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Subject: SPACE Digest V13 #339

SPACE Digest                                     Volume 13 : Issue 339

Today's Topics:
          Question about spacetrack report 3
       Chemical rocket complexities (was Re: "Follies")
     Re: Chemical rocket complexities (was Re: "Follies")
             Re: Project Iridium queries
              Re: SPACE Digest V13 #333
            Re: Station Atmosphere

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

Date: 30 Mar 91 17:46:27 GMT
From: att!news.cs.indiana.edu!nstn.ns.ca!ac.dal.ca!dal1![e-mail]
Subject: Question about spacetrack report 3

I recently picked up the "SPACETRACK REPORT NO. 3" from a friend
and have a couple of quick questions.

The report (dated 1980) mentions that the models presented were
modified with changes that were _expected_ to be implemented in
March 1981. Did this happen? It also states that the NORAD element
sets were expected to be based on the SGP8 and SDP8 models in the
future. Did this ever happen? Are yet newer models being used at
this time?

Being a neophyte to astrodynamics I have few clues about the
coordinate system the predictions are refered to. The report
doesn't mention them so I guess everyone's in agreement - but
I don't know what the agreement is. I'd expect Z to be the spin
axis of the earth and X to be fixed to Greenwich but who knows...
Can someone clarify this for me?

-Jeff [e-mail]    Technical University of Nova Scotia

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Date: 31 Mar 91 02:24:06 GMT
From: usc!zaphod.mps.ohio-state.edu!magnus.acs.ohio-state.edu!csn!pikes!mercury.cair.du.edu!isis!isis![e-mail]  (Glenn A. Serre)
Subject: Chemical rocket complexities (was Re: "Follies")

Preliminary remarks:
1. I personnally agree with Nick that convential chemical rockets are
unlikely (at best) to be able to provide 4 orders of magnitude reduction in
launch costs.
2. I also agree that we (U.S. taxpayers) should be financing research into
"exotic" launch schemes (light gas gun, E-M launchers, etc. ).
However,
3. I disagree that chemical rocket costs cannot be reduced significantly
(2 to 10 times reduction).
4. I disagree that [all] current rocket designs are at or near their their
"technical limits".

Following are comments to a portion of one of Nicks posts (I chose Nick's
post because it seems like a good starting-point.).
Nick's post:
Fine, please introduce some technical details that are more relevant.
For example, we might want to talk about the complexity involved in
gyroscopes and the precise gimballing of high-power thrusters, high-power
cryogenic pumps, tracking, the handling of large amounts of flammable
oxidizers and liquid oxygen, the handling of large ductile structures,
etc.  etc. You don't want to talk about that, because then the necessary
complexity of rockets, and the reason they aren't an exception to the
vehicle/fuel cost and fuel/payload mass ratio curves, would become readily
apparent.

Me:
Precise gimballing of high-power thrusters:
Thrusters don't neccessarily need to be gimballed.  You can
a. Use verniers.
b. Inject fuid into the nozzle to change the thrust vector, which is
exactly what the current Titan IV and Commercial Titan SRMs do.

High-powered cryogenic pumps:
You don't neccessarily need the pumps to be high-powered or cryogenic.
The Titan rockets (and Ariane) don't use cryo fuel in the lower stages.
What was the pressure at the pump outlet of the F-1's?  Probably not nearly as
high as for the SSMEs.

Tracking? I'm not sure tracking is very expensive.  How expensive is it to
track an airliner?

Handling large amounts of propellents:
Large amounts of gasoline and liquid oxygen and shipped everyday by truck
and rail.  LNG is shipped in tankers.

Handling large "ductile" structures (I think flexible is more what you mean,
but there's probably an even better word, somewhere :-):
To take a real-life example, the Titan IV 1st and 2nd stages are transported on
trailers towed by truck to and from the airport.  To erect  them, a "spider"
is attached to the top ring and a crane lifts the top end, pivoting the tank
to vertical.  The bottom end pivots on a fixture on the trailer.  Total
crew required is 5-10 persons (if you include Safety, Quality, Hangers-on,
etc it probably comes out to about 50 people actually present :-).  total time
ismuch less than one shift, including mounting the stage to the launch heads
or lower stage.

Gyroscopes:
I don't know how much these cost, anyone else out there have a clue?

What other reasons are there for chemical rockets to be complex and cost a
lot of money?  Inquiring minds want to know.

--

--Glenn Serre
[e-mail]
--

--Glenn Serre
[e-mail]

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

Date: 31 Mar 91 20:47:58 GMT
From: rochester![e-mail]  (Paul Dietz)
Subject: Re: Chemical rocket complexities (was Re: "Follies")

In article <[e-mail]> [e-mail] (Glenn A. Serre) writes:

>High-powered cryogenic pumps:
>You don't neccessarily need the pumps to be high-powered or cryogenic.
>The Titan rockets (and Ariane) don't use cryo fuel in the lower stages.

Indeed, in some case you do not need pumps at all.  If one is
designing a large, heavy, sea-recoverable first stage, the tank walls
will be pretty thick.  If so, the tanks should be able to sustain
considerable pressure, so why not a pressure-fed first stage?  The
chamber pressure and therefore Isp is somewhat lower, but that is not
much of a problem on a first stage.

>What was the pressure at the pump outlet of the F-1's?  Probably not nearly as
>high as for the SSMEs.

I don't know the pressure at the pump outlets, but the chamber pressures
are 1122 psia (F-1) and 2970-3250 psia (SSME, nominal and max).  Source:
Sutton, 5 ed., page 196.

    Paul F. Dietz
    [e-mail]

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

Date: 31 Mar 91 22:02:32 GMT
From: milton!sumax!thebes!polari![e-mail]  (Charles Radley)
Subject: Re: Project Iridium queries



Last July I attended Vandenburg Spaceweek
where a Motorola representitive stated that several third world
countries have expressed interest in Iridium to the extent of
wanting to help fund its development in proportion to the  coverage
provided in their country.
  Many third world countries lack telephone service, and cannot
afford to fund a geosynchronous system, nor big ground stations
for Intelsat type service.    hey see iridium as a quick and dirty
short cut to getting a first time telephone service to open up
large inaccessible areas.
.

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

Date:         Sun, 31 Mar 91 18:23:38 EST
From: Tommy Mac <[e-mail]>
Subject:      Re: SPACE Digest V13 #333

Re:  Brian Rice's viewing of Aurora

[Expressed dismay at not seeing the 'shimmering curtain' he expected]

Don't worry, no one has decieved you.  The last time I saw any aurora, about 8
years ago in Mid-Michigan, it was indeed a shimmering curtain, although the
curtain was less prominent than the shimmering as the night went on.  I was
particulary lucky that night, since it lasted about 6 HOURS!  About 2a.m., I
started seeing very faint flashes that seemed to move across the whole sky,
from South to North.

I was thinking, 'lucky suckers', last week, since I got up the mext morning to
radio report that 'Illinois residents were treated to a rare show of the
northen lights...etc etc'.

But then, my sister, in Washington (state) says she sees them about 5 times per
month, to the point that they are common as rain.  Maybe we're lucky that it's
as rare as it is....

Tommy Mac
18084tm@msu
Acknowledge-To: <18084TM@MSU>

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

Date: 31 Mar 91 19:59:12 GMT
From: world!ksr![e-mail]  (Chris Jones)
Subject: Re: Station Atmosphere

In article <[e-mail]>, vec@acadia (Vance
Cochrane) writes:

>I have a general question.  When the soviets are up in their Mir for many
>months at a time, how is the atmosphere provided? Do they cart it up every so
>often (sounds doubtful) or do they ( or we for that matter ) use some sort of
>chemical regeneration?

A little of both.  They do have chemical regeneration units which first
dehumidify air (reclaiming the water for later use), and then pass the dry air
over sheets of potassium superoxide.  Carbon dioxide reacts with these sheets,
forming potassium carbonate and oxygen.  Excess carbon dioxide is removed from
the air using lithium hydroxide, as is done on US flights.  There have been
plants on board some of the Salyuts and Mir, but any oxygen replenishment they
provided was incidental; they were being used to study plant growth in
microgravity.  There are tanks on board which contain the nitrogen and oxygen
which make up the station's atmosphere, and the Progress resupply ships carry
tanks to replenish amounts lost during EVAs, as well as new potassium
superoxide sheets and LiOH cannisters.  The consumed regeneration units and
LiOH cannisters are either dumped overboard or put into a Progress which is
later deorbited and burned up on reentry.

--
Chris Jones    [e-mail]    {world,uunet,harvard}!ksr!clj

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

End of SPACE Digest V13 #339
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