Space & Astronomy/Space and Astronomy (October 1993).iso/mac/TEXT/SPACEDIG/V15_4/V15NO449.TXT

Internet Message Format | 1993-07-13 | 33KB

Date: Mon, 23 Nov 92 04:59:58
From: Space Digest maintainer <[e-mail]>
Reply-To: [e-mail]
Subject: Space Digest V15 #449
To: Space Digest Readers
Precedence: bulk


Space Digest                Mon, 23 Nov 92       Volume 15 : Issue 449

Today's Topics:
           Aerobraking [was Re: Magellan Update - 11/20/92]
                       Ariane v.55 Mission Data
               DC Engines (was Re: Shuttle replacement)
                         Dyson Spheres, again
      Head of Russian Space Agency Coming to Southern California
                           Laser Divergence
                      Magellan Update - 11/20/92
                     Mars Simulation in Antarctic
                           Patriot Missile
                          Shuttle computers
                     Shuttle replacement (3 msgs)
       Skywatch from McDonald Observatory - Moved to sci.astro

    Welcome to the Space Digest!!  Please send your messages to
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    (THENET), or [e-mail] (Internet).
----------------------------------------------------------------------

Date: 22 Nov 92 12:33:07 EST
From: Chris Jones <[e-mail]>
Subject: Aerobraking [was Re: Magellan Update - 11/20/92]
Newsgroups: sci.space

In article <[e-mail]>, henry@zoo (Henry Spencer) writes:
>In article <[e-mail]> [e-mail] (Chris Jones) writes:
>>>>BTW, I think Magellan will become the first spacecraft to conduct an
>>>>aerobraking maneuver to change its orbit, right???
>>>Wrong.  Hiten ... did a small Earth aerobraking maneuver in spring 1991.
>>
>>At least two of the Soviet circumlunar Zond flights used an aerobraking
>>maneuver to minimize the G forces on reentry...
>
>All the Apollo lunar missions, and various other spacecraft, likewise did
>two-phase reentries.  But maneuvering during reentry is not normally referred
>to as aerobraking, and such reentries are *not* composed of two separate
>encounters with the atmosphere; they're one encounter following a complex
>down-up-down trajectory.

At least one reference I checked *did* call it aerobraking.  All referred to it
as a skip reentry.  The claim is that the Zonds entered, left, and reentered
the atmosphere; whether you count this as one encounter or two is a matter of
semantics.  I haven't heard the Apollo maneuver described as a skip reentry
(though one reference did say Apollo flew a similar trajectory).

>
>The question was about *changing orbits* with aerobraking.

I was adding information, not contradicting what had been posted previously
(unlike you, I didn't start my reply with "Wrong.")
--
Chris Jones    [e-mail]

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

Date: 23 Nov 92 06:20:56 GMT
From: Dean Adams <[e-mail]>
Subject: Ariane v.55 Mission Data
Newsgroups: sci.space

ARIANESPACE FLIGHT 55

The 55th Ariane launch is scheduled to place the SUPERBIRD-A satellite into
a geostationary transfer orbit (GTO) using an Ariane 42P launch vehicle
equipped with 2 solid strap-on boosters (PAP).  This is the 4th flight of
an Ariane 4 in the 42P configuration.  It will be launched from the Ariane
launch complex ELA 2, in Kourou -- French Guiana.

The launch vehicle performance requirement for this mission is 2,826 kg,
of which 2,780 kg represents the satellite mass.  The total vehicle mass
at liftoff is 320,214 kg.


Required Orbit Characteristics:
  Perigee Altitude ..... 200 km
  Apogee Altitude ...... 35,963 km at injection
  Inclination .......... 7 degrees


The Ariane 42P lift-off for Flight 55 is scheduled on Tuesday December 1,
1992, as soon as possible within the following launch window:

     Kourou Time       GMT               Washington, DC
     19:48 - 20:39     22:48 - 23:39     17:48 - 18:39


LAUNCH VEHICLE:

Ariane 42P.  This is a three-stage liquid fueled launcher with solid fueled
strap-on boosters.  The first stage (L220) is built by Aerospatiale, and is
powered by 4 liquid fueled Viking V engines.  The second stage (L33) is built
by MBB Erno and is powered by a single Viking IV engine.  Both the Viking IV
and V engines are manufactured by SEP.  The first and second stages use a
biliquid UH25/N2O4 fuel.  The third stage is built by Aerospatiale and is
the H10 "plus", with larger fuel tanks and increased performance over past
models.  It uses a cryogenic H2/O2 fueled HM-7B engine built by SEP. The two
strap-on boosters (PAP) are built by BPD and use a solid Flexadrine propellant.
The fully assembled launch vehicle stands 54.5 meters high on the pad.
It uses the type 01 Ariane Short payload fairing.


Flight Profile:

 +01:30  Solid strap-on booster jettison
 +03:28  First stage separation
 +03:30  Second stage ignition
 +04:23  Fairing jettison
 +05:38  Second stage separation
 +05:43  Third stage ignition
 +18:11  Third stage shutdown / orbit injection
 +20:42  SUPERBIRD-A separation
 +20:46  Third stage avoidance maneuver
 +22:23  End of Ariane mission 55


PAYLOAD:

Superbird-A is the fourth satellite of a series built by Space Systems/LORAL,
Palo Alto, Ca. for Space Communications Corporation (Mitsubishi Group), Japan.
It will be used for domestic communications purposes.

  Total mass at lift-off .... 2,780 kg
  Mass at GEO insertion ..... 1,665 kg
  Dry mass .................. 1,155 kg
  On-board power ............ 3,800 W (end of life)
  Nominal lifetime .......... 10 years
  Span of solar panels ...... 20.3 m
  On-Orbit position ......... 158 degrees east, over the Pacific Ocean

 Transmission capacity:
   Ku-band: 23 transponders (+8 spares) of 36 mhz bandwidth
   Ka-band: 3 transponders of 100 mhz bandwidth

 In-flight operations:
   Solar array deployment ....... about 2.5 hours after lift-off
   First apogee motor firing .... about 26 hours after lift-off at 3rd apogee
   Second/third apogee firings .. at 5th and 7th apogee


LAUNCH COVERAGE:

All Ariane missions are broadcast live via satellite from Kourou.
Coverage begins at 30 minutes before launch and continues until
all payloads have been deployed.

-{ Dean Adams }-

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

Date: 23 Nov 92 06:23:33 GMT
From: Bruce Dunn <[e-mail]>
Subject: DC Engines (was Re: Shuttle replacement)
Newsgroups: sci.space

> Allen W. Sherzer writes:
>
> DC-Y will use larger engines (about 200K pounds of thrust each). There
> are two options available:
>
> 1. A new engine called the RL-200 which initially is composed of some
>    off the shelf components and some new components.
>
> 2. Using Apollo J2 engines. This will significantly cut into payload
>    but will support continuous imporvement of the overall system.


        Any possibility of using the HM-60 engine being developed for the
Ariane V?  A 5 year old book (Advanced Chemical Rocket Propulsion by Y.M.
Timnat) gives the following:

                          RL-10 A3-3  J2       HM-60      SSME

Vacuum thrust, kN          67         1044     1025       2130
Vacuum Isp                 444        425      430        455
Mixture ratio              5          5.5      5.1        6
Combusion Pressure, MPa    3.2        5.36     10         20.7
Expansion Ratio            40         27.5     106.2      77.5
Length, m                  1.91       3.38     2.9        4.24
Mass                       132        1542     1100       3065

        If these projected number have been realized, the HM-60 looks like a
slightly lighter substitute for the J2.  Buying them might be easier than
reactivating J2 production.  I am somewhat surprised that the HM-60 Isp is
only 430, considering the low mixture ratio, the high expansion ratio, and
the higher chamber pressure.

--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: 23 Nov 92 02:00:45 GMT
From: "Frederick A. Ringwald" <[e-mail]>
Subject: Dyson Spheres, again
Newsgroups: sci.space

In article <[e-mail]>
[e-mail] (Edward V. Wright) writes:

> Well, Dyson himself did not actually propose a solid sphere, which would
> require materials that are not only unavailable but unreasonably strong,
> given our understanding of physics.  What he invisioned was a large number
> of habitats in orbit about a star which, together, would completely
> encircle the star in a ball-of-twine formation.  From a distance, it would
> look like a solid shell.

Have you read Dyson's original article? I have it here in front of me.
He says:

"The material factors which ultimately limit the expansion of a
technically advanced species are the supply of matter and the supply of
energy...The reader may well ask in what sense can anyone speak of the
mass of Jupiter or the total radiation from the sun as being accessible
to exploitation...the mass if Jupiter, if distributed in a spherical
shell revolving around the sun at twice the Earth's distance from it,
would have a thickness such that the mass is 200 grams per square
centimeter of surface area (2 to 3 meters, depending on the density). A
shell of this thickness could be made comfortably habitable, and could
contain all the machinery required for exploiting the solar radiation
falling onto it from the inside."

This sounds like a solid sphere to me. He goes on to say:

"If the foregoing argument is accepted, the the search for
extraterrestrial intelligent beings should not be confined to the
neighborhood of visible stars. The most likely habitat for such bveings
would be a dark object, having a size comparable with the Earth's
orbit, and a surface temperature of 200 deg to 300 deg K. Such a dark
object would be radiating as copiously as the star which is hidden
inside it, but the radiation would be in the far infrared, around 10
microns wavelength."

The jist of my (month-old) posts was that even if Dyson's basic idea is
right, the details probably aren't. A genuine Dyson sphere probably
would have plenty of starlight shining through it: a solid shell 2 or 3
meters in thickness simply would not be rigid enough to withstand the
pressure of the sun's gravity, unless made of material with properties
that don't look too plausible. In other words, a Dyson sphere probably
would not be a dark object. It would more probably look like a normal
F-K dwarf, with a slight IR excess that might be hard to distinguish
from a quite-natural circumstellar dust shell or ring.

Then again, never second-guess an alien intelligence. Ideas about
completely reworking a planetary system, often involving draining
matter off the star, come to me in the night, and force me to conclude
that, like most things in SETI, there's an infinity of possibility even
within the narrow confines of the known laws of physics. We really
don't even know enough to ask intelligent questions. Jill Tarter is
taking as flexible approach as she can with the NASA HRM survey, and it
may well be that the SETI project that succeeds will be done by
astronomers with SETI initially being the farthest thing from their
minds. (Then again, watch out for fascinating false alarms, such as
Martian canals, pulsars, and gamma ray bursts.)

By the way, the idea of a swarm of independent space habitats wasn't
Freeman Dyson's, it was Gerard O'Neil's, circa the late '60s, about ten
years after Dyson's 1960 paper, which I quote above. I know,
Tsiolkovsky, Bernal, and a legion of sci-fi writers had thought of it,
too, but the credit still should go to O'Neill for getting the
technical community to take the concept at least halfway seriously, as
a place to live and not just an orbiting laboratory, and as something
more than strictly sci-fi. After all, his 1974 paper did make the front
cover of Physics Today.

I recommend to anyone a look at Dyson's original paper; the reference
is:

Dyson, F. J. 1960, Science, vol. 131, p. 1667 (No. 3414, 1960 June 3).

You'll see immediately it's a one-pager, in the fine tradition of Fermi
(i.e., say your piece and get out). While looking up this paper, I came
across an interesting ad, in the same volume: a 1960 announcement that
Werner von Braun had just left the U.S. Army Redstone Arsenal to join
NASA, with a photo of him talking with several Mercury astronauts,
including Gordon Cooper and John Glenn - before their space flights, of
course. (Thanks goodness hairsyles have changed!)

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

Date: 22 Nov 92 20:42:44 GMT
From: [e-mail]
Subject: Head of Russian Space Agency Coming to Southern California
Newsgroups: sci.space

A friend had asked me to post this, since they need people to attend...
FOR IMMEDIATE RELEASE

       LOCAL TECHNICAL SOCIETY BANQUETS
       HEAD OF RUSSIAN SPACE AGENCY
       DECEMBER 2ND, 1992 IN HUNTINGTON BEACH

On the evening of December 2, 1992, the Orange County Chapter of the
American Institute of Aeronautics and Astronautics (AIAA) is
honoring Yuri Koptev, the director of the Russian Space Agency.
This banquet follows the first visit by Koptev to the West coast of
the United States, and highlights a whirlwind tour of local space
industries in Southern California, arranged by Rep. Dana Rohrabacher
(45th Congressional District).

"I'm very pleased that the AIAA can host this event", says Dallas
Bienhoff, Chair of the Orange County AIAA section.  "It gives a
chance for Director Koptev to meet more than just a few executives
involved with Southern California's space industry.  The AIAA has
over 1200 members in Orange County alone."

Koptev was appointed to head the newly organized Russian Space
Agency in February of this year, by Russian President Boris Yelstin.
Under Koptev, the Russian Space Agency is beginning to radically
transform the Russian space and rocket program in line to better
meet the needs of the Russian people, to compete on a world-class
quality basis, and to slim down to within a shrunken government
budget.

Under Koptev, all Russian government funds for space activities are
now funneled through the Russian Space Agency.  Despite the serious
financial and economic problems in Russia, Koptev has managed to
secure funds to keep most of the Russian space program alive.  At
the urging of Koptev and other Russian space leaders, Russian space
products are now emerging onto the international markets, and
cooperative ventures with US and other international firms and
agencies are being formed.

The public is invited to this event.

The banquet will be held at The Waterfront Hilton, located at 21100
Pacific Coast Highway, in Huntington Beach, California. To reach the
restaurant, take Beach Boulevard south from the 405 Freeway to
Pacific Coast Highway.  Turn right (north) on Pacific Coast Highway
for approximately 1.5 miles.

The banquet cost is
   $40 with reservations by 28 November
   $35 for AIAA members)
   $20 for Students (or under age 18)

The evening schedule is
   6:00 PM  Social/Cocktails
   7:00 PM  Dinner
   8:00 PM  Program

For reservations call the AIAA West Coast Office, phone 800-683-AIAA

The AIAA is a non-profit organization representing over 37,000
members nationwide for aerospace, space, and aviation.  The Orange
County Section has over 1200 active members from major employers in
Orange County such as Hughes, McDonnell Douglas, Rockwell
International, and TRW.

For more information contact:
  Wally McClure, AIAA Orange County Section Vice Chair for Public
     Policy,  [phone] (days), or
  Kim Chilcot, AIAA Orange County Section Vice Chair for Programs,
[phone], ext. 7-1204 (days)

FOR IMMEDIATE RELEASE

OC AIAA Rel. 92-02



--- Maximus 2.00

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

Date: Sun, 22 Nov 92 08:49:32 GMT
From: "Andrew H. Bond" <[e-mail]>
Subject: Laser Divergence
Newsgroups: sci.space

[e-mail]  writes:
>
> Hi.  I look in from time to time.
>
> I'm looking for information about interstellar lasers.  They sound like a
> great idea.  My question is: what keeps the laser beam from diverging
> over long distances?
>
> A carbon dioxide laser in a physics lab has a 1/4 inch beam when it leaves
> the laser and a one inch or two inch spotlight on the far wall.
>
> Can I make the following assumptions?:
>
> 1.  The divergence of the beam is inversely related to the square of
> the beam width, at any certain distance.
>
> 2.  The divergence of the beam is somehow related to the wavelength.
> ------------------------------------------------------------------------
> Thanks,
> Paul Klinkman
> Scavenger of arcania.

A laser beam diverges as a gaussian beam. i.e. the cross
section has a gaussian distribution as it propogates through
space. Over a very long distance, the spot size is asymptotic
to an angle.

The expansion angle of the beam is:

         Theta            2 * Lambda0
    --------    =    ---------------
       2              pi * n * w0

where:

Theta   = expansion angle
Lambda0 = wavelength
w0      = radius of beam waist (waist = min. spot size)
n       = index of refraction of medium

To make a long story short interstellar lasers will diverge no
matter what! All we can hope to do is make this divergence very
small. We can do this by

1. using a very short wavelength
2. having a very large beam waist

note: for most lasers the beam waist is in the middle of the
lasing cavity: diam of beam at aperture is a good approx.

Hope this helps. --AHB
--
Andrew H. Bond, Roanoke Valley Graduate Center

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

Date: 23 Nov 92 05:06:55 GMT
From: Ron Baalke <[e-mail]>
Subject: Magellan Update - 11/20/92
Newsgroups: sci.space,sci.astro,alt.sci.planetary

In article <[e-mail]> [e-mail] (Claudio Egalon) writes:
>I have a question about the aerobraking maneuver that the Magellan
>will perform; Is there any possibility that any of the components of
>the Magellan be damaged during this maneuver??? ...

There is some risk involved, but the aerobraking maneuvers will be spread
out over a peroid of 100 to 150 days.  Magellan is currently in a elliptical
orbit with a periapsis of 289 km (closest point of the orbit to the planet)
a apoapsis of 8458 km (farthest point), and a peroid of 3.26 hours.  The
aerobraking will be done in three major steps.  The first step is to
use a relatively large orbit trim manuever to lower the periapsis to about
140 km into the upper atmosphere of Venus.  The spacecraft will be low
enough to experience drag, but still high enough to escape any excessive
heating.  Magellan will also be in a tail-first position so that the
backside of the solar panels will have the maximum surface area exposed for
maximum drag.  The second step requires that Magellan stay in this
position for 100 to 150 days.  Each pass through the atmosphere will lower
the apoapsis, and small thruster maneuvers will be used to keep the
perapsis at a stable distance.  During this time the apoapsis will be
lowered from 8458 km to 250.  Once the apoapsis reaches 250 km, then
the third step will be executed and a propulsive manuever will be performed
to raise the periapsis to 250 km, achieving orbit circulization.  The orbit
peroid is estimated to be about 1.5 hours.

Note that funds to support Magellan beyond Cycle 4 has not been allocated
by Congress, and the spacecraft is still scheduled to be turned off in
May 1993, before any aerobraking maneuvers will be performed.

>BTW, I think Magellan will become the first spacecraft to conduct an
>aerobraking maneuver to change its orbit, right???

Hiten performed some aerobraking experiments through the Earth's atmosphere
in March 1991.  Pioneer Venus in the week preceding its demise last month
passed through the upper atmosphere of Venus a number of times while
its orbit decayed.
     ___    _____     ___
    /_ /|  /____/ \  /_ /|     Ron Baalke         | [e-mail]
    | | | |  __ \ /| | | |     Jet Propulsion Lab |
 ___| | | | |__) |/  | | |__   M/S 525-3684 Telos | Learn to recognize the
/___| | | |  ___/    | |/__ /| Pasadena, CA 91109 | inconsequential, then
|_____|/  |_|/       |_____|/                     | ignore it.

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

Date: 22 Nov 92 17:27:00 GMT
From: Bruce Dunn <[e-mail]>
Subject: Mars Simulation in Antarctic
Newsgroups: sci.space

> Frank Crary writes:
> MacMurdo Station, the main US base in the Antarctic, used to operate
> such a reactor. It was _not_ a space-related system such as the SNAP
> designs, just an ordinary, small, Earth-based system. I don't know
> if it is still opperational...


        Any idea on power output, mass and heat rejection requirements?


--
Bruce Dunn    Vancouver, Canada   [e-mail]

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

Date: 23 Nov 92 06:41:52 GMT
From: Paul Morville <[e-mail]>
Subject: Patriot Missile
Newsgroups: sci.space

Could anyone tell me when the Patriot Missile came into being?  When was it
first lauched, tested, etc.  I was under impression it was finished just
prior to the Persian Gulf conflict.  Is this correct?

Please E-Mail.

                    Thanks

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

Date: 22 Nov 92 21:31:33 GMT
From: Henry Spencer <[e-mail]>
Subject: Shuttle computers
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Craig Keithley) writes:
>> It's not a cycle-by-cycle lockstep like some redundant systems.  Every
>> couple of milliseconds, the four computers in the main redundant set
>> compare notes...
>
>I seem to recall that this is correct; that the four computers running the
>same code are on something like a 40ms main event loop...

When I said "every couple of milliseconds", I meant it. :-)  It's actually
about 440 cycles per second, which may be what you're remembering.  This
is from the National Space Transportation System Reference manual (not to
be confused with the Shuttle News Reference, which is more readily available
but much thinner).  My copy is a few years old; it's just possible this has
changed with the newer and faster computers, although I'd expect not.
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

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

Date: Sun, 22 Nov 1992 19:15:24 GMT
From: "Allen W. Sherzer" <[e-mail]>
Subject: Shuttle replacement
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Brian Stuart Thorn) writes:
>Allen...

>There is still *one* thing that the Space Shuttle can do that no other
>launch system is capable of... bringing things back from orbit.

At the moment there is no requirement for this capability. There simply
isn't anything we can return. The only things brought back have been LDEF
and a coupld of satellites. LDEF can be split up into several experiments
(which would allow greater access) and fly every Soyuz mission.

Satellites cannot be brought back in a cost effective manner. The only
ones brought back had to recive hundreds of millions is subsidies from
us taxpayers.

>Whether or not it is efficient to do so is another question. I posted
>another question about why Hubble Space Telescope is not brought back
>home for repairs. There are many reasons in this case, mostly concerning
>cost and loss of productivity (however limited it would be).

Brinning Hubble back and flying it again would cost well over a billion
$$. For less, we could build a new one and launch on a Titan.

>The Shuttle, as you continually point out, is enormously expensive to
>operate and inefficient when it is operating. But I don't think putting
>a Soyuz on an Atlas (which *doesn't* have the lift capacity, BTW) or a

Atlas is close. If it can't, we can go with Titan III for far far less.

>Titan IV (which isn't much better than Shuttle) is a reasonable solution.

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

>Shuttle certainly does not have 'twice the lift capacity' of Titan IV as
>an earlier poster contended, but it does have about one-third more, I
>believe.

The new Titan SRMs will close most if not all of that gap.

>Someday, we might actually
>have a payload requiring all that lift, or return capacity, and as we did
>after the demise of Saturn V, we'll be saying "why did we abandon it?"

We wo't have those payloads as long as Shuttle is consuming a third of
the NASA budget. It is a millstone holding us all to the Earth.

There are plenty of heavy lift options we can go with when we need them.
All are far cheaper than Shuttle.

On a related topic (your informative background on Delta Clipper) this
>sounds like an excellent idea, but I'm nervous about it. Having grown up
>in the Cape Canaveral area, and seen my share of boosters blow up or go
>tumbling into the Atlantic,

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

>the idea of a powered descent and vertical
>landing gives me the willies...

Much safer than airplanes for most people. A DC crash will only affect the
Spaceport. When aircraft crash they tend to kill people on the ground.

>I sure hope that thing has plenty of
>redundancy... rocket engines have a way of conking out at innopportune
>times.

All SSTO designs I have ever seen have at least one engine out capability.

  Allen

--
+---------------------------------------------------------------------------+
| Allen W. Sherzer | "A great man is one who does nothing but leaves        |
|  [e-mail]     |  nothing undone"                                       |
+----------------------153 DAYS TO FIRST FLIGHT OF DCX----------------------+

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

Date: 22 Nov 92 21:22:36 GMT
From: Henry Spencer <[e-mail]>
Subject: Shuttle replacement
Newsgroups: sci.space

In article <[e-mail]> [e-mail] (Allen W. Sherzer) writes:
>>the idea of a powered descent and vertical
>>landing gives me the willies...
>
>Much safer than airplanes for most people. A DC crash will only affect the
>Spaceport. When aircraft crash they tend to kill people on the ground.

And as any Harrier pilot will tell you, a vertical powered landing is
safer than a horizontal powered landing.  And either one is *much* safer
than a Shuttle-style horizontal landing *without* power.
--
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  [e-mail]  utzoo!henry

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

Date: Mon, 23 Nov 92 04:05 GMT
From: Karl Dishaw <[e-mail]>
Subject: Shuttle Replacement

Has the shuttle ever lifted more than 20 tons (vs. the rated capacity
of 30 tons)?  I was looking through a space almanac once and noticed all
the flights with payload weights given were around 15-20 tons.

Karl
[e-mail]

"Sold my soul to Uncle Sam . . . now marked down for resale."

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

Date: 22 Nov 92 17:17:36 GMT
From: Tom Parish <[e-mail]>
Subject: Skywatch from McDonald Observatory - Moved to sci.astro
Newsgroups: sci.space

I'll post another issue for Nov 29-Dec 5 however, a number of folks
suggested I put Skywatch on sci.astro.  It doesn't really make any
difference to me.  Take care and enjoy the holidays (if you are
in the states).

Tom Parish
------------------------------------------------------------------
Star Date                                                        Turning Point

                                 SKYWATCH
                          November 29-December 5

                       An Asteroid Approaches Earth
                              by Jeff Kanipe
                         Editor of Star Date Magazine


                                  PLANETS

     * Mercury is very low in the southeast just before sunrise. It is
     more visible later in the month.

     * Venus is the bright "evening star" in the west after sunset. It
     sets about three hours after sunset.

     * Mars rises 3 hours after sunset in the constellation Gemini.

     * Jupiter rises just after midnight in Virgo.

     * Saturn is in the south at sunset in Capricornus. It sets about
     midnight.

                                  EVENTS

     Nov. 30: Saturn is just south of the crescent moon this evening.

     Dec. 1: The moon is at apogee, 405,070 km (251,698 mi).

     Dec. 2: First quarter moon.


                     TOUTATIS: PROTECTOR OF THE TRIBE
                     --------------------------------

     The 4-mile-wide asteroid Toutatis will pass within 2.5 million
     miles of Earth the morning of December 8, a distance ten times
     that between Earth and the moon. Toutatis is the closest
     encounter we have had with a celestial body other than the moon
     that has been predicted far in advance (its orbit was determined
     in January 1989). Astronomers discovered that Toutatis has an
     orbit very much like a short-period comet, that is, it describes
     a path through the solar system that is more stretched-out than
     a simple elliptical orbit.

     Toutatis was named after the Gallic god, the "protector of the
     tribe." Gauls, whose religious leaders were Druids, believed
     Toutatis prevented the sky from falling on them!

     Toutatis is classified as an Apollo asteroid, one of about 100
     known asteroids that actually cross Earth's orbit periodically.
     Its comet-like orbit may be due to the gravitational sling-shot
     effect of the planet Jupiter. At one time, Toutatis may have
     been an ordinary asteroid. But then during a close passage to
     Jupiter, the huge planet may have managed to impart some of its
     gravitational energy to the asteroid and, like a mean game of
     crack- the-whip, accelerated the asteroid toward the inner solar
     system--and us.

     Next week, Toutatis will be five times closer than it was in
     1989. Astronomer Art Whipple of the University of Texas at
     Austin McDonald Observatory calculates  the asteroid's closest
     approach will occur December 8. Toutatis will be brightest,
     however, the morning of December 12. Observers with small
     telescopes won't see much: a very faint, tiny point of light
     among hundreds of other points of light-- stars--about 12 degrees
     south- southeast of the bright star Regulus in the constellation
     Leo. (Twelve degrees is slightly greater than the area of sky
     covered by the typical fist held at arm's length.) If you watch
     carefully over a period of about fifteen or

     twenty minutes, though, you may see one of the stars move
     slightly with respect to the background stars. That will be
     Toutatis.

     Toutatis passes Earth quickly, but returns in September 2004,
     when it will come with 966,000 miles of Earth, just four times
     the Earth-moon distance.

     Astronomers estimate there may be more than 1,000 Toutatis-like
     asteroids more than a half-mile in diameter shuttling unnoticed
     across Earth's orbit. And indeed, in the last few years, more of
     these Earth- crossers have been discovered by patrol cameras.
     But not to worry. Our home planet is a very small target in a
     very large universe. The odds of Earth being struck are quite
     (pardon the pun) astronomical.


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     Jeff Kanipe is editor of Star Date Magazine, published by
     McDonald Observatory at the University of Texas at Austin. Write
     to Star Date at 2601 University, Room 102, the University of
     Texas at Austin, Austin, TX 78712 for subscription information.
     It is very reasonable in cost, informative and colorful.

     Copyright 1992 The University of Texas McDonald Observatory.
     Material is intended for personal education and should not
     be rebroadcast in any written or verbal form without
     prior permission from the University of Texas.

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

             Also see the daily scripts from the Star Date
                   Radio Program on the Turning Point.
                           HST/DS 512-219-7848

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End of Space Digest Volume 15 : Issue 449
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