Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V16_3/V16NO328.ZIP/V16NO328

Internet Message Format | 1993-07-13 | 31KB

Date: Thu, 18 Mar 93 05:06:43
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #328
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 18 Mar 93       Volume 16 : Issue 328

Today's Topics:
                    20Khz Power supplies. (2 msgs)
                      cancel wars accountability
                            DC-X (2 msgs)
             Dennis and new tech (was Re: Without a Plan)
                   Hobbies (was Re: Without a Plan)
                 Info: Equations for path of planets?
                Just a little tap (was Re: Galileo HGA
               Just a little tap (was Re: Galileo HGA)
                          Life in the Galaxy
              Looking for Johnson's Space Center Co-ops.
                   Mars Observer Update - 03/16/93
             Response to various attacks on SSF (2 msgs)
                          Retraining at NASA
        Sisters of Mars Observer (was Re: Refueling in orbit)
               Venus and Mars, was Re: TIME HAS INERTIA
    Water Simulations (Was Re: Response to various attacks on SSF)

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

Date: Wed, 17 Mar 1993 14:26:25 GMT
From: Gary Coffman <ke4zv!gary>
Subject: 20Khz Power supplies.
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>>... Name 3 projects that have used 20Khz  power.  name 3 companies
>>>that produce 20Khz power components.
>>
>>How about Lambda, ACDC Electronics, IBM, Apple, and zillions of Tiawan
>>clone makers. 20 kHz power is old hat. Likely the computer you are
>>reading this on uses 20 kHz, or higher, frequencies in it's power
>>systems...
>
>*In* its power systems.  Not outside them.  Come now, Gary -- Pat wasn't
>asking for people who make 20kHz transistors, he was asking for people
>who make 20kHz lightbulbs or fans or breaker panels or radios.

Light bulbs generally don't care, and if you want to dim them then
20 kHz power makes it easier. Most all variable speed equipment fans
now have internal switchers to control the speed. Our Sony recorders
even have Hall effect sensor feedback in the cooling fans. When asked
why, the Sony rep said it was cheaper to measure fan load than to have
air stream sensors for protective shutdown. Not having to do the intitial
chopping of the incoming power actually simplifies the fan design. Radio
power systems also benefit from this simplification.  Breakers can be a
bit touchier depending on internal design. Magnetic trips could use less
mass in their cores while thermal trips would be unaffected.

>And when it comes to actually distributing power to its internals, that
>computer uses DC.  (It just might use 60Hz AC for its fans.)

Well some of them do. Others with board level regulators prefer their
power already chopped. Our Harris transmitters distribute chopped power
to the various modules where it's regulated. I believe it's also common
in larger computer mainframes to take this approach.

>Gary is also correct, in a way he didn't intend :-).  *Within* power
>systems, 20kHz is old hat, i.e. obsolete.  Modern switching power supplies
>are moving strongly towards much higher frequencies.

The higher the frequency, the better the efficiency, within limits. When
you venture over 100 kHz, skin effect rears it's ugly head. Also if you
wish to distribute the chopped power, distributed capacitance becomes
more of a problem as the frequency goes up. You like to maintain nice
sharp square waves for efficiency, but the capacitance begins to round
them off. The way around this is to use RF transmission line techniques
for power distribution. At 20 kHz, twisted pair works fine, at 100 kHz
you want to start looking at coax or ladder lines. Load termination
impedances start to be an issue up around 100 kHz as well.

20 kHz is a nice compromise frequency. Weight of inductors is sharply
reduced, but skin effect is still rather unimportant, and distributed
capacitance is not too bad a factor, power switching devices are still
cheap and efficient, and you have much finer control in the time domain
of regulation than you do with lower frequency power. This improved
dynamic regulation is valuable when you have many intermittant loads.

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, 17 Mar 1993 14:29:28 GMT
From: Gary Coffman <ke4zv!gary>
Subject: 20Khz Power supplies.
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Pat) writes:
>
>Actually the thing that really sets off my warning bells on 20Khz,
>is that no-one knows how this would behave in the LEO environment.
>
>Henry,  wasn't most of the Canadian Long haul grid knocked down one
>time by sun spots?  Up there, god knows what kind of crzy interactions
>would occur every time we had asolar flare.

The reason long haul networks are vulnerable has nothing to do with
power frequency. The geomagnetic variations caused by solar flares
can induce voltages in the long exposed cables that can cause circuit
trips. That's not an issue in a relatively small box in orbit, none
of the cable runs are long enough to pick up significant induction
currents.

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, 17 Mar 93 14:51:00 GMT
From: Jay Maynard <[e-mail]>
Subject: cancel wars accountability
Newsgroups: comp.org.eff.talk,alt.privacy,sci.space,sci.astro,news.admin.policy

[Bogus Distribution: inet changed to world.]

In article <[e-mail]> [e-mail] (Lazlo Nibble) writes:
>Depew's superiors and Julf are, in each case, the person most immediately
>empowered to take care of the perceived problem.  You won't find an exact
>parallel between the two situations, but this is a reasonable one.

Not even close. Julf can't get the coward fired from his job.
--
Jay Maynard, EMT-P, K5ZC, PP-ASEL | Never ascribe to malice that which can
[e-mail]      | adequately be explained by stupidity.
        You won't see this on TV: (video of Mount Carmel compound)
        "This is David Koresh, of Waco, Texas. He cannot be seen."

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

Date: Wed, 17 Mar 1993 13:43:00 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: DC-X
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Dave Michelson) writes:

>Your description of your tour of the DC-X was one of the most exciting posts
>that I've ever read here!  History as it happens and all that.  Wow!

>It goes without saying that the DC-X team certainly have *my* support.

I hope you have written to VP Gore and told him you support their efforts
and ask for full funding of the DC-Y.

Support without action won't accomplish much :-)

  Allen
--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |

+----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: Wed, 17 Mar 1993 13:45:51 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: DC-X
Newsgroups: sci.space

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

>Hating to sound cynical,  but note how different the Management
>structure and design philosophy of DC-X is from SSF...

>I suspect the management structure is very small.

I don't know about the MD side but the SDIO side is very small. There
are only two people working this contract from the government side. I
have worked on contracts half the size of DCX with five times as many
government people overseeing the work.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: 17 Mar 93 10:00:20 -0600
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: Dennis and new tech (was Re: Without a Plan)
Newsgroups: sci.space,talk.politics.space

In article <[e-mail]>, [e-mail] (Bill Higgins-- Beam Jockey) writes:
> In article <[e-mail]>, [e-mail] (Josh Hopkins) writes:
>> Nick, Dennis was working on a tethered satellite system which, according to
>> Space News, is scheduled to launch this week with a total project cost of
>> $10 million to NASA.
> (Though I think
> Dennis's payload goes up on the *second* SEDS launch, not the current
> one.)

Dennis has confirmed this by e-mail.  There are 368 days until the
scheduled launch of SEDS 2/SEDSAT 1.  (SEDSAT 1 is the end mass on
SEDS 2's tether; instead of a dumb lump of metal it is instrumented
with a panoramic camera, fancy image-processing computers, and a new
kind of solar cell.)

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

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

Date: 17 Mar 93 15:47:32 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Hobbies (was Re: Without a Plan)
Newsgroups: sci.space,talk.politics.space

In <[e-mail]> [e-mail] (Bill Higgins-- Beam Jockey) writes:

>In article <[e-mail]>, [e-mail] (Pat) writes:
>>
>> Wow.  This is a hard one for me.  Defending Szabo.  ack....
>>
>> But the guy has one critical valuable point to make.
>> That is a sustainable economy must be the basis of space  activities.
>>
>> Any non viable system, remains a hobby.

>That sums it up.  I agree heartily with Pat and Nick on this point.
>Nothing wrong with having "hobbies," but the solar system holds some
>promise to sustain spaceflight activities by bringing economic
>benefits to humanity.  If we exploit this promise space science,
>technology, development, exploration, and colonization will blossom.
>If we don't, space will remain an expensive sideshow indefinitely.

>I think it is rational to make plans to open these doors.  Fred McCall
>evidently doesn't.

Please try to avoid telling me what I think, Bill.  My objection to Mr
Szabo isn't what he is calling for, some of which is a good idea.  It
is, rather, to his position that anyone doing anything else *must* be
attacked as a fool and gutted.  There is also the problem that his
'long term vision' basically calls for not having anyone doing
anything in space other than automated probes for the remainder of
your and my lifetime.  I don't think you get men out in space that
way.  I disagree with Mr Szabo in that I think one way you find out
things that having men in space is good for is by putting men in space
and trying things out, while he thinks that men should not be in space
until it can be economically justified by private industry.  Given
that approach, airplanes would still be back at the barnstorming
stage.

--
"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: Wednesday, 17 Mar 1993 02:31:00 EST
From: [e-mail]
Subject: Info: Equations for path of planets?
Newsgroups: sci.space

Greetings. I'm building  (2-d map representation of)xyz cartesian coordinate
space in a MOO. Are there algebraic equations using x, y & z that provide an
approximate description of the movements of the moon, earth & inner planets
around the sun?  If there are, and you know them, please e-mail me the info.
At this time I'm using circles, testing orbital radius every step.  Thanks
in advance.  To visit via Telnet, send me e-mail.

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

Date: Wed, 17 Mar 1993 15:29:49 GMT
From: "Don M. Gibson" <[e-mail]>
Subject: Just a little tap (was Re: Galileo HGA
Newsgroups: sci.space

In article [e-mail], [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Bill Higgins-- Beam Jockey) writes:
>>> You mean sideswiping an asteroid to try to knock the antenna loose is out :-)
>>
>>Hmm, they're going past Ida in August, and a zero-distance flyby is well
>>within the propellant margins, I'm sure...
>
>Jordin Kare, in his Clementine talk at Making Orbit, mentioned that they
>had seriously discussed an "aim for dead center, it's not going to hit it
>and we'll get great closeups" philosophy for the Clementine asteroid
>encounter.  He said this did make people a little nervous, but more to
>the point, it made it difficult to get good imaging both inbound and
>outbound, because the asteroid goes from almost-dead-ahead to almost-
>dead-astern very quickly and the probe can't re-point its sensors all
>that rapidly.  A substantial miss distance limits the closeups but gives
>better return overall.

as an example (from my fading memory) Galileo required a Mosaic of
46 images to ensure (to 3 sigma certainty) that the closest Gaspra
image would be "in the frame".  and if you remember, GLL didn't get
all that close to Gaspra.  Now, if your S/C has semi-realtime
imaging then you can feed that knowledge back into your instrument
pointing and get much closer.  --DonG

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

Date: 17 Mar 93 17:10:52 GMT
From: Jeff Bytof <[e-mail]>
Subject: Just a little tap (was Re: Galileo HGA)
Newsgroups: sci.space

This is really off the wall, but would there be any way to calculate
the effect of forces due to induced magnetic fields on the spacecraft
structure and antenna as it passes through the intense Jovian magnetic
and particle fields?  Perhaps a way could be found by proper orientation
of the spacecraft to apply differential pressure to some critical area
of the structure.

-rabjab

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

Date: 17 Mar 93 17:20:29 GMT
From: Jeff Bytof <[e-mail]>
Subject: Life in the Galaxy
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Paul Carter) writes:

>I think the annihilation model is unnecessarily pessimistic. I suspect that
>the only civilisations that could survive to the point of space mastery
>would be those that have overcome many war-like tendencies.
>The rest would probably self-destruct with their world-killer toys.

I would not presume that a civilization that would choose to annihilate
us to be necessarily warlike.  It may just be their equivalent of bug-spray,
to eliminate a nuisance that might grow to really annoy them later on.

>Monsters in far away lands are a common, and inaccurate, theme in human history.
>Compare maps produced in the middle ages with popular modern science fiction.
>'Here be dragons' is simply replaced with 'here be vogons'.

"We have met the enemy, and it is us".

-rabjab

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

Date: 17 Mar 93 15:52:49 GMT
From: Mary Shafer <[e-mail]>
Subject: Looking for Johnson's Space Center Co-ops.
Newsgroups: sci.space,sci.astro

On Wed, 17 Mar 93 04:16:18 GMT, [e-mail] (Ryan Korniloff) said:

RK> I have a friend who is currently a student at U of Alabama and
RK> wants to transfer to U of Houston Clear Lake, Texas. He is very
RK> much interested in knowing weather there are any co-op programs
RK> for Clear Lake students at Johnson's Space Center.  Any
RK> information whould be GREATLY appreciated.  Please respond by
RK> mail, otherwise I might not get your reply.  Thank you..

Call JSC and ask for the co-op coordinator in the personnel office.
JSC's number is 713 483-0123.

Why ask us when you can ask the person who really knows?
--
Mary Shafer  DoD #0362 KotFR NASA Dryden Flight Research Facility, Edwards, CA
[e-mail]                    Of course I don't speak for NASA
 "A MiG at your six is better than no MiG at all."  Unknown US fighter pilot

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

Date: 17 Mar 1993 09:13:10 -0500
From: Pat <[e-mail]>
Subject: Mars Observer Update - 03/16/93
Newsgroups: sci.space

Actually, under the KISS princople, you may not want the command receiver
to do any coding.  coding means chips and additonal complexity.
IF the command reciever dies, the bird is F******.

simple rugged, reliable cheap is the word on that one.
and the DSN has plenty of power to beam up to the command reciever.

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

Date: Wed, 17 Mar 1993 13:57:36 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Response to various attacks on SSF
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (David B. Mckissock) writes:

>>    3)  Total failure to practice EVA until this year.

>Another common fiction on sci.space. NASA has two facilities
>for practising EVA's in water tanks,

Another common NASA fiction. As the intelsat rescue showed water tanks
are not high enough fidelity simulations of micro-g.

More importantly, NASA put a huge amount of faith in those tanks with
almost no real life experience to see just where the shortcomings are.

>WP-4 has tested many of our EVA procedures in these facilities.

Fine, but will those procedures work in orbit? At the moment there
is no particular reason to think they will or will not. If they don't,
we will sure wish we did more real EVA a long time ago so the weakness
in the models could have been discovered.

   Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: 17 Mar 1993 16:14:56 GMT
From: Andy Cohen <[e-mail]>
Subject: Response to various attacks on SSF
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Pat)
wrote:

> Boeing has a small fleet of planes that just take off and land every day
> to test landing cycles.  They have pressure hulls, that they pressure
> cycles thousands of times to test for stress.  They have old birds on
> dynamic test beds to test wing load over time.
>
> I don't see that kind of approachin SSF.  All the old NASA programs
> built  spares and ground simulators to test all systems.  SSF
> has too much tied to the flight hardware only.


You are very correct that SSF focuses only on flight HW. And it is a
problem. However, your description of commercial product focus on safety
via flying test cycles and pressure cycles does not happen in any manned
space NASA programs.  True, the shuttle had lots of mockups (remember
Enterprise), but the shuttle is STILL flown like a test article and not
like a well matured flight system.   It costs too much to tear a wing off a
shuttle to get a measure of wing capability.
Sorry, the Apollo mission as well as political momentum is gone.

Now that's what we need political momentum......

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

Date: Wed, 17 Mar 1993 14:07:19 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Retraining at NASA
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Brian Donnell) writes:

>> Of course it's hard to have a strategic vision when 50% of all effort is
>> devoted to maintaining a center and it's contractor community.

>If you don't have an infrastructure to support day-to-day business,
>how do you suggest things get done?

Talk to SDIO. Their support infrastructure for SSRT represents less then
1/60 of the program cost. Yet they are doing more to support cheap routine
access to space than NASA has ever done.

>But surely you recall how many times in NASA's history that Congress
>has allocated a set level of funds for a project only to slice it
>later.  How can NASA possibly hope to do anything but patchwork when
>the funding is constantly fluctuating?

Agreed that is a problem. Yet other parts of government deal with the
same problems all the time.

>> No more difficult then that of other agencies.  SDI has to cope with
>> this.

>True enough. But I would argue that these agencies don't have any
>better track record than NASA.

Clementine, Delta Clipper, Timberwind...  I'll stack SDIO's record for
promoting space against NASA any day. Better, cheaper, faster is new
to NASA but it was always SOP at SDIO.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------91 DAYS TO FIRST FLIGHT OF DCX-----------------------+

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

Date: Wed, 17 Mar 1993 16:53:45 GMT
From: Eric H Seale <[e-mail]>
Subject: Sisters of Mars Observer (was Re: Refueling in orbit)
Newsgroups: sci.space

[e-mail] (Henry Spencer) writes:

>>...But wait -- now
>>your solar arrays generate TOO MUCH power while you're at Earth (gotta
>>resize the power control circuitry)...
>No, just tilt the arrays until you're out at Mars distance.  I believe
>that's what Mars Observer did, and it's certainly what Mariner 10 did
>to solve a similar problem.
That, and MO leaves its arrays partially folded-up until it gets to Mars
(personally, this gives me the willy's -- remember what happened to
Galileo's HGA thanks to a delayed deployment).  Actually, I mis-spoke
here.  Another part of the argument is that you need to account for
array degradation from cosmic ray bombardment (considerably more severe
once you get out of the Van Allen Belts -- no sweat if you're adapting a
Geosynch satellite, a slight problem if you're working with a LEO bird).
You need to size your solar panels for "end-of-life", which leaves you
with considerable excess power at "start-of-life" (you hope).
Off-pointing your solar arrays is great if you can handle the
operational impact (Magellan, at least, had too great a power cycle to
track power-need-changes with panel motion).

>>And did you remember to add the extra propulsion gear
>>to get into Mars' orbit?
>Why not just use a solid motor, like Magellan did?  You don't need
>spacecraft mods for that (assuming power etc. for cruise is okay in
>a high-gee configuration).
Solids tend to burn pretty fast.  Depending on your spacecraft
configuration, you may wind up pulling 15-20 g's during orbit insertion
(I don't remember what we had to put up with on Magellan -- just 7 or 8
g's, as I recall).  For us, a bigger problem was the acoustic loading on
the spacecraft (i.e., vibration) -- once you deploy anything for cruise,
flexible body effects become a BIG concern.

Bear in mind that there is some reluctance to use solids for orbit
insertion (to my knowledge, Magellan was the first example of a 3-axis
stabilized spacecraft to use a solid for orbit insertion).

Why?
  -- Solids burn fast (if anything goes wrong, it's guaranteed to be
     catastrophic)
  -- Solids tend to produce off-axis thrust (we had to put some pretty
     big hydrazine engines on Magellan strictly for attitude control
     during the burn -- i.e, spacecraft mods)
  -- Solids can be "shakey" (flexible body effects make for a stiffer /
     heavier structure -- more mods)
  -- Solids can't be turned off (failure modes again)
  -- Hadn't been done before (program managers tend to be a conservative lot)


>>It's not at first apparent, but by "customizing" an existing spacecraft,
>>you can easily end up with a more expensive bird than if you had just
>>started from scratch...
>No argument there.  It's easy to just let change after change creep into
>the design.  You need hard-nosed management that insists that the words
>about "minimum changes" be taken seriously, even if it means compromises.

Agreed.  A big problem is "creeping elegance" -- starting with a small,
cheap, simple design & then saying things to the effect of "well, gee,
since we're going to Planet X, can't we just add this one little
sensor..."

>.. it *can* turn out that using the existing
>design just doesn't work -- but there are more variables than just the
>technical ones...
Agreed -- the biggest non-technical variable is human nature (for both the
customer -- NASA or whoever -- and the contractor).

>...and I suspect those extra variables were more important
>in the case of the Observer design.

I wasn't involved with MO, so I can't speak to this -- any GE folks
tuned in to this discussion?  I was just trying to point out that "reuse"
tends to be touted as a cure-all for the expenses involved in
exploration.  Re-use of an existing design is great when you can swing
it, but first you need to take a long, hard, critical look at the cost
trade-offs of adapting your existing bird...  Until someone invents the
transporter beam, planetary spacecraft are tightly constrained on
size/weight -- thanks to this, designs wind up being so tightly coupled
that changes in one system tend to affect all the other systems.

Eric Seale

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

Date: Wed, 17 Mar 1993 15:39:07 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: Venus and Mars, was Re: TIME HAS INERTIA
Newsgroups: sci.space

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

>In article <[e-mail]>, [e-mail] (Eric H. Taylor) writes:
>-| In article <[e-mail]> [e-mail] (Alexander Abian) writes:
>-| >[...]
>-| >VENUS should be given an near Earth like orbit to become a Born Again Earth
>-|

>Talk about a sledgehammer to crack a nut. Plain old moss loves the constituents
>of the Venus atmosphere, and is highly resistent to attack from UV, acid etc..
>If its spores were released at high altitude on Venus, they would happily float
>around converting the CO2 to Oxygen. It would take roughly 100 years for the
>spores to reach the surface of Venus, by which time the atmosphere would also
>have been converted. I think terraforming is really a branch of bioengineering.
>Other approaches just don't make economic, or practical sense.

The closing statement seems to be true, but your timescale of a few
hundred years simply seems much too short.  There is also the question
of where all the excess carbon is going to go.

--
"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: 17 Mar 1993 11:06 CST
From: [e-mail]
Subject: Water Simulations (Was Re: Response to various attacks on SSF)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Allen W. Sherzer) writes...
>In article <[e-mail]> [e-mail] (David B. Mckissock) writes:
>
>>>    3)  Total failure to practice EVA until this year.
>
>>Another common fiction on sci.space. NASA has two facilities
>>for practising EVA's in water tanks,
>
>Another common NASA fiction. As the intelsat rescue showed water tanks
>are not high enough fidelity simulations of micro-g.
>
>More importantly, NASA put a huge amount of faith in those tanks with
>almost no real life experience to see just where the shortcomings are.
>

Hey Allen I don't know how old you are but do you remember the old days at
NAsa? ALL of the EVA's for Skylab were practiced here at MSFC before
implementation. Remember the spacewalk to free the solar array? Done in the
Tank at MSFC. Remember eh New Heat shield? Done in the tank first. How about
the Spacewalks in Lunar orbit for the retrieval of the film from the CSM?
Done first in the tank and then in space. Never had too many problems that
I remember.

What about all of the Gemeni EVA's (well a couple of them) They were done
in the tank first. There were many EVA's during skylab for film retrevial
from the ASTM and they were all practiced in the tank first.


>>WP-4 has tested many of our EVA procedures in these facilities.
>
>Fine, but will those procedures work in orbit? At the moment there
>is no particular reason to think they will or will not. If they don't,
>we will sure wish we did more real EVA a long time ago so the weakness
>in the models could have been discovered.
>
>   Allen
>

Do your remember the EVA's done before Challanger where trusses were built
and Large solar arrays were deployed and many many other station type tasks?

I totally agree that there should not have been a stand down from EVA's after
STS-25 BUT to imply that we have no experience there or that the
tanks cannot give a good idea of what is faced up there is simply not
consistent with almost 30 years of NASA history.

The primary problem that was faced on the Intelsat mission is that the
tank simply cannot accurately mimic the moments of inertia of large
structures in orbit.  Maybe they need to look at regimens to compensate
better for this difference between water and vaccuum.

Dennis, University ofg Alabama in Huntsville

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End of Space Digest Volume 16 : Issue 328
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