On the afternoon of March 24, 2020 EDT, I noted a modulated carrier on 236.7487MHz. I wasn’t looking here by accident, I was looking for LES-5 and after almost 53 years in space and 49 years since it was suppose to have been switched off LES-5 [2866, 1967-066E] had been discovered alive. What follows is a discussion of the methods used to identify the satellite as LES-5 and determine that the telemetry transmissions may have scientific value as if the spacecraft is sending meaningful telemetry, researchers may be able to obtain valuable information on how hardware launched into orbit 53 years ago has faired.
What is LES-5?
LES-5 was an experimental communications satellite developed by MIT Lincoln Laboratory to test the viability of a UHF communications satellite in a near geostationary class orbit.
LES-5 was launched along with IDCSC 16-19 and DODGE 1 into a nearly circular orbit with a nominal altitude of 33,000km on July 1, 1967.
Here is an old US government documentary on LES-5 called The Tactical Satellite Communication Program, Part 1, Program 591. In this documentary the film makers outline the value of a UHF communications satellite in geostationary orbit and how LES-5 was build, launched and tested to understand the requirements of each sector of the armed forces. It should provide the reader with a wealth of historical information for context.
Finding Something the Old Fashioned Way, “Doing the Homework”
Lincoln Experimental Satelite 1 (LES-1) was recovered on the 237MHz band by Philip Williams, G3YPQ in 2013. This curiosity peaked my interest as to what else may be emitting signals in this now largely unused portion of the radio spectrum. As 237MHz is far away from most active amateur radio bands and there has been only limited use of the band for satellite operation dating back decades and few have seriously studied it for satellite emissions it seemed like a place to conduct a search.
Upon setting up my 237MHz antenna I was literally greeted instantly to emissions from LES-1 on 237.0MHz.
LES-1 captured literally as I plugged in the coax for my 237MHz 6 element yagi antenna.
Some years ago, I had noted the S-band emissions of LES-9 a nuclear RTG powered communications test satellite launched with LES-8 in 1976 and my interest was peaked into the history of the MIT Lincoln Laboratory series of satellites. I gathered many papers published online and over time began digesting the programs history and operational characteristics.
I then tracked down an old paper on LES-5 and noted with interest that LES-5 had beacons on 236.75 and 228.43MHz.
LES-5 communications system block diagram showing references to telemetry and transponder frequencies.
A quick check of the position of LES-5 on the afternoon of March 24, 2020, revealed it was in my sky to the south east. So I aimed the antenna and went back inside…
A Needle in a Haystack
Knowing where to look greatly simplified discovering LES-5. The VHF radio bands have become a clutter of radio frequency interference from all the modern conveniences of life. As LES-5 is in a subgeo-synchronous orbit the Doppler effect on the satellites signal is negligible over time so the techniques I commonly use to find and identify a satellite are largely ineffective.
Even with knowing where to look for LES-5 the challenge of finding the signal in the thicket of noise on the 237MHz band was a challenge. The animation below conveys some of that challenge. As I sifted through the noise I noted one ‘carrier’ that slightly stood out from the others and zoomed in, increased the FFT size until I could resolve the modulation on the carrier and become suspicious I had detected something other than radio frequency interference.
Zooming in on LES-5 in the noise found on the 237MHz band. It was like finding a needle in a haystack.
Once I had begun to suspect I was detecting LES-5, I went outside and turned the antenna orthogonally to the heading that LES-5 was on and the signal completely disappeared while most of the noise signals remained. I repeated this test a number of times with different headings and found that the signal peaked to my south east in roughly the spot LES-5 should be.
Timing an Eclipse of LES-5
Doppler analysis of an object in near geostationary orbit can be difficult and or impossible as the Doppler effect is literally overwhelmed by other factors such as the stability of the spacecraft oscillator and perturbations to the satellites velocity relative to the observer by the Sun and Moon’s gravity tugging on it. But as fate would have it we have another reliable technique to locate a satellite very accurately in a geostationary class orbit. During the equinoxes satellites in geostationary and similar orbits undergo nightly solar eclipses and we just so happen to have arrived at the Spring equinox so nature was co-operating.
Spacecraft with good batteries usually display some sort of carrier frequency anomaly as they pass through eclipse.
GOES-13 undergoes a solar eclipse and displays a carrier frequency anomaly. Timing the anomaly allows an observer to locate the spacecraft. Given knowledge of the expected orbit one can accurately confirm the identity of a spacecraft using this technique.
In the case of LES-5, it never had a battery that supplied the payloads (i.e. transponder and telemetry beacon). Ironically, the only battery onboard was suppose to turn off the satellite after five years. I guess this is one of those “You only had one job!” MEME moments!
LES-5’s battery had “Only One Job”, to turn off the satellite after 5-years.
Many old decommissioned missions still emit RF and I have observed them over the years and used the phenomenon to identify them prior to many of the objects being declassified. Recently I used the technique to confirm GOES-13 wasn’t decommissioned as it stealth-fully left its perch over North America and headed to a new home over the Indian Ocean last year.
DSP-F15 a retired missile early warning satellite undergoing a solar eclipse.
Armed with the knowledge to wait for the eclipse, I set out to predict the timings and setup to record the data. For fun I shared the moment LIVE on Twitter with a number of interested people. Follow the link to enjoy the moment of discovery shared with a few hundred of my Twitter followers.
LES-5’s signal disappear part way through the penumbra portion of the eclipse and reappeared also in the penumbra portion of the eclipse. Perhaps this is a good indication of the health of the solar array?
Summary of the LES-5 eclipse monitoring results. As you can see the spacecraft signal disappeared and returned as predicted.
Interestingly the stability of the LES-5 local oscillator is rather amazing. Other than a brief transient drift in frequency during the power off/on segment the carrier returned to 237.7487MHz very quickly without the usual recovery period seen in more modern satellites.
LES-5 frequency vs time plot of the eclipse. Note the remarkable stability for the carrier frequency.
On March 27, 2020 the twitter user @supertrack_it reported the LES-5 signal as the satellite drifted into view of Italy. He provided signal reports and repeated the eclipse timings experiment.
LES-5 observed from Italy entering and exiting eclipse on March 27, 2020.
The Space-Track TLE used for generating the eclipse timings used was EPOCH 20086.84975933. The Italian observers results matched those of mine. I believe this confirms the identify of the spacecraft.
Twitter user @supertrack_it provide confirmation observations and eclipse timing on March 27, 2020 to confirm my observations.
Is LES-5 Saying Anything Meaningful?
I recorded a fair amount of IQ and .WAV audio data files of the LES-5 signal before is set over my eastern horizon. I sent those files to Dr. Daniel Estévez, EA4GPZ who specializes in the decoding of satellite signals.
Daniel was able to decode the emissions into bit streams and make a number of findings about the signal. The spacecraft is emitting 100bps BPSK.
Dr. Daniel Estévez decoded the 100bps BPSK telemetry into readable bit streams and concludes that with documentation the contents of the telemetry could be understood to determine spacecraft health.
Daniels results are interesting as he concluded the following in his blog post – Decoding LES-5:
“So far, my impression is that the data is valid, so at least a good part of the onboard computer is working. It would be very interesting to decode it, as probably it can show us something about the spacecraft’s health. However, this might not be so easy, as the documentation from this very old satellite might be long gone.”
March 27, 2020 Dr. Daniel Estévez
Based on the results of amateur observers LES-5 has been confirmed to be sending telemetry on 237.5487MHz. The telemetry appears to indicate deciphering it may provide a means of determining satellite health. The purpose of this blog post is to assist in obtaining support from persons involved in the LES-5 mission so that further research can be conducted to determine the health of the spacecraft and see if there is anything that can be learned from a mission that has been in space for 53 years.