henry@zoo.toronto.edu (Henry Spencer) (05/10/91)
[This is the "forecast and inventory" issue, light on current news.]
Editorial suggesting that the best way to sort out US space policy, and
lack thereof, is to substitute the word "purpose" for "policy".
NRC Space Studies Board criticizes current space station design as being
ill-suited for either life-science or materials microgravity work.
Workforce reductions at Reston as station cuts sink in.
DoD re-warms to NASP, saying technical progress has been remarkable and
several military applications for hypersonic cruise are now seen.
Stafford group will strongly back restarting nuclear-rocket programs for
use in Mars exploration. Both nuclear-thermal and nuclear-electric systems
are of interest, but nuclear-thermal looks most promising for openers: it
offers a high enough exhaust velocity to make fast trajectories possible,
greatly reducing worries about radiation and free-fall effects, and it has
enough thrust to make far more abort modes available in case of trouble.
The downside of all this is public antinuclear hysteria and its political
effects, very uncertain costs, the possibility that the push for high
performance may lead to exotic designs that worsen development problems
(in particular, sources say "They're doing a lot of evaluation by rocket
people and not enough by nuclear people"), and lack of effort on important
but unglamorous supporting technologies ("either way you go, chemical or
nuclear, you're going to need new ways to store and handle liquid hydrogen...
but what's the funding for cryogenic technology? Zero!").
The Stafford group reportedly will reject the Augustine commission's open-
ended approach, and urge setting a specific schedule for a return to the
Moon and an expedition to Mars.
First Titan IV launch from Vandenberg March 8, probably carrying a Lacrosse
military radarsat.
Titan IV launch schedule to be cut about 30% during the rest of this decade
due to tight budgets and reduced payload requirements. One problem is what
effect this will have on the work to convert the Vandenberg shuttle pad to
a Titan IV pad: the new schedule is probably too busy for one Vandenberg
pad but will come nowhere near full use of two.
Big excitement about tactical missile defence in the aftermath of the Gulf
War: it now seems indisputable that the missile threat is real, US nuclear
forces cannot deter it, US conventional forces are not good at finding and
destroying missiles before launch, and missiles can be intercepted. What
sort of hardware this translates into is another question. SDIO is basically
reshuffling its organization to bring as much of it as possible under the
new hot "tactical" label, but Congress probably won't buy the same old
programs with only the labels new. One area where real changes are likely
is sensor satellites. Another is that SDIO has now formally abandoned the
1993 target date for a decision on major SDI deployment; Congress has always
considered this deadline early and arbitrary anyway.
Long overview story on new space-technology efforts. Current efforts are
pretty small; one of note is a project looking at monitoring rocket-engine
health by optical sensors looking at the exhaust plume, which seems to
have some predictive value and could perhaps detect impending engine failure
ahead of time. Near-future efforts are planned to emphasize funding for a
small number of major topics: an advanced space engine to replace the RL-10
oxyhydrogen rocket motor, planetary rover technology, nuclear propulsion,
and life support (particularly radiation protection).
Story about planned upgrades and possible future directions at the Cape.
Current approaches to launcher and payload processing, and current launchers
themselves, are considered inadequate for future activity. "We've forgotten
that launch vehicles are transportation systems."
Soviet space program facing budget difficulties. In particular, the future
of the "Mir 2" efforts is now uncertain.
--
And the bean-counter replied, | Henry Spencer @ U of Toronto Zoology
"beans are more important". | henry@zoo.toronto.edu utzoo!henrywiml@milton.u.washington.edu (William Lewis) (05/19/91)
In article <1991May10.034743.29351@zoo.toronto.edu> henry@zoo.toronto.edu (Henry Spencer) writes: >Stafford group will strongly back restarting nuclear-rocket programs for >use in Mars exploration. Both nuclear-thermal and nuclear-electric systems >are of interest, but nuclear-thermal looks most promising for openers: it >offers a high enough exhaust velocity to make fast trajectories possible, ^^^^^^^^^^^^^^^^^ >greatly reducing worries about radiation and free-fall effects, and it has >enough thrust to make far more abort modes available in case of trouble. What does a "fast trajectory" mean? Faster than a Hohmann orbit? Or faster than some other orbit I'm not familiar with? How much time would this hypothetical trajectory take, and how picky is it about planetary alignments? Inquiring minds want to know ... -- wiml@milton.acs.washington.edu Seattle, Washington (William Lewis) | 47 41' 15" N 122 42' 58" W "Just remember, wherever you go ... you're stuck there."
henry@zoo.toronto.edu (Henry Spencer) (05/19/91)
In article <1991May18.231158.24883@milton.u.washington.edu> wiml@milton.u.washington.edu (William Lewis) writes: >>offers a high enough exhaust velocity to make fast trajectories possible, > ^^^^^^^^^^^^^^^^^ > What does a "fast trajectory" mean? Faster than a Hohmann orbit? Yes, plus more amenable to short overall missions. Using Hohmann orbits for Earth-Mars-Earth is awkward because there is a *long* wait at Mars for the return window. Faster trajectories not only take less time themselves, they give you more flexibility in planning the stay time. -- And the bean-counter replied, | Henry Spencer @ U of Toronto Zoology "beans are more important". | henry@zoo.toronto.edu utzoo!henry
fcrary@lightning.Berkeley.EDU (Frank Crary) (05/20/91)
In article <1991May18.231158.24883@milton.u.washington.edu> wiml@milton.u.washington.edu (William Lewis) writes: > What does a "fast trajectory" mean? Faster than a Hohmann orbit? >Or faster than some other orbit I'm not familiar with? How much time >would this hypothetical trajectory take, and how picky is it about >planetary alignments? Inquiring minds want to know ... > A fast trajectory means faster than a hohmann orbit. In fact a specific transfer orbit. While I don't recall the details, I seem to remember that it is the "next step down" e.g. all the other orbits, except a hohmann orbit, are less efficient. In the case of a Earth to Orbit transfer the fast, or "opposition" class, orbit still takes months (about 3 or 4) as opposed to the 260 days of the Hohmann transfer. The big problems are fuel, about 150% the C(3) energy of a hohmann is required (how 50% more energy translates into fuel mass depends on the design, but a 200 - 400% increase might be a good ball park guess.) Also, a "opposition" class orbit reaches Mars only a week or two before the launch window for an Earth return. As a result, there are two possibilites: 1) Four months in transit to Mars, 2 weeks on the surface, four months returning to Earth. or 2) Four months in transit to Mars, 26 months on the surface, four months returning to Earth. (E.g. miss the first return window and wait for the next.) Neither is too appealing, the first allows not enough time on the surface to justify a manned mission (e.g. the work that men could do in this short time could be just as well done by robots. Men need to be there a while for the advantages of a manned mission to matter.) The second alternative is just TOO LONG for a safe, productive mission (almost 3 years). As a result, the Case For Mars IV, Launch, Assembly and Transportation Workshop recomended that "fast" missions be ignored. The 1000 day hohmann orbit requires not only less fuel, but provides a reasonable ammount of time on the surface (about 460 days.) Frank Crary UC Berkeley
carroll@cs.uiuc.edu (Alan M. Carroll) (05/22/91)
In article <1991May20.034518.6909@agate.berkeley.edu>, fcrary@lightning.Berkeley.EDU (Frank Crary) writes: > The second alternative > is just TOO LONG for a safe, productive mission (almost 3 years). > Workshop recomended that "fast" missions be ignored. The 1000 day hohmann > orbit requires not only less fuel, but provides a reasonable ammount of > time on the surface (about 460 days.) I'm missing this. The fast orbit takes a total of 34 months, or roughly 1020 days. That's too long, but a 1000 day mission isn't? -- Alan M. Carroll <-- Another casualty of applied metaphysics Epoch Development Team Urbana Il. "I hate shopping with the reality-impaired" - Susan
fcrary@lightning.Berkeley.EDU (Frank Crary) (05/22/91)
In article <1991May21.192557.12347@m.cs.uiuc.edu> carroll@cs.uiuc.edu (Alan M. Carroll) writes: >I'm missing this. The fast orbit takes a total of 34 months, or >roughly 1020 days. That's too long, but a 1000 day mission isn't? I should have been more exact. The stay on the surface is too long. Either transfer orbit will result in long stay on the surface. In the case of a minimum energy transfer, 400 days or so. The "fast" orbit could give you a stay of 700 - 800 days. However, the "fast" orbit requires MUCH more fuel. A "fast" mission could only land a limited amount of equipment. Not enough for 26 months of surface exploration. Spending only 400 days, with the equipment needed to do a good, detailed job of exploring is much more effective. In general, "fast" missions are suggested to shorten the trip: The fuel costs are almost prohibitive, but if you HAVE to return in less than one year, this is the only way. A "fast" mission that waits on the surface for the next launch window (26 months) does not do this, but still has to pay the price in fuel. Frank Crary UC Berkeley
nickw@syma.sussex.ac.uk (Nick Watkins) (05/23/91)
From article <1991May10.034743.29351@zoo.toronto.edu>, by henry@zoo.toronto.edu (Henry Spencer): > > Story about planned upgrades and possible future directions at the Cape. > Current approaches to launcher and payload processing, and current launchers > themselves, are considered inadequate for future activity. "We've forgotten > that launch vehicles are transportation systems." Has interesting artist's impression of Cape in future. Appears to show pad 20 & pad 34 back in use. Anybody know which boosters they assumed to be using them ( were once Titan I/II and Saturn I respectively)? Also, has anybody any pics of Atlas Agana launches from pad 13 post 1969 ? I'm interested in the late model of the Atlas Agena D. Nick -- Dr Nick Watkins, Space Plasma Physics, Univ. of Sussex, Brighton BN1 9QH, UK JANET: nickw@uk.ac.sussex.syma BITNET: nickw%syma.sussex.ac.uk@uk.ac ISU Class of '91