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starship-design: Re: Solar sails and mission structure
At 6:30 PM 11/11/96, Nick Tosh wrote:
>Hello again everybody.
Hi Nick!
Welcome back. I forwarded your post to the starship design mailing list.
Oh, have you seen the new draft sites at:
http://165.254.130.90/LIT/
or
http://www.urly-bird.com/LIT/
?
>Sorry I'm so slow to contribute, but I'm very busy working for my A-levels
>- British equivilent of American high school graduation, only harder ;) and
>preparing for an admissions interview for Cambridge University (British
>equivilent of Harvard, only... no I'm not gonna say that). I'm afraid I'll
>be a bit out of phase with everyone else for a while.
Good luck.
>Thanks everyone for the mailing list info, I've just sent my subscription
>mail. It doesn't send everything as one big mail does it? It's just that my
>family's getting a bit fed up of finding 70 odd mail messages for me every
>week!
No it sends then one at a time. We're not generally posting as much as we
used to.
>Kelly wrote about my solar sail post:
>
>>The stellar radiation would be too breif and weak to help us much.
>
>I know it wouldn't be much good for a multimillion ton Asimov, but I had in
>mind a light interstellar shuttle to ferry personel and light supplies
>between the target star system and Earth, for which a solar sail might
>provide helpful additional breaking, especially at highish velocity, maybe
>passing the target star completely and reversing back, with the sail furled
>of course (and using gravity to help) - see my last mail. (By the way,
>Timothy, thanks for telling me that I can either count the photons OR
>calculate the Doppler shift. I knew that particle and wave mechanics have
>to be kept separate, so I'm not sure why I was being stupid. Always glad to
>have you to correct me!) This really links in to my ideas on the mission
>structure that I mailed to LIT just before I went off line (must be about a
>year ago now). I've dug it out and pasted it below. Is anyone still
>interested in mission structure? I don't recall we ever reached a complete
>agreement. Please let me know your reactions to this concept.
Solar energy is very weak. Even huge sails on light weight ships, only get
low acceleration very deep in the solar system. For a starship you need
very high acceleration, for long distences. Even if the solar sail had
virtually no cargo it couldn't do interstellar well.
>Posted: 4 October 1995
>
>>I've got a few points to make about the general structure of the mission.
>>
>> Firstly, the mission should make future journeys to TC more
>> feasable - this would require the setting up of a small but expandable
>> permanent presence on one of the terrestrial planets. The ultimate
>> aim would be for the TC 'colony' to be effectively self-supporting.
>> The mistakes of the Apollo program must be avoided - it will be
>> essential to maintain the momentum of the program, since the other
>> alternative would probably be a general loss of intrest and a set
>> back of manned interstellar travel.
This presuposes you want and can afford a colony there. Given one would be
very expensive to maintain (all those long supply flights), its unlikely to
be maintained. Be self sufficent would require a huge population and
investment in equipment. Which seems unwarrented. We also haven't
identified a reason to colonize there.
If you did want to colonize their you wouldn't want to go to the planets.
Its harder to find and process raw materials their, and since you can't use
the biosphere anyway, build a space colony.
Apollos problem wasn't that it lost momentum, it was that it had completed
its goals. Apollo was a race. We won, But after a race, you don't keep
going around the track over and over.
>> Secondly, I've always felt that using the Asimov to bring the
>> crew home is an inefficient solution. The Asimov is designed to be
>> a heavy exploration vessel, not a ferry. Once it has delivered its
>> huge payload of machinery and material to TC, using it to transport
>> a relatively few number of people back to Earth is somewhat ridiculous.
>> I would propose a fairly radical change to the mission plan.
>> - The Asimov should be designed as a one way vehicle for
>> exploration. Its effectiveness in this role can be maximized if
>> the return flight is no longer an issue.
>> - On arrival in the TC system it would serve as a permanent
>> space-based command, control, and support centre for the develpment
>> projects on the planet. Thus a permanent foothold can be established
>> before planetary construction is even begun.
>> - The construction of a 'colony' would be less frantic if
>> those involved knew that there already existed a safe haven for
>> them in-system.
>> - Two or more dedicated personnel transport vessels, designed
>> separately from the Asimov, should be constructed. They would only
>> have to ferry people and small quantities of light supplies and
>> equipment, and so would have a tiny fraction of the mass of the
>> Asimov. It might therefore be possible to propel this type of
>> vessel using solar sail and magsail technology, augmented by an
>> artificial particle beam during the early phase of the flight, and
>> a small on board antimatter engine for maneuvering and possibly
>> as an early boost. Ultimately, a two way particle beam between
>> Earth and TC would be established. It is even possible that the
>> Asimov's engines might be used to produce a beam to increase the
>> acceleration of the small transport vessels back to Earth. Cetainly
>> it could provide many support functions for the transports (eg
>> communication relay, TC based mission control, repair).
>> - These vessels would be used to relieve the crew of the
>> Asimov with fresh people. The round trip (time dilated) for the
>> original crew might be 25-30 years (some might want to stay longer).
>> With two vessels, a relief ship might arrive in TC every 15 years
>> (TC time)
>>
>> If a permanent presence is to be established, it is clear that an
>>interstellar shuttle system is needed. Further, it is obvious that a
>>prohibitively expensive Asimov type vessel it not appropriate for this
>>function. I conclude that if an austere ferry system will have to be built
>>eventually, it makes sense to incorporate it into the original mission.
>> The advantages of having the huge Asimov remaining as a planet-orbiting
>> base in TC are obvious.
>>
>> Please respond with any opinions you might have about what I've said.
>> Do you agree with my basic argument, if not the details?
The idea of a big construction ship sent out once to set up catcher
facilities for later faster sail craft has been tossed about. (We were
leaning toward microwave sail vs partical beam thou.) But the leaving the
main ship there might not make a lot of sence. The ship is largely huge
fuel reserves and engines with habitation and equipment added on. You
could build a colony platform and park most of the equipment on that. Or
even build stations near each of the more interesting areas/planets in the
system, and disperse equipment amoung them.
However since you need the hab deck systems and suplies to get back, and
probably need the engines, you might as well take the striped down main
ship back. The exception of course would be if you had built catcher
facilities for faster follow on ships (interstellar shuttles?). In that
case it may or may no make more sence (and be quicker) to leave the ship
and take a fast shuttle home.
>On another topic, I'm still not happy with the stellar drive system. It
>still seems to me (after reading everyone's mails on the subject) that for
>it to obey Newton's Third Law, it depends on a particular distribution of
>charge around the drive that may (or may not, for all I know, I haven't
>looked at this thoroughly) be statistically very probable, but surely isn't
>an absolute requirement. So I ask again: does this concept put conservation
>of momentum on an equal footing as the laws of thermodynamics (which are
>essentially statistical, not absolute)? If it does, either it's very wrong,
>or I'll be very, very, unhappy.
>
>Sorry I haven't responded as fully as I'd like to other people's mails, but
>I am reading them and keeping fairly up to date.
I'm not sure what drive system your talking about? The three we are mainly
discusing now are:
The Explorer classes pure fusion rockets, with acceleration fuel laser
launched to it as it leaves Sol. (Top cruse speed 1/3rd C ?)
The Fuel/sail Class, where the deceleration fuel (Lithium-6) is spreed out
into a big microwave sail. The ship is accelerated out of our system via
microwaves. The contracts the sail, and burns it in fusion motors to
decelerate into the target starsystem.
MARS, which uses a microwave sail to accelerat away from earth, and then
uses the microwave beam to power deceleration rockets on entering the
system.
Also Argosey/tradwinds was discused before its advocate droped off line (or
sent us a copy of the web page for it!). It used microwave shuttle craft
between the stars, AFTER a predicesor ship set up the microwave transmitter
platforms in the target starsystem.
Kelly
P.S.
I moveing to a new city next week, so I may be offline for a while.
----------------------------------------------------------------------
Kelly Starks Phone: (219) 429-7066 Fax: (219) 429-6859
Sr. Systems Engineer Mail Stop: 10-39
Hughes defense Communications
1010 Production Road, Fort Wayne, IN 46808-4106
Email: kgstar@most.fw.hac.com
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