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A Shuttle Avionics Integration Laboratory (SAIL) is planned for JSC to provide the necessary test area for integrated electronic hardware and software operation to prove or recommend design changes for the avionics equipment. This will allow verification and necessary revisions to occur in adequate time for final development. This laboratory will also be available to support flight crew procedures development.

Propulsion-In order to satisfy the requirements of its assigned missions and associated operational modes, the Space Shuttle employs primary and secondary propulsion systems (see figure 129, p. 409). The primary propulsion system, which provides the thrust necessary to send the vehicle from lift-off to staging and then into Earth orbit, consists of the three reusable liquid oxygen/liquid hydrogen rocket engines and the twin recoverable solid rocket boosters (SRB). These propulsion systems will be discussed in detail later.

The secondary propulsion system of the Orbiter consists of Reaction Control (RCS), Orbital Maneuvering (OMS), and Airbreathing propulsion (ABPS) subsystems. The RCS provides the thrust necessary for on-orbit attitude control and minor maneuvering for braking actions and docking maneuvers. The OMS furnishes the propulsive thrust for major on-orbit maneuvers including circularization of orbit, orbital transfer, rendezvous and deorbit. The airbreathing engines are used for horizontal flight test in the atmosphere and for ferry operations. The Reaction Control Subsystem (RCS) consists of three self-contained and independent propulsion modules: one is located in the Orbiter nose section and the other two in each of the aft (Orbital Maneuvering System) pods (figure 133). Each module contains a helium pressurant storage and distribution system

ORBITER REACTION CONTROL SYSTEM (RCS)

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for forcing the propellant through the engines; a monopropellant (Hydrazine) storage and distribution system; and multiple thrusters, each operating at a rated vacuum thrust of 4900 newtons (1100 pounds). The forward module contains 16 thrusters and each aft module in the OMS pod contains 12 thrusters. All thrusters, tanks and components are designed to be interchangeable in all

modules.

Functionally, the RCS provides attitude control and three-axis translational capability during both orbital and entry phases of the mission. During the orbital phase, the RCS provides precise attitude and translational control capability required for rendezvous and docking Orbiter stabilization. The RCS can also act as a backup in case of OMS subsystem failure by providing roll control, steering and a deorbit capability.

Following an in-depth study effort directed toward evaluation of alternate RCS concepts with low development risk and cost, the monopropellant, easily storable hydrazine was selected. Additional advantages offered by this selection are exhaust cleanliness, and ease of checkout and maintainability, which are important characteristics in meeting the design goal of 2-week turnaround for all systems. The Space Division of Rockwell International (RI) conducted a trade study on the RCS to optimize engine thrust level vs. number of engines, to assure the best match of performance parameters prior to procurement of this subsystem scheduled for the fourth quarter of calendar year 1973.

RI intends to subcontract the RCS module detailed design, development and production. The RCS thrusters and propellant tanks will also be subcontracted by NR and furnished to the RCS module subcontractor for installation and integration.

The Orbital Maneuvering Subsystem (OMS) when used sequentially or in combination with the RCS provides the Orbiter vehicle its maneuvering capabilities to perform designated missions ranging from on-orbit docking maneuvers for satellite recovery or repair to space rescue. Specifically, the OMS is designed to provide the thrust for orbit circularization, orbit transfer, rendezvous and deorbit.

The current engine design and placement for the OMS (figure 134) calls for

ORBITAL MANEUVERING SUBSYSTEM (OMS)

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two reusable, pressure-fed rocket engines to provide 26,700 newtons (6000 pounds) of thrust each. Propellant for each engine is stored in tankage located in each pod. When additional orbital maneuvering capability is required OMS "kits" may be mounted in the cargo bay.

As with the RCS, both cryogenic and storable propellants have been examined to select the propellant which would provide the least development risk and offer

the best compromise between system weight, volume, and program cost. A storable bipropellant mixture was chosen that consists of nitrogen tetroxide (N2O.) as the oxidizer and monomethyl hydrazine (MMH) as the fuel. A prototype orbital maneuvering engine injector is being evaluated for performance, heat distribution and stability (figure 135).

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The broad technology base available from development of the Apollo CSM service propulsion subsystem minimizes the development risk associated with the concept proposed by NR, which plans to subcontract the OMS pod assembly on a competitive bid basis. The Request for Proposals (RFP) for design of the OMS pod was released in November 1972 and selection of a subcontractor and authority to proceed is expected before the end of FY 1973.

The Airbreathing Propulsion Subsystem (ABPS) will be needed only for the horizontal flight test program and ferry operations. Elimination of airbreathing engines from orbital flight simplifies the overall Orbiter design while increasing the amount of payload that could be transported to and returned from orbit. Program costs are kept low by reducing the number of engines required and eliminating the need for qualifying these engines for orbital flight.

The airbreathing engine configuration on the Orbiter vehicle is the subject of ongoing technical trade studies. A number of engines either currently in production or under development are being considered for use on the Space Shuttle Selection of a candidate engine is scheduled for CY 1973.

Thermal Protection. To meet thermal protection requirements for the Space Shuttle, a NASA funded technology program in support of materials development has been underway for several years. This effort involved a spectrum of mate rials to provide a data base for comparing candidates for the very high temperatures and high heat loads (figure 136) expected in areas such as the nose and wing leading edges (temperatures from 2100° to 3000° F.) and different materials in the other areas where temperatures are lower than 2100° F. Great progress was made in these investigations and in general nonmetallics were developed to provide excellent protection against the high temperatures. Test evaluations are being conducted in arc-jet tunnels, radiant heating ovens, and on vibration, acoustic and strength testing machinery (figure 137).

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Baseline materials are currently being selected for the Orbiter vehicle (figure 138). For the lower temperature areas an elastic reusable surface insulation

ORBITER THERMAL PROTECTION SYSTEM

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(RSI) will be used. This will be applied to the lower temperature areas on the top side of the Orbiter. A silica based RSI will be used on the underside, front, rudder, and certain high temperature areas of the Orbiter. Sample nonmetallic tiles are being mounted on the underside of an actual aircraft wing to test application to a typical airframe surface (figure 139). A reinforced carbon-carbon material will be used to protect the highest temperature areas at the nose and leading edges of the wings. The prime contractor will soon select subcontractors to develop the actual components for the Orbiter thermal protection system.

During fiscal year 1974, it is planned to complete material development to insure proper temperature control while in orbit, to develop a compatible coating for waterproofing and in the case of the leading edge, to protect against oxidation.

Other development effort will provide materials for penetrations such as the landing gear doors, sliding seals for the aerodynamic control surfaces and antenna windows. Verification of analytical predictions through large-scale tests will be needed for flight certification.

Crew systems and life support.-Crew and passenger compartments are located at the forward end of the Orbiter (figure 140). In addition to the life support and environmental control equipment, the cockpit and passenger areas contain the avionics equipment, airlock entrance to the payload bay docking module and basic living equipment and furnishings.

The environmental control and life support system (ECLSS) currently being designed includes eight basic subsystems (figure 141) (see p. 418). The ECLSS requirements for the Orbiter have been timed so that all the life-support subsystems of the Shuttle can take advantage of the practical experience and possible improvements to come from other manned space programs such as Skylab. ECLSS primary features as currently baselined, are as follows:

Dietary systems.-The type and amount of food, selected for the Orbiter crew diet is based on personal preference and physiological (dietary) considerations. Crew desires, physical requirements, and psychological test results will be analyzed to determine the final provisions to be included on board the Shuttle for crew and passengers. These will include combination frozen and freeze-dried foods.

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