Date: Tue, 10 Jan 1989 22:20-EST From: space-tech-request@CS.CMU.EDU To: "~/st/lists/stdigest" Subject: Space-tech Digest #19 Contents: Paul Dietz Orbital Tug as Upper Stage for Spaceplane Paul Dietz Ram Accelerator Paul Dietz Magnetically Insulated Impact Fusion Marc Ringuette Satellite servicer Paul Dietz Re: Satellite servicer Paul Dietz Asteroid Orbits Paul Dietz microspacecraft Ollie Eisman Re: microspacecraft ------------------------------------------------------------ Date: Tue, 20 Dec 88 13:45:05 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Orbital Tug as Upper Stage for Spaceplane Dani Eder in a posting to sci.space outlined a system for getting material into orbit more cheaply. His system uses a platform suspended at the bottom of a long tether to reduce the velocity the launch vehicle must attain by itself, from Mach 25 down to Mach 15-20. It seemed to me that this means the tether has to be awfully long. However, the idea of using ET resources to reduce the cost of getting into space is an interesting one. How about this: as suggested, fly a vehicle at Mach 17 (say) on a trajectory out of the atmosphere. Maneuver an orbiting tug to intercept. The tug might be slowed to suborbital speeds aerodynamically. After rendevous and grappling, the tug boosts back to orbital velocity. For this scheme to make sense, there has to be a cheap source of fuel in orbit, either ET or gun-launched. The scheme is reminscent of the idea of using a OMV in HEEO as a mass catcher for use with a gun-type launcher. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Fri, 30 Dec 88 15:02:13 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Ram Accelerator I've received copies of some recent papers on the ram accelerator. The most interesting is: "The Ram Accelerator: A Chemically Driven Mass Launcher" P. Kaloupis and A. P. Bruckner. AIAA-88-2968. Presented at the 24th Joint Propulsion Conference, Boston, July 11-13, 1988. The paper describes the components of a system that can place a 2000 kg vehicle into LEO. The details are apropos to the discussion in this mailing list about gun based launchers. The launch vehicle has a diameter of .76 m and is 7.5 m long. It is first accelerated by a methane/air gun to 700 m/s. The ram accelerator contains nine different gas mixtures at 33 atmospheres (the gas mixtures tailored to have the correct properties for different ranges of projectile speed). The mixtures range from 0.5 CH4 + O2 + 3 CO2 (.7 to 1.1 km/s) to 8 H2 + O2 (7.2+ km/s). Peak acceleration is < 1000 g. The vehicles are made of graphite epoxy and have a total structural mass of 625 kg. The graphite epoxy is coated with carbon-carbon ablator. This heating is apparently not as bad as I had feared. Total mass loss for a 9 km/s launch velocity due to atmospheric heating (starting at 4000 m altitude) is only about 38 kg for a 16 degree angle of elevation, about 20 kg for 22 degrees. Velocity loss ranges from 10% (30 deg.) to 20% (16 deg.). It is claimed that mass loss from ablation decreases as muzzle velocity increases, because although the heat load is higher, the vehicle is not exposed to the heating for as long a time. It is also claimed that the heating is largely convective, not radiative. In-tube ablation due to passage through the propellant gas is less than 1 kg; ablation in the combustion zone, less than 3 kg. Unfortunately, the vehicle is aerodynamically unstable. They'd better add fins, I think. For a 9 km/s launcher, the launch tube is 5.1 km long and is made of 41,700 tonnes of AISI 4340 steel. The paper talks about orbital maneuvesrs. Solid rocket motors are ruled out because they could not withstand launch, and have insufficient performance. Instead, they propose using nitrogen tetroxide and monomethylhydrazine, pressurized by a gas generator using hydrazine. Isp = 297 sec, thrust = 10,000 newtons. Hardware mass of the propulsion system is approximately 200 kg. The vehicle is aerobraked down to LEO in one pass at 30-50 km without the use of special aerodynamic devices. This apparently does not present heating problems. Mass fraction to LEO ranges from 19% (8 km/s launch velocity, angle 22 deg) to 43% (10 km/s, 18 deg). However, they have apparently not addressed the problem of matching orbital planes, perhaps because they think waiting for precession to match planes is too time consuming. I find it encouraging that low launch angles lead to acceptable ablation. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sat, 31 Dec 88 12:26:29 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: Magnetically Insulated Impact Fusion I noticed the following abstract in Bull. APS (33(9), Oct. 1988): Compact Magnetically Insulated Impact Fusion (MIIF) System D. C. Barnes et. al. (SAIC, Austin, TX and U. of Washington) Previously reported theoretical studies of MIIF physics provide a complete conceptual design of a fusion system. It is shown that fusion parameters may be achieved in a very modest experiment. A wall confined spheromak is first formed by mechanical injection of magnetic helicity [Phys. Fluids, Aug. 1988, pp. 2214-2220] and preheated to T > 50 eV by a linear compression ahead of a shaped projectile. Then, the projectile impacts a symmetric target and compress [sic] the plasma quasispherically. The figure of merit is va, where v is the impact velocity and a the initial system size. A range of va of 20-100 m^2/s corresponds to plasma parameters of n = 10^21 cm^-3, T = 6.5 keV, tau_E = 10^-6 s, B = 3 megagauss. *Present* railgun technology can achieve this va at, e.g. v = 6 km/s, a = 5 cm, M = 200 g, W = 3.6 MJ. Thus, such an experiment can be planned and carried out with no technology extrapolation. [ n = ion density, T = temperature, tau_E = energy confinement time, B = (mean?) magnetic field. Note that n tau_E = 10^15 s/cm^3, so this exceeds the Lawson criterion for DT, and beta >> 1, so the plasma is in contact with the walls. The magnetic field is there to reduce thermal conductivity, not contain the plasma. ] It seems to me that this system, if it would work and if the gain were high enough, might make an ideal engine for an asteroid tug. Debris from the explosion could hit a pusher plate or, if sufficiently ionized, could be redirected magnetically. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Sat, 7 Jan 1989 22:41-EST From: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU To: space-tech@cs.cmu.edu Subject: Satellite servicer Hey, gang, how about this idea for an interesting space project: a satellite servicer with a couple of small teleoperated robot arms, video, communications, and ion propulsion. It would weigh maybe 100 pounds and have solar cells for power. It motors up to a satellite and gives a tug to the solar panel that wouldn't deploy, or whatever. Maybe it should have the ability to spin/de-spin a satellite. Then you just put it up in geosynchronous orbit and say "first come, first served." Questions for the floor: 1. Do you think it would be useful? 2. How small and low-power can the video transmission hardware be? 3. What does it take to rendezvous with a satellite? Can you do it from ground-based sensing plus video, or do you need some sort of radar? 4. Is there something important I forgot? ---------------------------------------------------------------------------- | Marc Ringuette | mnr@cs.cmu.edu | "Gaston...a bucket for Monsieur" | | CMU Computer Science | 412-268-3728(w) | -- watch this space for other | | Pittsburgh, PA 15213 | 412-681-5408(h) | quotes from great literature | ---------------------------------------------------------------------------- ------------------------------ Date: Mon, 9 Jan 89 11:32:55 EST From: dietz@cs.rochester.edu To: Marc.Ringuette@DAISY.LEARNING.CS.CMU.EDU Cc: space-tech@cs.cmu.edu Subject: Satellite servicer Some comments on the satellite servicer: Is it reasonable to have an solar ion engine propelled craft spiral up through the radiation belts? I think 100 pounds might be too little for a servicer. If it isn't, then it might make sense to make the servicer a one-shot device. Then you might not need an ion engine, since the delta-v to get to GEO is much lower than the exhaust velocity of an ion engine. Considering the constraints on amateur space projects, how about the idea (I believe from AMSAT) of using solar electric power to electrolyse water? The gases are stored under pressure and burned in a small thruster. One can pump an elliptical orbit by firing the thruster at perigee, using gases accumulated during the rest of the orbit. If you can get an amateur satellite to GEO, you should be able to get it away from earth entirely. Assuming communication isn't too difficult, how about lunar or asteroid fly-bys? There should be a lot of demand from space scientists for small, low cost spacecraft of this sort. A nice project would be a TV camera on a spacecraft just inside earth's orbit, to look for co-orbital asteroids (which could be reached with very little delta-v). To my knowledge (which may not be up to date) no large asteroids exist in the earth-sun L4 and L5 points, but there might be asteroids trapped between those points on the side opposite the earth. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Mon, 9 Jan 89 13:36:27 EST From: dietz@cs.rochester.edu To: klaes%mtwain.DEC@decwrl.dec.com Cc: space-tech@cs.cmu.edu Subject: Asteroid Orbits > What do you mean by asteroids on the side "opposite" Earth? > Have I read your sentence wrong? Aren't all sides of Earth viewable to > space? Please elaborate. My comment was too cryptic, so let me elaborate. I meant the other side of earth's *orbit*, where the orbit is divided into two pieces by the earth-sun L4/L5 points. As I recall, simulations have shown that asteroids cannot be stable at the earth-sun L4/L5 points. However, there are stable orbits that shuttle back and forth between these points. That is, the asteroid is first in an orbit just outside the earth's. As the earth overtakes the asteroid, it gradually moves towards the leading Lagrange point. Near that point, the asteroid is moved down to an orbit inside earth's. It then starts to overtake the earth, moving towards the trailing Lagrange point, where it gets perturbed outside the earth's orbit, etc. I wonder if debris blasted off the moon by impacts could collect in those orbits. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Mon, 9 Jan 89 15:07:04 EST From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: microspacecraft Marc's note made me think: how small can a spacecraft be? How small can an *amateur* spacecraft be? People at JPL have thought about microspacecraft with a mass of 1 kg. Such small spacecraft might be very attractive as amateur projects, since they could be cheaper and should be easier to launch and propel once in space (for example, Freeman Dyson proposes using 1 kg microspacecraft propelled by 30 meter solar sails). The JPL proposal involved firing the spacecraft out of orbiting railguns at 100 km/s; amateur microspacecraft could be launched conventionally. A spacecraft has many subsystems. How might they be miniaturized? Control logic: electronics can be integrated ("wafer scale spacecraft?"). Some radiation tolerance is necessary, as well as low power consumption. Am I correct in my understanding that AMSAT has used some kinds of commercially available chips with good results? Power: solar cells and batteries can be made small. Power conditioning? I guess this can also be miniaturized, if power levels are low enough. Communication: a microspacecraft will not have much power available, so it will have to have a tight beam. That means optical communication. Tiny semiconductor lasers are available; we'd need an optical system to focus the beam. The beam will have to be well directed. Has AMSAT considered an optical communication system in one of their satellites? Would FCC have any jurisdiction? Attitude control: the spacecraft must be able to sense its attitude in space and to correct errors. Rapid rotation could be sensed with microaccelerometers. Slow rotation can be sensed with CCD star trackers and sun sensors. We must also be able to change attitude. I suggest micromachined hydrazine thrusters. That is, etch nozzles, valves and pipes into pieces of silicon, integrated with thruster control logic. Feed hydrazine from a small tank. Maybe someone could get a hold of the JPL report and summarize it? Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: Tue, 10 Jan 89 10:00:03 MST From: ==== SEDS-UNM ==== To: dietz@cs.rochester.edu, space-tech@cs.cmu.edu Subject: Re: microspacecraft AMSAT is currently preparing to launch a series of small satellites called MICROSATS. They measure 9 x 9 x 9 inches. One of the nice things about this size is that piggy-back launches are more readily available. Watch QST for more info., or contact AMSAT. Ollie N6LTJ ------------------------------ End of Space-tech Digest #19 *******************