Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/spacedig/v11_3/v11_318.txt

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Subject: SPACE Digest V11 #318

SPACE Digest                                     Volume 11 : Issue 318

Today's Topics:
         Space Station Distribution Frequency
              Re: Dyson spheres?
                Re: HST focus
            Re: Vandeburg Launch Schedules
          Re: TV gaffes during Hubble launch
           Re: Need info on Space Stations
     Re: PegBlimp (was Re: Pegasus launch from Valkyrie  (or ...)
                Re: Our galaxy
             Re: Other Big Bangs
                Re: Our galaxy
----------------------------------------------------------------------

Date: 25 Apr 90 13:35:52 GMT
From: eagle![e-mail]  (Dave McKissock)
Subject: Space Station Distribution Frequency

Summary for those who are short on time:
The selection of the type of power distribution for Space Station (AC
or DC, AC frequency, voltage) involved rather lengthly technical
discussions after perform many analyses. The original 20 kHz selection
was NOT "insane", but rather based on sound technical reasoning.

You may now hit "n" to go to the next message, or read my lengthly
rebuttal to Mr. Spencer.....

In article <[e-mail]>
 [e-mail] (Henry Spencer) wrote:

>In article <[e-mail]> [e-mail] (Steve Nuchia) writes:
>>To include a shred of space relevance, which power distibution
>>scheme is currently in vogue for the space station?  ...

>DC.  For a while they were planning an insane 20kHz system, which would
>have meant custom-building everything from wiring to lightbulbs.  When
>they abandoned that as a cost-cutting measure, I guess it would have been
>humiliating to admit the mistake, so they went straight to DC instead of
>using the aviation standard of 400Hz AC.


I have been reading sci.space for around 3 weeks, and have found the
postings from Mr. Spencer to be well written and accurate. In this
response, however, I believe Henry went a little overboard in his
criticism of NASA. My dictionary defines insane as "mentally
disordered: exhibiting insanity (which is defined as "extreme folly or
unreasonableness, something utterly foolish or unreasonable"), absurd."

The branch I am in at LeRC, called Systems Engineering & Analysis
Branch, is responsible for ensuring that all trade studies performed by
Work Package 4 (that's "us", LeRC & Rocketdyne, the team responsible
for the power system on Freedom) have a consistent approach. Although
I am a lowly mechanical engineer, admist a sea of electrical engineers
here at LeRC in the Space Station Directorate, I seem to be the only
one around who reads sci.space and wishes to take on the powerful guns
of Henry. Here goes...

The selection of the distribution frequency for the Space Space was the
topic of one of many trade studies performed in Phase B of the program.
Major decisions were made during Phase B concerning the type of power
generation (Nuclear, Photovoltaic, Solar Dynamic [suns energy used
to drive a heat engine]), energy storage type for the Photovoltaic
systems (NiCd batteries, Nickel Hydrogen Batteries, Regenerative Fuel
Cells, fly wheels), Power distribution architecture (ring, star), &
Power distribution type (AC vs DC, voltage).

Prior to Phase B, LeRC had been sponsoring research in high frequency
power converters and switchgear for possible use in future space
missions. EE's tell me that it is desirable to maximize the power
system control response, and minimize the systems component mass and
it's delivery of energy under fault conditions. These considerations
drive power systems toward the highest possible frequency. However, in
the multikilowatt power range, certain problems become noticeable for
high frequency systems. Things like parasitic inductances
(V = L di/dt, so larger di/dt cause bigger problems). Thus the research
to find solutions to the problems.

As I said earlier, one of the Phase B trade studies involved the type
of power distribution. Actually, SEVERAL studies concerning this
technical issue were performed. In a report in 1985, Rocketdyne
(one of our Phase B contractors) recommended 400 Hz as the distribution
frequency, based on the results of their trade study. They noted in
their report, however, that "quantitative (objective) values do not
provide an overwhelming discriminator between power distribution
types". I recall our second Phase B contractor recommended 20 kHz as
the distribution frequency. This particular selection generated lots of
interest outside of our work package, so folks from JSC, MSFC, the
Internationals (NASA lingo for ESA, Japan, Canada), NASA headquarters,
& academia go together & decided to baseline 20 kHz as the Station
distribution frequency.

A year or so into Phase C/D, and two (or was it three) program managers
later, Level II decided to reconsider the distribution frequency
decision. The concern was not from LeRC (i.e. we weren't experiencing
any development problems with 20 kHz), but rather folks from JSC & MSFC
were concerned about having to interface with 20 kHz power, instead of
the regular old DC power they are used to. It wasn't a problem of
developing "20 kHz lightbults" as Mr. Spencer stated (LeRC was
developing a family of load converters to convert the 20 kHz into 400
Hz, 5Vdc, 28Vdc, 150Vdc, to name a few examples), but rather the lack
of familiarity with 20 kHz on the part of the other folks. In an
interesting aside, during the "2nd look" at the distribution frequency,
Canada said they were far enough into their design such that they
preferred we maintain the 20 kHz, & that if the Station went DC Canada
would like a DC to 20kHz converter to be developed so the Mobile
Servicing Center could use 20 kHz. Canada, however, was a "voice in the
wilderness", & everybody else (except LeRC of course) voted to "dump
20 kHz" and go with 160 Vdc.

I find the most "insane" thing about all of this is that the
government spent millions of bucks in Phase B of the program to select
an electrical power system design that made the most sense, and then
reversed a Phase B decision in Phase C/D. Why perform expensive trade
studies in Phase B if your just going to redo the studies in Phase C/D?

--
-----------------------------------------------------------------------
Dave McKissock              [e-mail]
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
NASA LeRC: Responsible for the remarkable & ingenious Space Station
           Freedom Electrical Power System
= = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = = =
Opinions expressed herein probably bear absolutely no resemblance to
the official NASA position.
-----------------------------------------------------------------------

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

Date: 26 Apr 90 01:36:27 GMT
From: usc!oberon.usc.edu![e-mail]  (Steve Robiner)
Subject: Re: Dyson spheres?

In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>In article <[e-mail]> [e-mail] (Steve Robiner) writes:
>>In article <[e-mail]> [e-mail] writes:
>
>
>It's a common misconception that Dyson was talking about a single
>solid sphere of material.  In fact, he was talking about a large
>collection of objects, independently orbiting at different distances
>from the star, that (collectively) englobe the star.

This is an even sillier concept.  Any large number of objects orbiting within
the environmental correct range would be forever perturbing the orbits of
the other planetoids in the 'sphere'.

=steve=

Also,
a d

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

Date: 25 Apr 90 19:15:10 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: HST focus

In article <[e-mail]> [e-mail] (John Roberts) writes:
>>... The image is not expected to reveal anything,
>>except perhaps that more work is needed on focusing. :-)
>
>... Designers have tried to construct the frame so it will have an optimal
>shape when fully dry and in 0g. In the meantime, it should still be usable
>due to the range of motion provided by the actuators.

After they've figured out the proper settings for the actuators, that is,
which will probably require some experimenting.
--
If OSI is the answer, what on |     Henry Spencer at U of Toronto Zoology
Earth could be the question?? | uunet!attcan!utzoo!henry [e-mail]

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

Date: 25 Apr 90 22:33:44 GMT
From: manta![e-mail]  (Michael A. Simpkins)
Subject: Re: Vandeburg Launch Schedules

In article <[e-mail]> [e-mail] (Doug Braun ~) writes:
>A little while ago, this subject was brought up.  I would love to see a launch
>there, but I don't have a clue how to find out when something will be launched.
>Does anyone know when there will be a launch, or how to find out?
>I NEVER hear about these in the papers before they happen.
>
>Doug Braun                Intel Corp CAD
>                    408 765-4279
----------------------------------------------------------------------------------------------------------------------------------------------------------------
In all my years growing up there I can't say that I remember any of the
launches being "officially" announced.  Everyone on base knows that there is
going to be a launch, so most of their families know there's going to be a
launch.  At the appointed hour school classes in town file outside and workers
on base take their breaks (The base commander is always furious to see everyone outside waiting for a classified launch).  There's just no way to keep the
local population from finding out about these and other events.

If you happen to be in town the day before you might hear about it, but in
general it's no big deal to the locals (except the TITAN IV's of course!) so
the news media just doesn't seem to find out about it.  If I wasn't afraid
of being dragged off by the men in dark suits I'd give y'all the heads up.

Hey! what are you guys doin' in hear.....I did'nt tell them.......AAAAAAAAAA!!

                R.I.P -simpkins- 8-O

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

Date: 25 Apr 90 22:22:22 GMT
From: mtxinu!sybase!alf![e-mail]  (brook mantia)
Subject: Re: TV gaffes during Hubble launch

Actually, the BEST way to view the launch was on NASA Select.  YOU TOO
can have a front row seat thanks to *space technology*, and bypass all
the stupid, inane network commentators' blithering.

A group of about 20 of us got up in the wee hours and assembled at
Ricky's Sports Lounge at 5:00am (Pacific Time) in San Leandro to watch
the launch.  Ricky is a great guy who was very intrigued about the idea
of tuning his satellite dishes into NASA Select, instead of the usual
sports events he airs at his establishment.  (He's considering changing
the name of their place to Ricky's Sports and Space Lounge...) :-)

We even managed to get a fair amount of publicity on the local TV news
stations, as well as radio & newspapers.  Of course, this was the
second round--we were all there (along with the media) two weeks ago
when we tried to get her up the last time.  Both events were a lot of
fun.  But I'm glad I don't have to get up at 3:30am again for a while.

Anyhow, next time there's a significant mission, you might see if there
are any sports bars in your area that would want to host such a launch
party.  It's always much more fun to share this kind of thing with a
group of people than to sit at home alone.

GO DISCOVERY!  GO HUBBLE!  AD ASTRA!

Brook Mantia, Events Coord.
Golden Gate Chapter, NSS   (and Proud of It!)

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

Date: 25 Apr 90 19:21:23 GMT
From: usc!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Need info on Space Stations

In article <[e-mail]> [e-mail] (Mark Perew) writes:
>Doesn't the "habitable volume" of an orbiter depend on the positioning
>of the airlock?  If the airlock is mounted in the middeck it reduces
>the "habitable volume" from what it would be if the airlock were
>mounted in the cargo bay.

Correct.
--
If OSI is the answer, what on |     Henry Spencer at U of Toronto Zoology
Earth could be the question?? | uunet!attcan!utzoo!henry [e-mail]

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

Date: 22 Apr 90 18:46:17 GMT
From: b-tech!kitenet![e-mail]  (Russ Cage)
Subject: Re: PegBlimp (was Re: Pegasus launch from Valkyrie  (or ...)

In article <[e-mail]> [e-mail] (Tom Neff) writes:
>What about launching Pegasus from a dirigible?
>
>OK, you don't get as many initial MPH as from a Buff [...] does
>it matter that much?

Yes, it matters a great deal.  Mass-ratio requirements increase
EXPONENTIALLY with the required delta-V.  Shaving a small margin
off the delta-V increases the payload fraction by a much greater
amount.  Increase delta-V, eventually payload goes to zero.

Assume a rocket which carries 10,000 kg of fuel, and has an
exhaust velocity of 3000 m/sec.  It must get up to 8000 m/sec
to go into orbit (assume no air drag, no climbing).  The
structural mass is 5% of the fuel mass.  This rocket can orbit:

0   kg  if launched with a 1134 m/sec penalty;
125 kg  if launched with a 500  m/sec penalty;
247 kg  if launched with a 0    m/sec advantage (blimp into polar orbit);
317 kg  if launched with a 250  m/sec advantage (airplane into polar orbit);
385 kg  if launched with a 470  m/sec advantage (eastward launch from equator);
469 kg  if launched with a 720  m/sec advantage (eastward airplane launch).

Note that a 9% advantage in launch speed gives a *90%* increase
in payload.  This translates to a big cut in $/kg to orbit.

LTA craft have other problems:  their lifting gas expands with
altitude, which gives them a service ceiling usually < 15,000 ft.
An airplane can climb above much more of the atmosphere, which
reduces drag penalties as well.  In short, an airplane is a much
better launcher candidate than a blimp or dirigible.
--
              Oversimplification doesn't solve problems, it just
[phone]          changes them into less tractable problems.
Russ Cage, Robust Software Inc.            [e-mail]

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

Date: 24 Apr 90 01:43:28 GMT
From: uokmax!munnari.oz.au!csc!csc3!ccadfa![e-mail]  (Christopher JS Vance)
Subject: Re: Our galaxy

[e-mail] (Will Martin) writes:

| In a related topic, is there any "better" name for our galaxy than "the
| Milky Way"? Something that sounds more like a proper name and is more

| "dirt"... Is there *any* Earth language that has a name for the planet
| that is different from the word for "dirt" or "soil" or "ground"?]

`Galaxy' is derived from the Greek word for milk.  So even on the
galactic scale we're pretty parochial in our naming system.

And `Sol' is just Latin for sun, isn't it?

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

Date: 25 Apr 90 11:36:31 GMT
From: agate!oreo![e-mail]  (Greg)
Subject: Re: Other Big Bangs

In article <[e-mail]> [e-mail] (Tim Maroney) writes:
}>In article <[e-mail]>, vac@sam (Vincent Cate) writes:
}>) The evidence will reliably show that there are stars expanding from a few
}>) other points in similar numbers to what we see expanding away from the
}>) location of our big bang.
}Oh boy.  Haven't even caught up with the state of cosmology in the 1920's,
}have we?  There is no discernable center of the expansion.

Tim, for someone who thought that gravity run backwards in time is
anti-gravity, you sure are arrogant!

Don't take him too seriously, Vincent.  His physics is no better
than his manners.
---
Greg

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

Date: 25 Apr 90 15:23:56 GMT
From: voder!dtg.nsc.com![e-mail]  (Alan Hepburn)
Subject: Re: Our galaxy

In article <[e-mail]> [e-mail] (Garrett A Wollman) writes:
>
>Of course, that's cheating.  What we need is a numbering system that's
>not so geocentric; we should chose some other center (perhaps that
>hypothetical point 10 kpc away?) from which to base our system...still
>purely arbitrary, but it would at least free us to speak in less charged
>terms about our home.
>
>

     Actually, I think that referring to Earth as SOL-3 is more
heliocentric than geocentric.  To be really detached, maybe we
should refer to it on the basis of our position in the galaxy, or
something along those lines.






--
-------------------------------------------------------------------------------
Alan Hepburn                       "Everybody is ignorant, only on
mail: [e-mail]         different subjects."  - Will Rogers
-------------------------------------------------------------------------------

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

End of SPACE Digest V11 #318
*******************