reqs_doc_v51 - Space Systems Product Development Spring...

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Space Systems Product Development – Spring 2002 CDIO S PACE S YSTEMS P RODUCT D EVELOPMENT P UBLICATION 41.1 R EQUIREMENTS D OCUMENT Department of Aeronautics and Astronautics Massachusetts Institute of Technology Revision 5.1 March 21, 2002 Murillo, Oscar Soffer, Leah Sullivan, Maggie Massachusetts Institute of Technology 1 Dept of Aeronautics and Astronautics
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Space Systems Product Development – Spring 2002 1. Introduction and Background Formation flight of satellites is the technology by which a cluster of satellites maintains a specified formation in orbit. Although formation flight of satellites has yet to be used in practice, it is being discussed in the aerospace industry as a way to provide new mission capabilities for satellites. The MIT SSL SPHERES project demonstrated the initial feasibility of the use of a group of satellites in formation flight. The CDIO3 class aims to expand on the SPHERES research with the electromagnetic formation flight project. Electromagnetic control of satellites essentially means that electromagnets will act as the force producers to control the relative position, attitude, and angular rate of a cluster of satellites. This control can be achieved by varying the current in the coil of an electromagnet to vary the B field the electromagnets provide. A number of current satellite missions are considering multiple spacecraft architectures for a variety of reasons. First, multiple spacecraft can be separated to large baselines thereby improving angular resolution for imaging, astrometry, and planet detection. Second, each spacecraft in the formation can be smaller than a single spacecraft designed to perform the same mission and thereby provide easier packaging, launch, and deployment. Third, since inter-spacecraft interfaces are soft (e.g., communications, optics, control, metrology), if a spacecraft fails, it can easily be removed from the formation and replaced with a functioning spacecraft. Fourth, as technology improves, replacement spacecraft can be launched and integrated into the array thereby evolving the formation’s capabilities without the costly “block changes” typical of past programs. (Miller, D. et. al., EMFF for Sparse Aperture Telescopes) While the benefits of formation flight are clear, there are several drawbacks to the current method of thruster actuation. As one explores the design of these systems in more depth, one recognizes that there is a miss-match between the geometric requirements that the formation must achieve and the way in which that geometry is controlled. Specifically, the relative separations between spacecraft, not the absolute inertial position in space, is important. However, thrusters actuate inertial degrees-of-freedom. In addition, precision formation flight of the satellites in the array requires that propellant be expended to maintain the formation geometry. This has several implications. First, propellant is a consumable which, once depleted, renders the satellite useless. Second, the impingement of a thruster plume on a
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reqs_doc_v51 - Space Systems Product Development Spring...

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