Re: starship-design: Never ever lasting (was: What is safest?)

[Kelly St <KellySt@aol.com>]

Hi Tim.

In a message dated 1/10/98 1:14:39 PM, TLG.van.der.Linden@tip.nl wrote:

>Hi Kelly,
>
>>>Explorers of the past could haul large amounts too, however it hindered
>>>their progress, often too much to reach their goal.
>>>We may be able to carry enough to fix sophisticated equipment, but it
likely
>>>would increase ship weight (and crew) far beyond what would be the minimum
>>>for a succesful mission.
>>
>>Hard to answer without a very detailed analysis of the stuff we'ld be
carring,
>>and what we'ld need to keep runing.  Rough guess, longer the mission, the
less
>>that will be working.  However, if its something that is really needed,
we'ld
>>be forced to carry every support systems and suplies nessisary to assure we
>>could keep 'it' runing.
>
>Explorers of the past also had to take equipment to keep stuff running. Even
>the fact that we won't have access to raw materials while cruising has a
>quite good analog for the ocean travelers who didn't have much more than
>salt water as an external source.
>
>So indeed unless we're making a voyage that (in relative sense) is shorter
>than that of past explorers we'll need to carry repair and manufacturing
>equipment.

Or one shorter then the equipment life expectancy of the gear.  Their are some
advantages to 21st century equipment.  ;)  But I do agree some gear would be
nessisary.

>>>Well let me give a simple example then: Say you've two gears, in the past
>>>the quality of steel was rather poor, so they had to be big to have a
>>>reasonable lifetime. Now we can control the strength of steel much better
so
>>>can make these gears thinner and smaller and still have the same lifetime.
>>>I'd guess that if we used better steel and kept the same size as in the
>>>past, then we'd really increase lifetime.
>>>Indeed the much larger mass of such a gear may not be acceptable, but if it
>>>means that it will need much less maintenance, thus less crew, thus less
>>>food, thus a smaller habitat, then I wonder if it really is less
acceptable.
>>
>>Good trade off case.  Thats why I'm assuming the heavy industrial and
>>structural systems would be over built to allow a long enough service life.
>>But then gears and metal components are pretty long lived anyway.  Things
get
>>much more brittel with high precision systems, especialy things like
>>electronics that arn't normally designed to work for decades.
>
>Well, it often depends on how heavely their load is. Often failures are the
>result of overheating. For that matter Lee is right, the larger limits of
>military equipment make it more resilient (however we may not need the same
>(amount of) limits as the military).

Thermal cycling is an issue, but radiation and ionic flows get to be a problem
after a while.  Or simple corosion.

>>>Well, would todays technology combined with shortlived 2050 technology
>>>really be too crude for an interstellar exploration mission?
>>>(The 2050 equipment would be used until it failed and then the old and
>>>easier to repair technology would be used for further exploration.)
>>
>>Certainly the systems of most concern (computers, electronics, chemical
>>systems, etc..) would be unlikely to benifit from using 50 year old
versions.
>>Thou their probably is some way to make custom designs for some systems that
>>would be more durable then their standard 2050 counterpart.
>
>Of course there is a limit to how old technology you could use. Using tubes
>rather than silicon chips would be an example of being too extreme. However
>we now can make components that have much wider ranges of use that past
>components.
>The market reacts to that by either using these new limits or by keeping the
>old limits but reducing the "wasted" parts of the components. As a result
>the components will be used upto its limits, which likely would make them
>fail earlier than when they would be used well within the extremes.
>The benefit of using what you calling "old versions" and what I like to call
>"updated old versions" is that they last longer, which has the advantage of
>freeing manpower. Clearly we've to find a balance between computing power
>and repairtime.
>Even with short missions repairtime may be an issue, or should I say:
>Especially with short missions repairtime is an issue.
>
>>>I wasn't comparing with a computer core, but with a chemical propulsion
>>>system (although I could have been more explicit). I believe that according
>>>to Lee todays propulsion systems do have a MTBF long enough for a two-way
>>>mission.
>>>I wondered whether fusion rockets would have similar reliability, since
they
>>>likely are more complex than their chemical counterparts. And if our
rockets
>>>are pulsed, they may get much more structural stress than chemical rockets
>>>that as far as I know are continuous.
>>
>>Chemicals do need to deal with presure and vibration.  Hopefully fusion
>>systms would be less erratic, but if not the levels would need to be kept
>>similar or the vibration loads could shake the ship up badly.
>
>The pressure with fusion is much much higher than with chemical reaction.
>This is of course logical since it produces more power and higher exhuast
>velocities. My guess is that vibration too increases with power levels.
>Likely many small engines would push the structural demands less than a few
>big engines. Of course many small engines would be heavier and have more
>parts that could fail.

Since the "pressure" would be held by magnetic or electrical fields (assuming
it was held at all) it wouldn't have the same fategue load on the structure.

>>>Furthermore, while a fusion rocket may not need to turn the heat into
>>>electricity, it still is comparable with a fusion powerplant, since it too
>>>has to control the energy flow. It can't just be compared to a H-bomb,
which
>>>can freely expand in all directions and hoped to do as much damage as
>>possible.
>
>>>How do these [broken circuit boards] kill people rapidly? I'd expect some
>>>autonomous backup systems.
>>
>>Assuming the backup control signals didn't need to feed through the circut
>>that died.   ;)
>
>That's what I mean with "autonomous". They either don't need these cables
>(ie. they will react to a certain critical situation by themselves) or they
>have other cables to use as well.

Then the "autonomous" systems would need on-board systems to control them.
The failure of their circut board (or whatever) would crash that system.

>Timothy

Kelly