motors; 16 units
frustum and aft skirt; 0.66 sec,
Is = 250 sec
vehicle after cut-off
1. MMH, monomethylhydrazine and NTO, nitrogen tetroxide.
2. 70% Ammonium Perchlorate; 16% aluminum; 12% polybutadiene acrylic acid binder; 2% epoxy curing agent.
along the flight path, such as for orbit insertion or orbit change maneuvers) and secondary propulsion functions in these vehicles. Some of the secondary propulsion functions are attitude control, spin control, momentum wheel and gyro unloading, stage separation, and the settling of liquids in tanks. A spacecraft usually has a series of different rocket propulsion systems, some often very small. For spacecraft attitude control about three perpendicular axes, each in two rotational directions, the system must allow the application of pure torque for six modes of angular freedom, thus requiring a minimum of 12 thrust chambers. Some missions require as few as four to six rocket units whereas the more complex manned spacecraft have 40 to 80 rocket units in all of its stages. Often the small attitude control rockets must give pulses or short bursts of thrust, necessitating thousands of restarts.
Table 1-5 presents a variety of spacecraft along with their weights, missions, and propulsion. Although only U.S. launch vehicles are listed in this table, there are also launch vehicles developed by France, the European Space Agency, Russia, Japan, China, India, and Israel that have successfully launched payloads into satellite orbits. They use rocket propulsion systems that were developed in their own countries.
The U.S. Space Shuttle program, using technology and experience from the X-15 rocket-powered research airplane, the Mercury and Gemini orbital flights, the Apollo lunar flight program, and Skylab, provided the first reusable spacecraft that lands on a runway. Figure 1-13 shows the basic configuration of the Space Shuttle, which consists of two stages, the booster and the orbiter. It shows all the 67 rocket propulsion systems of the shuttle. The orbiter is really a reusable combination vehicle, namely a spacecraft combined with a glider. The two solid propellant rocket motors are the largest in existence; they are equipped with parachutes for sea recovery of the burned-out motors. The large liquid oxygen/liquid hydrogen (L02/LH2) external tank is jettisoned and expended just before orbit insertion (see Ref. 1-18). Details of several of these Space Shuttle rocket propulsion systems are given elsewhere in this book. The Space Shuttle accomplishes both civilian and military missions of placing satellites in orbit, undertaking scientific exploration, and repairing, servicing, and retrieving satellites.
A reusable single stage to orbit, experimental vehicle with a novel rocket engine is currently (1997) under development in the USA. It is a combination launch vehicle and spacecraft. The design takes advantage of advances in lightweight structures, a clever lifting aerodynamic body concept, and a tailored novel rocket engine that requires little space and fits well into the flight vehicle. This engine, known as a linear aerospike, has a novel configuration and is described further in Chapter 8.
The majority of spacecraft have used liquid propellant engines, with solid propellant boosters. Several spacecraft have operated successfully with electrical propulsion for attitude control. Electrical propulsion systems will probably also be used for some primary and secondary propulsion missions on long-duration space flights, as described in Chapter 19.
TABLE 1-5. Selected United States Spacecraft
Space Maneuver Propulsion
Pioneer 10, 11 Viking
Apollo command and service module
Space Shuttle orbiter
Fleet Communications Satellite Photo Recon
Intelsat V communication satellite Deep Space I (DS1)
100 lbf 16 units
93 lbf 6 units (secondary)
Two 6000-lbf units (primary)
38 units ® 900 lbf (secondary)
Six 25-lbf units (secondary)
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