Τετάρτη, 13 Απριλίου 2011

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

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.
Continued on the next page.
The payload bay is half of the total length of the orbiter, and is designed to cope with the flexing loads it will experience in space from extremes of temperature. Photo: North American

Mid Fuselage

This is the structural backbone of the Orbiter, incorporating the cargo bay and its doors, and provides support for the forward fuselage, the aft fuselage and the wings. Built by General Dynamics in San Diego, California, it is about 60ft long and 17ft wide with a height of 13ft and it weighs about 13,500lb. It is assembled from twelve main, vertical, frame assemblies, each with special weight-saving boron/aluminum trusses for strength, with reinforced skin and longerons. The two top edges of the midfuselage are especially strong. In addition to supporting the sills for the payload bay doors, they also take bending loads for the entire Orbiter and it is from these and the longerons that the payloads are ‘hung’. Unique at the time the Orbiters were first manufactured, skins for the mid-fuselage were machined integrally by numerical control.
The floor of the mid-fuselage consists of the wing carry-through box and the wings themselves are attached to the outer surface of this section. The first few Shuttle flights provided important measurements about stresses and temperatures that were higher than expected when the designers put together the midfuselage. To strengthen this area, engineers attached torsional straps to tie together all the stringers thereby, in effect, creating what amounts to a box-section. Early Orbiters were retro-fitted with vulcanized silicone rubber inserts to absorb heat and distribute it more uniformly across the lower section of the midfuselage structure.
The payload bay (or cargo bay as it is sometimes known) is capable of handling equipment up to 60ft long and 15ft in diameter and is covered by two doors, left and right of the centerline. Each door is assembled from five sections connected by circumferential expansion joints and connected to the midfuselage sill by 13 hinges, of which 8 are ‘floating’ to allow expansion and contraction of the mid-fuselage section due to mechanical stresses and to the wide variations in temperature the Orbiter experiences in space. Five hinges are fixed.
The payload bay is a relatively air-tight structure, achieved by means of a seal that runs right around the outer edge of each door. The payload bay is not pressurized, but the seals prevent leakage of heat from the top of the Orbiter to the interior. Because the Orbiter re-enters the atmosphere nose-up, the payload bay doors experience relatively low temperatures, shielded as they are from the build-up of heat on the main undersurfaces of the Shuttle.
Structural loads from the wings, the main engines and the aft body flap are carried by the U-shaped fuselage section, which also provides the void for the cargo bay. Courtesy NASA
Each door is 60ft long by 10ft across the radius, locked down onto the rest of the structure by 16 latches along the centerline and 8 latches at each end, the forward fuselage and the aft fuselage. The doors are manufactured from a composite material of graphite-epoxy and Nomex, saving about 23 per cent of the weight of a similar structure made from aluminum. Because the right-hand door (as viewed from the top looking forward) carries the latching mechanism, it weighs 2,535lb, compared with 2,375lb for the left-hand door. The doors open through an angle of 175.5°.
The interior surfaces of the payload bay doors each support four radiator panels running down the entire length of the bay, each panel measuring 15ft long and 10ft across the curve. They are there to control the amount of heat removed from the interior of the Orbiter and ejected into space to reduce overheating from the spacecraft’s systems or from the sun’s energy. The two forward panels are hinged so as to tilt upwards by about 35° from the payload bay doors when they are opened after reaching orbit, thereby allowing heat to be ejected from both sides of the radiator. The two rear panels are fixed, but extra panels can be carried for some missions.
The radiators were manufactured by the LTV Corporation (now part of Lockheed Martin), and NASA upgraded them after delivery to prevent damage from micrometeoroids. They comprise a series of tubes, each of the four deployable panels carrying 68, with each of the 4 aft (fixed) panels supporting 26 tubes, all with a diameter of about 0.1in. The tubes are connected to the Freon coolant loops, separate systems on respective door panels, which control the temperatures inside the Orbiter. The modifications consisted of thin metal strips placed above each tube to prevent an impact from space debris creating a puncture and threatening the mission.

Aft Fuselage

This section comprises a structural mount for the vertical tail, the hinged body flap and a so-called thrust structure, containing the three main rocket engines and the plumbing necessary to bring fuel and oxidizer from the External Tank. It also supports the two removable orbital maneuvering system/reaction control system (OMS/RCS) pods. These pods carry propellant tanks, plumbing and rocket motors for maneuvering in space and for\ keeping the Orbiter at the correct attitude in orbit and during the early phases of re-entry, where the air pressure is too low for the aerosurfaces to control the vehicle like an aircraft. Manufactured primarily out of graphite epoxy composite material and aluminum, each pod measures 21.8ft in length and 11.4ft wide at its after end, and approximately 8.4ft wide at the forward end.
The aft-fuselage section is dominated by the thrust structure, designed to transmit loads from the three main engines. The orifices for the engines are clearly visible. Photo: North American
Like the mid-fuselage, the aft-fuselage is also a load-bearing structure, transmitting forces from the main engines up through the Orbiter and across the rear face of the wing carry-through structure, which is part of the mid-fuselage. While the mid-fuselage acts as a strong-back for the Orbiter, the aft-fuselage serves to transmit loads from the three main engines to the Orbiter and the External Tank. Comprising an outer shell, thrust structure and internal secondary structure, the aft-fuselage is about 18ft long, 22ft wide and 20ft high. It serves as an interface with the main wing spar and provides the aft closeout bulkhead at the forward end with the midfuselage and payload bay, comprising machined and beaded sheet metal aluminum segments. The upper part of the bulkhead attaches to the front spar of the vertical tail.
The internal thrust structure serves as a support for the three main engines (SSME) with a load reaction truss, engine fittings and the actuator support structures. The aft fuselage also supports the SSME low-pressure turbo pumps and propellant lines and attachment points for connecting the Orbiter to the External Tank. The internal thrust structure is primarily 28 machined, diffusion-bonded truss members, where titanium strips are bonded under heat and pressure which, over time, fuses them into a single, hollow mass that is much lighter and much stronger than a machined part.
The outer shell of the thrust structure is formed from integrally machined aluminum. Exposed areas are covered with thermal protection materials to help insulate the structure from the heat of re-entry. A secondary structure fabricated from aluminum supports a variety of brackets, webs, machined fittings and avionics bays, which are shock-mounted to the structure itself.
The body flap is a 21ft-wide aluminum structure where it attaches to the aft-fuselage, and 18¼ ft wide at the trailing edge. It is 7.24ft long and can be pivoted 15.7° up and 26.55° down so that it can serve as a pitch trim for the Orbiter during its descent through the atmosphere. The body flap also serves to shield the three SSMEs from the heat of re-entry.

Vertical Tail

This consists of a fin 26ft 4in tall incorporating a split rudder/speed brake, the fixed portion of the fin being built up from aluminum ribs and spars and attached to the upper structural surface of the aft-fuselage. The rudder is 16.6ft tall and 7½ft wide at the base, and is of similar construction to the fin but of two separate halves co-located at the hinge line. As a rudder the two closed surfaces can move 27° either side of the centerline or, when operating as a speed brake, the drive shafts turn in opposite directions to spread the two halves of the rudder to a maximum 49.3° each, presenting a spread of 98.6°.

Wing

The broad torque box provides the wing carry-through junction at the attachment to the center fuselage, and the aluminum facing panels on the leading edge provide a mount for the carbon-carbon heat shielding. Courtesy NASA
The Orbiter’s wing is the aerodynamic lifting surface that provides conventional lift and control for the vehicle when it is within the earth’s atmosphere. Each wing has a glove, an intermediate section, a torque box, a forward spar to which is attached the leading edge thermal protection, elevon surfaces along the trailing edge and a main landing gear well. The wing itself is built up in a multi-rib and spar arrangement, with stiffened stringers supporting the exterior skin. Each wing has a length of about 60ft and a thickness of 5ft and the forward wing box aerodynamically blends the leading edge into the mid-fuselage wing glove, or fillet. This is made up from aluminum ribs, tubes and tubular struts.
The wing contains four major spars, each constructed of corrugated aluminum to minimize thermal loads. The forward spar is used to attach the curved Reinforced Carbon-Carbon (RCC) heat shield and to form the rounded profile of the wing leading edge. The rear spar is the attachment surface for the trailing edge elevon hinges. The two-piece elevons are of conventional aluminum rib and beam construction and are divided into two segments per wing, each segment supported by three hinges. Attached to the flight control system hydraulic actuators, each elevon travels a maximum of 40° up and 25° down.
Each outboard elevon is just over 12ft long, 3¾ft wide at the outermost edge and 6ft at the inboard edge where it lies adjacent to the inner elevon, 13.8ft long and 8.7ft wide at the inboard edge. The main landing gear doors are 5ft wide and 12.6ft long and are located in the wing intermediate section. During the weight reduction program prior to the assembly of wings for OV-103 (Discovery) and OV-104 (Atlantis), certain areas of the structure were redesigned as a result of loads measured in flight by previous Orbiters and found to be greater than predicted. Doublers and stiffeners were applied to OV-102 (Columbia) and OV-099 (Challenger) to maintain safety levels.

http://www.wired.com/wiredscience/2011/04/shuttle-manual-excerpt/all/1

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