Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!henry From: henry@utzoo.UUCP (Henry Spencer) Newsgroups: net.space Subject: Re: Money to burn Message-ID: <5629@utzoo.UUCP> Date: Sat, 25-May-85 20:22:29 EDT Article-I.D.: utzoo.5629 Posted: Sat May 25 20:22:29 1985 Date-Received: Sat, 25-May-85 20:22:29 EDT References: <1925@mordor.UUCP> Organization: U of Toronto Zoology Lines: 120 > PS "It can't be done" is not an acceptable answer!!! It is probably the only answer right now! The BIS Daedalus study concluded that a less-demanding mission (15% of c rather than 20%, with encounter taking place at full interstellar velocity rather than after deceleration to 5% of c) was possible given the following improvements on today's technology: 1. He3-D fusion engine. 2. Propellant collection from the atmosphere of Jupiter (there is no other good source of He3!) 3. Advanced self-maintaining computers with software that could plan and conduct the final encounter without any help from humans. The Daedalus probe weighed something like 40000 tons at launch, by the way. You won't fit that in one shuttle load! More specifically... > 1. Assume only near term technology and assets. For example, no > space station. You are allowed two shuttle payloads if necessary - doing > it in one gets bonus points. The major problem, as you point out elsewhere, is propulsion. With the current and foreseeable technology, this means mass... lots of it. The BIS study, assuming better-than-current technology, still had a total-to- payload mass ratio of about 100:1. Two shuttle payloads just will not hack it to get a substantial payload to the stars. Note that one shuttle payload is just sufficient to get the Galileo probe to Jupiter! > 2. Must be ready to launch within 5 years. NASA cannot launch *any* major mission that quickly. NASA knew how to launch a space station nearly 20 years ago; the Skylab technology is that old. The ETA for the space station was ten years, and is already slipping further into the future. Personally I think a space station could be launched almost at once if the project was headed by some nasty person who was authorized to bypass NASA bureaucracy and normal purchasing procedures, with a firm objective of getting hardware flying ASAP rather than maximum sophistication and gosh-wow factor, but one might as well wish for wings. > 3. Assume a target star 20 light years away. The BIS assumed Barnard's Star, 8 LY away, and found it hard. > 4. Intial data must be received from target star system within 100 > years. At 20 LY, this gives 20% of c. The BIS set this as their original goal, but found it so hard that they slipped the specs to 15%. More significant was their rationale for the original speed: getting results within 40 years provides continuity within a human lifetime, because people who were young staff members at launch time get to see the results come in. This is psychologically important to both the staff and the people who vote on the funding. > An interesting question is what collection strategy to use. You could > adopt a cometary orbit or try to look for planetary body etc. Minimum > requirement is a fly-through at less then .05C mean. The propulsion requirements are so fierce that even the BIS very quickly opted for an undecelerated flyby as the only feasible mission. > Remember that your > communications lines have a 40 year turnaround. This means that for all practical purposes the mission must be 100% automatic; there is no realistic prospect of ground control. We are not really up to that unless you are willing to be quite unfussy about the nature of the flyby. Don't forget that communication over distances of 20 LY is very hard. You will need plenty of power, which is a problem in itself. There is *no* self-contained power source now existing that will give useful output after 100 years. > 5. Maximum cost will be 1 billion in current dollars. It may be > competing in Congress with a submarine base in Arizona so the cheaper > the better. NASA probably cannot launch anything anywhere near so ambitious for this kind of money. The Viking mission cost over $1e9, as I recall, and that was a couple of orders of magnitude less fancy. (It was also paid for in early-70's dollars.) Again, I suspect serious cost reductions if radically different management approaches were adopted, but the vastly greater mission complexity more than cancels those gains. > 6. Worship the KISS principle. This thing has to go a long way on > it own. Probably too long a way. Self-repair is almost certainly needed, and that kills simplicity right off the bat. Remember that NASA cannot spend lots of money on a mission that has a good chance of failing; they can't bet unless it's nearly a sure thing, politics being what they are. If one were willing to accept a high chance of failure (i.e. launch several to have a reasonable chance of useful return), I suspect one could dispense with self-repair, given limited objectives for encounter observations. The odds of keeping a fusion rocket engine, or the equivalent, operational for that long without on-board maintenance would also seem minimal, so deceleration is out for yet another reason. Some of the stiffest life requirements in the world are those of the phone companies; they only specify a 40-year life, and this assumes human maintenance. Sorry to be so negative, but it really is a fiercely hard problem. The BIS was optimistic about our ability to solve it (without some of the constraints you impose) before too long. I am actually more optimistic than they were, because the propulsion assumptions they made are now sounding a bit conservative in some ways. For example, Robert Forward says that antimatter propulsion requires no serious breakthroughs and could be a cost-effective alternative to H2-O2 for in-space propulsion (note that lifting quantities of H2-O2 from the ground is expensive) very soon. But I don't think "5 years" and "2 shuttle payloads" are viable constraints right now. -- Henry Spencer @ U of Toronto Zoology {allegra,ihnp4,linus,decvax}!utzoo!henry