[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

RE: starship-design: Re: Perihelion Maneuver

On Monday, December 01, 1997 1:46 PM, Isaac Kuo [SMTP:kuo@bit.csc.lsu.edu] 
> Getting back to the point of this discussion, I was making the claim
> that 10%c was good enough to start launching flyby probes.

It is.

> Kelly disputed this, and among other things noted that you wouldn't
> launch such a thing if you only had to wait a couple decades to
> acheive better.


> I replied saying that you would if you didn't think those next
> couple decades would make enough of a difference.

Who can tell? I'm not a fortune teller.

> To put some perspective on this, consider a flyby mission to
> Alpha Centauri which are around 4 light years away.  A 10%c
> mission would get there in 40 years from the launch date.
> What if we wait 20 years?  _If_ those 20 years allow launching
> a 20%c probe, then it could get there as fast as the earlier
> mission possibility.
> Can you bet on doubling performance in just 20 years?  Maybe,
> maybe not.  There are plenty of examples of technology which
> haven't "doubled" their performance in as much time.

Well, actually I think you are both right. But it isn't just a matter of 
time. It is a matter of economics and above all, politics. Those sorts of 
arguments did not stop the Apollo program, which in hind sight if we had 
waited twenty years, we COULD have done much easier and quicker. (There are 
currently plans to return using an improved lander.) But we went ahead and 
did it anyway, at enormous cost, the brute force way. On the other hand, it 
is working exactly the other way around at the moment...

I have no problem with unmanned probes at 0.1 c, I have already stated on 
this forum that we need to start sending out unmanned probes at 0.03 c 
right now...so that we will be getting meaningful information back in fifty 
years or so.

What I don't believe in is human interstellar travel at those velocities. 
Hardware is cheap, life isn't. Unless we can push the 99% c envelope, we 
aren't going to be able to do it. Think about the average lifetime of some 
of the relatively mundane things you take for granted: socks, soap, 
notepaper, air filters, toilet bowl valves, doorknobs, light bulbs, ball 
bearings, switches, circuit boards, power supplies, etc. The MTBF on ALL of 
these items is currently way below 10 years.

I'm not denying that we CAN build these and other items on an interstellar 
ship to last this long. Just suggesting that we can't do it economically at 
this time and probably not in the foreseeable future. The alternative is to 
build in sufficient redundant capacity to support the extra mass of enough 
spares to build two or even three ships or reduce the round trip (you one 
way types out there just hold on and don't shoot me) travel time to less 
than the MTBF rate of the major systems at least. I use round trip as a 
safety margin in case the mission has to be aborted. Personally, I would 
prefer a four fold safety margin. (Now you can shoot me.)


                                                          (o o)
Where are they?
	- Enrico Fermi (Fermi's Paradox, sans preamble, 1943-50)