The Satellite

Big Bird was a 'low altitude surveillance platform' (LASP), the main US spysat during the 1970s. The core of the Lockheed-built satellite was a large Cassegrain telescope with a 2.4 m (8 ft) focal length. Behind the telescope itself were two cameras: a KH7 Eastman Kodak one for photographing large areas, and a Perkin-Elmer high resolution camera for detail (0.3 m resolution from 160 miles up, allegedly). Big Bird was basically a cylinder about 15.2 m long and 3.05 m in diameter, and weighed about 8,165 kg. Power came from two large solar arrays, and a fat battery for darkside work; a 6 m extendable antenna allowed it to communicate with its controllers. Big Bird was manoeuverable too: it carried a restartable liquid propellant engine, which was periodically refired to keep the thing in orbit.

Big Bird could also carry another satellite as piggy-back, usually an ELINT electronic warfare one which would be sent into a higher orbit of its own. Carrying another satellite would bump Big Bird's weight up to at least 11,000 kg or so.

The first Big Bird was launched on 15 June 1971 from Point Arguello at Vandenberg AFB. The last one was launched in 1984.

Big Bird 16

This one was launched from Vandenberg AFB on top of a Titan 3D rocket at 10.48 am local time (18.48 GMT) on Wednesday 18 June 1980. The satellite went into a 96.46% orbit (as determined by the Royal Aeronautical Establishment the day after its launch), which is a polar one typical of spy satellites; the satellite orbits the poles while the Earth slowly revolves beneath it, allowing the satellite coverage over the whole of the Earth's surface. The orbit was also extremely low - only 265 km up at its highest altitude - again typical of spysats, as the lower the camera the better the pictures. Such a low orbit necessitated a fast orbit speed (Big Bird 16 circled the Earth every 88.87 minutes), and had the effect of substantially limiting the satellite's life, as at that altitude it was only a matter of time before the drag of the atmosphere sucked it back towards Earth. Even with a booster engine on board Big Birds could only stay up for about six months or so.

Like all satellites, Big Bird 16's orbit was elliptical, although only slightly so in Big Bird's case, its orbital eccentricity being 0.007, essentially circular. However, Big Bird 16 definitely did have a lowest point of approach to Earth (169 km at its lowest, rather than 265 km at its highest) and it would make sense to collect a dropped film capsule on its low pass rather than a higher one. This lowest point is known as the 'argument of perigee'; for Big Bird 16 it was 145%, which translates as a latitude of 35% north, with the satellite on its southward pass.

Big Bird 16 was "de-orbited" on 6 March 1981 after 261 days in orbit. Instead of allowing it to re-enter the atmosphere, with the possibility that would bring of bits of Big Bird falling to the ground anywhere the Soviets might pick them up, the USAF controllers detonated an on-board explosive.

Note on designation

The launch on 18 June 1980 is generally recognised to be that of the sixteenth Big Bird. Jane's however designates it as Big Bird 15, not recognising a 1977 launch as being a Big Bird one.

The international designation for Big Bird 16's launch is 1980-52 A, which is how it is identified in the Royal Aeronautical Establishment's satellite orbit tables.

The film capsules

Big Bird 16 carried six recoverable film capsules, each with its own de-orbit engine. Over the course of its six month life, BB 16 dropped all of these, and the core of this theory is that such a film capsule was dropped on the night of 27/28 December 1980. The precise structure of a film pod is still classified, as far as I am aware, but it is still possible to reason out what it would have been like. A film capsule would have contained:

1 a solid fuel de-orbit engine. Solid fuel allows a design with as few moving parts as possible. The engine ejected before the capsule re-entered the Earth's atmosphere.

2 drogue and main parachutes and cords, which would have taken up most of the bulk of the capsule. When (if) the capsule lands in the sea, explosive bolts would fire to eject the parachutes and so prevent the capsule from being dragged underwater by current.

3 a barometric pressure gauge, to begin parachute deployment at the right altitude, and to eject the parachute again if necessary before hitting the water.

4 a telemetry beacon, keeping in radio contact with the ground crew.

5 possibly a more basic radio beacon too, sending out simple pulses, so the capsule can be located if the telemetry link is broken, and to guide the aircraft in to its general position at night.

6 a massively powerful light, so that the aircrew can home in on the capsule during a night pick-up, and for the helicopters to locate it in the sea if the Hercules fail.

7 a battery to run all of this equipment.

8 a solidly-built heat shield, which would also eject should the capsule hit water.

9 possibly some sort of self-righting equipment (balloons or floats) if it hits water.

10 and, of course, the exposed film itself.

All of this is based on what is known about other American capsule recoveries, such as Discovery, the space shuttle solid fuel rocket boosters or the Apollo missions (see Satellite Recoveries). It's clear that the term 'film capsule' applies to a fairly large and expensive piece of kit.

On to Satellite Recoveries

Return to Introduction