Nimbus B, 3

Nimbus B [NASA]

The Nimbus-B meteorological R&D satellite was designed to serve as a stabilized, earth-oriented platform for the testing of advanced systems for sensing and collecting meteorological data. The spacecraft consisted of three major structures:

• a sensor mount,
• solar paddles, and
• the control housing unit, which was connected to the sensor mount by a truss structure.

Shaped somewhat like an ocean buoy, Nimbus-B was nearly 3.7 m tall, 1.5 m in diameter at the base, and about 3 m across with solar paddles extended. The torus-shaped sensor mount, which formed the satellite base, housed the electronics equipment and battery modules. The lower surface of the torus provided a mounting space for sensors and telemetry antennas. An H-frame structure mounted within the center of the torus provided support for the larger experiments and tape recorders. Mounted on the control housing unit, which was located on top of the spacecraft, were sun sensors, horizon scanners, gas nozzles for attitude control, and a command antenna. Use of the attitude control subsystem (ACS) permitted the spacecraft's orientation to be controlled to within plus or minus 1 deg for all three axes (pitch, roll, and yaw). Primary experiment subsystems on Nimbus-B consisted of

• a satellite infrared spectrometer (SIRS) for determining the verticle temperature profiles of the atmosphere,
• an infrared interferometer spectrometer (IRIS) for measuring the emission spectra of the earth-atmosphere system,
• both high- and medium-resolution infrared radiometers (HRIR and MRIR) for yielding information on the distribution and intensity of infrared radiation emitted and reflected by the earth and its atmosphere,
• a monitor of ultraviolet solar energy (MUSE) for detecting solar UV radiation,
• an image dissector camera system (IDCS) for providing daytime cloudcover pictures in both real-time mode, using the real-time transmission system (RTTS), and tape recorder mode, using the high data rate storage system (DHRSS),
• a radioisotope thermoelectric generator (RTG), SNAP-19, to assess the operational capability of radioisotope power for space applications, and
• an interrogation, recording, and location system (IRLS) designed to locate, interrogate, record, and retransmit meteorological data from remote collection stations.

The spacecraft never achieved orbit because of a malfunction in the booster guidance system forced the destruction of the spacecraft and its payload during launch. No radioactivity was released in the environment. The SNAP-19 RTG was salvaged from the water, refurbished and later flown on Nimbus 3.

Less than 1 yr later, an identical payload was successfully flown on Nimbus 3. Nimbus 3 was successful and performed normally until July 22, 1969, when the IRIS experiment failed. The HRIR and SIRS experiments were terminated on January 25, 1970, and June 21, 1970, respectively. The remaining experiments continued operation until September 25, 1970, when the rear horizon scanner failed. Without this horizon scanner, it was impossible to maintain proper spacecraft attitude, thus making most experimental observations useless. All spacecraft operations were terminated on January 22, 1972.