Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_2/V16NO240.TXT

Internet Message Format | 1993-07-13 | 27KB

Date: Mon,  1 Mar 93 05:19:22
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #240
To: Space Digest Readers
Precedence: bulk


Space Digest                Mon,  1 Mar 93       Volume 16 : Issue 240

Today's Topics:
                           Aurora (rumors)
                         Battery help needed!
                         Cheap access to LEO
                  Getting people into Space Program!
                       Instead of Fred.. ETCo?
                   Looking for Lunar Ephemeris S/W
                          military aircraft
                 Posting MSFC Morning Status Reports
    Reboosting a denser station (was Re: payload return from Fred)
                          Refueling in orbit
    Reliable Source says Freedom Dead, Freedom II to be developed
                Robert Goddard or liquid-fuel rockets
                         Satellite Directory
                 SOLAR gravity assist? Yup. (3 msgs)
                        Spy Sats (Was: Are La
           SSF Resupply (Was Re: Nobody cares about Fred?)

    Welcome to the Space Digest!!  Please send your messages to
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----------------------------------------------------------------------

Date: Fri, 26 Feb 1993 12:59:03 -0500
From: Lawrence Curcio <[e-mail]>
Subject: Aurora (rumors)
Newsgroups: sci.space

I'm impressed by the side-looking radar argument. I find the argument
regarding speed less impressive. If you spy on me frequently, and I hear
enough booms, you're going to find me ready for you one day. It matters
only a little that you're gone when I find out you've been there.

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

Date: Fri, 26 Feb 1993 15:30:56 GMT
From: "anthony.r.rizzo" <[e-mail]>
Subject: Battery help needed!
Newsgroups: sci.space,sci.electronics,sci.aeronautics,sci.chem,sci.engr

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (anthony.r.rizzo) writes:
>>You might consider using a fuel cell.  NASA already uses a bunch
>>of them on the shuttle.  So safety should be less of a problem.
>
>On the contrary, it'll be more.  NASA uses lots of things on the shuttle
>that individual experimenters (especially in secondary payloads) are not
>allowed to even think about.  For example, Galileo flew on the shuttle
>with lithium batteries aboard -- that's how its atmosphere probe is
>powered.
>
>If they object to lithium batteries, imagine what their reaction will
>be to liquid hydrogen and oxygen.
>--
>C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology
>effect since OS/360.                    |  [e-mail]  utzoo!henry


I recall reading about iron-titanium-hydride (or some similar material)
for storing H2 in a high energy density, low pressure, room temperature,
mostly solid form.  To me, at least, that seemed like a relatively
safe way to handle H2.  O2 would have to be in a high pressure bottle.
Liquid cryogenic storage of H2 and O2 couldn't possibly be done
safely in the shuttle compartment, since the containers would have to
be vented to prevent them from rupturing.  But Fe-Ti storage
could be done without venting and at much lower pressures than
simply compressed H2.  Unfortunately, I don't know of a similar
way of storing O2.

Since there is already O2 in the crew compartment, leakage of O2 from
the high pressure bottle would pose little added risk.  The risk
comes from leaking H2, IMHO.  But Fe-Ti storage of H2 is one of
the safer methods, because the extraction process (if I remember
correctly) is endothermic.  A leak cools the Fe-Ti container and
actually helps to diminish the leak rate.    But this is only
one man's opinion, of course.  ;-)

Tony

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

Date: Fri, 26 Feb 1993 12:53:07 -0500
From: Lawrence Curcio <[e-mail]>
Subject: Cheap access to LEO
Newsgroups: sci.space.shuttle,sci.space

LEO for $22.00/lb - that's all we need! At that rate, we'd have to levy
a tax to raise the price of space junk.

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

Date: 26 Feb 1993 10:18:31 -0500
From: Pat <[e-mail]>
Subject: Getting people into Space Program!
Newsgroups: sci.space

 Gee, Gary, You forgot to rave about the canadarm.  You must be getting
old:-)   Memory is the second thing to go:-).....

I think you miss the point.  20 missions/year  any of which could have
qualified as a space shot, over a 9 year period during a test program
is quite  a record.  When a "test" vehicle can maintain a sorty
rate twice that of a "operational" vehicle, there is a problem.

Sure they are different vehicles,  but one could reliably plan on X-15
availabilty during it's test program, and one still has trouble
planning on shuttle availabity and it's "operational".

Sure, they are significantly different vehicles,  rather like an F-15
compared to a 727,  but if you could only book passage on a 727
6 years in advance, wouldn't that indicate a problem?

You can stop raving about cargo capacity, and crew size and the arm
and the payload bay.  We all know about that.  My point is that
any system witha  low availability rate like the shuttle
hardly qualifies as "operational"....

pat

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

Date: Fri, 26 Feb 1993 15:29:27 GMT
From: WELLS <[e-mail]>
Subject: Instead of Fred.. ETCo?
Newsgroups: sci.space

In article <[e-mail]> Charles Chung,
[e-mail] writes:
>What if NASA contracted the External Tanks Corporation for a space
>station.

This was studied in the '85 to '86 time frame. The concept was to strap
a large number of ET's together to make a platform for an SPS or Solar
Power Satellite. The ET's were to be taken to orbit while attached to
the orbiter, final kick to be accomplished using a small strap on
propulsion module on the aft end of the ET that burned its residual
prop. Problems with the approach were numerous and included quantity and
mixture ratio uncertainties of residual H2 and O2, dealing with
propellant pressure and phase uncertainties, how to tie in to the ET
both structural and fluid, control, and the "crumby" tank itself (the
tank insulation would crumble and spall off after a period on orbit).
...fun to dream, though.

Dennis W.

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

Date: 26 Feb 93 16:16:28 GMT
From: "Kieran A. Carroll" <[e-mail]>
Subject: Looking for Lunar Ephemeris S/W
Newsgroups: sci.space,sci.astro

I am posting on behalf of a fellow engineer who is working
on a spacecraft mission planning project with a tight deadline.
She is wondering if there is source code available (in C
or F77) for software for predicting the location of the Moon
relative to the Earth. I suppose the ideal case would be a
self-contained subroutine or module that carried out just this
one function. Extreme accuracy is not necessary, but the
software is needed in about the next 2 weeks.

Any help in locating such software would be greatly appreciated.
Please respond via e-mail; if there's much interest shown, I'll
summarize and post responses. Thanks in advance!
--

     Kieran A. Carroll @ U of Toronto Aerospace Institute
     uunet!attcan!utzoo!kcarroll [e-mail]

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

Date: Fri, 26 Feb 1993 16:14:14 GMT
From: Dillon Pyron <[e-mail]>
Subject: military aircraft
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Brian Stuart Thorn) writes:

  WARNING WILL ROBINSON!!!  DANGER!!!  DANGER!!!
>>The A-12 was intended to replace the aging A-6.  It ran into
>>management problems, overran budget, and has been cancelled.  Aurora
>>is the (rumoured only) replacement for the SR-71 Recce aircraft, which
>>has (once again, rumoured only) reportedly been flying for a number of
>>years now.
>
>    The writer probably confused "Aurora" and "Avenger". However, I'm
>    not sure that the A-12 Avenger II was even supersonic, much less
>    designed for Mach 4.

The A-12 which the Navy crushed was a stealth plane of maybe Mach capacity (it
was only a paper airplane).  The A-12 which went really fast was the
predecessor to the RS-71 (did Johnson really rename SR-71 by accident?)  I
never heard the A-12 called the Avenger II.

So, we have:
A-12  CIA
SR-71 CIA/NSA/USAF/NASA
A-12  USN
"Aurora" ?????
--
Dillon Pyron                      | The opinions expressed are those of the
TI/DSEG Lewisville VAX Support    | sender unless otherwise stated.
[phone] (when I'm here)     |
[phone] (when I'm home)     |No people gave up their rights all at once.
[e-mail]          |Preserve the Bill of Rights.
PADI DM-54909                     |Protect the Second Amendment.
Happy Birthday William F. "Buffalo Bill" Cody

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

Date: 26 Feb 93 16:16:31 GMT
From: [e-mail]
Subject: Posting MSFC Morning Status Reports
Newsgroups: sci.space

Would anybody be interested in seeing the morning status reports which
come out of Marshall Space Flight Center?  They contain information
which duplicates some of that in the KSC Shuttle Status Reports.
They're pretty technical, and they go into a lot of detail on the
current work being done on the propulsion systems, but they're probably
not of much interest to most of us.  However, if there's enough
interest, I'd be willing to arrange for these things to be piped into
sci.space.news every day.  Please e-mail your response to me, pro or
con.  I've attached a sample.

Now, the next question is, will I be *allowed* to post these things....

-- Ken Jenks, NASA/JSC/GM2, Space Shuttle Program Office
      [e-mail]  [phone]

     "The earth is the cradle of humanity, but mankind will not stay in
     the cradle forever." -- Konstantin Tsiolkvosky
-----------------------------------------------------------------------
 Responsibility: Houston/Clever                             Updated: Daily
 Note: All times Eastern                     Note: Dates Subject to Review

                         MSFC/RO MORNING REPORT 02/25/93

 STS55/SL-D2 LAUNCH DATE: NET 03/13/93
 ORBITER: OV102/14 (Pad A)
     INTEGRATED ACTIVITIES: Engine 1,2 and 3 HPOTP securing is continuing.
     Preps are in work for pre-launch propellant loading, scheduled for
     Wednesday.  SSME FRT's and aerosurface cycling are scheduled to begin
     Saturday at 0800.  The blanking plates are installed in support of Helium
     Signature Test scheduled for Tuesday.
 SSME ASSIGNMENTS: 2030,2034,2011
     GENERAL: All engines HPOTP securing is in work.  Leak checks are scheduled
     for Friday.
     SSME 2030:
     SSME 2034:
     SSME 2011:
 SOLID ROCKET MOTORS AND BOOSTERS RSRM30/BIO57
     GENERAL: Preps for propellant load are in work.
 EXTERNAL TANK: ET56
     ET56: Installation of the GH2 blankoff is complete.

 STS56/ATLAS-2 NEW TARGET LAUNCH DATE: 04/01/93
 ORBITER:OV103/16
     SCHEDULED ACTIVITIES: OMS Pod structural leak checks are complete.  Orbiter
     aft closeouts are continuing.  ET door cycles are complete.  Heat shield
     rework is continuing.  Orbiter/ET umbilical umbilical closeout and door
     functional are complete,  OMS/RCS flight control checkout is complete.
     Rollover to the VAB for mate is scheduled for 3/2/93.
 SSME ASSIGNMENTS: 2024,2033,2029
     SCHEDULED ACTIVITIES: Engine removal is complete.  All engines are
     currently in the engine shop.
     SSME 2024: Hot gas leak checks are complete.  Preps for flow checks are in
     work.
     SSME 2033: HPFTP U/N 6107 securing is in work.  HPOTP receiving inspection
     is in work on U/N 6109.
     SSME 2018: HPOTP U/N 4602 securing is in work.
 SOLID ROCKET MOTORS AND BOOSTERS RSRM31/BIO58
     ET/SRB MATE: The LH S&A leak checks are complete.  RH S&A leak checks are
     continuing.
 EXTERNAL TANK: ET54 (ET/SRB MATE: SCHEDULED 03/03/93)
     ET54: Installation of aft fairing is complete less a DR on bare metal.  Aft
     fairing PDL closeout is scheduled for Friday.  Removal of the umbilical
     covers and Bi-pod installation is scheduled for Friday.

 STS57/SPACE HAB 1 NEW TARGET LAUNCH DATE 04/28/93
 ORBITER: OV105/04 (H/B-1)
     SCHEDULED ACTIVITIES: Ammonia boiler servicing is complete.  Payload
     premate test is continuing.  Spacehab installation is scheduled for 3/3.
     Tunnel adapter installation is complete.  OMS pod functionals are complete.

 SSME ASSIGNMENTS: 2031,2109,2029
     GENERAL: Engine installation is scheduled for mid-April at the pad.
     SSME 2031: No SSME activity.
     SSME 2109: No SSME activity.
     SSME 2029: No SSME activity.
 SOLID ROCKET MOTORS AND BOOSTERS RSRM32/BIO59
     GENERAL: Orbiter mate is scheduled for March 26th.  Rollout to the pad is
     scheduled for March 31th.
     LH AFT JT: Cork is in cure.
     LH CTR JT: The installation of heater and sensor is complete.  Cork bonding
     preps are in work.
     LH FWD JT: The pin retainer band installation is complete.
     RH AFT BOOSTER: The booster is set down on the HDP's.  Stud installation is
     pending RTV cure time on two studs.
     RH AFT CTR: Awaiting stud installation prior to mate.
 EXTERNAL TANK: ET58 (Checkout Cell) ET/SRB Mate: 03/08/93
     ET58: LH2 QD purge barrier mod is complete.  Flapper valve access port
     closeout, LH2 is in work.  Move to the transporter is scheduled for 3/5.

     FROM DAILY KICS, TELECONS AND REPORTS FROM THIOKOL, USBI, MMC AND
     ROCKETDYNE LSS ORGANIZATIONS

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

Date: 26 Feb 93 04:28:07 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: Reboosting a denser station (was Re: payload return from Fred)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
> Why not?  Most of it will be more useful up there than down here.  And
> a heavier station is *better*, because it reduces the frequency with
> which reboost is needed; even trash is more useful as station ballast
> than as return cargo.

This is because air resistance is kinder to a dense object than a
flimsy one, for equal surface area. But obviously you need to consume
more propellant to reboost the heavier station when it eventually
*does* need a reboost.  Henry implies that this  tradeoff is
favorable.  Why?

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

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

Date: 26 Feb 93 15:58:44 GMT
From: Pat <[e-mail]>
Subject: Refueling in orbit
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Brian Stuart Thorn) writes:
>>In article <[e-mail]> [e-mail] (Brian Stuart Thorn) w
>r
|
|     Galileo: That's one.
|     Cassini: That's two.
|     Pluto Fast Flyby: Not on that budget, they don't. Hell, they are
I am glad to know you speak for staehle and the JPL.

|     considering, for cost reasons, using Proton instead of Titan IV,
|     never mind two Titan-class launches (Centaur and Centaur-refueler.)
 I believe the concept for centaur refueling involved the shuttle
and use of dregs fuel from the ET.  One mission, up and out.  Of course
that is more money then a T3 or T4,  but it would have been useful
for planning purposes.
|
|>That doesn't even consider potential missions that aren't even being
|>*planned* because they appear to be impractical within the limitations
|>of current boosters.
|
|     It doesn't seem likely to me that in 1994 NASA will decide to launch
|     a Mars Sample Return Mission in 1995. More reasonably, a big mission

I believe planners work from what's in hand, not what might be
done assuming people get some nerve and backbone.  Besides,
MO and it's sister birds could have planned on it.  put 2 of the
birds on shuttle centaur and get them there at teh same time.


|     like that will be years in the making (say, 5 at least) leaving
|     considerable time for developing cryo refueling capabilities. When
|     we need it, we'll develop it. Hasn't that *always* been the way?
|     They didn't mate Titan and Centaur until Voyager needed it.
|

I think it's easy enough to put a stage onto a rocket.  developing
techniques and hardware is a little bit harder.

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

Date: 26 Feb 93 05:40:58 GMT
From: Pat <[e-mail]>
Subject: Reliable Source says Freedom Dead, Freedom II to be developed
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>In article <[e-mail]>, [e-mail] (Pat) writes...
  I didn't realize people were so cavalier in cutting holes in submarine
hulls.  I thought that was reserved for overhaul.  My understnading
was pending that sort of thing, pretty much all of the major systems
could be broken down to pass through the hatches.  I had worked on
sonar systems, and the consoles and computers were all restricted to
a 23" circular size, i thought it odd until I was told why.

|>
|
|The problem with this design is that the problems with EVA and on orbit
|maintenance is magnifed tenfold. Not only do you have to do all of the
|EVA associated with the external structure, BUT you have to do EVA to
|install all of the internal equipment, life support..... AND then do
|all of your testing on orbit. Then when things don't work which will happen
|you have to have all of these contingency missions just to correct all of
|the things you did not know about till you got there.
|

Ah,  but what is the cost differential?  I mean, if you use a
Pre Integrated Truss Freedom already designed one,  and you plumb
the ETs,  then you have to EVA to attach a tank to thettruss and
handle the matings of piping, but Freedom had to do that.
THen you OPen the hatches on the ET and carry all the payloads
inside.   You can then pressurize and work near shirt sleeves.
It may be cold,  but you work on getting life supprot and heating
on first.  I don't think the EVA would be impossible in carrying in
Pallet gear.   Maybe you even design docking adapters to dock the
shutttle to the ET, and everything gets carried in dry.

|With the recent (91) redesign of SSF most of these issues were resolved by
|changes such as the pallet change outs and all of the other EVA reduction
|ideas that now are a part of the design. Don't get me wrong, there are many
|ways to reduce the cost of SSF but going to an external tank
|design is not one of them.
|
But if you have properly plumbed the ET, then most of the work the
on orbit specialists do is Pallett changeout and installs.

plus you get such abig gain in costs savings and space.
Really dennis, there have been a lot of serious ET proposals
in the past.  just because Fred shit canned the idea doesn't
make it bad.

pat

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

Date: Fri, 26 Feb 1993 13:13:01 -0500
From: Lawrence Curcio <[e-mail]>
Subject: Robert Goddard or liquid-fuel rockets
Newsgroups: sci.space

Check  _The Papers of Robert H. Goddard_ Mcgraw Hill 1970, Mrs. Esther
C. Goddard, Ed.

It's an interesting set. He's far more military-oriented than folks make
him out to be. Also, if you read Willie Ley's _Rockets, Missiles, and
Men in Space_, you'd think the Germans invented much of the stuff
Goddard invented. W.L. tells you the VFR was ignorant of Goddard's work.
In reality, Goddard and Oberth exchanged papers as early as 1922.
Goddard told Oberth about regenerative cooling. On the other hand,
Oberth told Goddard about atomizing propellants in the combustion
chamber, and Goddard didn't think it would work.

Good Luck,
-Larry C.

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

Date: Thu, 25 Feb 1993 20:30:00 GMT
From: Gary Hughes - VMS Development <[e-mail]>
Subject: Satellite Directory
Newsgroups: sci.space,sci.astro,alt.sci.planetary

In article <[e-mail]>, [e-mail] (WOODS DEBRA J) writes...
>
> Date: February 7,1993
> From: Mr. Phillip S Clark, Molniya Space Consultancy
> Subject: A New Monthly Satellite Directory
> Newsgroups: sci.space, sci.astro, alt.sci.planetary

Any chance of reposting this without the lines being truncated?

gary

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

Date: 26 Feb 93 04:21:26 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: SOLAR gravity assist? Yup.
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Paul Dietz) writes:
>
> Bill Higgins asks about a "solar gravity assist".
>
> This is *not* the same as the more well-known Jupiter gravity assist.

Yes, it is.  Shocked me.

> Rather, it is an example of the Oberth Effect -- rockets are more
> effective when fired deep in a gravity well.

Oops, I should have mentioned that Lars's message *also* triggered
off a discussion of this trick in alt.sci.planetary.  But I was
talking about using the Sun for pure slingshot, no propulsion.

During the first and second stage         Bill Higgins
flights of the vehicle, if a serious      Fermi National Accelerator Laboratory
irretrievable fault should occur and      [e-mail]
the deviation of the flight attitude of   [e-mail]
the vehicle exceeds a predetermined       SPAN/Hepnet: 43011::HIGGINS
value, the attitude self-destruction
system will make the vehicle
self-destroyed.
     --Long March 3 User's Manual
     Ministry of Astronautics, People's Republic of China (1985)

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

Date: 26 Feb 93 10:31:33 -0600
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: SOLAR gravity assist? Yup.
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Henry Spencer) writes:
> In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>>This is *not* the same as the more well-known Jupiter gravity assist.
>
> Paul, go back and read Bill's posting much more carefully.  He really
> is talking about a Jupiter-style gravity assist, not an Oberth gravity-
> well maneuver.  And no, he has not lost his marbles.

Thanks, Henry.  This is the nicest thing anybody's said about me all week...

Bill Higgins, Beam Jockey         | "I'm gonna keep on writing songs
Fermilab                          | until I write the song
Bitnet:      [e-mail]  | that makes the guys in Detroit
Internet:  [e-mail]  | who draw the cars
SPAN/Hepnet:      43011::HIGGINS  | put tailfins on 'em again."
                                            --John Prine

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

Date: Fri, 26 Feb 1993 16:23:38 GMT
From: fred j mccall 575-3539 <[e-mail]>
Subject: SOLAR gravity assist? Yup.
Newsgroups: sci.space

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

>In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>>Bill Higgins asks about a "solar gravity assist".
>>
>>This is *not* the same as the more well-known Jupiter gravity assist.

>Paul, go back and read Bill's posting much more carefully.  He really
>is talking about a Jupiter-style gravity assist, not an Oberth gravity-
>well maneuver.  And no, he has not lost his marbles.  Read his posting.

It seems to me that for a launch from Earth's orbit, you are going to
need so much delta-v to get that close to the Sun that you'd be better
off to use it in some other way.  After all, we're talking about
killing enough orbital velocity to get within a few (relatively
speaking) kilometers of the surface of the Sun.  There is also the
problem of the Sun's atmosphere eating up anything you gain by this
maneuver (due to atmospheric drag on the way past the Sun).

I'm afraid my intuitive answer is that this is a net Lose.  Do we
think that intuition is really far enough off in this case that we
need to actually ask someone to run the numbers?

--
"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: Fri, 26 Feb 93 14:51:09 GMT
From: Dean Adams <[e-mail]>
Subject: Spy Sats (Was: Are La
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Roland Dobbins) writes:
>DA>From: [e-mail] (Dean Adams)
>DA>OR, are you talking about Lacrosse or Aurora?

>
>Yes, among others . . .
>
>Although those two are primarily ELINT/SIGINT.

Lacrosse is a radar imaging satellite system, with two birds curently
on orbit.  Aurora is the "Mach 6" aerial recon platform that has been
much discussed lately.  Aurora, like the SR-71 and U-2/TR-1 would have
the ability to carry SIGINT sensor packages, but "on demand" photo
recon would be it's primary mission...

The space based ELINT systems have names like Rhyolite, Aquacade,
and Magnum.  These are placed into a GEO orbit with a little help
from an IUS, where they can deploy LARGE antenna arrays and ferret
out all kinds of interesting signals...

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

Date: Fri, 26 Feb 1993 16:44:33 GMT
From: Frank Crary <[e-mail]>
Subject: SSF Resupply (Was Re: Nobody cares about Fred?)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>>As for the thruster modules, since they are swapped
>>out every 180 days, it would be a simple matter to *add* valving
>>and fittings to a replacement pack to allow on orbit fueling at
>>any time.

>I'm glad you agree that it is simple. So let's do it now and
>save a few billion $$ by refueling in space?

>>Since we *are* counting on Shuttle for the
>>short run, there's no reason to incur the upfront costs of modifying
>>off the shelf thruster packs now.

>Let's see, we are looking at one to two flights a year dedicated to
>replacing thrusters. That's roughly 50 flights over the life of the
>station. Half could be eliminated with refueling so we are looking
>at a savings of over $12 billion by refueling in space.

That's not a very good economic model... More to the point, we would
be saving about $500 million per year while the station is operating.
Since people usually expect a 8% or so rate of return, this modification
would be a good investment if it cost under $4 billion.

                                                  Frank Crary
                                                  CU Boulder

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

End of Space Digest Volume 16 : Issue 240
------------------------------