Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_4/V15NO457.TXT

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Date: Thu, 26 Nov 92 05:00:08
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #457
To: Space Digest Readers
Precedence: bulk


Space Digest                Thu, 26 Nov 92       Volume 15 : Issue 457

Today's Topics:
                   Computer synchronisation by GPS
                         Dante on "Nightline"
                Data on Stars in the vicinity of earth
                             GAS (2 msgs)
                         HST black hole pix?
                           Hubble's mirror
            hypergolics (was Re: Pumpless Liquid Rocket?)
                       Nasa Calendar of events
                          Scientific method
                          Shuttle computers
                     Shuttle replacement (6 msgs)
                              Simplicity
                            Solar sailing

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

Date: 24 Nov 92 20:09:17 GMT
From: Craig Powderkeg DeForest <[e-mail]>
Subject: Computer synchronisation by GPS
Newsgroups: sci.space,sci.physics

In article <foo> [e-mail] (Henry Spencer) writes:
   In article <bar> [e-mail] (Dave Hopkins) writes:
   >As I understand it GPS has a number of accurate (atomic) clocks which are
   >fundamental to determining ones position. One of the quoted applications
   >for GPS is for synchronising computer systems across the world using this
   >time information.

    ... excellent explanation deleted ...

   ...with
   GPS, you *have* a common absolute time reference.  All GPS receivers,
   anywhere in the world, agree on the exact instant when the GPS system
   clock reads 1:45:67.8727634 (with several more decimal places if the
   receiver is a spiffy one).  If your computer has a GPS receiver, and you
   tell it to start processing at 11:17:05.8368461 sharp, it will start
   processing in exact synchronization with any other similarly-equipped
   computer that got the same instructions.

My immediate response was, `wait -- that can't be: the GPS receivers
are all separated by spacelike intervals!' -- but we all share a
common reference frame, and thus all pretty much agree on the angle of
the space axes.  (whew!  I know *you're* all relieved...) I suppose my
GPS receiver wouldn't work too well if I went zooming by at 0.5C on my
Honda GSX11,000,000 interstellar crotch-rocket!
--
DON'T DRINK SOAP! DILUTE DILUTE! OK!

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

Date: 25 Nov 92 14:17:01 GMT
From: John Thompson Reynolds <[e-mail]>
Subject: Dante on "Nightline"
Newsgroups: sci.space

Just out of curiosity, is there any valid Science being done by this NASA
"mission" to Antartica, or is this just showboating to get some network
coverage?  Assuming that science is in fact being done, what does it have
to do with Aeronautics and Space?  Why is NASA getting involved in
oceanography?  I can see them supporting other organizations such as NOA,
but I can't see why they would be "stealing the limelight".

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

Date: Wed, 25 Nov 92 11:04:21 -0800
From: [e-mail]
Subject: Data on Stars in the vicinity of earth

Someone out there (I forgot to save the message) asked if there was a source
of star data available.  My slow brain remembered, after I deleted the message,
that a person named M. Veikko from Finland posted a message to this group
about FTP sources of all sorts of information.  The sci.space valume was 15,
Issue number 147 dated 28 August, 1992.  I'm sure that one of the sources
that M. Veikko listed would have the data you want.

I still have the list, if you want it, send me your email address and I will
forward it to you.   You could also ask M. Veikko directly at
     [e-mail]

Grant Anderson
[e-mail]
Design Project Lead, Space Station WP-04, Lockheed.

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

Date: Wed, 25 Nov 1992 14:54:29 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: GAS
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:

-I hope you aren't referring to 'get away specials' since NASA doesn't fly
-them anymore.

>As of when? There have been plenty flown this year - in fact, I believe
>*Dennis* has flown at least one this year.

I believe they where halted after Chalenger. I read in a recent issue
of (I think) Space News that NASA was thinking of starting them up
again.

I believe the payloads you speak of where just normal payloads.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------150 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: Wed, 25 Nov 1992 17:30:31 GMT
From: Henry Spencer <[e-mail]>
Subject: GAS
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>I believe they where halted after Chalenger. I read in a recent issue
>of (I think) Space News that NASA was thinking of starting them up
>again.

They *have* started up again.  In my next AW&ST summary, you'll see coverage
of NASA hiking the prices, and GAS users muttering angrily.

In fact, some GAS cans have recently flown containing only ballast, because
although there are a lot of GAS reservations, very few of those projects
actually have payloads ready to fly.
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

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

Date: 25 Nov 92 10:52:02 -0600
From: [e-mail]
Subject: HST black hole pix?
Newsgroups: sci.space

Does anybody out there have a .GIF copy of the recent Hubble Space
Telescope image which purported to show the accretion disk of
a supermassive black hole at the core of some galaxy or other?

Or, does anybody know where such a file could be obtained by
anonymous FTP?

NASA? STSI? anyone??

I gotta have it.

Thanx in advance,

KB

--
*.x,*dna**************************************************************
*(==) Ken Barnes, LifeSci Bldg.                                      *
* \'  [e-mail]                                    *
*(-)**Memphis,TN********75320,[e-mail]**********************
"When I was a boy I was told that anybody could become President;
I'm beginning to believe it."--Clarence Darrow

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

Date: Wed, 25 Nov 1992 09:13:22 GMT
From: Joe Dellinger <[e-mail]>
Subject: Hubble's mirror
Newsgroups: sci.astro,sci.space

In article <[e-mail]>, [e-mail] (Greg Hennessy) writes:
|> the set of tests that you develop
|> to test a mirror BEFORE you know it has a certian problem is not
|> necessarily the same as the set of tests that you develop AFTER you
|> know it has a problem. PE developed a system of testing that they
|> THOUGHT would be good enough. Unfortunately it was not. At least we
|> can be pretty sure that this blunder won't be repeated.
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

But... PE's system of testing WAS good enough. They had three
redundant tests, so that if one test gave a false OK the other
two could catch it.

One test gave a false OK, and the other two caught it. The system worked!

The blunder was that they _ignored_ the test results that indicated
something was wrong.

The blunder was that the people paying for it weren't checking
over the shoulders of the ones being paid.

Human nature being what it is, I expect we will see these blunders repeated
again and again and again!

     /\    /\    /\/\/\/\/\/\/\.-.-.-.-.......___________
    /  \  /  \  /Hawaii Institute of Geophysics, Honolulu\/\/\.-.-....__
___/    \/    \/Joe Dellinger, Internet: [e-mail]\/\.-.__

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

Date: Wed, 25 Nov 1992 17:17:07 GMT
From: Henry Spencer <[e-mail]>
Subject: hypergolics (was Re: Pumpless Liquid Rocket?)
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Thomas Clarke) writes:
>I may have to build a small one.  Anyone know of safe
>(& cheap) hypergolic propellants?

Ain't no such thing, beyond the vinegar-and-baking-soda stage that Bill
suggested.  Not if you want safety in flight, anyway.  Rocket engines
(especially new ones) are dangerous pieces of hardware by their nature.

Something like high-test hydrogen peroxide plus kerosene is probably about
the closest you can come, for *on-the-ground* safety, if you want both
components liquid.  Or maybe concentrated nitric acid and alcohol.  Strong
oxidizers are dangerous by definition.

If you're willing to settle for a hybrid liquid/solid combination, water
and aluminum foil work once you get them started.  Aluminum is difficult
to ignite but is a *ferocious* fuel, enough so to rip oxygen out of water
molecules.  Don't be lulled into carelessness by the seemingly benign
nature of the ingredients, though -- once ignited, aluminum is not benign,
and you'll also get quite a bit of hydrogen gas.  Aluminum-water reactions
have caused powerful explosions.  The only reason aluminum is so safe
for normal uses is the tough oxide film on its surface.  (This is also
the reason why it's so hard to ignite.)
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

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

Date: Wed, 25 Nov 1992 12:11:58 GMT
From: Sam Drinkard <sam@wa4phy>
Subject: Nasa Calendar of events
Newsgroups: sci.space,sci.space.shuttle

Some time back, I pulled off a calendar of events that an individual had
posted, and I placed it on the amateur packet bbs network.  Apparently,
it got munged in its trip across the country, and I have been flooded
with requests for a repost.  If anyone has that calendar file, could
you possibly e-mail it to me or re-post it?  Sure do thank you..

sam

email to [e-mail]
--
     Sam Drinkard    |    internet: [e-mail]
     WA4PHY        |    internet: [e-mail]
     Augusta, GA 30907  |

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

Date: Wed, 25 Nov 1992 09:50:45 GMT
From: Hartmut Frommert <[e-mail]>
Subject: Scientific method
Newsgroups: sci.space

[e-mail] (Sam Warden) writes:

>It's been my very strong impression that very little working
>science is done according to this formal theory of hypothesis
>verifying, but rather the opposite: theories are in fact
>constructed to match the known facts.

I think it is not always quite this way, at least in fundamental theories
of gravitaty and particle physics. There new theories seem to be constructed
for more abstract or mathematical reasons, as GR was invented by Einstein to
establish the equivalence of all coordinate frames, and gauge field theories
for symmetry arguments (similar for most really innovative theories). Then,
hence in a second step, the observable output of the theory is considered,
parametrized, and compared with available experimental data, which may
contradict (and then abandone) the theory, or assign values and limits to
the parameters.

I'm aware that there's a second class of theories, for example the PPN
formalism for gravity, which are constructed phenomenologically to match
the observed facts (and give limits to the fundamental theories), as you
stated.
--

 Hartmut Frommert                 <[e-mail]>
 Dept of Physics, Univ of Constance, P.O.Box 55 60, D-W-7750 Konstanz, Germany
                                           -- Eat whale killers, not whales --

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

Date: Tue, 24 Nov 1992 18:56:00
From: Robert Dyess <[e-mail]>
Subject: Shuttle computers
Newsgroups: sci.space

* In a message originally to All, John Roberts said:

JR>Is it at all possible to reprogram the GPCs from the ground,
JR>or does it have to be done from onboard?

It's my guess that they can reprogram from the ground. They send program
revisions to space probes frequently. Why not the shuttle?

Robert

 * Origin: *AmeriComm* in Dallas,TX 214/373-7314 - The info source. (1:124/6507)

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

Date: Wed, 25 Nov 1992 04:05:27 GMT
From: Josh 'K' Hopkins <[e-mail]>
Subject: Shuttle replacement
Newsgroups: sci.space

[e-mail] (Allen W. Sherzer) writes:

>>>In the last ten years or so almost all the boosters have been blown up
>>>by range safety.

>>Small confort to a crewed vehicle. Boom is boom.

>If your in Shuttle, true enough. On the other hand if your in a Delta
>Clipper made of much simpler components (less likely to fail) and with
>abort modes throughout the entire flight envelope it is a great deal
>of comfort.

>A range safety officer can blow up a Shuttle, not so with Delta Clipper.

Why not?  Is there some reason why DC can't end up uncontrolled on a trajectory
that doesn't terminate on the pad?  It may be safer than shutte, but you need
to show this before you tell everyone that there won't be a need for range
safety.

--
Josh Hopkins                                          [e-mail]

    "Why put off 'til tomorrow what you're never going to do anyway?"

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

Date: Wed, 25 Nov 1992 04:24:30 GMT
From: Josh 'K' Hopkins <[e-mail]>
Subject: Shuttle replacement
Newsgroups: sci.space

[e-mail] (Pat) writes:

>I believe henry pointed out awhile ago  that the shuttle has no greater
>flight safety record then any expendable launcher.  actually i think
>he pointed out that the man rated versions of launchers were
>not statiscally significantly improved over the non man rated versions.
>fact is  you could describe the shuttle with the same Boom Boom.

There are ELVs with worse records that shuttle's, but I think there are also
a few with better records.

>Nonsense.  a booster destroyed by the RSO is part of a planned process.
>All previous manned missions had emergency escape provisions for the
>crew during boost.  I cant remember wether apollo used a escape rocket
>or the SM engines,

There was an special escape rocket on top of the stack.  It's easily visible
in most pictures.

>but probably no worse then ejection seats.  certainly any manned vehicle
>would have this capacity.

Actually, I'm not sure the shuttle has abort modes for the very first part of
flight and I know that most people don't consider certain abort modes
survivable.

>Henry,  does the Soyuz have an escape rocket????

It does indeed and I believe it's been used before.  In fact, some of the
pictures I've seen seem to have escape rockets on unmanned payloads.  Am I
mistaken or is there a reason for this?

>L-1011's flown in without elevator controls.  United almost landed
>a DC-10 minus an engine and all controls.  Convertibles have been landed.

Convertibles?  Do you fly them with the top down?

>Besides, a DC flies on LOX/LH.  coming in it should be low fuel and
>LOX/LH does not really explode effficiently.  you get steam and water
>not a big boom.  Several thousand pounds of JP-4 burns much better then
>LOX/LH i would bet.  the LOX should disperse rapidly and the LH burns
>but not as persistently as a petroleum fire.

I read a great anecdote relating to this when I was researching zeppelins.
Apparently the DOE once did a test of the flammability of hydrogen and gasoline.
They filled two eight foot balloons with hydrogen gas and gasoline vapors
resectively and then fired tracers into them.  The gasoline balloon ignited
immediately and exploded in all directions.  It took three tracers to ignite
the hydrogen balloon which then burned upwards for thirty seconds without the
flames ever touching the ground.

--
Josh Hopkins                                          [e-mail]

    "Why put off 'til tomorrow what you're never going to do anyway?"

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

Date: Wed, 25 Nov 1992 14:20:16 GMT
From: Dan Vento <[e-mail]>
Subject: Shuttle replacement
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Allen W. Sherzer)
wrote:
>
> In article <[e-mail]> [e-mail] (Dan Vento) writes:
>
> >> No, Spacelab and Astor are two payloads that we want very much to keep
> >> in orbit so they can be used.
>
> >No, you definitely want to be able to bring these kinds of payloads back on
> >a regular basis at least until we have gained much more experience.
>
> We want to bring back individual experiment racks. We don't want to bring
> back the entire lab.
>
> >if not most of the Spacelab type payloads are very new concepts, flying for
> >the first time, often built by organizations with little space hardware
> >experience. Rethinking and reflight are part of the learning curve.
>
> Exactly. Those users are ill served by a Spacelab which flies one time
> every couple of years. They WOULD be well served by something like
> ISF which is up there all the time and so offers far more flight
> opportunities.
>
> >Remember the Shuttle type small Space Experiments world (except for life
> >sciences) has really only been around since the late 70's
>
> I hope you aren't referring to 'get away specials' since NASA doesn't fly
> them anymore.
>
>     Allen
>

No I'm not referring to Get Away Specials. I mean all of the Middeck,
Hitchiker, MSL, MPESS, SMIDEX, Spacelab Glovebox, etc. experiments, most of
which get very little public attention. They fly as secondary payloads on
*every* flight and come from a wide variety of sources including
government, universities, and private industry. We (the world, not just
NASA) are in the process of inventing the business of space applications.
Much basic engineering needs to be rethought before you try to apply it to
microgravity.

An ISF type facility would be useful for some things, but I am skeptical
that there would be sufficient commercial interest to develope enough
hardware to fill it. The bean counters would not be able to see the return
on investment for an unproven $10 or $12 Million piece of industrial
hardware, where you might not even be able to get it back to make it work.
Most of the hardware that will be filling the experiment racks on SSF will
be checked out and tested on various Spacelab missions long before being
sent to SSF.

Note that NASA does fly "Get Away Specials" all the time, though they are
often called by other names (e.g. Complex Autonomous Payloads, GAS bridges,
etc.). The fact of the matter is that we currently have considerable excess
capacity in the system for smaller experiments. These smaller experiments
are the basic building blocks for the hardware that will fill your ISF or
long duration Orbiter, or SSF, or whatever.


Dan Vento
[e-mail]

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

Date: Wed, 25 Nov 1992 14:33:11 GMT
From: Dan Vento <[e-mail]>
Subject: Shuttle replacement
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Henry
Spencer) wrote:
>
> In article <[e-mail]> [e-mail] (Dan Vento) writes:
> >> No, Spacelab and Astor are two payloads that we want very much to keep
> >> in orbit so they can be used...
> >
> >No, you definitely want to be able to bring these kinds of payloads back on
> >a regular basis at least until we have gained much more experience...
>
> We want to bring back *individual items* from Spacelab, at varying times.
> But returning *small* payloads has never been a problem.  The issue here
> is whether we want to be able to return *big* payloads in one piece.  I
> see no major requirement to return a payload larger than one Spacelab
> experiment rack.  Taking the infrastructure -- pressure hull, services,
> etc. -- up and down all the time is crazy.  As is limiting the mission
> length to a week or two for the sake of hauling it up and down.
> --


I agree. But you will find that if you leave your Spacelab in orbit, you
still will need to haul up quite large resupply payloads containing gasses,
water, propellant, etc. Modifying the Shuttle - the only thing we will have
for some time to come - so it can carry Spacelab for 30 day missions is the
best we are going to be able to do. The Spacelab and the Shuttle were never
intended to be ends in themselves. Until either the government of the
private sector is willing to spend a $Billion or two, we need to live with
what we have.

Dan Vento
[e-mail]

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

Date: 25 Nov 92 15:08:42 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Shuttle replacement
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Josh 'K' Hopkins) writes:

>>A range safety officer can blow up a Shuttle, not so with Delta Clipper.

>Why not?

Same reason we don't have RSOs for airliners.

>Is there some reason why DC can't end up uncontrolled on a trajectory
>that doesn't terminate on the pad?

You mean like that 747 which smashed into the apartment complex? Sure
it could happen.

>It may be safer than shutte, but you need
>to show this before you tell everyone that there won't be a need for range
>safety.

It needs a degree of certification before it flies out of anywhere
(like civil aircraft) but it doesn't need destruct charges.

  Allen
--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------150 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 25 Nov 1992 11:26 CST
From: [e-mail]
Subject: Shuttle replacement
Newsgroups: sci.space

In article <[e-mail]>, [e-mail] (Allen W. Sherzer) writes...
>In article <[e-mail]> [e-mail] (Gary Coffman) writes:
>
>>Spacelab and Astro are two payloads that we want very much to return
>>from orbit on a regular basis.
>
>No, Spacelab and Astor are two payloads that we want very much to keep
>in orbit so they can be used. Building multi-billion $$ payloads and then
>flying them for a few days every two years isn't cost effective.
>

Allan, dost thou have a reference for your "multibillion dollar" statement.
Methinks the cost is far lower unless you count the cost of an entire spacelab
which you would have to do on a Titan flight.


>>Not that they are all that
>>cheap mind you, but the experimental community thinks them worthwhile.
>
>The experimental community doesn't pay for them so this should come
>as no suprise.

The experimental community does pay for the instruments in the spacelab, and
they also put several years of their lives into the effort.


>
>>Deadheading is never cost effective. But that's a management problem,
>>not a Shuttle problem per se. If you have to charge an entire Shuttle
>>mission against a satellite return, then it is expensive,
>
>To date it has never been done. Shuttle flights are so expensive
>that it isn't likely it can ever be done. You would need to return
>at least five or so satellites.
>

I seem to remember several satellites that were returned and later launched
on other vehicles. Also there was LDEF that is contributing greatly to
lowering the cost of all of the other spaceflight missions due to the
information gathered about the effects of materials in a long term LEO. Mind
you this is not figured in Allans accounting but it is in mine where my
reliablity is greater for the information.


>>>A Titan IV launch costs about a third of what a Shuttle flight costs.
>
>>Boom.
>

Last I heard Titan IV flights were $281 million according to Space Week. Your
own figures Allan put the Shuttle cost at $500 million per flight. Take a
look at the fraction, its kinda closer to 1.8 to 1.


>So? When a Titan goes boom the crew has a very good chance of surviving.
>There hasn't been a Titan failure which would have resulted in loss of
>crew for at least 10 and more likely 20 years.
>

Not so the Titan that blew up about 100 ft above the pad a few years ago.
There was zero warning, the SRB's just went poof

boom

>When Shuttle goes boom on the other hand, people die.
>

yep its called the cost of doing business

>>>The new Titan SRMs will close most if not all of that gap.
>
>>Boom, boom.
>
>Does the word 'Chalenger' ring a bell? Remember the old saying about
>people in glass houses?
>

yep sure do

>>That's the excuse used to abandon Saturn, Shuttle was supposed to be
>>far cheaper. Classic mistake to abandon working hardware until flight
>>proven replacements for the capabilities are in place.
>
>Would you consider a pickup truck which only worked one day a week and
>cost $200 per mile to operate 'working hardware'? I wouldn't which is
>why I don't consider Shuttle working hardware.
>

We are not talking about pickup trucks


>>>In the last ten years or so almost all the boosters have been blown up
>>>by range safety.
>
>>Small confort to a crewed vehicle. Boom is boom.
>

Not so the one right off the pad, it went boom with no warning.


>If your in Shuttle, true enough. On the other hand if your in a Delta
>Clipper made of much simpler components (less likely to fail) and with
>abort modes throughout the entire flight envelope it is a great deal
>of comfort.

Uh this is kinda strange when you think of all of the complex piping and
fittings and multiple engines on the bird. Seem to me that there is more
of a chance of a random or otherwise failure. One good aspect of this is that
DC is robust enough to compensate for the failure, unless they miswire the
controllers like they did on the first Saturn V flight.

>
>A range safety officer can blow up a Shuttle, not so with Delta Clipper.
>
>   Allen
>--
Hate to bust your bubble on this one but on ANY launch from ANY facility
operated by the US government, range safety can push the boom button whenever
they see the mission deviating sufficiently from its mission parameters. DC
will not be an exception for this.

Dennis, University of Alabama in Huntsville.

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

Date: Wed, 25 Nov 1992 12:44:14 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Simplicity
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:

-If your in Shuttle, true enough. On the other hand if your in a Delta
-Clipper made of much simpler components (less likely to fail) and with
-abort modes throughout the entire flight envelope it is a great deal
-of comfort.

>I'd say that's a little bit too strong a statement, in the general case.
>Reliability is dependent on many factors, of which simplicity is only
>one. If you took all the redundant components out of the Shuttle, it
>would certainly be simpler, but it would probably be *less* reliable.

Simple designs can have redundancy. DC is a simple design; all it is
is tanks, fuel, avionics, engines, and a payload. Yet it has enough
redundancy to provide for intact abort throughout its envelope.

Shuttle has redundancy but no simplicity. It has more and more complex
interfaces which reduces reliability. Reliable systems tend to be ones
where a single person can pretty much understand the operation of the
entire machine.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------150 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 25 Nov 92 12:35:13 GMT
From: Colin Tinto <[e-mail]>
Subject: Solar sailing
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (John Roberts) writes:

Interesting stuff deleted...

>Bonus question (meaning I don't have any idea how to work out the math):
>  In designing sails for sailboats, it usually works out that the optimum
>  sail is a nonplanar piece of fabric, mounted with some slack so that the
>  wind inflates it to a particular curved shape. Is that also the case
>  for a solar sail, when one wants to maximize tangential thrust per unit of
>  sail area? (If so, the mechanism would be multiple reflections.)
>
>John Roberts
>[e-mail]

I'm no expert on this (Maths, Space, Sails....) but I always thought sailboats
worked partly on differences in air pressure.

The sail having differing pressure on either side - sucking the boat along.

Now unless there is something like light pressure ???

:-)


--
/-----------------------------------------------------------------------------\
!   Colin Tinto            !  Time Travel Parcel Deliveries Inc          !
!   [e-mail]        !  The only courier with previous day service.!
\-----------------------------------------------------------------------------/

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

End of Space Digest Volume 15 : Issue 457
------------------------------