sound after lift-off?
- Sound moves out and away from you in a circle, like a ripple in a pond
from a stone, at a rate of about 700 mph. So if you fly 700 mph, all the
noise you make builds up as a wave that moves along with you. During launch,
we are going straight up, so that wave is travelling with us up. By the
time we turn to parallel the Earth's surface, we're so high that there's
no air to carry the sound. If you were in an a balloon at about 20,000
feet at the Cape, you would hear the Boom as the Shuttle climbed by. But
the folks on the ground are all behind the Shuttle, so they never hear
it. BACK
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