Introduction

Transit and Launches

The ERV

Resource Production

The Crew

Transportation Systems

Nuclear Surface Power

Conclusion

The Mars reference mission supports crews of six which explore the surface of Mars for nearly 500 days on the first and all subsequent missions, while limiting their exposure to the interplanetary space environment to periods near those of U. S. experience on Skylab and well within Russian experience from Mir. This surface-oriented philosophy emphasizes the development of high-leveraging surface technologies in lieu of concentrating exclusively on space transportation technologies. Thus, the mission relies on the in-situ production of CH4/O2 propellant for the crew's ascent vehicle and surface mobility, as well as the production of the necessary water and life support gases for the crew's entire surface stay. This mission emphasizes a robust suite of surface capabilities and high-leverage technologies.

The crew will travel to and from Mars on relatively fast transits (4 to 6 months) and will spend long periods of time (18 to 20 months; 600 nominal) on the surface, rather than alternative approaches which require longer times in space and reduced time on the surface, in order to be completely cost efficient. As a result, human missions to Mars can be accomplished without the need for complex assembly operations in low-Earth orbit. Both cargo and human missions are launched directly to Mars with the rendezvous occurring on the planetary surface. The associated reduction in total launch mass allows the first crew of six to explore Mars within a total of four launches of a Saturn IX-class launch vehicle. Shorter transit times reduce the time spent by the crew in zero g to the length of typical tours of duty on an international space station (as short as 130 days... shown right.). In addition, relatively fast transits will reduce the exposure to galactic cosmic radiation and the probability of encountering solar particle events. Reducing the exposure to zero g and radiation events help reduce the risk to the crew.

The strategy chosen for the reference mission, generally known as "split mission" strategy, breaks mission elements into pieces that can be launched directly from Earth with launch vehicles of the Saturn V or Energia class, without rendezvous or assembly in Low Earth Orbit (LEO). The strategy has these pieces meet on the surface of Mars, and the mobility of these elements will allow them to be connected or moved so they must be in close proximity. This allows the cargo to be shipped on a slower, low energy transit, and the crew on a fast, high energy transit. This gives the follow results for the human transit:

The first launch opportunity would send 3 cargo missions on minimum energy trajectories without any assembly in LEO. Launch 1 delivers a fully fueled Earth Return Vehicle (ERV) to Mars orbit. Launch 2 delivers an unfueled Mars ascent vehicle, a propellant production module, a nuclear power plant, liquid hydrogen, and 40 tonnes of additional payload to the surface.

During the second launch opportunity, two additional cargo missions and the first crew are launched. All assets previously delivered to Mars have been checked out, and the MAV, already on the Martian surface, is verified to be fully fueled before either the crew or the additional cargo missions are launched from Earth. The first cargo launch of this second opportunity is a duplicate of Launch 1 from the first opportunity, delivering a second fully fueled ERV to Mars orbit. The second cargo launch similarly mirrors Launch 2 of the previous opportunity, delivering a second unfueled ascent vehicle and propellant production module. These systems provide backup or extensions of the previously deployed capabilities.

See Transportation Systems

This mission builds upon Robert Zubrin's work with the Mars Direct Program. After the Mars Ascent Vehicle (MAV) lands on the ground it deploys a nuclear reactor several hundred feet from the ascent vehicle. Using the Mars atmosphere, the propellant production module begins to manufacture the nearly 30 tonnes of oxygen and methane that will eventually be required to deliver the crew into Mars orbit. The MAV is used at the end of a mission. All crew members board the tiny capsule (1.1) , and are launched (1.2) into orbit to rendezvous with an actual Earth Return Vehicle (ERV) (1.3). This fuel production plant goes through the same procedures as the one in the Mars Direct Plan. It creates methane gas (CH4). This gas is used for Rover fuel and MAV fuel.

The highly automated production of propellant from Martian resources is another defining attribute of the Reference Mission.The technology for producing methane and liquid oxygen from the Martian atmosphere and some nominal hydrogen feedstock from Earth is an effective performance enhancement and appears to be technologically feasible within the next few years. The split mission strategy allows the propellant production capability to be emplaced, checked out, and operated to produce the required propellant prior to launching the crew from Earth. In addition to spacecraft propulsion, the production capability on Mars can provide fuel for surface transportation, reactants for fuel cells, and backup caches of consumables (water, oxygen, nitrogen, and argon) for the life support system.

Humans are the most valuable mission asset for Mars exploration and must not become the weak link. The objective for humans to spend up to 600 days on the Martian surface places unprecedented requirements on the people and their supporting systems. Once committed to the mission on launch from LEO, the crew must be prepared to complete the full mission without further resupply from Earth. Unlimited resources cannot be provided within the constraints of budgets and mission performance. Their resources will either be with them or will have already been delivered to or produced on Mars. So trade-offs must be made between cost and comfort, as well as performance and risk. Crew self-sufficiency is required because of the long duration of their mission and the fact that their distance from Earth impedes or makes impossible the traditional level of communications and support by controllers on Earth. The crews will need their own skills and training in specialized support systems to meet the new challenges of the missions. The crew will have to specially regiment their time in order to complete all of their tasks. To the left is a time chart showing the probable time allotment for ground operations.

The nominal crew size for this mission is six. This number is believed to be reasonable from the point of view of past studies and experience and is a starting point for study. Considerable effort will be required to determine absolute requirements for crew size and composition. This determination will have to consider the tasks required of the crew, safety and risk considerations, and the dynamics of an international crew. Crew members should be selected in part based on their ability to relate their experiences back to Earth in an articulate and interesting manner, and they should be given enough free time to appreciate the experience and the opportunity to be the first explorers of another planet. Significant crew training will be required to ensure that the crew remains productive throughout the mission. A new addition to the mission is the utilization of inflatable structures (1.4, 1.5, 1.6) connected to the base. This would allow for a smaller shipping area, and an easily expandable habitat.

The habitat within which astronauts will travel to and from Mars is one of the most important elements in the Mars Reference Mission. This arises from the complexity of its requirements:

• Support a crew of 6 for approximately 180 days on the trip between the Earth and Mars.
• Land on Mars, with the crew, where the habitat will become part of the permanent surface facility
• Support a crew of 6 for approximately 180 days on the trip between Mars and Earth. This is a separate facility, hopefully identical to the trans-Mars habitat, which will be launched to Mars orbit two years prior to the launch of the first crew, and which will remain in standby for another two years before it is occupied and returns to Earth with the crew.
• Provide all of the systems required for maintaining the crew in good health for the mission.
• Be of low-enough mass to allow reasonable transportation cost.

The interplanetary transportation system consists of a Trans-Mars Injection (TMI) stage, a biconic (two winged) aeroshell for Mars orbit capture and Mars entry, a descent stage for surface delivery, an ascent stage for crew return to Mars orbit, an Earth-return stage for departure from the Mars system, and a crew capsule (similar to an Apollo Command Module) for Earth entry and landing (1.7). As mentioned earlier, the Reference Mission splits the delivery of elements to Mars into cargo missions and human missions, all of which are targeted to the same locale on the surface and must be landed in close proximity to one another for later positioning (1.8). The transportation strategy adopted in the Reference Mission eliminates the need for assembly or rendezvous of vehicle elements in LEO, but it does require a rendezvous in Mars orbit for the crew leaving Mars. The transportation strategy also emphasizes the use of common elements to avoid excessive development costs and to provide operational simplicity (1.9).

"With no known natural resources on Mars that can be used to generate power, a crew exploring Mars must rely on either converting solar radiation or using a power source they have brought with them. With Mars lying, on average, 50 percent farther from the Sun as Earth, only 44 percent as much solar radiation reaches that planet. This means a crew must bring 2.25 times as much solar energy collecting and converting systems to generate the same amount of power as could be generated on Earth. Add to this a day-night cycle (which requires the addition of an energy charging and storage system) as well as Martian dust storms (which significantly diminish the amount of light reaching the surface over extended periods of time) and the size of a solar power station on Mars becomes both large in area and mass and subject to interruption or diminished effectiveness due to the dust storms. Of those sources of energy that can be brought with the crews, only a nuclear power source can concentrate sufficient energy in a reasonable mass and volume. However, other concerns- environmental on Earth, operational on Mars, to name a few-are added to any mission that considers the use of a nuclear power source.

Given these kinds of considerations, a choice was made to rely primarily on nuclear power for systems operating on the Martian surface. Power provided by the solar arrays used during the transit to Mars will be available for backup and emergency situations. However, the solar arrays will not be sufficient to power the propellant manufacturing plants that are also a key feature of this mission architecture."

To summarize, the major distinguishing characteristics of the Reference Mission include:

• No extended LEO operations, assembly, or fueling.
• No rendezvous in Mars orbit prior to landing.
• Short crew transit times to and from Mars (180 days or less) and long surface stay-times (500 to 600 days) for the first and all subsequent crews exploring Mars.
• A heavy lift launch vehicle capable of transporting either crew or cargo direct to Mars, and capable of delivering in four launches all needed payload for the first human mission and in three launches for each subsequent opportunity.
• Exploitation of indigenous resources from the beginning of the program, with important performance benefits and reduction of mission risk.
• Availability of abort-to-Mars surface strategies, based on the robustness of the Mars surface capabilities and the cost of trajectory aborts.
• Common transit/surface habitat design.
• Maintenance of a robust, safe environment for crews throughout their exploration.
• Substantial autonomy of crew and system operations from ground control.