@S1-A.ARPA,@MIT-MC:rsf@Pescadero (05/26/85)
From: Ross Finlayson <rsf@Pescadero>
It seems to me that there are two basic psychological problems that are going
to stand in the way of any interstellar mission taking place in the (very)
near future.
The first problem can be illustrated as follows: Suppose that we currently
have the technology to send an (unmanned) probe to a nearby star, knowing that
it would take 100 years to get there. Suppose also that we are fairly
confident that in 20 years time, our technology will have improved
sufficiently to allow the trip to be made in 50 years instead of 100. Given
this scenario, would we seriously consider launching a probe in 1985? It
hardly seems likely - it would make far more sense to wait until 2005, and
thus save 30 years. However, come 2005, we might well feel that in another
10 years we would have the technology to make the trip in 30 years instead of
50. Thus, we would be tempted to postpone the mission until 2015, to save
another 10 years.
In other words, we would not send out a probe until we were confident that we
could not advance the arrival time by waiting for further advances in
technology. In an ideal world, this would be an optimal strategy. In
practice, however, a technological stasis is likely to result. Many early
probe designs will not get tested, and the actual rate of technological
advancement is likely to be considerably retarded, to the extent that we might
not reach the stars until several decades later than we could. (I suppose the
`ideal' probe would be one that is able to adapt itself to advances in
technology as they are discovered on Earth and radioed to the probe while in
transit :-)
The second problem is more obvious. Even if we were sure that we could not
improve significantly on the 100 year transit time (at least, not within the
next 100 years), how many people would be willing to support a multi-billion
dollar project, the results of which only their great-great-grandchildren
would see? I know I would, but many members of Congress seem unable to look
further than their next election. Our friend Sen. Proxmire woud have a field
day.
Fortunately Columbus, Magellan, Tasman, Cook etc. weren't faced with these
problems.
Ross Finlayson
Stanford CS Dept.
ARPA: rsf@su-pescadero.ARPA
UUCP: ...!{decwrl,ucbvax}!Glacier!Shasta!rsfhenry@utzoo.UUCP (Henry Spencer) (05/27/85)
As somebody (Pournelle?) once observed:
1. Alpha Centauri, the nearest star, is 4.3 LY away.
2. Assuming 0.99999c propulsion and radio/laser data return, the
round-trip time is thus 8.6 years.
3. The maximum US presidential term is 8 years.
4. 8 < 8.6, so no starprobes.
--
Henry Spencer @ U of Toronto Zoology
{allegra,ihnp4,linus,decvax}!utzoo!henry@S1-A.ARPA,@MIT-MC.ARPA:king@Kestrel (05/31/85)
From: king@Kestrel.ARPA One way of getting close approaches to the planets and still not have to decelerate is to have two probes; one would locate the planets and radio the information to its parner, a MIRVed probe approximately a year behind. The second prob has to be MIRVed because there is little chance of catching even two planets with one probe; gravitational manouvering doesn't work at .20C.
dbb@aicchi.UUCP (Burch) (06/02/85)
As for how to slow a probe at target when you are using "solar" sails as propulsion: In a DOD report, Robert L. Forward proposed using a light sail that is in to segments, a large outer ring and a small inner circle. When departing, the two segments are used as a single sail. When decelerating, the large outer ring is dropped, and the spacecraft with small sail attached turns around. You then (Well, you actually start years before) turn on your earth based LASERs. The large outer ring acts as a mirror, and reflects the light from earth onto the probe's sail. Needless to say, the reflector sail departs the probe at a healthy acceleration, but they are both so far from earth that the subtended angle will not change much over the course of the deceleration program. As a sind note, the light reaching the small sail would be extremely redshifted... -Ben Burch AIC
sean@ukma.UUCP (Sean Casey) (06/04/85)
In article <2010@mordor.UUCP> @S1-A.ARPA,@MIT-MC.ARPA:king@Kestrel writes: >One way of getting close approaches to the planets and still not have >to decelerate is to have two probes; one would locate the planets and >radio the information to its parner, a MIRVed probe approximately a >year behind. The second prob has to be MIRVed because there is little >chance of catching even two planets with one probe; gravitational >manouvering doesn't work at .20C. I'm going to get flamed for being this picky, but MIRV stands for Multiple Independently targeted Reentry Vehicle. I don't think he had reentry in mind. -- - Sean Casey UUCP: {cbosgd,anlams,hasmed}!ukma!sean - Department of Mathematics ARPA: ukma!sean@ANL-MCS.ARPA - University of Kentucky