Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V12_6/V12_672.TXT

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Subject: SPACE Digest V12 #672

SPACE Digest                                     Volume 12 : Issue 672

Today's Topics:
         Re: Shuttle Status for 12/06/90 (Forwarded)
Re: Who killed Nuclear Rockets? (was Re: The Next Ten Years In Space)
           Re: space news from Oct 6 AW&ST
      Astro-1 Status for 12/08/90 [2030 CST] (Forwarded)
               Re: Black Holes
      Astro-1 Status for 12/10/90 [0300 CST] (Forwarded)
               Re: Black Holes
               Re: Black Holes

Administrivia:

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

Date: 11 Dec 90 17:36:06 GMT
From: uvaarpa!murdoch!astsun.astro.Virginia.EDU![e-mail]  (Greg Hennessy)
Subject: Re: Shuttle Status for 12/06/90 (Forwarded)

In article <[e-mail]> [e-mail] (Alan Ruffer) writes:
#Lets hope that a little bacwards engineering occurs to determine what exactly
#the problem IS with the IPS and star trackers and what can be done to
#prevent this sort of thing from happening in the future.

Actually, on shift 17 the IPS started working, after another software
patch to correct the fact that the three star trackers were not
coplanar. They were built coplanar, and very painstakingly aligned,
but the launch knocked them out of alignment.

The bad news was that we stopped observing after shift 17. :^(

#Also there needs to be some detailed study of the DDUs that failed and some
#re-engineering there to prevent any future occurance of this problem.

Agreed. This will be done.

--
-Greg Hennessy, University of Virginia
 USPS Mail:     Astronomy Department, Charlottesville, VA 22903-2475 USA
 Internet:      [e-mail]
 UUCP:        ...!uunet!virginia!gsh7w

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

Date: 12 Dec 90 00:14:59 GMT
From: [e-mail]  (Kevin William Ryan)
Subject: Re: Who killed Nuclear Rockets? (was Re: The Next Ten Years In Space)

[e-mail] (Brian or James)
>    I dimly recall a Donald Kingsbury article on a high thrust
>nuclear rocket called (I think) 'Jumbo' or 'Dumbo'. Mid 70s, but it
>was in Analog Magazine, whose articles on high tech occasionally
>sacrifice accuracy and careful evaluation in favour of enthusiasm.
>The Analog is in my magazine collection, which means I can specify its
>location only to within a few feet :( and I don't feel like sorting through
>a dozen boxes. Anyone have anything concrete on this?

    Last year I had the opportunity to speak to someone who worked on
the NERVA engines, as well as evaluating other techniques for nuclear
propulsion. The Dumbo concept was a nuclear engine designed for
extremely high thrust and Earth liftoff. (NERVA as originally designed
was a low-thrust high-efficiency interorbit drive.)

    He told me that the design parameters required for the Dumbo,
specifically the small tolerances in the nuclear heat exchanger (mostly
machined fuel elements) were not considered workable. A heat exchanger
requires high surface area per fuel volume in order to transfer heat
rapidly - this translates to many small passages for fuel to flow
through the reactor, which by the nature of nuclear reactions must be
compact to sustain fission. These small passages would be difficult to
keep open under high temperatures, and you really don't want your
reactor melting itself down and using fuel elements as reaction mass. It
would do so if a thin passage thinned, reducing cooling flow, heating
the passage more...

    Despite his doubts, it might have been doable, but remember that
fuel elements made of materials chosen for fissionability, not low
thermal expansion coefficents. It seems to be difficult to do both.

                                                    kwr

Internet: [e-mail]

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

Date: 10 Dec 90 03:50:08 GMT
From: zephyr.ens.tek.com!tektronix!sequent!crg5![e-mail]  (Nick Szabo)
Subject: Re: space news from Oct 6 AW&ST

In article <[e-mail]> [e-mail] (Brian Yamauchi) writes:
>In article <[e-mail]> [e-mail] (Nick Szabo) writes:
>
>   the blossoming of space industry.  I eagerly await the death of Fred,
>   Colombus, Hermes, and the other punch-card era throwbacks so that we can
>   move forward more quickly into this new age of knowledge and commerce.
>
>But, if Fred dies, is there any guarantee that unmanned exploration
>will get the funds?

Nothing is guaranteed in this life.  :-)  Exploration is more likely
to be funded because the cancellation of these projects will show just
how good solar system discovery is in comparison.  Even if only 1/4 of
the funds that would have been wasted on Fred get put into exploration, that
will still fund dozens of probes that can return more and more varied data
than all missions ever launched so far.  Also, it puts one more notch into
the deficit fight, so we can get the prime rate down to enable more
private space industry financing.



--
Nick Szabo            [e-mail]
"We live and we learn, or we don't live long" -- Robert A. Heinlein
The above opinions are my own and not related to those of any
organization I may be affiliated with.

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

Date: 9 Dec 90 19:33:21 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Astro-1 Status for 12/08/90 [2030 CST] (Forwarded)


      Astro-1 Shift Summary Report #21
      8:30 p.m. CST, Dec. 8, 1990
      6/19:40 MET
      Spacelab Mission Operations Control
      Marshall Space Flight Center,
      Huntsville, AL

      Observation followed observation in a methodical pattern throughout
      the afternoon and evening hours of Saturday, as the Astro-1 mission
      of Space Shuttle Columbia continued to demonstrate some of the
      highest efficiency to date in its science operations.

      Crew members aboard Columbia and members of the ground support team
      by now have established a smooth pattern of working together.  With
      a combination of real-time communication over air-to-ground channels
      and coordinated use of the command-and-control functions, they used
      this consistency of operations to obtain near-maximum observation
      time from the opportunities in the mission timeline.

      At one point during this period (12 noon to 8 p.m. CST), Ken
      Nordsieck in the Huntsville payload control room was giving
      typically terse bits of feedback to Sam Durrance aboard Columbia:
      "Sam, you're within an arc-minute.  ...  OK, give me a mark when
      you're happy.  ...  The data's looking real good, Sam, we're seeing
      lots of photons down here."

      These were characteristic remarks typifying the mode of operations
      used during the past two days of the mission.  Alternate Payload
      Specialist Nordsieck and Payload Specialist Durrance, working
      together on the ground and aboard Columbia, respectively, have
      established a communications approach which allows them easily
      control the three Astro-1 ultraviolet telescopes despite the failure
      of both Spacelab data display terminals aboard Columbia.

      The Broad-Band X-ray Telescope, which requires no crew involvement
      in its observations, also continued to perform consistently
      throughout the afternoon and evening today.  The BBXRT made
      simultaneous stellar observations with the ultraviolet instruments
      as they pointed at nearby objects of special interest in the X-ray
      region of the spectrum.

      Observations by the telescopes during this period included the
      elliptical galaxy M49 in the Virgo cluster; the high-luminosity
      globular cluster NGC 1851, with its nearby X-ray burster source; the
      binary system UX Ursae Majoris located in the Big Dipper; and the
      prototypical Seyfert II galaxy NGC 1068.  The latter is a subject of
      interest to all of the Astro-1 science teams, among other things,
      because of the turbulent motion and intense emissions detected from
      the galaxy's center.

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

Date: 9 Dec 90 08:13:12 GMT
From: swrinde!cs.utexas.edu!news-server.csri.toronto.edu!utzoo![e-mail]  (Henry Spencer)
Subject: Re: Black Holes

In article <[e-mail]> [e-mail] (Norman Yarvin) writes:
>... Granted that if
>the star's escape velocity exceeds the speed of light, then a photon
>starting from the star's surface can't make it out.  But it seems to me that
>if one can propel some piece of matter any distance away from the black
>hole, then one can lift fuel up to that distance; using this fuel one can
>lift the next piece of matter even farther away from the center; and thus by
>degrees something could escape entirely from the black hole.

Not if we're talking about rockets.  That then is precisely equivalent to
saying that by expending enough fuel, you can exceed the speed of light.
Sure you can lift ever farther... but your increments get smaller and smaller,
so you approach but never reach escape velocity.

If we're talking about towers, similar problems appear -- the height has
to be infinite -- but there is no classical, intuitive explanation of why.
Intuition simply breaks down, as it does elsewhere in relativity and quantum
mechanics.

>Now, the other half of what I have heard about black holes refers to them
>having an 'event horizon', where 'the space-time structure curls back upon
>itself' or something similar...

The event horizon is, roughly speaking, the place where the escape velocity
hits the speed of light, so no event inside is observable from the outside.
There are a variety of other odd phenomena in its vicinity.
--
"The average pointer, statistically,    |Henry Spencer at U of Toronto Zoology
points somewhere in X." -Hugh Redelmeier| [e-mail]   utzoo!henry

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

Date: 10 Dec 90 20:06:53 GMT
From: trident.arc.nasa.gov![e-mail]  (Peter E. Yee)
Subject: Astro-1 Status for 12/10/90 [0300 CST] (Forwarded)


      Astro 1 Mission Report #43
      03:00 a.m. CST, December 10, 1990
      8/02:10 MET
      Spacelab Mission Operations Control
      Marshall Space Flight Center


      Today, the HUT team observed the brightest cataclysmic variable star
      known -- C48D 1557.  "We got a great spectrum with about 500 seconds
      of data on this high-mass-transfer object," said HUT Team Replanner
      Bill Blair.

      And tonight at approximately 11:30 p.m. CST, the Hopkins Ultraviolet
      Telescope collected data on U GEM.  "This is a very different
      spectrum situation from the other two (observations made within the
      last 24 hours)," said Blair.  The processes that are going on could
      be very different.  And that is why we want to get data on another
      binary, such as this, for comparison."

      Because extremely close binary systems consisting of a white dwarf
      star and a more "normal" star, like our Sun, interact violently,
      they are called cataclysmic binaries.

      Blair explained the powerful forces behind this system:  "Think of
      the Earth.  It takes Earth a year to go around the Sun, right?  Here
      are two stars that are going around each other in three to seven
      hours.  This is a very close orbit.

      "The gravitational attraction is so strong that the primary star
      starts to dump matter onto the white dwarf.  It doesn't just fall
      right onto that star, because of the angular momentum of the
      system.  As that material spirals in, it heats up and dissipates
      energy in the form of lots of ultraviolet and X-ray emission,"
      creating a ring called an accretion disc.

      "In very high-mass transfer objects, like this," said Blair, "the
      flow can be very unstable sometimes.  And there are these outbursts
      of intense light that we see in them."  To understand the physics of
      this process called accretion, the Johns Hopkins University team
      will study the ultraviolet emissions to pinpoint exactly where in
      the system these outbursts of light are coming from.

      Since the HUT team already knows the geometry of the cataclysmic
      variable star system, after studying the data collected during the
      Astro mission they will be able to answer questions on the sources
      of ultraviolet light.

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

Date: 10 Dec 90 17:15:51 GMT
From: mcsun!ukc!edcastle!hwcs![e-mail]  (Stewart T. Fleming)
Subject: Re: Black Holes

In article <[e-mail]>, [e-mail] (Raymond Seibert) writes:
> does, but matter keeps sticking onto the top of the existing matter.  Now
|> according to this theory, the black hole should at some point consume enough
|> matter to make it unstable.  This in turn would cause all the compressed
|> matter to be spewed out in a tremendous explosion.  Of course I have no

I think this is one point of view discussed by Stephen Hawking in his book
"A Brief History Of Time".

[Question : If you get a big enough black hole - one that absorbs all the matter in a
solar system/galaxy/Universe and then explodes, will the matter absorbed be regenerated ?]

|>                 Ray
|>                 [e-mail]

Stewart
--

[e-mail] or [e-mail] or ...ukc!cs.hw.ac.uk!sfleming
"Jedi programmers do it with byte sabres."

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

Date: 11 Dec 90 16:28:07 GMT
From: usc!snorkelwacker.mit.edu!thunder.mcrcim.mcgill.edu!clyde.concordia.ca!nstn.ns.ca!cs.dal.ca![e-mail]  (Jose Castejon-Amenedo)
Subject: Re: Black Holes


In article  <[e-mail]> Arnold Gill writes:
> In article <[e-mail]>, [e-mail] (Norman Yarvin) says:
> >
> >I have heard this explanation many times, and find it hard to understand
> >using a simple-minded or 'intuitive' view of relativity.  Granted that if
> >the star's escape velocity exceeds the speed of light, then a photon
> >starting from the star's surface can't make it out.  But it seems to me that
> >if one can propel some piece of matter any distance away from the black
> >hole, then one can lift fuel up to that distance; using this fuel one can
> >lift the next piece of matter even farther away from the center; and thus by
> >degrees something could escape entirely from the black hole.

>     No, that won't work, as Henry has posted already.  Think of it in terms
> of orbits around a massive body, in this case a black hole.  Until you reach
> escape velocity, you will always be describing some type of orbit around the
> black hole.  When you are outside the black hole (but nearby), the orbits are
> not too different from your normal orbits, but they are squashed a bit, so
> that only certain orbits actually lead away from the black hole.  Most of the
> rest intersect the "surface" -- the event horizon.  The closer you come to the
> "surface", the more orbits end up intersecting it.  When you reach the event
> horizon, all orbits intersect the "surface" and the number of orbits that
> could leave the black hole decreases to zero.  Inside the event horizon, no
> orbits exist that cross the event horizon (because that is, in part, how the
> event horizon is defined).  In fact, depending on the model used, all orbits
> inside the black hole hit the singularity in some finite local time.


    This explanation is correct, although matters are actually
"deeper" than that. From a mathematical point of view (and whether one
likes it or not, mathematics pervades general relativity) the roles of
the time coordinate and the radial coordinate are swapped beyond the
event horizon in a spherically symmetric black hole (I am thinking of
a Schwarzschild BH). In this region, travelling backwards along the
radial coordinate corresponds to travelling backwards in time, which
makes one realize about the difficulties of anything coming out of
these black holes (classically).

    There is nothing magic about horizons. In Minkowski (flat)
spacetime the lightcone of any event is a horizon (not an event
horizon, but what is technically known as a local isometry horizon). A
timelike curve can cross it once and only once. So if you stick your
fist through a lightcone, it will stay inside. The rest of your body
will be able to stay outside for a while, provided that you move
pretty fast.



JCA
[e-mail]

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

End of SPACE Digest V12 #672
*******************