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| 2 Strategy - A Concept | 2.4 Step 1 - Leaving Low earth Orbit |
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| 2 Strategy - A Concept | 2.4 Step 1 - Leaving Low earth Orbit |
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The critical technologies necessary for human exploration away from Earth are:
Ground Transportation The number of facilities should increase progressively to support transportation on the ground for humans and cargo. Different types of vehicles are required to do this. A long-range exploration vehicle will have a closed-loop life support system. Unmanned and manned robotic rovers for surface exploration could use the technology developed for the Apollo missions . The problem is that these rovers were not developed for long duration use. Martian rovers will use the concepts developed for the Moon, even if they have to be adapted to the Martian environment (stronger gravity, lower thermal gradient, etc.). It is not possible to use rovers on NEOs because of the lack of gravity. An alternative to this, is to use 'Hoppers', developed for the Phobos mission . A possible precursor mission on an asteroid could test Hoppers during step 1. For step 2, roads and railways could be implemented to satisfy the growing need for transport of resources. Ground to Orbit Transportation  Landing and launching vehicles are both required for the Moon and Mars. This technology has already been tested for the Moon (Figure 2-9) but needs to be applied for use on Mars. Aerobraking could be used in the terrestrial and Martian atmosphere (for Mars Sample Return for example) in step 0. A lunar spaceport near lunar habitats and factories that will use the propellant made on the lunar surface will be required for launching and landing facilities (Anderson et al, 1985). Launching from the Moon will save fuel, mass, and cost. During step 1, it could be implemented for the return of the cosmonauts only. Since base operations will be dependent on Earth supplies, the lander capability will not be very high in terms of mass and reusability. After the development of in situ resource utilization processes in step 2, it will grow. The lander could be designed to reach all the different colonies on the ground in step 2, to avoid long trip times. Electromagnetic mass drivers (Billy et al, 1988) and mass catchers could be a solution to transport lunar resources to orbit, but they need to be tested first and they require high precision and heavy infrastructure on the lunar surface. Their development should be accelerated once the exploitation of resources is complete in step 3. Chemical rockets are more economical for small launch rates of up to 40 tons/year (ISU, 1988). Interplanetary Transportation Human expansion in space will require orbital transfer vehicles (OTV) that can transfer human-rated spacecraft and large cargo ships. A large-scale exploration of space requires more efficient propulsion technology (Humble et al, 1995). The choice of the propulsion system depends on the transportation cost, capabilities, travel time and safety requirements. Chemical propulsion is widely used and highly reliable. Advanced oxygen/hydrogen engines have a high thrust and a specific impulse of 485 s, however, they require cryogenic storage. Nuclear Thermal systems have higher thrust, higher specific impulse (1000 s), but need to be tested and approved by public opinion. The thermal energy is provided by fission of Uranium 235. Crew and materials have to be protected from the radiation emitted by the nuclear core. Low thrust, high specific impulse (5000 s) ion engines have a longer travel time but allow considerable propellant savings. Ion propulsion requires a source of energy, which can be nuclear or solar. Solar electric propulsion is less dangerous and controversial, but needs large deployable structures (solar arrays). It has been tested successfully with Deep Space 1 this year. Nuclear electric propulsion (NEP) is a heavily reusable system. It requires a chemical transportation system to raise it out of the Earth's vicinity, for safety reasons. The Step-by-step strategy recommends using solar ionic propulsion for cargo ships travelling within the inner solar system (up to Mars). On the other hand, chemical propulsion is the preferred choice for human-rated interplanetary transfer vehicles and emergency re-supply missions. However, if nuclear propulsion support, humans could use NEP for longer trips. Robotic Systems Human bases on other planets will be multipurpose facilities for science and technology development and demonstration. They offer many opportunities for the use of advanced automation techniques and robotics. Space robotics is a fast-growing area (robots are an important part of the ISS today). They will pave the way for further human exploration and constitute major partners to humanity (refer to chapter 1). Several kinds of robots will be developed to support the deployment of a manned infrastructure on other planetary surfaces. Robots need to be adapted to the space environment and need to reach an efficient level of autonomy and durability. Reliability is the main problem because of the degradation of materials due to the harsh environment. More advanced computing systems, hardware adapted to the space environment, artificial intelligence, and teleoperation, are fields for future studies. Human presence will be required at the beginning because robots take time to be developed for specific tasks. Adaptive robotics with flexibility and interchangeability will be required. Human-machine interface development is crucial. Complexity and increase of autonomy will be implemented progressively, with specialized industries reaping the benefits of robotics development. Power Power will be needed to support human activities, life support systems, transportation and communications. Because of the growth of human activities in outer space, power for surface facilities is a key driver and should adapt to this expansion. Power may be generated mainly from solar and nuclear energy. The advantage of solar cells is cost effectiveness, high reliability and easy manufacturing. In the case of the Moon, solar energy plants can be based on the lunar poles during step 2, but for the other places, a power system based entirely on solar energy will require massive energy storage capacities because of the long lunar nights. Use of photovoltaic cells for surface operations, represents a well-proven method for power supply (400 W/kg). There are also some possibilities to manufacture them in situ. Solar Power Satellites will provide a large amount of energy, transmitted by microwave to the Earth, LEO and the Moon. Nuclear technology still needs the support of the public because it is very controversial and introduces political opposition when it has to be launched from the terrestrial environment. Humans need to be protected on the surface from nuclear induced radiation, so the plants have to be buried or covered by soil and far from the habitats. The Step-by-Step Strategy recommends the use of photovoltaic cells whenever possible until nuclear power sources become more acceptable in the eye of the general public. Habitats and Radiation Shielding Inflatable structures will be developed on the ISS and lower the mass of future habitats. Once mining operations are fully operational, the development of more and larger habitats could be initiated. The growth and expansion of human habitats requires the utilization of in situ resources. Orbiting structures are very different from planetary habitats (gravity, less radiation and temperature gradient). First we need to increase our knowledge of the lunar environment in step 0 and 1.  The lunar regolith for example contains absorbed light gases and indigenous oxygen that can be extracted for use as propellant and life support. The regolith could serve as a source of concrete and metals for construction on the Moon (Cullingford et al, 1988). The feasability of using water, regolith layers, or natural lunar structures (craters, lava tubes or buried habitats (Figure 2-10), Horz, 1985) to provide shielding for habitats against radiation, will be studied in a second phase. A minimum of protection for the base will be sufficient during periods of low solar activity. However, a buried emergency shelter will be required for periods of high solar activity. Life Support Systems A completely closed-loop life support system (CLSS) is required, with a comfortable place to live for permanent settlers. Redundancy is required for safety purposes. The various experiments conducted on ISS will be good preliminary studies for a lunar CLSS. The station provides life support resources, waste management and regulation of temperature, pressure and atmospheric composition. A CLSS will ensure a better autonomy but it will increase mass, power and thermal requirements. Current systems are all non-regenerative physiochemical systems, which need to be re-supplied. The question of whether artificial gravity (using centrifuges, for example) is feasible should be solved during step 0. The feasibility of creating a small closed inhabited ecosystem with biological components regenerating the environment has been proven by the experiments done by the former Soviet Union in the BIOS-3 facility, for example, but the system is not yet operational with humans. Prototype agriculture systems will be tested at the beginning of steps 0 and 1. Large amounts of carbon and artificial lighting will be needed for growing plants which will provide some oxygen and food. A soil-based agriculture that could incorporate lunar regolith has to be studied (Henninger, 1988) during step 2 and hydroponics systems could be a good alternative. Unfortunately the recycling of nutrients into hydroponics solutions requires development. A complete CLSS built with extraterrestrial resources during steps 2 or 3 is a very critical point to allow the autonomy of the colony. It will be a slow progression to reach this goal, from a human and technological point of view. The infrastructure on the Moon once developed will give an easier and faster access to space for the continuation of human exploration. Communication Networks Future communication systems need to provide a high bandwidth on demand, high data rates and should enable long distance communications. Communications will be implemented at different levels. As a consequence of the growth of human expansion on other planetary surfaces, communications systems should allow a high-level of autonomy for the different elements. They must be generic and modular in expansion of coverage. The different levels of implementation are the following:
There will be a large number of facilities and habitats from lunar equatorial to polar regions, from the near side to the far side during step 2. The use of antennas versus communication satellites will depend on the location. If we begin at the lunar pole, a big antenna should be enough for step 1. With expansion, a constellation of microsatellites using the libration points will assure full coverage during steps 2 and 3. Industries could benefit from this future market. Communications with Mars and NEOs will be done through the Earth thanks to antennas and satellites. With the development of human settlements on Mars, the different colonies should not be too dependant on communications with the Earth, because of the high time delay. In comparison with the implementation on the Moon, Ka-band and IR/optical laser communications technology have to be developed in the near future for step 2, to keep a link with Mars. A deep-space network with Earth-receiving stations and relays in heliocentric orbits during conjunctions and oppositions should be implemented, considering the growth of needs for step 3. NEXT > [Home] [ISU] |