HILAT (P83-1)

HILAT [USAF]

The HILAT (High Latitude Reseach Satellite) spacecraft (also known as P83-1) was the refurbished Transit-O 16 spacecraft, which carried experiments intended to provide remote-sensing and in situ measurements of physical quantities likely to provide insight into the dynamics of plasma-density irregularity formation in the high-latitude ionosphere. The main objectives of the HILAT mission were:

• to extend the data base on irregularity strength and three-dimensional shape,
• to probe several hypotheses about the development, transport, and decay of scintillation-producing irregularities,
• to document the role of convective instabilities at high latitudes, and
• to describe the role of peculiarly high-latitude influences such as particle precipitation and other aspects of ionospheric/magnetospheric coupling.

The satellite was three-axis stabilized by means of a Transit gravity-gradient boom and an added momentum wheel for yaw stabilization. The altitude was selected to be sufficiently high for scintillation and imager operation but low enough for the various in situ measurements. The inclination was chosen to give overhead passes nearly along the geomagnetic meridian at the preferred receiving locations. The orbit precessed 24 hours in approximately 6 months, so that observations during all hours of the day and night were possible in roughly one calendar season.

Following instruments were on board:

• 138, 390, 413, 536, 1239 MHz Coherent Beacon Experiment
• 3 - 100 m Density Fluctuations, 30 m/s Precision Drift Velocity Plasma Monitor
• 50-ms Resolution Three-Axis Fluxgate Magnetometer
• 20 ev - 20 keV, 16-Channel, 3-Angle Electron Spectrometer
• 1150-2000Å, 8-km Resolution Scanning Auroral Ionospheric Mapper

The Langmuir probe instrument failed on launch, and the Auroral imager failed on 23 July 83. All other instruments functioned until the final failure of the power source on 5 June 89.