Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V08/V8_310.TXT

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Date: Tue, 2 Aug 88 01:06:04 PDT
From: Ted Anderson <[e-mail]>
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Subject: SPACE Digest V8 #310

SPACE Digest                                      Volume 8 : Issue 310

Today's Topics:
                  Ramscoops
              Re: tacking of Solar Sails
      What should a PRO-space political action organization do?
             Re: Orbital Elements
               Re: Solar Sails
                Re: Ramscoops
        Re: International agreements on space station
               Re: Solar Sails
              Re: Spy Satellites
               Re: Solar Sails
             Re: Von Braun quote
          Re: Trust Fund Proposed for Space Ventures
             Re: Von Braun quote
----------------------------------------------------------------------

Date: Fri, 22 Jul 88 15:40:08 -0400 (EDT)
From: Ted Anderson <[e-mail]>
X-Andrew-Message-Size: 1387+0
Cc: [e-mail]
Subject: Ramscoops

   a.cs.uiuc.edu!p.cs.uiuc.edu![e-mail]  writes:

>One more question I can think of off the top of my head -- what happens
>to heat dissipation as time slows down?  As the fusion reactor approaches
>light-speed, would its heat dissipation also slow down, thus causing
>a meltdown?

     My first reaction to the above was "AAAAAAAArrrrrrrrrgggggghhhh!!!!!!".
The person asking the question obviously knows very little about
relativity.  Time only "slows down" for the stationary observer
comparing his/her time measurements of something happening at high
velocity with those of the observer who is moving at that velocity.  In
the case of the ramscoop, the fusion/magnetic field generators are also
travelling at the high velocity, and thus experience no time dilation.
Thermodynamics are exactly normal.  However, an observer who sees the
ramscoop travelling at relativistic speeds will see a lot of red or blue
shifted thermal radiation profiles from the ramscoop.


-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-
Arnold Gill                              | If you don't complain to those who
|
Queen's University at Kingston           | implemented the problem, you have
|
gill @ qucdnast.bitnet                   | no right to complain at all !
|

-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-

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

Date: 22 Jul 88 17:05:32 GMT
From: pioneer.arc.nasa.gov![e-mail]  (Eugene N. Miya)
Subject: Re: tacking of Solar Sails


This, I think, is part of the beauty of experimental research.  There
are preliminary ideas about the use of sails, but we really have to test
them.  Face it, we don't know many of these questions with certainty,
now that's where part of the human in space fun will be!  It's amusing
to hear about sailing (real sailing) from landlubbers and on the other
hand the salts will probably have their intuition jolted.  We're just
learning this stuff.  "Jibe ho!"

Another gross generalization from

--eugene miya, NASA Ames Research Center, [e-mail]
  resident cynic at the Rock of Ages Home for Retired Hackers:
  "Mailers?! HA!", "If my mail does not reach you, please accept my apology."
  {uunet,hplabs,ncar,decwrl,allegra,tektronix}!ames!aurora!eugene
  "Send mail, avoid follow-ups.  If enough, I'll summarize."
  I'll crew on your boat anytime.

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

Reply-To: mordor!rutgers!trout.nosc.mil!pnet01!jim
Date: Thu, 21 Jul 88 20:25:35 PDT
From: mordor!rutgers!pnet01.cts.com!jim (Jim Bowery)
To: crash![e-mail]
Subject: What should a PRO-space political action organization do?

There are rumors that, due to difficulties with existing organizations,
a new political action organization is forming to promote PRO space
positions with the US government.  I'd be interested in hearing from
people who are dissatisfied with existing organizations claiming to
promote space.  What positions would YOU like to see a new organization
to promote?  Please send your responses to me via personal email.


Jim Bowery                   PHONE: [phone]


UUCP: {cbosgd, hplabs!hp-sdd, sdcsvax, nosc}!crash!pnet01!jim
ARPA: crash!pnet01![e-mail]
INET: [e-mail]

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

Date: 22 Jul 88 00:07:51 GMT
From: tektronix!sequent!mntgfx![e-mail]  (Mike Butts)
Subject: Re: Orbital Elements

From article <[e-mail]>, by [e-mail] (Andrew Vaught):
>
> I appreciate people posting the orbital elements of various (Soviet)
> spacecraft. Unfortunately, I don't know enough orbital mechanics in order
> to convert these to a time/position for my long./lat.  Could someone post
> a good reference to how to do this, or tell me where a conversion program
> (preferably source) is archived?
>
Several posted requests prompt posting a general reply:

Tracking programs for many personal computers are in a list available
from AMSAT (Radio Amateur Satellite Corp.), which is the non-profit
organization responsible for Amateur Radio comm-sats.  They conducted
the recent sparklingly successful OSCAR-13 launch via Arianne 4. (Yayyy!!!)

(OSCAR-13 is a public-access radio repeater in a Molniya-type 12-hour
elliptical orbit which allows hams to conduct inter-continental voice
contacts for hours at a time with relatively modest 10 watt VHF
equipment.)

I don't know where generic source code is available, but someone else
on the net probably does. (???)

You may also buy some of these programs from AMSAT.  Quik-Trak for
IBM PCs seems to be popular, and I'm happy with MacTrak for
Macintosh.  These programs will give you orbital tracks in real
time or in the future, with tabular or graphical map output, given
the Keplerian elements often posted on rec.ham-radio and sci.space.

Inquires about membership and ham-sats in general should be sent to
AMSAT, P.O. Box 27, Washington, D.C.  20044.  Donations may be tax
deductible.  You may call at 301-589-6062 for information
or to order satellite tracking software.

--
Mike Butts, Research Engineer         KC7IT           503-626-1302
Mentor Graphics Corp., 8500 SW Creekside Place, Beaverton OR 97005
...!{sequent,tessi,apollo}!mntgfx!mbutts OR  [e-mail]
These are my opinions, & not necessarily those of Mentor Graphics.

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

Date: 22 Jul 88 19:05:41 GMT
From: aplcen!aplcomm!stdc.jhuapl.edu![e-mail]  (Jim Meritt)
Subject: Re: Solar Sails

In article <[e-mail]> [e-mail] (Mike Wooding) writes:
} An earlier poster suggested tacking (sailing up wind - er is that
} up light?) might be possible. How's that work. Doesn't a sail boat
} depend on keel and aerodynamic effects on sail? Would "solar" wind
} be "channeled" to produce high and low pressure areas?


Gravity - use vector component of reflected light to speed or slow
orbital velocity, and so go insun & outsun.

Can't tack with solar flux, only photons...


Disclaimer: Individuals have opinions, organizations have policy.
            Therefore, these opinions are mine and not any organizations!
Q.E.D.
[e-mail] 128.244.65.5  (James W. Meritt)

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

Date: 23 Jul 88 04:23:10 GMT
From: [e-mail]  (Paul F. Dietz)
Subject: Re: Ramscoops

>>One more question I can think of off the top of my head -- what happens
>>to heat dissipation as time slows down?  As the fusion reactor approaches
>>light-speed, would its heat dissipation also slow down, thus causing
>>a meltdown?
>
>     My first reaction to the above was "AAAAAAAArrrrrrrrrgggggghhhh!!!!!!".
>The person asking the question obviously knows very little about
>relativity.

My first reaction was similar.  But there's a good point.  The power
output of the fusion reactor must increase as the vehicle accelerates,
if thrust is to be constant.  This is true even in a newtonian universe.
If fractional losses are constant then waste heat will increase with
velocity.

    Paul F. Dietz
    [e-mail]

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

Date: 22 Jul 88 05:06:07 GMT
From: attcan!utzoo![e-mail]  (Henry Spencer)
Subject: Re: International agreements on space station

In article <[e-mail]> [e-mail] (RON PICARD) writes:
>Is Fletcher crying wolf or is this the next (final) step in
>eliminating any credibility NASA may still have?  It should
>at least make the Russians think twice about a cooperative
>mission to Mars anytime soon.

Fletcher has been crying awfully hard lately, but as I have said before,
I rate the station's chances as poor going on abysmal.  NASA has taken
a perfectly straightforward idea and gold-plated it beyond what the US
feels like paying.

Anyone who undertakes *any* cooperative space project with the US these
days and doesn't consider it a high-risk venture needs his head examined.
NASA's credibility in this area has been nearly zero for a long time.
--
Anyone who buys Wisconsin cheese is|  Henry Spencer at U of Toronto Zoology
a traitor to mankind.  --Pournelle |uunet!mnetor!utzoo! henry @zoo.toronto.edu

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

Date: 22 Jul 88 05:17:56 GMT
From: attcan!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Solar Sails

In article <[e-mail]> [e-mail] (Steve) writes:
>If the light bounces off the sail, how does it impart momentum.  What
>energy of the photon is now reduced?  I think the photons must be
>ABSORBED by the sail for this to work.

No.  Momentum, not energy.  Momentum is a vector quantity; the photon has
not lost energy, but it has changed direction.  It has gained momentum
in one direction, the sail has gained it in the other.  No conservation
laws are violated in providing thrust without losing energy (the chair
you are sitting on has to thrust upward against your behind to keep you
from falling to the floor, but it is not expending energy to do so).

If the sail is accelerating, as opposed to (say) hovering against the
Sun's gravity, then it is gaining kinetic energy as well and that energy
has to come from somewhere.  And it does:  as the sail accelerates, the
light reflected from it is Doppler-shifted to longer wavelengths by the
sail's motion, i.e. the light is losing energy.  Not much, but then the
sail isn't gaining much either, at typical solar-sail accelerations!
--
Anyone who buys Wisconsin cheese is|  Henry Spencer at U of Toronto Zoology
a traitor to mankind.  --Pournelle |uunet!mnetor!utzoo! henry @zoo.toronto.edu

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

Date: 21 Jul 88 16:48:47 GMT
From: mnetor!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Spy Satellites

In article <[e-mail]> [e-mail] (Obnoxious Math Grad Student) writes:
>Cryptological information is born classified.  And probably some stuff
>involving optics.

Please cite references for this.  I, too, thought this at one point, but
was corrected (over in sci.crypt, whose participants include some ex-pro
cryppies).  NSA would undoubtedly *like* "born classified" status for
crypto stuff, but they haven't managed to arrange it.

The much-heralded cases in recent years of heavy-handed DoD suppression
of papers at the last minute, etc., have either involved DoD funding which
had explicit strings attached, or were cases of bureaucratic intimidation
without legal basis.
--
Anyone who buys Wisconsin cheese is|  Henry Spencer at U of Toronto Zoology
a traitor to mankind.  --Pournelle |uunet!mnetor!utzoo! henry @zoo.toronto.edu

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

Date: 22 Jul 88 21:32:18 GMT
From: thumper![e-mail]  (Phil R. Karn)
Subject: Re: Solar Sails

We had a big discussion on this some time ago. The answer is that you
can't "tack" in the same way that a sailboat can, but you instead
exploit the laws of orbital mechanics to do interesting things.  You
have some limited control over the direction of the force on your sail
by changing the angle of the sail to the sun, since the net momentum
imparted by a solar photon is the vector sum of the incident and
reflected photon momenta.

The instantaneous force will always have a component pointing away from
the sun.  However, if you're in orbit around the sun, you can orient
your sail to create a velocity component that either adds to or
subtracts from your orbital velocity vector, so it's possible to either
raise or lower your orbit.  I suppose this could be called "tacking" in
a loose, metaphorical sense.

Phil

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

Date: 22 Jul 88 21:51:43 GMT
From: thumper![e-mail]  (Phil R. Karn)
Subject: Re: Von Braun quote

> > I've never understood why it's so necessary to put humans into space in
> > order to benefit from their ability to react to unforseen circumstances.

> But it would'nt be near as much fun!

*NOW* we're getting somewhere. I'd object far less to the human-in-space
camp if they were only up front and honest about their motivations. I
enjoy a shuttle launch as much as anyone (I was one of the few people
who saw Challenger blow up in real time on TV) but I don't fool myself
into believing that flying humans on a Shuttle is the best way to launch
a geostationary communications satellite.

There *are* a few legitimate applications for humans in orbit, such as
life sciences research, or even Christa McAuliffe's planned science
class demonstrations. I also appreciate the human adventure and the
sheer entertainment value more than you might think. BUT I am careful to
distinguish these latter aspects from practical issues like
cost-effectiveness.

Unfortunately, many people simply don't do this. The result is something
resembling a religious cult that spends much of its time reinforcing
each others' rationalizations for putting as many humans into space as
possible, whether or not it makes rational, economic sense.

Phil

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

Date: 22 Jul 88 13:01:53 GMT
From: b.gp.cs.cmu.edu![e-mail]
Subject: Re: Trust Fund Proposed for Space Ventures

In article <[e-mail]>, [e-mail] (Paul S. R. Chisholm) writes:
}[Typical of N.J. reps; "I'm in favor of the space program, if you can
}build an interstate to orbit."]

Hmm, I wonder if the Launch Loop would apeal to him....

--
UUCP: {ucbvax,harvard}!cs.cmu.edu!ralf -=-=-=- Voice: [phone] (school)
ARPA: [e-mail]  BIT: ralf%cs.cmu.edu@CMUCCVMA  FIDO: Ralf Brown 1:129/31
Disclaimer? I     |Ducharm's Axiom:  If you view your problem closely enough
claimed something?|   you will recognize yourself as part of the problem.

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

Date: 22 Jul 88 21:14:30 GMT
From: mnetor!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Von Braun quote

In article <[e-mail]> [e-mail] (Phil R. Karn) writes:
>Henry, I'm impressed. You *have* been reading up on us, haven't you!

No, actually, I was on the net and watching the Amsat news when it first
happened...

>But since you like to quote anecdotes, let's pick the Solar Max rescue
>mission. Remember how George ("Pinky") Nelson grabbed one of the solar
>arrays in an attempt to stop the satellite from spinning? ...

Phil, I didn't say humans were immune from stupidity.  Especially since
the instructions for that EVA specifically said "hands off the solar
arrays"!  Note that a similar, but slightly better thought-out, method
worked perfectly for the Leasat repair.

>... And I won't even mention the strong likelihood that
>the rescue mission cost more than a simple replacement would have.

Sure sounds to me like mentioning it... :-)  The economics of many of
these things are sensitive to what assumptions one makes about launch
costs.  One would hope that people saying "humans in space aren't worth
it" would preface it with "at current launch prices"... but they don't.
Do remember that the Solar Max rescue mission wasn't a dedicated shuttle
flight; the reason they had practically the entire payload bay empty was
the LDEF deployment.

>I've never understood why it's so necessary to put humans into space in
>order to benefit from their ability to react to unforseen circumstances.

It isn't necessary, it just helps a lot.  Teleoperation has some -- not
all, but some -- of the same limitations as automation.  Especially since
really general-purpose waldos are still in a very primitive state.

>[The human crew] need not be
>prime physical specimens; they can be chosen solely for their technical
>skills and perhaps even their understanding of the basic physics of
>rotating bodies (unlike Pinky Nelson).

This problem is already mostly licked, since the shuttle's acceleration
is deliberately held down to the point where any healthy adult could fly
on it.  This was a specific design goal, as I recall.  Don't confuse silly
NASA policies with fundamental hardware constraints.

>Your arguments represent a convincing case for versatile remote control,
>not for manned spaceflight...

I would agree, were it not that I know of no remote-control hardware that
I would call "versatile".  Remote control is great if the problems you
run into are along the lines that the designers anticipated.  The Voyager
team has done minor miracles with remote control... but considering how
badly Voyager 2 is limping, I suspect any of them would sacrifice one or
two semi-essential parts of his/her anatomy to get a repair technician
out to V2 for six hours.

>[AO-10] With the help of a versatile on-board computer
>that can be completely reprogrammed from the ground,  we were able to
>save the mission.

Correct me if I'm wrong, but as I recall the operative words were "save
the mission", as opposed to "carry out the mission as if nothing had
happened".  You did have to accept some penalties, did you not?
--
Anyone who buys Wisconsin cheese is|  Henry Spencer at U of Toronto Zoology
a traitor to mankind.  --Pournelle |uunet!mnetor!utzoo! henry @zoo.toronto.edu

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

End of SPACE Digest V8 #310
*******************