Lincoln Experimental Satellite 4, also known as LES-4, was a

communications satellite A communications satellite is an artificial satellite that relays and amplifies radio telecommunication signals via a Transponder (satellite communications), transponder; it creates a communication channel between a source transmitter and a Rad ...

, the fourth of nine in the

Lincoln Experimental Satellite The Lincoln Experimental Satellite series was designed and built by Lincoln Laboratory at Massachusetts Institute of Technology between 1965 and 1976, under USAF sponsorship, for testing devices and techniques for satellite communication. Develo ...

, and the first of the series designed for operations at

geosynchronous A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...

altitudes. Launched by the

United States Air Force The United States Air Force (USAF) is the Air force, air service branch of the United States Department of Defense. It is one of the six United States Armed Forces and one of the eight uniformed services of the United States. Tracing its ori ...

(USAF) on 21 December 1965, it demonstrated many then-advanced technologies including active use of the military's SHF (super high frequency) band (7 to 8

GHz The hertz (symbol: Hz) is the unit of frequency in the International System of Units (SI), often described as being equivalent to one event (or Cycle per second, cycle) per second. The hertz is an SI derived unit whose formal expression in ter ...

) to service hundreds of users.

Background

After the successful development and deployment of Project West Ford, a passive communications system consisting of orbiting copper needles, MIT's Lincoln Laboratory turned to improving active-satellite space communications. In particular, Lincoln aimed to increase the transmission capability of communications satellites ("

downlink In a telecommunications network, a link is a communication channel that connects two or more devices for the purpose of data transmission. The link may be a dedicated physical link or a virtual circuit that uses one or more physical links or shar ...

"), which was necessarily constrained by their limited size. After receiving a charter in 1963 to build and demonstrate military space communications, Lincoln focused on a number of engineering solutions to the downlink problem including improved antennas, better stabilization of satellites in orbit (which would benefit both downlink and "uplink"—communications from the ground), high-efficiency systems of transmission modulation/de-modulation, and cutting-edge error-checking techniques. These experimental solutions were deployed in a series of nine spacecraft called

s (LES). Concurrent with their development, Lincoln also developed the Lincoln Experimental Terminals (LET), ground stations that used interference-resistant signaling techniques that allowed use of communications satellites by up to hundreds of users at a time, mobile or stationary, without involving elaborate systems for synchronization and centralized control. The 1st, 2nd, and 4th satellites in the LES series were designated "X-Band satellites," designed to conduct experiments in the "X-band", the military's SHF (super high frequency) band (7 to 8

) because solid-state equipment allowed for comparatively high output in this band, and also because the band had been previously used by West Ford. LES-1, launched 11 February 1965, failed to depart from its original circular medium orbit when its onboard thruster failed to fire. The resultant tumbling and the improper orbit rendered the satellite useless for experimentation purposes. LES-2, launched 6 May 1965 was used in a number of communications experiments and met all expected objectives. The satellite was automatically shut down by its internal clock in 1967. With medium orbit experiments complete, the experimenters then focused on conducting X-band experiments from

geosynchronous orbit A geosynchronous orbit (sometimes abbreviated GSO) is an Earth-centered orbit with an orbital period that matches Earth's rotation on its axis, 23 hours, 56 minutes, and 4 seconds (one sidereal day). The synchronization of rotation and orbital ...

Spacecraft design

LES-4 was an evolution of the LES-1/2 design for a much higher orbit. It carried more solar cells to run a more powerful transmitter and a greater number of Sun and Earth sensors. In addition, LES-4 was equipped with an electron

spectrometer A spectrometer () is a scientific instrument used to separate and measure Spectrum, spectral components of a physical phenomenon. Spectrometer is a broad term often used to describe instruments that measure a continuous variable of a phenomeno ...

to measure radiation in orbit in the 130

KeV In physics, an electronvolt (symbol eV), also written electron-volt and electron volt, is the measure of an amount of kinetic energy gained by a single electron accelerating through an electric potential difference of one volt in vacuum. When us ...

to 4 MeV range, both for scientific purposes and to correlate the effect of radiation from the intense

Van Allen Belts The Van Allen radiation belt is a zone of energy, energetic charged particles, most of which originate from the solar wind, that are captured by and held around a planet by that planet's magnetosphere. Earth has two such belts, and sometimes ot ...

on spacecraft functions. The satellite was spin stabilized, designed to rotate perpendicular to its orbital plane.

Mission and results

LES-4, along with LES-3,

OV2-3 Orbiting Vehicle 2-3 (COSPAR ID: 1965-108A, also known as OV2-3), the second satellite of the second series of the United States Air Force's Orbiting Vehicle program, was an American solar astronomy, geomagnetic and particle science research sat ...

, and

OSCAR 4 OSCAR IV ( OSCAR 4) was the fourth amateur radio satellite launched by Project OSCAR and the first targeted for Geostationary orbit on 12 December 1965. The satellite was launched piggyback with three United States Air Force satellites on a Titan ...

was launched on the third Titan IIIC test flight on 22 December 1965 at 14:00:01 UT from Cape Canaveral LC41 just one second behind schedule. From an initial parking orbit of , the Titan's Transtage boosted into a transfer orbit pending a final burn to circularize its orbit. However, this final burn, scheduled for T+6:03:04 after liftoff, never occurred due to a leaking valve in the booster's attitude control system. LES-3, LES-4, and OSCAR 4 were released from the Transtage, albeit much later than intended; OV2-3 remained attached and did not operate. Stranded in an unintended orbit, and misaligned with the sun, the satellite's solar panels only produced enough power to run onboard telemetry. Before the New Year, however, the spin axis of the satellite had precessed enough for the panels to provide sufficient power for all systems. Due to the improper orbit, the magnetic spin axis orientation system, as well as one of the onboard antenna switching control systems were rendered inoperable. The other antenna switching control system did operate properly, and all communications and scientific objectives were met. LES-4 stopped transmitting in October 1968. The satellite reentered the Earth's atmosphere on 1 August 1977.

Legacy and status

The LES program continued through nine satellites, culminating in the launch of LES-8 and LES-9 on 14 March 1976.

References

{{Orbital launches in 1965 Spacecraft launched in 1965 Communications satellites of the United States Lincoln Experimental Satellite