ASI W9900326r1.1
#107 July 1997
Section 6.9.3.2.107.of the Artemis Data Book
Concept Papers from Seattle Lunar Group Studies, Part II.
Cislunar Ferry
Magsail Asteroid Survey Mission
Magsail Mars Missions
Magsail Stabilization of Lagrange Point Structures
Remote Lunar Geological Survey
Clear Span Lunar Base Structures
Survey of Earth-Crossing Objects
Food Animals in Biological Life Support Systems
An Artificial Lunar Magnetic Field
Magnetic Radiation Shields
Regolith as Propellant for Mars Missions
A Major Contribution of Seminal Concept Papers to MMM. Theseare the work of a significant brainstorming group in Seattle whichhas continued over a span of many years. MMM thanks David Graham andHugh Kelso for permission to reprint these papers. The firstinstallment was published in MMM # 106. We will finish republicationof these papers in MMM #108
Whether the paper was in response to a request for input forthe Space Exploration Initiative (SEI) or for the StaffordCommission, is indicated in the byline for each.
Cislunar Ferry
(SEI; Stafford) by Gordon Woodcock and Joe Hopkins
We propose a vehicle be developed to utilize swing orbits(Woodcock, 1). The vehicle would be designed to travel in the lunarplane between Earth and Luna, providing frequent and regular accessto both bodies.
This vehicle could be viewed as a cislunar ferry. In its initialform, the orbiter would be a small, no gravity, passenger/freightcarrier. The cycling orbiter could be configured to provide radiationshielding for the passenger section. If gravity becomes necessary, itcould be simulated by spinning equal massed compartments oppositeeach other on a tether.
Actually, it is not necessary that both opposing componentsbe equal in mass - unless equal levels of artificial gravity arerequired at both ends. If this is not required and the two componentsare unequal in mass, the center of gravity or fulcrum simply liesproportionately closer to the heavier mass while the gravity felt inthe lighter more distant component will be the greater. -Editor.
Regular, inexpensive transportation between the Earth and Moon isthe main purpose of the orbiter. Cargo and passengers would betransported on and off of the orbiter in specially designed taximodules. Passengers would generally remain on board for only one legof the trip at a time; three to five days.
Over time, with a system like the cislunar ferry, transshipmentsfrom the Moon to low Earth orbit would become cheaper than suchshipments from Earth. Early shipments could include oxygen,unprocessed lunar rock (for shielding) and agricultural products. Aslunar bases develop, processed metals and glasses could beincluded.
Shipments from Earth to the Moon would be precision toolingequipment and electronic supplies. Organic waste generated onboardthe cislunar ferry and in low Earth orbit could be sold to Moonbasefarms. The orbiter would also be valuable as a research facility.(SLuGS)
(1) Woodcock, Gordon R., Transportation Networks for LunarResources Utilization, Space Manufacturing 5; Engineering with Lunarand Asteroidal Materials, American Institute of Aeronautics andAstronautics, New York, Proceedings of the 7th Princeton/AIAA/ SpaceStudies Institute Conference, May 8-11, 1985.
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Magsail Asteroid Survey Mission
(SEI; Stafford) by Stan Love and Dana G. Andrews
The asteroids, lying principally between the orbits of Mars andJupiter, have long been considered one of the best potential sitesfor near term access to extraterrestrial resources. To fully assessthe value of asteroids for commercial use, and also to gainscientific knowledge about them which is critical to ourunderstanding of the formation of the solar system, it is necessaryto examine a large number of them a very close range, perhaps evencollecting samples of their surfaces for analysis on Earth. Such amission is unthinkable with current chemical rockets, however. Eachflyby would require a few km/s of velocity change (henceapproximately doubling the initial mass of the spacecraft) and nosurface landings could occur without expending a prohibitive amountof propellant.
The magnetic sail (Andrews, D.G. and Zubrin, R.M., "Progress inMagnetic Sails," AIAA Paper 90-2367, 1990) suggests a solution tothis problem. It would derive its thrust from the interaction of thesolar wind with the magnetic field around a loop of super conductingcable several dozen km in diameter. As long as current flows in thecable (once set up, it will continue to flow indefinitely) the sailwould develop a small amount of thrust, which could be directed byaltering the orientation of the loop or by changing the current,easily accomplished with a modest-sized solar array. Since it wouldproduce a continuous force without expending any propellant, amagsail could orbit the sun in the asteroid belt indefinitely,visiting tens or hundreds of objects at a relative velocity of a fewkm/s.
Asteroids possess no magnetic fields to hinder the use of amagsail. Neither do they have strong gravitational gradients, whichare difficult for any low-thrust vehicle to overcome. If the missionprofile allowed the necessary deceleration time, the spacecraft couldrendezvous with asteroids to take samples of their surfaces. Properalignment of the sail and the asteroid could be arranged so that thesail force and the gravitational attraction of the asteroid exactlybalance one another, allowing samples to be taken of the surface froma motionless spacecraft. After sampling a number of asteroids, thespacecraft could return to Earth to drop off material samples andundergo routine maintenance. It could then return to the asteroidbelt for further exploration. (SLuGS)
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Magsail Mars Missions
(SEI; Stafford) by Dana G. Andrews, Stan Love, and Joe Hopkins
Regular round trip missions to Mars could be undertaken using amagnetic sail, or magsail, spacecraft. A magsail would derive itsthrust from interaction between the thin plasma of the solar wind andthe magnetic field surrounding a current-bearing loop ofsuperconducting cable roughly 100 km in diameter. Once a current wasestablished in the loop, it would continue to flow indefinitely,providing thrust until the current was cut.
Directing the thrust could be accomplished by changing theorientation of the loop or by altering the current; both easilyaccomplished with a modest-sized solar array. The magnetic sailconcept was originated by D. G. Andrews in 1968, but was not feasibleuntil recent developments in superconductors that allow for cablethat could be kept below its critical temperature with a simple andlightweight passive cooling system.
An additional advantage of the magsail is that the current loopwould generate its own magnetosphere, much like that of the Earth,but on a much smaller scale. The magnetic field of the sail wouldprotect the spacecraft's payload (and, in particular, its livingpassengers) from most charged particle radiation, decreasing therequirement for massive and costly radiation shielding on mannedmissions.
A recent paper (Andrews, D.G. and Zubrin, R.M., "Progress inMagnetic Sails," AIAA Paper 90-2367, 1990) describes a manned missionto Mars in 2007 with an initial mass of 200 tons and a payload of 140tons. This payload is comparable with the payloads of otherlow-thrust manned systems currently under consideration.
A flyby of Mars is projected 164 days after departure from Earth.The payload and crew taxi would return to high Earth orbit after atotal of 668 days. The spacecraft could then be refitted for the nextlaunch window, occurring 90 days after arrival. Since properalignment of the two planets occurs at regular intervals and themagsail could make the round trip with time to spare, it could beused as a permanent facility cycling between Earth and Mars.(SLuGS)
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Magsail Stabilization of Lagrange Point Structures
(SEI; Stafford) by Stan Love
In numerous schemes for the development of cislunar space,propellant depots, mass catchers, and other facilities have beenproposed at the various Lagrange points of the Earth-Moon system. Ofthese five points, only two, L4 an L5 (at 60° leading andtrailing the Moon in its orbit) are stable against the small,constant gravitational perturbations present in the system. The twoLagrange points nearest the Moon, L1 and L2, are probably the mostuseful for lunar missions. Facilities constructed there would have tobe constantly supplied with propellant to compensate forgravitational perturbations, or they would soon drift into other,less useful orbits.
The magnetic sail (Andrews, D.G. and Zubrin, R.M., "Progress inMagnetic Sails," AIAA Paper 90-2367, 1990) suggests a solution tothis problem. It would derive a small amount of thrust from theinteraction of the solar wind with the magnetic field around a loopof super conducting cable roughly 100 km in diameter.
As long as current flows in the cable (once set up, it willcontinue to flow indefinitely) the sail would develop a small amountof thrust, which could be directed by altering the orientation of theloop or by changing the current, easily accomplished with amodest-sized solar array. It would be capable of making the necessarycontinuous orbit modifications without expending any propellant atall, hence eliminating the need for large resupply missions.Operating a magsail in the near-Earth environment would require thatsome consideration be made of the Earth's magnetotail, but this wouldprobably not impact the sail's usefulness.
Another advantage of the magnetic sail is that it could generateits own magnetosphere, much like that of the Earth, but on a muchsmaller scale. The magnetic field of the sail would provide goodshielding against charged particle radiation for anything in itsimmediate vicinity, and would thus lessen the need for heavy andexpensive radiation shielding of manned outposts.(SLuGS)
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Remote Lunar Geological Survey
(SEI; Stafford) by Stan Love and Robert Lilly
For the development of a manned presence on the Moon, it iscritical to determine the mineral resources available locally. TheMoon is too large and travel across it is too difficult for adetailed, ground based global geologic survey to be feasible in thenear term. An alternative to the collection of soil samples on thesurface is determination of the soil composition via remote means.This could be done in a crude manner by observing the spectrum ofsunlight reflected from the Moon. A more sophisticated method wouldbe the use of laser Raman spectroscopy, wherein a laser is directedat the surface, with the spectrum of light scattered at wavelengthsnear that of the incident laser providing accurate determination ofthe composition of the surface. Laser Raman spectroscopy is commonlyused at close range in the laboratory, but could be applied at longerdistances.
Placing a satellite equipped with a 100 W laser in polar orbitaround the Moon would allow a Raman survey of the entire body with aresolution as small as 25 cm. At 100 km altitude, the Raman signal(10-6 of the incident intensity) would outshine full Earthlight.Sunlit regions could not be surveyed. A 10 cm telescope with aspectrograph and CCD detector aboard the craft would be able toobtain a spectrum, with a signal-to-noise ratio of 10, in roughly 200seconds, less than the 1200 seconds it would take for the satelliteto travel across the sky of a given point. Both telescope and laserwould have to track with an accuracy of 0.5 arcsec.
Each spectrum, one CCD frame, would contain about 20 M bits ofinformation. The spacecraft must be able to store at least 20 framesof data while out of sight of Earth, requiring roughly 50 M bytes ofstorage, perhaps on tape. Transmission of data to Earth would requirea rate of at least 200 k bits per second for a continuous survey.
The most difficult aspect of this mission would be providing powerfor the laser, which would operate only over shadowed terrain. Thepower requirement of the rest of the electronic equipment is small incomparison with the laser's consumption, several kilowatts. Powermust come from solar panels via fuel cells, batteries or othersuitable sources. The expense of such a system would certainly beless that of a ground-based survey of similar scope, and thespacecraft could be retrieved at the end of its mission andredeployed to other bodies in the solar system.(SLuGS)
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Clear Span Lunar Base Structures
(SEI; Stafford) by Hugh Kelso, Joe Hopkins, et. al.
We present a design for a lunar base that provides a generic,multipurpose environment; the location of which is not dependent uponnatural geological features. Clear-span construction creates largeopen spaces that can be subdivided according to use and need. Itcould be developed along the lines of an industrial park with theflexibility to accommodate a wide variety of uses while at the sametime providing varied services to its customers.
This design is of steel construction and is divided into upper andlower pressure areas. The upper area provides a pressure environmentequivalent to two miles above sea level (9.5 psi) for agriculturaluse while the lower area provides an atmospheric pressure equivalentto one mile above sea level (12 psi) for habitation and work areas.Elevators which service the base also act as air locks between thepressurized areas.
Our design encloses a space 30 meters high and 50 meters square. Alayer of excavated regolith would be spread over the top of the baseand compacted to a depth of 10 meters. This would serve as both ashield against radiation and as a dead load to counter balance someof the atmospheric pressure within the base. Other uses for theexcavated material might include the extraction of iron, oxygen, andhydrogen. The construction process of the base would be similar tothat of a building on Earth, and could be repeated as growthrequires.
This base concept permits many interior configurations. Servicesthe base would provide include such things as the basic maintenanceof the base itself, power, lighting, air, waste disposal, food,living quarters, recreational areas, communications facilities,computer support, and medical services. Modules could be configuredto include fabrication and processing facilities, a gymnasium, parkareas, conference rooms, media production studios, and whatever elsewas needed or desired. Heavy industrial processes, such as smelting,and other activities which may harbor health risks would be carriedout in modules separated from those that house personnel.(SLuGS)
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Survey of Earth-Crossing Objects
(Stafford) by Stan Love
Asteroids whose orbits carry them across the orbit of the Earthare of extreme interest for a number of reasons. Only half of theestimated 1,000 such objects with diameters greater than 1 km havebeen discovered. Since Earth-crossing asteroids present a directthreat to all life on Earth, a large-scale astronomical survey shouldbe undertaken to detect as many of them as possible.
Currently, knowing that such an object was on a collision coursewith the Earth would be of no use, as there exists no capability toalter its course. This unhappy state of affairs will change in thefuture, however, so a good knowledge of the population of 1 kmobjects in the inner solar system could prevent a disaster the likesof which have not been seen on Earth in millions of years.
Although the impact of a 1 km object would have dire consequencesfor most life on Earth, the chances of such a collision arecomfortably remote: only about 1 in 100,000,000 per year. SomeEarth-crossing asteroids are of interest for reasons other than fearof collision.
Many of these objects can be reached with only a few kilometersper second of velocity above Earth escape, and hence represent animportant and relatively accessible source of extraterrestrialmaterials. Many such objects are thought to contain, among otheruseful resources, several weight percent of water present in hydratedminerals. An astronomical survey of such objects can determine notonly their orbital parameters and hence ease of access, but can alsoproduce indications of their basic chemical composition and likelyavailable resources. (SLuGS)
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Food Animals in Biological Life Support Systems
(Stafford) by Stan Love
A great deal of research has been done regarding the use of plantsas part of life-support systems for space habitats. Plants areexcellent recyclers of air and water, and if the system is plannedcarefully enough and the substantial startup mass is allowable, avegetable garden (equipped with a few mechanical devices, such as anoxidation reactor for waste products) in a space habitat can performcomplete recycling of air and water for the crew, and also providealmost all of their nutritional needs.
In typical biological life support systems of this kind, about 3percent of the dietary needs of the crew are left to be filled byoutside sources, primarily as vitamin and amino acid supplements. Thebulk of the diet, however, would necessarily be vegetarian, which maynot appeal to all astronauts.
It is interesting to note the changes necessary in a biologicallife support system if it is required to produce even a modicum ofanimal protein for crew consumption. Let us assume that 10 percent ofthe crew's diet is to be derived from animals, such as rabbits orfish, grown along with the vegetables in a biological system. Agenerous estimation of the fraction of a meat animal that is edibleand palatable (i.e. not hair or bones or viscera) is 50 percent.
Let us also assume that the a mass of living food animals equal tothe mass of a person metabolizes air, water, and food at the samerate as the person does, again a generous assumption since smallanimals have higher metabolic rates than human beings. A general ruleof thumb quoted in ecology is that raising an animal takes ten timesthe animal's weight in food. Using these very general rules, if 10percent of mass in the crew's diet is animal products, twice thatmass of animals (because the whole animal is not used) must be raisedcontinuously, requiring 20 times that mass of plants to be fed to theanimals.
The life-support system for the animals, then, requires 20 times10 percent, or two times, the "acreage" as that for the human crew,effectively tripling the mass of the entire system.
In conclusion, it is probably not feasible to have a closedbiological life-support system provide meat for its crew if mass is adeciding factor in the design. Astronauts in such missions will belargely vegetarian, in spite of any personal preferences.(SLuGS)
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An Artificial Lunar Magnetic Field
(Stafford) by Stan Love
The Moon possesses no magnetic field of its own. As a consequenceof this, and the fact that it has no atmosphere, it is constantlybombarded by cosmic rays both from deep space and from the Sun. Forhuman activity on the Moon over any length of time, great care willhave to be taken to provide shielding from harmful cosmic rays. TheMoon's bulk itself can provide more-than-adequate shielding fromsolar cosmic rays during local night, but solar flares cannot becounted on to occur only when the sun is below the horizon.
A far-fetched but effective solution to the shielding problem isto gird the Moon with a loop of superconducting cable bearing enoughcurrent to generate an artificial "bubble" in the solar wind largeenough to contain the entire Moon. A current on the order of 1million amperes should suffice. Once the current is induced in thecable, it will continue to flow undiminished forever, so the powerrequirements for such a system are negligible. The magnetic fieldwould protect the whole surface of the Moon, greatly reducing theflux of charged particle radiation both for permanent habitats andfor astronauts working on the surface. It would also allow compassesto be used for orientation on the Moon .
Some drawbacks to this idea are the large initial cost ofproducing and laying the cable, and the fact that the artificialmagnetosphere would probably generate zones of intense radiationsimilar to the Earth's Van Allen belts, creating radiation hazards inlunar orbit. It would also prevent the solar wind from striking theMoon's surface, thus eliminating the primary remover of gaseouspollutants from the Lunar environment.(SLuGS)
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Magnetic Radiation Shields
(Stafford) by Stan Love
The powerful and wide-reaching magnetic field of a magnetic sail(Andrews, D. G. and Zubrin, R. M., Progress in Magnetic Sails, AIAAPaper 90-2367,1990) provides good protection against charged-particleradiation for its payload, and indeed anything inside itsmagnetosphere, as a secondary effect of the thrust it produces. Therewill be many applications in near-term space exploration for whichthrust will not be required, but cosmic-ray shielding will: namely,any fixed activity taking place outside the Earth s magnetosphere. Insuch cases, shielding could be provided with a loop ofsuperconducting material similar to a magnetic sail, but with asmaller dipole moment. The resulting magnetic field could protect anarea a few kilometers across, and would produce negligiblethrust.
Stations in geosynchronous or other high Earth orbit, permanentinstallations at the Lagrange points or in orbit around planets suchas Mars or Venus, and bases on the surfaces of the Moon , theAsteroids, or any airless body without a magnetic field will all needto provide shielding for their inhabitants. Vehicles that travelroutinely through the Van Allen belts would also benefit from havingeffective charged-particle radiation shielding. Surface bases mayblock radiation with thick layers of local material, but transportinglarge amounts of massive material for shielding is not economicallysound for orbital bases when a lightweight loop of superconductingcable could do the job equally well.(SLuGS)Back to List at Top of Page
Regolith as Propellant for Mars Missions
(Stafford) by Brian Tillotson
This is a proposal to use a coaxial electromagnetic accelerator(a.k.a. coil gun or mass driver) as a rocket engine for a Marsmission. The proposed propellant for the outbound journey to Mars isregolith (dirt) from the Moon, and the propellant for Mars orbitalmaneuvers and for return to Earth is regolith from Demos orPhobos.
O'Neill proposed use of a coil gun or mass driver as a rocketmotor which ejects inert material at high speed to produce thrust.Recent coil gun demonstrations show that technology is in hand torealize this propulsion concept. With this concept, raw regolith is asuitable propellant. Regolith is less expensive than other proposedextraterrestrial propellants, which require heavy equipment deliveredfrom Earth to chemically process raw materials.
Value: Use of planetary regolith addresses two needs for Marsmission design: low IMLEO and protection of the crew from galacticcosmic radiation (GCR). The concept avoids the cost of launchingpropellant from Earth, and the regolith can be used as shielding formost of the mission.
Several other advantages are realized. Propellant is stored in abag which is folded and launched empty from Earth; this gives lesslaunch volume than liquid propellants which are launched in rigidpressure tanks. Neither cryogenic storage nor in-space fluid transfertechnology is required. Smaller power systems are required than forion-propelled vehicles. Crews need not crowd into a storm shelterduring solar flares. The proposed Moonbase finds a clear purpose.
Performance Characteristics: Using assumptions described inthe background paper, the proposed vehicle's Earth mass (includinglunar infrastructure) is 24% lower than a solar electricion-propelled vehicle's mass. GCR dose to the crew is cut by morethan half. The required electrical power is only 26% as large as foran ion vehicle.
Enabling Technologies: Coil gun launcher technology isadvancing rapidly. Development should be directed to two new areas:1) coil guns as flight-qualified rocket engines, and 2) a coil gunlauncher on the lunar surface.
Relation to Mission Objectives: This concept may beenabling or enhancing for a manned Mars mission in two major ways.First, it may be cost enabling or enhancing by reducing the mass ofEarth material launched into space. Second, it may be medicallyenabling or enhancing due to reduction of crew radiation dose. Byproviding a rationale for lunar support of a Mars mission, theconcept increases the political likelihood of a permanent mannedreturn to the Moon (SLuGS)