Tuesday, April 12, 2011

Book Excerpt: Space Shuttle Owners’ Workshop Manual

Book Excerpt: Space Shuttle Owners’ Workshop Manual: "

The following is an excerpt from the new book NASA Space Shuttle Owners’ Workshop Manual.

Chapter 3: Anatomy of the Space Shuttle

Author David Baker worked with NASA on the Gemini, Apollo, and Space Shuttle programs between 1965 and 1984. He has written more than 80 books on spaceflight technology including his latest, the NASA Space Shuttle Owners’ Workshop Manual.

The Shuttle Orbiter is a reusable vehicle intended to carry astronauts and cargo to and from space. It is about the size of a DC-9 airliner and is designed to survive the rigors of launch and landing, including vibration, high acoustic levels from the rocket engines, high levels of acceleration and various heat loads on different parts of the structure. The layout is dominated by just two requirements – to carry a design payload of up to 65,000 lb to orbit, and to fly back down through the atmosphere like an aircraft, landing like a glider so that it can be used again.

Because of these requirements the Shuttle is shaped to look like an aircraft but to operate as a spacecraft. The structure of the Shuttle Orbiter comprises nine separate sections, or elements: the forward fuselage, the forward reaction control system module, the mid-fuselage, the payload bay doors, the aft fuselage, the vertical tail, the two orbital maneuvering system/reaction control modules and the wing.

The demands are greater than is usually the case with a conventional aircraft because the stresses imposed upon the structure are unique to the Shuttle. Because of this, the design team at North American Aviation had no precedents on which to base their prototype. It was the first of its kind, without the advantage of any previous learning curve, and one of a kind without parallel.

Very few aircraft designed for operational use break completely new ground in their operating environments. Two may be considered as such: the Mach 3 Lockheed SR-71 spy plane and the 1,400mph Concorde, the world’s first commercially viable supersonic airliner. But the Shuttle would follow its own development path. At first it was an experimental vehicle designed to be adapted later to operational requirements, which included carrying satellites into space. It would also be called upon to lift large modules into orbit for a space station, and carry a wide range of satellites and spacecraft to be deployed in different trajectories, some of which would be sent to the outer regions of the solar system by the rocket motors attached to them.

The pressure vessel, comprising the habitable flight deck and middeck areas, is lowered into the lower half of the forward fuselage. Photo: North American

Forward Fuselage

This consists of upper and lower sections divided horizontally, which fit like a clamshell over the pressurized crew compartment where the astronauts live and work when they are not space walking or transferring to another spacecraft. The forward fuselage is fabricated from 2024-T81 aluminum alloy with skin-stringer panels, frames and bulkheads. The stringers are located 35in apart while the vertical frames are 30–36in apart, riveted to the stringer panels.

The pressurized crew compartment is attached to the forward fuselage at four locations. It is of welded construction to achieve an air-tight pressure vessel capable of providing a shirt-sleeve environment and of sustaining the crew with an atmosphere of oxygen and nitrogen at sea-level pressure (14.7 lb/sq in).

The distribution of spacecraft systems is accommodated within a generally simple structural design, using standard aircraft manufacturing practices. Courtesy NASA

The crew compartment has three levels. There is only one way in or out of the Orbiter on the ground, through the 40in diameter circular side hatch which, with the Orbiter on its landing gear, opens downwards or, with the Orbiter on the launch pad, to the side. It can also be used to escape from the Orbiter if it is unable to land after re-entering the atmosphere. The mid-deck area is accessed directly when the vehicle is on the ground, with the flight deck above and the equipment bay below. In weightlessness, access to the flight and mid-deck areas is a matter of simply floating through one of two hatches, each 26 in x 28 in. The pressurized crew compartment is 17½ft high, 16½ft long and the forward cylindrical nose section is 10.6ft in diameter. It also has provision for an airlock that allows astronauts to leave the crew compartment and move into the unpressurised cargo bay, which forms the main section of the mid-fuselage assembly.

There are 11 main windows in the crew compartment: 6 wrapped around the forward area of the flight deck, 2 in the aft bulkhead, which faces directly into the payload bay, 2 in the roof of the flight deck and 1 in the side hatch on the left side of the crew compartment in the mid-deck area. The forward-facing windows are used by the two pilots for entry and landing as well as some on-orbit operations. The two rear-facing and upper facing windows are used for rendezvous and docking maneuvers and for observing activity in the payload bay.

The six forward windows are the thickest ever assembled with optical quality and comprise three separate panes: the innermost for withstanding crew compartment pressure, the middle one providing an optically transparent thermal shock layer, and the outer pane providing both thermal and impact protection. Both inner and outer panes are each 0.6in thick. The inner and middle panes are attached to the crew compartment while the outer pane is attached to the upper section of the forward fuselage.

The critical dimensions of the orbiter were shaped by the requirement to provide a cargo bay 60 feet long and 15 feet in diameter. Courtesy NASA

The critical dimensions of the orbiter were shaped by the requirement to provide a cargo bay 60 feet long and 15 feet in diameter. Courtesy NASA

The total interior volume of the crew compartment is 2,325cu ft and the atmosphere, maintained at 14.7lb/sq in, is a constant 80/20 mix of nitrogen and oxygen. Usually, four seats are provided on the upper flight deck with a further three seats on the mid-deck area. Although additional seats could be installed for emergencies or for exceptional needs, the Shuttle usually flies with a complement of seven astronauts. The two pilots’ seats (the left seat being the commander’s position) are occupied for all launch, re-entry and major propulsive burns in orbit. The other seats are for mission specialists – astronauts who are not necessarily selected for their piloting skills, but who are there to conduct mission operations and sundry scientific tasks, as well as to assist with moving payloads in or out of the cargo bay and to perform space walks (called EVA or extra-vehicular activity). Mission specialist seats are stowed during orbital operations and re-installed for re-entry and landing.

According to mission requirements, bunks can be installed in the mid-deck area as well as a galley for food preparation. The waste management facility (toilet) is installed in the mid-deck, too, and this area provides 140cu ft of stowage area with modular lockers for astronaut gear, personal hygiene equipment and for experiments – in all, 42 identical boxes, each 11in x 18in x 21in.

Below the mid-deck area is the equipment bay. It is here that the astronauts can gain access to waste management equipment, air revitalization systems, pumps, fans, lithium hydroxide canisters for removing carbon dioxide breathed out by the crew, together with an additional five spaces for extra crew equipment stowage.

The mid-deck area also serves to house the cylindrical airlock, with an interior diameter of 5ft 3in and a length of 6ft 11in, and two 40in diameter circular openings and pressure tight hatches. One hatch is on the front facing inside the mid-deck, the other on the opposite side of the airlock and is attached direct to the aft bulkhead which, upon opening, allows access into the payload bay. The airlock can also be installed on the inside of the payload bay, attached to a tunnel adapter leading to a pressurized research module such as Spacelab or Spacehab, where the astronauts can work in a shirt-sleeve environment on scientific experiments carried up from the ground and installed in racks. The airlock is big enough to contain two fully suited crewmembers simultaneously.

The forward reaction-control-system module is detachable for servicing, and its removal enables access to the lower nose section and upper landing gear bay. Courtesy NASA

The forward fuselage also supports the reaction control system module (RCSM), which carries the nose thrusters for attitude control in space. This section is removable for servicing, replenishing the propellant (fuel and oxidizer) tanks and attending to the plumbing. The RCSM is removed and serviced in the Orbiter Processing Facility (OPF) where the vehicle is turned around after each flight and made ready for the next launch. The forward fuselage also contains the forward landing gear.

Escape from the crew compartment is possible during descent when the Orbiter is off target and likely either to ditch or to crash-land without reaching a runway, but only if it is in a controlled glide. Because of the shape of the Orbiter and its large delta wing, an astronaut leaping from the side hatch would in all probability strike the leading edge of the wing itself. To throw the astronaut beyond the wing, an escape pole can be quickly fitted to the inside of the Orbiter mid-deck, extended to its full length of 10½ft and projected through the open hatch. Wearing a partial pressure suit and with a parachute, the astronaut would place a looped lanyard over the pole and leap from the side hatch. Instead of being thrust back against the wing or the fuselage by the slipstream, the lanyard and attached astronaut would slide down the pole and be catapulted in a slingshot maneuver away from the Orbiter.

Commitment to the emergency escape method would be made with the Orbiter descending through 60,000ft; when the Orbiter reaches 30,000ft the speed has reduced to 230mph. At about 25,000ft a crewmember nominated as jump master prepares the equipment, and the flight control system on the Orbiter maintains the angle of attack at 15°. With the escape pole inclined downwards from the side hatch it would take only 90 seconds for all seven crewmembers to get free, the last at an altitude of about 10,000ft. The Orbiter would crash, but the crew would have escaped. Two additional emergency escape procedures cover situations on the ground after landing, via an escape slide from the side hatch and out of an emergency escape hatch in the roof of the flight deck.

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