Subject: Space-tech Digest #116 Contents: DAEDALUS star probe and its "wardens" (9 msgs) Galileo antenna rescue & launcher choice (4 msgs) P2 launcher (1 msg) regarding the repeated detonation of fuel (1 msg) Delta Clipper (1 msg) ------------------------------------------------------------ Date: Tue, 14 Apr 92 07:48:26 PDT From: "CUIP, PKO3-1/27D, Pole 27-C, 223-3283" To: space-tech@cs.cmu.edu Cc: klaes@verga.enet.dec.com Apparently-To: space-tech@cs.cmu.edu Subject: DAEDALUS star probe and its "wardens". Though I realize this has little to do with the GALILEO Jupiter probe, I thought it would not hurt to mention that the idea of mechanical "attendants" for space probes is not unheard of. In 1973, the British Interplanetary Society (BIS) came up with the concept of an unmanned interstellar probe named DAEDALUS which would be able to conduct a one-way mission to the red dwarf Barnard's Star, 5.9 light years from Earth. DAEDALUS would use technologies that should be available by the middle of the Twenty- First Century. DAEDALUS was designed as an unmanned fusion-powered craft which would be built in orbit around Jupiter's moon Callisto for easier access to the helium-3 fuel in the Jovian atmosphere required for fueling the probe's fusion reactor. After an estimated twenty-year construction, the probe would be sent on its way to Barnard's Star, reaching its destination in about fifty years with a velocity of 38,400 kilometers (24,000 miles) per second. Zipping through the entire Barnard system in a matter of hours, DAEDALUS would make a quick study of the system with a variety of instruments, including large telescopes and a series of smaller probes to be sent towards any planets orbiting the star. Side Note: One reason that Barnard's Star was chosen as a target at the time was based on evidence in the 1960s that the red sun had several planets circling it. This evidence has since come into question. I think it would be more practical if our first interstellar vehicles were sent to the Alpha Centauri star system 4.3 light years from Earth, as it could be reached in only 38 years using DAEDALUS. Since DAEDALUS would be in deep space for decades, regardless of either target, and communications between the craft and Earth would take years at the speed of light - as opposed to hours for even the PIONEER and VOYAGER probes at the edges of our solar system - a system had to be devised so that the craft could take care of itself should an emergency arise while in transit. Thus were designed the "wardens". Wardens are small robots with a variety of mechanical arms and tools which would fly about DAEDALUS making repairs as necessary. The robots would be controlled by the main computer on the probe. The BIS envisioned the main computer as semi-intelligent, which was thought to make the utility of the wardens easier. Another type of warden would protect the vehicle in other ways. Since DAEDALUS would be traveling at very high speeds, impacts with even grains of dust would be fatal. The DAEDALUS designers came up with two ideas to protect the craft: One is a beryllium shield at the front of the ship. The other is a warden robot called the "bug". It would be launched several kilometers ahead of the probe and spray gas in its flight path. Most celestial matter such as meteors would be vaporized by the high-velocity impact with the gas, reducing the danger to the main vessel. Whether we eventually build DAEDALUS or something similar to it when we begin our exploration of the stars, I am certain that the concept of the wardens as mechanical maintenance craft will be a requirement for all such future probes exploring deep space. Larry Klaes klaes@verga.enet.dec.com or - ...!decwrl!verga.enet.dec.com!klaes or - klaes%verga.dec@decwrl.enet.dec.com or - klaes%verga.enet.dec.com@uunet.uu.net "All the Universe, or nothing!" - H. G. Wells EJASA Editor, Astronomical Society of the Atlantic ------------------------------ From: henry@zoo.toronto.edu Date: Tue, 14 Apr 92 12:55:44 EDT To: "CUIP, PKO3-1/27D, Pole 27-C, 223-3283" Cc: space-tech@cs.cmu.edu Subject: Re: DAEDALUS star probe and its "wardens". > Side Note: One reason that Barnard's Star was chosen as a > target at the time was based on evidence in the 1960s that the red > sun had several planets circling it. This evidence has since come > into question. I think it would be more practical if our first > interstellar vehicles were sent to the Alpha Centauri star system... Indeed, if you read the "targeting" paper in the Daedalus report, you find that Alpha Centauri, not Barnard's Star, comes out as having the highest figure of merit: the shorter distance speeds up science return, it's a multiple-star system, one of the stars is fairly Sun-like, etc. Barnard's Star was just the nominal design mission; they recognized that the hardware would be useful for other purposes. > Wardens are small robots with a variety of mechanical arms and > tools which would fly about DAEDALUS making repairs as necessary. > The robots would be controlled by the main computer on the probe. > The BIS envisioned the main computer as semi-intelligent, which > was thought to make the utility of the wardens easier. Actually, *something* in the system has to be semi-intelligent, because speed-of-light lags make teleoperated repair work impossible, and the system would be in space for so long that it has to be able to cope with the unexpected. > Another type of warden would protect the vehicle in other ways. > Since DAEDALUS would be traveling at very high speeds, impacts with > even grains of dust would be fatal. The DAEDALUS designers came up > with two ideas to protect the craft: One is a beryllium shield at > the front of the ship. The other is a warden robot called the "bug". > It would be launched several kilometers ahead of the probe and spray > gas in its flight path. Most celestial matter such as meteors would > be vaporized by the high-velocity impact with the gas... Tsk tsk. Haven't you *read* the Daedalus report? :-) The "dust bugs" aren't wardens, and what they spray is a dust cloud, not a gas cloud. (Gas disperses too quickly.) The bow shield is considered sufficient for interstellar cruise. The dust bugs are essential for the target- system encounter, where much more debris is likely. Several would be carried because there is a significant chance of hits large enough to wreck a dust bug. Maintaining the dust cloud from the main probe was assessed as significantly more difficult. The impacts need to be well ahead of the probe, so that the fireballs have a chance to thin out before the probe reaches them. Simple, expendable flunkies stationed well ahead seemed the simplest method of maintaining the cloud. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ From: tneff@haleiki.NYC.NY.US (Tom Neff) Date: Tue, 14 Apr 1992 21:52:06 EDT X-Mailer: Mail User's Shell (7.1.1 5/02/90) To: space-tech@cs.cmu.edu Subject: Re: DAEDALUS star probe and its "wardens". On Apr 14, 7:48am, "CUIP, PKO3-1/27D, Pole 27-C, 223-3283" wrote: > Another type of warden would protect the vehicle in other ways. > Since DAEDALUS would be traveling at very high speeds, impacts with > even grains of dust would be fatal. The DAEDALUS designers came up > with two ideas to protect the craft: One is a beryllium shield at > the front of the ship. The other is a warden robot called the "bug". > It would be launched several kilometers ahead of the probe and spray > gas in its flight path. Most celestial matter such as meteors would > be vaporized by the high-velocity impact with the gas, reducing the > danger to the main vessel. I would further suggest something that the BIS didn't anticipate for this work: aerogels. A large yet lightweight aerogel or "frozen smoke" hyperboloid of rotation could be stationed at some distance in front of the probe. With the proper "warden" technology, its integrity could be continuously maintained by fresh gel generation and patching. I do think it is worth pointing out, though, that you can't simply "station" your shield in front of a vessel designed to accelerate nonstop, as with DAEDALUS. You have to accelerate the shield, too, either by physically attaching it to the spacecraft and letting one set of engines do all the work, or by powering it separately. If you physically attach the shield, you may be severely limited in how much distance you can put between shield and craft, which might matter a lot if you're worried about radiative blast effects from a hit on the shield. On the other hand, if you're willing to do separate guidance, you can put your shield a nice safe distance in front, but now you have an unwieldy and risk prone system to manage. Another, less critical issue is that you'd like to be able to see where you're going. At the eventual speed of system penetration for Barnard's or Centauri, most of the prime observing time is going to occur with the target directly ahead (or behind). Periastron itself is going to involve some hellish slew rates. You could drop your shield on approach, of course, but that's just when it gets dustiest. I don't know the answer. ------------------------------ Date: Wed, 15 Apr 1992 00:50 EDT From: "GORDON D. PUSCH" Subject: Interstellar dust and gas protection To: space-tech@cs.cmu.edu I'm not sure that "fireballs" and "blast effect" describe the dynamics very well. At .128c, impacting atoms carry an energy of about *7.7 MeV/nucleon*, --- comparable to what comes out of the ``business end'' of the heavy-ion cyclotron I work at, albeit at a substantially higher beam-current :-T. Attempting to imagine what a dust-grain impact would look like at those energies grossly exceeds even my (fairly high) boggle-threshold ... I *guess* it would be *SOMEWHAT* like a cosmic-ray secondary cascade raised to the umpteenth power --- although the per-nucleon energy is quite modest, well below the pion or even positron-production thresholds, but still large enough to produce some interesting nuclear reactions. The impact plasma *might* be hot enough to emit gammas; however any conceivable shield would almost certainly be too thin for complete absorption --- most of the energy will just shower through in the secondaries. The flux of secondary radiation will be so large that it is meaningless in rads/sec; it's best measured in milliWatts per square meter !!! (example: \Phi = n m c^3 \beta (\gamma-1), where n := {number density of interstellar gas (100/m^3 sticks in mind)} m := {mass of atom (~938 Mev/c^2 for hydrogen; ~932MeV/c^2/nucleon for anything else)} c := {speed of light} \beta := v/c \gamma := 1/sqrt{1-\beta^2} at such ``modest'' velocities, \Phi ~= (1/2) n m c^3 \beta^3 is a good approximation. I get 48 mW/m^2, from just the interstellar H2, assuming I've remembered "n" correctly; however a nice, fluffy one-*micro*gram dust particle carries about 740 *MEGA*Joules of energy! Now, imagine that being dumped into an area a few hundred microns on a side --- because *I* sure can't! Then, remember what dust at a measly 100 kps relative velocity did to Giotto ... ) I submit that while the beryllium shield *might* provide some interstellar gas protection, something more will be needed for the dust ... I also submit that DAEDALUS's electronics better be *REALLY* rad-hardened :-T --- maybe something like the ``field-emission cathode vacuum-microtube ICs'' I once read an article about ... ;-) Gordon D. Pusch ------------------------------ Date: Wed, 15 Apr 1992 00:58 EDT From: "GORDON D. PUSCH" Subject: Interstellar dust and gas protection (erratum) To: space-tech@cs.cmu.edu Oooppsss! I goofed on at least *one* point :-( > I *guess* it would be *SOMEWHAT* like a cosmic-ray secondary cascade > raised to the umpteenth power --- although the per-nucleon energy is > quite modest, well below the pion or even positron-production thresholds, > but still large enough to produce some interesting nuclear reactions ... The positron threshold *WILL* be exceeded; still no pions, though ... Gordon D. Pusch ------------------------------ From: henry@zoo.toronto.edu Date: Wed, 15 Apr 92 13:18:28 EDT To: space-tech@cs.cmu.edu Subject: Re: DAEDALUS star probe and its "wardens". >I do think it is worth pointing out, though, that you can't simply >"station" your shield in front of a vessel designed to accelerate >nonstop, as with DAEDALUS. You have to accelerate the shield, too... Quite true, except that Daedalus was *not* a nonstop accelerator. It spent about a month accelerating, I believe, using D-He3 fusion rockets (two stages). It needed no advance shield during this period, because it would be well out of the solar system before velocities got particularly high. The bow shield handled interstellar dust and gas during coasting, with reasonably high probability. (If you hit a pebble at 0.15c, you're dead, but they're not common.) Some small amount of maneuvering, using the second-stage engine, would be done to set up for the target-system flyby. The flyby itself, where heavy dust protection is really needed, would again be unpowered. >Another, less critical issue is that you'd like to be able to see where >you're going. At the eventual speed of system penetration for Barnard's >or Centauri, most of the prime observing time is going to occur with the >target directly ahead (or behind)... An undecelerated flyby at interstellar speeds is indeed a rather brief event. This is one reason why Daedalus included sub-probes, to be placed on encounter trajectories as part of the pre-flyby maneuvering, so that multiple interesting places could be looked at simultaneously. This adds another requirement for considerable on-board intelligence, by the way, because targeting of the sub-probes has to be done without consultation with Earth -- by the time the main probe is close enough to the target system to get good optical observations of potential sub-probe targets, speed-of-light lag is too long to permit consulting Earth before sub-probe deployment. (Yes, this also means carrying a substantial telescope, with a right-angle mirror so you can look forward without exposing the main mirror to dust erosion.) Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ From: henry@zoo.toronto.edu Date: Wed, 15 Apr 92 13:22:48 EDT Subject: Re: Interstellar dust and gas protection To: space-tech@cs.cmu.edu >I'm not sure that "fireballs" and "blast effect" describe the dynamics very >well. At .128c, impacting atoms carry an energy of about *7.7 MeV/nucleon*... The probe itself has to have adequate shielding against loose atoms and the like. Daedalus's bow shield was a non-trivial piece of hardware. The point of the dust shield for target-system encounter is to convert more substantial objects into fireballs -- i.e., loose atoms -- before they reach the probe. I forget whether the electronics also had to be rad-hardened; possibly. I do remember that one could expect the bow shield to be warm throughout interstellar cruise. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Wed, 15 Apr 1992 13:44 EDT From: "GORDON D. PUSCH" Subject: Interstellar dust and gas protection (erratum.2) To: space-tech@cs.cmu.edu Paul Dietz correctly pointed out to me that I botched that dust-grain kinetic-energy calculation: a one *milli*gram dust grain at .128 c has a kinetic energy of 740 megajoules. I stupidly calculated the K.E. of a 10^-6 *kg* dust-grain --- mea maxima culpa :-( Gordon D. Pusch ------------------------------ Date: Thu, 16 Apr 92 06:42:42 CDT From: ssi!lfa@uunet.UU.NET (Louis F. Adornato) To: uunet!cs.cmu.edu!space-tech@uunet.UU.NET Subject: Re: DAEDALUS star probe and its "wardens". Years ago I read about an idea to use superconductors (this was long before the recent "high temp" advances) to generate a magnetic bottle, to contain a cloud of free electons well ahead of a probe. The idea was that approaching dust would be ionized, and then repelled from the negatively charged hull. There was also something about extending the bottle to surround the entire probe (like a portable van allen belt...), to reduce the effects of background radiation on the electronics What effect this would have on anything other than optical instrumentation I couldn't say, but the idea of sub probes has already been mentioned. Of course, either the "stand off" distance of the electron cloud or the charge on the hull (or both) would have to be pretty much in the boggle range. Lou Adornato uunet!ssi!lfa | The secretary (and the rest of the company) Supercomputer Systems, Inc | have disavowed any knowledge of my actions. Eau Claire, WI | ** Space IS our future! ** ------------------------------ Date: Sat, 18 Apr 92 13:04:21 EDT From: SATELLITES-R-US Subject: Galileo Antenna Rescue To: space-tech@cs.cmu.edu Lou Adornato writes: >CITE testing would be fairly short for a self contained payload - the >PAM modules have standard STS interfaces and the integration is pretty >well understood and crew procedures are already in place........ Why would you propose launching such a probe on the shuttle. I think the shuttle would be completely inappropriate (and the Galileo project at JPL has more than enough bad shuttle experiences to push them toward an expendable). Such a small probe would be more appropriately launched by a Delta or Atlas, or if schedule is really important and processing cost MUST be kept low, by Ariane. Launching spacecraft on Shuttle adds to the cost and complexity due to the additional safety requirements and the need to deal with the JSC/KSC integration bureaucracy. Additionally, shuttle can never support a schedule the way an expendable can. -Dave Huff ------------------------------ Date: Sat, 18 Apr 92 13:29:03 EDT From: SATELLITES-R-US Subject: Trucking Galileo... To: space-tech@cs.cmu.edu Phil Fraering writes: >Granted, I should apologize for the forcefulness of my objection; >but the question still remains: has anyone looked at the possible >shuttle vibration loads on Galileo? Someone with a payload guide, >possibly? The vibration environment experienced by a shuttle bay payload during launch is a combination of random vibration and acoustic excitation components. The random vibration transmitted to a payload through the orbiter logerons is defined by the orbiter/cargo ICD. The far more dominent effect, the spacecraft response to the orbiter acoustic environment, is a function of the particular properties of the spacecraft in question. As mentioned previously, while the launch vibrations are more severe than a truck ride, they are of very short duration. Two key ascent events expose a shuttle bay payload to strong acoustic fields. These are liftoff which exposes the payload to an overall environment of 138 db for 5 seconds, and passage through max-Q which is an overall environment of 133.5 db for 10 seconds. Dave Huff ------------------------------ From: henry@zoo.toronto.edu Date: Sat, 18 Apr 92 17:43:36 EDT Subject: launchers and schedules To: space-tech@cs.cmu.edu >Additionally, shuttle can never support a schedule the way an expendable >can. Well, yes and no. Arguments like this tend to involve careful selection of the evidence. It's not that hard to find cases where expendable launches have slipped again and again, such as the recent DSCS 3 Atlas launch that was something like six months late (and it wasn't because the customer wasn't in a hurry, either). The shuttle probably *is* worse, overall, but the US expendables are not the paragons of precise scheduling you would imagine from the way some people talk... Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Mon, 20 Apr 92 10:59:28 -0500 From: ewright@bach.convex.com (Edward V. Wright) To: ssi!lfa@uunet.uu.net, cs.cmu.edu!space-tech@uunet.uu.net Subject: Re: Galileo Antenna Rescue >I also know that NASA would rather mount >this on a Shuttle, and I was looking for the most realistic scenario. Not necessarily, given your requirements for "minimal testing." The safety requirements for anything carried aboard the Shuttle are *very* stringent. ------------------------------ From: henry@zoo.toronto.edu Date: Thu, 16 Apr 92 13:12:30 EDT To: space-tech@cs.cmu.edu Subject: Re: P2 Launcher (minor comments) I finally got through another pass on the P2 proposal, and have some further small thoughts... One wart of using the SRB nozzle, thrust-vectoring system, etc. is that these systems are very maintenance-intensive if you want to reuse them. The number I've heard is that 5000 parts get removed, inspected, replaced, tested, etc. on each SRB after each launch. >... Optimization of stage sizes always drove initial >accelerations for stages 1 and 2 down to 1.2 G... This is not surprising, since -- as I understand it -- you assumed friction and gravity losses to be fixed. You're essentially asking for optimization for a given delta-V in free fall in a vacuum, and under those conditions, lower thrusts always win because of lower structural masses etc. For a launcher, lower thrusts and the resulting lower accelerations will increase gravity losses for sure, and will affect friction losses although I don't have any good feel for which way. I think a more sophisticated model is needed for realistic optimization. >... it might be economically feasible to detach the propulsion and >avionics from the tankage, and return them to earth by shuttle ... I'd suggest a ballistic capsule rather than the shuttle for this. It's no longer realistic to depend on the shuttle for *anything*. >... I have to >date been unable to obtain information about the Ariane IV engine... Let me dig a little, I may have numbers somewhere. Henry Spencer at U of Toronto Zoology henry@zoo.toronto.edu utzoo!henry ------------------------------ Date: Sat, 18 Apr 92 18:09 CDT From: moe@nuchat.sccsi.com (Norman C. Kluksdahl) To: space-tech@DAISY.LEARNING.CS.CMU.EDU Subject: regarding the repeated detonation of fuel. Sender: mnr@DAISY.LEARNING.CS.CMU.EDU it has been evaluated and modeled, as a creature called the pulsed detonation wave engine. recent studies (late 1991) show possibilities of operation from 0 to mach 25. it is speculated that DoD became very interested, especially since a PDWE would leave a 'cotton-balls- on-a-string' contrail, and such contrails have been observed. Aurora? Advances on the PDWE to operate in rocket mode are quite attractive. N. Kluksdahl ..!nuchat!moe ------------------------------ To: space-tech@cs.cmu.edu Subject: Re: Delta Clipper Date: Tue, 21 Apr 92 00:09:30 -0700 From: Doug Reeder The speaker at the Oregon L-5 Society lecture was Dr. William Gaubatz, program manager of the Delta Clipper project at McDonnell Douglas Space Systems Company. On page 5 of a flyer entitled "SSRT: Single Stage Rocket Technology: Because It's the Right Thing to Do", distributed by Dr. Gaubatz at the lecture, on a chart labeled Technology Improvements That Make SSTO Possible Today, is the notation "Improved Ceramic Composite TPS [Thermal Protection System]". In other, more comprehensive documents, thermal protection is identified as being carbon-carbon or Advanced Flexible Reusable Insulation. Can anyone say more about these materials? One design change from earlier documentation: wheels (for ground movement) will be attached after landing, not integral. I asked Dr. Gaubatz about unmaned control during that part of re-entry where radio communication is impossible. He stated that modern avionics would allow the craft to fly itself through all phases of operation. Some addenda to my earlier post: Aerodynamic control is by the engines and, on descent, four flaps. One flap is split to allow the vehicle to roll around its flight vector, and thus gives it its crossrange capabilities. In closing, I should, perhaps, note that I am president of the Oregon L-5 Society, which sponsored the talk, which drew a standing-room-only crowd of perhaps 100 to 150. (Dairy Goat Day had already reserved the main auditorium.) We were pleased to have so many people show, stay (even if they had to stand), and ask knowledgeable questions. Doug Reeder USENET: ...!tektronix!reed!reeder Internet: reeder@reed.EDU BITNET: reeder@reed.BITNET "They were conversing strictly in Looks, a language which to the untrained eye seemed to consist entirely of sidelong glances." _Schismatrix_,Bruce Sterling ------------------------------ End of Space-tech Digest #116 *******************