Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V10_0/V10_025.TXT

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Subject: SPACE Digest V10 #25

SPACE Digest                                      Volume 10 : Issue 25

Today's Topics:
      Exotic Thrusters (was Re: Where the hell are electric...)
         NASA Headline News for 08/30/89 (Forwarded)
              Re: solar orbiting probes
      Re: Where the hell are electric-ion thrusters????
          Post- Star Wars space habitability
                 V'ger update
           Re: VOYAGER DATA GRAPHICS FORMAT REQUEST
----------------------------------------------------------------------

Date: 30 Aug 89 06:26:07 GMT
From: [e-mail]  (Terry Hancock)
Subject: Exotic Thrusters (was Re: Where the hell are electric...)

In article <[e-mail]> [e-mail] (Neal Woodall) writes:
>In article <[e-mail]> [e-mail] (Paul Dietz) writes:
>
>This answers one of the questions I posted just minutes ago. Thanx.
>
>>Perhaps he was thinking of a magnetoplasmadynamic (MPD) engine.
>
>Please, some details!! Perhaps we can start a thread on "exotic" thrusters
>which would be good for the next generation of planetary probes. I am
>
>Neal

    I'd like to second that idea.  Would Paul Dietz mind enlightening
us with further details (or anyone else who has a good idea what he's
talking about)?  I gather this is something based on the MHD principle
(magnethydrodynamic), although that's usually described in the reverse
sense -- i.e. decelerating a plasma to generate power rather than using
power to accelerate the plasma.  I would have thought that such a
mechanism would be very inefficient used this way, perhaps I'm wrong.

    By the way, I appreciate that many people noticed I said that
Cesium is radioactive.  It's not.  I was thinking, I believe, of
radioactive isotopes of cesium which are the only forms of it I've
ever heard of being used (some sort of radioactive tracer, I think).
What else is it used for, by the way?

    I'd also like to add that Mercury has other things going for
it than weight -- anyone notice it's one of only two elements that
are liquid at standard temperature and pressure? (the other is Bromine)
It's also a metal, which I think makes the ionization easier
(I'm getting a little timid about my chemistry now :-)).

    According to the same papers I used to give the specifications
for the 30-cm drive, another, more powerful drive was tested.  Although
I'm not certain it was the same drive, a 150-cm drive and one capable
of generating 4 N (~1 lb) thrust were mentioned.  I can imagine the
power requirements must have been enormous.  This is the sort of drive
you'd want to push around "large masses" as was described.  The info
given on it was pretty spotty though (this is about it), I gather it
was seen to be of less practical use than the other systems
described -- and therefore probably not as adequately tested.

    I don't see any reason why the ion drive technology can't be
pushed that far, however, since it seems fairly easy to scale it up
or down, depending on what you really need.  As for the Specific
Impulse, I don't think 3000 lbf-s/lbm is a physical or engineering
limit -- it is, rather, an ideal value to trade-off the amount of
fuel required with the size of the Power Processing Unit used (which
is a fairly significant mass).  As the total delta-V of the mission
increases, the ideal goes toward higher Specific Impulse, so that
really long haul missions would prefer using roughly 30,000 lbf-s/lbm
or more, which is probably closer to the engineering limits for the
technology.  Also, the technology for the PPU may have improved from
1977 so that it could be built lighter (I don't know), also pushing
up the specific impulse.

    By the way, the source, (ION Propulsion for Spacecraft,
Publication of NASA Lewis Research Center 1977) lists the following
additional info about the 30-cm drive:

    Thrust                     65 to 129 milliNewtons
    Specific Impulse             2560 to 2900 lbf-s/lbm
    Power required by PPU            1600 to 3000 W
    Thruster Mass                8.8 kg
    PPU mass                43 kg
    Gimbal Mass                3 kg
    Design Life                15,000 hours
    Propellant Mass (To
        last Design Life)        240 kg
    Propellant tank mass            12 kg
    Total Impulse of Single Thruster    7,100,000 N-s


    Lastly, I would like to respond to Henry Spencer about the
use of Specific Impulse rather than Exhaust Velocity.  While I
agree that Specific Impulse, if written in more sensible units, is
roughly the same as the exhaust velocity, it isn't exactly.
    For one thing, no thruster emits thrust exactly straight
behind it, there's always a bit of fanning out.  This is, I believe,
the meaning of "thruster efficiency."  It's also true that you
may use a significant amount of mass in order to make the energy
which you impart on the reaction mass -- thus the mass-rate-of-flow
is slightly higher due to the usage of energy-generating mass.
    Consider the Nuclear Electric Propulsion System, for
instance -- you will spend some mass (Uranium) in generating the
energy you need.  This is not merely the amount you convert
directly to energy, mind you (that would be negligible), but the
total mass you have to have to generate the power.  You also have
to note whether the spent fuel is to be jettisoned or not.  This
doesn't become REALLY significant until you get to VERY high
specific impulse, of course.

    I hope this is interesting to some people, sorry it's so
long.




**************************
Terry Hancock
[e-mail]
**************************
**************************

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

Date: 31 Aug 89 00:55:38 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: NASA Headline News for 08/30/89 (Forwarded)

-----------------------------------------------------------------
                          NASA Headline News
Wednesday, August 30, 1989                     Audio:202-755-1788
-----------------------------------------------------------------

This is NASA Headline News for Wednesday, August 30......

At the Kennedy Space Center's Launch Pad 39-B, the Space Shuttle
Atlantis was powered up this morning as preparations continue
toward the launch of STS-34.  Galileo, the mission's principal
payload, is scheduled to be inplemented [?-PEY]  into Atlantis'
payload bay this afternoon.   Launch of STS-34 and the Galileo
probe to Jupiter remains targeted for October 12.

Also at the Kennedy Space Center, Mobile Launcher Platform number
three is being moved inside the vehicle assembly building where
the flight elements for STS-32 will be stacked on top of it.  MLP
3 has been undergoing modifications for the last few years, and
STS-32 will mark the first time this platform will be used for a
shuttle launch.

Voyager 2 is continuing its journey outward and is now almost
five million miles from Neptune.  Next spring, mission managers
will turn the spacecraft's cameras, infrared detector and light
sensors off to preserve power.  Scientists should be able to
track Voyager for another 25 years until its power supply
expires.

A star tracking satellite launched by the European Space Agency
on August 8 is being called a failure, according to an official
of the Italian Space Agency.  The spacecraft has not yet reached
orbit, and there have been five unsuccessful attempts to start
its kick motor.  The official said his agency is prepared to ask
ESA for funds to replace the satellite.

                 *        *        *


















---------------------------------------------------------------
Here's the broadcast schedule for public affairs events on NASA
Select TV.  All times are Eastern..............
---------------------------------------------------------------

Thursday, August 31 through Wednesday, September 6......

NASA Update will be shown beginning at 11:30 A.M. Thursday and
will repeat several times during the following few hours.  The
next NASA Select coverage will be at 1:30 P.M. on September 5
when Galileo mission managers and the lead flight director for
STS-34 hold a briefing and press conference.  The five-member
STS-34 flight crew will hold a press conference at 11:15 A.M. on
September 6.  Transponder 13 on Satcom F2R and Transponder 21 on
Aurora 1.

All events and times are subject to change without notice.

---------------------------------------------------------------
These reports are filed daily Monday through Friday at 12 noon,
Eastern time.
---------------------------------------------------------------

A service of the Internal Communications Branch, (LPC), NASA
Headquarters.

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

Date: 30 Aug 89 09:51:56 GMT
From: mcsun!ukc!icdoc!syma![e-mail]  (Nick Watkins)
Subject: Re: solar orbiting probes

In article <[e-mail]> [e-mail] (Ignac Kolenko) writes:

>            ...     probes ended up in solar orbit. has anyone launched
>a probe that purposely ended up in solar orbit to study the sun?? would
>there be any benefit to doing so rather than keeping the probe in orbit
>around the earth (ie: solar max mission)??
 Yes. US/West German Helios mission of 1974 (2 satellites, 2 Titan
Centaurs). Also the 4 ( and one failed) Pioneers which studied the
interstellar medium. Main advantage is its closer to the Sun ...

>by the way, what's the oldest probe/satellite that we still have contact
>with?? anything from the 60's still communicating??
One of said Pioneers was transmitting for a very long time, maybe
someone knows if it is still on.

Nick
--
Nick Watkins, Space & Plasma Physics Group, School of Mathematical
& Physical Sciences, Univ. of Sussex, Brighton, E.Sussex, BN1 9QH, ENGLAND
JANET: [e-mail]   BITNET: [e-mail]
Voice: [phone]

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

Date: 29 Aug 89 20:15:25 GMT
From: thorin!alanine![e-mail]  (Jonathan Leech)
Subject: Re: Where the hell are electric-ion thrusters????

In article <[e-mail]> [e-mail] (Neal Woodall) writes:
>Now here is a subject that I have been meaning to bring up lately:
>ion thrusters. Where the hell are they?

    Dr.  Fisk of the Space Science Office mentioned something about
electric propulsion "always being appropriate for the *next* mission"
in a press conference a few days ago.

>All of the JPL people on TV the other night were saying that this is the
>last Neptune mission in their lifetimes (even some of the younger ones said
>this)

    This came up during the final Voyager press conference today;
apparently there are some Jupiter-assist trajectories in the early
2000's which would get orbiters to Uranus, Neptune, and Pluto in 10-15
years.    But it's probably the last mission in their working lifetimes
(personally, I hope Al Hibbs is pulled out of retirement again to be
the Voice of Galileo :-)
--
    Jon Leech ([e-mail])    __@/
    ``Are there any more questions, besides the ones from the
      liberal communists?''
    - George Uribe, natl. director of "Students For America"

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

Date: Wed, 30 Aug 89 08:59:20 PDT
From: [e-mail]
X-Vmsmail-To: SPAN::AMES::"[e-mail]"
Subject: Post- Star Wars space habitability


    Anybody out there have any idea how long near-Earth space would
be uninhabitable after activation of an ICBM Shield?  I'm talking mainly
about debris left behind by things like kinetic-kill weapons,
destruction of orbiting battle stations by ASATs, explosion of neutron
bombs (for decoy discrimination), etc.  Has anyone done any
environmental impact studies of this, or do the SDI people assume a)
nobody's going into space for a long time after a nuclear war anyway or
b) it's a small price to pay for national security, or what?
    Just curious.

----
"That which you call,            |         Dale M. Greer
         'E Plabnista...'"        |   Center for Space Sciences
             -- J.T. Kirk    | University of Texas at Dallas
                    | UTSPAN::UTADNX::UTDSSA::GREER
The opinions are my own, and may or may not reflect those of my employer.

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

Date: Wed, 30 Aug 89 11:49:43 PST
From: Peter Scott <[e-mail]>
Subject: V'ger update
X-Vms-Mail-To: EXOS%"[e-mail]"

Extracted from NASA's _Voyager Bulletin_, Mission Status Reoprt No. 92
(realized permission was never necessary since the government can't
copyright anything):

[Most of this bulletin is composed of pictures.]

In some regions, Neptune's weather is perhaps as dynamic and variable as
that of the Earth.  However, the scale is immense by our standards -- the
Earth and the Great Dark Spot (GDS) are of similar size -- and in Neptune's
frigid atmosphere, where temperatures are as low as 55 degrees K, the
cirrus clouds are composed of frozen methane [...].

Large changes can be seen in the clouds at the western end of the GDS.
A dark extension apparent in earlier images converges into an extended
string of small dark spots over the next five rotations.  This "string
of beads" extends from the GDS at a surprisingly large angle relative
to horizontal lines of constant latitude.  The large bright cloud at the
southern border of the GDS is a more or less permanent companion of the
GDS  [we've been observing it for a few weeks and already its "permanent"?]
The apparent motion of smaller clouds at the periphery of the GDS suggests
a counterclockwise rotation of the GDS [confirmed in ABC morning news today]
-- reminiscent of flow around the Great Red Spot of Jupiter.  The activity
of the GDS is surprising because the total energy flux from the Sun and
from Neptune's interior is only 5% as large as the total energy flux on
Jupiter.


Peter Scott ([e-mail])

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

Date: 30 Aug 89 07:39:07 GMT
From: agate!shelby!portia!hanauma![e-mail]  (Joe Dellinger)
Subject: Re: VOYAGER DATA GRAPHICS FORMAT REQUEST

In article <[e-mail]> [e-mail] (Adam Glass) writes:
>Could someone with all of the Voyager pics (that were originally on the
>Stanford machine in EPS format) kindly convert them to raw data (i.e.,
>the bits, the whole bits, and nothing but...).

They ARE in raw format, NOT Postscript. Really. If you take the given bytes
and dump them into a grey-scale array of pixels 640 left-to-right (fast
dimension) by 480 top-to-bottom (slow dimension) you'll have the picture.
If the software and device you've got demand some special header, bit
fiddling, etc, sorry, that's up to you!
\    /\    /\    /\/\/\/\/\/\/\.-.-.-.-.......___________
 \  /  \  /  \  /Dept of Geophysics, Stanford University \/\/\.-.-....___
  \/    \/    \/Joe Dellinger [e-mail]  apple!hanauma!joe\/\.-._

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

End of SPACE Digest V10 #25
*******************