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

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

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

>>>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.

Yes, it may be more than 50% likely--but it's not certain.  It will
not absolutely certainly necessarily happen, which is what you wrote
(see "...it will fail...").

>>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.

Yes, assuming that.  But there is no _inherent_ reason why those
assumptions can never be satisfied.

Try and remember.  I am arguing that there is no inherent reason
why the crew of a 1-way mission starship would necessarily die
prematurely.

In case you don't know what "inherent" means--X is inherent in Y
if and only if the existence of Y logically implies X.

>>>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.

40 years?  You mean we're just going to go there and immediately
come back?  Now _that_ sounds like a sad waste.

But then again, you are also assuming twice the delta-v capability,
which could blow up the fuel costs a thousandfold or more.

>>>>>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.

I am talking about shelf life.  Reread the text I quoted.  It says,
"Many can't last a few years on the shelf".

>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.

Huh?  It's symmetric.  You can afford many of your braking engines
to fail during "storage"--you just need to start your deceleration
run earlier.  Naturally, you will start the run early enough so
that you have room to spare in case some engines fail during the
braking run.

For the return journey, OTOH, you can't just take as long as you
like.  You need to get back before your supplies run out, and
losing most of your engines could result in extending your
acceleration run several decades, assuming you somehow (how?)
refuel in system.

If you're not refueling in system, then you can afford only a
few rockets remaining for your return acceleration because of
the greatly reduced mass relaxing thrust requirements.

If you are refueling in system in a fuel/sail like starship,
then the mass during the deceleration run and the return
acceleration run are equivalent.  Losses in rockets in either
leg have the same effect on extending the mission time.

If you are refueling in system in a pure rocket starship, then
you can ill afford much loss in rockets because of the greatly
_increased_ mass compared to during the deceleration run.

Engine failures for the deceleration and return acceleration runs
will both extend the mission time.

>>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.)

Not really.  That's the way respiration works.

>>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.

Stainless steel isn't plentiful anywhere except maybe landfills.  It
has to be refined.  This is something where spares will have to be
brought, but these spares should last practically forever in
storage.

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

>The containers arn't likely to last for centuries!

In low pressure storage hermetically sealed in inert gas?  I don't
see why not.

>>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.

I haven't found this to be the case with the junk we have in my
robotics lab, a lot of which has sat unused for easily a decade.
They've been through a lot, too.  We have horrible humidity
problems which rusts _everything_ (all of my tools are in sad shape).
Some of this junk has come from junk heaps in even worse condition;
not even temperature controlled.

However, it amazes me how everything on all these circuit boards
still work.  Even the servos and stepper motors work.

>>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.

I don't think cryogenic storage is a practical option for most of
these things.  However, I think the problem with things degrading
is overstated.  Most of the things we make which fall apart on
their own accord are made so cheaply because there's no reason to
make them last.

>>>>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?

Not too long, but if I have 5 cars I can live with one of them
breaking down.  Remember, we're talking about the last one or two
survivors living in a habitat designed for at least a dozen.
That leaves a lot of room for redundancy.

>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.

Yes, that stuff takes a beating.  They're combat machines that have
to directly compete with their own kind.  This starship isn't some
combat machine, and it's going to take things nice and slow.

>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!

When there's a full crew, most everything in the ship (outside of
spares and the propulsion systems) is needed to keep the crew alive.

When there's half the crew left, there's double redundancy (assuming
spares have lasted at least this long).

When there's a quarter of the crew left, there's still double
redundancy even if half the ship has failed.

>>>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.

You won't be able to easily shade the photosphere.

>Yes you can shade out the photosphere from here, especially from space.

With your "synthetic aperture" telescope, you'd need a shade at least
the size of your synthetic aperture and it would have to be placed
in interstellar space between the target star and your telescope
system (it has to appear the same size as the target star).

>Or, you could use electronic imaging systems that can see the corona
>without blocking the photosphere.

Doesn't work with LBI.

>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.

Samples?  Samples of what?  Sure, there _might_ be planetoids around
Alpha Centauri.  But those can be visited directly with the ship,
if need be.  Big planets with significant gravitational fields would
present a problem, but there's no reason for us to currently expect
any such things orbiting there.  Binary star systems don't make for
too many stable orbits.

>>>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?

How is this question relevant?  No oceangoing ship ever built is even
remotely like the starships we're discussing.

>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.

The arctic is frankly a pretty boring place.  Alpha Centauri is pretty
exciting place.

>>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.

These people aren't being abandonned.

>>>>>>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.

WHAT!!!!???!!!?!!!??!???????!!!!!????

What you just wrote makes no sense at all.  You write "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 short you say that in order to keep the fuel ratio the same
you'd have to square the fuel ratio.

Please, Kelly, try and get a thought straight in your head before
sending it out onto the mailing list.

My math is precisely correct.  Your rebuttal isn't even coherent.

My claim is that the cruise velocities are halved, if you keep
the fuel ratio the same (and don't refuel).

>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.

A 20 year 1-way trip is what we're discussing.  The tacit assumption
is that a faster cruise speed is unavailable.  Assuming a straight
fusion rocket like a highly refined MagOrion, a delta-v limit of
.4c (which implies a cruise speed of .1c) is rather reasonable.
This assumes the fusion rocket comes within an order of magnitude
of the theoretical maximum.

Honestly, I'd be half tempted to go on a .1c 1-way trip (40 years).
I picked .2c since it was fast enough so that I would _jump_ at
the opportunity to go.

>>>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..

It's theoretically possible to share those components, but entirely
impractical once you look at the differences between the systems.
A cryogenic cooler designed to cool a small space to 5 degrees K
isn't going to be much like a refrigerator designed to cool a large
space to 5 degrees Fahrenheit.  The micrometer stepping motors for
slowly slewing a camera with minimum vibration are radically
different from a brushless DC motor designed to run an air pump.
About the only common electronics components would be assorted
resistors, capacitors, and microcontrollers, but you're going to
have thousands of these in storage.  The camera itself is designed
for focus at infinity, which is very different from anything you'd
want for medical imaging...

>>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).

Most people work at least 40 hours a week, and spend maybe 8 hours
a week just eating.  Not counting 8 hours a day for sleeping (which,
if anything, counts towards time used up surviving), that's 43% of
the time.

If you're a farmer, then you probably spend a lot more time working.

>The scientists on the crew would be tyhere to do science and
>support personel would keep the ship runing.

At least for the cruise leg, everyone on board would be there to
keep the ship running, but it should be easy going early on.  At
the target system, everyone on board should be there to "do
science".  Even someone completely unfamiliar with astronomy
at the beginning of the mission could learn as much about
astronomy as any PhD in 20 years.

>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.

As I stated before, the ship would be maintained with replacement
parts, rather than canabalizing components.
-- 
    _____     Isaac Kuo kuo@bit.csc.lsu.edu http://www.csc.lsu.edu/~kuo
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