Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V16_5/V16NO513.TXT

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Date: Sun,  2 May 93 06:17:40
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V16 #513
To: Space Digest Readers
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Space Digest                Sun,  2 May 93       Volume 16 : Issue 513

Today's Topics:
                      Combo Propulsion System!?
     Electrical Spacecraft via Magnetic field of earth? (2 msgs)
           Gamma Ray Bursters How energetic could they be?
         HST Servicing Mission Scheduled for 11 Days (2 msgs)
      LLNL Inflated space stations (was Deployable Space Dock..)
                   moon image in weather sat image
              Mothership for Flybys and cutting costs..
                      Political banner in space
          Space Manuevering Tug (was HST servicing mission_)
                 Teflon (Re: Long term Human Missions
                         Vandalizing the sky

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Date: Sat, 1 May 1993 23:01:44 GMT
From: Henry Spencer <[e-mail]>
Subject: Combo Propulsion System!?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>How hard or easy would it be to have a combo mission such as a solar sail on
>the way out to the outer planets, but once in near to orbit to use more normal
>means..

If you've got a good propulsion system that's not useful for deceleration,
sure you can use chemical rockets for that part... but even just doing the
deceleration chemically is a major headache.  We're talking seriously high
cruising velocities; taking the velocity down nearly to zero for a Pluto
orbit isn't easy with chemical fuels.

Incidentally, solar sails are not going to be suitable as the acceleration
system for something like this.  They don't go anywhere quickly.  (I speak
as head of mission planning for the Canadian Solar Sail Project, although
that is more or less an honorary title right now because CSSP is dormant.)
They can't fly a mission like this unless you start talking about very
advanced systems that drop in very close to the Sun first.
--
SVR4 resembles a high-speed collision   | Henry Spencer @ U of Toronto Zoology
between SVR3 and SunOS.    - Dick Dunn  |  [e-mail]  utzoo!henry

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

Date: Sat, 1 May 1993 23:13:39 GMT
From: Henry Spencer <[e-mail]>
Subject: Electrical Spacecraft via Magnetic field of earth?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>Okay, the earth has a magnetic field ...
>...if you put a object in the earth magnetic field, it produces electricty..

Well, it's not that simple -- you're in Earth's magnetic field, and you
don't generate electricity -- but it can be done.

>Now the question. Can you use electricity to power a space/low earth orbit
>vehicle? and i fyou can, can you use the magnetic field of the earth to power
>it??

The way you power things is with electricity, so the answer to the first
question is definitely yes.  (If you meant to say "propel" rather than
"power", the answer is "sort of".)  Yes, you can use interaction with the
Earth's magnetic field to get electrical power, and there are potential
applications for this.

However, bear in mind that there is no free lunch.  The energy isn't
coming from nowhere.  What such systems do is convert some of the energy
of your orbital velocity into electrical energy.  There are cases where
this is a useful tradeoff.  Using power obtained in this way for propulsion
is useful only in special situations, however.

What you *can* do is get your power by some other means, e.g. solar arrays,
and run the interaction with the magnetic field in reverse, pumping energy
*into* the orbit rather than taking energy out of it.

If you want more information, trying looking up "electrodynamic propulsion",
"tether applications", and "magsails".

>Can the idea of a "dragless" satellite be used in part to create the
>electrical field?

No.  A "dragless" satellite does not magically have no drag; it burns fuel
constantly to fight drag, maintaining the exact orbit it would have *if*
there was no drag.  This is why there are quotes around "dragless".
--
SVR4 resembles a high-speed collision   | Henry Spencer @ U of Toronto Zoology
between SVR3 and SunOS.    - Dick Dunn  |  [e-mail]  utzoo!henry

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

Date: 2 May 1993 09:13:32 GMT
From: Isaac Kuo <[e-mail]>
Subject: Electrical Spacecraft via Magnetic field of earth?
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>Okay, the earth has a magnetic field (unless someone missed something?)
>
>Okay if you put a object in the earth magnetic field, it produces electricty..

No, if you put a conductor in a changing magnetic field, it produces a voltage.
The two ways you can do that with a permanent magnet is to move the magnet or
move the conductor.  The slow shifting of the Earth's magnetic field isn't
really significant, especially when you consider how weak the Earth's magnetic
field is to begin with.

>Now the question. Can you use electricity to power a space/low earth orbit
>vehicle? and i fyou can, can you use the magnetic field of the earth to power
>it??

Well, it would require generating an incredibly large magnetic field to repel
the Earth's magnetic field (as a magnet can repel another magnet).  Of course,
this force only works in one direction, and the magnetic field generated has
to be unimaginably powerful.  Magnetic repulsion drops off as 1/r^3, and the
earth's magnetic field on the surface is already very weak.  It would require
some sort of unknown superconductor, and special nonmagnetic construction.
And seriously hardenned electronics (optical computers, perhaps).  And the
physiological danger would be significant (due to the iron content in our
blood, among other things).  In other words, forget it.

>Can the idea of a "dragless" satellite be used in part to create the electrical
>field?
>
>After all the dragless satellite is (I might be wrong), a suspended between to
>pilons, the the pilons compensate for drag.. I think I know what I want to say,
>just not sure how to say it..
>
>A dragless satellite sounds interestingly enough liek a generator.

I missed out on the "dragless satellite" thread, but it sounds totally bogus,
from this little bit.
--
*Isaac Kuo ([e-mail])    *       ___
*                    * _____/_o_\_____
*    Twinkle, twinkle, little .sig,    *(==(/_______\)==)
*    Keep it less than 5 lines big.    * \==\/     \/==/

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

Date: 2 May 1993 01:51:04 -0500
From: Greg Howard <[e-mail]>
Subject: Gamma Ray Bursters How energetic could they be?
Newsgroups: sci.space,sci.astro

In article <[e-mail]> [e-mail] writes:
>In article <[e-mail]>, [e-mail] (John F Carr) writes:
>>
>>
>> How much energy does a burster put out?  I know energy depends on
>> distance, which is unknown.  An answer of the form _X_ ergs per
>> megaparsec^2 is OK.
>>
>different spheres: R=.25pc(Oort Cloud Radius), R=22.5pc(at the edge of the
>galaxy), R=183.5pc or the edge of the galactic corona, and lastly at a
>R=8800Mpc.
>        For a radius of .25 pc, we found an L around 10^32 erg/sec.  Pretty
>energetic for close by.  for the coronal model, we found around 10^43 erg/sec.
>And lastly, for the cosmological model an L=10^53. That's what you'd call
>moderately energetic, I'd say.  Any suggestions about what could put out that
>much energy in one second?
>                                                -jeremy
>
>

Supernovae put out 10^53 or 10^54 (i forget which, but it's only an
order of magnitude...).  Not in gamma rays, though.  You'd hafta get
all of that into gammas if they were at 9 Mpc, but if a decent fraction
of the SN output was in gammas it could reasonably be extragalactic
(but closer than 9 Mpc).  I dunno SN theory so well, but I can't think
of how to get many gammas out.  Maybe I should look it up.

Big radio galaxies can put out 10^46 erg/s *continually*.  That's just
in the radio... there are a lot of gammas around them, too, but "bursts"?
Nah.

Neither of these should be taken as explanations... just trying to show
that those energies *are* produced by things we know about.


greg

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

Date: 1 May 1993 14:44:02 -0400
From: Pat <[e-mail]>
Subject: HST Servicing Mission Scheduled for 11 Days
Newsgroups: sci.space,sci.space.shuttle,sci.astro

In article <[e-mail]> [e-mail] (Henry Spencer) writes:
|In article <1rrgu7$[e-mail]> [e-mail] (Pat) writes:
|>>No, the thing is designed to be retrievable, in a pinch.  Indeed, this
|>>dictated a rather odd design for the solar arrays, since they had to be
|>>retractable as well as extendable...
|>
|>Why not design the solar arrays to be detachable.  if the shuttle is going
|>to retunr the HST,  what bother are some arrays...
|
|They can be detached in an emergency.  But expensive hardware is not thrown
|away casually (bearing in mind that nobody knew the design was defective).
|If the deployment crew had found some nasty flaw -- the lid failing to open,
|for example -- it would have been a bit embarrassing to have to throw the
|solar arrays away to get the thing back in the payload bay.


I guess it's  kind of an aesthetics argument.

I can see the solar arrays being expensive,  and  there could be
contingencies where you would be throwing away brand new
solar cells,   but  it seems so cheap compared toa shuttle
mission, i wouldn't think they would bother.

pat

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

Date: Sun, 2 May 1993 07:08:00 GMT
From: David Ward <[e-mail]>
Subject: HST Servicing Mission Scheduled for 11 Days
Newsgroups: sci.space,sci.space.shuttle,sci.astro

In article <1rrgu7$[e-mail]>, [e-mail] (Pat) writes...
>In article <[e-mail]> [e-mail] (Henry Spencer) writes:
>>
>>No, the thing is designed to be retrievable, in a pinch.  Indeed, this
>>dictated a rather odd design for the solar arrays, since they had to be
>>retractable as well as extendable, and may thus have indirectly contributed
>>to the array-flapping problems.
>
>
>Why not design the solar arrays to be detachable.  if the shuttle is going
>to retunr the HST,  what bother are some arrays.  just fit them with a quick release.
>
I didn't think the bi-stem design was used so much for the retrieval as
for the ability to launch in a tight (size) STS envelope.  This is my own
guess, based on similar designs flown on other large STS-launched s/c
(GRO, UARS).  Also, there _might_ be some consideration given to mass
requirements (bi-stems weight less than conventional S/A).  Finally,
the HST arrays _do_ have the ability to be detached--remember, they're
going to be replaced with new arrays.

However, as an ACS guy who's seen his branch management pull their
collective hair out over HST, I would voice a hearty 'yea' to using
conventional arrays over bi-stems, whenever possible.  No half hertz
flexible modes, no thermal snap, no problem.

David W. @ GSFC

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

Date: Sat, 1 May 1993 20:36:23 GMT
From: Josh Hopkins <[e-mail]>
Subject: LLNL Inflated space stations (was Deployable Space Dock..)
Newsgroups: sci.space

Organization: University of Illinois at Urbana
Lines: 20
Source-Info:  Sender is really [e-mail]
Source-Info:  Sender is really [e-mail]

[e-mail] writes:

>: In article <[e-mail]> [e-mail] writes:
>: >Why not build a inflatable space dock.

[discussion of pros and cons deleted]

>These are some of the technical difficulties which the LLNL proposal
>for an inflatable space station dealt with to varying degrees of
>success.

Could someone give me the references to the LLNL proposal?  I've been meaning
to track it down in conjuntion with something I'm working on.  It's not
directly related to space stations, but I think many of the principles will
carry over.

--
Josh Hopkins                                          [e-mail]
            "Find a way or make one."
                 -attributed to Hannibal

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

Date: Sun, 2 May 1993 00:12:19 GMT
From: "Mr. Krinkle" <[e-mail]>
Subject: moon image in weather sat image
Newsgroups: sci.astro,sci.space,sci.geo.meteorology,sci.geo.geology

In article <[e-mail]> [e-mail] (Richard Ottolini) writes:
>In article <[e-mail]> [e-mail] (George Wm Turner) writes:
>>
>>
>>an image of the moon has been caught in a weather satellite images of the earth.
>Near midsummer, you can see the relfection of the Sun in the ocean.
             Cool!
>Also during solar eclise you can see the shadow of the sun move
>across the clouds.                       ^^^^^^^^^^^^^^^^^
    I think you mean Moon.
        (Sorry, I had to.)  ; )

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

Date: Sun, 2 May 1993 04:19:47 GMT
From: Henry Spencer <[e-mail]>
Subject: Mothership for Flybys and cutting costs..
Newsgroups: sci.space

In article <[e-mail]> [e-mail] writes:
>... design a mother ship that has piggy backed probes for
>different missions,namely different planets...

Not useful unless you've got some truly wonderful propulsion system for
the mother ship that can't be applied to the probes.  Otherwise it's
better to simply launch the probes independently.  The outer planets
are scattered widely across a two-dimensional solar system, and going
to one is seldom helpful in going to the next one.  Uranus is *not* on
the way to Neptune.  Don't judge interplanetary trajectories in general
by what the Voyagers did:  they exploited a lineup that occurs only
every couple of centuries, and even so Voyager 2 took a rather indirect
route to Neptune.

>Also the mother ship would be powered (if not the Mars Mission) by a normal
>propulsion, but also a solar sail ...

Solar sails are pretty useless in the outer solar system.  They're also
very slow, unless you assume quite advanced versions.
--
SVR4 resembles a high-speed collision   | Henry Spencer @ U of Toronto Zoology
between SVR3 and SunOS.    - Dick Dunn  |  [e-mail]  utzoo!henry

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

Date: 1 May 1993 15:02:37 -0400
From: Pat <[e-mail]>
Subject: Political banner in space
Newsgroups: sci.space

Well,  you better not get the shuttle as your launch vehicle.

and most ELV's have too  far of a backlog for political messages.

If during the campaign season,  the candidates for president had
launched one,  right around now we'd  be getting a launch
for PEROT 92.

and if they had used the shuttle,  we'd be seeing launches
for NIXON now more then ever.

pat

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

Date: 1 May 1993 15:25:38 -0400
From: Pat <[e-mail]>
Subject: Space Manuevering Tug (was HST servicing mission_)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Josh Hopkins) writes:
>[e-mail] (Pat) writes:
|
|>Given that what i described for the HST  seemed to be the SMT,   and given
|>the mass amrgins on the discovery mission  is tight enough that  spacewalking
|>has to be carefully constrained.....  No EDO pallets,  no spare Suits,
|>no extra MMU's.
|
|Has someone actually verified that mass is the predominant constraint on this
|mission?  You seem to be assuming it without giving supporting evidence.
|

Someone from NASA posted that there were very significant mass margins
on the HST re-boost mission.  A while back i had asked why not carry
the EDO pallet up,  and the answer was the mass margins were tight enough, they weren't even carrying extra suits.

|>WHy not do this?
|
|>    Quick Test  Goldins philosophjy  of faster cheaper, better.
|
|>Build a real fast Space TUg,  to handle the re-boost  of the HST  using
|>clean Cryo fuels,  and get it ready before the  HST mission.
|
|Pat, this would be slower, more expensive and worse.
|
|Slower:  The shuttle mission is scheduled to go up in December.  That's less
|than eight months away.  There is no way you could build new hardware, retrain
|and reschedule the EVA's in that time.
|

Where's wingo when you need him:-)

COme on.   Knock that S**T off.

YOu forget,  that during skylab,  they did  overnight mission planning
for the repair EVA's.   Also during the
Intelsat Mission,   they did overnight  WETF simulations.
I somehow think they could train up a new  EVA in  8 months.

And as for building hardware,  anything can  be built if you want it
bad enough.

YOu forget,  the  BUS 1  is already built.  all they'd ahve to do
is soup it up, even test it  on a delta mission.

Don't get into this mode of  negativism.   besides,  at the rate
missions slip,   the Discovery won't launch on this mission until
March.  that's almost a year.

|More Expensive:  Your proposal still requires the shuttle to do everything it
|was going to do execpt fire the OMS.  In addition, you've added significant
|extra cost for a new piece of complex hardware.
|

Ah,  but how much more expensive is the Second HST servicing mission.

YOu forget,  there is a bum FGS,  the Solar array electronics, are
getting hinky  and there is still 8 months until the servicing mission.

The time for the space walks are growing rapidly.  THis was orignally
planned out as 3 spacewalks,  now they are at 5 EVA's  with 3 reserve
walks.

If the SMT can avoid a second servicing mission that's $500 million
saved.  If the Weight savings,  means they  can sit on orbit  for 30 Days.
and  handle any contingency  problems,  that's quite a savings.

|
|According to a GAO report on the OMV I have before me, there are
|only two currently planned missions that could use such a vehicle -- HST and
|AXAF.  Since AXAF has since been scaled back and HST can rely on the shuttle,
|there doesn't seem to be any need for your vehicle.


Of course,  there wasn't any need for the Saturn  V  after apollo too.

as for the problems with the aperture door,  I am sure they can
work out some way to handle  that.  Maybe a Plug  made from
Frozen ice.?   it'll keep out any contamination,
yet sublime away  after teh boost.

pat

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

Date: 1 May 1993 15:06:54 -0400
From: Pat <[e-mail]>
Subject: Teflon (Re: Long term Human Missions
Newsgroups: sci.space,sci.space.shuttle,sci.astro

In article <1rtghr$[e-mail]> [e-mail] (Dan Tilque) writes:
>
|The material was useful for seals, but it had a major problem for, say
|the linings of vessels: it wouldn't stick to metal.  What the space
|program did was to find a way to get it to stick.  Thus we had no-stick
|frypans on the market in the late '60s.


Ejon Matejevic who was a full professor at Clarkson University, last
I heard,  developed the process for sticking Teflon to metals.

I don't think it was a NASA project, cuz i heard he held the patent
on it, and had made quite a bundle off it.

Anyone from Clarkson know the Exact story.  I never wanted to ask
him myself.

pat

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

Date: 1 May 1993 22:26:04 -0400
From: Pat <[e-mail]>
Subject: Vandalizing the sky
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Tom) writes:
|On the other hand, I lived in OakBrook IL for a while, where zoning
|laws prohibit billboards, as you mention above.  I think it was a
|fine law, despite it's contradictory basis.

And I lived out there too.  It was a nice sleepy farm valley until
the Butler family decided to stick up all sorts of really tacky
High RIse office buildings and ruin my view of the sky.

I guess i should have sued somebody :-;

pat

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

End of Space Digest Volume 16 : Issue 513
------------------------------