Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_2/V16NO243.TXT

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Date: Mon,  1 Mar 93 05:37:07
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #243
To: Space Digest Readers
Precedence: bulk


Space Digest                Mon,  1 Mar 93       Volume 16 : Issue 243

Today's Topics:
                   Apollo Missions (Recollections)
                   Book Computers/AI in Shuttle-SSF
                    Can Cassini Titan Probe float?
                          Cassini Rover idea
               Deadhead to orbit (WAS Re: SSF Resupply)
                    Hopkins Leaks (was Re: Blimps)
                          Magnetic elevator?
                McElwaine disciplined! (somewhat long)
                             Prez Powers
                          Refueling in orbit
       Reliable Source says Freedom Dead, Freedom II to be dev
    Reliable Source says Freedom Dead, Freedom II to be developed
            Scientists Foresee Strengthening El Nino Event
                     SOLAR gravity assist?  NOPE.
                 SOLAR gravity assist? Yup. (2 msgs)
           SSF Resupply (Was Re: Nobody cares about Fred?)

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Date: 26 Feb 93 22:15:11 GMT
From: John E Childers <[e-mail]>
Subject: Apollo Missions (Recollections)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] ((Michael Gerhard  aka Elmo P. Suggins)) writes:
>I don't know about you, but I never felt so good about the space program as
>when the early Apollo missions were happening.  People have posted about
>their Challenger remembrances.  How about Apollo.
>
[deletion]
>
>
>Anyone else with good memories?

When I returned the university life a few years ago I was forced to retake
some english classes and my big assignment was to write about a big event
in my life.  I chose the Apollo 11 landing.  I was 8 years old when it
happend and it had a big impact on me.  Its the reason I got into engineering.
Suprize, the kids (18 year olds) that made up the majority of the
class bearlly(sp? Hey I siad I was in engineering:-) knew what I was
writing about.  That made me fell a little older than I wanted to.


John Childers                            | Voting for Clinton may have been
University of North Carolina at Charlotte| a mistake, but voting for Bush or
Electrical Engineering Department        | Perot would have been just as
Charlotte NC 28223                       | big a mistake. :-(
Internet? Try [e-mail]   |
---------------------------------------------------------------------------
Disclaimer?  Does anyone on usenet ever offically speak for their computer?

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

Date: Fri, 26 Feb 1993 20:12:21 GMT
From: [e-mail]
Subject: Book Computers/AI in Shuttle-SSF
Newsgroups: sci.space

: In article <[e-mail]| [e-mail] (Henry Spencer) writes:
: |Actually, I believe the Shuttle program is already using infrared
: |technology for the communications headsets worn inside.

Pat ([e-mail]) wrote:
: I thought the SUits already had a qualified IR system.
: Is the IR system only for the crew area?

I don't recall an IR system on the EMU's.  They have 2 UHF radio
channels, but no IR comm.  Hmmm....  (Rumaging through training
documents...)  No IR Comm.

There is a "floating mike" (pun intended) used inside the Orbiter which
used IR.  At first it was a DTO, but it may have been made into a
regular piece of flight hardware by now.

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

     "It is mankind's manifest destiny to bring our humanity into space,
      to colonize this galaxy.  And as a nation, we have the power to
      determine whether America will lead or will follow.

      I say that America must lead."  -- Ronald Reagan

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

Date: 26 Feb 93 22:44:42 GMT
From: Jeff Bytof <[e-mail]>
Subject: Can Cassini Titan Probe float?
Newsgroups: sci.space

Will the basic design of the Cassini Titan Probe allow it to
float if it lands on a liquid medium?

How long will Cassini be in contact with the Titan Probe after
it enters the atmosphere?  Cassini goes on to Saturn orbit, correct?

-rabjab

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

Date: 26 Feb 1993 21:46:15 GMT
From: BAIRD <[e-mail]>
Subject: Cassini Rover idea
Newsgroups: sci.space

    This is a bit of a hair brained proposal but I thought it might be a
possible idea for the Cassini mission.....Again I don't have all that I need to
be able to say one way or another (including enough knowledge in the area of
probe and mission design since I am an undergrad and all) and that my efforts
to find an email address of someone who does has been blunted left and right
(politely, true for the ones that have written me back when I have inquired
about someone's email address at their institution)....anyways, here is the
idea for those that are interested......
    The idea is to have a relatively small autonomous rover on the Cassini
mission to get some mapping (visually) of the surface of Titan.  It would
ideally weigh about 20 kg.  It would drop in to the atmosphere of Titan with
the Huygens atmospheric probe.  At the altitude of about 600 m it would be
jettisoned and a parachute deployed to slow the small aerial rover to lower
speeds.  The fans in the rover (three of them in a radially symmetric
configuration) would start up and allow the probe to hover at an altitude of
three meters.  The probe would then explore as much of Titan as it could before
it succumbed to the bitter cold.  The ideal mission length for the probe would
be for about a month.  A small attempted ascii drawing is below of the probe.

    __
    | 0     0 <----- fans built for downward thrust and manauvering (sp)
    |  \   /
    3m   0  <------- instrument package and data dish as well as beamed power
    |    |            reciever(if applicable)
    |    0 <-----  another fan
    L_
     |__3m___|


    The probe would probably only carry a camera and some sort of
atmospheric chemical analysis device.  The onboard sensors for normal operation
would include three laser range finders (one in each arm) in order to maintain
a level flying pattern as well as a possible sonic or radar backup.  The CPU
would be housed in the central partition along with the camera and chem analyzer
Control would be maintained by three sets of thrust vectoring flaps under the
fans. (see ascii drawing below).

Turbine and control flap configurations:
----------------------------------------

          ^
        .________/_\________.
    |   Propelling Fan  |_____________________
    |                 |
    |                 |
    |                 |
    |                 |  To main instrument package ---------->
    |                 | _______________________
    .-------------------./
        O     O   O   O     O
    |     |   |   |     |
    |     |   |   |     |
    |     |   |   |     | <----- control flaps for the probe's fans

Fan direction and probe movement:
---------------------------------

    Each of the probes fans have the thrust vectoring flaps under the fans
that would be positioned perpendicular to the pylon attaching the fans to the
CPU and instrument package.  This would allow the probe to have a wide range of

possible movement directions and types (spins, forward on any axis, etc)

Possible problems that would need to resolved:
----------------------------------------------

    The com units that would be needed for this probe to communicate with
the stations on earth might be too heavy for the fans to carry as well as the
same problem with the electrical source for the probe as well.  The possible
solution that might be looked at would be to leave a small orbiting satellite
that would have multiple functions.  The first would be to be a communications
relay for the probe.  The second would be the possible use of a set of RTG's of
batteries that were mounted on the satellite to provide power to a dual purpose
microwave transmitter.  The first would be to power the probe (purpose of the
microwave transmitter) and the second would be to map the terrain the probe was
transversing with the microwave energy (ie radar style like what is being done
with Magellan and Venus).

Advantages and disadvantages:
-----------------------------
    The probe as is would be advantageous in one major way: it could care
less about the terrain it was covering.  Whereas a ground contacting rover would
have problems if the Huygens ended up over a "sea of hydrocarbons".  This design
would just hover over it just the same while the ground contacting rover would
sink.  The major problems would be the battery weight and transmitter weight as
well.   Those might be overcome though (?).






    Now that I have babbled about the idea, what do others think of it?
Too far fetched like the ice resupplying of SSF from the asteriod belt/outer
planets&moons?  Questions, comments, suggestions?

 Will

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

Date: 26 Feb 93 23:14:00 GMT
From: [e-mail]
Subject: Deadhead to orbit (WAS Re: SSF Resupply)
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (fred j mccall 575-3539) writes...
>In <[e-mail]> [e-mail] writes:
>
>Are you postulating that the typical Shuttle launch will be going to
>the station with over 20% deadhead carge space?  Sounds like time to
>build another vehicle and switch to it, to me, if that's the case then it
>is time to switch to another launch vehicle

Hey Fred if you look at the Expendables, most of them go up with anwhere from
5 to 25% deadhead.  The one that I am most familiar with is the Delta and
on the GPS missions has almost 1000 pounds of excess capacity.  In addition
to this there is over 2000 lbs of excess fuel left in the second stage after
orbit insertion.  It is very hard in the space world to exactly match the
capabilities of the launchers with the payload. Getting within 10% of that
is a very good goal.  This is why secondary payloads are a very good
market for expendable vendors to pursue.  Why this is not done every day
escapes me, but NASA is paying MacDac millions for our secondary payload
of 75 kg.  Not bad for basically free money.  Arianne does this with the
ASEP platform that launched the microsats.  It would be interesting to
see a survey of launcher capability vs launcher payload.  I will bet you
there is a lot of wasted capability in every program out there.

Dennis, University of Alabama in Huntsville

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

Date: 26 Feb 93 22:27:23 GMT
From: John E Childers <[e-mail]>
Subject: Hopkins Leaks (was Re: Blimps)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Bill Higgins-- Beam Jockey) writes:
>In article <[e-mail]>, [e-mail] (Josh Hopkins) writes:
>
>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...
>

Have you considered using a glider at Jupiter?  With all that convection
soaring might be practical.  The control system would be much more
complex than for a ballon but a glider would be realitively strong compaired
to a ballon.  Also, a windmilling propeller could be used to generate
electrical power if the soaring part worked.


John Childers                            | Voting for Clinton may have been
University of North Carolina at Charlotte| a mistake, but voting for Bush or
Electrical Engineering Department        | Perot would have been just as
Charlotte NC 28223                       | big a mistake. :-(
Internet? Try [e-mail]   |
---------------------------------------------------------------------------
Disclaimer?  Does anyone on usenet ever offically speak for their computer?

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

Date: 26 Feb 93 17:09:48 GMT
From: Henry Choy <[e-mail]>
Subject: Magnetic elevator?
Newsgroups: sci.space

What if we use a vertical maglev train to launch into space? Would it
be feasible for a large number of trips?


--

Henry Choy
[e-mail]

We are Borg. You will be assimilated. Resistance is futile.

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

Date: Fri, 26 Feb 1993 16:01:10 GMT
From: Robert Wiegand <[e-mail]>
Subject: McElwaine disciplined! (somewhat long)
Newsgroups: sci.skeptic,sci.space,sci.astro,sci.space.shuttle

[e-mail] (Benjamin T Dehner) writes:

>    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.

Perhaps we should return his articles since we don't want them.

Just imagine if he received a thousand copys back of each artice he
sends out.

He he he. It might be fun. :-)

--
------------------------------------------------------------------------------
Robert Wiegand - Motorola Inc.
motcid![e-mail]            uunet!motcid!wiegand
Disclamer: I didn't do it - I was somewhere else at the time.

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

Date: Sun, 28 Feb 93 23:13:29 EST
From: Tom <[e-mail]>
Subject: Prez Powers

[congress is given the power to tax & spend, voters should be responsible]

>>... if you'll continue your perusal of the document
>>mentioned above, you will also notice the tenth amendment, which limits the
>>powers of congress to those enumerated within the document.

>Yes, but your problem seems to be an incorrect or inadequate
>definition of 'powers'.

Actually, my problem is in trying to interpret the Constitution based on
what it meant to the writers, rather than what it means to the people
who gain something from it...but that's something for E-mail, not the net.

>>If you'd like some info on what the Libertarians are doing...

>No thanks.  I'm not interested in impractical or unworkable
>'solutions'.

Ah, than you didn't vote for Clinton :-)  Seriously, if you are going to
prejudge something, then you can hardly understand it.  But hey, you
have your free will...

----------

>>I'm a little hazy on the legal picture, but I've got an inkling that since
>>the fed agencies are considered part of the executive, that Prez. Clinton
>>can do what he damn well pleases (notwithstanding politics) WRT fred, etc.

>He can do anything he wants -- right up until the point where it costs
>money.  The Executive Branch is allowed to 'execute', but not to
>authorize spending.  That takes legislation (guess who does that).

So, if he has the inkling, he can cancel the program outright, assuming
he wants to deal with the political heat?

-Tommy Mac
-------------------------------------------------------------------------
Tom McWilliams | 517-355-2178 (work) \\     Inhale to the Chief!
[e-mail]  | 336-9591 (hm)\\  Zonker Harris in 1996!
-------------------------------------------------------------------------

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

Date: 26 Feb 93 23:17:49 GMT
From: Steinn Sigurdsson <[e-mail]>
Subject: Refueling in orbit
Newsgroups: sci.space

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


   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".

No offence to Bruce Murray, but take some of the episodes with a small
grain of salt. For example the evolution of Voyager/Viking and the
role of JPL and launcher selection is not entirely consistent with
Burrows account of the same process...

   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.

well, the Atlas-Centaur and Titan-Centaur combos have a interesting
development history. It is quite sad to read of the problems of
Atlas-Centaur in the early 1960's and then pick up news reports
showing essentially the same problems occuring with depressing
frequency in the early 1990's. :-(
    SSTO fans would do well to re-read the history of some
modern launchers, including the original Shuttle concept and how
it evolved. Might make some a little less firm in their cost estimates
and a little less ready to cut other transport systems before the
SSTOs have demonstrated operational ability... in particular Allen
might be astonished to realise that some of his DC claims look
like they were cut out from a NASA report circa 1971-1974 providing
STS claims ;-)

|  Steinn Sigurdsson    |I saw two shooting stars last night        |
|  Lick Observatory    |I wished on them but they were only satellites    |
| [e-mail] |Is it wrong to wish on space hardware?        |
| "standard disclaimer"    |I wish, I wish, I wish you'd care - B.B. 1983    |


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

Date: 26 Feb 93 20:23:54 GMT
From: Nick Szabo <[e-mail]>
Subject: Reliable Source says Freedom Dead, Freedom II to be dev
Newsgroups: sci.space,talk.politics.space

It's amazing how many people still think that the space station is
the Mother of All Space Projects.  Our current concept of "the space
station" is obsolete: space stations at this point in space development
by their nature get put in the wrong orbit, are overcentralized, and
claim far too large a share of the space budget.  No space fan likes
to see space projects cut, but few negative outcomes are more productive
than eliminating SSF from our plans.

It wouldn't have accomplished any major breakthrough in space
development, even in its original form.  It's time to put
our current overpriced, underfunctional concept of the
"space station" on the scrap heap of history along with the
zeppelin, and get on with developing an efficient, real
space program based on today's technology, not on the
expectations and artistic renderings of the 1950's.

Specifically, we have seen many proposals for making space
operations more self-sufficient by using materials on
Mars, asteroids, comets, etc.  Let's start putting NASA
money into that.  Our commercial space industry is the
most competitive in the world, especially in the rapidly
growing communications satellite industry; let's put NASA
research funds into improving and extending our commercial
space capabilities.  Let's put some more lobbying effort
and funds into COMET and its small-scale competitors, a
far more productive way of developing microgravity industry.
Let's put money into lowering launch costs with SSTO, gun
launchers and electric upper stages.  The space station budget at
$2 billion/yr could fund all of the above, if we didn't spend so
much time trying to save useless, lost causes like the space station.


--
Nick Szabo                     [e-mail]

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

Date: 26 Feb 93 22:56:00 GMT
From: [e-mail]
Subject: Reliable Source says Freedom Dead, Freedom II to be developed
Newsgroups: sci.space

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

>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
>

Hey I think using ET's are a great idea. I even worked on a Space Station
design for our NSS chapter a few years ago. BUT if you think the EVA
times
are long for SSF, they will be horrendus for an ET system.  The first problem
is that the insulation on the ET will detoriate within a short time period
in space.  The second problem is that micrometoroid protection is zero. The
third problem is that unless you take and do a lot of work to modify the
tank BEFORE lauch, (Which costs big bucks) YOu will be doing EVA until
the Moon turns blue to get it ready for doing real work. Then you have
the problem of stabilization to deal with.  Then you have the problem of
attaching external devices and drilling the holes for the wiring and etc....

Actually the best Idea I have seen on here is to have a module attached to
the tank that will provide all of the utilities, but then all you have is
a big gymnasium in space with a space station attached to it. Maybe we
can dock on to SSF one day and get the best of both worlds.

The most serious proposals that I have seen for the use of ET's is for
a large gamma ray imaging telescope.  That one could be done cheap and
would be a heck of a device. BUT you need a station like SSF, where the
manpower is available to do all of the EVA necessary to make the system
work.

Dennis, University of Alabama in Huntsville

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

Date: 26 Feb 1993 22:10 UT
From: Ron Baalke <[e-mail]>
Subject: Scientists Foresee Strengthening El Nino Event
Newsgroups: sci.space,sci.geo.meteorology

Brian Dunbar
Headquarters, Washington, D.C.
(Phone:  [phone])                                   February 26, 1993

Mary Hardin
Jet Propulsion Laboratory, Pasadena, Calif.
(Phone:  [phone])


RELEASE:  93-39

SCIENTISTS FORESEE STRENGTHENING EL NINO EVENT

    Scientists studying data from the U.S.-French TOPEX/POSEIDON
oceanographic spacecraft have observed an ocean phenomena in the equatorial
Pacific that will strengthen the ongoing El Nino event off the western coast of
South America.

    The scientists have been analyzing a prominent Kelvin wave that has
appeared in recent TOPEX/POSEIDON altimeter data.  A Kelvin wave is a large
warm water mass that moves along the Equator in the Pacific Ocean.  These
Kelvin wave pulses give rise to El Nino conditions in the eastern equatorial
Pacific.  The Kelvin wave pulse seen in the TOPEX/POSEIDON data also was
predicted by the global ocean numerical models developed on supercomputers
at the Naval Research Laboratory, Washington, D.C.

    The Kelvin wave pulse was excited by westerly wind anomalies in the
western Pacific in December 1992 and is projected to arrive at the South
American coast in late February or early March.  The satellite data indicates an
arrival in the early part of the window, while the Navy model points to a slight
later date.  The imminent arrival of this Kelvin wave pulse suggests that the
current warm conditions in the western Pacific will continue or possibly
intensify during March.

    The strengthening of the El Nino means that the weather conditions
associated with it are likely to continue said Dr. Jim Mitchell of the Naval
Research Laboratory.  These conditions include wetter than normal weather in
California, wetter and colder winters than normal in the eastern United States
and warmer and dryer summers than normal across the southern hemisphere.

    Launched Aug. 10, 1992, TOPEX/POSEIDON also is addressing long-term
climate issues.  By mapping the circulation of the world's oceans over several
years, scientists can better understand how oceans transport heat, influence the
atmosphere and affect long-term climate, said Dr. Lee-Leung Fu of the Jet
Propulsion Laboratory (JPL), Pasadena, Calif.  Dr. Fu is the TOPEX/POSEIDON
Project Scientist for NASA.

    Data from TOPEX/POSEIDON is distributed monthly to more than 200
scientists around the world for their analysis.

    TOPEX/POSEIDON is the second satellite in NASA's Mission to Planet
Earth, a comprehensive research program to study the Earth's environment as a
global system.  JPL manages the NASA portion of the mission for the Earth
Science and Applications Division of the Office of Space Science and
Applications, Washington, D.C.

- end -
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     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: 26 Feb 1993 21:30:55 GMT
From: "Robert M. Unverzagt" <[e-mail]>
Subject: SOLAR gravity assist?  NOPE.
Newsgroups: sci.space,alt.sci.planetary

In article <[e-mail]> [e-mail] (Bruce Dunn) writes:
>         In addition to a direct solar gravity assist for a Pluto, there might
> be some benefit in carrying propellant deep into the energy well of the sun,
> and burning it there to provide a boost to Pluto.  Is anyone familiar enough
> with the calculations to estimate what the benefit might be?

Sure, I'll take a stab at it.  The delta-v for a direct injection
to Pluto is about, er, 38,771 ft/sec.  That's 38,771 ft/sec added
to the earth's orbital velocity of 97,719 ft/sec in order to give
us an apoapsis of about 40 AU (Pluto's mean orbital radius, if
memory serves).  If we wanted to do a close pass of the sun, we
could add that 38,771 IN THE OPPOSITE DIRECTION OF EARTH'S MOTION
AROUND THE SUN to give us a periapsis closer to the sun (something
like a closest approach of 0.2 AU.

Do I need to go any further to show that there is no net benefit
of doing this?  Maybe I do -- obviously more delta-V will have to
be added at closest approach to raise apoapsis to Pluto's orbital radius.
About 27,500 ft/sec.  In fact, for decreasing periapsis altitudes
the penalty decreases.

Note that this assumes a Pluto flyby, not rendezvous.  The penalty
of the "gravity well drop" would be even greater if we wanted to
match orbits with Pluto.

In the orbital mechanics world this is called a bi-elliptic
transfer with interior conjunction.

Can the person who originally claimed a benefit for this please
explain again?  Maybe I missed something, but this sure sounds
like what you were talking about.

Shag

--
       Rob Unverzagt        |   Last call for alcohol.
  [e-mail]   |   Last call for freedom of speech.
[e-mail] |                            - Jello Biafra

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

Date: Fri, 26 Feb 1993 21:05:49 GMT
From: Paul Dietz <[e-mail]>
Subject: SOLAR gravity assist? Yup.
Newsgroups: sci.space

>> 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...


Yeah, yeah, I know, Henry.  I reacted as I did because the purely
gravitational boost from the acceleration of the sun by Jupiter is
going to be very small; naively, the effect at infinity will be at
most on the order of the velocity of the sun in the solar system rest
frame, which is on the order of 10 meters per second.  The potential
benefit from the Oberth effect is more than 3 orders of magnitude
larger.

    Paul

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

Date: 26 Feb 93 22:17:39 GMT
From: "Mark D. Looper" <[e-mail]>
Subject: SOLAR gravity assist? Yup.
Newsgroups: sci.space

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

> (lotsa interesting stuff regarding a pure gravity assist using the mass
   of the sun and its distance from the true solar system barycenter, which
   I hope to tackle during an airplane flight next week...)

>Extra credit questions: ...

>... 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.)

The Solar Probe spacecraft, a proposed mission to whip by the sun at about
3 solar radii above the photosphere, will hide behind a big conical heat
shield of "carbon-carbon" (whatever that is) composite material.  It will
not take pictures of the sun, but rather will carry instruments to measure
fields and particles that can come behind the shield to be observed; it
may also carry a camera to look _away_ from the sun to photograph light
backscattered off tenuous coronal material.  The weird-o thing about this
is that, whereas outer-planet spacecraft have to carry Radioisotope Thermal
Generators (RTG's) for power where sunlight is too weak for solar panels,
the Solar Probe will have to use RTG's where the sunlight is too _strong_
for solar panels!  Of course, in order to kill its angular momentum enough
to get that close to the sun, it may make use of Jupiter for a gravity assist
(as Ulysses did to get kicked out of the ecliptic plane), at which distance
it'd need RTG's anyway.  In a previous post, I mentioned that the idea of
a "Fire and Ice" trajectory using a solar assist to get to the outer solar
system more rapidly has been considered for the Interstellar Probe (a mission
_designed_ to reach the heliopause and the local interstellar medium, where
the Voyagers only _hope_ to do so); the composite heat-shield idea was to
be used there as well, I think.  Note, however, that this was not the "pure
gravity assist" being discussed, but rather incorporated a delta-v burn at
perihelion; presumably, whatever the merits of a pure gravity assist, it
works better to use thrusters too.

--Mark Looper
"Hot Rodders--America's first recyclers!"

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Date: Fri, 26 Feb 1993 19:20:24 GMT
From: Gary Coffman <ke4zv!gary>
Subject: SSF Resupply (Was Re: Nobody cares about Fred?)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>>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.
>
>Are you actually saying that saving $12 BILLION isn't a good reason to
>incur that upfront expense for something you say is simple to do?

I'm saying the reality of SSF upfront funding (remember the chart
you so convienently deleted?) is so constrained that we're using
hydrazine thrusters because development money wasn't available for
H2/O2 thrusters. It doesn't matter how much a technology may save
in the out years if funding to develop it isn't available in current
year budgets. This is similar to the situation that led to Shuttle
having SRBs instead of liquid flyback boosters, though on a smaller
scale. Without the upfront funding, you make do with what you already
have available.

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     |                     |

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End of Space Digest Volume 16 : Issue 243
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