Date: Mon, 20 May 1991 15:31-EDT From: space-tech-request@cs.cmu.edu To: ~/st/lists/stdigest Subject: Space-tech Digest #81 Sender: mnr@DAISY.LEARNING.CS.CMU.EDU Contents: Nick Szabo Re: Satellite repair robots Henry Spencer Re: Satellite repair robots Phil Fraering Re: Satellite repair robots Henry Spencer Re: Satellite repair robots Bill Davidsen Re: Satellite repair robots Allen Sherzer Re: Satellite repair robots Jim Meritt CAD/CAM construction of space craft Brian Yamauchi Re: Satellite repair robots Phil Fraering Automation Paul Dietz GPS and Launcher Guidance Henry Spencer Re: GPS and Launcher Guidance Paul Dietz Re: GPS and Launcher Guidance Pete Thomas Re: Ring Gyros (was GPS and Launcher Guidance) Vince Cate Ramjets to help rockets into space Bill Davidsen Re: Ramjets to help rockets into space ------------------------------------------------------------ From: Nick Szabo Subject: Re: Satellite repair robots To: space-tech@cs.cmu.edu Date: Wed, 1 May 91 21:46:30 PDT >>[Study blueprints beforehand to determine good torque-hold points] > ...Of the four US in-space > repairs done to date, three have found that the bird was not actually shaped > the way the blueprints said. The Solar Max repair nearly failed as a result, > and blueprint:hardware discrepancies were the whole problem with GRO. A > practical repair robot must stress versatility in equipment and procedures, > so that it can cope with surprises. Good point. One possible solution is a preliminary survey spacecraft. This would be a small sensor satellite that scans the derelict spacecraft with very high accuracy and resolution in several wavelengths. The goal would be to (a) determine any important discrepancies between blueprint and reality, and (b) determine if the satellite can in fact be fixed, and if so how. This would be a "reusable" satellite in the sense that it would take a slow journey analyzing several low equatorial orbit derelicts, then GTO, then GEO. It would contain a large amount of fuel for orbit changes, with a relatively small sensor payload. From this data, we would determine which satellites could be most easily fixed, and design missions accordingly. For example, if the problem is merely a stuck antenna, it might be easily dislodged by a spacecraft with a strong thruster and a lasso or crowbar. Several different, simple ways to fix the same problem would be built into each mission. BTW, does there exist a good reference from which one could create a list of existing derelict satellites? >> [what level of radiation hardening for repair spacecraft] > ...The GEO birds > are usually designed on the assumption that apogee-motor firing will not > be unduly delayed, so only a few passes through the inner belt will occur. > (Note, e.g., the initial concern that Hipparcos might die quickly when it > turned out to be stranded in transfer orbit.) This implies that most GEO-bound satellites stranded in GTO for more than a few months are probably damaged beyond repair. If we fix a stuck antenna, the electronics will probably be fried anyway. Is this a reasonable conclusion? ------------------------------ From: henry@zoo.toronto.edu Date: Thu, 2 May 91 14:09:54 EDT Subject: Re: Satellite repair robots To: space-tech@cs.cmu.edu > > [blueprints vs. actual hardware] A > > practical repair robot must stress versatility in equipment and procedures, > > so that it can cope with surprises. > > Good point. One possible solution is a preliminary survey spacecraft. This could indeed be a useful thing, but it won't tell us about (say) discrepancies in the interior. In any case, the belief in some quarters that if you pre-plan everything carefully enough, it will all work, is basically a myth. This is not the way real work on real hardware is done. In practice, the human-factors people have found that when an experienced user working with a complex machine reports "no problems", that really means "no problems that I couldn't routinely deal with". The user may be genuinely convinced that nothing went wrong, but videotapes show him encountering and solving a steady stream of small glitches. Planning to get yourself out of trouble is far more productive than investing vast efforts to try to avoid getting into it. This is not to say that the survey spacecraft wouldn't be useful, especially when the cause of failure is not well understood. It also might tie in with another idea people are interested in: an inspection satellite to verify space-weapons treaties. >> ...The GEO birds >> are usually designed on the assumption that apogee-motor firing will not >> be unduly delayed, so only a few passes through the inner belt will occur. > >This implies that most GEO-bound satellites stranded in GTO for more >than a few months are probably damaged beyond repair. If we fix >a stuck antenna, the electronics will probably be fried anyway. Is this a >reasonable conclusion? The odds are pretty good, yes. Things can sometimes be more durable than people expected, as witness Hipparcos, but inner-belt encounters are definitely very bad for electronics. My impression is that the worst problem is generally not damage to control electronics but degradation of solar-array output; that is actually a limiting factor (although not usually the dominant one) even in GEO, which is in the fringes of the outer belt. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Thu, 2 May 91 16:06:04 -0500 From: Fraering Philip To: henry@zoo.toronto.edu, space-tech@cs.cmu.edu Subject: Re: Satellite repair robots Henry's point about "no problems the experienced user couldn't handle" reminded me of the old joke: How many hardware engineers does it take to change a light bulb? "We'll fix it in software." How many programmers? "We'll deal with it in the manual." How many technical writers? "The user can work around any peculiarities." Seriously, shouldn't the design tools available to engineers today (CADM) avoid a lot of those problems? Are the spacecraft assembled by hand? Phil Fraering dlbres10@pc.usl.edu ------------------------------ From: henry@zoo.toronto.edu Date: Thu, 2 May 91 18:16:34 EDT To: space-tech@cs.cmu.edu Subject: Re: Satellite repair robots > Seriously, shouldn't the design tools available to > engineers today (CADM) avoid a lot of those problems? > Are the spacecraft assembled by hand? Spacecraft are in general hand-assembled. The production volume isn't sufficient to justify anything else at present. And CADM files are just electronic blueprints; they don't eliminate the question of whether the hardware matches the blueprints, not unless changes *never* get made by hand after manufacturing. "Rarely" is not good enough. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Fri, 3 May 91 08:20:23 EDT From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: Satellite repair robots Reply-To: davidsen@crdos1.crd.ge.com | Seriously, shouldn't the design tools available to | engineers today (CADM) avoid a lot of those problems? | | Are the spacecraft assembled by hand? Well... yes. They're one of a kind, or few of a kind, and not likely to be built on an assembly line. And if the drawings call for something physically impossible, the people building it make it possible, but they have little feedback to the specs, other than to note the changes on their drawings. Of couse no one uses their drawings, since the originals can be found in a computer... In this case the use of a computer has saved time, but the physical piece of paper is what people should be using. ------------------------------ Date: Fri, 3 May 91 09:04:15 -0400 From: "Allen W. Sherzer" To: space-tech@cs.cmu.edu Subject: Re: Satellite repair robots >Seriously, shouldn't the design tools available to engineers today >(CADM) avoid a lot of those problems? This is a serious problem in all manufacturing. People are usually just too lazy to update drawings when they make changes. GM is spending a lot of money in its Saturn plant to make it easy to update drawings so things can be kept straight. However, it still won't be 100% correct. In this aplication it may not be reliable enough. Any deviation could scrub the entire mission at a cost of millions. One failure early on could bankrupt the robto repair company. Now if you had people on site... Allen +---------------------------------------------------------------------------+ |Allen W. Sherzer | STOP NLDP NOW! | | aws@iti.org | LET'S NOT WASTE ANOTHER DECADE! | +---------------------------------------------------------------------------+ ------------------------------ Date: Fri, 3 May 91 09:18:45 EDT From: "James W. Meritt" To: space-tech@cs.cmu.edu Subject: CAD/CAM construction of space craft Components for satellites and space probes are built that way here. ------------------------------ To: space-tech@cs.cmu.edu Cc: yamauchi@cs.rochester.edu Subject: Re: Satellite repair robots Date: Sun, 05 May 91 18:39:26 -0400 From: yamauchi@cs.rochester.edu Allen writes: >>Seriously, shouldn't the design tools available to engineers today >>(CADM) avoid a lot of those problems? > >This is a serious problem in all manufacturing. People are usually just >too lazy to update drawings when they make changes. GM is spending a >lot of money in its Saturn plant to make it easy to update drawings so >things can be kept straight. However, it still won't be 100% correct. > >In this aplication it may not be reliable enough. Any deviation could >scrub the entire mission at a cost of millions. One failure early on >could bankrupt the robto repair company. This is an issue that came up during the IEEE Workshop on Intelligent Sensory Processing for Space Robotics last month. A number of the robotic systems proposed for Freedom seem to depend heavily on accurate CAD models of both the station and the objects being manipulated. Unfortunately, CAD models are almost never accurate. Last-minute fixes are often omitted from the database resulting in serious problems later. A better approach is to make the robots smart enough to deal with reality -- where "smart" here does not mean capable of complex abstract reasoning, but instead, capable of perceiving the environment and reacting appropriately. This way, if a handle happens to be 10cm to the left of where it should be, the robot won't put its gripper through the solar panel instead. Brian ------------------------------ Date: Sun, 5 May 91 23:42:56 -0500 From: Fraering Philip To: space-tech@cs.cmu.edu Subject: Automation What would be the problems involved in doing all of the design and redesign for a satellite on a computer drafting system, and then building the thing robotically, to make sure that the design matched the satellite? Are today's robots flexible enough to do this for single satellites, or a 'run' of less than ten? I'm sorry if these are stupid questions, but I'm not involved in automation, I'm in Physics, so I don't know anything about automation. Would a system run in that fashion be an extreme case of 'just in time' inventory/manufacturing? Phil Fraering dlbres10@pc.usl.edu ''It's a Flash Gordon/E.E. Smith war, with superior Tnuctip technology battling tools and weapons worked up on the spot by a billion Dr. Zarkovs.`` - Larry Niven, describing the end to _Down in Flames_. ------------------------------ Date: Fri, 3 May 91 11:51:29 EDT From: dietz@cs.rochester.edu To: space-tech@cs.cmu.edu Subject: GPS and Launcher Guidance I was talking the other day with a fellow who worked on the first Air Combat Maneuvering Range out in California. This system tracks aircraft in 3D above a test range using radar trilateration. This makes me wonder if GPS (which performs a similar function) could be used for launcher guidance. They found that trilateration alone is insufficient to get good velocity information, since that amounts to differentiating noisy data. Instead, they put a strapdown inertial navigation package (a collection of gyros and accelerometers rigidly attached to a pod, not in a stabilized gimballed package). Trilateration was used (via a Kalman filter) to correct, up to several time/second, for drift in the accelerometers and the gyros (which one could do because the vehicle was accelerating). I got the impression that strapdown systems are much cheaper than gimballed inertial navigation systems, and that a system that is updated for drift once a second or so can be cheaper than one that must go for minutes without updating. I wonder how cheaply one could make a guidance system for a launcher. There's no reason why a strapdown system need have any moving parts, and I understand that integrated optical gyros have already been made by Honeywell. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ From: henry@zoo.toronto.edu Date: Sat, 4 May 91 18:44:36 EDT To: space-tech@cs.cmu.edu Subject: Re: GPS and Launcher Guidance > I got the impression that strapdown systems are much cheaper than > gimballed inertial navigation systems... Generally true. They do take more computing, which is now very cheap. Gimballed systems are basically obsolete. > and that a system that > is updated for drift once a second or so can be cheaper than one > that must go for minutes without updating. Also true. In general, cost is inversely proportional to drift rate. The double integration (from acceleration to velocity to position) greatly magnifies the effect of the slightest error in the acceleration vector, which is what is actually measured. Lowering drift rate an order of magnitude means heroic efforts to reduce acceleration error. > There's no reason why a strapdown system need have any moving parts, Not entirely true. Current strapdown laser-gyro systems often do have moving parts. There is a problem with laser gyros: due to some obscure effect whose name I've forgotten, they tend to stick a bit at zero, so a very slow rotation would not be detected. The simplest solution is to rotate the gyro back and forth on its axis, and then subtract this oscillation out of the output signal, so the gyro never sits at zero. Last I heard, gyro manufacturers were working on ways of doing this electro-optically without moving parts, but hadn't yet made that work well enough for production systems. That may have changed by now. Paul's general idea -- use a low-precision inertial system with external updates to cancel drift -- has long struck me as a better way to guide *civilian space launchers* than using the high-precision inertial gear built for military missiles. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ To: space-tech@cs.cmu.edu Subject: Re: GPS and Launcher Guidance Date: Tue, 07 May 91 11:56:45 -0400 From: dietz@cs.rochester.edu Henry Spencer said: > There's no reason why a strapdown system need have any moving parts, Not entirely true. Current strapdown laser-gyro systems often do have moving parts. There is a problem with laser gyros: due to some obscure effect whose name I've forgotten, they tend to stick a bit at zero, so a very slow rotation would not be detected. This effect is due to a slight (10^-12) scattering of light off the mirrors from one laser beam into the counterrotating beam, causing their frequencies to lock together. Fiber optic gyros do not suffer from this problem, and need no dithering. I understand low-cost fiber optic gyros have drift rates of 1 to 100 degrees per hour, which is fine, I think, with frequent updating. Paul F. Dietz dietz@cs.rochester.edu ------------------------------ Date: 7 May 91 10:04:00 PDT From: PETE THOMAS Subject: Re: Ring Gyros (was GPS and Launcher Guidance) To: space-tech Isn't it possible to calibrate gyros for their drift rates? Or is it impossible to predict the drift? This would have the effect of decreasing the drift rate. I know that a lot of work has been done in the field of estimation of state and error propagation--perhaps this could be moved from the system level down to the component level. Just a random thought--and probably not practical. I'm curious to learn why, though. --Pete ------------------------------ Date: Wed, 15 May 1991 18:09-EDT From: Vincent.Cate@FURMINT.NECTAR.CS.CMU.EDU To: space-tech@CS.CMU.EDU Subject: Ramjets to help rockets into space I think the most profitable use of ramjets today would be to help rockets get payloads into space. If ramjets were added onto the Pegasus (which already has wings and is going fast when it leaves the B-52) it should be possible to more than double the payload. With the current payload capacity a Pegasus sells for about $8 million. If a ramjet could double the payload it would sort of be worth $8 million. Since it should not cost this much it should be possible to charge less per pound of payload and still make more money than before. Another way to look at this is that the first stage is about 2/3 of the rocket and it only gets to speeds not much over what a ramjet could get to. If you could use a reusable ramjet firststage you could save about 2/3 of $8 million on each flight. Again some of the savings could be passed on to customers reducing the cost of getting things into space. It might be necessary to use a normal jet engine to get the Pegasus up to the speed that a ramjet could work at since most seem to want to be going about Mach 1.5 to start. What is the highest speed a ramjet has been flown at so far? Who is the best at making ramjets today and what have they done? Lockheed? United Tech - Chemical Systems division (408) 281-1122 Marquardt (818) 773-2816 Pratt and Whitney ? Any other company names, phone numbers, or pointers to information on ramjets would be appreciated. -- Vince ------------------------------ Reply-To: davidsen@crdos1.crd.ge.com Date: Thu, 16 May 91 13:26:17 EDT From: davidsen@crdos1.crd.ge.com To: space-tech@cs.cmu.edu Subject: Re: Ramjets to help rockets into space > What is the highest speed a ramjet has been flown at so far? Who is > the best at making ramjets today and what have they done? > > Lockheed? The big names in jet engines are GE and Pratt & Whitney in the US, others, like Rolls Royce, in Europe. I think it's safe to say that the US companies have been looking at this, but high speed ram jets (mach 2-5) are still under investigation. And we are not about to publicise our results, I don't know about anyone else, until they show up on a spec sheet or publicity release. Sounds like you're reinventing the space plane, sort of, with multiple stages and unmanned. It's a good idea, but when a stage gets fairly simple it's cheaper not to resue it, because the checking between flights cost more in labor than you save in material. I have no idea if a jet powered first stage falls under this heading, but I bet the rocket stage does. ------------------------------ End of Space-tech Digest #81 *******************