Mission analysis techniques for attached Shuttle payloads

Visibility times, i.e., times at which desired targets are visible to a payload, are examined for attached Shuttle payloads. These times are affected by a number of constraints. Some constraints are examined along with mathematical or computer modeling techniques used to determine their effects. The constraints include oc- culation of the Earth, moon, and Sun, and limb avoidance angles of these bodies; orbit parameters such as inclination and ascending node, along with sensitivity to changes in these parameters; tracking and data relay satellite system acquisition; South Atlantic anomaly avoidance, nighttime viewing only; bright Earth avoidance angles; the field of view; Shuttle attitude; and Orbiter operational constraints. All of this information is in- tegrated and, with computer programs, a schedule of observations and Shuttle attitudes is obtained. ITH the advent of the Shuttle, new opportunities have opened up for flying payloads into space. In particular, the former sounding rocket user can look forward to in- creased time in space, from a few minutes to possibly many hours or days. He might also find lower costs since a sounding rocket is expendable, where an experiment container onboard the Shuttle is not. There are many factors involved which must be taken into account by the new user flying a payload onboard the Shuttle. Some factors which affect the ob- servation of desired targets are discussed in this paper as well as the mathematical formulation or computer modeling of each of these factors. This is not an exhaustive list, only currently typical. The purpose in presenting them here is twofold: 1) to make the experimenter flying a payload on the Shuttle first aware that there are constraints affecting the amount of visible time of his desired targets and, then, what some of these constraints are and how to determine their effect; and 2) to present at least an overview of these com- puter modeling or mathematical techniques in a common arena—the context of mission analysis techniques for at- tached Shuttle payloads. Figure 1 shows the target/visibility scenario graphically. Among the targets considered are the stars, planets, sun, moon, tracking and data relay satellite (TDRS), and points or areas of the Earth's surface. Many of the examples and much of the results presented here were taken from a study done for NASA's Office of Space Science-3 (OSS-3) mission. This uses a Shuttle pallet with three experiments mounted on a pointing system. Not all experiments flying on the Shuttle, particularly the sounding rocket type, will have their own pointing system. Nor may the experimenter have any say in Shuttle attitude or orbital characteristics. The reader should be aware of this and note that not all the information in this paper may apply to him, but he should extract what does affect his particular situation.