Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT_ZIP/spacedig/V16_2/V16NO237.ZIP/V16NO237

Internet Message Format | 1993-07-13 | 37KB

Date: Mon,  1 Mar 93 05:05:15
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #237
To: Space Digest Readers
Precedence: bulk


Space Digest                Mon,  1 Mar 93       Volume 16 : Issue 237

Today's Topics:
                    Battery help needed! (2 msgs)
                      Galileo Update - 02/25/93
                    Hopkins Leaks (was Re: Blimps)
                         Mars CD-ROM products
                McElwaine disciplined! (somewhat long)
                     Refueling in orbit (2 msgs)
                 Sky & Telescope Weekly News Bulletin
                 SOLAR gravity assist? Yup. (2 msgs)
            Soviet Energia: Available for Commercial Use?

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

Date: 25 Feb 93 21:44:37 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] (Benjamin John McCall) writes:
>Hi!
>
>I'm in charge of a student group at Caltech, and we're designing a small,
>self-contained payload for the space shuttle to observe gamma-ray bursts.
>
>One major problem we've encountered is the battery pack - we need about 200
>Amp-hours of power (at about 0.5 Amps), but it has to weigh less than 100
>pounds.
>
>SLA (Sealed Lead-Acid) doesn't seem to have the energy density, and
>Alkaline-Manganese (aka Duracell lantern batteries) have a very sloping
>discharge curve, making them undesireable.  NASA will not allow us to use
>any kind of Lithium-based cells.
>
>Does anyone have any information on alternative battery technologies, or
>even suggestions about who I might get in touch with (by phone or by email)?
>
>I've heard a little bit about Silver-Zinc, but have not been able to get in
>touch with anyone who has any information.
>
>Any help is greatly appreciated - please reply by email, as I don't necessarily
>read this newsgroup.
>
>Thanks in advance,
>
>Ben McCall
>[e-mail]
>
>--
>Ben McCall, Caltech - [e-mail]
>SEDS President, Technical Projects Coordinator


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.
A fuel cell also might have the appropriate energy density.
All you'd have to do is provide the fuel cell with the appropriate
supplies of O2 and H2, in the correct ratio of coarse.  The output
will be H2O + e.  It's been a long time since I read about
fuel cells, but I recall that 10 years ago there was considerable
discussion about small fuel cells with solid polymer electrolytic
membranes, i.e., no spillage of potentially toxic or corrosive
liquids.  I'm sure that NASA can give you more information
on the subject.  What do you think, RG?

Tony Rizzo

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

Date: 26 Feb 93 02:03:39 GMT
From: INNES MATTHEW <[e-mail]>
Subject: Battery help needed!
Newsgroups: sci.space,sci.electronics,sci.aeronautics,sci.chem,sci.engr

In article <[e-mail]> [e-mail] (Benjamin John McCall) writes:
>Does anyone have any information on alternative battery technologies, or
>even suggestions about who I might get in touch with (by phone or by email)?
>
>--
>Ben McCall, Caltech - [e-mail]
>SEDS President, Technical Projects Coordinator

How about an aluminum-air battery?  High-grade (>=99.99% Al) aluminum is the
anode and some inert, porous metal used as a cathode, through which you bubble
air.  It's apparently a fairly high-energy-density cell, insofar as you get
a great deal of electrical energy per kilogram (I don't have any sort of number,I'm afraid) and you get 2.7V per cell.

All of this stolen out of my first-year Chemistry text. :-)
Hope it's of some help.

--
                        Matt Innes
                        <[e-mail]>

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

Date: 25 Feb 1993 23:34 UT
From: Ron Baalke <[e-mail]>
Subject: Galileo Update - 02/25/93
Newsgroups: sci.space,sci.astro,alt.sci.planetary

Forwarded from Neal Ausman, Galileo Mission Director

                                   GALILEO
                       MISSION DIRECTOR STATUS REPORT
                                 POST-LAUNCH
                           February 19 - 25, 1993


SPACECRAFT

1.  On February 22, a NO-OP command was sent to reset the command loss timer
to 240 hours, its planned value during this mission phase.

2.  During the period from February 23 through February 24, a navigation cycle
was performed.  This navigation cycle provided near-continuous acquisition of
two-way doppler and ranging data during four consecutive passes of the
spacecraft over DSS-63 (Madrid 70 meter antenna), DSS-14 (Goldstone 70 meter
antenna), DSS-42 (Canberra 34 meter antenna), and then back to DSS-63.

3.  On February 24, real-time commands were sent to perform a Scan Actuator
Subassembly (SAS) friction calibration to verify that the friction level has
not changed; analysis of the data is in progress.

4.  On February 25, a wobble angle identification (ID) activity was performed
in the all-spin mode with the scan platform cone angle at 0 degrees and in the
dual-spin mode with the scan platform cone angle at 153 degrees; analysis of
the data is in progress.

5.  On February 25, Delayed Action Commands (DACs) were sent to turn the
Photometric Calibration Target (PCT) No. 1 heater on March 2 in accordance
with the Retro-Propulsion Module (RPM) pressure profile strategy.

6.  The AC/DC bus imbalance measurements have not exhibited significant change
(greater than 25 DN) throughout this period.  The AC measurement reads 19DN
(4.3 volts).  The DC measurement reads 141DN (16.6 volts).  These measurements
are consistent with the model developed by the AC/DC special anomaly team.

7.  The Spacecraft status as of pin Configuration - Dual-Spin
       c)  Spin Rate/Sensor - 3.15rpm/Star Scanner
       d)  Spacecraft Attitude is approximately 7 degrees
           off-sun (leading) and 7 degrees off-earth (lagging)
       e)  Downlink telemetry rate/antenna- 1200bps(coded)/LGA-1
       f)  General Thermal Control - all temperatures within
           acceptable range
       g)  RPM Tank Pressures - all within acceptable range
       h)  Orbiter Science- Instruments powered on are the PWS,
           EUV, UVS, EPD, MAG, HIC, and DDS
       i)  Probe/RRH - powered off, temperatures within
           acceptable range
       j)  CMD Loss Timer Setting - 240 hours
           Time To Initiation - 236 hours


GDS (Ground Data Systems):

1.  A review of the Phase 1 Telemetry Software Requirements Document (SRD)
was completed on February 24th.  No significant problems were identified.
A final version incorporating comments received at the meeting will be
published next week.  Phase 1 capabilities support the new mission baseline
through successful return of the Probe data and loading of the Phase 2 Flight
Software for orbital operations in April 96.

2.  Galileo participated in the DSN (Deep Space Network) Version 1.5 GCF
(Ground Communications Facility) upgrade data flow test on February 24, 1993
from 19:00 to 01:00 GMT using DSS-10.  The purpose of this test was to
demonstrate telemetry data flow path through the DSN SFOC Gateway (SG) to the
Error Correction and Switching (ECS) subsystem; the current data flow is the
External User Gateway (EUG) to the ECS.  This test exercised telemetry data
for Galileo only.  The test failed due to blocks of data being dropped between
the SG and the ECS.  The cause of this problem is unknown and is under
investigation.  A test report is expected from the DSN GCF cognizant engineer
during the week of March 1.  A retest of telemetry flow plus testing of
command, monitor and tracking data flow through the SG to ECS interface will
be performed prior to March 15, 1993.  The Version 1.5 GCF upgrade is
scheduled to be operational on March 15, 1993.

3.  The IBM 3090/200 to IBM ES/9000 transition certification testing
activities began on February 22.  Initial testing by the Data Management Team
(DMT) has uncovered job control default parameter differences between the two
machines which require modifications to runstreams used by the DMT. Flight S/W
certification testing is expected to begin during the week of March 1. Galileo
certification testing activities will continue thru March/April 1993.
Following successful completion of certification testing Galileo will
transition from the current IBM 3090/200 to the new IBM ES/9000-6121/610.


TRAJECTORY

     As of noon Thursday, February 25, 1993, the Galileo Spacecraft trajectory
status was as follows:

    Distance from Earth         62,966,500 km (0.42 AU)
    Distance from Sun           210,819,800 km (1.41 AU)
    Heliocentric Speed          112,400 km per hour
    Distance from Jupiter       639,964,600 km
    Round Trip Light Time       07 min. 02 sec.


SPECIAL TOPIC

1.  As of February 25, 1993, a total of 65066 real-time commands have been
transmitted to Galileo since Launch.  Of these, 59961  were initiated in the
sequence design process and 5105 initiated in the real-time command process.
In the past week, 18 real time commands were transmitted: 3 were initiated in
the sequence design process and 15 initiated in the real time command process.
Major command activities included commands to reset the command loss timer,
perform a Scan Actuator Subassembly (SAS) friction test, and a DAC to turn on
the PCT No. 1 heater.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | If you don't stand for
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | something, you'll fall
|_____|/  |_|/       |_____|/                     | for anything.

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

Date: 25 Feb 93 14:10:26 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: Hopkins Leaks (was Re: Blimps)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Josh Hopkins) writes:
> A _dirigible_ is a steerable vehicle.  It doesn't have to be rigid.  Rigid
> dirigibles are generally just called "rigids" (after you've established the
> context) or occasionally zeppelins after Count Ferdinand von Zeppelin.

If we're becoming *completely* pedantic, a "zeppelin" is a rigid
dirigible airship built by the Count's method; there are other
possible structures.  Nearly all the rigid airships ever built were
zeppelins (130 of them?  Or was it 130 German ones and three American
ones?) The British R100 and R101 are examples of non-zeppelin rigid
airships.

For the following paragraph we have the headline "Hopkins Leaks News
of Balloon Project."  (Or maybe it's just a trial balloon?)

> Lighter than air vehicles do indeed have lots of potential for Mars, though the
> difficulties can't be ignored.  It is however _far_ easier than floating a
> balloon on Jupiter, something Bill Higgins and I have been puttering around
> with.

Not much lately, though-- haven't had the time.  Most weekends I can't
even *get* to Jupiter...

Oh, by the way (though this quest failed on sci.aeronautics last
fall):  We're looking for a textbook that details balloon design!
Anybody know a good one?

Moira Higgins on astronomy:          Bill Higgins
"I can always find Orion.            Fermi National Accelerator Laboratory
Besides that the Moon                Internet: [e-mail]
is my only other specialty."         Bitnet:   [e-mail]

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

Date: Thu, 25 Feb 1993 21:29:46 GMT
From: Martin Connors <[e-mail]>
Subject: Mars CD-ROM products
Newsgroups: sci.space,sci.astro

I got together this list for my own use by using NODIS at NSSDCA. Since
interest may be stimulated by the Sky & Tel article and the fact that Mars
Observer looks like a go I thought I would post it. I have no commercial
interest in NSSDCA or the U.S. Government apart from a few promissary
notes (with G. Washington's picture on them) in my dresser drawer.
===
CD-ROM products relevant to Mars

Note that the MDIM is described in Sky & Telescope, March 1993, p. 94-96.
The Space Science Sampler apparently has a number of images of Mars'
moons.

Summary:  Space Science Sampler, Volumes 1 and 2 from the Planetary Data
System
(PDS).  Two discs contain 800 images of Uranus, its rings and satellites,
and
400 files of other space and Earth science data.

Contact:        Mr. Randal Davis
                LASP, Campus Box 392
                University of Colorado
                Boulder, CO  80309
                [phone], Fax [phone]

[] Mars Digital Image Model

The Planetary Data System (PDS) at JPL, the Mars Observer project and the
U.S. Geological Survey (USGS) has put together Mosaicked Digital Image
Models (MIDM) of the Martian surface taken by the Viking Orbiter
spacecraft.
This CD-ROM set is not to be confused with the Viking Orbiter CD-ROM set
released earlier.  The Viking Orbiter CD-ROM contains raw Viking images
only.
The MIDM CD-ROMs are images compiled from the raw Viking images which were
further processed to reduce radiometric and geometric distortions, and to
form
geodetically controlled mosaicked images.  The data are stored as digital
maps
at 1/256 degree/pixel resolution (231 meters) and 1/64 degree/pixel
resolution
(943 meters).  Also included are air-brushed maps of the entire planet of
Mars
at 1/16 degree/pixel resolution (3.69 km).

Contact:                NSSDC Coordinated Request and User Support Office

Originator:             Dr. Eric Eliason
                        USGS Geological division
                        2255 North Gemini Drive
                        Falgstaff, AZ 86001
                        [phone]
                        ASTROG::EELIASON

NSSDC ID                75-075A-01f/083A-01C
QUANTITY                06
COST                    $50.00 + $9.00 (Software) + $2.50 (USA) or
                        $10.00 (Overseas) Shipping/Handling
SUGGESTED SOFTWARE      IMDISP (DOS), or Image4PDS (Mac)

                                 NOTE

[] The cost of the set is $50.00.  You may request any subset or a
   combination of discs at a cost of $20.00 for first and $6.00 for
   each additional.
[] Volume 7 is not yet available.
[] Detailed information is listed below.

 (75-075A-01f)                  MDIM

 This data set contains a digital image map of Mars which is a
cartographic
 extension of a previously released set of CD-ROM volumes containing
 individual Viking Orbiter Images (PDS data sets VO1/VO2-M-VIS-2-EDR-V2.0
 (NSSDC IDs 75-075A-01c and 75-083A-01a) and VO1/VO2-M-VIS-2-EDR-BR-V2.0
 (NSSDC IDs 75-075A-01d and 75-083A-01b)). The data in these earlier data
 sets are pristine, in that they were processed only to the extent
required
 to view them as images. They contain the artifacts and the radiometric,
 geometric, and photometric characteristics of the raw data transmitted by
 the spacecraft. This new volume set, however, contains cartographic
 compilations made by processing the raw images to reduce radiometric and
 geometric distortions and to form geodetically controlled Mosaicked
Digital
 Image Models (MDIMs). It contains digitized versions of an airbrushed map
 of Mars as well as a listing of all IAU-approved feature names. Special
 geodetic and photogrammetric processing has been performed to derive
 rasters of topographic data, or Digital Terrain Models (DTMs). Because
the
 photometric processing used in this MDIM was over simplified,
quantitative
 radiometric analysis on these data is not possible. The MDIM CD-ROM
 collection serves two purposes. First, the image collection serves as a
 data base for interactive map browser applications. Secondly, the CD-ROM
 volume set provides a dense delivery medium to build higher-derived
 cartographic image products such as special map series and planning
charts
 for the Mars Observer Project. This set contains seven volumes. Volume 1
 contains images of the Vastitas Borealis Region of Mars, 373 image files
 covering the entire north polar region of Mars southward from the pole to
a
 latitude of 42.5 degrees North. Polar Stereographic projection images of
 the north pole area from 80 to 90 degrees are located in the POLAR
 directory on this disk. Volume 2 contains images of the Xanthe Terra
Region
 of Mars, 412 image files covering the region of Mars from 47.5 degrees
 North latitude to 47.5 degrees South latitude, and 0 degrees longitude to
 90 degrees West longitude. Volume 3 contains images of the Amazonis
 Planitia Region of Mars, 412 image files covering the region of Mars from
 47.5 degrees North latitude to 47.5 degrees South latitude, and 90
degrees
 West longitude to 180 degrees West longitude. Volume 4 contains images of
 the Elysium Planitia Region of Mars, 412 image files covering the region
of
 Mars from 47.5 degrees North latitude to 47.5 degrees South latitude, and
 180 degrees West longitude to 270 degrees West longitude. Volume 5
 contains images of the Arabia Terra Region of Mars, 412 image files
 covering the region of Mars from 47.5 degrees North latitude to 47.5
 degrees South latitude, and 270 degrees West longitude to 0 degrees West
 longitude. Volume 6 contains images of the Planum Australe Region of
Mars,
 373 image files covering the entire South polar region of Mars northward
 from the pole to a latitude of 42.5 South latitude. Polar Stereographic
 projection images of the south pole area from 80 to 90 degrees are
located
 in the POLAR directory on this disk. Volume 7 contains the Digital
 Topographic Map of Mars, MDIMs of the entire planet at 1/64, 1/16, DTMs
of
 the entire planet at 1/64, 1/16, and the digitized airbrush map of Mars
at
 1/16 and 1/4 degrees/pixel. Each of the first six volumes contains MDIMs
of
 the areas specified at resolutions of 1/256 degrees/pixel (231 m) and at
 1/64 degrees/pixel (943 m). Volumes 1 and 6 also contain MDIM coverage of
 the entire planet at 1/16 degrees/pixel (3.69 km). Each of the six
volumes
 also include a digitized airbrush map of the entire planet at 1/16
 degrees/pixel (3.69 km) and at 1/4 degrees/pixel. The Sinusoidal
Equal-Area
 Projection, is used as the map projection for this image collection. The
 tiling layout of the 1/64 degrees/pixel digital models is the same on the
 first six volumes. Note that the 1/64 degrees/pixel MDIM segments of
which
 appear in Volumes 1 through 6, is duplicated in its entirety on Volume 7.

 All of the resolution compressions were done by averaging, not by
 subsampling. A gazetteer of IAU-approved feature names, referenced by
 latitude/longitude coordinates is included as a table file on each of the
 seven volumes.

[] Viking Orbiter Images of Mars

From the Planetary Data System (PDS).  Eight image discs are available
with
compressed and browse images.  More are scheduled to be available soon.

Contact:                NSSDC Coordinated Request and User Support Office

Originator:             Planetary Data System
                        NASA/Jet Propulsion Laboratory
                        Mail Stop 525-3610
                        4800 Oak Grove Drive
                        Pasadena, CA  91109
                        [phone]
                        [e-mail]

NSSDC ID                75-075A-01c/d and 75-083A-01a/b
QUANTITY                10
COST                    $74.00 + $9.00 (Software) + $2.50 (USA) or
                        $10.00 (Overseas) Shipping and Handling
SUGGESTED SOFTWARE      IMDISP (DOS) or Image4PDS (Mac)

                        NOTE
[] The total cost of this set is $74.00.  You may request any subset or a
   combination of discs at a cost of $20.00 for the first and $6.00 for
   each additional.
[] There is no volume 9 for this set.
[] Detailed information is listed below.


Vol. Number             Frame Numbers
    1                   122S01-166S24
    2                   167S01-210S42
    3                   211S01-251S30
    4                   252S01-321S72
    5                   319S12-363S56
    6                   365S01-405S30
    7                   406S11-436S36
    8                   437S01-467S36
   10                   003A01-038A32
   11                   039A01-070A32

See section on MDIM for the difference between Viking CD-ROM set
the MDIM set.  All volumes of the Viking contain both browse and
compressed images.
--
Martin Connors         |
Space Research         | [e-mail]  [phone]
University of Alberta  |

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

Date: 25 Feb 93 18:50:03 GMT
From: "Richard M. Warner" <[e-mail]>
Subject: McElwaine disciplined! (somewhat long)
Newsgroups: sci.skeptic,sci.space,sci.astro,sci.space.shuttle

In article <[e-mail]> [e-mail] (Benjamin T Dehner) writes:
>Xref: sjsumcs sci.skeptic:25845 sci.space:24536 sci.astro:16739 sci.space.shuttle:4280
>Path: sjsumcs!octopus!pyramid!gossip.pyramid.com!olivea!charnel!rat!usc!wupost!crcnis1.unl.edu!moe.ksu.ksu.edu!hobbes.physics.uiowa.edu!news.iastate.edu!pv7440.vincent.iastate.edu!btd
>From: [e-mail] (Benjamin T Dehner)
>Newsgroups: sci.skeptic,sci.space,sci.astro,sci.space.shuttle
>Subject: Re: McElwaine disciplined! (somewhat long)
>Message-ID: <[e-mail]>
>Date: 24 Feb 93 16:43:52 GMT
>References: <[e-mail]> <[e-mail]>
>Sender: [e-mail] (USENET News System)
>Organization: Iowa State University, Ames IA
>Lines: 57
>In <[e-mail]> [e-mail] (Jason Cooper) writes:
>
>>> Maybe it's about time a lot of these people learned about
>>> a newsreader called 'nn'.
>
>>BRAVO!
>
>>                                                Jason Cooper
>
>    The issue here is not about content, but about volume.  McElwaines
>megalithic posted at frequent intervals take up network resources and disk
>space wether or not I read them or kill them.  Furthermore, it seems that
>McElwaine himself never discussed his posts, but simply reposts and reposts
>and reposts; in short, an automated pamphlet mailer, as someone else pointed
>out.

>Ben

An additional orthogonal issue to the comments on bandwidth and disk
space is that many folks pay $$$ for their news feeds, and long
irrelevant posts are money down the drain (you cannot select before
downloading).

>---------------------------------------------------------------------------
-->Benjamin T. Dehner    Dept. of Physics and Astronomy
>[e-mail]       Iowa State University
>                      Ames, IA 50011
>--
>-----------------------------------------------------------------------------
>Benjamin T. Dehner    Dept. of Physics and Astronomy
>[e-mail]       Iowa State University
>                      Ames, IA 50011

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

Date: Thu, 25 Feb 1993 21:29:30 GMT
From: Henry Spencer <[e-mail]>
Subject: Refueling in orbit
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>>>The Centaur which could have benefitted from on-orbit refueling
>>>>never had a test program to achieve this mission...
>
>I was under the impression that Centaur has flown on unmanned launchers
>many times since 1962...
>... Certainly Titan IV can carry anything a Shuttle can into orbit.

Not into the same orbit, it can't.  That is exactly the issue here:
Shuttle-Centaur has noticeably better performance than Titan-IV-Centaur.

On-orbit fueling also opens additional possibilities, like stacking up
more stages than will fit in a single launch now, e.g. *two* Centaurs
or a Centaur with an IUS on top.

The attempts to shoehorn a Mars sample return into Titan-IV-Centaur's
capabilities produced some, uh, *interesting* mission plans... not ones
that any sane planner would want to rely on.

Nearly thirty years ago, we demonstrated the ability to mate a spacecraft
to a separately-launched rocket stage in orbit, to give performance beyond
what a single launch could provide.  We're still not making any operational
use of this capability, despite flying missions that really could use it.
--
C++ is the best example of second-system| Henry Spencer @ U of Toronto Zoology
effect since OS/360.                    |  [e-mail]  utzoo!henry

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

Date: Thu, 25 Feb 1993 23:22:48 GMT
From: Dave Michelson <[e-mail]>
Subject: Refueling in orbit
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>
>I was under the impression that Centaur has flown on unmanned launchers
>many times since 1962. Didn't both Vikings ride Centaurs without Shuttle
>assist? Certainly Titan IV can carry anything a Shuttle can into orbit.
>Why is Centaur a Shuttle only playload?

If nothing else, this whole discussion underscores the need for rational
long term planning for space science probes and solar system exploration.
My hair practically stood on end while I read some parts of Bruce Murray's
"Journey into Space".

Centaur continues to evolve.  AW&ST recently carried an item about General
Dynamics looking for funding to develop a single engine version of the
Centaur to increase both payload (marginally) and reliability.  I guess
price would also decrease slightly as well since it's easier to test and
verify one engine than two.

---
Dave Michelson                             University of British Columbia
[e-mail]                                  Antenna Laboratory

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

Date: 25 Feb 93 19:59:29 GMT
From: Henry A Worth <[e-mail]>
Subject: Sky & Telescope Weekly News Bulletin
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (ARLIN B COLLINS) writes:
> *** Please note S&T  email addresses listed about the middle
> *** of this text.
>
>  SKY & TELESCOPE NEWS BULLETIN -- February 20, 1993
>
>  MORE HUBBLE WOES
>  The Hubble Space Telescope (HST) suffered its third gyroscope failure,
>  out of six on board, leaving the spacecraft's pointing-control system
>  without any backup. Earlier gyro shutdowns apparently occurred when
>  solder joints came unbonded. This latest failure occurred on November
>  18th, but its cause was still unclear as of mid-February. Should
>  another gyro fail, HST would automatically stop observing and put
>  itself in a "safe mode." Furthermore, the current draw on one of the
>  remaining gyros increased for no apparent reason last summer and has
>  risen further since then. Space Shuttle astronauts will try to replace
>  as many as four gyros during the HST repair mission now scheduled for
>  December 1993. Details of this story appear in S&T's April issue, now
>  on press.

   Apologies in advance if this has been already thrashed to death, this
group has so much volume its so easy to miss so much.

   Does the gyro-loss safe mode put Hubble into a slow stablization spin,
or in the case of complete gyro loss does it become just a matter of time
(and flapping solarpanels) until Hubble begins to tumble and has to be
written off? How much lattitude does the repair mission have to safely
repair a gyro-less Hubble, is the shuttle and arm even capable of coping
with a slow spin, I don't recall there being a co-axial capture point
(remember the difficulties with Solar Max, and the Hubble is so much
bigger - one wrong move and they could lose a lot more than an astronaut
- I'm still amazed that they took that risk)? Would they even be allowed
to attempt approach and capture, even if the Hubble was still stable?


--
Henry Worth
No, I don't speak for Amdahl... I'm not even sure I speak for myself.

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

Date: 25 Feb 93 13:48:45 GMT
From: Bill Higgins-- Beam Jockey <[e-mail]>
Subject: SOLAR gravity assist? Yup.
Newsgroups: sci.space,sci.astro,alt.sci.planetary

This is long, but you'll like it, I promise.  Recently on
alt.sci.planetary I answered a post from a student who, I thought, had
made an elementary error.

>In article <[e-mail]>, ljensen@plains (Lars Jensen) writes:
>> I am currently designing a space probe for flyby missions which will
>> perform multi-purpose tasks to explore both Mercury and Pluto.
>
>"This is an ambitious young man," I thought.
>
>> one component staying in Mercury's orbit to map the Mercurian surface,
>> while the other component travels with gravity-assistance of the sun to
>> explore Pluto and Charon.
>
>*Bzzt* Wrong, but thank you for playing our game.  Using the Sun for a
>gravity assist is impossible.  (You are welcome to try to convince me
>otherwise.)
[Note the hedging. Even when I am being arrogant I try to mitigate the
risk of humiliation.]

>In a gravity assist, you steal energy from the motion of
>a planet around the Sun... in the planet's reference frame, you gain
>no energy, but relative to the Sun you change your speed and direction
>so you win.
>
>For moving around the Solar System, this trick is not possible using
>the Sun.
>
>If you want to send a spacecraft to Pluto, you will have to do it by
>more conventional means (like gravity assist from mere gas giants).

I went on to answer his request for information about Pluto, to prove
I was really not such a nasty guy.

Shortly, I received e-mail from Dr. Bill Cochran of the University of
Texas.  He pointed out that all objects in the solar system orbit
around the "barycenter," the center of mass.  This point is *not*
(usually) inside the surface of the Sun!

I replied (with a copy to Lars Jensen):

>Wow, this is certainly astonishing.  This will teach me to make arrogant
>pronouncements to undergraduates...
>
>Assuming Jupiter is the only planet, and it's in a circular orbit,  I
>get a distance of 7.43E10 cm between the barycenter and the Sun's
>center of mass, and the solar radius is 6.9599E10 cm in the book I
>looked in (which insists on cgs units).  This is only 93.7% of the
>distance to the barycenter, a good 47,000 km from the edge of the Sun.
>(But where is the edge?  Suddenly the uncertainty in solar radius
>measruments becomes interesting, and my handbook-- Zombeck's *Handbook
>of Space Astronomy and Astrophysics*-- is silent.)
[Bill noted in reply that my figure is correct for the equatorial
solar radius.]

>Continuing these assumptions, the Sun would describe a circle around
>the barycenter once per Jovian year, covering (two pi R) 292,700 km
>in 4332.589 days, or 67.56 km per day, 78.2 centimeters per second.
>Hmm.  Jogging speed.

[Then we discussed Lars's hypothetical gravity-assist maneuver.]

>Good puzzle.  Want to tackle it?  Can our friend in North Dakota
>actually pick up useful speed, provided his Pluto probe passes closer
>than 47,000 km to the Sun?  What's the upper limit on the delta-V you
>can get this way?  And is the performance increase mitigated by the
>amount of suntan oil you have to bring along?
>
>I'm not familiar with making gravity-assist calculations.  Maybe
>somebody on the Net will have a textbook with formulas...

Bill is a specialist in  looking for planets in other solar systems by
the perturbing effects they have on their stars.  No wonder he knew
that the barycenter is (often) outside the Sun!

So I'm posting this not only for everybody's amusement, but to take it
further.  What is the maximum delta-V available from a solar gravity
assist in a Sun-Jupiter solar system, assuming your probe can skim the
surface of the Sun?

There must be somebody out there taking astrodynamics this term, or
even *teaching* it.  (If so, I've just given you an exam problem.) Or
maybe it's a good coffee-machine problem around JPL or Lewis or some
astronomy department...

Extra credit questions:

1. If the answer is usefully large, can you follow a solar slingshot
with a Jovian slingshot and get even more energy?  Can you somehow
repeat this trick for endless energy pumping, or show that this is
impossible?

2. How much help do you get when you throw in Saturn? Rs= 1.427E9 km,
Ms= 5.688E26 kg, Msun=3498.5 Msaturn.

3. [Library question:] What is the uncertainty in the solar radius?
What is the density profile of the solar atmosphere?  How did people
measure these things?

4. How *do* you engineer a spacecraft to go arbitrarily close to the
Sun?  (Spare me Brin's "refrigerator laser,"  I already know about it
and his ship uses magic technology for its other systems.)

5. (We're beginning to get into thesis material here) The extent of
the solar atmosphere must limit you somehow, even if your probe can
stand the near-Sun radiation environment indefinitely.  How do you
solve the problem for a non-negligible solar atmosphere?  All right, I
know we don't have materials that will stand 5800 K, let alone the
frictional heating you'd get at speeds where you're practically fall
into the Sun.  But suppose the probe is a big comet that just
happens to fall in along the right path, and it survives to emerge as
a little comet.  What is its optimal path if you take
helioaerodynamics into account?

I *told* you this was going to be fun.

Bill Higgins, Beam Jockey              | Here Lies Bill Higgins:
Fermi National Accelerator Laboratory  | He Never Ever Learned
Bitnet:           [e-mail]  | To Play Guitar So Well
Internet:       [e-mail]  | But He Could Read and Write
SPAN/Hepnet:           43011::HIGGINS  | Just Like Ringing A Bell

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

Date: 26 Feb 93 02:31:27 GMT
From: Paul Dietz <[e-mail]>
Subject: SOLAR gravity assist? Yup.
Newsgroups: sci.space

Bill Higgins asks about a "solar gravity assist".

This is *not* the same as the more well-known Jupiter gravity assist.
Rather, it is an example of the Oberth Effect -- rockets are more
effective when fired deep in a gravity well.

Imagine the following occurs.  A spacecraft falls from infinity along
a near-parabolic orbit towards the sun.  At perihelion, it is moving
at (say) 200 km/s.  It fires its rocket, adding 4 km/s to its
velocity.  It is now travelling at 204 km/s.  How fast will it be
going at infinity?

Answer, from conservation of energy:   sqrt((204)^2 - (200)^2)
= 40.2 km/s!

Viewed another way: the spacecraft moved a long distance while the
rocket was firing at perihelion, so the work done on the spacecraft
(force x distance) was large.

Where did this extra energy come from?  The reaction mass expelled by
the spacecraft is now in a more tightly bound orbit.  The
gravitational potential energy liberated has been given to the
spacecraft as kinetic energy.  So, I really lied: this *is* a little
like the Jupiter gravity assist, except that instead of bouncing the
spacecraft off Jupiter, we're bouncing it off the reaction mass.

    Paul F. Dietz
    [e-mail]

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

Date: Thu, 25 Feb 1993 22:24:59 GMT
From: "Garret W. Gengler" <[e-mail]>
Subject: Soviet Energia: Available for Commercial Use?
Newsgroups: sci.space

Can anyone tell me if the Soviets are still offering their launch vehicles,
specifically the Energia, for commercial use?

I'm having trouble finding any information that is at all recent.  The latest
info I have is from an article in the Washington Post, February 22, 1992,
when the head of NPO Energia "invited US officials to consider buying or
leasing (the Energia) ..."

I'm involved in a spacecraft design course here at the U of I and the launch
requirements are tremendous.

Any recent information on the Energia would be very helpful.
Please respond via email to g-gengler@uiuc, since I don't read this group.

Thank you for your time.
Garret Gengler
[e-mail]

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

End of Space Digest Volume 16 : Issue 237
------------------------------