What is the highest that any shuttle
has flown? What is the lowest that any shuttle has flown?
How many thrusters does the
Attitude Control System use and what type of fuel is used in them?
How can you change your
heading in space without air?
While the Shuttle is in space
flight is the fuel that is used is burned or just jettison for thrust?
How would a comet such as
Hale-Bopp affect the Shuttle?
How is guidance using the
inertial guidance systems achieved?
What is the meaning of the
term MAX Q?
Does the space shuttle navigate on
GPS or does it navigate by the stars?
Is it true that the orbital speed of
the Shuttle is several thousand kilometers an hour?
Approximately how much
propellant is required for attitude control?
Why do the astronauts open
the payload doors once in orbit, even if there is no payload?
Who drives the shuttle when the
astronauts are asleep?
What is the highest that any shuttle has flown? What is the
lowest that any shuttle has flown?
ANSWER from Jack Knight on March 10, 2000:
The Hubble Space Telescope (HST) missions (STS-31, 61, 82
and 103) achieved altitudes of approximately 330 nautical miles (nm). STS-59
and STS-68 with the Space Radar Laboratory (SRL) payload were low altitude
flights. They inserted into an approximate 120 nm orbit and deorbited from 110
nm.
How many thrusters does the Attitude Control System use and
what type of fuel is used in them?
ANSWER from Greg Katnik on March 14, 2000:
The Orbiter has 44 thrusters. They are fueled with a
hypergolic type of fuel. That means two components, the fuel and the oxidizer,
will react when mixed together and do not need an ignition source, like a
spark, to begin the ignition process. The fact that ignition sources for 44
thrusters are not needed is a safety feature important for operations in space.
How can you change your heading in space without air?
ANSWER from Eric Hammer on April 1, 1997:
Since space is a near vacuum. Without air, there is no way
to generate aerodynamic lift. The Space Shuttle has 46 different rocket
engines. Two of these are called the OMS (orbital maneuvering system) engines
and are able to move in different directions to help guide the Space Shuttle.
The other 44 engines are smaller and do not move. By firing different
combinations of these engines, the Space Shuttle is able to move in any
direction.
In case of emergency, can the pilot fly a shuttle manually,
just using the hardware, like a fighter pilot?
ANSWER from Jon Blitch on February 24, 2000:
It's a great question so I forwarded it on to the Crew
Module Manager, Mike Parrish, in order to give you the best possible answer.
Yes, the pilot or the commander can take over from the computer by pushing one
button labeled CSS. (crew stick steering) They can also give the control back
to the computer by pushing the AUTO button. When the pilot takes over he uses a
rotational hand controller that uses fly by wire technology to process the
commands to move the flight controls.
While the Shuttle is in space flight is the fuel that is
used is burned or just jettison for thrust?
ANSWER from Mike Wilhoit on December 3, 1997:
The fuel used to maneuver the Shuttle while on orbit is
indeed burned and is different stuff than what is used in the main engines
during the eight and a half minutes of launch. The maneuvering fuel and
oxidizer are hypergolic, which means that they will ignite merely by contacting
each other, without an extra ignition source. The main engines use liquid
hydrogen and liquid oxygen and require an electronically produced spark to
catch fire. There are igniters, which are like fancy spark plugs, in several locations
on each engine because the propellants are "pre-burned" to help drive
the liquid pumps, then remixed and burned again in the main combustion chamber.
What you see coming out of these engines during launch is a slightly fuel-rich
steam, mostly water.
How would a comet such as Hale-Bopp affect the Shuttle?
ANSWER from Merton C. Flemings, Sc.D. on May 7, 1997:
Fortunately a comet presents no danger either for the Space
Shuttle or for us here on Earth. Comets are composed mostly of ice, rock, and
dust, so there could indeed be damage to the Space Shuttle if Hale-Bopp were to
pass close enough to it; since the Shuttle is moving at many thousands of
kilometers per hour through space, any small pieces of matter that it
encounters can potentially damage its hull. Fortunately, even at its closest
approach, the comet will still be about 120 million miles away--even further
away from the Shuttle than the Sun is!
How is guidance using the inertial guidance systems
achieved?
ANSWER from Victoriano Untalan on July 12, 1999:
The Space Shuttle has Inertial Measurement Units (IMUs) which
are a combination of gyros and accelerometers on an inertially fixed platform.
The spinning gyros keep a platform inertially fixed in space so it doesn't move
with respect to the stars. The shuttle moves about this fixed platform by a set
of gimbals. Sensors called resolvers detect the angle in which the shuttle
moved with respect to the inertially fixed platform. The accelerometers measure
changes in velocity (acceleration). The space shuttle position and velocity
with respect to the earth are derived from the accumulation of these
measurements over time.
For more information visit the Scientific and Technical
Information website.
http://www.nasa.gov/techinfo.html
What is the meaning of the term MAX Q?
ANSWER from Lorraine Lavorata on September 19, 2000:
Max Q stands for maximum dynamic pressure, on a launch
vehicle during ascent. After about 1 minute after launch, the loads on the shuttle
are greatest, (MAX Q). This is when the shuttle is throttled down until it
reaches the thinner part of the atmosphere. In the case of the Shuttle, it
begins to build around 35 seconds after liftoff, as the vehicle accelerates
through the sound barrier. The engines are throttled back to 65 percent power
to slow the acceleration until the vehicle ascends into thinner atmosphere and
the pressure on windscreens, nose cap and wing and tail leading edges drops.
Subsequently, at around 65 seconds, the engines are throttled back up to 104
percent power, which is full throttle.
Does the space shuttle navigate on GPS or does it navigate
by the stars?
ANSWER from David Melendez on April 9, 1997:
Actually there are two parts to this issue: "State
Vector" and "Attitude" (or trajectory and orientation). The
state vector contains information on where the Orbiter is and how fast it is
moving at a given instant in time. This navigation information is supplied by
the onboard Inertial Measurement Units (IMUs). The IMUs also provide Orbiter
attitude information (i.e., nose forward payload bay to earth, tail forward
payload bay to space etc.). The IMUs are built with mechanical gyroscopes that
drift due to friction. To compensate for this drift the IMUs are corrected by
ground uplink of tracking data. This corrects the state vector information. To
correct the attitude information, the Shuttle takes star sightings every so
often to keep the error in the attitude bellow .25 degrees. We have used GPS in
tests but only as stand-alone systems. We have never used the information from
GPS to actually compensate the IMU's or to assist with Shuttle navigation. The
Space Station, on the other hand, will be using GPS for all its attitude and
state vector data; there will be no IMUs on board.
Is it true that the orbital speed of the Shuttle is several
thousand kilometers an hour?
ANSWER from Scott Colloredo on September 15, 1997:
To maintain its orbit at 115 to 250 miles above the earth,
the Space Shuttle orbiter must travel at great speeds. The orbiter's velocity
in space is approximately 17,322 statute miles per hour (or 27,880 kilometers
per hour). For landing, the shuttles speed decreases to approximately 205 mph
(or 330 kilometers per hour) during reentry.
Approximately how much propellant is required for attitude
control?
ANSWER from Bryan Lunney on April 2, 2000:
There are two types of thrusters, vernier thrusters (25
pounds of thrust) and the primary thrusters (875 pounds of thrust). Both types
of thrusters fire in 80 millisecond (0.080 sec) increments. The duration is dependent
on how much the autopilot determines is required. A single pulse every few
minutes on verniers is usually sufficient to maintain a stable attitude, but
the actual frequency and duration is highly dependent on the commanded
attitude, the particular autopilot variables being used, and a few other
factors. The vernier thrusters have a steady state flow rate of 0.0923
pounds/second. Thus, a single pulse (80 ms) will use about 0.0073 pounds of
propellant (oxidizer and fuel). The primary thrusters have a steady state flow
rate of 3.14 pounds/second. Thus, a single pulse (80 ms) will use about 0.25
pounds of propellant (oxidizer and fuel).
Why do the astronauts open the payload doors once in orbit,
even if there is no payload?
ANSWER from Michael P. Moses on November 16, 1998:
The inside of the payload bay doors contain radiators that
provide cooling for the space shuttle. With all the electronics on-board, the
shuttle's systems get very hot very quickly. The system used to provide cooling
during ascent only has a limited lifetime (The water and ammonia used by the
system provides cooling during ascent and entry). Once in orbit with the doors
open, freon is circulated through the radiators in the shuttle payload bay
doors to provide a cooling loop, much like a home air conditioning unit.
Opening the doors is the most important thing done when the shuttle reaches
orbit. If for some reason the doors would not open, the shuttle would have to re-enter
at the next opportunity.
Who drives the shuttle when the astronauts are asleep?
ANSWER from Jerry P. Jason & James B. McDede on April 7,
1997:
The shuttle in effect has cruise control called the DAP (Digital Auto Pilot). When on orbit, the shuttle gets attitude information from IMU's (Inertial Measurement Units). Attitude is different from altitude. Attitude is the orientation of the shuttle. The GPC (General Purpose Computer) uses the IMU information to calculate when the shuttle needs to fire RCS (Reaction Control System) Jets. The RCS jets firing adjusts the attitude of the shuttle. The GPC monitors and maintains the shuttle attitude continuously, except when the crew takes manual control.