Return-path: X-Andrew-Authenticated-as: 7997;andrew.cmu.edu;Ted Anderson Received: from beak.andrew.cmu.edu via trymail for +dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl@andrew.cmu.edu (->+dist+/afs/andrew.cmu.edu/usr11/tm2b/space/space.dl) (->ota+space.digests) ID ; Sun, 26 Nov 89 01:27:46 -0500 (EST) Message-ID: Reply-To: space+@Andrew.CMU.EDU From: space-request+@Andrew.CMU.EDU To: space+@Andrew.CMU.EDU Date: Sun, 26 Nov 89 01:27:21 -0500 (EST) Subject: SPACE Digest V10 #277 SPACE Digest Volume 10 : Issue 277 Today's Topics: Time for USSR's Mir expansion set for 16:00 Nov. 26 UK/USSR cosmonaut's named for Juno mission to Mir Space-tech excerpt: Mars ships ---------------------------------------------------------------------- Date: Sat, 25 Nov 89 22:55:17 EST From: Glenn Chapman Subject: Time for USSR's Mir expansion set for 16:00 Nov. 26 The Soviet shortwave has announced the launch time of the D expansion module for their Mir space station (a 20 Tonne section expanding the volume of Mir by about 50%). Take off will occur on Nov. 26 about 16:00 hours (Moscow time I think, though they did not say - that corresponds to 8:00 am EST). Docking will take place on Dec. 2 (no announced time). It appears that the launch will be broadcast live, so if you have a short wave the best frequency to tune in is 6.000 Mhz on the east coast during the morning. If it is broadcast on Soviet television CNN will probably carry it also. I will cover this flight as best as possible but on Dec. 2 I will be flying off to Vancouver for a week on a working trip. Hope someone will cover for me. Glenn Chapman MIT Lincoln Lab ------------------------------ Date: Sat, 25 Nov 89 23:27:10 EST From: Glenn Chapman Subject: UK/USSR cosmonaut's named for Juno mission to Mir The British have announced (on Nov. 25th) the finalist for the UK/USSR Juno mission in Apr. 1991. The first of the comosnauts is Miss Helen Sharman from Surrey, UK. Aged 26 she is a research chemist with Mars Confectionery and has worked in electronics engineering. The other is Major Timothy Mace of the Army Air Corps. from Weyhill, Hampshire, UK. Aged 33 he is a graduate aeronautical engineer, and an advanced helicopter trainer pilot. They are heading to Russia for a 18 month training course. Currently the sponsor money is still being raised for the mission. (BBC news Nov. 26, Financial Times Nov. 6 for the bios). This is the first nongovernmental visitor to the Soviet Mir. I guess that qualifies Mir as the first space hotel. Glenn Chapman MIT Lincoln Lab ------------------------------ Date: Sat, 25 Nov 1989 01:45-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU Subject: Space-tech excerpt: Mars ships I've excerpted the following discussion from the space-tech mailing list. The topic was the design of a ship for a Mars mission; we mainly discussed how to provide simulated gravity. It's a total of 515 lines. ------------------------------ From: al@questar.QUESTAR.MN.ORG (Al Viall) I would really like varied input on what you might think the ship for a Mars Mission would look like and how it would operate. Such a ship would most likely be designed to incorporate some sort of artificial gravity for the two-year journey there and two-years back. But details, lets hear details.......... ------------------------------ From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To provide artificial gravity, you should put two capsules on a cable 100m to 1000m in length, spinning to provide between .1 and 1 G. My guess is, say, a 500m cable providing 1G might be most practical. That's no sweat. Probably one capsule will contain the people and life support, and the other one will contain random stuff to balance the weight (although exact balance doesn't matter). As much as possible can be left in at the center axis to reduce load on the cable. The astronauts would probably have a small electrical cable-climbing winch to transport one of them up the cable to the center, to get more supplies or do maintenance. [ Aside: ring-shaped structures are unnecessary and not as flexible as just two masses on a cable, spun up to speed after the mission starts. ] [ Aside #2: why waste all that microgravity time? Set up some tended experiments at the hub, and possibly have workspace for 1/3 of the crew so you can work there in shifts. ] Ion propulsion is a likely engine setup. Its practicality might depend on the power requirements once the mission has reached Mars. The bigger the power requirements at the destination, the more power-generating capability you're going to bring along, which would be available to fire reaction mass out the back end of the vehicle in transit. I'm very fond of ion propulsion and would try to design the mission using it. If that's done, then the ion propulsion unit and solar collectors would sit at the center axis, in the null gravity region. I don't have figures on the quantity of supplies you'd need, but probably some effort to recycle air and water would be made, and perhaps growing plants would be brought along. ------------------------------ From: dietz@cs.rochester.edu I wonder if it would be possible to ameliorate the bad effects of microgravity by *sleeping* in one gee. I imagine a small radius centrifuge with ordinary beds. Perhaps if properly strapped in (so the head cannot move) Coriolis forces would not be important. Perhaps the same centrifuge could be used for exercise, if the crew are careful not to turn their heads. The downside would be that the crew would have to move between one and zero gee every day. They would have to be selected for resistance to space sickness. Paper studies I've seen point towards MPD [MagnetoPlasmoDynamic --M] rather than ion engines. Also, in a large vessel a nuclear reactor is better than solar arrays, I think, if only because the solar arrays would be severely degraded spiralling up through Earth's radiation belts. My personal opinion is that while it will be possible to visit Mars, and perhaps even set up a base, using chemical or fission-electric propulsion, real exploration and colonization will require high power fusion rockets. ------------------------------ From: dietz@cs.rochester.edu (Paul F. Dietz) Marc asked: how does an MPD thruster work? A coaxial MPD thruster consists of two concentric electrodes. The inner electrode is a rod, the outer a cylinder. The inner electrode may be longer or shorter than the outer. A gas is introduced between the electrodes at one end. A strong current passes from one electrode to the other through the gas. The currents in the electrodes produce a magnetic field which circles the inner electrode. The Lorentz (JxB) force propels the ionized gas down the barrel. You can think of this as a railgun that accelerates a plasma rather than a solid object. Beyond the electrodes, the plasma can continue to carry current. If properly designed, the magnetic field can be such that the JxB force has an inward directed component (pinch force), which helps reduce the lateral expansion of the plasma. In continuous mode, an MPD thruster needs megawatts of power to operate at high efficiency. If lower average power (and thrust) is desired, you can operate the thruster in a quasisteady mode (plateaus of current with low duty cycle) or in a pulsed mode (even shorter pulses). Solid-fueled MPD engines have been investigated for use in stationkeeping of satellites, since they can produce strong, short pulses of thrust (good for maneuvering rotating satellites) and are smaller than ion engines. ------------------------------ From: Korac MacArthur I think that the tether idea would not be as good as a rotating cylinder. The cylinder would allow for cargo to be stored at the walls, serving as a rad hard shelter (especially if it was water and fuel tanks, metal parts,etc). Even better for control would be the two cylinder design (opposite rotation) so an outer framework would not spin, and allow good null-gee areas as well as a stable platform for course correction thrusters instead of stopping the rotation or figuring how to time the thrusters right. Admittedly, two cylinders and a framework would take longer to build, but if you can't do it right the first tim e... I'd hate to have a tether snap, then all the parts go their separate (off course) ways. At worse, a more solid hulled ship would still be on course if anyone could fix it by the time the injection burn had to be made. ------------------------------ From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU > I think that the tether idea would not be as good as a rotating cylinder.... Eek! You're comparing apples and oranges. A tether would add little weight to the system, and can be an add-on to most Mars mission scenarios. A cylinder would change everything, be extremely heavy, and make any mission many times more expensive. The gains are dubious also. Structural strength just isn't an important factor in a planetary mission; null-gee areas should be available regardless; and shielding would be very inefficiently placed at the rim of a rotating structure where it would require even greater structural strength. ===== The amount of thrust required to spin up a rotating structure is something to check; the velocity required of the capsules is the square root of the desired acceleration times the radius. For a 500m tether (250m radius), the capsules must be going 50 m/s relative to the center to produce 1 g at the outside. That's not too much compared to the thousands of m/s needed for the mission. ===== How about the shielding question, though? Should my Mars scenario include a well-shielded "box" for the astronauts to hide in during solar maxima? Maybe someone could check on that. ------------------------------ From: John Roberts Disclaimer: Opinions expressed are those of the sender and do not reflect NIST policy or agreement. A system of two pods of equal mass connected by a cable and spinning in free-fall is very simple to describe, and I am willing to believe that it will perform as stated. When these conditions are altered, however, I am concerned that several problems might arise that would reduce the usefulness of the approach. Some of the possibilities: + Pods of unequal mass: presumably the two pods would move in circular paths at different distances from the center of mass, which would not be halfway along the line. The lighter pod would experience higher acceleration (not necessarily a problem). + Shifting masses: moving masses up and down the connecting cable would perturb the motion of the pods and the cable, for instance setting up oscillations which could last for hours or longer. + Center pod halfway along cable: I believe this would allow conditions in which the three pods were no longer in a straight line. Depending on the relative masses and the magnitude of perturbing forces, significant deviations could arise, including permanent imbalances and long-term oscillations. As a simple example, with unbalanced outer pods, the contents of the center pod would "slosh" around in small circles several times per minute. + Thrust applied while spinning: Any thrust applied while the system was spinning would have to be carefully calculated to avoid perturbing the internal motion of the system. I'm not saying that the system is impractical, but that the calculations to prove that it is practical are not trivial. (By the way, does anybody know of a computer program that can simulate the motion of a system such as this?) ------------------------------ From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU On the weight issue: I got some sales literature from DuPont about Kevlar cables. Kevlar is roughly equivalent to steel cable of the same size, but has about 1/6 the weight. They quote 2.76E9 N/m/m tensile strength for Kevlar 29. A cable which can hold 100T at 1 gravity is 14 sq. cm. in cross section, assuming a 4x safety factor. At 1.44 g/cc, a 500m cable to hold 100T weighs 1T. I believe this is an actual practical figure, since they use this stuff to anchor oil rigs. That is, a 500m cable to hold up against 1 gravity can hold 100 times its own weight; since there are two capsules, that makes .5% of the mass of the system. The 500m length is arbitrary, but the rest are pretty solid. ========== John Roberts mentions some interesting questions... - shifting masses: if this is a problem, and to save energy, use a funicular setup with an hourglass-shaped crank near the axis. The crank would look like this: ------- ------- | ------- -------| | | | | ------ ------ | | | | | | | | ||||||||||| | | | | | | | | ------ ------| | | | | | | | | ------- | ------- | | | | ------- | ------- | | | weight | at | top | | | | | | | person at bottom Cute, huh? It preserves constant tension and costs no energy. - Oscillations: This is something to be dealt with at some point; part of the solution may be some small thrusters that do active damping of oscillations. - Thrust: good question! What's a good way to apply thrust to a rotating system like this? The axis stays mostly fixed, so it isn't possible to always thrust along the axis, unless you can change the axis as quickly as the thrust direction. But how do you apply thrust out of the axis without causing trouble? Perhaps you attach thrusters to every chunk of mass in the system and accelerate them equally... Anyone have an idea? ------------------------------ From: Tero Siili I don't want to spoil anybody's enthusiasm in brainstorming for a Mars mission; however, some people at JPL have been thinking about these things and I assume, that a report has also been published. A rotating spacecraft has been proposed, but looking like three spokes; the spokes are tunnels, NOT tethers (and with three spokes tethers would be complicated, if not impossible). When contemplating artificial gravity solutions, one must keep in mind, that - the positive or preventive effects of artificial gravity have not been demonstrated yet - we don't know, what level of AG - g/2, g/3, g/6 - would be sufficient to prevent adverse effects - tests have indicated, that humans do not feel comfortable, if the rotation rate exceeds approximately 2 rpm; this together with the required gravity level will dictate the diameter of a rotating spacecraft. The open questions must be studied carefully before a humanity embarks on a Mars mission. For these studies a special laboratory will be needed, a Variable Gravity Research Facility (VGRF). This problem has quite recently been studied by the students of the International Space University in Strasbourg, France this summer. A report will most probably be out by January 1990. To give you an idea of the costs, this prerequisite for the Mars mission would cost 30 000 M USD! Concerning radiation, some type of "safe haven" is probably mandatory. If the spacecraft is designed with the spoke concept, every spoke can have its own shelter. ------------------------------ From: Jonathan Leech Re the discussion about artificial gravity, here's a tangentially (sic) related reference: in Nature V340 (31 Aug 1989), pg. 681, "Space Sickness on Earth": "Sir: We report here the surprising aftereffects of prolonged centrifuge runs in which we, the three scientist-astronauts on board the D-1 Spacelab mission, have participated. We think we can simulate the space adaptation syndrome..." To summarize, they found that after several hours of centrifuging at 3G, they felt SAS-like effects upon returning to 1G, and suggest this provides a good way of studying SAS. This is a letter, not an article, so details are sparse. ------------------------------ [ taken from sci.space ] From: shelle@caen.engin.umich.edu (Thomas A Kashangaki) I know of two very complete sources for references and information on Rotating Space Stations. The first is a series of NASA Contractor reports that cover a detailed design of: AN ADVANCED TECHNOLOGY SPACE STATION FOR THE YEAR 2025 The Bionetics Corporation/ NASA Langley Research Center CR # 178345 (and three or four others). This is a very detailed study of all the different technology issues that have to be addressed before a rotating space station is a viable option. It is probably the most complete and up-to date study of rotating spacecraft to date. I am sure Bionetics or Langley would be willing to provide copies of the reports. And the one that I am more familiar with is a two year study performed here at the University of Michigan under the NASA/USRA Universities Advanced Design Program: PROJECT CAMELOT (Circulating Autonomous Mars-Earth Orbital Transport) Senior Design project 1986/87 and 1987/88 University of Michigan Aerospace Engineering Dept. Ann Arbor, MI 48109 These two reports describe a large 20-man spacecraft that would be used in support of a manned Mars base. The reports are quite complete and have good bibliographies and reference lists. Reports can be obtained by writing to Prof. Harm Buning at the above address. ------------------------------ From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU I've been thinking about how to do off-axis accelerations of a rotating capsule system. I think I've got it! Check this out: have a triangular arrangement of capsules with cables at high tension connecting each to the other two, stiffening the structure through tension: ------------------------------- \ --_ _-- / \ --_ _-- / \ --_ _-- / \ --_ _-- / \ X / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \ | / \|/ Accelerations off the axis just increase tension on some of the cables. This has the really great feature that all stiffening is done by tension. This allows the use of lightweight cables rather than stiff structural materials which would undoubtedly be much heavier. This reminds me of Buckminster Fuller...I wonder if there's a more efficient arrangement than the one I describe? The parameters can vary, and this may change the configuration. Let's hold the 1 g radial acceleration fixed. If a low-thrust system is used, side acceleration may be limited to, say, .01 g; so the cables at the "edges" of the triangles above needn't be very large. If a high-thrust chemical system is used, it may be impractical to keep the system spinning at all; or maybe some sort of weird pentagon will have sufficient rigidity to handle off-axis accelerations. Hmm. I haven't worked out any numbers, but I'm pretty happy with this triangle deal for low accelerations. Fun! === I'm still not convinced one way or the other on the exact best form of a rotating structure. I'm definitely convinced that cables are better than a fixed structure for any large diameters (which are probably necessary for strength and dizziness reasons). I'm not so sure how to accomplish off-axis accelerations: my triangle idea is one way that seems to hold up under a little analysis; maybe just very small accelerations at the axis of a single-cable system would be adequate; or if the mission requires only a small number of course corrections, perhaps de-spinning the system would avoid the problems of oscillations in the system. Let me know if you think I've missed something. ------------------------------ From: dietz@cs.rochester.edu (Paul F. Dietz) Here is some information from the 1986 NASA Mars Conference on possible mission plans... (1) Conjunction Class Missions The most traditional type. It is relatively low energy, with a long stay time. Outbound 270 Stay 530 Return 209 ------------------- Total 1009 days (2) Opposition Class Missions Very high energy, much shorter trip time, but also shorter stay time. Outbound 254 Stay 20 Return 245 ------------------- Total 519 days An inbound swing-by of Venus reduces the energy requirements of this class of missions, and increases the stay time, at the cost of a slight increase in trip time: Outbound 267 Stay 60 Return 366 ------------------- Total 693 days (3) Low Thrust Transfer Missions These employ low thrust electric rockets or solar sails. They include a coasting portion during the middle of the trip when no thrust is applied. Earth Spiral 52 Outbound 510 Mars Spiral 39 Stay 100 Mar Spiral 23 Return 229 Earth Spiral 16 ------------------- Total 969 Not all of this time need be taken by the crew; the crew could board after the vehicle has spiralled above the van Allen belts. I do not know what acceleration these numbers imply; an ultra low mass solar sail could probably do better. The inbound spiral at Earth could be avoided by parking the vehicle in HEO and returning the crew via OTV. (4) VISIT (Cycler) Orbits The next two concepts use "spaceports" in solar orbit as stepping stones to/from Mars. The VISIT-1 orbit is a 1.25 year orbit that swings close to Earth once every five years while approaching Mars once every 3.75 years. The VISIT-2 orbit is a 1.5 year orbit that approaches Earth once every three years while approaching Mars once every 7.5 years. The orbits would have to be retuned once every 20 years or so, and do not exploit planetary swing-by. (5) Escalator (Cycler) Orbits Unlike VISIT orbits, these orbits (due to Buzz Aldrin) use planetary swingby to rephase the cycler orbit. Basically, it is a more elliptical orbit that passes by the Earth once an orbit and Mars twice an orbit. At Earth, a wingby redirects it on to the next Mars encounter. The orbit's period is about 2 years. It would require a bit of nudging at times, for a total of about 2 km/s over 15 years. The orbit is high energy. ------------------------------ From: sci!daver%gungnir@Sun.COM (Dave Rickel) I haven't seen much yet about environment. It seems pretty clear that you'll want to recycle air and water. I dimly recall something about how bubbling contaminated air through superheated water would break down most of the nasty compounds. Anyway, it seems that life support would probably be some sort of algae to handle 95% of the recycling/detoxification, and some non-biological system (involving heat, electricity, chemicals (hmm, sounds like something you'd use on Godzilla), filtration, or whatever else is handy) to deal with the rest. Any ideas of how good you'd get? How much per man such a system would weigh, how many kg of consumables you'd have to carry per man per day? I've no idea what the state of affairs is regarding long-term life support systems, i suspect that we don't know nearly enough yet to get to Mars and back (i also suspect that something good enough could be put together in five to ten years, if we were really serious). ------------------------------ From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU I hope we can discuss some other aspects of the design of a Mars ship: - Is laser communications practical? How much dispersion is there, and if it is low, how do you aim the lasers? - What kind of power systems are good for this kind of mission? Could we use a rotation-stiffened mylar mirror to magnify sunlight to solar cells or a thermionic generator? - How many exercise bikes should you bring along? - What kind of mass is involved in each subsystem you need to bring? Can you think of anything else? ------------------------------ [ end of excerpt ] [ Space-tech is a mailing list for discussing concepts for space development, with emphasis on the technical problems and and how to solve them. Past topics have included EM launchers, orbiting tethers, and Mars missions. To join, send mail to space-tech-request@cs.cmu.edu. ] ------------------------------ End of SPACE Digest V10 #277 *******************