The Way Things Work |
 |
Guidance, Navigation, and Control SystemGuidance, navigation, and control (GNC) are accomplished using GNC sensors that detect the vehicle motion and inform the GPCs what is happening to the vehicle. Guidance is where the shuttle is going, navigation tells you where it currently is, and flight control is how it will get to where you want it to go. Click here for more information about the DPS. Guidance software contains equations and tables of numbers that guide the shuttle to a desired position and velocity. For example, first-stage ascent guidance steers the shuttle to the proper attitude and velocity for booster separation. The function of navigation is to maintain an accurate estimate of the shuttle's current position and velocity. Flight control software issues commands to the main engines, boosters, thrusters, RCS jets, and aerosurfaces of the Orbiter (elevons, rudder, etc.) Click
here
for more information about guidance and navigation. |
Electrical Power SystemElectrical power for the shuttle is generated by three fuels cells that use cryogenic hydrogen and oxygen reactants. When liquid hydrogen and liquid oxygen are mixed in each fuel cell (in the prescence of the catalystplatinum), the chemical reaction produces electricity, heat and water. This process is the reverse of electrolysis in which electricity splits water into oxygen and hydrogen. The fuel cells generate direct current (DC) electricity. |
|
|
DC power is used for many things on board the shuttle including lights, fans, and computers and is also converted to alternating current (AC) for some systems. systems. |
|
Electrical power is distributed via a network of three main DC buses, each connected to a fuel cell. Most systems use two or three DC buses for redundancy, and all three DC buses are protected by circuit breakers. Click here for more information about the electrical powers Environmental Control and Life Support SystemThe environment control and life support system (ECLSS) provides a comfortable shirt-sleeve environment inside the crew module and rids the Orbiter of excess heat. It consists of four major systems. |
 Astronauts Claude Nicollier (left) and Jean-Francois Clervoy on STS-103 |
The pressurization system provides a sea-level atmosphere. The air revitalization system controls the humidity of the atmosphere between 30 and 65%. Carbon dioxide and carbon monoxide levels are controlled, and excess heat is removed by circulating the air over heat exchangers that transfer heat to water cooling loops. The water loops pick up additional heat and transfer the heat to the active thermal control system. The active thermal control system collects excess heat from the electrical and mechanical systems and transfers that heat to the exterior of the spacecraft via heat exchangers, radiators, evaporators, and ammonia boilers. |
| The
supply water system stores the water for crew consumption
and cooling. Excess water can be dumped overboard. The waste water
system stores both liquid and solid waste. Solid waste is returned
to Earth, and liquid waste can be dumped overboard or, in an emergency,
used in the cooling systems. |
 Click here for more information about the ECLSS. |
Auxiliary Power Units/Hydraulics Systems |
| Three hydraulic systems drive the aerosurfaces of the Orbiter, the main engine control valves and gimbals, the brakes, nosewheel steering, and the landing gear. Each system is pressurized by a main pump to 3000 psi. |
|
The source of power for each pump
is an auxiliary power unit or APU. The three APUs use hydrazine
as a fuel, that decomposes into the ammonia and hydrogen gas that drives
a turbine, and that in turn, through a gearbox, drives the main pump.
Each APU/hydraulic system uses a water boiler to cool the APU gearbox
lube oil and hydraulic fluid. The three systems are used during
ascent and reentry. |
 Click here for more information about the hydraulics system. |
Caution and Warning SystemsDuring flight, the caution
and warning (C&W) system uses audio and visual
alerts to inform the crew of anominal or out-of-limit conditions and
emergency situations. The C&W hardware system monitors all
Orbiter systems and failures from any system causes an audio alarm,
and illuminates an indicator on the flight deck panel. |
Fire Suppression and Detection SystemsThe
fire and smoke emergency system
consists of three permanent fire extinguishers located in the middeck
avionic bay and smoke detectors throughout the crew cabin. The
permanent fire extinguishers are electronically activated by switches
located in the cockpit. Portable fire extinguishers are also
placed throughout the Orbiter. |
Communications and Tracking System |
|
The communications and tracking system for the space shuttle allows for voice and data exchange between the Orbiter and payloads and mission control personnel. Signals from the shuttle to the ground are called downlink (voice, video, and data) and signals from the ground to the Orbiter are called uplink (voice and commands to the computers). Four systems are used for communications and tracking. |
 Astronaut Stephen K. Robinson, spacecraft communicator (CAPCOM), monitors a television downlink from the space shuttle Discovery during the first spacewalk for STS-103. Linda Ham, flight director, is in the background. |
|
The audio distribution system routes crew intercom capability through headsets and speakers, routes voice for downlinks and uplinks voice data back to the crew from the control center. It is also used to send caution and warning audio tones to the headsets and speakers. The S-band system provides the main link between the Orbiter and the ground. All voice, telemetry, and video can be downlinked via the S-band system. All voice and computer commands are uplinked using the S-band system. The system uses a phase modulated (PM) transponder for audio and digital data and two frequency-modulated (FM) transmitters for video and analog data. The Ku-band system is a high-frequency communications link for the tracking and data relay satellite system (TDRSS). This advanced system is used by NASA to track Earth-observing satellites, space shuttle missions, and special spacecraft like NASA's Hubble Space Telescope. TDRSS are in geosynchronous orbit around the Earth, where they provide continual tracking and relay during missions. Since the Ku-band system channel bandwidths are greater than both the PM and the FM S-band systems combined, they therefore permit higher data rates especially for video and payload telemetry. Ku-band is available for on-orbit operations only as the antenna is deployed once in orbit and then stowed for reentry. Click here to see a video about the TDRSS satellites. The ultra-high frequency (UHF) system is used primarily during approach and landing for voice communications with the flight control tower and with chase planes. On flights where there are spacewalks, the UHF system is used between the Orbiter and the spacewalking crewmembers. It is also a backup for the S-band system. Click here for more information about the communications systems. Click
here
to review a typical shuttle mission profile. |
Orbital Maneuvering System |
|
Two orbital maneuvering system (OMS) engines are used to place the Orbiter in orbit, and for major velocity maneuvers. They are also used to slow the Orbiter for reentry into the Earth's atmosphere, an event called the deorbit maneuver. Normally, two thrust maneuvers are used to place the Orbiter in an orbit, and one thrust maneuver is used to deorbit. The deorbit maneuver decreases the orbital velocity by approximately 205 mph or 300 feet per second, enough to begin the descent back into the Earth's atmosphere. For deorbit, the Orbiter is rotated tail first in the direction of the velocity by the primary RCS engines. Then the OMS engines are used to decrease the Orbiter's velocity. Each OMS engine has a capacity of 6,000 pounds of thrust. |
|
In some missions, only one OMS thrust maneuver is used to reach orbit. This is called a direct insertion. It is a technique used when there are specific high-performance requirements, such as a heavy payload, or when a high orbital altitude is needed. This technique uses the space shuttle main engines to achieve the desired apogee (high point in an orbit) altitude, thus conserving fuel. |
 Rotational Maneuvers  Pitch Diagrams
copyright Wayne Lee, NASA/JPL, 1999 |
There
are 44 reaction control system (RCS) engines located on the Orbiter.
The first use of the RCS engines occurs when the external tank separates
from the Orbiter. The RCS engines are used to provide attitude control
of the shuttle during the separation and help move the Orbiter away
from the external tank. Thirty-eight primary and 6 vernier RCS engines
(for fine adjustments) are used on orbit to make pitch, roll, and
yaw or rotational maneuvers as well as translation maneuvers
along the X, Y, and Z axes. Click here for more information about the RCS engines. |
Remote Manipulator System |
|
The payload deployment and retrieval system includes an electromechanical arm built by the Spar Aerospace Ltd., a Canadian company, that is called the remote manipulator system (RMS). The RMS can maneuver a payload from the payload bay to its deployment position and release it. It can also grapple a free-flying payload, maneuver it to the payload bay, and berth it so that astronauts can make repairs or stow it for return to Earth. |
 Astronaut Janice Voss working on the RMS on STS-101 |
|
Click here to watch the robotic arm grapple the Hubble Space Telescope. Click here to watch another robotic arm grapple the Hubble Space Telescope. |
|
The RMS arm is 50 feet 3 inches long and 15 inches in diameter, and it has 6 degrees of freedom. This means that it has six joints similar to the joints of the human arm, with shoulder yaw and pitch joints; an elbow pitch joint; and wrist pitch, yaw, and roll joints. |
 The image above shows the pitch, roll, and yaw axis. |
| The end effector is the unit at the end of the wrist that actually grabs, or grapples, the payload. The two boom segments are called the upper and lower arms. The upper boom connects the shoulder and elbow joints, and the lower boom connects the elbow and wrist joints. The RMS arm attaches to the Orbiter payload bay at the shoulder. |
 |
The RMS is capable of deploying or retrieving payloads weighing up to 65,000 pounds. It can also be used as a mobile extension ladder for space-suited astronauts. A camera mounted on the arm is used as a tool to help the astronauts view the Orbiter or any payloads. |
|
The arm is controlled from inside the flight deck by a crewmember, often assisted by a second crewmember, using rotational and translational hand controllers. The RMS operator looks out of the aft flight deck and overhead windows into the payload bay as he/she controls the arm and through closed-circuit television monitors in the payload bay and on the arm itself. |
 Astronaut controlling the robotic arm from inside the shuttle Click here for more information about the RMS. |
Satellite DeployWhen the space shuttle needs to loft satellites into geosynchronous orbit (where it remains over one point on the Earth at all times), 22,300 miles from Earth, it uses an inertial upper stage (IUS) vehicle that uses solid rocket motors. The IUS was also used to loft the Magellan, Galileo, and Ulysses planetary missions to Venus, Jupiter, and the Sun respectively. Click here for a movie showing the IUS launching Chandra. Click
here for
more videos showing the deploy of the Chandra Space Telescope using
the IUS. |
Thermal Protection |
| The Orbiter's outer skin is composed of aluminum and graphite epoxy. Thermal protection system (TPS) materials, which are placed over the outer skin, protect the Orbiter in temperatures that range from -250°F in the cold of space to reentry temperatures that can reach 3,000°F. The TPS is composed of reinforced carbon-carbon (RCC) on the wing leading edges, the nose cap, and the area around the forward Orbiter/external tank structural attachment. |
 |
The RCC protects areas that experience temperatures over 2,300°F. Black high-temperature insulation tiles are used in areas on the upper forward fuselage, around the windows, and on the entire underside of the vehicle (where RCC is not used). These tiles protect areas where temperatures are below 2,300°F. |
| White, low-temperature insulation tiles are used in selected areas of the forward, mid, and aft fuselages of the tail and wing. These tiles protect areas where temperatures are below 1,200°F. After delivery of the first shuttle, Columbia, an advanced flexible insulation was developed that was made of insulation batting quilted between two layers of white fabric. It was used on subsequent shuttles to replace most of the white tiles. |
|
Later, Columbia also was modified to replace most of the white tiles with blankets. These blankets provide a significant weight reduction over that of the tiles. Additional white blankets, made of coated Nomex felt insulation, are used on the upper payload bay doors, portions of the mid fuselage, and on the aft fuselage sides and the upper wing. |
 A loose piece of thermal blanket, white tiles on the OMS pod and black tiles on the tail can all be seen in this image looking back through the payload bay. |
 |
These
blankets protect areas where temperatures are below 700°F. The port
and starboard payload bay doors incorporate radiators that are deployed
on orbit in to reject excess heat when the doors are open. An electromechanical
actuation system on the door unlatches and deploys the radiators
when they are open and latches and stows the radiators when they
are closed. |
 |
AbortsIf a problem occurs in the first 8 minutes after liftoff, one of five different abort modes may be used. Only one of these aborts has ever been used, the ATO on STS-51F. An abort may become necessary if there is a failure that affects vehicle performance, such as the failure of a main engine or the orbital maneuvering system. Other failures, such as a cabin leak, might require an abort. There are two basic types of abort modes, intact aborts and contingency aborts. Intact aborts are designed to provide a safe return of the Orbiter to a planned landing site. Contingency aborts are designed to permit flight crew survival following more severe failures when an intact abort is not possible. A contingency abort would generally result in a ditch operation and loss of the vehicle. There are four types of intact aborts: Abort
To Orbit - An ATO is used to boost the Orbiter to a safe orbital
altitude when it is impossible to reach the planned orbital altitude.
If a space shuttle main engine fails in a region that results in
a main engine cutoff under speed, the Mission Control Center will
determine that an abort mode is necessary and will inform the crew.
The orbital maneuvering system engines would be used to place the
Orbiter in a circular orbit. This
mode gives the crew and ground control time to choose either an
early deorbit maneuver or an orbital maneuvering system thrusting
maneuver to raise the orbit and continue the mission. Abort Once Around - The AOA is used in cases when it is impossible to achieve orbit. In addition, it is used in cases in which a major systems problem (cabin leak, loss of cooling) makes it necessary to land quickly. This mode generally involves two orbital maneuvering system thrust maneuvers, with the second being a deorbit maneuver. Thus, an AOA results in the Orbiter circling the Earth once and landing approximately 90 minutes after liftoff. |
 |
Return to Launch Site - The RTLS abort mode is designed to allow the return of the Orbiter, crew, and payload to the Kennedy Space Center approximately 25 minutes after liftoff. |
|
It is
designed to accommodate the loss of thrust from one space shuttle
main engine between liftoff and approximately 4 minutes 20 seconds,
at which time not enough main propulsion system propellant remains
to return to the launch site. The RTLS mode involves flying downrange
to dissipate propellant and then turning around under power to return
directly to a landing at or near the launch site. The goal is to leave
only enough main propulsion system propellant to be able to turn the
vehicle around, fly back towards KSC and achieve the proper main engine
cutoff conditions so the vehicle can glide to KSC after external tank
separation. |
|
Transatlantic Abort Landing - A TAL abort permits an intact landing on the other side of the Atlantic Ocean. It was developed to improve the options available when a main engine fails after the last RTLS opportunity but before the first time that an AOA can be accomplished with only two main engines or when a major Orbiter system failure (i.e., a large cabin pressure leak or cooling system failure) occurs after the last RTLS opportunity, making it imperative to land as quickly as possible. In a TAL abort, the vehicle continues on a ballistic trajectory across the Atlantic Ocean to land at a predetermined runway. Landing occurs approximately 45 minutes after launch. Currently, the three landing sites that have been identified for a due east launch are Moron, Spain; Banjul, Gambia; and Ben Guerir, Morocco. Contingency aborts are caused by the loss of more than one main engine or failures in other systems. Loss of one main engine while another is stuck at a low thrust setting may also necessitate a contingency abort. Such an abort would maintain Orbiter integrity for in-flight crew escape if a landing cannot be achieved at a suitable landing field. |
|
Contingency aborts due to system failures other than those involving the main engines would normally result in an intact recovery of vehicle and crew. Loss of more than one main engine may, depending on engine failure times, result in a safe runway landing. However, in most three-engine-out cases during ascent, the Orbiter would have to be ditched. The in-flight crew escape system would be used before ditching the Orbiter. |
 Abort switch on flight deck panel |
|
The Mission Control Center in Houston is prime for calling these aborts because it has a more precise knowledge of the Orbiter's position than the crew can obtain from onboard systems. Before main engine cutoff, Mission Control makes periodic calls to the crew to tell them which abort mode is (or is not) available. If ground communications are lost, the flight crew can use display information to determine the current abort region. Which abort mode is selected depends on the cause and timing of the failure causing the abort and which mode is safest or improves mission success. If the problem is a space shuttle main engine failure, the flight crew and Mission Control Center select the best option available at the time a space shuttle main engine fails. There is a definite order of preference for the various abort modes. In cases where performance loss is the only factor, the preferred modes would be ATO, AOA, TAL, and RTLS, in that order. The mode chosen is the highest
one that can be completed with the remaining vehicle performance.
In case of some support system failures, such as cabin leaks or
vehicle cooling problems, the preferred mode might be the one that
will end the mission most quickly. In these cases, TAL or RTLS might
be preferable to AOA or ATO. TAL or RTLS are the quickest options
(35 minutes), whereas an AOA requires approximately 90 minutes.
Which of these modes is elected depends on the time of the failure
with three good space shuttle main engines. A contingency
abort is never chosen if another abort option exists. |
In-flight Crew Escape System |
 Jump Master Astronaut John M. Grunsfeld in training |
The in-flight crew escape system is provided for use only when the Orbiter would be in controlled gliding flight and unable to reach a runway. It provides the flight crew with an alternative to water ditching or landing on terrain other than a landing site. The probability of the flight crew surviving a water ditching or a landing on terrain other than a landing strip is very small. The crew would make the escape decision at an altitude of approximately 60,000 feet and would immediately activate the flight control system autopilot. |
| At approximately 25,000 feet, a crewmember called the 'jump master' in the mid-deck activates the pyrotechnics for the depressurization valve to equalize the crew compartment cabin and outside pressure before the side hatch is jettisoned. At this time, the software for the automatic autopilot mode changes the Orbiter's angle of attack to approximately 15 degrees. |
|
This angle of attack must remain nearly constant for approximately 3 minutes until the Orbiter reaches an altitude of approximately 2,000 feet. Then the jump master jettisons the side hatch, and pyrotechnics jettison the tunnel/hatch from the Orbiter at a velocity of approximately 50 feet per second. |
 Escape pole in training exercises |
|
The jump master then extends the two telescoping sections of the escape pole through the hatch. Each crewmember takes a lanyard assembly consisting of a hook attached to a Kevlar strap that surrounds the escape pole. Five roller bearings on each strap surround the pole and permit the lanyard to roll freely down the pole. Each flight crewmember positions himself or herself at the hatch opening and attaches himself or herself to the escape pole via the lanyard hook assembly and jumps out the hatch opening. |
 |
|
The crewmember slides down the escape pole and off the end into a free fall. The escape pole extends downward 9.8 feet from the side hatch, thus providing the crewmember with a trajectory that will carry him or her beneath the Orbiter's left wing. |
 |
|
It would take approximately 90 seconds for a maximum crew of eight to bail out. After the first crewmember bails out from the middeck, the remaining crewmembers follow at approximately 12-second intervals until all are out by approximately 10,000 feet altitude. The crew wears brightly colored orange safety suits called partial-pressure shuttle launch and entry garments that are outfitted with a parachute, a life raft, a radio, food, water, a first-aid kit, and survival gear. |
 Cosmonaut Valery V. Ryumin (front) and astronaut Franklin R. Chang-Diaz, both attired in partial-pressure shuttle launch and entry garments during training. |
 |
Click here for more information on Orbiter flight crew escape systems including ground egress procedures. Click here for brief summaries of all of the space shuttle missions through the Challenger accident. |
Questions to think about:
|
|
In the next chapter, you will learn about how the Mission Control team operates. Did you know that you can track the space shuttle in the sky during a mission? You can also see the International Space Station fly overhead at certain times. Click here to find out how! For some fun space trivia,
click here! |
 Landing at Edwards Air Force Base |
| Next... Ground
Control |