Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V11_1/V11_149.TXT

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Subject: SPACE Digest V11 #149

SPACE Digest                                     Volume 11 : Issue 149

Today's Topics:
           Re: Artificial Gravity rephrased
        Re: Resolving Power of Hubble Space Telescope
             Payload Status for 03/14/90
              RE: SPACE Digest V11 #145
                 Lunar Comm.
             coordinate data for shuttle?
         Re: SR-71 Record Flight Information
           Re: Solar System Questions from a Novice
        Re: Resolving Power of Hubble Space Telescope
----------------------------------------------------------------------

Date: 14 Mar 90 07:23:34 GMT
From: cs.utexas.edu!ut-emx!walt.cc.utexas.edu![e-mail]
Subject: Re: Artificial Gravity rephrased

In article <[e-mail]> [e-mail] (Robert Casey) writes:
)If I was in that spaceship that was in _2001_, in the spinning section, seems
)that I could throw a baseball in such a way as to cancel the spin speed.  Then
)the baseball would seem to take a circular path thru the spinning section at
)the height from the floor where I threw it.  Then I better duck at one
)rotation! :-)  Seen from outside the spinning section of the ship, the
)baseball would be staying put in one spot.  So, the artifical gravity wouldn't
)grab the ball.  Make sense?

    Sure, so long as you enjoy throwing baseballs in a vacuum.
If you put air into your spaceship then viscous drag will accelerate
the ball until it spins along with everything else and artificial gravity
"grabs" it.




^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Radey                                      I am NOT a cretin.  --Epimenides

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

Date: Wed, 14 Mar 90 13:55:27 +0100
From: [e-mail] (Daniel Fischer)
Subject: Re: Resolving Power of Hubble Space Telescope

Don Barry <9 March 90 19:57 GMT> writes:
> As stated correctly by several posters, the HST will have a limiting
> performance of 0.1 arcseconds.
There is a firm consensus in the press and also in Netland that the resolving
power of the HST is 1/10 arc sec - _but_the_literature_says_different_!_
  In the book "The Faint Object Camera for the Space Telescope" (ESA SP-1028,
Oct.1980) on this European focal plane instrument we find on pages 15/16:
]
] 2.2.2 The very high resolution apodizer (f/288 mode)
]
] The theoretical Rayleigh limit (1.22 lambda/D) [that yields radian, to get the
] answer in arc sec, use 251643*wavelength/diameter] for the angular resolution
] of the ST is 0.066 arcsec at 633nm and 0.013 arcsec at 125nm. The optical
] quality of the ST guarantees near diffraction-limited performance at 633nm;the
] FOC imaging at f/96 exploits this resolution capability. There is a reasonable
] probability that near diffraction-limited performance will be reached by the
] ST at shorter wavelenghts but, even at wavelengths where the diffraction limit
] cannot be reached by the overall optical quality, the telescope aberrations
] will produce a stationary speckle pattern. [Got what that means? The UV images
    have 0.013 arcsec resolution but are blurred by the residual deficiencies
    of the mirror (point spread function). This blurring is quite similar to
    the image degradation by atmospheric turbulences (seeing), but those
    'speckle images' change 20 times per second. The HST speckle pattern,
    however, does not move, and that is a big advantage.]
] Deconvolution of this pattern may then be possible, thereby yielding diffrac=
] tion-limited images at the shortest detectable wavelenghts. To exploit this
] exceptional resolution capability, a facility for imaging at f/288 can be in=
] serted into the f/96 optical path, giving a pixel size of 0.007 arcsec (cor=
] responding to the rms guiding error of the ST): this is sufficient to sample
] the speckle pattern even at 125nm... The f/288 facility is a compact Casse=
] grain assembly which produces a magnification of x3... The total f/288 field
] of view will then be 7.5x7.5 arcsec...
]
Though this funny machine (remember: you insert another telescope into the HST
to see its faults perfectly...) couldn't be tested with actual stars, I've seen
very convincing computer simulations. First, you have a nice galaxy, then you
fold it with the point spread function of the HST optics, and the image is
blurred beyond recognition. But then you run a so-called 'roll deconvolution'
of two images with different HST orientations (somehow like in X-ray tomography)
- and out pops the galaxy with the original 0.01 arcsec resolution! Whether that
works in reality will be tested in the HST commissioning phase, so we might know
already this summer.
  This method is *much* easier than the ground-based speckle techniques Barry
mentions, because here the speckle pattern changes so quickly. What the Center
for High Angular Resolution Astronomy is doing, according to my knowledge, is
not imaging but just measuring star diameters by speckle *interferometry*. The
real challenge lies in speckle *imaging*, where you have the same data but
extract 2D images with sub-arcsec resolution. Less than five groups in the
world have succeeded in doing so (Knox-Thompson method, Speckle Masking) - it
takes months to process one image, but real-time reconstruction remains the
ultimate goal.
  Dan Briggs <10 March 90 21:56 GMT> writes in his reply:
> ... aren't speckle images often subject to fairly severe image defects?
Early results tended to contain complex artefacts, but speckle masking works
very reliably now (though still very slowly): the main advantage over other
methods is that you do not only remove the atmospheric blurring but also defects
in the telescope - it's the famous phase closure you also have at the V.L.A.
> ... some speckle images of the pluto-charon system ... were questioned ...
Again, these were very early results: now we have high-resolution autocorrela=
tions where you can actually follow Charon orbiting Pluto. Real images are in
the making. However, don't expect to see much detail on Pluto: it *is* small!
> All of the speckle images I have seen have been very simple objects.
You haven't seen the exciting stuff yet that hangs on the office walls in our
institute (not everything has been published widely, I confess)! E.g., there's
a detailed image of the asteroid Vesta with a crater(?) and a mare(??), a movie
showing Ceres rotate is in the making, and there are hi-res views of the core
of the Seyfert galaxy NGC 1068 (to appear in the ESO Messenger shortly).
  Don Barry also mentioned:
> The "CHARA Array", a network of 7 1-meter telescopes distributed over a 400-
> meter circle, is currently under consideration for funding... The Array will
> have a limiting resolution of 0.2 milliarcseconds..., and the Array will have
> limiting magnitude of 11 initially...
Don't forget the Very Large Telescope the European Southern Observatory *has*
already funded: somewhere in Chile 4 telescopes, each with 8-meter mirrors, will
be able to work interferometrically with a 100-meter baseline around the year
2000. This interferometer will have a limiting magnitude of approx.15 (some be=
lieve: 18) - image reconstruction, again, already 'works' in striking computer
simulations. And each of the 8-meter telescopes will also support a speckle
camera that might give 0.01 arc sec images down to 20th magnitude. So there you
have it, the *big* step forward the Edwin P.Hubble Space Telescope actually
represents: it gives you 1/100 arcsec resolution, 28th or fainter limiting
magnitude and UV light *at*the*same*time*. Both high resolution and faint stars
you can get from the ground by now (ESO's New Technology Telescope gets to 27 in
just one hour - and it has just a good 3.6-meter mirror), but not simultaneous=
ly: that's why a 'son of HST' with at least 10-meters diameter is already under
consideration, be it in geostationary orbit or on the moon.

+- [e-mail] --- Daniel Fischer --- [e-mail] -+
| Max-Planck-Institut f. Radioastronomie, Auf dem Huegel 69, D-5300 Bonn 1,FRG |
+----- Enjoy the Universe - it's the only one you're likely to experience -----+

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

Date: 15 Mar 90 04:37:59 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Payload Status for 03/14/90


    Daily Status/KSC Payload Management and Operations 03-14-90


    -STS-31R HST (at VPF) -

    HST flight battery charging, at the VAB, was worked
    yesterday.  Also, the transcan was moved to the VPF air lock
    yesterday.  HST final closeouts ops are continuing and PDT
    testing is in work along with west cell VPHD alignment.  The
    sim run countdown (OMI S0044) is active today.


    -STS-32R SYNCOM/LDEF (at SAEF-2) -

    LDEF deintegration continues.


    -STS-35 ASTRO-1/BBXRT (at O&C) -

    The final MLI installation was worked yesterday and
    continues today.


    -STS-40 SLS-1 (at O&C) -

    The systems test and module ECS systems test were active
    yesterday and will continue today.  Experiment functional
    checks will also continue today.


    -STS-42 IML (at O&C) -

    Racks 3, 5, 7, 8, 9 and 11 had staging operations worked
    yesterday and will continue today.


    -STS-45 Atlas-1 (at O&C) -

    Pallet to pallet joint installation on frame 4 was worked
    yesterday and will continue today.

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

Date: Wed, 14 Mar 90 09:10 CST
From: [e-mail]
Subject: RE: SPACE Digest V11 #145


Help! Help!..How can I get NASA headlines, or it's public broadcasts over
the TV or radio..without calling their (202) number..or BITNET!!!!
ARAS TAHA
T.C.U.
Ft.Worth, Tx.

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

Date: Wed, 14 Mar 90 10:56 CST
From: [e-mail]
Subject: Lunar Comm.

Several weeks ago there was a question posted regarding communications
on the moon between two bases 1000km apart.  Several ideas were proposed
including fiber optic cable, plain old ordinary cable, relaying everything
via the Earth, using relay satellites in a variety of lunar orbits and
microwave and laser links on towers.  I vote for lasers on towers.
The formula used to calculate the surface distance from an observer to the
horizon is:

X = R * ATAN [SQRT {h/R*((h/r)+2)}]     where R is the objects radius
                                              h is the observers height
                                              X is the surface distance
(note: this equation was donated by [e-mail])

According to the CRC 65th edition the radius of the moon is 1738.3 km plus
or minus 1.1 km.  For the purposes of the following calculations I chose
R to be 1738.5km.

 h (in meters)   X (in km)     Number of towers needed to cover 1000km
 -------------   ---------     --------------------------------------
   100             18.6                 54
   200             26.4                 38
   400             37.3                 27
   500             41.7                 24
  1000             60.0                 17
  2000             83.4                 12

A note on tower height:  I stopped at 2000m tall towers because that's where
it started to look like the payback in increased range gets eaten by the extra
tower height.  Tower 2km tall in 1/6 gee with no wind loads (i.e. built on
the moon) would be easy to build.

I assume that the primary purpose of this link is to talk between the two
bases.  Some other communication needs are 1. To teleoperate  things  2. To
communicate with vehicals and crew out wandering around the surface
3. Navagation beacons.
The need for 1, 2 and 3 will probably be concentrated around the two bases.

I propose a total of 23 towers: Two 1000m tall ones, one at each
base, and twenty one 500m tall relays between the two bases.
The 1000m towers will serve as the platforms for the interbase comm. link,
for teleoperation and for "local" communications i.e. to crew and vehicals.
The 500m towers will act as relays between the bases.
The comm. link itself will be based on lasers both for the higher bandwidth
than radio and to avoid mucking up the radio astronomers. (After all, radio
astronomers are people too :)  Power will be provided by the
appropriate radioisotope generator.  Although the electronics will need
hardening, it should be a simpler task than shielding kilometers of fiber
optic cable.  When the growth of the bases requires more bandwidth either
a parallel set of towers could be installed or more/upgraded hardware could
be stuck on each tower.  As other bases are built they can be added to the
system.  It should be possible to build the towers out of available materials,
the lasers and detectors may need to be imported from earth.
Practice building towers out of lunar materials will be useful when we start
building power satellites, radio astronomy antenna farms, geosynch. orbit
communications platforms etc.

Towers are simple. (as compared to anything in any orbit)
Towers are resistant to radiation. (as compared to fiber optics)
Towers are expandable.  (use all the bandwidth you want. we'll add more)
Towers will lead to a 3.3ms lightspeed delay. (rather than the seconds for
                                               moon-earth-moon relays)
Towers can be built with local materials. (this means cheap)

I apologize for the length, I wanted to make sure I covered all of my reasoning
... well, most of it anyway.

George K. Ott  University of WI - Madison High Energy Physics Department
[e-mail]

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

Date: 14 Mar 90 21:43:05 GMT
From: wuarchive!mailrus!uflorida!ziggy![e-mail]  (Ken Hughes)
Subject: coordinate data for shuttle?

A professor on our campus is looking for coordinate data for the
space shuttle to use in a raster graphics course.  Preferably he
would like it described as bicubics or polygonal patches but anything
would be OK.  If anyone has such data or knows of a internet site
which does, please contact him or myself via e-mail at [e-mail]
or [e-mail].  Thanks.

Ken Hughes
sysadm
Dept of Comp Sci and Eng
University of South Florida
(watch our basketball team get beat by Arizona this coming Friday)

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

Date: 13 Mar 90 19:32:04 GMT
From: [e-mail]
Subject: Re: SR-71 Record Flight Information

-Message-Text-Follows-
In article <[e-mail]>, [e-mail] (John F Nixon) writes...
>[e-mail] (Bruce Lowerre) writes:
>>The SR-71 was
>>developed to replace the U-2.  The U-2 became obsolete when the Russians
>>developed a cannon ball that could be blasted high enough to shoot it down.
>>The SR-71 became obsolete when satellites were developed with telescopic
>>cameras good enough to photograph the license plate of a car.
>
>But satellites cannot provide the "unexpected" coverage of the SR-71!  You
>Know where a satellite is, and where it will be, all the time.  There aren't
>that many in orbit (on the US side, anyway :-).  One never knows when a
>quick look could be vitally important.
>
>This issue has been argued before.  I can't believe that *some
>aircraft* didn't replace the 71.  Maybe something unmanned, smaller,
>with similar performance, but surely something...
>
>----
  I also wonder if new fueling systems for the satellites aren't being
used. 1-2 shuttle flights a year dedicated primarily to fuel would make
for a pretty maneuvorable sattelite. Of course a titan load of fuel would
be just about as useful.

  A cruise missle beaming its images up to a sattelite and then self-
destructing is another reasonable possibility.

                Chuck

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

Date: 13 Mar 90 17:16:35 GMT
From: hub!castor![e-mail]  (David Stoms)
Subject: Re: Solar System Questions from a Novice

In article <[e-mail]> [e-mail] (John F Nixon) writes:
>[e-mail] (Christopher Neufeld) writes:
>>3) A given planet revolves around one star then the other in a figure eight
>>pattern, while the suns revolve around each other. I believe this situation
>>is unstable.
>No, there are stable orbits around binary stars!  I wish I could remember the

In fact, on my Mac I have software called Orbital Mech which lets you
play with a ship that orbits around one or two suns. By accident I
actually setup a stable orbit around binary stars. It still amazes me
every time I look at it.

Josh.

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

Date: 15 Mar 90 03:39:58 GMT
From: unmvax!nmtsun![e-mail]  (Daniel Briggs)
Subject: Re: Resolving Power of Hubble Space Telescope

In article <[e-mail]> [e-mail] (Tom Neff) writes:
>One quick question, if speckle interferometry is 'solid' now: was
>that early Betelguese disk image bogus or not?  Are stellar disks
>being resolved now?

The Mar. '90 issue of GEMINI (Newsleter of the Royal Greenwich Observatory) has
two images of the surface of Betelgeuse on the front cover, (7100 and
6330 angstrom).  The image is about 80 milliarcsec in diameter.  The quoted
resolution in the article is 38-54 mas.  There is a clearly  resolved feature
on the 7100 angstrom image.  They suggest that this is a hotspot caused by
large scale convection in the stellar atmosphere.  (BTW, The pressure
scale height of the amosphere is of the same order as the stellar radius.  If
you were to look at Betelgeuse close up, it would look "fuzzy".)  The data was
taken with a non-redundant mask on the William Herschel telescope.  ('Fraid
that I don't happen to know how large that is.)  I don't really know what the
*precise* definition of speckle-interferometery is.  This certainly isn't the
classical sorts of techniques, but it's derived from the same genealogy.

-----
This is a shared guest account, please send replies to
[e-mail] (Internet)
Dan Briggs / NRAO / P.O. Box O / Socorro, NM / 87801  (U.S. Snail)

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

End of SPACE Digest V11 #149
*******************