ARTEMIS Mission Design

The ARTEMIS mission takes two of the five THEMIS spacecraft beyond their prime mission objectives and reuses them to study the Moon and the lunar space environment. Although the spacecraft and fuel resources were tailored to space observations from Earth orbit, sufficient fuel margins, spacecraft capability, and operational flexibility were present that with a circuitous, ballistic, constrained-thrust trajectory, new scientific information could be gleaned from the instruments near the Moon and in lunar orbit. We discuss the challenges of ARTEMIS trajectory design and describe its current implementation to address both heliophysics and planetary science objectives. In particular, we explain the challenges imposed by the constraints of the orbiting hardware and describe the trajectory solutions found in prolonged ballistic flight paths that include multiple lunar approaches, lunar flybys, low-energy trajectory segments, lunar Lissajous orbits, and low-lunar-periapse orbits. We conclude with a discussion of the risks that we took to enable the development and implementation of ARTEMIS.     

Communication Subsystem Design Trends for the Defense Satellite Communications Program

The Initial Defense Communication Satellite Program (IDCSP) hasbeen implemented successfully and is handling unique and vital militaryary communications. Tradeoff studies now being made are intended todefine the characteristics of the next phases of the Defense Satellite Communications Program (DSCP). This paper discusses briefly thecommunication subsystem design of the IDCSP for backgroundfor-information, and then discusses the design trends for future phases of the DSCP.The communication subsystem for the IDCSP is characterized bya single hard-limiting, low-power repeater with a toroidal patternantenna. Future trends in design will be toward multiple beams andmultiple repeaters with very wide bandwidths, high-powerquasilinear operation, and highly directive antennas. Several alternatetransponder configurations are evaluated in this paper, and an illustrativeive example is shown. Although long life is essential to future systems,as it was to the IDCSP, the trend will be to adding more complexity inthe satellite to increase the system capacity, while at the same timerequiring less complexity in earth terminals.