Discoverer 2 was a cylindrical satellite designed to gather spacecraft engineering data and to attempt ejection of an instrument package from
orbit for recovery on Earth. The spacecraft was launched into a 239 km
x 346 km polar orbit by a Thor-Agena A booster. The spacecraft was
three-axis stabilized and was commanded from Earth. After 17 orbits,
on 14 April 1959, a reentry vehicle was ejected. The reentry vehicle
separated into two sections, one consisting of the protection equipment,
retrorocket and main structure and the other the reentry capsule. It
was planned that the capsule would reenter over the vicinity of Hawaii
for recovery, but a timer malfunction caused premature capsule ejection
and reentry over the north polar region. The capsule was never recovered.
The main instrumentation payload remained in orbit and carried out
vehicular performance and communications tests.
The spacecraft was 1.5 m in diameter, 5.85 m long and had a mass after
second stage separation, including propellants, of roughly 3800 kg. The
mass excluding propellants was 743 kg, which included 111 kg for the instrumentation payload and 88 kg for the reentry vehicle. The capsule section of the reentry vehicle was 84 cm in diameter and 69 cm long and
held a parachute, test life-support systems, cosmic-ray film packs to
determine the intensity and composition of cosmic radiation (presumably
as a test for storage of future photographic film), and a tracking beacon.
The capsule was designed to be recovered by a specially equipped aircraft
during parachute descent, but was also designed to float to permit
recovery from the ocean. The main spacecraft contained a telemetry
transmitter and a tracking beacon. The telemetry could transmit over
100 measurements of the spacecraft performance, including 28 environmental,
34 guidance and control, 18 second stage performance, 15 communications,
and 9 reentry capsule parameters. Electrical power for all instruments was
provided by NiCd batteries. Orientation was provided by a cold mitrogen
gas jet-stream system, a scanner for pitch attitude, and an inertial
reference package for yaw and roll data.
The Discoverer 2 mission successfully gathered data on propulsion, communications, orbital performance, and stabilization. All equipment functioned as programmed except the timing device. Telemetry functioned until April 14, 1959, and the main tracking beacon functioned until
April 21, 1959. Discoverer 2 was the first satellite to be stabilized
in orbit in all three axes, to be maneuvered on command from the earth,
to separate a reentry vehicle on command, and to send its reentry vehicle
back to earth.
The Discoverer program was managed by the Advanced Research Projects Agency
of the Department of Defense and the U.S. Air Force. The primary goal of
the program was to develop a film-return photographic surveillance satellite
to assess how rapidly the Soviet Union was producing long-range bombers and ballistic missiles and where they were being deployed, and to take photos over the Sino-Soviet bloc to replace the the U2 spyplanes. It was part of the secret Corona program which was also used to produce maps and charts for the Department of Defense and other US government mapping programs. The goal of the program was not revealed to the public at the time, it was presented as a program to orbit large satellites to test satellite subsystems and investigate the communication and environmental aspects of placing humans in space, including carrying biological packages for return to Earth from orbit. In all, 38 Discoverer satellites were launched by February 1962, although the satellite reconnaissance program continued until 1972 as the Corona project. The program documents were declassified in 1995.