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Date: Mon, 8 Aug 88 01:04:01 PDT
From: Ted Anderson <ota@angband.s1.gov>
Message-Id: <8808080804.AA01923@angband.s1.gov>
To: Space@angband.s1.gov
Reply-To: Space@angband.s1.gov
Subject: SPACE Digest V8 #318

SPACE Digest                                      Volume 8 : Issue 318

Today's Topics:
		    Re: Are these postings useful?
Contractor selected for solid-fueled rocket motor bondline study (Forwarded)
		 Re: Time skew -- does it hurt SETI?
		    Re: Are these postings useful?
		  Re: query about 'escape velocity'
		  Re: query about 'escape velocity'
			   Re: Solar Sails
		     Re: Libertarian space policy
			     Re: E stamp
		    Re: Are these postings useful?
			  orbital mechanics
----------------------------------------------------------------------

Date: 30 Jul 88 17:41:29 GMT
From: pyrnj!dasys1!tneff@rutgers.edu  (Tom Neff)
Subject: Re: Are these postings useful?

In article <19880728032142.7.MAEDA@PELE.ACA.MCC.COM> maeda@MCC.COM (Christopher Maeda) writes:
>You are sucking up a lot of bandwidth.  Perhaps you could make them
>available by FTP and just send a message about how to get it.

Disagree!  It's not a lot of bandwidth -- check the arbitron and uunet charts.
And the s/n ratio is BEAUTIFUL -- all hard info.  I love it.  The only thing
I could sincerely do without is "catching up" on 2+ month old
AvWeek issues.
-- 
Tom Neff			UUCP: ...!cmcl2!phri!dasys1!tneff
	"None of your toys	CIS: 76556,2536	       MCI: TNEFF
	 will function..."	GEnie: TOMNEFF	       BIX: t.neff (no kidding)

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

Date: 31 Jul 88 02:21:58 GMT
From: yee@ames.arc.nasa.gov  (Peter E. Yee)
Subject: Contractor selected for solid-fueled rocket motor bondline study (Forwarded)

James Cast
Headquarters, Washington, D.C.                      July 29, 1988

Bob Lessels
Marshall Space Flight Center, Huntsville, Ala.


RELEASE: 88-107

CONTRACTOR SELECTED FOR SOLID-FUELED ROCKET MOTOR BONDLINE STUDY


     NASA's Marshall Space Flight Center, Huntsville, Ala., has 
selected Science Applications International Corp., San Diego, 
Calif., for final negotiations leading to the award of a contract 
to perform a study aimed at developing an engineering technology 
base to improve the bondlines of solid-fueled rocket motors.

     The value of the contract, including options, is expected to 
be approximately $21 million and will run for 2 years, with three 
1-year options to extend.

     Bondline integrity is critical to the successful operation 
of solid-fueled rocket motors.  Bondlines are the regions where 
the solid fuel is bonded to the motor's liner or insulation, 
which, in turn, is bonded to the motor case walls.  These bonds 
prevent the hot combustion gases inside the motor from reaching 
the motor case wall, where the gases could burn through the wall 
and cause failure of the motor.

     The work is part of the agency's Solid Propulsion Integrity 
Program.  The objective of the program is to increase the success 
rate of solid-fueled rocket motors by improving basic engineering 
capability in such areas as material characteristics, design 
analysis, fabrication and assembly processes and production 
evaluation and verification.

     The program originated from joint NASA-Department of 
Defense-industry studies which identified critical shortfalls in 
the U.S. engineering technology for solid-fueled rocket motors.

     In June, Hercules Aerospace Co., Magna, Utah, was selected 
as the contractor for the Solid Propulsion Integrity Program 
nozzle work packages.  The two work packages represent NASA's 
contribution to the tripartite effort.

     NASA engineers managing the program expect to improve 
confidence in solid rocket motor launch systems by establishing 
urgently needed engineering tools, techniques and data bases 
specifically applicable to the current civil and military family 
of solid-fueled rocket motors.

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

Date: 31 Jul 88 03:00:30 GMT
From: mike@arizona.edu  (Mike Coffin)
Subject: Re: Time skew -- does it hurt SETI?

A point that hasn't been made: even if electromagnetic radiation is
the last word in communication, why spray most of the power into empty
space?  I would think that advanced civilizations would probably use
modulated lasers or some other point-to-point method of communicating.
Not only would this save power, but it doesn't pollute the
electromagnetic spectrum.  That would make detection on earth a pretty
low probability event --- we would have to me almost exactly in the
right place at the right time to detect anything at all, and if we
*did* it would probably be a brief, unrepeated message.
-- 

Mike Coffin				mike@arizona.edu
Univ. of Ariz. Dept. of Comp. Sci.	{allegra,cmcl2,ihnp4}!arizona!mike
Tucson, AZ  85721			(602)621-4252

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

Date: 31 Jul 88 06:40:31 GMT
From: jplpub1!jbrown@elroy.jpl.nasa.gov  (Jordan Brown)
Subject: Re: Are these postings useful?

In article <5813@dasys1.UUCP> tneff@dasys1.UUCP (Tom Neff) writes:
>The only thing I could sincerely do without is "catching up" on 2+
>month old AvWeek issues.

Take heart, Henry - I think your AvWeek digests are one of the greatest
things since the airplane... they're one of the few ways I keep in touch
with what's happening in aviation & space technology & politics.

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

Date: 31 Jul 88 15:29:41 GMT
From: cfa!cfa250!mcdowell@husc6.harvard.edu  (Jonathan McDowell)
Subject: Re: query about 'escape velocity'


From article <3451@polya.Stanford.EDU>, by crew@polya.Stanford.EDU (Roger Crew):
 In article <1020@cfa237.cfa250.harvard.edu} mcdowell@cfa250.harvard.edu ..                          
 > velocity (in a direction away from the Earth!)
 Actually, it doesn't matter what direction you're pointed in,
 so long as there's nothing directly in your path that is going
 to slow you down (like an atmosphere or a swarm of rocks).
.     
yes, I meant in any direction that does not intersect the Earth's
surface. In arguments between the Earth and a spacecraft, the Earth
tends to win, it has more momentum you know :-). Sorry, I should
ave been more precise in my choice of phrase.
       
       Jonathan

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

Date: 31 Jul 88 15:18:01 GMT
From: cfa!cfa250!mcdowell@husc6.harvard.edu  (Jonathan McDowell)
Subject: Re: query about 'escape velocity'

From article <1068@cfa.cfa.harvard.EDU>, by wyatt@cfa.harvard.EDU (Bill Wyatt):
> The above is correct except I think you have to emphasize that the
> escape velocity varies with the square root of the distance from the
> Earth's (or other gravity well's) center. Thus, if you have sufficient
> thrust to move away from the Earth at 55 mph, I calculate that
> somewhere in the vicinity of Jupiter's orbit you'll be at the escape
> velocity of Earth. After that point, even stopping the thrust will not
> let you fall back to Earth (assuming no perturbations, etc.), although
> you'd presumeably orbit or fall into the Sun!

Thanks for the clarification, Bill.  You're quite right, at 9 AU ( about
the orbit of Saturn) 55 mph is indeed escape velocity from Earth.  But
what happens if the thrust stops at that point? You're not travelling at
55 mph relative to the Sun..  

Either: the problem implies one travels in a straight line with constant
velocity relative to an inertial frame instantaneously fixed in the
center of the Earth at the moment of takeoff (remember that at 55 mph
the Earth has made 1700 revolutions of the Sun by the time you get to
the point in question!) In this case one is no longer travelling at 55
mph relative to the Earth, but relative to where the Earth was. 

Or: You keep a constant 55 mph velocity relative to the center of the
Earth at all times.  This is very tricky as the Earth is accelerating
around the Sun.  In either case, you do not have the local orbital
velocity relative to the Sun, you have the Earth's Keplerian orbital
velocity. 

Since the escape velocity at a given point is root 2 times the orbital
velocity, and both decrease with the root of the distance from the
central mass, you just have to double your distance from the central
mass while keeping the same velocity to achieve escape; so you have
escape velocity relative to the Sun by the time you get to 2 AU. 
You're headed out into the Great Unknown.

Of course, the point you make is that we shouldn't be trying to keep our
velocity low anyway, since that's not what costs..it's only relative. 
The trick is to keep your energy requirements low, since that's what you
pay for. 

Jonathan McDowell.

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

Date: Sun, 31 Jul 88 14:09:31 CDT
From: sedspace@doc.cc.utexas.edu (Steve Abrams)
Posted-Date: Sun, 31 Jul 88 14:09:31 CDT
Subject: Re: Solar Sails


In V8 #306, Eric "TheBoo" Bazan (eric@shorty.cs.wisc.edu) writes:

>My question is this: just how does the sun 'push' against the sail? Is it the
>solar wind of charged particles (protons and electrons), or the actual
>photonic flux, or both?

	Since the wave and particle paradigms for electromagnetic radiation are
equivalent, you can certainly think of "material" photons bouncing off a sail
film and, thereby, transferring momentum to the sail.  However, I assume you
want to view it from the wave perspective.

	With the propagation of electromagnetic radiation (light energy) there
is a flow of energy.  However, you've probably also heard that mass and energy
are equivalent (E=mc^2).  Therefore, you have a mass-equivalent entity traveling
with a velocity...the product of mass and velocity is linear momentum.  More mathematically, the "momentum density", g, is equal to a constant (the product of
the permeability and permittivity of free space) times the "Poynting vector" 
(since we're in a vacuum).  The Poynting vector is simply a vector defining the
energy flow of the light (EM radiation).  The value for this Poynting vector
is just the solar constant you mention, 1.353 kW/m^2.

	The physical process is (loosely) that the photon is "absorbed" by an
atom in the sail film.  The energy is used to raise an electron's energy level.
That electron then spontaneously decays thereby emitting another photon *with
the same energy* as the original photon but in the opposite direction.  In each
process of absorption and re-emission, momentum is transferred in the same 
direction to the sail film.  The energy of the photon doesn't change (a scalar
quantity) and the magnitude of the velocity of the photon doesn't change *BUT*
the direction changes.  By Newton's Third Law (Action/Reaction), momentum is
transferred to the sail from the photon.

	I realize that this won't satisfy purists, but it should be sufficient
for someone with a poor physics background.

	Incidentally, the book Eric is probably referring to is _Starsailing_
by Louis Friedman.  It is an excellent introductory, survey-type book on
the subject.  Does anyone know if a more technical, mathematically-oriented
sequel is in the works?


					Ad Astra,

					Steve Abrams


 \                                                                       /
--"You have twenty seconds to put down your slide rule...19...18...17..."--
 /                                                                       \
                                                     --  RoboDweeb

2721 Hemphill Park, Apt. C	ARPANET:  sedspace@doc.cc.utexas.edu
Austin, TX  78705		CompuServe:  [70376,1025]
(512)480-0895			
				OR
     c/o Students for the Exploration and Development of Space
   P.O. Box 7338, 358 Texas Union, University of Texas at Austin
              Austin, TX  78713-7883  (512)471-7097

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

Date: 31 Jul 88 06:01:40 GMT
From: tektronix!percival!bucket!leonard@ucbvax.berkeley.edu  (Leonard Erickson)
Subject: Re: Libertarian space policy

In article <355@gronk.UUCP> johnl@gronk.UUCP (John Limpert) writes:
<In article <8807251911.AA01355@angband.s1.gov> WALL@BRANDEIS.BITNET (Matt) writes:
<> If you would like to see an analagous situation, look at Antarctica. 
<> The goal of international control for the benefit of humankind was
<> corrupted by attaching property "rights" to any sort of presence, in
<> fact, specifically to 'scientific' presence. 
<
<The only reason the 'corrupted' situation in Antarctica exists is
<because it is a compromise between the two extremes.  A treaty has
<to consider the views and interests of all concerned parties.
<"International control for the benefit of Mankind" may be a nice
<idea to some people, but in its idealogically pure form, it isn't
<a practical basis for a treaty.  The reason for the acceptance of
<the current treaty was the perceived uselessness of Anarctica.
<If someone discovers valuable mineral deposits, the current treaty
<may not last very long.

Try *since* valuable mineral deposits *have been* discovered, the
current treaty *isn't* going to last much longer. Coal has been
discovered, and it looks like there may be oil as well. (In case 
you didn't know, the *real* reason that Britain and Argentina
went to war over the Falklands was that it looks like there may
be a major oilfield in the South Atlantic and the Falklands are the
nearest land. Own the Falklands and you own the oil..)

Note that Argentina has *already* started claiming *soveriegnty
over it's portion of Antartica. And there are lots of people making
noises about the need to re-negotiate the treaty...
-- 
Leonard Erickson		...!tektronix!reed!percival!bucket!leonard
CIS: [70465,203]
"I used to be a hacker. Now I'm a 'microcomputer specialist'.
You know... I'd rather be a hacker."

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

Date: 31 Jul 88 23:02:12 GMT
From: bobmon@iuvax.cs.indiana.edu  (RAMontante)
Subject: Re: E stamp

joe@hanauma.stanford.edu (Joe Dellinger) writes:
+	Anybody looked closely at the new U.S. "E" stamp?
+
+	Notice anything funny about it?
+	(Hint: where's the terminator, and which direction does it run?)
+
+	Perhaps we really DO need to spend more time studying
+	before launching anything!

Yeah -- like which star will go supernova to produce this effect?  And
will we have time to get observer satellites up?  :-)

Maybe Henry Spencer's "Post Office" quote has more depth than we all thought!
-- 
	bob,mon				(bobmon@iuvax.cs.indiana.edu)
"`This must be deep' means `I can recognize all these words individually,
but dam' if I can make any sense out of the order in which they currently
appear....'"	- Gil Scott Herron

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

Date: 1 Aug 88 04:56:39 GMT
From: att!lzaz!lznv!psc@ucbvax.berkeley.edu  (Paul S. R. Chisholm)
Subject: Re: Are these postings useful?

< "Would you buy a used operating system from these guys?" >

In article <5813@dasys1.UUCP>, tneff@dasys1.UUCP (Tom Neff) defends the
orbital elements summaries:
> Disagree!  It's not a lot of bandwidth -- check the arbitron and uunet charts.
> And the s/n ratio is BEAUTIFUL -- all hard info.  I love it.  The only thing
> I could sincerely do without is "catching up" on 2+ month old AvWeek issues.

Disagree!  Not only are Henry's summaries from Aviation Week and Space
Technology useful to us non-subscribers, they stir up some informative
debate.  (And some real time wasters, but *no* posting is so pure that
it can't be followed up by trash [PLEASE don't prove my point!!!])

> Tom Neff, UUCP: ...!cmcl2!phri!dasys1!tneff, CIS: 76556,2536, MCI: TNEFF
> GEnie: TOMNEFF, BIX: t.neff (no kidding)

-Paul S. R. Chisholm, {ihnp4,cbosgd,allegra,rutgers}!mtune!lznv!psc
AT&T Mail !psrchisholm, Internet psc@lznv.att.com
I'm not speaking for my employer, I'm just speaking my mind.

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

Date: Mon 1 Aug 1988 10:32:11 EST
From: Harold Mueller <mueller@nrl-radar.arpa>
Subject: orbital mechanics
To: munck@mitre-bedford.arpa
Cc: space@angband.s1.gov

I can recommend a couple of good books.

Bate, R. R., D. D. Mueller, and J. E. White, "Fundamentals of
Astrodynamics", Dover, 1971 is a good general overview.  They go into
computing position/velocity vector at a future time from a known
position/velocity vector at some past time.  It's available in paperback.

Escobal, "Methods of Orbit Determination", 1965, 1985 Krieger
Publishing Company, Inc., Krieger Drive, Malabar Florida 32950, ISBN
0-88275-319-3, $39.50 in April, has a couple of great
appendices.  Appendix I has transformation matrices between all the
commonly used (and not commonly used) coordinate systems.  This means
you can, say, solve your motion problem in the plane of the orbit
(pretty easy) and then transform it into the azimuth/elevation/range of
an earth-based observer's POV, or into 3-d rectangular for off-world
display.  

Appendix II is titled "A complete algorithm for two-body motion in
space".  I haven't tried the stuff in it, but the rest of the book is
good so I assume this is as well.  It's a skeletal flow chart with
equations (not even refined to pseudocode yet), and handles the cases
for circular/elliptic, parabolic, and hyperbolic orbits (all require
different equations).

You are attacking a non-trivial problem.

Harold Mueller <mueller@nrl-radar.arpa>
Bendix Field Engineering Corporation
c/o Code 5360
Naval Research Laboratory
4555 Overlook Avenue, SW
Washington, DC 20375
(202) 767-3240/3356     AUTOVON 297-3240/3356

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

End of SPACE Digest V8 #318
*******************