Hi,

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 published.

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 -

UOSAT-1 8910120203424 COMPUTER GENERATED TELEMETRY 00100101020302645503000304000405591806275607397A08450909557E 10100011010112000313000214024315832D163545176303184508195418 20150621020122615223000124009F25412026425727334128450B295608 30000331020032666733244234011735306336354737392C38457D39541A 40110441080D42743643000744140545001046003147447448463D494898 50110551080C52272053156454463055361456444757447558461E59471E

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 calculated.

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, G3LDI, G3FMQ, G4CUO, G4FKC, PA0DLO, G0BAF, G4ULS, VE3EFX and WB6LLO, who 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.

73

Clive G3CWV

Hitchin, North Hertfordshire, UK.