ONCE THE SHUTTLE has completed its trial voyages, the list of those who may go into space will be greatly enlarged. No longer will travel beyond Earth's security blanket of atmosphere be restricted to a select population of physically perfect and intensively trained astronauts.
Acceleration stresses felt by the Orbiter's crew and passengers during launch and ascent to orbit are never more than three times normal gravity, only a third of the peaks hit on earlier manned flights and well within the physical limitations of non-astronaut scientists and technicians, who now can go into space for the first time to tend their own experiments there and observe the results. The spacious cabin (71.5 cubic meters: 2500 cu ft) provides separate working and living quarters supplied with ordinary air - 22 percent oxygen, 78 percent nitrogen - at standard sea-level pressure of 14.7 pounds per square inch and comfortable temperatures of 11° C to 27° C. The humidity is controlled, and odors and carbon dioxide are continuously filtered out.
The upper section of the cabin is the flight deck, from which the Shuttle is controlled and most payloads are handled. It somewhat resembles the cockpit of it DC 10) jetliner. There is a conventional pilot-copilot arrangement of forward-facing seats for the ship commander (on the left) and pilot, TV-like displays, and duplicate sets of conventional-looking hand controllers, pedals, levers, and switches with which either astronaut can fly the craft alone. During ascent and return the mission specialist, who is also a NASA astronaut, and the non-astronaut payload specialist, if there's one along, sit behind the pilot and commander.
Behind and alongside the seats are four standup duty stations, two facing aft with windows and a windowless one along each side of the deck, w here the crew and payload specialist work while in orbit. Looking aft on the left is the rendezvous and docking station, usually occupied by the commander, containing radar displays and controls for maneuvering the Orbiter close to another spacecraft. Alongside it, to the right, is the payload handling station, with displays and controls to manipulate, deploy, release, and capture payloads. The crew member at this station, usually the pilot, earl open and close the payload doors; deploy the cooling radiators; deploy, operate, and stow the manipulator arm; arid operate the lights and television cameras in the payload bay. Two TV screens display the pictures from the remote cameras.
The mission station, just behind and to the right of the pilot's seat and occupied by the mission specialist, contains controls to manage the Orbiter's interconnections with payloads and their equipment that is critical to the Orbiter's safety. The station is equipped to monitor, command, control, and communicate with payloads attached to the Orbiter or flying nearby; a caution and warning display alerts the crew. members to malfunctions in payload components. Orbiter functions that are not immediately critical to the flight can also be managed from here.
On the opposite side of the flight deck, behind and to the left of the commander's seat, is the payload station, occupied by a payload specialist when the mission requires one. Payloads are checked out and managed from here, and the station includes a surface two meters square for removable displays and controls that can be changed for different payloads on different missions. A cathode-ray-tube display and keyboard for communicating with payloads through the Orbiter's data processing system may be added. Electrical power and air conditioning for payloads that need them are regulated from this station.
The Shuttle's flight is controlled by what aerospace engineers call fly-by-wire: there are no old-fashioned rods, cables, or hydraulic linkages. Movements of the pilots' hand controllers and pedals are converted into electronic signals and, like the programmed instructions for automatic flight, are routed through computers. The computers relay commands to the...
...engines and attitude thrusters during launch, ascent, orbital operations, and reentry or to the hydraulic actuators that operate the elevon flaps, rudder, and speed brake during descent and landing. Data on the vehicle's performance, attitude, position, acceleration, velocity, and direction flow to cockpit displays and to the computers from rate gyros, accelerometers, star trackers, inertial measuring units, thrusters, thrust-direction controls, air-speed probes, radar altimeters, and air navigation and microwave landing systems. Four computers (there's also a backup one) process the same data simultaneously. Each compares its computations with those of the others and agreed-upon commands are sent to the appropriate control actuator. If and when there is disagreement, the computers in effect vote, and commands from the outvoted computer are ignored.
The cabin mid-deck, reached through an open hatch from the flight deck above, is the living area. ( It also contains much of the Orbiter's electronics gear. ) Here are three extra seats for additional payload specialists when the Shuttle is carrying the manned Spacelab. Along the left side of this deck are the galley and a washroom With a toilet. The galley includes an oven, hot and cold water dispensers for preparing freeze-dried foods, storage for seventy-four kinds of food and twenty beverages, places for drinking cups and eating utensils, a shelf for dining trays, a water tank, and trash bins. On the right, besides boxes for the crew's personal things, are three bunks and a "vertical sleep station." On a mission to rescue the crew of another Orbiter stranded in space, the bunks could be removed and three more seats installed. The total of ten seats, six here and four on the flight deck, then would accommodate the rescue flight crew of three and the maximum of seven from the disabled craft.
A lower section of the cabin module, beneath the living quarters and reached through removable floor panels, contains more storage space and the Orbiter's environmental-control equipment.
From the back of the mid-deck an airlock - a cylindrical compartment With air-tight hatches on opposite sides - leads into the cargo bay. Astronauts in space suits enter from the cabin and close the hatch on that side before opening the other one, thus preventing cabin air from escaping into the unpressurized bay and the vacuum of space. Handrails, hand holds, and foot restraints at various locations in the cabin,  airlock:, and payload bays help the weightless crew members, scientists, and technicians to move about and work as if neutrally buoyant underwater. They can go along a handrail on the load-manipulating mechanical arm to work on a payload at the far end of the bay; to reach a satellite held out in space by the arm during deployment, refurbishment, or retrieval; or to get at parts of the Orbiter itself that may need inspection or servicing.
Backpacks worn with the space suits provide oxygen and suit cooling for six hours, and the Orbiter carries supplies for two more six-hour periods of EVA - "extravehicular activity" - for two crew members. A space-suited astronaut can also wear on his back a personal rocket kit, called the manned maneuvering unit, to fly outside the cargo bay. With this hand-controlled propulsive device he can reach a nearby free-dying satellite, transport cargo of moderate size such as may be required for servicing a spacecraft, or retrieve small free-flyers that may be sensitive to perturbation or contamination by the Orbiter's attitude-control thrusters. The maneuvering unit's own low-thrust nitrogen propellant causes minimal disturbance and no contamination.
EVA tasks may include: inspecting and photographing payloads or their components; installing, removing, or transferring film cassettes, materials samples, protective covers, and instruments; operating equipment, tools, and cameras; cleaning optical surfaces; connecting, disconnecting, and stowing fluid and electrical lines; repairing, replacing, calibrating, and inspecting modular equipment and instruments; deploying, retracting, and positioning antennas, booms, and solar power panels; transferring cargo; performing experiments in the cargo bay; and possibly repairing some damaged or malfunctioning Orbiter mechanism in orbit.
In case of serious trouble during ascent to orbit that made it impossible or unwise to continue the mission to its full duration, the Orbiter is expected to get back to Earth with its personnel safe and its payload intact.
If a decision to cut the flight short had to be made during the first four minutes of powered ascent on the main engines, they would if possible be kept firing until the vehicle reached an altitude of some 100 kilometers ( 60 mi ) . There the atmosphere would be thin enough so that the Orbiter, with the External Tank still attached, could flip over and point backward toward the launch site. Continued engine thrust....
....would slow the tail-first velocity to zero and then accelerate the vehicle, nose first, back toward the launch site. When it reached the point where the Orbiter alone could glide home, the engines would be shut down and the tank jettisoned into a not-too-busy ocean area selected ahead of time. A computer guidance program for just such an emergency would control critical maneuvers until the Orbiter glided within range for the crew to make a manual landing on its usual base runway, about twenty minutes after liftoff.
In a mission aborted during the last half of the launch phase there would be enough thrust left to power the Shuttle to just short of orbital velocity. The External Tank would be dropped into the normal disposal area, and the Orbiter's trajectory would take it once around the globe for a nearly normal reentry and landing on the home runway about ninety minutes after takeoff. If the trouble came in the last few minutes of ascent, the tank would be discarded into the planned area and the Orbiter would make orbit, maybe at a lower altitude than planned, by firing its orbital maneuvering engines longer than usual. The mission, though probably shortened, might last several days and would conclude with a normal return to Earth.
If an emergency during orbital operations required urgent return, the crew could decelerate from orbit promptly but in the normal way and, if not within range of home base, come into one of several air fields with long, strong runways that NASA has lined up as emergency landing sites.