peterb@pbear.UUCP (02/25/85)
Regarding light sails, I don't know if mylar is the best, but I think that it will work quite well. When building a light sail, there are a few design problems that have to be overcome, such as weight (obviously) rigidity, ease of deployment, and resistance to damage from micro meteors. I remember a story called "Sun Jammer" that described an earth to moon race by solar yachts. These varied in design, and the story described quite a bit about the problems of solar sails. One of the problems is how do you deploy a sail that is a few miles in surface area, and then once deployed how do you keep it in shape. One of the obvious ideas it to spin the sail and use centrifical force to keep the sail in place while it is being deployed. This is assuming that the sail has been packed in a tube with the shrouds to be released first and then as the tube rotates the rest of the sail pulls it self out. Also the speed of rotation would drop as more and more sail is released until the entire sail is released. Once released and spinning the sail would form a circle with a depressed center (from photon pressure) and has to be strutted in order for it to keep its shape for a few millenia. One idea I thik would work is to us an foaming agent that is released into mylar tubes that are bonded to the sail (backside so as not to interfere with the mirror). As the foam expands, it would rush to the extreme end of the tube that is exposed to vacuum. Also the centrifical force would help it on its way. Then the foam would vacuum cure and become rigid. This may be a little messy, but it would be quite simple in design. Also the tubes would not have to worry about crimping since the foam would expand slightly as it cured and cause the tubes to assume the largest volume (a circle). The tubes can all be connected to a central valve at the apex of the sail and once the foam is injected and cured the deploment tube can jus cut itself away and the sail would start on its journey. Steering the sail would be difficult, and I don't have the answers to that one. I would wish someone would pick up the idea and bounce it around. Peter Barada ima!pbear!peterb
karn@petrus.UUCP (02/27/85)
Does anyone know just how high you have to be to construct a "high performance" solar sail? Aside from atmospheric drag (which makes your average space shuttle orbit useless) there is also a rather large gravity gradient at low altitudes which might rip a delicate sail. Phil
al@ames.UUCP (Al Globus) (02/28/85)
> Steering the sail would be difficult, and I don't have > the answers to that one. I would wish someone would pick up the > idea and bounce it around. > > Peter Barada > ima!pbear!peterb With all this talk about solar sails on the net I thought you might like to know that the World Space Foundation is actually building one and expects to fly it. The have built two prototypes, one full size, and have had an upper stage donated to them. They still need a launch - either shuttle or Ariane - and I don't think they've started on the flight article. They main players are experienced people from JPL, they know what they're doing. I don't know how far they've got on control, but the last I saw there were two small rotatable sails on the end on one of the booms for pitch and roll control. There is also a movable mass near the center of the sail for yaw. If anyone has the address available, why don't you post it? Most of their labor is volunteer. If you want to help, contact Robert Staehle (sp?) at JPL in Pasadena, CA.
karn@petrus.UUCP (03/04/85)
> With all this talk about solar sails on the net I thought you might like > to know that the World Space Foundation is actually building one and > expects to fly it. The have built two prototypes, one full size, and have had > an upper stage donated to them. They still need a launch - either shuttle > or Ariane - and I don't think they've started on the flight article. > They main players are experienced people from JPL, they know what > they're doing. > > I don't know how far they've got on control, but the > last I saw there were two small rotatable sails on the end on one of > the booms for pitch and roll control. There is also a movable mass near > the center of the sail for yaw. > > If anyone has the address available, why don't you post it? Most of > their labor is volunteer. If you want to help, contact Robert Staehle (sp?) > at JPL in Pasadena, CA. The World Space Foundation is indeed a serious group. They have approached AMSAT, the radio hams who build amateur communications satellites and have proposed a joint venture in which AMSAT builds the communications hardware to fly on their sail. They get command, telemetry and tracking facilities, something that AMSAT can do well, and we (AMSAT) get a slow but free ride for a transponder into a useful communications orbit, something that AMSAT is always looking for. We were all impressed with their technical knowledge of the subject, and they seem to have a viable organization. A possible joint project is only in the very preliminary stages at the moment, but one thing that can make it emerge into reality very fast is for volunteers to step forward and actually take on part of the design job. The primary contact person on the AMSAT side for the project is Dr. John Champa, K8OCL. John recently moved to Michigan and I don't have his new address handy, but mail to him can be forwarded via the AMSAT address (PO Box 27, Washington, DC 20044). Feel free to contact him if you think your interests might lie in the electronics side of such a project. Here's YOUR opportunity to do something "up there" besides talk about it idly on net.space! Regarding photon pressure and spinning toys: AMSAT-Oscar-7, launched in 1974, made practical use of this phenomenon. In those days, amateur satellites had no propulsion systems or active attitude control systems, but something had to be done to keep them from tumbling uncontrollably. The end-over-end motion was easy enough, you just stick a big bar magnet along the main axis of the spacecraft. Within days after launch the whole thing aligns itself with the earth's magnetic field and the satellite turns end-over-end slowly twice per orbit (this is a polar orbit). The remaining problem was to control roll about the magnet axis, and for this task photon pressure was used. The satellite had four antenna elements bent towards one end, which were fabricated out of ordinary carpenter's rule (the kind that's yellow or white, with inch markings). One side of each element was painted white, the other black. The result was a net torque from radiation pressure that slowly rolled the spacecraft about its magnet axis at almost exactly the predicted rate. Very simple, very effective. Phil Karn Asst. VP Engineering, AMSAT