On Wed, 06 Feb 2008 22:42:16 -0500, Phillip Thorne <pethorne@[EMAIL PROTECTED]
>
wrote:
>On 2 Feb 2008, jdnicoll@[EMAIL PROTECTED]
(James Nicoll) wrote:
>> In reality, if someone dumped an FTL drive like that in our
>>laps, one that offers no quick solution to getting around in stellar
>>systems, where the jump point isn't conveniently located, how long do
>>you think it would take before someone got around to sending a probe
>>out to the jump point?
>I'm replying here because I've got some new points, and the rest of
>the discussion has diverged into heated animosity.
>1. ISTM that space probes take years to develop because of the
>necessity they be low-mass: there's little margin for structural
>redundancy, so most everything has to be custom-made. With a bigger
>mass budget, you could dispense with a lot of the optimization and
>testing.
Except that nobody has any experience actually doing things that
way. Which means the first group to try, will make lots of mistakes,
which will slow them down.
In the long run, this is something we will want to know how to do.
But it's not the way to get your *first* bird up, fast. Well, not
if you also want it to actually work.
For that, you really do want to do things about the way we do them
now. Not just because it is what we know best, but because the way
we do things now is a relic of the Space Race - where the one and
only goal was to get the first working bird up, fast. That's caused
us no end of problems when the goals changed and the techniques didn't,
but here we're imagining a scenario right out of the old Space Race.
>2. Can you solve this problem by throwing more money at it? Maybe.
>The SpaceX (www.spacex.com) Falcon 9 is rated for 5,000 kg payload to
>LEO when launched from Kwajalein Atoll (9°N), at a cost of $55M. The
>Falcon 9 Heavy can do 11,500 kg, at $90M.
>Of course, the Falcon 9 hasn't been flight-tested yet (it won't before
>2008Q4), and neither of the Falcon 1's reached space, but its rapid
>development (since ~2005) bodes well. For this hypothetical scenario,
>anyway.
Actually, the whole Falcon program is a perfect example of people
trying to do things in a new and better way and suffering years of
delay due to the inevitable mistakes, er, learning experiences. In
the long run, this will be worth doing.
But here and now, even a Falcon 9 won't do anything an Atlas V won't
do just as well. Except cost less and take longer. If you're in a
hurry and you're throwing money at the project, you want the Atlas.
>For comparison, the Cassini-Huygens Saturn probe massed 5,820 kg, of
>which 3,100 kg was propellant.
Bear in mind, that was 5,820 kg launched to Earth escape with roughly
5.5 km/s of hyperbolic excess velocity, whereas the payloads you are
quoting for the Falcon are for low Earth orbit.
To get from LEO to 5.5 km/s past escape, you need a rather substantial
propulsion module - a classic Centaur, roughly 18 tons and 10 meters
long, would about do it.
To get 5,820 kg plus a Centaur into LEO, you need a Delta IV Heavy,
or maybe a Proton or an Ariane 5, or one of the viewgraph launchers
that doesn't actually exist.
>3. And why do we have to fit the entire probe and its upper rocket
>stage in a single launch vehicle? If it's really important to verify
>jump point, why not assemble the craft in orbit, from several
>launches? The development of automated rendezvous systems in the ESA
>_Jules Verne_ craft (to resupply the ISS), and fuel transfer with the
>USAF's recent automated orbital resupply test, demonstrate that
>capability.
Because _Jules Verne_ is years behind schedule, and while _Orbital
Express_ was reasonably successful in the end, DART was a complete
failure. This is another one of those things that, while it will
certainly be useful in the long run, we don't really know how to
do yet and so don't want to tie a crash program to.
Nor do we need to; a single heavy launcher will suffice for a basic
Saturn orbiter. There are problems with that approach, but we know
what those problems are, which makes it almost certainly faster than
dealing with the unknown problems of a new approach.
--
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