The preferred option was now an "all-up" approach in which the crew and all the cargo were dispatched on one vehicle. The 1989 Mars expedition case study ground rules included: a single expendable vehicle would be launched to low Earth orbit; a zero-gravity vehicle would be used; three crew members would descend to the surface for 20 days; and aerobraking would be used at Mars.
In the course of the expedition, the environment, geological features, and material of Mars would be studied to advance knowledge of the origin of the solar system and to survey the potential for using Martian resources.
Two different trajectory options were initially considered for this case study. The first of these options was the "split/sprint" approach, carried over from the FY 1988 studies, in which a cargo vehicle delivered a portion of the cargo to Mars orbit, followed by a second vehicle carrying the crew and the remainder of the hardware. The second option was an "all-up" approach in which the crew and all the cargo were dispatched on one vehicle. Both options had similar characteristics regarding trajectory type and mission duration. The mission description was based on the (new) second option.
Upon completion of the orbital mating operations between the vehicle and the propulsion stages, the three-member crew would depart for Mars in a zero-gravity transfer vehicle on a 500-day roundtrip trajectory with a free flyby/return capability in case of mission abort. Depending upon the particular launch year, a Venus gravity-assist swingby might be utilized to reduce the trajectory energy requirements. Aerobraking, a technique that used the planetary atmosphere to slow the vehicle, would be employed upon arrival to capture the spacecraft into a 500-kilometer circular orbit. Five days would be allowed for lander preparation, after which the excursion vehicle would separate from the cruise module, carrying all three crew members to the Martian surface.
During their 20-day stay on Mars, the crew would conduct geologic and geophysical observations near the landing site on foot and by rover, collecting rock, sediment, and exobiology samples. Instrumentation would be deployed for the crew to conduct short-duration experiments, such as seismic tests, atmospheric balloons and rockets, and microbe/ bacterial/plant organics exposure tests. In addition, a geophysical/atmospheric science station would be left on Mars to measure properties and processes that could be monitored from Earth on a long-term basis. Because their stay on Mars was short, the crew would reside in the in-transit habitation module in the Mars excursion vehicle.
The crew would depart with selected surface samples to rendezvous with the interplanetary transport parked in orbit. Five days would be allowed for departure preparations, for a total stay time of 30 days at Mars. The return trajectory was either direct or by way of Venus, again depending on the launch year. As the interplanetary vehicle approached Earth, the crew, with samples, would transfer to an Earth crew return vehicle and separate from the larger cruise module. Return to Earth's surface would be via direct atmospheric entry and aeromaneuvering to landing. The total length of the mission would be 16 to 17 months.
In the time frame considered for this case study, there were four all-up mission opportunities to Mars. All outbound trajectories had a free-abort capability in the event of a major propulsion system failure detected en route to Mars as well as a powered abort capability in the event of some other system failure. Free aborts required longer-than nominal trip durations (20 to 24 months); powered aborts could return the crew faster, but not in less than 13 months.
The major trade-off result showed that the all-up mission option was preferable to the split/sprint option on the basis of total mass required in low Earth orbit and the number of Earth-to-orbit launches. The split/sprint concept was modified from 1988's configuration by removing the trans-Earth injection stage from the cargo flight and placing it on the piloted flight to assure crew safety. This strategy then negated the mass advantage of a separate cargo flight.
Limited but important science could be accomplished on the Martian surface during the 20-day stay. Significant science investigations, referred to as "cruise science," could also be conducted on the long trips to and from Mars. In particular, studies of human responses to radiation and zero gravity would be conducted. Particles and fields experiments and astronomical observations would also be possible.
A critical requirement for this case study was a heavy lift launch vehicle. Technology requirements were a highly reliable environmental control and life support system, propellant tanks with low inert mass and boil-off rates of cryogenic propellants, propellant transfer capabilities, remote rendezvous and docking in Mars orbit, high-energy aerobrake for Mars capture, hazard avoidance systems for a safe Mars landing, and short-range forecasting technology for solar flares.
This case study was a continuation of the FY 1988 preliminary examination of Mars expeditionary requirements, with more in-depth analyses and trade studies of mission options and techniques. A Mars Expedition would offer the national prestige of mounting a mission to land humans on another planet early in the next century. However, significant challenges pervaded this approach. The expeditionary pathway emphasized a major, highly visible effort without the burden and overhead associated with constructing permanent structures and facilities on Mars. Implementation of this approach relied on current or near-term technology and expendable vehicle systems.
Although similar to an Apollo-type mission, the Mars Expedition would, nonetheless, stimulate the development of technological and operational capabilities to test avenues of future expansion of exploration opportunities. In addition to its primary objective, the Mars Expedition would investigate the environment, geology, and materials of Mars that were relevant to the advancement of scientific knowledge as well as the potential for longer-term habitation and resource utilization. This mission could serve as a precursor to future Mars outpost development, and it could help identify prime sites for an outpost as well as return samples of the Martian atmosphere and soil, which could be analyzed for potentially useful resources and the presence of hazardous materials.
The case study methodology used during fiscal years 1988 and 1989 provided a systematic mechanism for a closer examination of the many pertinent parameters of human exploration of the Moon and Mars. These case studies built directly on earlier analyses conducted in support of the National Commission on Space and the Ride Task Force.
Mars Expedition 1989 Mission Summary: