STS FAQ

The STS FAQ collects questions and answers related to the real STS, not the various available addons.

Mission profile

Ascent

What does the radio call "Single engine 104" mean?

It refers to the throttle setting. Nominal thottle setting is 104.5%, but the Block II SSMEs can go all the way up 109% if needed. So Single engine 104 means that nominal MECO targets with a single engine running at 104.5% nominal thottle setting.

How do you control the main engines?

The nominal operation mode is fully automatic, controlled by the GPCs. But the speedbrake/throttle controllers allow manual take over in emergency. This operation requires pressing a button on the controller and move the throttle controller to the current automatic power setting and release the take-over button. If you have moved the controller to the right setting, indicators on the forward panel light and indicate that you know have manual control.

Additionally, there are a number of switches and pushbuttons to manually cut off the SSMEs and manage the main propulsion system, for example power-down the controllers or manually initiate propellant dump and inert sequences after MECO.

Aborts and emergencies

Are there ejection seats on the Orbiter?

There are no ejection seats in the Orbiter. The chutes are used in a bailout situation, where the crew module is depressurized and the side hatch is jettisoned and all the crew members hook themselves to a curved pole sticking out of the side hatch and slide on it away from the orbiter and below the wings.

This can only be done while in controlled flight and at subsonic speeds, while the orbiter is still capable of gliding. The procedure can of course be done under control of the autopilot.

Columbia had two ejection seats in its initial test flights, but they had been disabled from STS-5 on and removed before STS-61-C.

What is the "Green Apple" and why should an astronaut pull it in emergency?

"GREEN APPLE - PULL" is a common line in Shuttle Checklists, but what is the green apple?

The "Green Apple" is a tiny green ball connected to the pressure suit with a cord. When the astronaut pulls on the cord, he activates the emergency O2 supply of his suit by opening the valve connected to the cord.

Payloads

What are the maximum dimensions and mass for a payload in the Shuttle?

STS Payload Bay has a diameter of 4.6 m and a length of 18.2 m. For ISS missions, however some of the space is taken up the Orbiter Docking System so the available free length of the PLB is approx. 16.25 m.

Maximum payload mass depends on orbiter vehicle and orbit needed for the payload. It can take more into a 300x300x28.5° orbit than a 400x400x51.6° orbit.

As a space plane, the payload, which can be returned (download) to Earth, is also limited by cross range and CoG requirements.

Subsystems

APU

What are the APUs and why are they needed?

The orbiter has three independent hydraulic systems. Each consists of a main hydraulic pump, hydraulic reservoir, hydraulic bootstrap accumulator, hydraulic filters, control valves, hydraulic/Freon heat exchanger, electrical circulation pump, and electrical heaters.

Each system provides hydraulic pressure to position hydraulic actuators for:

1. Thrust vector control of the main engines by gimbaling the three SSMEs
2. Actuation of various control valves on the SSMEs
3. Movement of the orbiter aerosurfaces (elevons, body flap, rudder/speed brake)
4. Retraction of the external tank/orbiter 17-inch liquid oxygen and liquid hydrogen disconnect umbilicals within the orbiter at external tank jettison
5. Main/nose landing gear deployment (system 1)/(system 1 or 2)
6. Main landing gear brakes and anti-skid
7. Nose wheel steering (system 1 with backup from system 2).

Each hydraulic system is capable of operation when exposed to forces or conditions caused by acceleration, deceleration, normal gravity, zero gravity, hard vacuum, and temperatures encountered during on-orbit dormant conditions.

Three identical, but independent, improved auxiliary power units (APUs; also called IAPUs) provide power for the orbiter hydraulic systems. The APU is a hydrazine-fueled, turbine-driven power unit that generates mechanical shaft power to drive a hydraulic pump that produces pressure for the orbiter’s hydraulic system. Each unit weighs approximately 88 pounds and produces 135 horsepower.

The three APUs and fuel systems are located in the aft fuselage. Each APU fuel system supplies storable liquid hydrazine fuel to its respective fuel pump, gas generator valve module, and gas generator, which decomposes the fuel through catalytic action. The resultant hot gas drives a single-stage, dual pass turbine. The turbine exhaust flow returns over the exterior of the gas generator, cooling it, and is then directed overboard through an exhaust duct at the upper portion of the aft fuselage near the vertical stabilizer.

What does a APU consist of?

Each APU consists of a fuel tank, a fuel feed system, a system controller, an exhaust duct, lube oil cooling system, and fuel/lube oil vents and drains. Redundant electrical heater systems and insulation thermally control the system above 45° F to prevent fuel from freezing and to maintain required lubricating oil viscosity. Insulation is used on components containing hydrazine, lube oil, or water to minimize electrical heater power requirements and to keep high surface temperatures within safe limits on the turbine and exhaust ducts.

Why do the APU's operation create smoke puff?

The vapor clouds are coming from the Water Spray Boilers (WSB) that are used to cool the lube oil of the APU turbines by spraying a small bit of water on the heat exchanger lines. The water vaporizes and the overpressure gets vented to the outside. The turbine exhaust of each APU on the other hand is invisible.

The lube oil of each APU is circulated through a heat exchanger in a corresponding water spray boiler. Three water spray boilers (WSBs), one for each APU, cool the lube oil systems. The hydraulic fluid of each hydraulic pump driven by an APU is also circulated through a hydraulic heat exchanger in the corresponding water spray boiler to cool hydraulic fluid during hydraulic system operation. The three WSBs are also located in the aft fuselage of the orbiter.

Are they active on orbit as well?

No. Shut down shortly after MECO and aren't used again until the standard Landing-1 day aerosurface checkout.

What fuel is used for powering the APUs?

They're monopropellant which means they only use one propellant which in this case is hydrazine.

Guidance, Navigation and Control

How is the Space Shuttle controlled in real life?

The orbiter is usually controlled automatically by the GPCs except during landing and some orbit maneuvers (eg docking). Manual control is possible by using Rotary hand controllers and Translation hand controllers, which can be used in many different operation modes.

Communications

What is the purpose of the Ku-Band antenna?

The Ku-Band antenna gets used for:

• High speed communication with ground stations
• Communication with the TDRSS.
• As rendezvous radar for tracking the rendezvous target.

Payload Deployment and Retrieval System (PDRS)

What is the PDRS?

The PDRS is used to maneuver itself or an attached payload in orbit. It consists of the Remote Manipulator System (RMS), Manipulator Positioning Mechanism (MPM) and Manipulator Retention Latches (MRLs), and interfaces with other orbiter systems such as the SM GPC, the EPDS, and the CCTV.

The RMS consists of the arm itself and the controls and interfaces needed to maneuver it. It is located on the port longeron.

The MPM consists of the torque tube, the pedestals, the MRLs, and the jettison system. The MPM must be stowed whenever the payload bay doors are closed and must be deployed for any loaded operations. The pedestals contain the MRLs and the jettison electronics and mechanics and are the supports on which the RMS rests while it is cradled. The MRLs latch the arm to the MPM and restrain it during periods of RMS inactivity. The jettison allows the arm, the arm and pedestals, or the arm/payload combination to be non-impulsively separated from the orbiter if the arm cannot be cradled and stowed prior to payload door closure.

The on-orbit arm operations fall into six categories:

• contingency-only unloaded operations
• unloaded operations
• loaded operations
• deploy operations
• retrieve operations
• deploy and retrieve operations.

How does the PDRS get controlled?

All RMS operations involve a two-person operator team. Each member is vital to the success of the mission. The PDRS controls are located primarily on panels A8L, MA73C, and A8U. Other panels that affect the RMS are ML86B, A14, A7U, A6, and R13. The major PDRS CRT display is SPEC 94 PDRS CONTROL. PDRS OVERRIDE SPEC 95, PDRS STATUS DISP 169, and PDRS FAULTS SPEC 96 also control and monitor the RMS. DISP 97 PL RETENTION monitors payload retention device status.

The arm has three basic modes of operation:

• single joint modes
• manual-augmented modes
• auto modes.

How is the RMS arm stored in the cargo bay while launch and reentry?

The RMS arm is held in place by a set of Mechanic Retention Latches(MRL) of the Manipulator Positioning Mechanism (MPM).

Thermal protection system (TPS)

If there will be a damaged heat shield how will the crew change it?

Currently, there's no no way to repair the orbiter's heat shield or thermal protection system. The TPS consists of both thermal blankets, silica tiles and reinforced carbon carbon(RCC) nosecap and wing leading edge panels.

How is a damaged Thermal Protection System detected?

During launch and ascent, there's a whole bunch of ground tracking cameras and radars that observes the space shuttle for any debris events. There's even a set of seven cameras on the shuttle itself!

Here's the locations of those cameras:

• In LOX feedline fairing(black object on the middle of the External Tank). This one transmits directly to the ground during launch
• 3 cameras on each Solid Rocket Booster. These cameras are not available "live" but they're retrieved when the spent SRB casings have been towed back to Port Canaveral.

And when on-orbit, the crew will use a 15 m long Candian built Orbiter Boom Sensor System to get a real close up of the TPS. The OBSS is equipped with a Laser Camera System, Laser Dynamic Range Imager and black&white Intensified TeleVision Camera.

Also during rendezvous with the International Space Station, the orbiter will do a 360° pitch-around manuever that will allow the ISS crew to photograph the TPS that will later be downlinked to the ground.