A pressurized rover was seen as critical for extensive surface exploration. The 16.5 metric ton vehicle would allow sorties of up to 20 days away from base.
On the regional scale, beyond the safe range for exploration on foot or in unpressurized rovers, crews would explore in pressurized rovers, allowing them to operate for the most part in a shirtsleeve environment. The rover was assumed to have a nominal crew of two people, but to carry four in an emergency. Normally the rover would be maneuvered and EVAs would be conducted only during daylight hours, but sufficient power would be available to conduct selected investigations at night. Crew accommodations inside the rover would be relatively simple: a drive station, a work station, hygiene facilities, a galley, and sleep facilities. An airlock on this rover would be capable of allowing not only surface access for an EVA crew, but also direct connection to the habitat, thus precluding the need for an EVA to transfer either to or from the rover.
Each day on an excursion away from the main surface facilities, the rover had the capability of supporting up to 16 person-hours of EVAs. Facilities for recharging the portable LSSs and for making minor repairs to the EVA suits were also included. The work station would be used, in part, to operate two mechanical arms that could be used to manipulate objects outside the rover without leaving the pressurized environment. These arms, along with other mobility subsystems, could also be operated remotely by Earth-based personnel. This feature was required to allow many of the deployment, setup, and monitoring activities to be carried out prior to the arrival of the first crew.
A final feature of this rover was the power system. This system would be mounted on a separate trailer to be towed by the rover whenever it was in operation. At times when the rover was dormant, the power trailer could be used for other purposes, including its use as a backup power source for any of the surface facilities.
Two pressurized rovers were to be carried to the surface. This allowed for redundancy in this function, including the possibility of rescuing the crew from a disabled rover located at a distance from the habitats. Each rover was driven by four cone-shaped wheels and was estimated to have a mass of 16.5 metric tons.
Several power source options were evaluated for the rovers, including solar arrays/RFCs, combustion engines, and isotopes. Solar array systems were not considered due to the large size of the array needed to support each vehicle. The long-range pressurized rover had to be able to support a crew of 2 to 4, with a 500- km range sortie (5 days out, 10 days at site, 5 days back). The power estimate for this rover was 10 kWe continuous. It was also anticipated that the pressurized, regional rover or its power system would be used to assist in the deployment of the main power system, situate future habitat modules, and serve as backup emergency power when required.
A desirable feature for the rover power system was that it be mounted on its own cart. This would add considerable versatility to its use when the rover was not on a sortie. The Dynamic Isotope Power System (DIPS) was considered primarily for its low mass and significantly lower radiator size compared to the photovoltaic array (PVA) area. The 238-Pu isotope had a half-life of 88 years and could be the same design as the flight-proven radioisotope thermoelectric generator (RTG). The isotope fuel would be reloadable into other power units in the event of a failure, thus preserving its utility. Another feature of isotope fuel was that it did not need to be recharged and was always ready as a backup, emergency power source independent of solar availability or atmospheric conditions. However, the 238-Pu isotope availability, quantity, and cost were issues that would have to be addressed.
The PV/RFC power option seemed impractical for the regional rover due to the large array area. The arrays would have to be sized to provide required power output during a local dust storm, the worst-case scenario, anticipating suspended operations during potential global dust storm season. Methane was a possible fuel for the rover since the propellant plant could produce additional fuel, given that extra hydrogen was brought from Earth. Methane could be used in an appropriately designed fuel cell. The reactant water would be returned and fed through an electrolyzer to capture the hydrogen. However, once the water has been electrolyzed into H2 and O2, which the fuel cell actually used to operate, it was not prudent from an energy utilization standpoint to make methane again. Storing and maintaining reactants on the rover also needed further study. A methane-burning internal combustion engine could be used to operate either rover. However, combustion materials would need to be collected to reclaim the H2.
The alternate Rover Power System Characteristics were assessed as follows:
Crew Size: 2.
Gross mass: 16,500 kg (36,300 lb).
Height: 2.00 m (6.50 ft).