Page 77 - Intro to Space Sciences Spacecraft Applications

64 Introduction to Space Sciences and Spacecraft Applications

Figure 3-5. Apollo Service Module propulsion systems. The large aft nozzle
was used for orbital maneuvers and the smaller nozzles around the body
were used for attitude control.

craft, rockets that deliver a spacecraft to its operating position are more
likely to be existing systems which are chosen for specific performance
characteristics and to which the spacecraft must be designed for compati-
bility. Specific systems that are available to meet these requirements will
be presented in Chapter 8. The following sections describe the propulsion
aspects that must be taken into account when discussing these systems.

Orbit Establishment

Several factors are involved in reaching the desired orbit, including
establishing the correct burn-out conditions, staging, launch timing,
launch pad location, and launch direction. Figure 3-6 depicts a typical
launch situation from the U.S. launch site at the Kennedy Space Center
(KSC) in Florida.

Burn-out Conditions. The launch vehicle both accelerates and raises the
payload from the surface of the earth along a predetermined launch path
(trajectory). The launch path must intersect the desired orbit, and the inter-
section must occur such that the rocket velocity (vector) and altitude cor-
respond with those for the desired orbit ut that point. Since the rockets
cease burning fuel at this point, the velocity and altitude achieved are
known as the launch vehicle bum-out conditions. If the burn-out condi-
tions do not match the orbit characteristics at that point, within some
allowable tolerance, adjustments using supplemental propulsion systems
may be required.