A Case Study in NASA-DoD - The Black Vault

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either higher orbital altitudes or inclinations will degrade the on-orbit
space shuttle payload. For example, to increase the orbit altitude to
300 n mi (with an inclination of 28.5 deg), the payload decreases from
65,000 lb to about 53,000 lb; an increar- in the orbital inclination to
56 deg results in a similar payload reduction. For a polar orbit with
an altitude of 150 n mi, the space shuttle payload is about 39,000 lb.
In addition to the payload weight constraints, the shuttle payload
bay is also limited in size. The main cargo bay is 15 ft in diameter
and 60 ft long. As will be discussed later in this section, the method
of allocating the cost of a space shuttle launch to the various users
has not yet been determined, but payload length and weight and orbital
altitude and inclination are being considered by NASA as parameters for
determining the shuttle tariff schedule.
Because of the Space Test Program Office's interest in retaining
the option of operating as a secondary payload status, nominal shuttle
parking orbits with an altitude of 150 n mi and an inclination of 28.5
and 90 deg are used for this study. Nearly all of the Space Test Program
missions require orbital translations from the shuttle parking orbit to
the desired mission orbit. To accommodate this translation, solid .propellant
rockets sized for the specific velocity requirements and mission
payloads are used.
Generally, two rockets are required--one for apogee
and one for perigee. In this study, all of the solid rockets are drawn
from the inventory of existing solid rocket motors.
In special cases where large velocity increments are required and
the Space Test Program payload is large, the IUS is used as the translation
stage. This stage is being developed by the Air Force to support
the space shuttle operations. It consists of two solid rocket stages
and an instrument module capable of guiding the payload into orbit.
The translation is accomplished in a three-axis-stabilized mode as compared
to a spin-stabilized mode when the smaller solid rocket motors are
used.
* Secondary payload status refers to the case where the Space Test
Program mission does not determine the shuttle altitude, inclination,
or launch schedule and flies on a space-available basis.