Date: Sun,  1 Nov 92 05:02:04    
From: Space Digest maintainer <digests@isu.isunet.edu>
Reply-To: Space-request@isu.isunet.edu
Subject: Space Digest V15 #364
To: Space Digest Readers
Precedence: bulk


Space Digest                Sun,  1 Nov 92       Volume 15 : Issue 364

Today's Topics:
              "Earth Gains a Retinue of Mini-Asteroids"
                 Automated space station construction
                        Dyson sphere (2 msgs)
                        getting hit by a comet
                       GPS orbital information
           Gravity Assists (Was Re: Query Re: pluto direct)
                  Need help FAST! Looking for answer
      pocket satellite receivers (was Re: how much is the 95LX)
               Re:Swift-Tuttle Comet a threat to earth?
               REPOST!  UN Space/Moon Treaty?! (2 msgs)
                             Solar Sails

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

Date: 31 Oct 92 07:55:47 GMT
From: Jim Scotti x2717 <jscotti@lpl.arizona.edu>
Subject: "Earth Gains a Retinue of Mini-Asteroids"
Newsgroups: sci.astro,sci.space

In article <1992Oct29.170729.20363@cs.rochester.edu> dietz@cs.rochester.edu (Paul Dietz) writes:
>Science (10/16/92, page 403), reports that Gehrels and colleagues in
>the Spacewatch program have detected 8 very near earth asteroids over
>the last two years with sizes from 5 to 100 meters.  This implies that
>at any time, there are as many as 50 mini-asteroids passing between
>the Earth and Moon every day.  This figure is some 100 times larger
>than had been inferred from observations of the number of larger
>bodies.
>
>Since the Tunguska event is thought to have been due to a 40 meter
>body, and such events were calculated to occur once every 2 to 3
>centuries, something is screwy here.

Not really screwy.  The number of 50 meter objects is enhanced by
about 10 times and the Tunguska type events probably happen once
or a few times per century.  Remember, 3 out of 4 enter over water
and may be less likely to be detected.  Also, perhaps a large
fraction of them disintegrate higher in the atmoshpere, causing
a much smaller disturbance in the lower atmosphere than that of
the Tunguska event.  Also, the best guess I've heard for the size
of the Tunguska progenitor is between 50 and 100 meters.  The 10
meter sized objects are enhanced by a factor of 100 and the trend
from the larger objects to the smallest is a gradual transition
that starts at around 100 meters size.

>The orbits of the bodies are unexpectedly similar to Earth's.
>Two have orbits more like earth's than any known body; one was that
>asteroid that was mistaken for a spent rocket body.

Also known as 1991 VG.
 
>These couldn't be Frank's minicomets, could they?  His putative
>objects are supposedly in prograde, earth-like orbits, to reduce the
>impact velocity enough to avoid observational constraints.

Frank's minicomets were estimated to be 10-30 meters in size.  The
number of objects in this size that he estimated to account for
what was probably detector noise was at least a million times the
the number extrapolated from the larger Near Earth asteroid population
and therefore is a population at least 10,000 times more numerous than 
what has now been found by Spacewatch.  In short, with our sensitivity,
we should see at least 1000 of Frank's minicomets each NIGHT!!!!!!  I
think the Spacewatch survey has now effectively disproven Frank's
hypothesis used to explain his so called "atmospheric holes".

Incidentally, an earlier CCD developed by Spacewatch in the
early 1980's (an old RCA 320x512 chip) was used by a colleague
of Frank's from JPL to survey for the minicomets directly.  This
investigator claimed to have detected at least one such object
on two consecutive images.  Without consulting the Spacewtach
crew, he announced his "discovery".  When we were finally able
to look at his images, we concluded that what he was looking 
at was detector noise!

>
>	Paul F. Dietz
>	dietz@cs.rochester.edu

Jim.
---------------------------------------------
Jim Scotti 
{jscotti@lpl.arizona.edu}
Lunar & Planetary Laboratory
University of Arizona
Tucson, AZ 85721 USA
---------------------------------------------

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

Date: 1 Nov 92 01:54:55 GMT
From: Charles Frank Radley <3001crad@ucsbuxa.ucsb.edu>
Subject: Automated space station construction
Newsgroups: sci.space

In article <1992Oct31.023129.9034@access.usask.ca> choy@skorpio.usask.ca (I am a terminator.) writes:

>Can robots be launched to build the space station? They can work overtime.

>Henry Choy
>choy@cs.usask.ca
This is how space station Freedom will be built.
Extensive use will be made of robotics, including the
Shuttle Remtore Manipulatoir System (robot arm)
and the Mobile Transporter (I am on the MT design team
at Astro Aerospace Corp, in Carpinteria, CA).
 After about MB-6 the space station will have uits own arm
to complete the assembly.
  The truss section will be automatically fastened together
using remotely operated electrical self-spinning motirzed bolts.
  Crew EVA time will be kept to a minimum and confined to
essential tasks.

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

Date: 29 Oct 92 18:31:08 GMT
From: Ralph Buttigieg <ralph.buttigieg@f635.n713.z3.fido.zeta.org.au>
Subject: Dyson sphere
Newsgroups: sci.space

Original to: 3001crad@Ucsbuxa.Ucsb.Edu
  3001crad@ucsbuxa.ucsb.edu (Charles Frank Radley), wrote:

 3> Does a Dyson sphere spin or rotate?

 3> For a nonspinning sphere, does it have an atmosphere on 
 3> the outside(for lifeforms to breathe?

 Will if it was spun there would be artificial gravity on the equator
 with lessening gravity closer to the poles. The atmosphere would be the
 thickest at the equator. However the strong gravity area would still be
 GIGANTIC.


 3> Heavy objects on the inside of the sphere will fall into the Sun,
 3> so inhabitants must live on the outside, in near total darkness.

 As there might be leakage of air to the outside this might form an
 external atmosphere. Some types of life do not require light. They may
 exist quite happly on the outside.

 ta
 Ralph

--- Maximus 2.01wb
 * Origin: Vulcan's World-Sydney Australia 02 635-1204 (3:713/635)

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

Date: 30 Oct 92 16:36:22 GMT
From: Ralph Buttigieg <ralph.buttigieg@f635.n713.z3.fido.zeta.org.au>
Subject: Dyson sphere
Newsgroups: sci.space

Original to: Henry@Zoo.Toronto.Edu
 henry@zoo.toronto.edu (Henry Spencer) wrote:


 h> Depends on the level of technology used to build it.  Dyson's original
 h> concept -- a cloud of smaller habitats individually in orbit --
obviously
 h> did.  The problem with a solid sphere is, what *holds it up*?  Even if
 h> you spin it, that only supports the equator -- what keeps the poles from
 h> falling inward?

 The SF writer Jack Williamson wrote about a design for a Dyson Sphere
 he did for a novel with Frederik Pohl. He proposed to surround the star
 with several layer of ring shaped tubes. The tubes would have a
 low-viscosity fluid flowing fast enough so centrifugal force would hold
 everthing up.

 ta
 Ralph Buttigieg

--- Maximus 2.01wb
 * Origin: Vulcan's World-Sydney Australia 02 635-1204 (3:713/635)

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

Date: 29 Oct 92 19:35:01 GMT
From: Mal Logan <Mal.Logan@f546.n635.z3.fidonet.org>
Subject: getting hit by a comet
Newsgroups: sci.space

I personally couldn't think of a better way to get rid of all our nukes - aim
it at the comet -

It might not save planet earth, but it would make the Greenies happy -

Mal

ps/ I also think that Dan Q would make a perfect leader of the free world.

:-------( 

 * Origin: Ground Zero BBS - 61-3-314-7107 (3:635/546)

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

Date: 1 Nov 92 02:57:58 GMT
From: Steve Linton <sl25@cus.cam.ac.uk>
Subject: GPS orbital information
Newsgroups: sci.space,sci.physics

Are lunar and/or solar tides relevant?

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

Date: 1 Nov 92 04:12:48 GMT
From: Josh 'K' Hopkins <jbh55289@uxa.cso.uiuc.edu>
Subject: Gravity Assists (Was Re: Query Re: pluto direct)
Newsgroups: sci.space

baalke@kelvin.jpl.nasa.gov (Ron Baalke) writes:

>In article <1992Oct30.163302.15547@rcvie.co.at>, se_taylo@rcvie.co.at (Ian Taylor) writes...
>> 
>>While I'm here, anyone know if a gravity assist trajectory can be used to 
>>*reduce* speed?  

>Sure.  Mariner 10 used a gravity assist of Venus to help it decelerate towards
>Mercury.  Voyager 2 lost speed when it flew by Neptune on its way out of
>the solar system. 

[other examples deleted]

Flyby the "back" of a planet (relative to it's orbital motion) and you speed up.
Flyby the "front" of a planet and you'll slow down.
Both techiniques are useful.  

-- 
Josh Hopkins                                          jbh55289@uxa.cso.uiuc.edu

"We can lick gravity, but the paperwork's a bit tougher."  Wernher von Braun

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

Date: 1 Nov 92 01:57:18 GMT
From: Charles Frank Radley <3001crad@ucsbuxa.ucsb.edu>
Subject: Need help FAST! Looking for answer
Newsgroups: sci.space

In article <1992Oct29.213056.23537@cbfsb.cb.att.com> jweber@cbnewsg.cb.att.com (jodi.weber) writes:

>Help! I need a fast answer to the following questions:

>What are the Leonids?
>What did the Leonids do in 1799 and 1833 that was spectacular?

>Please e-mail me or post any response ASAP!  Thank you!!

>Jodi Weber
>jodiweber@attmail.com   or   jweber@cbnewsg.cb.att.com
The Leonids are an annual meteor shower.
In those years, and more recently, the meteor intensity was
very high, hundreds per minute.
  I forget which time of year they occur,
somebody on  sci.astro should help you there.
  The increase in intensity is due to non-uniformity of the
meteor stream, it is highly dens near the location of the parent comet, whose name I forget too.
  Again, try sci.astro

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

Date: 30 Oct 92 16:04:58 GMT
From: Ralph Buttigieg <ralph.buttigieg@f635.n713.z3.fido.zeta.org.au>
Subject: pocket satellite receivers (was Re: how much is the 95LX)
Newsgroups: sci.space

Original to: Anthony@Csd4.Csd.Uwm.Edu
  anthony@csd4.csd.uwm.edu (Anthony J Stieber) wrote:


 a> Motorola has talked about some sort of future low earth orbit satellite
 a> system for two way radio communications, but I don't know much about it.

 a> Perhaps someone on sci.space knows more about it.
 a> --
 a> <-:(= Anthony Stieber   anthony@csd4.csd.uwm.edu   uwm!uwmcsd4!anthony

 The company STARSYS intends to put up a system of 24 LEO satellites
 that will provide world-wide messaging an position-location. They are
 currently conducting tests with the French ARGOS satellite. Although
 more of a global paging service then a full comunication service, it
 should be a lot cheaper then Motorolas Iridium.

 ta
 Ralph

--- Maximus 2.01wb
 * Origin: Vulcan's World-Sydney Australia 02 635-1204 (3:713/635)

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

From: Mario Wolczko <mario@cs.man.ac.uk>
Subject: Re:Swift-Tuttle Comet a threat to earth?
Newsgroups: sci.astro,sci.space

Message-Id: <1992Oct31.184122@cs.man.ac.uk>
Date: 31 Oct 92 18:41:22 GMT
References: <1992Oct26.170011.1@uwovax.uwo.ca> <ALTI.92Oct28201543@tanera.dcs.ed.ac.uk>
Sender: news@cs.man.ac.uk
Followup-To: sci.astro
Organization: Dept Computer Science, University of Manchester, U.K.
Lines: 8
Source-Info:  Sender is really news@CRABAPPLE.SRV.CS.CMU.EDU
Source-Info:  Sender is really isu@VACATION.VENARI.CS.CMU.EDU

In article <ALTI.92Oct28201543@tanera.dcs.ed.ac.uk>, alti@dcs.ed.ac.uk (Thorsten Altenkirch) writes:
> I would like to know what would happen in the
> case such a big object would collide with our planet?

  "What happens if a big asteroid hits the Earth?  Judging from
   realistic simulations involving a sledge hammer and a common
   laboratory frog, we can assume it will be pretty bad."
	Dave Barry, "Well Dressed for Disaster"

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

Date: 1 Nov 92 03:04:07 GMT
From: Steve Linton <sl25@cus.cam.ac.uk>
Subject: REPOST!  UN Space/Moon Treaty?!
Newsgroups: sci.space

|> the
|> late lamented L5 Society.

When/how did it die?

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

Date: Sun, 1 Nov 1992 04:32:24 GMT
From: Henry Spencer <henry@zoo.toronto.edu>
Subject: REPOST!  UN Space/Moon Treaty?!
Newsgroups: sci.space

In article <1992Nov1.030407.6269@infodev.cam.ac.uk> sl25@cus.cam.ac.uk (Steve Linton) writes:
>|> the late lamented L5 Society.
>
>When/how did it die?

The death certificate was the merger of L5 and NSI to form NSS, a few years
ago.  However, what really killed L5 was the massive overdose of internal
politics that changed "we want to go!" into "rah, rah, go NASA!", and that
happened rather earlier.

The one exception to this is that L5 had a strong local-chapters setup, and
many of those chapters survived the merger and are still active.  Some of
them are still doing useful things, unlike NSS HQ.
-- 
MS-DOS is the OS/360 of the 1980s.      | Henry Spencer @ U of Toronto Zoology
              -Hal W. Hardenbergh (1985)|  henry@zoo.toronto.edu  utzoo!henry

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

Date: 1 Nov 92 01:59:34 GMT
From: Charles Frank Radley <3001crad@ucsbuxa.ucsb.edu>
Subject: Solar Sails
Newsgroups: sci.space

Solar sails use radiation pressure, NOT pressure from
particles.
The TV station was incorrect as usual

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

End of Space Digest Volume 15 : Issue 364
------------------------------