Flying the Shuttle FAQ

 

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?

In case of emergency, can the pilot fly a shuttle manually, just using the hardware, like a fighter pilot?

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?

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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!

 

Return to top.

 

 

QUESTION:

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

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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).

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.

 

 

QUESTION:

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.

 

Return to top.