Mission to Alpha Centauri

I did a few calculations on what it might take to do a flyby of Alpha
Centauri, so, like a fool, I propose to rush in (to this newsgroup) where
angels fear to tread.

I read that Deuterium-Helium3 fusion would give an exhaust velocity of about
0.1 c if there was 100% efficient conversion of energy to thrust (neglecting
the fact that no one knows how to do this).

My thought was that a 2-stage intersteller rocket design could potentially
be used as follows (and if I've reinvented someone else's idea I apologise):

stage 1: stage 2 41 tons
stage 1 rocket 410 tons
DHe3 fuel 13500 tons

stage 2: Instrument probe 1 ton
2nd stage rocket 10 tons
DHe3 fuel 30 tons

I chose v/ve = 1 for convenience. Stage 1 would accelerate stage 2 to 0.1c,
stage 2 would accelerate the instrument probe to 0.2c which would pass alpha
centauri about 20 years after launch. The telemetry would arrive back about
24 years after launch. Instructions for detailed investigation would be
beamed back to stage 1 which could then manouver for further investigations
on it's flyby 40 years after launch.

Though the technology probably won't exist for decades or centuries, and
though the above masses for engines etc are sheer guesswork, I wondered what
"blue sky" interstellar vehicle proposals or mission outlines exist in the
research community that are more than just sceince fiction.

Also, has anyone considered the size and communications capability needed
for a low-relativistic payload, and the data that could be gained in a flyby
that would last about 24 hours (neglecting how the payload would be
accelerated).

In article ,
Roger Stokes wrote:
I read that Deuterium-Helium3 fusion would give an exhaust velocity of about
0.1 c if there was 100% efficient conversion of energy to thrust...
My thought was that a 2-stage intersteller rocket design could potentially
be used as follows...
Though the technology probably won't exist for decades or centuries, and
though the above masses for engines etc are sheer guesswork, I wondered what
"blue sky" interstellar vehicle proposals or mission outlines exist in the
research community that are more than just sceince fiction.

See, in particular, the BIS's "Project Daedalus" in the late 1970s, which
proposed a two-stage D-3He fusion rocket for a Barnard's Star flyby
mission. Some of the details of their design probably would not work, in
hindsight, but they explored the issues in considerable depth.

(Unfortunately, the Daedalus report is not exactly easy to find unless you
have a good library handy.)

There has been quite a bit of speculation in similar veins since.

Also, has anyone considered the size and communications capability needed
for a low-relativistic payload, and the data that could be gained in a flyby
that would last about 24 hours (neglecting how the payload would be
accelerated).

Yes. :-)

Size depends on what you want to do, but you'd want something fairly
substantial. If memory serves -- my copy of the report isn't handy at the
moment -- Daedalus specified a 100t payload, which included a variety of
sub-spacecraft.

Communications is not a big problem, given large dishes and ample power,
and given that data can trickle back to Earth over a period of several
years. (The probe's own decision-making has to be entirely autonomous
anyway, since by the time it's close enough to get new data, there is no
time to consult Earth about how to proceed.)

And the fast flyby is definitely a problem, but probably a manageable one.
This was one of the reasons why Daedalus had sub-probes, so that it could
do close flybys of all planets in the target system simultaneously.
--
MOST launched 1015 EDT 30 June, separated 1046, | Henry Spencer
first ground-station pass 1651, all nominal! |

"Roger Stokes" writes:

I did a few calculations on what it might take to do a flyby of Alpha
Centauri, so, like a fool, I propose to rush in (to this newsgroup) where
angels fear to tread.

I read that Deuterium-Helium3 fusion would give an exhaust velocity of about
0.1 c if there was 100% efficient conversion of energy to thrust (neglecting
the fact that no one knows how to do this).

My thought was that a 2-stage intersteller rocket design could potentially
be used as follows (and if I've reinvented someone else's idea I apologise):
[...rest deleted...]

You've re-invented the British Interplanetary Society's "Project Daedalus,"
modulo your choice of target star (the BIS chose Barnard's Star, since back
then it was suspected to have at least one planet). See:

http://www.angelfire.com/on2/daviddarling/Daedalus.htm
http://www.geocities.com/TelevisionCity/2049/DAEDALUS.HTM
http://members.nova.org/~sol/solcom/stars/barnards.htm

-- Gordon D. Pusch

perl -e '$_ = \n"; s/NO\.//; s/SPAM\.//; print;'

In article ,
Roger Stokes wrote:
I did a few calculations on what it might take to do a flyby of Alpha
Centauri [[...]]

I read that Deuterium-Helium3 fusion would give an exhaust velocity of about
0.1 c if there was 100% efficient conversion of energy to thrust (neglecting
the fact that no one knows how to do this).

My thought was that a 2-stage intersteller rocket design could potentially
be used as follows (and if I've reinvented someone else's idea I apologise):
[[...]]

If you can find a copy,

A. R. Martin, editor,
"Project Daedalus: The Final Report on the BIS Starship Study"
published as a supplement to JBIS, 1978
no ISBN

gives 192 pages of detailed information about a similar study done
in the early-to-mid 1970s. I believe this JBIS issue is long out
of print, but a library with back files of JBIS might have a copy.

I don't know of any online copy. It would be nice if someone who
has a paper copy could get permission from the copyright holders,
then scan it and put it online...

Daedalus was an unmanned undecelerated flyby probe to Barnard's Star
(distance about 6 light years or so). The design goal was to complete
the mission (including data return) within the lifetime of the youngest
engineers working on the project, and to use minimal extrapolations
from present-day technology. They originally hoped for a 40 year
flight time at 0.15c, but their final design went to 50 years at 0.12c.
They used a 2-stage D-He3-pellet nuclear-fusion rocket, to be launched
from solar orbit out beyond Jupiter. I don't recall the launch mass or
mass ratio, but as I recall the final payload mass was 50 tonnes.



There was supposedly also some info about a NASA study on interstellar
flight concepts in the Feb 1999 issue of Scientific American. Searching
http://www.sciam.com/issue.cfm?issueDate=Feb-99
might turn up some tidbits.

ciao,

--
-- "Jonathan Thornburg (remove -animal to reply)"
Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
Golm, Germany, "Old Europe" http://www.aei.mpg.de/~jthorn/home.html
"Washing one's hands of the conflict between the powerful and the
powerless means to side with the powerful, not to be neutral."
-- quote by Freire / poster by Oxfam

Why do you need staging in space?

You need staging for ground-LEO because you need lots of thrust to get
going, and the engines to produce that thrust, as well as the tanks to
withstand it and accelerate the propellants, are all heavy and useless
once you've got your gravity losses down and you want to dump them as
soon as possible thereafter. But, short of having REALLY big engines,
I don't think you're going to do much about your (solar) gravity losses
from LEO-alpha centauri, nor do I think you need to.

So how about this:
DHe3 fuel 13500 tons
rocket 10 tons
probe 1 ton

Sure, the acceleration is miserable. Yes, you get some gravity losses
because most of your thrusting is done well away from the Sun, rather
than doing the plunge to Mercury and blasting away there. But you only
have one set of engines instead of two, and so you get _better_ mass
ratio.

For a "tank", I'd use some sort of thin aluminized plastic film that
can keep the DHe cold and contain sublimation. As the DHe evaporates,
the gas is routed back to the engines where it's either burned or
refrigerated. Micrometeoroid impacts and the resulting leaks are a
problem. Distance and thin films are the solution.

And finally, with an exhaust velocity of .1c, why have such a huge
mass ratio in the first place? If you want to get to .2c, you just
need a mass ratio of 7.5. Was the .1c Ve a typo?

Iain McClatchie wrote:

Why do you need staging in space?

The same reason you would need staging anywhere; it's a method of
achieving the necessary mass ratio.

Jim Davis

Hello
I have two questions in this regard:
1. How large is the danger of the spacecraft being pulverized by space-
debris at these speeds? I would think that at such high speeds even smallest
debris (even if it is only a few molecules in size, or even some clouds of
gas) would be very dangerous, right?
2. If it is going at high speeds like these, does Einsteins relativity
affect the flight- time? I mean if the probe is on its way for so many years
at such high speeds. How much longer would that make the journey appear to
us on earth? Or the other way round, how much shorter would it appear on the
spacecraft? Or wouldnt there be any effect at all?
CU
Elmar


"Roger Stokes" schrieb im Newsbeitrag
...
I did a few calculations on what it might take to do a flyby of Alpha
Centauri, so, like a fool, I propose to rush in (to this newsgroup) where
angels fear to tread.

I read that Deuterium-Helium3 fusion would give an exhaust velocity of
about
0.1 c if there was 100% efficient conversion of energy to thrust
(neglecting
the fact that no one knows how to do this).

My thought was that a 2-stage intersteller rocket design could potentially
be used as follows (and if I've reinvented someone else's idea I
apologise):

stage 1: stage 2 41 tons
stage 1 rocket 410 tons
DHe3 fuel 13500 tons

stage 2: Instrument probe 1 ton
2nd stage rocket 10 tons
DHe3 fuel 30 tons

I chose v/ve = 1 for convenience. Stage 1 would accelerate stage 2 to
0.1c,
stage 2 would accelerate the instrument probe to 0.2c which would pass
alpha
centauri about 20 years after launch. The telemetry would arrive back
about
24 years after launch. Instructions for detailed investigation would be
beamed back to stage 1 which could then manouver for further
investigations
on it's flyby 40 years after launch.

Though the technology probably won't exist for decades or centuries, and
though the above masses for engines etc are sheer guesswork, I wondered
what
"blue sky" interstellar vehicle proposals or mission outlines exist in the
research community that are more than just sceince fiction.

Also, has anyone considered the size and communications capability needed
for a low-relativistic payload, and the data that could be gained in a
flyby
that would last about 24 hours (neglecting how the payload would be
accelerated).

"Iain McClatchie" wrote in message
om...
And finally, with an exhaust velocity of .1c, why have such a huge
mass ratio in the first place? If you want to get to .2c, you just
need a mass ratio of 7.5. Was the .1c Ve a typo?

My rocket equation physics is undergraduate level. If I recall, the 0.1c ve
is actually 0.09c, and I posted late at night after three beers so
(moderator permitting) if you believe that 0.2c per stage is achievable I
would be very interested to hear the rationale. :-)

starting beer #3 now...

--Roger

"Roger Stokes" wrote:
Also, has anyone considered the size and communications capability needed
for a low-relativistic payload, and the data that could be gained in a flyby
that would last about 24 hours (neglecting how the payload would be
accelerated).

The flyby would necessarily last days, effectively, regardless
of the speed. Communications would be fairly straightforward
at those distances (up to ~5 ly). What you want is big mirrors
and lasers. We can just about make 6m mirror space-based
telescopes now, and there's quite a lot to suggest that 10 or
20m shouldn't be too much of a hassle. Then, you hook up your
high power lasers and/or sensitive photometers to your mirror
(for transmit or receive). You should be able to get decent
data rates with fairly modest technology that way. Up to 5 ly,
kilobit/s rates would be easy, megabit/s and gigabit/s would be
moderately challenging but not terribly so. Your probe is
going to need a big telescope anyway, so it might as well do
double duty. The real difficulty would probably be science
collection planning. The only good way to do that is to create
a collection plan (i.e. observation plan) based off the most
recent science data, but with a two-way comm-lag of up to
almost a decade, that's a non-starter, so the craft is going to
need some quite impressive smarts. As for observations, the
obvious, and necessary, choice is high-resolution imagery. The
target system is certain to have many targets spread around it
which are worthy of interest (planets and whatnot) and the
probe is certainly not going to closely flyby *all* of them, so
it needs to observe most of them from several AU away, so you
want to bring as big a telescope as you can (luckily, you've
already got one! how convenient). Also, you'll want to stretch
out the science collection as much as possible, so that you can
collect useful data for the longest duration, that means you
need to expand the start and stop points out as far as
possible, and that in turn means you need to be able to collect
good data at as far a distance away as possible. Reasonably,
the flyby encounter is going to occur over years and transition
through different data collection modes, from low-rate data
collection out far away, to jumpin' all over the place working
as fast as you can at closest approach, back to low-rate data
collection again, with intermediate steps in between
appropriate to the distance from the system.

"Iain McClatchie" wrote in message
om...

Why do you need staging in space?
Sure, the acceleration is miserable.

The beer wore off :-)

Very low acceleration would prolong trip time so I assumed a certain minimum
acceleration of (say) 0.1g would be needed to actually be going at 0.2c for
most of the trip. This would require rigid fuel tanks, and increase the mass
of the vehicle.

What values of space fuel tank mass/volume ratio are achievable today -
depends on acceleration, and type and volume of fuel I know but any figures?