A report discusses a network of spacecraft, in orbit around Mars, used to relay radio communications between Earth stations and mobile exploratory robots (rovers) as well as stationary scientific instruments that have been landed on the Mars surface. The relay spacecraft include two already in orbit plus several others planned to arrive at Mars in the years 2004 through 2008. A major portion of the report is devoted to the orbit of the G. Macroni Orbiter, which is in the midst of an iterative design process and is intended to be the first Mars orbiter designed primarily for radio relay. Candidate orbits are analyzed with a view toward choosing one that maximizes the amount of time available for communication with surface units, taking account of visibility as a function of position, the limit on communication distance at low power, and the fact that surface units can transmit more easily when they are in sunlight. Two promising new orbits for Mars relay satellites are identified: a 1/2-sol apoapsis-at-constant-time-of-day equatorial orbit and a 1/4-sol apoapsis-at-constant-time-of-day, critical-inclination orbit.
This work was done by Gary Noreen, Roger Diehl, and Joseph Neelon of Caltech for NASA's Jet Propulsion Laboratory.
NPO-30639
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Spacecraft Orbits for Earth/Mars-Lander Radio Relay
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Overview
The document discusses advancements in spacecraft orbits designed for radio relay communications between Earth and Mars, specifically focusing on the G. Marconi Orbiter (GMO). Developed by NASA’s Jet Propulsion Laboratory (JPL), the GMO aims to enhance the communication capabilities of mobile exploratory robots (rovers) and stationary scientific instruments on the Martian surface.
Historically, Mars orbiters have been primarily designed for scientific missions, with their relay functions being secondary. This has limited the effectiveness of communication with landers, which are most active during sunlight when they can generate solar power. The GMO is set to change this paradigm by being the first Mars orbiter specifically designed for relay support, significantly improving connectivity and operational flexibility for in-situ missions.
The report identifies two innovative orbit designs: the 1/2-sol Apoapsis-at-Constant-Time-of-Day Equatorial (ACE) orbit and the 1/4-sol Apoapsis-at-Constant-Time-of-Day Critical-Inclination (ACCI) orbit. The ACE orbit is particularly advantageous as it maximizes daytime coverage for relay users, allowing for extended communication periods with landers. This orbit provides approximately 11 hours of coverage for the Mars Science Laboratory (MSL) rover during daylight, ensuring that all landers can communicate effectively.
The ACCI orbit, while offering a greater coverage area, provides less daytime coverage for the MSL rover. Both orbits are designed to address the limitations of traditional areostationary satellites, which can only cover half of Mars and operate at a high altitude, making communication less efficient.
The document emphasizes the importance of these new orbits in increasing the data returned from Mars missions, potentially by an order of magnitude or more. By combining high-performance relay payloads with custom relay orbits, the GMO will enable new relay services and enhance the overall effectiveness of Mars exploration.
In summary, the report outlines a strategic shift in Mars exploration communication, highlighting the GMO's role in establishing a robust relay network that will significantly improve data transmission and operational capabilities for future missions on Mars.
