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

[Kelly St <KellySt@aol.com>]

In a message dated 12/9/97 12:55:55 PM, kuo@bit.csc.lsu.edu wrote:

>>>>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.

The mean unrepaired service life of a systems is less then the mtbf of any of
its parts.  The higher percentage of parts with MTBF less then the desired
service life, the higher liklyhood failure before then.


>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.

Assuming the spare can last that long on the shelf, and you can carry that
many extras.


>>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.

True I was suggesting a service life goal for a 2 way ship at 40 years, which
seems a streach, but probably doable.  But adding a few decades on the end
would significantly cut you odds.


>>>>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.

Given they rockets are only need to decel into the system and later burn out
of it back to Sol.  They reallu only need to work for a couple months to
years, and be storable in hard vac for a couple decades.

Actually since you need all engines working to brake you into the system, but
can take as long as you like to burn you way back up to speed on the way back,
the return boost can afford for most of the engines to fail or be dumped.


>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.

Scrubbers wouldn't work, but we could synthasis the ox out of water in the
air.  (Odd bit of matabolism I found.  The ox we breathing winds up in the
water we excreat, the ox in the CO2 comes from other sources.  weird.)


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

Boil it to steam and condese it out.  Replace burned out reaction chambers
every few years(?).  Foutunately stainless steel is plantifull in asteroids.

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

The containers arn't likely to last for centuries!


>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.

Electrical and electronic systems tend to degrade to junk after a few years on
the shelf.  They actually last longer ion use then stored in many cases.


>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.

Anything that will chemically react with its storage environment, or itself,
will degrade in storage.  Thats why everything from drugs to batteries has an
experation date on it.  As Lee mentioned even plastics on the shelf break
down.  Circutry components (like the inside of an IC chip) chemically react to
consume themselves on the shelf.  Storing things at cryo in nitrogen helps,
but the chill down can destroy the internal structure of material or
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.)

How many months with out service would you expect your car to keep runing
after the check engine light comes on?  Why do you think ship and subs keep
such large maintenece crews, and airplaces often need days of support crew
time for every hour they fly.  This stuff takes a beating.  And if any of the
parts cut out, the system starts to fail.  If you don't fix things they stop
working, and as the crew gets smaller, their are fewer of them to fix all the
stuff they need to stay alive.  I.E. most everything in the ship!


>>>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.)

Actually telescopes arn't worth sending, you can see the systems perfectly
well from here with a big enough scope.  FAR easier to build a scope here with
a synthetic apiture a few light secounds across, rather then keep a 1 meter
scope working a few light years from home.

Yes you can shade out the photosphere from here, especially from space.  Or,
you could use electronic imaging systems that can see the corona without
blocking the photosphere.

No observation studies (assuming you can keep the scopes working without
needing to strip their aiming and stabalization systems, or cooling, or the
rest), arn't going to cut it.  You have to get direct data from drop probes or
samples, preferable bringing some samples home where the better lab gear is.

>
>>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.

How many ships crew, deside to beach their ship and hope they die before it
does?  Or how many arctic explorers would agree to go knowing they'ld live out
their days in those cramped tents or shacks in the ice.  Nothing to do but try
to stay alive a few days longer.


>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.

People don't mind you using expendable equipment and abandoning it when your
done, but they get very upset when you do the same to personel.


>>>>>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.

You math doesn't add up.  If you were keeping the fuel ratio the same and
assuming an unrefulled round trip you'ld have to square the fuel ration not
double it.

In anyevent no one waas suggesting a unrefueled return.

Also you might note my Explorer system has over a .3 c cruse speed, and the
fuel sail has over a .4c cruse speed.  .1 or .2c speeds would require flight
times of 20-50 years each way.  Totally unfeasable.

>>>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.

Coverd elsewhere by me and others.


>>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.

The IR cameras cryo cooler, aiming motors, and electronics could be used in
everything from food processors to refrigeration systems, the images might be
needed for medical, etc..


>>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).

Very little of the time spent in current life is related to survival.
Probably less then 1/5-1/20th (depending on how you figure it).  The
scientists on the crew would be tyhere to do science and support personel
would keep the ship runing.  But as the ship deteriorated it would require
exponential growth in sevicing, and the science gear, crew, and systems would
be droped, or canabalized to service the rest.


>-- 
>    _____     Isaac Kuo

Kelly