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Phobos Expedition 88

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Status: Study 1988.

A primary objective of the mission was the establishment of early leadership in the human exploration of the solar system. To that end, baseline vehicles were designed for minimum dependence on advanced technology, and human presence was extended only to Mars orbit and the surface of Phobos. The study found that the Phobos mission could be an excellent precursor to a piloted Mars landing mission. Most importantly, it allowed a "Mars class" mission to be accomplished by 2003, four and a half years before the first Mars landing of the all-up Mars expedition case.

Other key objectives were to conduct enhanced robotic exploration of Mars itself from Mars orbit, using rovers, penetrators, balloons, and sample collectors, and to return samples of Mars and Phobos to Earth for detailed analysis. The expedition to Phobos combined human exploration objectives with those of previously studied Mars Rover/Sample Return (robotic) missions, but allowed different approaches to the exploration of Mars because of the capability for nearly real-time teleoperation of robotic systems from the vicinity of Mars.

Mission Description

The mission scenario employed a "split/sprint" trajectory: a cargo vehicle carrying the Phobos and Deimos exploration equipment, Mars rovers, and the crew's return propellant would be launched via an expendable escape stage on a minimum-energy trajectory in February 2001. Upon arrival, this vehicle would be placed in Mars orbit to await the piloted flight. In August 2002, approximately 18 months after the first launch, a second vehicle carrying a crew of four would be launched via an expendable escape stage on a high-energy sprint-class trajectory, which requires about 9 months to reach Phobos. Upon arrival in Mars orbit, the piloted vehicle would rendezvous with the cargo vehicle. Two crewmembers would transfer to a Phobos Excursion Vehicle and depart for a 20-day exploration of the Martian moon. During that time, the crew on Phobos would make observations, conduct experiments, and gather samples during a total of 24 hours of extravehicular activity. The two crewmembers who remained in the orbiting vehicle would teleoperate, or remotely control, rovers which would gather samples from the surface of Mars. After spending a total of 30 days in the Martian system, the crew would return directly to Earth, a 4-month trip. The total length of the mission was 440days.

The Phobos mission was potentially the earliest to arrive of the four case studies. A number of factors unique to this mission contributed to this capability. First of all, it could be possible for the expedition to Phobos to be completed without an assembly node in low-Earth orbit (LEO). However, two operations had to take place in LEO: mating of elements and payloads, and transfer of propellant (either fluid transfer or exchange of tanks) between Earth-to-orbit delivery vehicles and the vehicles carrying cargo and crew to Mars. In Mars orbit, a stage exchange or propellant transfer was effected between cargo and piloted vehicles. Therefore, the systems and techniques to robotically join elements and payloads in low-Earth orbit had to be developed, in addition to those for cryogenic propellant storage and transfer in Earth and Mars orbit.

The fact that the crew did not land on the surface of Mars simplified both the scenario and the requirements for the mission, and substantially increased the likelihood of achieving the principal goal of being first. With the exception of the rover systems, no other Mars surface landing systems were needed, either for equipment or for crew. This greatly reduced the initial mass to LEO requirement, as well as the time required for exploration program development and for the supporting technology and precursor programs.

The Phobos mission could be an excellent precursor to a piloted Mars landing mission. The robotic exploration of Mars would provide improved knowledge of the Martian environment. The Phobos mission would provide a unique opportunity to perform a systems checkout and verification of flight hardware and environment without the increased difficulty of a Mars landing. Given the ground rules and assumptions for the FY 1988 studies, these considerations allowed a "Mars class" mission to be accomplished four and a half years before the first Mars landing of the Mars expedition case.

The Phobos Expedition was baselined for the FY 1988 studies to assume propulsive capture into orbit about Mars. Subsequent analysis showed that such large masses in LEO were required that it was unlikely that this expedition could be flown without at least some infrastructure in LEO. This was because the mass requirement in LEO results in 20 to 30 ETO launches and the resulting integration in orbit. As would be discussed later in this report, aerocapture upon Mars arrival was found to offer such a significant improvement in IMLE0 that the results presented in this report assumed the aerocapture option for the Phobos Expedition.

Human Expedition to Phobos Mission Summary:

• Summary: NASA-wide analysis of exploration options; provide focused program for human exploration of solar system
• Propulsion: LOX/LH2
• Braking at Mars: aerodynamic
• Mission Type: opposition
• Trajectory Profile: Cargo: Minimum energy; Crew: Sprint
• Number Of Flights: 1 Cargo; 1 Crew
• ISRU: no ISRU
• Launch Year: 2003
• Crew Size: 4 (2 to Phobos surface)
• Mars Surface payload-metric tons: 8
• Outbound time-days: 286
• Mars orbit Time-days: 30
• Return Time-days: 124
• Total Mission Time-days: 440
• EVAs (8 hours per EVA; two crew per EVA): 4 EVA'S at Phobos
• Total Payload Required in Low Earth Orbit-metric tons: 765
• Mass to LEO in Peak Year: 453 metric tons in 2002 (aerocapture option)
• Propellant Mass (metric tons): Cargo vehicle 234 t; Piloted vehicle 318 t
• User Allocation in Mars orbit: 2 metric tons (includes Phobos expedition)
• User Allocation on Mars surface: 7 metric tons, includes 2 teleoperated explorers on Mars
• Mass per crew-metric tons: 190
• Launch Vehicle Payload to LEO-metric tons: 85
• Number of Launches Required to Assemble Payload in Low Earth Orbit: 9
• Launch Vehicle: Shuttle C or ALS