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Zombie satellite hunter finds 53-year-old signal in the noise

Nestled in a clearing in the forests of Roberts Creek is a little house and on that house are a few antennas looking up, and listening.

Nestled in a clearing in the forests of Roberts Creek is a little house and on that house are a few antennas looking up, and listening.

With a pandemic unfolding and time on his hands, amateur radio operator Scott Tilley found something new for them to hear.

On March 24 Tilley confirmed a U.S. military satellite launched during the Vietnam War is still alive. The so-called “zombie satellite” appears to be receiving and transmitting data – essentially functioning like normal – long after it should have been silenced.

“Most zombie satellites are sending nonsense,” said Tilley. “That’s what makes LES-5 special. It still works after 53 years and we have data from the satellite itself to support that.”

Launched July 1, 1967, Lincoln Experimental Satellite – 5 (LES-5) is one of a series of satellites built by MIT’s Lincoln Laboratory under contract with the U.S. Department of Defence. 

At the height of the Vietnam War satellite communications technology was still in its infancy, and the U.S. military needed a way to communicate in real time with soldiers deep in the rainforests of Southeast Asia.

The satellite program was intended to test the usefulness of communications in the ultrahigh frequency (UHF) band. The LES-5 was the first “full-blown” experiment, and was deployed “very quickly,” said Tilley, after the military realized just how valuable the UHF band would be. “When you’re reading the papers on it, you can get the sense from these researchers just how hard they were pushed to develop this technology and get it into orbit.”

Despite its foundational contribution to telecommunications, LES-5’s mission was meant to be short lived. A small battery on board was supposed to switch off the experimental satellite after five years in orbit. “It only had one job and failed very, very badly,” said Tilley.

Still, it was a pioneering mission. Today, society depends on the UHF band for television, mobile phones, global positioning systems (GPS), and of course, military communications.

Ironically, those modern conveniences of life have crowded that band with noise, so picking up the signal of that pioneering spacecraft was a feat in itself.

First, Tilley had to construct the appropriate antenna and install it on his roof to pick up the right frequency. Then, he had to run a series of tests to confirm the signal, including measuring the satellite’s transmission as it passed through a solar eclipse. An amateur radio operator in Italy independently verified LES-5 as it tracked over Europe.

Staying at home during the COVID-19 lockdown gave him the days to spend on the project, said Tilley. “You can only garden so much until you need something else to do.”

His needle in the haystack found, the next step was understanding how the satellite was operating, what it was transmitting and hearing.

Tilley scoured the Internet for research, uncovered declassified military documents, which he sent to peers in the United States and Spain who specialize in decoding satellite signals. The research was used to build software, allowing them to partially reverse-engineer the mission.

Tilley likens their decoding work to learning another language – parsing out the satellite’s grammar and words over time, allowing the researchers to “see amazing things.” 

Now Tilley and his collaborators can hear what LES-5 is hearing when it listens to a slice of the radio spectrum. “We expect to understand more of the words it is sending in time as we gather more and more data from the satellite,” he said.

The LES-5 was equipped with solar panels and was used to test UHF communications. - Image via Lincoln Laboratory

Hunting for transparency

This isn’t the first zombie satellite Tilley has tracked, and efforts like his and other hobbyists play a large and critical role in helping the public understand what’s going on a few hundred kilometres over our heads.

In 2018 Tilley received worldwide attention after discovering the signal of NASA’s IMAGE (Imager for Magnetopause-to-Aurora Global Exploration), a $154-million satellite that malfunctioned five years after launch in 2000. The agency considered it the second most important science-generating mission in the 2000s but was forced to abandon the project.

After IMAGE, Tilley began hunting for “zombie sats” – satellites no longer under human control, but not totally inert. Maybe they’re actively controlling themselves, or else emitting signals.

IMAGE and LES-5 are the most coherent satellites of the approximately 50 he has found so far.

However, unlike NASA’s response to his IMAGE discovery – the agency rebooted a team and gave regular updates to the public – MIT’s Lincoln Lab was initially radio silent.

When Tilley reached out, he heard nothing back. The lab didn’t respond to a request for comment from National Public Radio when they covered the story at the end of April.

When Coast Reporter requested comment, Lincoln Lab’s communications manager David Granchelli confirmed the satellite is not “actively being used” since it completed its mission long ago.

“We have been informed of a number of civilian observations which have been hypothesized to be its telemetry transmissions. Our onsite staffing has been reduced in response to COVID-19, but we plan to investigate further when we return to more normal staffing levels,” said Granchelli.

“If the LES-5 telemetry stream is active, it is a remarkable achievement to still have any functionality as it approaches its 54th birthday. The legacy of the entire series of Lincoln Experimental Satellites (LES) was already secure as they paved the way for most of the U.S. milsatcom systems, but these longevity milestones are a nice additional accomplishment at the end of a long career.”

In the case of both IMAGE and LES-5, the question of what happens at the end of a long career hangs in the air like so much space dust.

It’s a question that continues to motivate Tilley and one of his collaborators, Dr. Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics.

McDowell hunts black holes for his day job, and in his spare time documents objects launched into space, their payloads and basic orbital parameters, and then studies how well countries are complying with international law and treaty obligations.

For McDowell, the recovery of LES-5 “emphasizes the importance of satellites switching off properly at the end of their mission.”

The concern, he said, is that if lots of old satellites are still transmitting, they’ll cause interference with new satellites, which can devolve into international disputes.

Tilley wants to create a comprehensive list of how many zombie satellites are in orbit, compare that list against what is operationally declared and publish it. Doing so could sway policymakers to act to quiet the noise.

“The radio spectrum is a very valuable resource. It’s already cluttered with lots of noise, overlapping signals,” said Tilley. “It’s like living in a city when you’ve got street lights everywhere, porch lights on and you want to see the night sky.”

McDowell, whose office is a stone’s throw away from Lincoln Lab in Lexington, Mass., supports satellite hunters like Tilley who expose zombie satellites. The need for transparency is critical, he says, since it establishes to what extent different countries respect treaties and regulations that govern the use of outer space.

“To have objective, external, non-affiliated people be able to assess that, is actually very useful,” McDowell told Coast Reporter.

It’s especially important as regulating bodies are already bogged down. One treaty, for example, requires the countries to register their satellites with the United Nations. The United States has registered, said McDowell, but the UN hasn’t posted that information on its website for the past three years because of a backlog.

“This treaty that was meant to make things transparent is not doing its job, because it’s not very helpful to be transparent four or five years after the event,” McDowell said.

When zombie satellites such as LES-5 and IMAGE are found and reported, they get picked up by academics and think tanks, said McDowell. “That then actually has an influence on policy.”

And so, the amateur radio operators of the world, including the one with homemade equipment on a roof in a clearing in Roberts Creek, do their part by listening.