General outline of the Polish design proposal
for the Mars Pressurized Vehicle (MPV)

In behalf of a design team established by Mars Society Polska (the Polish Chapter of The Mars Society) I am hereby submitting an outline of our design proposal for a pressurized vehicle for Mars Direct program.

Krzysztof Lewandowski, M.Sc., Ph.D. Student,
Institute of Construction and Exploitation of Machinery,
Wroclaw Technical University,
Wroclaw, Poland.
lewand@pojazdy.ikem.pwr.wroc.pl

K. Lewandowski's M.Sc.Thesis (completed in 1998) concerned a conceptual design of a chassis for the moon vehicle and was based on the works and concepts of M.G. Bekker (a Polish-American enginneer and general designer of the Lunar Roving Vehicle for the Apollo missions, (see http://www.uranos.eu.org/biogr/bekkere.html).

Mars Pressurized Vehicle (MPV)

1. General principles.

1.1. The vehicle is designed for continued use by three members of the Mars Direct mission program. In emergency conditions, the vehicle could be inhabited by four members of the Mars Direct mission (i.e., the full mission crew).

1.2. The vehicle design is based on detailed analysis of Martian terrain environment, as reported by the Viking 1, Viking 2, and Pathfinder Mars landers, as well as on pioneering works by M.G. Bekker on off-the-road locomotion (confirmed by his design for Lunar Roving Vehicle for the Apollo missions).

1.3. The vehicle is designed for a two-month continued activity on Mars.

2. Basic vehicle systems:

2.1. Vehicle structure:

2.1.1. Tires - to properly negotiate the difficult Martian terrain, rigid tires of the general design following that of the NOMAD vehicle are assumed. These tires proved to be very successful in the 1997 tests of the NOMAD vehicle under the Desert Trek program on the Atacama Desert, followed recently by the tests in Antarctic.  

       Fig 1. The tire of the NOMAD vehicle.

2.1.2. Suspension - six-wheeled, individually suspended system, based on steel springs made of maraged steel, with shock-absorbers of the same material. Six wheeled system assures excellent negotiation of the articulated Martian terrain as well as the possibility of continued operation even after total loss of two of the tires. In the future, an alternative design using a hydraulic system with electrorheologically or magnetorheologically controlled fluids can be considered as well. The design of the frame, suspension and traction system is based on theoretical results obtained by M.G. Bekker http://www.uranos.eu.org/biogr/bekkere.html, so excellenttly confirmed by his design of the Lunar Roving Vehicle for Apollo missions. From the mobility point of view,
it seems that the best solution would be the system designed by Bekker for the MOLAB vehicle, but with different construction of the wheels (see Sec. 3.4. below for additional discussion).

2.1.3. Chassis / Frame - a special design following the design of an airplane fuselage with reinforcements in places of reaction forces from the suspension. We assume the use of sandwich materials with honeycomb layers, with the rest of the construction made of light alloys.

2.1.4. Pressurized envelope / Body - made of sandwich material. Interior volume is designed to house three crew members. In emergency conditions, the vehicle could be inhabited by four members of the Mars Direct mission (i.e., the full mission crew). A sketch of the proposed interior is shown below.

                      Fig 2. Interior sketch of MPV.

2.1.5. Pressure ports - we insist at providing an integrated airlock for MPV. We think that the biological safety of the crew is the most important principle under the first manned mission to Mars, and we cannot assume that there are no biological organisms
on Mars, nor can we predict their possible influence on humans. The extremofile forms of life found in certain places on Earth can easily live in the temperature/pressure conditions around the three-point of water. There are several places on Mars where these condition are met, like: Vallis Marineris complex in the region of Noctis Labirynthus, an outlet of Vallis Marineris complex into Chryse Planitia, Argyre Planitia impact crater, and Hellas Planitia impact crater. Moreover, we think that the problem of dust during an activity on Mars will be very serious. The airlock will to a significant degree separate the cabin environment from the penetration of dust - much better than any design without them.

2.2. Power plant - we assume a hybrid power system for MPV.

2.2.1. Engine - the MPV is propelled by independent electrical motors placed inside its NOMAD-like wheels. They use the electrical energy stored in vehicle batteries, and produced by several independent power sources as described below.

             Fig 3. A scheme of the power system structure for MPV.

2.2.1.1. The basic level of power is provided  by two or three RTGs (Radioisotope Thermal Generators), similar to SNAP generators, mounted outside the vehicle.
These generators may additionally use a cooling gas (helium) to power the heating system for the vehicle through a heat exchanger.

We think that:

a) RTGs are the most reliable means for continued and low maintenance work in the hostile environment on Mars - in fact, the reliability of RTGs is the highest among all kinds of power systems.

b) Radiological safety of recent RTGs is excellent - the possible level of a radiation leak is negligible compared to the level produced by solar and cosmic radiation during the interplanetary journey, and on the surface of Mars.

c) In the case of emergency, the generators constitute the most reliable source of power for critical life support systems of MPV.

2.2.1.2. The main energy source is provided by fuel cells. They will use the fuel produced by the ISPP (In-Situ Propellant Production) installation.

             Fig 4. Sketch of the driver control area of the MPV

2.2.1.3. An additional source of power is provided by solar cells that can be unfurled over the roof of the vehicle. Solar cells serve as a backup energy source, using the most reliable solar energy to replenish the batteries of MPV.

2.2.2. Electrical system - conventional, 12 V rechargeable batteries.

2.2.3. Fuel - the fuel cells will use the fuel produced by the ISPP installation.

2.2.4. Speed - 32 km/hr over "very easy terrain", 2-5 km/hr over rough terrain.

2.3. External fittings:

2.3.1. Crane - an operational area of more than 180 degrees around the rover.

2.3.2. Winch - designed for use with both electrical and manual operation.

2.3.3. Detachable tools.

2.3.4. Sample stowage - external.

2.3.5. Sample pressure port - none. We think it is not necessary, as all
important investigations can be conducted on board of a habitat module.

2.3.6. EVA equipment stowage - external.

             Fig 5. Simplified sketch of the MPV

2.3.7. Manipulators - two, in front of the vehicle.

2.3.8. Tow bar connect - provided. In case of emergency it can be used for towing of other vehicles or even the habitat module.

2.3.9. Communications - antennas for communications between the habitat module, EVA activities and others.

2.4. Internal fittings.

2.4.1. Life Support System.

2.4.1.1. Waste disposal - chemical marine toilets, similar to tourist chemical toilets. Containers for waste human products are placed inside the vehicle, in one or more grouped containers. No waste human products should be dumped on the Mars surface.

2.4.1.2. Water supply - about 300 liters for drinking, food rehydration and dish washing. We suppose to use partial recovery of water vapour from atmosphere through air recycling.  Water will be produced by the ISPP installation.

2.4.1.3. Heating, ventilation and air conditioning:

Heating - the main element of the heating system will be RTGs, through a heat exchanger connected with the air conditioning system.

Ventilation - we assume the use of few ventilators inside the cabin, with constant air flow forced by the air conditioning system.

Air conditioning - air will move through a water vapour recovering module, carbon

dioxide reducer, and smells absorber. Then it will be enriched with oxygen, then possibly with water vapor in a moisture controller, and finally aromatized. There will be also a heater and a ventilator.

Atmosphere: 40% of oxygen, the remaining 60% - nitrogen and other gases.

Pressure: 400 hPa (like around 4 km above sea level).

Temperature control: between 15 and 30 degrees Celsius.

Water vapour: around 75%.

In emergency, air recycling will be provided by a manual ventilator, with carbon dioxide absorber and oxygen enricher. All elements of life support system will be placed inside the cabin. The air and EVA systems should be designed to account for certain loss of atmosphere gases from the cabin. Oxygen will be provided by the ISPP installation.
Lost nitrogen and others components must be carried in high pressure reservoirs.

2.4.2. Furnishings - each crew member will have for his disposal an individual seating and sleeping place. Three berths will be installed on one of the cabin walls, with a possibility to regulate the distance between them. Three seating places will be provided at the front of the vehicle. The habitat part could be separated from the control part by a sliding partition. In emergency, an additional crew member can sleep in a hammock, and use an additional unfolding seating place inside the cabin.

2.4.2.1. Food preparation - casual, as during a space flight. Food storage for two months activity for three members of the crew.

2.4.3. EVA systems - EVA suits will be carried in special chests next to the airlock with a capacity for three suits. One more suit can be carried inside the airlock in an air-tight chest. There will be also suits for activity inside the cabin. Outside the vehicle, beside the airlock door there will be a system of blowers using high pressure gas (carbon dioxide) for blowing off dust from EVA suits before a crew member can walk into the airlock. The problem of dust contamination during an activity on Mars will be very serious. The EVA and airlock systems proposed will, to a significant degree, separate the cabin and habitat environment from the penetration of dust - much better than any design without the airlock.

2.4.4. Science systems - a volume of 0.5 cubic meters should be sufficient. In the future, all science systems will be miniaturized and lightweight. We assume their total mass of about 50 kg.

2.4.5. Vehicle control - all systems will be in the front of the cabin. All necessary instruments for driving, steering as well as power and communication control will reside there. Owing to the use of RTGs, the vehicle could be controlled remotely from Earth
to the next landing site, during the spaceflight of the next human mission to Mars. A significant assistance of the local artificial intelligence "driver" would be needed to assure safe locomotion under the signal time delays involved.

3.0. Performance Requirements

3.1. Speed - 32 km/hr over "very easy terrain". Yes, very easy. Unfortunately, there seems to be no "very easy terrain" on Mars. The soil is similar to sand-gravel combination ground on Earth, but with lots of medium size rocks scattered around. A terrain profile is very complex. There are many undulated areas with medium degree
of inclination, but with a lot of ditches of almost vertical slopes. Therefore we do not think the attainment of this speed on Mars will be possible for anything more than a few tens of meters...

3.2. Range - we suppose that due to a hybrid power system, the vehicle will have excellent prospects for long range activity around the landing site. We assume a range of over 400 km.

3.3. Vehicle mass - we assume that a dry mass of 1500 kg only will be very hard to attain under the stated requirements. Hence, the use of high-tech construction materials will be indispensable. Hard terrain conditions require a very good suspension system, with a generous allotment of mass for the suspension. We think that assuring adequate performance may require the total dry mass of at least 2500 kg.

3.4. Terrain - we optimized the vehicle for Martian terrain profile based on the topography map of previous Mars landing sites. We suppose that comparing the results of rock investigations from Viking and Pathfinder landing sites we can arrive at the best solution for the suspension system for MPV. The design of the vehicle, especially of the frame, suspension and traction system is based on theoretical results obtained by M.G. Bekker http://www.uranos.eu.org/biogr/bekkere.html, so excellenttly confirmed by his design of Lunar Roving Vehicle for the Apollo missions. From the mobility point of view, it seems that the best solution would be the system designed by Bekker for the MOLAB vehicle, but with different construction of the wheels. Differently than on the Moon, on Mars the main problem arises not from the mechanical properties of the soil comparable to Earth's sand-gravel soil), but from the highly developed surface morphology (an abundance of stones and boulders of a wide spectrum of sizes).

3.5. Logistics - the vehicle should be transportable via the C-130 Hercules airplane. Because an operating external dimensions are larger than C-130 cargo cabin, the wheels and suspension, and some other external elements of our vehicle are folded in the transportation configuration. The folded dimensions are 7.3 m in length, 2.7 m in width and 2.6 m in height. During the flight to Mars, the vehicle is not available for inspection
by the crew. For discharge, the use of an elevator and a special inclined plane winches build into the cargo cabin of the habitat module are provided.

3.6. Crew - the vehicle is designed for continued use by three members of the Mars Direct mission program. In emergency conditions, the vehicle could be inhabited by four members of Mars Direct mission (i.e., the full mission crew).