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Subject: SPACE Digest V11 #303

SPACE Digest                                     Volume 11 : Issue 303

Today's Topics:
          Re: Radar (was Re: Drake Equation
               ometary Missions
           Jonathan's Space Report, Apr 19
             Apollo-Soyuz Reunion
----------------------------------------------------------------------

Date: 22 Apr 90 01:40:25 GMT
From: calvin.spp.cornell.edu![e-mail]  (John Sahr)
Subject: Re: Radar (was Re: Drake Equation

In article <[e-mail]> [e-mail] (Dan Tilque) writes:
[]
>Now the largest military radars (as I said in an earlier post) are
>large phased array systems which watch for ICBMs.  The U.S. has five of
>them (or did that last I heard).  Three of these, located in Alaska,
>Greenland and England, look for missiles launched from the Soviet
>Union.  The other two are located on the U.S. east and west coasts and
>look for submarine launches missiles.  These last two use over the
>horizon radar (using a troposcatter effect, I think) so much or most of
>their emissions probably do not escape to space.
[]

OTH radars use ionospheric refraction to see "over the horizon."
Tropospheric scatter has its uses, but the big OTH radars don't rely
on it.  The one I know about is several MW continuous power, using an
FM ramp to determine range (and other techniques to determine Doppler
shift).  It has the ability to pick an operating frequency from 3-20
MHz or so to pick optimum "skip."

[]
>In order to detect ICBMs, these radars would have to have ranges of
>about 2 or 3 times that of regular radars.  That means that (assuming
>similar receiver sensitivity) they would use 16 to 81 times the power
>of ordinary radar (which typically run about 2-5 MW).

Not necessarily true.  For an OTH radar, the signal return is
currently limited by clutter, notably ionospheric irregularities.
Thus, increasing the transmitter power just increases the clutter.

Even for the DEW-line radars, it may be pointless to increase the
power.  Consider that the "E-region horizon" is only 1100 km away (you
can see a 100 km tall mountain from 1100 km), and ICBM trajectories
are fairly low.  Also, there can be a lot of ionospheric junk
happening during magnetic disturbances, and these radars are bothered
by such clutter.  The thermal fluctuation of the ionospheric plasma is
enough to cause noticable backscatter ("incoherent scatter"), even
when the ionosphere is "calm."

High altitude bombers are only up about 15 km or so, and low altitude
bombers can be very low indeed.  It is pointless to increase the
transmitter power to see them any better (unless you want more detail,
perhaps).

>of ordinary radar (which typically run about 2-5 MW).

2-5 MW is a pretty boss transmitter, no matter what.  There are
certainly radars with much lower power.  The CUPRI radar, for upper
atmospheric irregularity studies, has a transmitter (peak) power of
about 40 kW, and I have heard of two radar systems that used only
about 1 kW.

Radio amateurs familiar with "meteor scatter" accompish hard target
scatter at hundreds of kilometer ranges with a few hundred watts of
transmitter power.

--
John Sahr,                   | Electrical Engineering - Space Plasma Physics
[e-mail] | Cornell University,         Ithaca, NY  14853

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

Date: 20 Apr 90 13:05:15 GMT
From: spock![e-mail]  (Tom Gray)
Subject: ometary Missions


In the popular press there are explanations from astronomers on the reasons
that some comets (ie Austin and Kahoutek) are anomolously bright when
discovered. The reason given is that these comets are entering the solar system
first time. They are losing an excess amount of mass at large distances since
they are losing low boiling point "volatiles" that have been lost from periodic
comets.

My naive interpretation of this is that the composition of a comet will change
with the number of entries to the inner solar system. The outer layers of the
comet will become depleted in materials at different rates depending on their
volatilities. The structure of the comet will thus become differentiated with
the chemical composition of the core differing from the outer crust. Is this
interpretation correct?

One of the justifications of cometary missions was to collect material which
would indicate the chemical composition of the primordial solar nebula. If the
composition of periodic comets has become differentiated, is this justification
proper? Did the measurements of the compostion of Halley's tail indicate the
composition of the solar nebula or just the composition of a periodic comet?
Solar nebula measurements would seem to justify the expense of the missions
much more than a cometary composition measurement.  There have been suggestions
of missions to land on comets and analyze samples. Would these samples have to
be taken from a subsurface region?

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

Date: 19 Apr 90 19:30:28 GMT
From: frooz!cfa250![e-mail]  (Jonathan McDowell)
Subject: Jonathan's Space Report, Apr 19

Jonathan's Space Report

Apr 19, 1990 (no.35)
----------------------------------------------------

The launch of orbiter Discovery and the Hubble Space Telescope
has been rescheduled for Tuesday, Apr 24.

Anatoli Solov'yov (Komandir) and Aleksandr Balandin (Bortinzhener)
continue in orbit aboard the Mir complex. The Soyuz TM-9 transport
and the Progress M-3 freighter are currently at the station.
Solov'yov and Balandin have been in space for 67 days. The launch
of the Kristall module has been delayed until June.

The second of the two satellites retrieved by Discovery in 1984, Palapa
B-2, was relaunched into orbit on Apr 13 by a Delta 6925 rocket from
Cape Canaveral.  (The first was Asiasat, formerly Westar 6, relaunched
last week from China.) Palapa is owned by the Indonesian
telecommunications agency Perumtel and will be used to relay
communications and TV between the islands of the Indonesian archipelago.
It is a Hughes HS-376 class comsat, and is the third Palapa B to reach
stationary orbit. Palapa was owner by the insurers after recovery,
and then sold to Sattel, Inc. which later sold it back to the Indonesians.
(If anyone can shed light on the complicated ownership history of Westar,
please let me know.)

Three small DoD research satellites were launched by an Atlas E from
Vandenberg on Apr 11.  The Atlas carried an Altair III upper stage left
over from the Scout program.  (Reports that the vehicle was an
"Atlas-Scout" are rather an overstatement; the Altair is the fourth
stage of the Scout vehicle.) The three satellites are: Polar Orbiting
Geomagnetic Survey, Transceiver Experiment, and Selective Communications
Experiment.  The first will map the Earth's magnetic field, while the
other two will study radio communications through the ionosphere.

NASA's Pegsat released its first barium canister on Apr 15.  The barium
spreads along the magnetic field lines, allowing the field to be traced.

The Kosmos-2062 recon satellite landed on Apr 5.

Eight small Soviet Navy communications relays, Kosmos-2064 to Kosmos-2071,
were launched on a single Kosmos rocket on Apr 6. This is the 43rd launch
of this type since the program began in 1970. A new program began in 1985,
with 6 satellites at a time launched on the newer Tsiklon vehicle, and
this may eventually supersede the 8-satellite program.

Kosmos-2072 was launched on Apr 13. No details yet.

Glavkosmos launched a Foton materials processing satellite on a two week
mission on Apr 11.  This is the seventh launch of a Foton (the 3rd to be
officially named) and carries a French experiment among its payload.
The Foton uses a Vostok spacecraft bus and carries several processing
furnaces to process crystals and pharmaceutical materials.  There is one
flight per year, each April. Launches are from Plesetsk aboard a Soyuz
rocket.

Summary of previous Foton flights:
ID    Name        Date            Dur(d)    Orbit (km, deg)
-----------------------------------------------------------------------
FotA1    Kosmos-1645    1985 Apr 16-29        13    215x390x62.8
FotA2    Kosmos-1744    1986 May 21-Jun  4    14    219x373x62.8
FotA3    Kosmos-1841    1987 Apr 24-May  8    14    218x381x62.8
FotA4    Foton        1988 Apr 14-28        14    219x374x62.8
FotA5    Foton        1989 Apr 26-May 12    16    222x378x62.8
FotA6    Foton        1990 Apr 11-*


(c) 1990 Jonathan McDowell
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------------------------------

Date: 22 Apr 90 05:25:34 GMT
From: uokmax!uokmax.ecn.uoknor.edu![e-mail]  (Jonathan A Bishop)
Subject: Apollo-Soyuz Reunion


     Tom Stafford is hosting a reunion of all five Apollo-Soyuz astronauts and
cosmonauts in Oklahoma City for the 15th anniversary of the flight.  Other
than a brief article in the local paper announcing it, not much has been
published.  I will post more info when it becomes available.
--
[e-mail]

"I'm President of the United States and I'm NOT going to eat any more
broccoli!" -- George Bush

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

End of SPACE Digest V11 #303
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