Message-ID: <4ZwVFsK00VcJ4CiU5=@andrew.cmu.edu>
Reply-To: space+@Andrew.CMU.EDU
From: space-request+@Andrew.CMU.EDU
To: space+@Andrew.CMU.EDU
Date: Mon,  5 Mar 90 02:25:45 -0500 (EST)
Subject: SPACE Digest V11 #115

SPACE Digest                                     Volume 11 : Issue 115

Today's Topics:
		      News From OSCAR-11 03Mar90
			    Space tomatoes
		       Re: Atlantis has landed
		       Large antennas in orbit
----------------------------------------------------------------------

Date: 3 Mar 90 15:19:14 GMT
From: zaphod.mps.ohio-state.edu!rpi!crdgw1!ge-dab!tarpit!peora!tsdiag!ka2qhd!kd2bd@tut.cis.ohio-state.edu  (John Magliacane)
Subject: News From OSCAR-11 03Mar90


**UOSAT 2 COMPUTER STATUS INFORMATION**

FAD1 Operating System v2.0b
Today's date is 3 /3 /90 (Saturday)
Universal Time is 14 :30 :48
Auto Mode is selected

SPIN PERIOD IS - 292

Z  MAG firings = 0
+ SPIN firings = 1
- SPIN firings = 1
RAM Wash Pointer at 275
WOD commenced 3 /3 /90 at 0 :0 :10
with channels 10 ,11 ,19 ,29 ,
Last cmd was 109 TO 0 WITH DATA 0

Attitude control initiated, mode 1

Digitalker active


   **** UoSAT-OSCAR-11 BULLETIN - 208      3rd March 1990 ****

                   UoSAT MISSION CONTROL CENTRE
    University of Surrey, Guildford, Surrey, GU2 5XH, England

Data Formats

UO-14 continues to run the FORTH DIARY on the 1802 OBC, using Data formats
distributed just after launch.  The development, publication and
implementation of downlink data formats for OSCARs is a delicate business,
especially early in a mission.  We do not want to publish data formats if they
are likely to change quickly, lest people waste their time implementing
software which will later become useless.  On the other hand, if we do not
publish formats, you cannot listen to the satellites - and that's what they're
there for!

In the next month, we will be changing operating regimes on UO-14, as the
PACSAT Communications Experiment is brought on line.  Once this happens,
asynchronous data formats (as used by the DIARY) will give way to synchronous,
AX.25 packet formats.

As soon as possible, the PACSAT Communications Experiment on UO-14, and the
BBS systems on PACSAT-OSCAR-16 and LUSAT-OSCAR-19 will be brought on line for
general use.  All three of these satellites will be running the same software,
using the same protocols - developed jointly by UoSAT and AMSAT-NA.
NK6K and G0/K8KA have already published a standard for a broadcast
(e.g. bulletins and whole-orbit-data protocol.  A final specification should
be distributed soon, and early transmissions from the UO-15 PCE will use this
protocol.  Specification of the message-transfer protocol is well under way.


Thus, the stable state, which we expect to reach sometime this spring, is that
UO-14, PO-16 and LO-19 bulletin boards will be accessible with the same
groundstation protocol software.  Broadcasts from these satellites (e.g.
bulletins and whole-orbit data will also come down in a single standard data
format.  Until we change this state, groundstation software developers are
advised to make their programs modular and be ready to revise!

DownlinK Modulation

UO-15 is capable of transmitting either 1200 bits/second AFSK (as used on all
previous UoSATs and currently transmited by UO-15), or 9600 bits/second FSK.
Ultimately, the PACSAT Commuications Experiment on UO-15 will support only
9600 bps FSK.  During the transition from DIARY operations to PCE operations,
however, we will also be transmitting AX.25 packets at 1200 bits/second AFSK.
Like DOVE, this should be copyable with a standard, unmodified, TNC.

de G0/K8KA.

* UoSAT-OSCAR-15 *

Experiments are under way using a large (150ft) antenna at Stanford (SRI-USA)
to attempt to detect very low level signals leaking from the UoSAT-4 on-board
uplink receiver local oscillators.  If the spacecraft power systems are still
functioning, then these signals should always be present since the receivers
cannot be switched off.  However, these leakage signals are deliberately
minimised during the design of the satellite and so they are very weak (-60
dBm = one thousand, millionth of a watt or the equivalent to looking for a
single Xmas tree light in Australia!).  The experiments at Stanford are
therefore very demanding: it will only be possible to extract the signals from
the background noise using sophisticated off-line FFT signal processing, and a
one second error in antenna tracking time may miss the satellite altogether!

de G3YJO


-- 
AMPR : KD2BD @ NN2Z (Neptune, NJ)
UUCP : ucbvax!rutgers!petsd!tsdiag!ka2qhd!kd2bd
       "For every problem, there is one solution which is simple,
       neat and wrong." -- H.L. Mencken

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

Date: Sun, 4 Mar 90 19:36:52 EST
From: John Roberts <roberts@cmr.ncsl.nist.gov>
Disclaimer: Opinions expressed are those of the sender
	and do not reflect NIST policy or agreement.
Subject: Space tomatoes


>From: trident.arc.nasa.gov!yee@ames.arc.nasa.gov  (Peter E. Yee)
>Subject: NASA Headline News for 03/02/90 (Forwarded)

>The Park Seed Company announced that some of the 12.5 million 
>tomato seeds exposed to the rigors of six years of space travel 
>on LDEF appear to be germinating normally.  A summary report this 
>fall will reveal the response to radiation that may indicate a 
>difference in the growth process and color -- revealing a loss in 
>chlorophyll -- which will determine whether food can be grown in 
>outer space.

Maybe in a few years, they'll have a new entry in their catalog:
  "The Triffid Tomato - it walks right into your kitchen!"  :-)
                           John Roberts
                           roberts@cmr.ncsl.nist.gov

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

Date: 5 Mar 90 02:05:17 GMT
From: zaphod.mps.ohio-state.edu!usc!jarthur!jokim@tut.cis.ohio-state.edu  (John H. Kim)
Subject: Re: Atlantis has landed

Atlantis has landed.

And Discovery/HST is next!!!
-- 
John H. Kim                 | (This space to be filled when I
jokim@jarthur.Claremont.EDU | think of something very clever 
uunet!muddcs!jarthur!jokim  | to use as a disclaimer)

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

Date: Fri, 2 Mar 90 22:22:53 EST
From: John Roberts <roberts@cmr.ncsl.nist.gov>
Disclaimer: Opinions expressed are those of the sender
	and do not reflect NIST policy or agreement.
Subject: Large antennas in orbit


>From: cs.utexas.edu!jarvis.csri.toronto.edu!utgpu!utzoo!kcarroll@tut.cis.ohio-state.edu  (Kieran A. Carroll)
>Subject: Large Orbiting Radio Antennas

>Actually, Ron, large radio antennas in GEO are nowhere near being so
>impractical. An early version of Canada's MSAT satellite (the "lazy Z"
>configuration, or "operational MSAT", as it was known circa 1982) was to
>use a 40 m diameter deployable antenna. It was to be built by Lockheed,
>using their "wrap-rib" design concept, and was to be launched by the space 
>shuttle. I suspect that the antenna massed no more than 2 tonnes, so a 70 m
>diameter one would likely mass about 3 times that. As for the 400-ton mass
>of an earth-based antenna, most of that is structural mass used to maintain the
>antenna's shape against the forces of gravity and high winds, neither of
>which are a problem in orbit (except very low orbits :-).

>     Kieran A. Carroll @ U of Toronto Aerospace Institute
>     uunet!attcan!utzoo!kcarroll kcarroll@zoo.toronto.edu

The local gravitational gradient places a limit on the maximum size of
a space structure of a given strength. ("Size" here refers to the maximum
difference in distance to the center of the earth.) My calculations indicate
that a good approximation for "small" objects is that the gravitational
gradient will be roughly equal to the local acceleration due to gravity
times two, divided by the distance to the center of the earth. The number
is given in inverse seconds squared, which is multiplied by the length of the
object to get meters per second squared. Thus for LEO, the gravitational
gradient is about 2.7E-6 s^-2. (Does anybody have a more exact figure?)
This is not a strong gradient, but it is enough to eventually force elongated
objects to point toward the center of the earth. Pointing a very large
antenna might be difficult if it is not carefully balanced.

Exercise: What would the gravitational "pull" be on a person 1.8 meters
tall, orbiting around a large neutron star (2 solar masses) at a distance of
3000km from the center of the star?
                           John Roberts
                           roberts@cmr.ncsl.nist.gov

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

End of SPACE Digest V11 #115
*******************