Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_1/V11_174.TXT

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Subject: SPACE Digest V11 #174

SPACE Digest                                     Volume 11 : Issue 174

Today's Topics:
              Re: Sandia Railgun
     Re: Coilgun on a 747 - supplies to orbit at $20/lb?
               Getting Drafted
                  Space List
             Re: SR-71 and dates
            Re: More space station news...
         Austrailian Reduced Wobble telescope
            Re: SR-71 ( as a collectable )
              Re: Strange flash of light
     Re: Coilgun on a 747 - supplies to orbit at $20/lb?
----------------------------------------------------------------------

Date: 17 Mar 90 23:34:25 GMT
From: haven!uflorida!uakari.primate.wisc.edu!samsung!cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Sandia Railgun

In article <[e-mail]> [e-mail] writes:
>2) The article quotes 10,000G's of acceleration; mil-spec electronics
>can withstand 10G's at most.  (Allows bulk material only.)

Not so.  The military fires electronics from guns every day (e.g. the
Copperhead laser-homing antitank shell) and has been doing so since World
War II (proximity fuzes).  The design has to pay attention to the problem,
but drastic measures are not needed.  The Copperhead electronics simply use
fairly small boards that are very well built and well supported.  Proximity-
fuzed antiaircraft shells contained *vacuum tubes* until the late 50s.

Admittedly, there is the question of whether you want to build all your
space hardware to withstand gun launches.  Probably you don't.  But it can
be done for most things.  If gun launch is sufficiently cheaper than using
rockets, it may be worthwhile.
--
MSDOS, abbrev:  Maybe SomeDay |     Henry Spencer at U of Toronto Zoology
an Operating System.          | uunet!attcan!utzoo!henry [e-mail]

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

Date: 18 Mar 90 04:49:22 GMT
From: sam.cs.cmu.edu![e-mail]  (Vincent Cate)
Subject: Re: Coilgun on a 747 - supplies to orbit at $20/lb?



Kevin Strietzel:
>At 100% efficiency, 20,000 kw is about 27,000 horsepower.  The biggest diesel
>engines I know of only do 4200hp (about 3,100 kw).  How about a gas turbine?
>Maybe then it could burn jet fuel instead of having lots of extra tankage for
>diesel oil; 747-100B could do something like 9 hours in the air with reserves.

A gas turbine (or two) probably is the way to go.  I recall these being one of
the types of engines that are around 1 hp/lb.

Running off the tanks in the wings would be great!  Some of these big planes
can carry a lot of fuel.  I know they started flying some large plane from
San Fransisco California to Sidney Australia this summer - 16 hours non-stop.
A quick estimate puts the fuel consumption of a 20,000 kw generator at a little
under that of the engines on a 747. Thus using the same tanks would about
cut flying time in half.  I like it!!!!

>        payload(kg/lb)    comments
>        --------------    --------
>747-200F    113400/250000    cargo

Looks like we might be able to use 200,000 lbs just for the electromagnetic gun.
If we have not already made a gun this light that shoots 25 kg projectiles at
orbital velocity, I'll bet we could.  Actually, we can probably do 50 kg
projectiles with such a heavy gun.

This looks more and more like a good way to get supplies into space!!!!!

Thanks for the info,

   -- Vince


PS   What is the hard part for this type of approach?
     Getting a gun that weighs less than 200,000 lbs?

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

Date: 21 Mar 90 17:06:40 GMT
From: mcsun!ukc!edcastle![e-mail]  (A J Cunningham)
Subject: Getting Drafted


In-Reply-To: Mary Shafer (OFV's message of 20 Mar 90 18:45:30 GMT


> The Air Force, Navy, and Marines did NOT draft people.  Army troops
> (who may have been drafted) rode in helicopters flown by pilots who
> had volunteered.  (Yes, this latter is hair-splitting.)  Even in World
> War II, all air crew were volunteers.
>
> The same is true, I understand, of the Royal Air Force, the Royal
> Navy, and the Royal Marines--National Service was in the British Army.

    Well plenty of Army personnel were herded into gliders for
Airborne assaults (e.g. Operation Overlord, Operation Market Garden). I
doubt if that meny of them were volunteers. I accept your point that
American Air crew in WWII were all volunteers although I don't know if
the same was true for British pilots and air-crew and it probably wasn't
the case for Russians. (You did say no-one in your original article)
        Tony

--
Tony Cunningham, Edinburgh University Computing Service. [e-mail]

    Yuppies think I'm a wino 'cos I seem to have no class,
    Girls think I'm perverted 'cos I watch them as they pass.

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

Date: Wed, 21 Mar 90 14:35:33 PST
From: [e-mail]
X-Vmsmail-To: UTADNX::UTSPAN::AMES::"[e-mail]"
Subject: Space List


    Much time, mental energy and net bandwidth is wasted because many
of the people on this net don't have the knowledge or expertise to to make
a simple reality check on some of the ideas presented here, or on ideas
that they may come up with independently.  There isn't really that much you
need to know to be able to do this sort of check, and it seems to me that
many of the creative minds out there could be much more fruitful if such
knowledge were easily available.
    So I propose the compilation of a list, something like that of E.
D. Hirsch's in his book _Cultural Literacy_, but much shorter and having
numbers and equations relevant to space science and exploration.  Once
having been compiled, this list could be posted occasionally like the
_Frequently Asked Questions_ list.
    I haven't the time to compile this list by myself, but if people
will email their suggestions to me, or if they can't reach me, to the
Space_Digest, I'll put them together and post the result.
    Here's a meager start.  Numbers in parentheses are approximations
that will serve for most blue-skying purposes.

Numbers
  7726 m/s        (8000)  -- Earth orbital velocity at 300 km altitude
  3075 m/s        (3000)  -- Earth orbital velocity at 35786 km (geosync)
  6378 km        (6400)  -- Mean radius of Earth
  1738 km        (1700)  -- Mean radius of Moon
  5.974e24 kg        (6e24)  -- Mass of Earth
  7.348e22 kg        (7e22)  -- Mass of Moon
  1.989e30 kg        (2e30)  -- Mass of Sun
  3.986e14 m^3/s^2  (4e14)  -- Gravitational constant times mass of Earth
  4.903e12 m^3/s^2  (5e12)  -- Gravitational constant times mass of Moon
  1.327e20 m^3/s^2  (13e19) -- Gravitational constant times mass of Sun
  384401 km        ( 4e5)  -- Mean Earth-Moon distance
  1.496e11 m        (15e10) -- Mean Earth-Sun distance (Astronomical Unit)

Equations
  Where d is distance, v is velocity, a is acceleration, t is time.

  For constant acceleration
        d = d0 + vt + .5at^2
        v = v0 + at
    v^2 = 2ad

  For circular Keplerian orbits, where u is gravitational constant, a is
    semimajor axis of orbit, P is period.
    v^2 = u/a
    P = 2pi/(Sqrt(u/a^3))

  Miscellaneous
    f=ma    -- Force is mass times acceleration
    w=fd    -- Work (energy) is force times distance

  Atmospheric density varies as exp(-mgz/kT) where z is altitude, m is
  molecular weight in kg of air, g is acceleration of gravity, T is
  temperature, k is Bolztmann's constant.  Up to 100 km,
    d = d0*exp(-z*1.42e-4)
  where d is density, d0 is density at 0km, is approximately true, so
    d@12km (40000 ft) = d0*.18
    d@9 km (30000 ft) = d0*.27
    d@6 km (20000 ft) = d0*.43
    d@3 km (10000 ft) = d0*.65


Ok, so it's a short list, but I have to get back to work.  What I'd like to
see is stuff like basic rocketry numbers and equations, maybe some
aerodynamical stuff, and just whatever you think might be helpful in making
rudimentary space related engineering calculations, or stuff you think is
essential for a rudimentary understanding of space exploration problems. It
would also be nice to have some comparative items like how much energy it
takes to get the shuttle into orbit, how much it would take to get
something small like the shuttle up to X% of the speed of light, how much
energy a typical American city with a million people uses, etc.

-------------
Dale M. Greer, whose opinions are not to be confused with those of the
Center for Space Sciences, U.T. at Dallas, UTSPAN::UTADNX::UTDSSA::GREER
      While the Bill of Rights burns, Congress fiddles. -- anonymous

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

Date: 9 Mar 90 16:21:59 GMT
From: m2c!wpi![e-mail]  (Tom [Chris] Murphy)
Subject: Re: SR-71 and dates

In article <[e-mail]> [e-mail] (Commander Krugannal) writes:
>
>
>      Someone mentioned attaching the Pegasus vehicle to the SR-71.
>   Someone (from Orbital Service I believe) replied that there
>   was no place to do it. Actually that is wrong. Soon after the
>   SR-71 was built, a drone was built based on the J-58. This was
>   called the D-21. It used the same engine (the J-58) and same

I believe this project was halted for safty reasons after
an accident that killed the rear-seat officer in an SR-71.  So it
might not be a great idea.

Thomas C. Murphy                        |  Internet:   [e-mail]
Worcester Polytechnic Institute CAD Lab |              [e-mail]
100 Institute Road                      |  BITNET:     [e-mail]
Worcester, MA  01609                    |  CompuServe: 73766,130
Phone [phone]                    |
Fax   [phone]                    |

If the Universe is constantly expanding, why can't I ever find a parking space?

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

Date: 21 Mar 90 15:49:18 GMT
From: news-server.csri.toronto.edu!utgpu!watserv1!watcgl!watnow![e-mail]  (Mark Earnshaw)
Subject: Re: More space station news...

In article <[e-mail]> [e-mail] writes:
>Thought my fellow netters would be interested in this report on the
>Incredible Shrinking Violet Space Station, ExpensiveDom... These
>stories came off the AP wire today (3/19/90):
>
>Report: NASA Investigators Conclude Space Station Plans Flawed

[Description of how Freedom will "fall apart" before it is finished]

I give up.  Why don't we contract Freedom out to the Soviets?  At least we
know their design works.

:-(

--------------------------------------------------------------------------------
Mark Earnshaw, Systems Design Engineering       {uunet,utai}!watmath!watnow!mark
University of Waterloo, Ontario, Canada         [e-mail].{edu,cdn}

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

Date:     Wed, 21 Mar 90 13:25 EST
From: <[e-mail]>
Subject:  Austrailian Reduced Wobble telescope


        Awhile back on the Discovery Channel, I saw a piece on these guys
down under at one of the universities that had crafted an optical telescope
that had the capability to adjust for the wobble of stars due to the air.
It essentially consisted of two small telescopes a few meters apart that had
their mirrors hooked up to some sort of computer controled, peizoelectric
driven movement devices.  Supposedly, the computer tracked the star's image
and minutely adjusted the postion of the mirrors to keep up with it with a
minimal delay time.  They claimed that a future version to be built would
have better resolving power than Palomar.  Any Aussies on the net care to
comment/correct on this?  It sounds interesting to me.

                                Korac MacArthur

"Death before disclaimer!"

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

Date: 21 Mar 90 20:28:44 GMT
From: zaphod.mps.ohio-state.edu!brutus.cs.uiuc.edu!ux1.cso.uiuc.edu!deimos.cis.ksu.edu!iowasp![e-mail]
Subject: Re: SR-71 ( as a collectable )


>Now that the SR-71 is being decommissioned I'd like to know: are the
>junked planes going to be for sale? Hell of an acquisition for a
>vintage plane collector.

    I would say no mainly becuase the SR-71 is made mostly of titanium
alloys and would be recycled before they were sold.

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

Date: 21 Mar 90 16:46:55 GMT
From: cs.utexas.edu!news-server.csri.toronto.edu!utgpu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Strange flash of light

In article <[e-mail]> [e-mail] (Joseph T. Klein) writes:
>This is an odd event. Why do the space/astro people shy away from talking
>about these events? ...

Probably because the space/astro people are waiting for detailed technical
reports so they can argue from known facts, a constraint that has never
bothered the UFO people...
--
Never recompute what you      |     Henry Spencer at U of Toronto Zoology
can precompute.               | uunet!attcan!utzoo!henry [e-mail]

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

Date: 21 Mar 90 16:55:59 GMT
From: cs.utexas.edu!samsung!uakari.primate.wisc.edu!nic.MR.NET!timbuk![e-mail]  (Lou Adornato)
Subject: Re: Coilgun on a 747 - supplies to orbit at $20/lb?

Caveat: I don't think anyone has answered the question of whether a
coil gun can be fit into the ~70m body of a 747, leaving enough room for a
power supply ,recoil travel, shock absorbers, and a useful fuel load.  The
following assumes that the answer is at least "maybe".

Instead of firing the projectile forward, why not fire it out the tail
(aside from the scatalogical inferences that critics will undoubtedly use)?

The stall speed of the 747 is such a small fraction of orbital velocity that
it shouldn't make a difference, either way.  You're still high enough to
expend less of your muzzle velocity shouldering aside air molecules, you
still get the improved launch angle, and now that the recoil is taken by the
747 in the direction direction of thrust, you don't need as much CG travel
(since you can stop the gun faster). Other benefits: there won't be a 400kt
wind blowing into the muzzle, and the 747 won't have to fly through a
hypersonic shock wave.

BTW, I think that the CG problem might have been overstated.  As I
understand it (from seemingly endless ground school lectures), the reason
that eceeding the CG envelope is a Bad Thing is that it can cause the craft
to become stable in a stall (or spin?).  However, nothing says that the gun
can't be moved after it recoils.  If we're starting at 40,0000+ ft, even if
we immediately start to fall like a rock, in the 30 seconds that it takes to
winch the gun back into position, we've fallen less than 15,000 ft.  Once the
CG is returned to its envelope the stall condition is unstable, the plane
falls back into controlled flight, the pilot wrests his/her fate from the
jaws of death, and everyone gets to go home.

Lou Adornato    |  Statements herein do not represent the opinions or
Cray Research   |  attitudes of Cray Research, Inc. or its subsidiaries.
[e-mail]    |       (...yet)

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

End of SPACE Digest V11 #174
*******************