494. Preliminary Weight Estimation and Sizing of Lifting Spacecraft
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Paper
Abstract
It is frequently desirable to make a rapid weight estimate of a spacecraft for purposes of evaluation before committing a more intensive effort to its preliminary design, and it is often necessary to make weight predictions and to size many configurations in a very short time. The weight engineer is also required to determine the effect of specific perturbations on the baseline spacecraft. He must answer such questions as, what is the effect on the spacecraft if we require more velocity for increased plane changes, or increase the cargo carrying capability of the spacecraft, etc. Rather than employing a time-consuming detailed redesign of the vehicle, the weight engineer can be of great value to a program if he can determine the effect of the modifications in a short period of time and with a reasonable degree of accuracy.
The purpose of this paper is to demonstrate a rapid, parametric approach to solving the above problems. In order to demonstrate the use of this parametric method, certain general assumptions such as the spacecraft’s lift-to-drag ratio and location of the subsystem components were made. For different configurations the weight equation must be appropriately modified; however, the basic parametric methods presented in this paper can be applied to any type of spacecraft configuration.
This paper develops a method of providing an explicit equation for determining spacecraft weight as a function of spacecraft length, propellant weight, crew size, mission duration, cargo weight, and several other mission parameters, thus saving the additional time required by a reiterative process. Volumetric analyses are performed in a graphical manner when it is necessary to determine the minimum length spacecraft that can perform the mission. Crew headroom is also considered as a limitation on vehicle size. Other important parameters such as wing loading and impulsive velocity are presented, since the maximum allowable wing loading may be a limitation on the spacecraft, and a given amount of impulsive velocity may be required.
