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TRAAC (Transit Research And Attitude Control) tested gravity gradient stabilisation for the operational Transit satellites. Additionally, it carried Solar Cell Experiments and a Neutron Detector. TRAAC was launched with Transit 4B on a Thor-DM21 Able-Star launch vehicle.

The objectives of the mission were:

  1. Back up Satellite Transit 4B with respect to increasing knowledge of earth's gravitational field.
  2. Demonstrate the principle of gravity gradient stabilization by which one satellite face may be permanently oriented toward earth.
  3. By means of particle detectors: (a) improve the delineation of the number density of protons in the inner Van Allen Belt, (b) search for trapped particles heavier than protons, and (c) check the cosmic ray neutron albedo theory of the origin of the inner Van Allen Belt.
  4. Test advanced engineering concepts (such as deployment of a weak "lossy" spring one coil at a time, from a subliming encapsulation, and the damping of libration by means of this spring).

Since Satellite 4B met all objectives, the first objective was not necessary. Objectives 3 and 4 were met. TRAAC contained the first gravity gradient stabilization system orbited (Objective No. 2). This system responded to the extension command but, shortly thereafter, a drive motor malfunctioned and the 60-foot gravity gradient stabilization boom did not extend fully. After launch, it was difficult to execute operational commands while the TRAAC doppler transmitters were on, so that this system was maintained in the off position for substantial periods.

TRAAC contributed some early measurement data of the space environment resulting from the Pacific high altitude nuclear tests (Johnson Island). The albedo neutron flux was measured over a nine-month period. The gravity gradient libration damping spring operated satisfactorily.

This satellite was the first to employ electromagnets for temporary magnetic stabilization.

The satellite had an operating life of 270 days. As with Satellite 4-B, the TRAAC power system was greatly affected by artificial radiation and the satellite ceased transmitting 12 August 1962.

Nation: USA
Type / Application: Technology
Operator: USN
Contractors: Johns Hopkins University Applied Physics Laboratory (APL)
Equipment: ?
Propulsion: ?
Power: Solar cells, batteries
Lifetime: 270 days (design)
Mass: 109 kg
Orbit: 957 km × 1109 km, 32.4
Satellite COSPAR Date LS Launch Vehicle Remarks
TRAAC 1961 αη 2 15.11.1961 CC LC-17B Thor-DM21 Able-Star with Transit 4B