Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v16_2/v16no271.txt

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Date: Thu,  4 Mar 93 06:50:30
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #271
To: Space Digest Readers
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Space Digest                Thu,  4 Mar 93       Volume 16 : Issue 271

Today's Topics:
                   Alternate Space Station Designs
                   Alternative space station design
                   Alternative space station power
                          Blaming the victim
                           Bullets in Space
                       Design Process and Fred
                          Followon missions
                 I have a dream! People into Space..
                                 KIDS
                   Low Earth Orbit in a Mars Blimp?
                           Mars exploration
      One Pu release (was Re: Alternative space station design)
     Plutonium terror (was Re: Alternative space station design)
            Sexy batteries (was Re: Battery help needed!)
                    Spaceflight for under $1,000?
                         Stupid Fred Question

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Date: 3 Mar 93 20:04:56 GMT
From: Edward Dansavage Wright <[e-mail]>
Subject: Alternate Space Station Designs
Newsgroups: sci.space

Information received to date....

I would like to thank the various researchers who have responded
to my request for information concerning alternate designs for
the space station.

References, sites and author names I have obtained...

**Oliver Harwood
"Safe Access to Pressurized Haibitable Spaces"
Journal of the British Interplanetary Society
v 39, n8 August 1986 p. 331-338

**Lawrence Livermore National Labs (LLNL)

**Dr. Normal LaFave....
Redesign work on the SSF (posted to this newsgroup)


I have not gotten copies of much of this information as yet.
I still need to contact NASA and LLNL.

Again, my thanks.

As always,
Ed Wright
Department of Engineering Mechanics and Astronautics
University of Wisconsin at Madison

------------------------------

Date: 3 Mar 93 19:45:42 GMT
From: "Dr. Norman J. LaFave" <[e-mail]>
Subject: Alternative space station design
Newsgroups: sci.space

In article <[e-mail]> Kieran A. Carroll,
[e-mail] writes:
> >* Alternative modular structures (NO TRUSS):
> >  ...both of these designs are free of the troublesome flexibility
inherent
> >  in the truss ...
> >
> This is a curious misapprehension---the truss is there to
> separate the solar arrays, to avoid problems like shadowing
> of payloads that want to see space, and plume impingement.

As someone who does plume analysis, I can state that the problem
is still there despite the distance. Furthermore, the flexible
dynamics of the solar arrays are worsened by the truss through
dynamic coupling.

> Since the solar arrays are large, the separation distance
> also needs to be large. The truss itself is designed to
> *minimize* flexible effects; the benefit of using a truss
> rather than (say) a bunch of modules strung together (a la Mir)
> is that a truss can have a much larger bending stiffness for
> a given amount of structural mass.

True. However, the operable word here is mass. I contend that, although
cans weigh more, the extra pressurized space as well as
increased stiffness make them far better.
The weight arguement, in my way of thinking, is an arguement FOR
heavy lift capability, not FOR the truss.

> For example, most of
> the hundred lowest-frequency structural vibration modes of the
> current baseline SSF design are solar-array modes, that involve
> little bending or twisting of the truss.

However, do a NASTRAN analysis of the station with a less-flexible
truss and the stresses on the solar arrays are lessened due to less
structural coupling.

>
> Of course, your next suggested design feature does away
> with the solar arrays, eliminating one of the main reasons
> for wanting the space station to be physically large...
> >
> >* Primary power source---NOT solar arrays!
> >
> >  RTG pallet---known technology...not subject to shadowing problems...
> >  eliminates primary plume impingement problems....eliminates largest
> >  flexibility problems, both control and structural....proven
> >  safety.
> >
> RTGs are a reletively mass-inefficient way to generate power,
> I seem to remember. They also have limited lifetimes, so they'd
> probably have to be replaced every few years. Of course, they'd
> eliminate the need for batteries, which also need frequent
> replacing,

That was our thought exactly.

> and which also are very massive, so on the basis
> of total up-mass they might be a net win. Their main problem
> is the issue of safety, both real and perceived. Remembering
> Skylab, *many* people would undoubtedly be nervous about having
> a large amount (probably several tonnes) of plutonium flying
> overhead every day. Come to think of it, *I* would probably
> be nervous about this, and I'm a fairly pro-nuclear person.

The U.S.has had 6 RTG re-entries with not one leak. The USSR
had one rupture in Canada, but it was found to have insufficient
shielding. The safety issue is one of perception.

>
> >  Secondary source: Thermal gradient power generation---This is an idea
> >  we are toying with. The idea is simple.
> >  Use the huge temperature gradients
> >  that can be generated between sunlit and shadowed plates to generate
> >  power. This is much like the concept which was studied to generate
power
> >  using the thermal gradient between the ocean's surface and the ocean
> >  depths.
> >
> What's the difference between this concept and the Solar Dynamic
> power generation system that was eliminated during the last design
> scrub? The latter concept simply used mirrors to heat up a working
> fluid, which was passed through (I think) a Stirling (Sterling?) engine
> to produce mechanical power, which was then put through an alternator
> to produce electrical power; the working fluid was then cooled using
> radiators looking at deep space. Of course, you could do the same thing
> using thermocouples, but the power conversion efficiency would be much
> lower, I think.

This was an attempt at a lower cost solar dynamic system. Imagine a plate
built as a three-layered sandwich---two heat conductors with a good
thermal insulator between them. Point one conductor at the sun (the other
one is then in shadow) and run a thermocouple between the conducting
plates. Of course this is less efficient than the old solar dynamic system
concept, but it is much simpler and the efficiency would probably still
be much better than the photovoltaic cells.

I should also point out that we are proposing these two power sources
as a package, not as alternatives. I'm sorry I did not make that clear.

>
> BTW, this post isn't meant to be negative, but merely critical
> (in the constructive sense---when a new design concept is proposed,
> try to define its constraints, so that you can get a handle on
> whether its possible for them all to be satisfied at once). It
> sure is fun to re-visit the conceptual design stage for space station;
> that's the stage when the sky is the limit, before the the inevitable
> messy trade-offs force a beautifully simple concept to be bent out
> of shape. Reminds me of the good old days of '82 thru '86...
> --

We hope that this becomes more than a fun exercise.   :-)

Thanks for the comments.

Norman

Dr. Norman J. LaFave
Senior Engineer
Lockheed Engineering and Sciences Company




When the going gets weird, the weird turn pro
                               Hunter Thompson

------------------------------

Date: 3 Mar 93 21:51:27 GMT
From: Henry Spencer <[e-mail]>
Subject: Alternative space station power
Newsgroups: sci.space

In article <[e-mail]> Dr. Norman J. LaFave <[e-mail]> writes:
>This was an attempt at a lower cost solar dynamic system. Imagine a plate
>built as a three-layered sandwich---two heat conductors with a good
>thermal insulator between them. Point one conductor at the sun (the other
>one is then in shadow) and run a thermocouple between the conducting
>plates. Of course this is less efficient than the old solar dynamic system
>concept, but it is much simpler and the efficiency would probably still
>be much better than the photovoltaic cells.

I doubt it very much.  Have you *looked* at thermocouple efficiencies?
They are, roughly speaking, terrible... even by photovoltaic standards.
Why do you think they haven't replaced photovoltaics already?  There
are plenty of commercial satellite builders who would kill for better
power systems.

The old solar-dynamic concept, while it was a bit costly and involved
a moving part (yes, one moving part, not counting valves), had the huge
advantage that it could use thermal storage to eliminate the battery
pack... thus considerably reducing operating costs by eliminating
battery-replacement resupply missions.  (Not to mention the savings
in reboost fuel from smaller array drag.)
--
C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology
effect since OS/360.                    |  [e-mail]  utzoo!henry

------------------------------

Date: Wed, 3 Mar 1993 16:33:03 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Blaming the victim
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Tom) writes:


>I said;
>>>No no.  You've got it wrong.  The victims are completely innocent.

>Fred replied;
>>Well, I'll agree with that.  That's why I think it's a stupid position
>>to say that if a directory is left open that it's ok to read it,
>>notices to the contrary notwithstanding.

>But, if it's left open, it's possible to read it.  Sure, it's not the
>fault of the person who left it open, if it's read, but, that person
>would probably like a solution to her/is problem, rather than just
>assurances of thier innocence.

And if you leave your door unlocked, it's possible to go in and carry
off all your stuff.  that doesn't make it ok for someone to do so.

>All the blaming and pointing and talking of 'stupid positions' isn't
>nearly as effective as, say, locking the directory.

>>>They are merely the ones who got raped or burglarized.

>>>If you can't see the difference between 'watching out for yourself'
>>>and 'taking the blame', well, no wonder you feel angry.

>>Gee, thanks for the mind reading, Tommy.  What makes you think I feel
>>angry?  Would you like to tell me what emotion I'm feeling now, too,
>>since you must think you know better than I do?

>Sorry about that Fred, I was merely applying a reasonable guess for
>intonation, based on the context of the post.  I apologize if I
>got it wrong.  I could be wrong again, but since you took issue with
>my guess, I imagine I was pretty close the first time, and probably
>close again, when I guess that you now feel snitty, affronted, perhaps
>flustered.

No, I simply feel that you're a juvenile with an overactive
imagination, to be able to "imagine" all those things that are
contrary to reality and then further "imagine" a bunch of reasons why
your imagination is right and reality is wrong.

>The point is, making reference to a possible solution, and the fact
>that the victim may have not been a victim, if that solution was
>used, is not the same as blaming the victim.  One is true, the other
>is not.  Many people mistake the one for the other, and they feel
>angry when others address one issue without being clear in the fact
>that they aren't addressing the other.

Perhaps this is because the tone usually taken by those "making
reference to a possible solution" is that of lecturing that if the
'victim' had taken proper precautions in the first place they would
not have been a 'victim'.  And as for "they feel angry", I'm curious
where you get this idea?  Must someone "feel angry" to disagree with
you?

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

------------------------------

Date: Wed, 3 Mar 1993 15:58:27 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Bullets in Space
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Ryan Potts) writes:

>On Feb 28 17:16, Frank Crary of wrote:
> > (By the way, the rifleman wouldn't fly backwards under the
> > recoil, as is often thought: The linear momentum transfer is
> > quite small and the shooter's final velocity would be under 1
> > m/s (3.6 km/hr). The angular momentum, however, is very
> > significant: If he fired the rifle from the shoulder, he'd
> > wind up spinning at something like 50 rpm...)
>But isn't o2 needed to aid in the combustion of the gunpowder in the round? :)

Check the composition of gunpowder.  You'll find that it includes its
own oxidizer, like any other rocket fuel.  "It's in there."

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

------------------------------

Date: Wed, 3 Mar 1993 17:31:58 GMT
From: "Brian A.Laxson" <[e-mail]>
Subject: Design Process and Fred
Newsgroups: sci.space

Okay, Politcs aside, Fred needs to go through a design process.  This is
just a short description of a design process which make scrapa and
redesing unnecessary:

    1 - Problem Defintion:  Figure out what you are looking for

    2 - Needs Analysis:  Re-examine what you really need

    3 - Generate Criteria:  Decide how you will rate the different
proposals.

    4 - Solution Generation:  Generate MANY MANY ideas on how to do
things.  Through in silly ideas, conservative ideas, and useless ideas.
Don't put down any  ideas yet as there are useful things to learn, and new
approaches are important.

    5 - Select A Design

    6 - Impliemnt a Prototype:  Each time you do this add more and
more capabilty

    7 - Restart at 1 with the info you have


    This way you cycle through a process that is always making
progress.  You also learn more along the way.

    Scrap + Redesign does occur every once and a while but not on the
order of magnitude of Fred's shortening to Barney.

    This is the sort of thing that gets assumed not explained.  If you
think it's useful pass it on.  If you want more detailed info I can track
some down.


Brian Laxson

------------------------------

Date: Wed, 3 Mar 1993 17:41:43 GMT
From: Henry Spencer <[e-mail]>
Subject: Followon missions
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Matthew DeLuca) writes:
>>>... For myself, I'd like to see what Galileo discovers before
>>>trying to design a followup to it; there's no telling what we may want...
>
>>Nonsense; there is considerable telling what we may want.
>
>I suspect we have a semantic difference here.  A 'followup' mission implies
>that it is building on what was learned from previous missions.  What you are
>suggesting are missions that happen to follow in time.  Certainly a good idea,
>but not exactly the same.

You are assuming that a 'followup' mission must have its *hardware* custom
built to reflect what the previous mission found.  But in fact, you could
often do a very effective followup simply by adjusting mission plans, which
can typically be done after launch or even after arrival.

I'll say it again:  while we cannot predict *exactly* what hardware and
overall mission plan would be optimal for a followup mission, we usually
have a pretty good idea of how to do a pretty good job.  There would be
times when folks would say "argh, if only we'd put an XYZ spectrometer
on the followup!"... but this sort of thing can happen anyway, given how
long the data analysis from a major mission can take.

The Landsat people get upset when they talk about a "data gap" of a year.
When you don't even start lining up funding for a followup until after
the precursor mission is over, data gaps of 10-15 years are hardly a
surprise.  As I said:  this is not a space *program*, it's just a random
grab-bag of missions.
--
C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology
effect since OS/360.                    |  [e-mail]  utzoo!henry

------------------------------

Date: 3 Mar 93 18:30:59 GMT
From: Gary Coffman <ke4zv!gary>
Subject: I have a dream! People into Space..
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>
>
>    International involvement would also help get people into space.
>Many conutries can accomplish more together, just like more people can.
>The international aspect would make it likely to accomplish some important
>goals even if the main objective fails, particularly increase involvement
>of people in space.

Unfortunately, international involvement is like the UN. The only things
that get done are those that everyone agrees on. The larger the group,
the harder it is to reach consensus on any objective or procedure. NASA
already suffers from group think. What we need is a small core group
of Germans who have a tightly focused mission objective, a hard deadline,
and a relatively free hand and cubic money to accomplish it.

Gary

Gary
--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

------------------------------

Date: Wed, 3 Mar 1993 18:05:15 GMT
From: Timothy Kimball <[e-mail]>
Subject: KIDS
Newsgroups: sci.space

Bob McGwier ([e-mail]) wrote:
: I really had it brought home to me yesterday how far in the past the moon
: program is to today's kids...

There was another example in the Sunday comics.
In "Funky Winkerbean", Jan 17, 1993, some kids are touring
the National Air and Space Museum.  Standing in front
of an Apollo exhibit, one of the kids says,

    "Which planet was it they landed on again?"

The comic's writer, Tom Batiuk, has a note alongside:

    "I actually heard someone say this when I was there.
     I did not make this one up!"

--

/* tdk -- Opinions are mine, not my employer's. */

------------------------------

Date: Wed, 3 Mar 1993 17:45:49 GMT
From: Henry Spencer <[e-mail]>
Subject: Low Earth Orbit in a Mars Blimp?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>I know this is a wierd idea, but seeing other articles on blimps, what is the
>possibility of using a blimp or soem form of it, to get out of earth orbit or
>atleast to put yourself into low earth orbit...

The central problem of attaining orbit is velocity, not altitude.  Balloons
can't operate to anywhere near orbital altitude, although they can be a
useful first step:  there have been balloon-launched sounding rockets.
But the velocity gap is even larger.  You don't see many Mach 1 blimps,
much less Mach 25 blimps.
--
C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology
effect since OS/360.                    |  [e-mail]  utzoo!henry

------------------------------

Date: 3 Mar 93 18:24:01 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Mars exploration
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Timothy Banks) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>
>>In 1969 no one had even heard of VR telepresence. We still don't do it
>>very well. One of the larger problems even today is dealing with the
>>time lag for feedback. Round trip speed of light time to the Moon is
>>on the order of 2.5 seconds
>
>    Unfortunately I don't have a reference handy, but wasn't the
>    Lunikhod (spelling?) remotely controlled?

Of course, but not by VR telepresence. It was a matter of study the
terrain, order a move of one meter, wait for a new picture to be
downlinked, study the terrain, order a move of one meter, ad infinitum.

Gary

--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

------------------------------

Date: 3 Mar 93 09:22:45 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: One Pu release (was Re: Alternative space station design)
Newsgroups: sci.space

In article <[e-mail]>, Dr. Norman J. LaFave <[e-mail]> writes:
> In article <[e-mail]> Kieran A. Carroll,
> [e-mail] writes:
>> Remembering
>> Skylab, *many* people would undoubtedly be nervous about having
>> a large amount (probably several tonnes) of plutonium flying
>> overhead every day. Come to think of it, *I* would probably
>> be nervous about this, and I'm a fairly pro-nuclear person.
>
> The U.S.has had 6 RTG re-entries with not one leak.

I don't know how you're counting but there certainly *was* one release
of plutonium in 1964.  Details below.

(Oops, remembering our audience, we need to say something here.  Take
a deep breath. For the benefit of the nuclear-impaired, let's repeat
our mantra:
A Radioisotope Thermoelectric Generator is not a reactor.
A Radioisotope Thermoelectric Generator is not a reactor.
A Radioisotope Thermoelectric Generator is not a reactor.)

> The USSR
> had one rupture in Canada, but it was found to have insufficient
> shielding.

Not sure what you're referring to here.  Kosmos 954 had a reactor, not
an RTG, and I would count it as a fairly awful nuclear accident,
mitigated only by the fact that it smacked down in a fairly
unpopulated area.  It smeared fission products across the ground in a
wide region.  I think the Russians have dropped at least one other
reactor into an ocean.  Are you referring to these, or to RTG
accidents?

>The safety issue is one of perception.

Oversimplification.  Space nuclear safety includes responsible
engineering and operating practice, too.

For the curious, I've dredged up an old posting on RTG history  from
the debates we had before the Ulysses launch.  This stuff is probably
familiar to Norman but others may be interested.

=============================
NASA Office of Space Science and Applications, *Final Environmental
Impact Statement for the Ulysses Mission (Tier 2)*,  (no serial number
or GPO number, but probably available from NTIS or NASA) June 1990.

The following is a quote from the document.  (I'll retain NASA's
punctuation, though as a writer and editor it makes me itch.)
== == == == == == == == == == == == == == == == == == == == == ==

RTG Performance History

RTGs have been used in the U.S. space program since 1961 and have
powered some of this nation's most successful missions including the
Apollo Lunar Surface Experiment Packages (ALSEPs), the Viking Lander
on Mars, Pioneers 10 and 11 and Voyagers 1 and 2. In all, there have
been 40 RTGs involved in 22 previous U.S. space missions.

Three U.S. spacecraft powered by two RTGs have failed to achieve their
intended mission and two have involved accidental reentries.  In each
case the malfunction was neither caused by nor related to the RTG, and
in fact, the RTGs on these spacecraft performed entirely as intended.
The RTGs on each of these spacecraft responded to the reentry
environment as designed.

Early RTG models carried only a few pounds of radioactive material and
were built to burn up at high altitude during accidental reentry.
When the Navy's Transit-5BN-3 navigational satellite malfunctioned in
1964 and failed to achieve orbit, the RTG on board met the design
criteria by burning up in the upper atmosphere upon reentry.  A total
of 17,000 curies were dispersed high in the stratosphere.  Local dose
levels were small compared to background radiation (see DOE 1980).

Since 1964, RTGs have been designed to contain or immobilize their
plutonium fuel to the maximum extent possible during all mission
phases regardless of the accident environment.  This design philosophy
has performed flawlessly in two subsequent mission failures where RTGs
were present.  In May 1968, two SNAP 19B2 RTGs landed intact in the
Pacific Ocean after a Nimbus B weather satellite failed to reach
orbit, and the fuel was recovered. Even though the recovery took 5
months, there was no release of plutonium.  In April 1970, the Apollo
13 lunar module reentered the atmosphere and its SNAP 27 RTG heat
source, which was jettisoned, fell intact into the 20,000 feet deep
Tonga Trench in the Pacific Ocean.  The corrosion resistant materials
of the RTG are expected to prevent release of the fuel for a period of
time equal to 10 half-lives of the Pu-238 fuel or about 870 years (DOE
1980).

[DOE 1980] U.S. Department of Energy, *Transuranic Elements in the
Environment*, Wayne C. Hanson, editor; DOE Document No. DOE/TIC-22800;
Government Printing Office, Washington, D.C., April 1980.

--
     O~~*           /_) ' / /   /_/ '  ,   ,  ' ,_  _           \|/
   - ~ -~~~~~~~~~~~/_) / / /   / / / (_) (_) / / / _\~~~~~~~~~~~zap!
 /       \                          (_) (_)                    / | \
 |       |     Bill Higgins   Fermi National Accelerator Laboratory
 \       /     Bitnet:     [e-mail]
   -   -       Internet:  [e-mail]
     ~         SPAN/Hepnet:      43011::HIGGINS

------------------------------

Date: Wed, 3 Mar 1993 16:23:26 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Plutonium terror (was Re: Alternative space station design)
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Pat) writes:

>ANd besides, maybe the CI might have a point when it comes to
>LEO radio nucliedes, in high concentration, that are vulnerable to
>any cessation in flight ops.   Look how freaked people got
>when a russian rac crashed in canada.  Imagine if SKYLAB had
>carried a RAC, instead of solar cells.  Even MIR uses primary solar.
>The russians got quite a bell ringing from that canada incident,
>and that was duringthe evil empire.

Note that what the Soviets dropped was *not* an RTG; it was the
remains of an old reactor.  Once a nuclear reactor powers up, it
rapidly builds up quantities of some pretty nasty stuff.  Dropping an
RTG in someone's neighborhood probably isn't all that bad even if it
hits rock (unless it lands on someone).  Dumping a reactor that has
been running and producing power, however, is generally conceded to be
a Bad Thing.

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

------------------------------

Date: Wed, 3 Mar 1993 17:27:35 GMT
From: Marco Claro Pineda <[e-mail]>
Subject: Sexy batteries (was Re: Battery help needed!)
Newsgroups: sci.space,sci.electronics,sci.aeronautics,sci.chem,sci.engr

In article <[e-mail]> [e-mail] (Bill Higgins-- Beam Jockey) writes:
>In article <1n02n5$[e-mail]>, [e-mail] (Chad Barret Wemyss) writes:
>> In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>>>
>>>I think I'd look into the sexier battery technologies, like nickel-hydrogen
>>>or silver-zinc, first.
>>>--
>>
>> And just how does one decide which batteries are "sexy"  :-)
>

It's whatever turns you on, man!

;-)
*************************************************************************
* "Captain, he's hiding something."                 | [e-mail] *
* "Carpe Cibum" (Seize the Food)                    | M. Pineda         *
*************************************************************************

------------------------------

Date: 3 Mar 93 17:57:03 GMT
From: Gary Coffman <ke4zv!gary>
Subject: Spaceflight for under $1,000?
Newsgroups: sci.space

In article <1mv48g$[e-mail]> [e-mail] (George William Herbert) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>It's also worth noting that AMSAT found out that some shielding is worse
>>than no shielding at all.
>>[...]
>
>Yes, however, there's this inconvenient problem that normal packaging
>(vehicle structure, systems, unit packaging (nice metal cases etc...)
>often is enough to go past this limit.  Adding more to reduce the secondaries
>isn't so hard.  Neither is it painless, though.  You don't get light little
>computers.

Actually you can. Look at AMSAT's microsat series. You've got 8 megabytes
of main memory and a V40 processor in a 9 inch cube with radios, another
housekeeping computer, batteries, power management system, and an experiment
module, often carrying a camera. All in about 20 pounds. According to a
recent AMSAT bulletin, all system crashes so far have been traced to
software bugs. No crashes due to radiation. Now LEO is fairly benign.
Oscars 10 and 13 are in Molniya orbits. Oscar 10's computer failed
after 5 years. Oscar 13's computer is still operating. Oscar 10's
computer was shielded with tantalum foil. Oscar 13's computer is
unshielded. It does use Harris rad hard parts though, as did Oscar
10. The microsats use off the shelf commercial parts.

I probably wouldn't trust Shuttle flight systems to such computers,
but they appear to be robust and usable enough for satellites.

Gary

Gary

--
Gary Coffman KE4ZV          |    You make it,     | gatech!wa4mei!ke4zv!gary
Destructive Testing Systems |    we break it.     | uunet!rsiatl!ke4zv!gary
534 Shannon Way             |    Guaranteed!      | emory!kd4nc!ke4zv!gary
Lawrenceville, GA 30244     |                     |

------------------------------

Date: Wed, 3 Mar 1993 16:41:35 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Stupid Fred Question
Newsgroups: sci.space

In <[e-mail]> [e-mail] (Kenji Saito) writes:

>In article <[e-mail]> you write:
>>In the close-up GIF of the space station,
>>on the one module, what does NASDA stand for ?

>NASDA is the Japanese version of NASA. I do not know what the name stands
>for, but it must be something like National AeroSpace D? Agency. The module
>must be JEM, Japanese Experimental Module.

I would be inclined to suspect the "N" is for Nippon; of course,
acronyms from Kanji probably aren't going to be real 'predictable' in
any case.  ;-)

--
"Insisting on perfect safety is for people who don't have the balls to live
 in the real world."   -- Mary Shafer, NASA Ames Dryden
------------------------------------------------------------------------------
[e-mail] - I don't speak for others and they don't speak for me.

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From: Jon Leech <[e-mail]>
Newsgroups: sci.space
Subject: Re: Gravity simulations
Date: 3 Mar 1993 17:03:04 GMT
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In article <[e-mail]>, [e-mail] (Bill Broadley) writes:
|> I'd like to get ahold of some source code that would allow me to do
|> a 2d or 3d gravity simulation of N object in O(N) time.

    Actually, you probably don't want this. Not only is Greengard's
algorithm enormously complex, but it has a very large constant in front of
the N. My understanding is that it doesn't become competitive until N ~
1,000 - 10,000, which would hardly be interactive.

    You can do a couple of dozen bodies with the stupid N^2 algorithm at
reasonable frame rates (on high-end workstations).

    Jon
    __@/

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End of Space Digest Volume 16 : Issue 271
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