Re: Re: Re: starship-design: One way (again...)

[kuo@bit.csc.lsu.edu (Isaac Kuo)]

KellySt@aol.com wrote:
>In a message dated 12/6/97 12:08:42 PM, kuo@bit.csc.lsu.edu wrote:

>>>>>>> I disagree.  If I were offered the chance to fly on a 1 way mission
>>>>>>> to the Alpha Centauri systems at .2c (where I'd then spend the rest
>>>>>>> of my life), I for one would jump at it. I'm sure there are many
>>>>>>> others who'd be just as excited to do so.
>>>>It's not a suicide mission.  Suicide is purposefully dying prematurely.
>>>>With a couple hundred years of life support supplies, there's no
>>>>inherent reason why the crew would die prematurely.

>>>Actually even if you had a couple hundred years of suplies its unlikely the
>>>ship could stay functional for more then a few decades.

>>Even if that were the case, it's not _certain_ to fail.  At least
>>in American culture, this is a critical difference.  It's why we
>>were willing to enlist in 2 dozen bombing mission tours but never
>>even considered Kamikaze missions.

>It is statistically certain to fail.  I.E. if you are asking a
>systems to work longer then the average mean time to failure of
>its parts, it will fail without the replacement of those parts.

No it won't.  The average mean time is an average.  The part might
fail before, or it might fail later.  It could fail today.  It
could fail in a century.

But there's no inherent reason why we would ask the systems to
work longer than their average mean time to failure.  We can
bring spares to replace systems before they wear down dangerously.

>If the parts are primary structure (remember we'll be shaving
>weight margines to get the thing flying) you need major shipyard
>facilities.

I don't think we'll be shaving weight.  Even at .2c, the
thing has _got_ to last at least 20 years or the whole endeavor
wasn't worth a damn.

>>>Normal systems on that scale usually burn out after 40-50 years.
>>>Given the lack of replacement parts (stored parts also don't last
>>>forever),

>>They don't have to last forever.  They just have to last several
>>decades.

>Many can't last a few years on the shelf.

Like what?  The mission critical systems are:

1. The deceleration rocket systems.  These have to last 2 decades
   and there's little margin for spares.  However, after that
   they are no longer mission critical.

2. Oxygen recycling and CO2 scrubbers.  At least with current
   technology, they have a limited expected life span, but
   they are relatively lightwieght so many spares can be
   carried.  I'm not sure about their shelf life.

3. Water recycling.  I'm not sure about this part.

4. Food storage.  Irradiated canned food will easily last a couple
   hundred years.

5. Spare parts to repair hull problems.  Aluminum nuts, bolts,
   welding solder, and wrenches in vacuum storage practically last
   forever.  Arc welders also last practically forever since they're
   relatively simple devices easy to repair.

6. Spare solar panels and electrical components.  Last prctically
   forever in storage.

Really, the only mission critical items which I can see having
a problem with storage life are the recycling systems, which
might require somewhat chemically active components.

>>Why would the crew be wearing out?  We'd be getting old after a
>>while, but at that point it would be getting less and less
>>important to have the equipment last much longer.

>It has to keep working for the crew to keep living.  If it
>needs repair NOW, you can't just hope it woun't fail for
>a decade or two for the last crewman to die.  It almost
>certainly will fail in months to years.

Why would it almost certainly fail in months or years?  Exactly
what mission critical components are certain to fail, even with
triple redundancy?  (If there's only one or two crew left,
the life support systems will be well below capacity.)

>>The life expectancy would indeed be greatly reduced compared to
>>staying at home.  Besides the lack of medical facilities, there's
>>the issue of improvements in technology back at home.

>>The worst case possibility is if someone develops a "fountain of youth
>>pill", which can be manufactured on the ship.  Then the crew would
>>be guaranteed to die due to lack of supplies and/or ship failure.

>>But none of this is _guaranteed_.  So it's not a suicide mission.

>Your sending people out to to a decade or two of work (at most until the
>exploration gear become unservicable) and then sit in the deralic ship until
>they die.  

Why would the exploration gear become unservicable so quickly?
At the very least, we can expect handheld optical telescopes
to last hundreds of years.  Even that alone, at such a close
range, is enough to do serious scientific observations impossible
from the Solar System.  (Even if we figured out a way to make
astronomically huge optical telescopes able to equal their
resolution, we could not make fine corona observations since
we'd lack the ability to shade out the photosphere.)

>Thats effectivly a suicide mission.  I know a few folks in this group
>disagree, or don't care, but it still would meen no government on earth could
>get permision for such a mission.  I.E. your throwing away a crew for no
>critical reason.  Specifically your doing it to save money, which is really
>not going to sell.

By your logic, life is a suicide mission.  No matter what, you're
going to die somewhere.

Honestly, if I and others like me were sent on a _2_ way mission, We'd
be more than halfway tempted to disobey orders and simply stay.

That aside, the crew isn't thrown away.  They're simply taking the
"retirement plan" of their choice.

Anyway, doing something to save money has long been a strong selling
point.  That's why Mars pathfinder is this tiny little cart which
can't even send data up to orbit rather than the originally
envisionned self-sufficient rovers bristling with sensors.  It's
why Magellan has only the rather limited radar rather than radar,
IR, and optical, and it's why they trashed it into Venus's
atmosphere when it could have continued operating it for years.

>>>>As for 2-way vs. 1-way, I gave as an example a .2c cruise speed.
>>>>A 2-way mission at .1c would take at least 80 years to get there
>>>>and back!  With current human lifespans, that sounds to me a
>>>>hell of a lot worse than going one way in 20 years and then spending
>>>>the next half century or so basking in the warmth of alien suns.

>>>I don't follow the numbers.  First you state a .2c cruse speed vs a .1.  Why
>>>would a 2 way mission use a slower ship?

>>Because a 1 way mission can go at 1/2 delta-v of a rocket, while a
>>2 way mission can only go at 1/4 delta-v.  Alternatively, if beams
>>are used for the acceleration run (and the deceleration run of the
>>return journey), the 1 way mission can go at 100% delta-v, while
>>the 2 way mission can only go at 50% delta-v.

>The delta-v potential of a ship is related to the fuel mass ratios.  The fuel
>mass ratios are exponetial, not linear.  I.E. a ship that needs to accelerate
>and decelerat with onboard fuel (Li-6 fusion fuel) needs 400 times the fuel
>load of one that just needs to accelerat or decelerate not both.  Or for a 2
>way unrefueled mission it would need 400^3 as much fuel.

I didn't say this was using Li-6 fusion fuel.  In fact, I didn't
specify the method at all.  I did make the tacit assumption that
whatever it was, .2c was pretty much it's practical limit for
the 1 way mission.

In other words, the 1 way mission at .2c needs a mass ratio so
high that much higher isn't affordable.  Let's say the mass ratio
is 10,000.  In this case, it's obviously ridiculous to talk about
a 2 way mission at .2c (unrefueled).  That would require a mass
ratio of 100,000,000, and increase fuel costs by 10,000.

Therefore, if we want to talk about a 2 way mission, we've got to
keep the mass ratio about the same.  It would have to be a .1c
cruise velocity mission in order to keep the mass ratio about
the same.

>>Alpha Centauri includes a binary system.  It would indeed take decades
>>to study this system, which is very different from our own.  Being
>>on site means being able to rig up whatever equipment is needed to
>>make whatever observations are desired (a 2 way mission could leave
>>behind unmanned probes, but they'd have more limited capabilities and
>>wouldn't be able to react to scientific advances prompting new
>>observations as quickly).

>Without tools?  The systems will wear out and your light years from the
>manufacturing infastructure needed to keep all the stuff working.  As a wrough
>guess I'ld expect the transport shuttles and such to burn out in under 20
>years, and the main ship sensors and systems to be maybe good for 40.

Transport shuttles?  What's the point?  You'd want some unmanned
probes so you can get data from multiple points without wasting
months and fuel flitting around (e.g. an orbiting probe to measure
magnetic fields at various distances).

Most observations, however, could and would be made from the main
ship directly.  I'm not sure why you expect the ships sensors and
systems to wear out after only 40 years.

>Past
>that your need to strip those systems for pars to regulate life support,
>medical, etc..

Huh?  Keeping the systems alive will be a matter of repairing them
with spares.  There's not much commonality between a CO2 scrubber
and an IR camera.

>I.E. you not talking about spending your life studing the starsystem.  Most of
>the time your just going to be working to keep the last of the ship (and
>yourselves) alive.

Most of the time spent on a manned spaceship, at least currently, is
keeping yourself alive.  That's a given.  But really that's not so
different from life here on Earth (especially if you're a farmer).
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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