[amsat-bb] Recollections of OSCAR-9 & Salyut Decay Competitions

Clive Wallis clivew at zetnet.co.uk
Fri Jan 11 04:08:29 PST 2008


Here is some information about the OSCAR-9 & Salyut-7 decay competitions.
I've compiled this from OSCAR News (the magazine of AMSAT-UK), and from my
own records and memory.  I would be most interested in any additional
information about these activities, which may have been remembered or

The decay competition was first suggested by Craig Underwood, G1WTW of
the University of Surrey (UoS), in February 1989. In a text bulletin
broadcast on OSCAR-11, he anounced the rules of the competition which was
to predict the day on which UoSat-1 will decay completely. the entry to be
sent at least one month before the prediction.  The prize for the winning
entry was a UoSAT sweatshirt.  Craig also posted a table of satellite
height and mean motion, showing the orbital decay between mid 1988 and end
of January 1989.

The task of running the competition was then passed to  AMSAT-UK, who
added additional prizes, any item of AMSAT software and two AMSAT-UK T
shirts.  Five entries were allowed per person, to be precicted one  month
before the event.

OSCAR-9 decayed at 07:51:49 UTC on Friday 13 October 1989.  The results of
the competition were anounced by Ron G3AAJ on the AMSAT-UK eighty metre
net the following Sunday.  The winner was Geoff Roberts G3ENY (15
October). My entry was second or second equals (October 11), Unfortunately
I can't remember the other runners up.

In his monthly news bulletin, broadcast at the end of October, Richard
G3RWL reported -

"Max White at the Royal Greenwich Observatory reports that UoSAT-OSCAR-9
(UoSAT-1) decayed on Friday 13th October at 0751.49 GMT on Rev 44761.

Two possible locations for the final decay are given by different agencies:
49.2S 220.9E and 46.4S 220.0E

These locations are over the South Pacific and were probably out of range of
any receiving stations. The last report of telemetry we have so far is from
K9CIS at the Richmond Community College in the USA. They heard the satellite
between 03:43 and 03:49 on 13th October, and reported good signal strength and
nominal telemetry. Any telemetry or reports from the last 6 hours of UO-9's
life would be appreciated by the UoS."

The following announcement appeared in the news bulletin on OSCAR-11 -

"UoSAT-1 decayed on 131089 at 0751.49 GMT on Rev 44761 around 49.2S 220.9E
and 46.4S 220.0E.  Any telemetry or reports from the last 6 hours of
UO-9's life would be appreciated by UoS - thanks to all those who have
already submitted reports."

The winner of the competition was also mentioned in the next OSCAR News,
December 1989, but no mention of the runners up!  I never received a prize,
(I didn't like to ask!).

Interestingly, there was also an item in the same issue of Oscar News from
'The Westlink Report' saying that UO-9 was last heard on 435.025 MHz. by
ZS6CCD at 12:00 UTC.

I last heard OSCAR-9 on 12 October at 20:31 UTC (TCA) transmitting
telemetry & WOD.  Here is one of the last frames I received -


Examination of this telemetry, shows that the 435 MHz. beacon is OFF.

There had been some interest in the decay of OSCAT-9's orbit well before
the competition was suggested.  At the 1987 AMSAT-UK Colloquium, Peter
Cleal G8AFN presented a paper describing factors affecting the decay of the
satellite. He queried why the satellite was still in orbit when the
expected orbital life was five years from 1981, and why the orbital
calendars for UO-9 were often incorrect.  Peter precicted that the
satellite would decay in March 1990, plus or minus three months.  Excellent
for such a long term prediction.  This paper was published in OSCAR News
April 1988. There were no Colloquium proceedings in those days.

At the 1989 AMSAT-UK Data Space Collloquium, Peter presented another paper
detailing how he related the decay of the satellite to variations in solar
activity and other factors.

Geoff G3ENY was a worthy winner of the competition, as his entry dated 30
June was published in August's OSCAR News.  It showed graph of height
against time.  His predictions (all guesses he said) varied from 06 August
to 10 November, with the winning entry 15 October nicely in the middle of
the range.  Geoff also wrote two articles in OSCAR News about solar
activity, and mentioned that a burst of solar activity in March had
doubled the rate of UO-9's decay.

Regarding my own predictions, after some initial unsuccessful attempts at
curve fitting, I decided a scientific approach was needed.  The
density of the exosphere appeared to be the most likely factor determining
the rate of decay, which could be integrated to give change in height. The
density is a function of height and exospheric temperature, and was
determined by using a simple look-up table.  The temperature was determined
by solar radiation, and some periodic time related factors.

The method I used was to statistically analyse the historic data. This
produced results which were then used with solar predictions, to do a day
by day calculation of decay rate & height until the critical re-entry
height was reached. I used a floppy disk based BBC-B Micro computer
programmed in BASIC, for all the calculations.

My source of the daily 10.7GHz. solar information was the weekly printed
bulletins from the U.S Solar Observation Centre at Boulder, Colorado.
The values of 3-monthly flux were obtained from tables published in
the Wireless Engineer magazine.  Those were the days before the Internet!

The method only yielded partial success, and I tended to get different
results every time the software was run.  My five predictions dated
between 27 August and 10 September, were October 11, 17, 20. 24 & 31

One problem in 1989 was getting Keplerian elements. AMSAT-UK usually
downloaded them from a bulletin board in North America via an expensive
transalantic telephone call. These were then read out on the AMSAT-UK 80
metre net. Often there was a burst of interference just as the vital mean
motion was being read out!  Keplers were also available on the packet radio
system and on OSCAR-11. Peter G8AFN and I often used to meet at Stevenage
railway station, where we changed trains on our way to work, in the mornings.
We exchanged the latest Keplers, and details of our observations.

To obtain updated values of mean motion I developed a method of using the
observed values of the time of closest approach (TCA), ie zero Doppler. The
error between actual TCA and predicted TCA could then be used to correct the
mean motion. Thus daily values of mean motion and decay rate were

One interesting outcome of this study was that I found that the measured
decay rate was usually twice the 'Drag' value in the Keplerian elements.
The units of drag are often wrongly described as revs/day/day.  They should
be double-revs/day/day.  This may have accounted for errors in the orbital
calandar for OSCAR-9.

The Salyut-7 decay competition was organised by Pat Gowen G3IOR and
AMSAT-UK. Details were published in OSCAR News December 1990. The time and
date of re-entry was required, which had to be received at least one week
before the event. Three entries were allowed. The prize was a handsome set
of commemorative Soviet space stamps.

Salyut-7 crashed to earth in Chile at 03:44 UTC on 07 February 1991.
Details were published on the amateur packet/satellite network and in OSCAR
News April 1991. There were over 100 entries, from all over the world.  The
winner of the competition was Mike Billow N1BEE, who predicted 03:30, just
17 minutes early.  Second was Hazel, XYL of G3FMQ at 04:19.  I came third
at 08:24.  Other close contenders included LA4XC, G4ODC, G4BDW, W3/G3ZCZ,
all came up with predictions superior to the estimates produced by the
professional agencies.

I received a magnificient certificate, designed and hand painted by Norma,
G3IOR's XYL. Duplicates of the space stamps were also included.

A similar method was used for the calculations, which used files of mean
motion, solar flux, and historic three month solar flux data.

Trust this is of interest, and looking forward to any comments.

	 Clive    G3CWV

         Hitchin, North Hertfordshire, UK.

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