OneWay to Mars George William Herbert Retro Aerospace George William Herbert Retro Aerospace 2240 Blake St #101 Berkeley CA 94704 gherbert@crl.com rev 1.5 0.0 Abstract Traditional modern manned mars missions [1] have suffered severe technical challenges due to the need to provide return capability for the crews at the end of the mission. This negatively affects the initial mass and/or development cost and/or risk, and the time available for the explorers on the surface of Mars. I propose a one way mission using some mars resources as a more valuable goal and describe such a mission. Advantages include simple and robust mission design and much longer effective research times on the surface, hundreds of man-years instead of a few. 1.0 Introduction It is often a useful mental challenge to do what-if mission architecture development, assuming some fundamental shift in technology or other parameters. This paper addresses just such a mission architecture for manned Mars exploration with two such what-if assumptions: * What if we do not have to return the explorers to earth, and * what if we can launch 100 ton class payloads to Mars for $250 million per flight. We will justify the first what-if at the beginning of this paper. The second is addressed in a seperate technical report on the Retro Aerospace GRAND-3 launch vehicle [2]. 2.0 Why OneWay Why are we thinking of sending humans hundreds of millions of miles across empty and dangerous space, and then back again? Existing Manned Mars Exploration mission architectures are preoccupied with the assumption that the explorers sent to Mars must be returned to Earth. This is at its root a variant of the Flags and Footprints approach; even if the explorers stay for many months, they can only explore the area around their lander. The mission constraints imposed by return vehicle launch windows and by fueling those return vehicles (even using in-situ propellant production) severely hamper the amount of science return. Let us instead find a set of astronaut/explorers who are willing to spend the rest of their lives on the surface of Mars exploring it in great depth. Instead of a single field tour with inadequate offroad capability or time for good exploration, we land the equivalent of the South Pole science bases down on Mars and send a crew of explorers on a 40 or 50 year exploration stay. Instead of two man-years on the surface (Mars Direct, per mission) we could have two orders of magnitude more useful exploration at lower technical risk. Upon simple examination, the life support requirements of humans can largely be met with easy extraction of in-situ resources (water, oxygen from the atmosphere) or brought along for relatively limited mass penalties, with minimal overall development or technical risks and development costs. If we select 35 year old explorers then they will have perhaps 30 years of active exploration ahead of them at Mars, with some decades more lifespan being less active. A six-person OneWay mission (the initial manned expedition planned here) would thus provide about 180 man-years of time at Mars, of which at least half would be useful science and exploration. An ongoing program flying more supplies and more explorers would rapidly explore Mars. There are two large obstacles to such a mission. One is the psychology of the explorers and to a lesser degree their physical health. While their isolation can probably be alleviated by lavish communications with earth, the time delay of those communications and the cramped living quarters which will be available, along with the limited number of other onsite humans, will surely take its toll on the explorers. Careful selection of those able to work and psychologically function largely alone for the rest of their lives will prove difficult. This author feels that it is quite possible, however. The second large obstacle is public and political opinion. Undoubtedly some will cry that we are sending astronauts to their certain deaths with this sort of mission. This can be argued on two fronts: practical and visionary. The practical approach is simply to point out that no human being will live forever given existing biological limitations and medical technologies. As long as we do not significantly artificially shorten their lives, the explorers will presumably live as long on Mars as on Earth. Given the supplies and habitats to live out their old ages and barring accidents during exploration, the astronauts should live long lives. The visionary approach is that this is a grand adventure of opening a new frontier, and that these explorers will spend the rest of their lives breaking new ground for humanity. As Robert Zubrin has so eloquently described in his essay on the significance of the Martian frontier, the concept of The Frontier was a significant part of early american culture and society. Mars represents the best frontier available to humanity at this time. It is reachable with todays technology and feasible amounts of funding, and a mission such as OneWay would provide an even better beginning to opening the Martian frontier than missions which return the crews to earth. These crews would be the first pioneers setting off, committing themselves to the new frontier, rather than mere explorers interested in science. Both approaches can be used together, and reinforce each other with many target audiences. It is felt likely that together they can overcome social and political resistance to one way missions. 3.0 Mission Architecture At the beginning of the OneWay program, five years are expended doing initial R&D and vehicle qualification. At the end of the R&D period, a first unmanned pathfinder mission is sent to Mars to qualify a number of components. From that time on, one mission is sent every 2 years (planetary lineup for minimum energy transfers) with two launches. Launch vehicle for the OneWay mission architecture is a GRAND-3 heavy-lift launch vehicle with worst-case payload to Mars transfer orbit of 100 tonnes. GRAND-3 is an enhanced version of the GRAND-2 big dumb launch vehicle; the first two stages are pressure fed propane/nitric acid propellant steel tank big dumb booster vehicles, with GLOW around 20,500 tonnes. The third stage is a modified space shuttle external tank with two SSME-type motors and a 10-meter payload shroud above the oxygen tank. Each launch will send three standardized capsules on a minimum energy transfer orbit to Mars. The 32-tonne capsules look like larger, stubbier versions of the Soyuz re-entry capsule: a rounded bottom, truncated cone top, ten meters in diameter at the largest and 6.5 meters tall. Inside are three decks. The capsules are designed to aerocapture and brake at mars, then land softly on the surface using parachutes and terminal retro-rockets. Useful payload for the capsule is 16 tonnes. The first phase of the program will take six years and involve five launches, bringing a total of six explorers to Mars. The pathfinder mission is sent to prove out the capsule/base design, aerocapture and landing, and systems testing of the oxygen generation and water extraction local resource utilization. A secondary goal is further onsite exploration of the proposed main Mars base, using rovers transported by the pathfinder landers. Ideally, the three landers will land at two seperate sites (a future main and secondary base of operations) which have pre-emplaced radio beacons. Landing accuracy can thus be gaged and if necessary have systems re-engineered before the production missions begin. Two years after the pathfinder mission, the first manned mission lifts off. Two crew in one habitation-equipped capsule are the first explorers to be sent. Both of the initial crew are assumed to be flight engineer types, not science oriented, as the risks of not having enough personel skilled in repair tasks initially at the manned base are too large. The rest of the mission payloads is one lab-equipped capsule and four dedicated to cargo and supplies. All six of these capsules are intended to put down at the same main base site where two of the three pathfinder capsules landed. The crews then proceed with initial area surveys and base integration for the units already present. One of the cargo items is two large, long range rovers capable of extended unsupported exploration extending to perhaps a years duration. Initially they is used as an emergency measure: they land after the manned capsule, should the manned capsule set down too far from the main base site the rovers will land next to it and provide surface transport to the base, or other transport capability as needed. The second manned mission will carry four more astronauts, two more lab modules, and two cargo modules to Mars. Two of these four crew are planetary science experts, along with two more engineers. Major exploration can begin immediately using the various rovers. The second phase of the OneWay architecture can begin immediately after the end of the first. This simply is four more sets of launches with one manned vehicle / two crew, and five unmanned capsules each. This will provide additional exploration capability, science and analysis gear, and skilled personel to expand the capabilities of the set of explorers. Once biological CELSS systems capable of supporting humans on an ongoing basis with little input are sufficiently developed, the exploration can shift to phase 3. Each launch would then consist of one habitation module, one cargo module, and one greenhouse module. Detailed planning for phase 3 is not being performed yet. 4.0 Resource Transport and Utilization Some local resources are easy to exploit on mars. Carbon Dioxide gas is the major constituent of the atmosphere and is available merely for the mass and electrical power for a small compressor unit. CO2 can be split into oxygen gas and carbon monoxide relatively easily with additional electrical power, providing a fuel/oxidizer combination if need be and providing pure oxygen for life support (with CO waste vented). Water can also be extracted from the atmosphere fairly easily. A mostly closed-loop water cycle could replenish itself via this mechanism. The most promising system to date is the WAVAR [3] adsorbtion method. Its early design indicates requirements for continuous power of only 212 watts and about 56 kg equipment per kg of water output per martian day. Oxygen can be generated from CO2 as mentioned above, but it appears more power efficient (the limiting factor) to electrolyze water obtained using WAVAR, so while both systems are provided for redundancy the bulk of O2 produced would be from water. In addition to oxygen, there will be losses of the buffer gases used in the capsule atmospheres due to EVA operations and normal slow leakage from the pressure hull. Replacing the buffer gases will be necessary over time. Fortunately, there is roughly 2.7% nitrogen and 1.5% argon in the Mars atmosphere. An extraction mechanism should be fairly easy to develop and both gases are useful as buffer gases. Food production and organic oxygen cycle replenishment would be a highly complimentary technology, perhaps using local soils and/or CO2, but it is not yet a proven technology and is not assumed in the first phase mission architecture. Sufficient prepackaged food for the astronauts is sent as cargo. In the second phase, closed loop biological life support systems suppliment or replace the prepackaged foods. In the first phase, a food budget of 1.0 kg/day is assumed. This is enough to include a relatively good variety of diet for the explorers, needed largely for psychological reasons. One additional required resource is martian soil. Radiation exposure over the lifetime of the crews would be somewhat high if the habitats are not shielded to at least 35 g/cm^2 worth of additional radiation shielding [4]. Earthmoving attachments on the rovers will provide the capability to pile Mars dirt on top of the habitation modules to add additional shielding and keep crew medical impact of radiation to a minimum. 5.0 Capsule Details and Variants There are two structural variations on the basic OneWay capsule design; the standard, two-deck capsule, and a shorter one deck capsule designed for carriage of outsize cargos (large rovers). The two-deck model is 6.5 meters high and 10 m in extreme diameter. The overall form is a truncated cone similar to the Soyuz reentry vehicle. Both decks are 2.5 meters high including ducting and floor structure. The lowest deck extends one meter below the widest point and 1.5 above it. Its floors angle up from 2.5 meters from the centerline to fit the heatshield profile. The second deck is 9 meters diameter at its floor level and 7.4 meters at its ceiling. The two-deck or tall module masses 15 tonnes including internal and external structure, thermal protection systems, and re-entry and landing hardware. 5.1 Heavy Cargo Capsule The heavy cargo variant truncates the cone at the roof of the first deck, providing a 100 cubic meter pressurized cargo capacity and the ability to carry rovers up to 7 meters long, 3 meters wide, and over 3 meters high. Mass for this version excluding payload is 13 tonnes due to the lower structure. Nominal payload for the heavy cargo version is 10 tonnes of food, consumables, and spare parts, with a 9 tonne rover. 5.2 Hab Capsule The Hab capsule is configured to support two astronauts for the trip in space and then provide life support and quarters on the surface for an extended period of time (three or more decades). The payload includes two light (500 kg class) unpressurized rovers suitable for day expeditions and one larger (2000 kg class) pressurized rover. 5.3 Cargo Capsule The standard Cargo capsule has the same life support systems and power systems, though they are unused in the initial flight. It has no mobility systems or science cargo; its sole payload is 9 tonnes of food, sundry consumables and spare parts. 5.4 Lab Capsule The Lab capsule has the same life support systems, additional electrical power available, and science / geology lab and field equipment as well as more rovers. 5.5 Long Term Uses of Capsules As the mission is intended to stay on Mars for the lifetime of the explorers, additional habitable units and space are both valuable, for psychological reasons and for redundancy should capsule life support systems suffer catastrophic failures. Towards those ends, all of the capsules except the Heavy Cargo capsule are fully equipped with the power and life support systems to serve as living quarters. It is expected that some of the modules will be so utilized over time by the explorers. Should an accident befall the Hab modules during transit to the surface of Mars, the Lab modules are fully prepared as backup quarters and will keep the crew intact. 5.6 Capsule Subsystems The various capsule types have the subsystem mass breakdowns listed in Table 1. Table 1: Payload mass breakdown of capsule types Equipment Category Hab Cargo Lab HvyCargo ECLSS-O2 gen/CO2 rem 2.2 2.2 2.2 - ECLSS-O2 for space 1 - 1 - Power: gen & distn 1.5 1.5 2 - Power: batteries 3.3 3.3 3.8 - Science 1 - 4 - Mobility / EVA gear 4 - 2 9 Cargo / food 4 10 2 10 5.61 ECLSS Subsystem On the habitable modules, a total of 2.2 tonnes is assumed for the ECLSS systems. Of that, 1,500 kg is related to the water loop and 500 kg to the oxygen and CO2 loops. 100 kg is assumed for human waste control and 50 kg for food preparation gear. Using the WAVAR water recovery method requires approximately 212 watts and about 56 kg equipment per kg of water output per martian day. The water loop is assumed to require 28 kg per day; 20 for sanitation, 4 for drinking and food preparation, and 4 for EVA activities. The EVA uses are assumed lost; the rest are recycled with an 80% assumed closure. Total water-loop water usage is therefore 9kg per day. Additional water for other life support uses is assumed to require another 9 kg per day. WAVAR design requirements are then roughly 4 kW power and 1000 kg for total output of 18kg/day. 3 kg of water per day is produced as excess for generic uses including water loop or oxygen loop life support. The 80% closure on the water loop is accomplished with 500 kg worth of multistage osmotic filtration units capable of processing the required 24 kg/day throughput at 80% closure. The primary oxygen generation system is assumed to be electrolysis of water to hydrogen and oxygen. 5 kg of oxygen is the baseline daily requirement, which is provided by electrolyzing roughly 6 kg of water. A 25kg generator using 0.5 kW of power will handle the process and has excess capacity to generate up to 10 kg of oxygen/day if needed. Hydrogen produced is stored for future use. In an emergency, breathing oxygen can be supplied by reduction of CO2 to carbon monoxide and oxygen at 1100 C. As Oxygen is only used for ongoing life support requirements and not for propellant, total amounts needed are much smaller than those in other proposed missions. A 250kg reactor is provided to allow minimum 10kg/day output of O2 via this manner, though the power requirements would preclude doing so as regular generation. CO2 filtration systems are assumed to be merely a set of CO2 permeable membranes allowing capsule atmosphere CO2 to diffuse into the external atmosphere. 10 square meters of membrane in a system massing 100 kg total are assumed. Internal air circulation systems are baselined at 100 kg. Production of replacement atmospheric buffer gasses will extract the nitrogen and argon present in the Mars atmosphere. For now it is assumed that 5 kg per day are required and that it is provided by 100 kg of compressors and filters using 2 kW of power and operating only during the day. 5.62 Power Subsystem The power budget is broken down into day and night segments. These are arbitrarily defined as 8 and 16 hours long respectively. During the day, all systems are run. At night the lab equipment mostly powers down and some of the in-situ resources extraction systems are idled. Daytime loads are 12 kW and nighttime 5.5 kW Overnight power requirements including margins come to roughly 90 kWh. The batteries are baselined as nickel-hydrogen batteries, with lifetimes of 2x10^4 cycles (about 50 years) limiting depth of discharge to 45%. A raw energy density of 60 w-Hr/kg is assumed, for total battery mass of 3.3 tonnes. Power generation requirements including a 40% margin for battery charging losses come to 18.3 kW. 20 kW is assumed as the end of life minimum acceptable array performance. Array performance is assumed to be 15% at end of life (gallium arsenide cells) and insolation of 675 W/m^2 for the furthest mars distance from the sun. Array size is thus 200 m^2, at an assumed power per mass efficiency of 20 W/kg. Array mass is thus computed as 1.0 tonne. An additional 0.5 tonne is allowed for power conditioning and distribution systems. The Lab module has an additional set of solar arrays to produce 30 kW instead of 20, and additional batteries slightly boosting the nighttime load capacity, to allow for some continuous science analysis rather than having to power down the labs at night. All the power breakdowns assume that no internetworking of capsules power systems will occur. That is an option for balancing out life support loads and system capacity at the base once sufficient capacity is in place. 5.7 Actual Flight Cargo Loads The basic designs and payloads all assume a nominal 100 tonne mars transfer payload which is the worst-case for the GRAND-3 vehicle and unfavorable orbital conditions. Further modeling indicates that on the average perhaps 10% more capacity might be available. No module will ever fly light. The landing and thermal protection systems are sized to be able to land a maximum design mass of 38 tonnes, a 6 tonne increase over the nominal maximum load. It is expected that most flights will have 34 or 35 tonne gross wt capsules with correspondingly higher amounts of cargo. Such analysis requires evaluation of the actual likely required delta-V in upcoming launch windows rather than worst case or average situations, and this is planned as future work. 6.0 Costing Overall cost estimates for the OneWay mission are $11 billion through the end of the first manned phase, with possible followon missions for $8 billion for the second phase and $8 billion for the third phase. 6.1 Development Costing Total program development costs are estimated at $5 billion. This is broken down into the following major areas: $1.0 billion Rovers $2.5 billion Capsule and systems design $1.0 billion Science systems development $0.5 billion EVA systems development We assume a 5 year program at $1 billion per year will be sufficient to finish development. It is important to note the development cost saving effects of the mission architecture chosen. In a number of cases, mass is being thrown at problems to keep the solutions simple, thus lowering the development risk and cost. No rocket engine development is needed for new propellant combinations and return vehicles; there are none. No fuel production or storage technologies require development. biologically closed life support systems are not needed for the first two phases of the mission to be entirely successful. The ongoing use of in situ resources for life support requires technologies that are almost off the shelf at this point. 6.2 First Exploration Phase Costing The first five vehicle launches (pathfinder and 2 manned missions) take place over 6 years at an annual cost of $1 billion. The average procurement rate during that period is about one launch per year, with one launch vehicle at $250 million and three capsules at about $400 million total. Science equipment, spare parts procurements, and rover procurements are estimated at $100 million per year. Total direct flight costs are $750 million per year. Indirect costs include $100 million per year for flight control center and engineering support staffs and overhead, $50 million per year for science planning specifically chargable to the program, and $100 million per year for biological closed-loop life support systems R&D specifically chargable to the program. 6.3 Second Exploration Phase Costing The hardware used in the second phase is the same as that used in the first phase, along with similar launch plans. A total of four missions over eight years are planned for the second phase, with the annual budget being $750 million in flight costs per year ($250 million for the rocket, $500 million for the payloads) and $250 million per year for ongoing project engineering, management, science support, and R&D. 6.4 Third Exploration Phase Costing The third phase planning has not yet been done at the same detailed level as the first two phases. It is assumed to consist of four further missions over eight more years at the same annual cost of the second phase, but with biological CELSS systems replacing much of the transported food and additional exploration equipment brought with the weight savings. 7.0 Fallback Scenarios It is important that the capability exist at any time to terminate further flight operations with only a single additional 2-year flight cycle (2 more launches, all cargo vehicles) and provide all expected food, sundry consumables, and parts reqirements through the longest credible astronaut lifetimes at Mars should the funding environment collapse. The planned mission architecture should accomplish that at any time during the mission. It is planned that there be an onsite 40-year food supply from the first manned landing and continuously maintained at that level or greater during operations. Along with the ability to cannibalize capsules for parts as time goes on, this will hopefully provide the astronauts with sufficient capability to survive to the end of their natural lives should for example Earth technologically collapse and be unable to send further supplies or expeditions. This will require that the one cargo module in the pathfinder mission land successfully, or that one of the two lab modules in the second manned expedition be swapped for a cargo module should the pathfinder cargo module fail to land intact. The critical point in this case is the arrival of the second manned mission and its four crew at the end of the first phase of the mission. Supplies brought in the first and second manned missions will only total 35 years worth excluding the pathfinder mission and capsule swaps on the second mission. 8.0 Summary 9.0 Acknowledgements This paper has been reviewed by Geoffrey Landis and Frank Crary. The author is grateful for their input. The paper was typed with the assistance of the author's kitten, who is probably responsible for several unnoticed typos. 10.0 References [1] Mars Direct: Combining Near-Term Technologies to Achive a Two-Launch Manned Mars Mission, D. Baker and R. Zubrin, JBIS Nov. 1990 [2] GRAND-3: a low cost heavy lift booster for planetary missions, George William Herbert, Retro Aerospace Tech Report 96-3, July 1996 [3] Design of a Water Vapor Adsorption Reactor for Martian In Situ Resource Utilization, Bruckner, A.P., Coons, S.C., and Williams, J.D., http://weber.u.washington.edu/~stevenc/WAVAR/ [4] Mars Direct: A Simple, Robust, and Cost Effective Architecture for the Space Exploration Initiative, Baker, D.A., Zubrin, R.M., Gwynne, O., AIAA-91-0328, 1991