Hearing the term “zombie satellite” immediately conjures an image of a poor plot device for some scifi B-movie where dead satellites come to life looking to consume the brains of a group of unsuspecting space travelers. But zombie satellites are a real thing, although they are not looking for brains. Instead, they are a satellites that begin transmitting again for no apparent reason after an extended period of inactivity. There are several such satellites that have been observed by amateur radio enthusiasts specializing in tracking satellites. One of the older and more interesting examples is the Lincoln Experimental Satellite 1 (LES 1) launched back in 1965.
The Lincoln Experimental Satellite
The Lincoln Experimental Satellite series was part of a USAF-sponsored program run by the MIT Lincoln Laboratory in Lexington, Massachusetts. With eight satellites launched between 1965 and 1976, the purpose of the series was to develop new communication technologies and techniques to support future Department of Defense (DoD) communication satellite needs. As its name implies, LES 1 was the first satellite in this series.
The LES 1 experimental communications satellite, with its Star 13A injection motor attached, shown during ground testing. (Lincoln Laboratory)
The goal of the LES 1 mission was to test an all-solid-state X-band transmitter on an Earth satellite for the first time as well as several other enabling technologies. Built by TRW, LES 1 was a 26-sided polyhedron 61 centimeters across with a mass of 31 kilograms (a microsatellite by today’s definition). Its 18 square faces were covered with 2,376 solar cells that generated a minimum of 26 watts to power the satellite when it was in sunlight. While in the Earth’s shadow, the satellite would shut down until orbital dawn. The other 8 triangular faces supported Earth and Sun sensors and semi-directional antennas. This mission would test an electronic switching system that used readings from the Earth sensors to selectively activate the antennas pointing at the Earth as the satellite spun in orbit. The spin-stabilized satellite made use of passive thermal control and a set of magnetic torquers to orient the satellite to optimize its solar power supply and thermal balance.
A cutaway diagram of the LES 1 satellite. Click on image to enlarge. (Lincoln Laboratory)
Operating at a frequency of about 8 GHz in order to make use of existing satellite communications infrastructure at Lincoln Lab, LES 1 would use its 200-milliwatt X-band transmitter, employing a variety of complex signal modulation schemes, to relay voice and data between two points on the Earth which were equipped with 18-meter dish antennas. The ground element of this program included a sister project, Lincoln Experimental Terminal 1 (LET 1), designed to evaluate mobile satellite ground station technologies. In addition to its X-band experiment, LES 1 included a UHF transmitter operating at 237 MHz to transmit telemetry using bi-phase modulation for the first time. The satellite included a timer to shut down its transmitters after two years in orbit.
A photograph of the Lincoln Experimental Terminal 1 (LET 1). It was designed to test the use of portable ground terminals for DoD satellite communications. (Lincoln Laboratory)
The launch vehicle for LES 1 was the three-stage Titan IIIA being used for test flights of hardware for use in the larger Titan IIIC rocket being developed by the USAF. The first two-stages of the Martin Marietta Titan IIIA were upgraded versions of the Titan II ICBM which had been structurally reinforced to handle additional stages and larger payloads. The third stage, called the Transtage, used a pair of restartable Aerojet AJ10-138 engines to place payloads into their required high Earth orbits. While the Titan IIIA (which was capable of placing up to about four metric tons into low orbit or about a metric ton into a geosynchronous transfer orbit) could have been used as a medium-class launch vehicle in its own right, in the end it was flown only to support development of other members of the Titan III rocket family. The Titan IIIA was meant to serve as the core of the larger Titan IIIC which would use a pair of 3-meter solid rocket motors to improve its payload capability significantly.
Cutaway drawing of the Titan IIIC. The Titan IIIA served as the core of this launch vehicle. Click on image to enlarge. (USAF)
The LES 1 Mission
LES 1 was slated to be flown on the third development flight of the Titan IIIA. Since the primary objective of this flight was to test the rocket, LES 1 was being flown as a secondary payload on a noninterference basis with the needs of the engineering tests taking precedence. In addition to LES 1, the 485-kilogram payload carried on this flight included a truss structure to support satellite payloads until their deployment. The plan was for the Transtage to make a series of burns after launch to reach a near-circular 2,780-kilometer orbit. LES 1 would then be spun up to 180 rpm and deployed. LES 1 included a Star 13A solid rocket motor manufactured by Thiokol that generated 6.2 kilonewtons of thrust to increase the payload’s velocity by 1,500 meters per second and boost the satellite into its intended elliptical orbit with an apogee of about 18,500 kilometers – well into the van Allen radiation belt encircling the Earth in order to test the radiation resistance of the satellite’s systems. After its Star 13A solid rocket motor finished its job, it would be jettisoned leaving LES 1 to start its two-year mission.
Launch of the third Titan IIIA, No. 3A-3, from LC-20 on February 11, 1965 carrying LES 1. (USAF)
The third Titan IIIA, number 3A-3, lifted off from Launch Complex 20 at Cape Kennedy (which reverted to Cape Canaveral in 1973) at 10:19:05 AM EST on February 11, 1965. After the first two stages of the Titan IIIA completed their task, the Transtage separated and coasted for 13 seconds before igniting its engines for the first time. The initial 290-second burn then placed the Transtage and its payload into a 185-kilometer parking orbit. About two thirds into its first orbit, the Transtage ignited its pair of engines for a second time for 37 seconds to raise its apogee to 2,795 kilometers. After coasting for another orbit and a half, the Transtage ignited its engines for a third time for 28 seconds to circularize its orbit to 2,779-by-2,785 kilometers with an inclination of 32°. Shortly afterwards, LES 1 was deployed but its rocket motor failed to fire as intended because of an ordinance wiring error. Instead of being injected into an elliptical orbit with a 18,500-kilometer apogee, LES 1 was stranded in a lower 2,777-by-2,806-kilometer orbit.
An artist’s depiction of the initial burn of the Transtage. (USAF)
Despite the failure of Star 13A rocket motor to fire, LES 1 was able to gather some useful communication experiment data including voice transmissions between Lincoln Lab’s facility in Westford, Massachusetts and a ground station in Pleasanton, California. With the rocket motor still attached, the initial spin about the long axis of the combination eventually evolved into a dynamically more stable, end-over-end tumble a few days after launch. At this point, additional communications tests were no longer possible because the rotation axis had moved 90° away from that which its Earth sensors and antennas were designed to operate. And with the heavy rocket motor still attached, the satellite’s magnetic torquers were ineffective in altering the spacecraft’s attitude. After 4½ months of operation in a high radiation environment, no significant circuit or component malfunctions were noted. However, solar cell output was being affected over time. With LES 1 dutifully shutting down its transmitters in 1967, its objectives were eventually met by the nearly identical, 37-kilogram LES 2 successfully launched on May 6, 1965 on the last development flight of the Titan IIIA.
It’s Alive!!!
Normally, this would have been the end of the LES 1 story. It was expected to continue circling the Earth silently for millennia to come as its high orbit slowly decayed over time. But on December 18, 2012, Phil Williams from North Cornwall, England (call sign G3YPQ) detected a signal from LES 1 after almost 46 years of silence. Williams’ detection was quickly confirmed by other amateur radio enthusiasts who discovered that whenever the satellite was illuminated by the Sun, its 237 MHz telemetry system was found to be transmitting data. Apparently, a short had developed in the old satellite’s systems allowing power from the solar cells to reach the transmitter directly. A sample transmission received in Brazil at Amateur Radio station PY2ZX in December 22, 2012 is provided in the video below. The tumbling of the satellite modulates the sound being received as its solar panels are periodically shaded by the attached rocket motor. Almost a decade after coming back to life, the zombie LES 1 continues to transmit to this day, although who knows for how long.
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Related Reading
“The First Titan III Launches”, Drew Ex Machina, September 1, 2014 [Post]
“The First Missions of the Titan IIIC”, Drew Ex Machina, June 18, 2015 [Post]
General References
N. Cornwall, “American satellite starts transmitting after being abandoned in 1967”, Southgate Amateur Radio News, February 26, 2013
H. Sherman, D.C. MacLellan, R.M. Lerner and P. Waldron, “Lincoln Experimental Satellite Program (LES-1, -2, -3, -4)”, Journal of Spacecraft and Rockets, Vol. 4, No. 11, pp. 1448-1452, November 1967
William W. Ward and Franklin W. Floyd, “Thirty Years of Space Communications Research and Development at Lincoln Laboratory”, in Beyond the Ionosphere: The Development of Satellite Communications, SP-4217, NASA, 1997
“Third Titan 3A Vehicle Carries Experimental Comsat into Orbit”, Aviation Week and Space Technology, Vol. 82, No. 7, p. 26, February 15, 1965
“Lincoln Experimental Satellite”, TRW Space Log, Vol. 5, No. 2, pp. 39-41, Summer 1965
I would also like to thank one of my long-time readers, Robert Oler, for an update on the current status of transmissions from LES 1.
A short made it work again ? Good engineering anyway!
A/The “good” effect cosmic rays