Chapter 10 SPACECRAFT DESIGN , STRUCTURE AND OPERATIONS

SPACECRAFT DESIGN PROCESS Regardless of how long it takes, spacecraft design and development typically occur in phases identified as: requirements definition, conceptual design, preliminary design, and detailed (or critical) design. These phases and their sequential relationships are shown in Figure 10-1. The design and development of a spacecraft is an engineering process divided into identifiable phases. In the past, the spacecraft development process required several years to accomplish, especially if it was a government project. Recent advances in satellite manufacturing technology, coupled with the growth of commercial markets in satellite communications and imaging, have significantly shortened the process. This change is described by a former commander of U.S. Air Force Space Command: Spacecraft development begins by defining needs or requirements the system is to satisfy. For example, the need to gather and store weather images and data. Or, take photographic images with less than 15 meter resolution and transmit the information in real time. The spacecraft mission will be a major determiner of the type orbit chosen for the space craft. "...new commercial geosynchronous satellites are available 18 months after order—soon to be down to 12 months. For the small LEO systems, time from order to delivery is about three years...In contrast, the acquisition of national security systems runs 10 to 15 years... Next is the conceptual design phase, in which various system concepts which can satisfy the mission requirements are considered and subjected to analysis. The most proficient means to carry out the mission is selected and major risks, costs, and schedules are identified. The preliminary design phase follows conceptual design, and may stretch over a couple of years (Fig. 10-2). During this phase, variations of the concept chosen in the conceptual design phase are analyzed and refined. Subsystem and component level specifications are defined and major documents such as the interface control document are written. Anticipated performance of systems and subsystems is substantiated and, from the detailed specifications, a preliminary parts list is identified. the same plant will build three hundred Teledesic satellites in three years and 15 Global Positioning System (GPS) satellites in seven years...”