Please make a donation to support Gunter's Space Page.
Thank you very much for visiting Gunter's Space Page. I hope that this site is useful and informative for you.
If you appreciate the information provided on this site, please consider supporting my work by making a simple and secure donation via PayPal. Please help to run the website and keep everything free of charge. Thank you very much.

Explorer: DME (ISIS X)

Explorer 31 (DME A) [NASA]

DME (Direct Measurement Explorer) or Explorer 31 was a small ionospheric observatory which worked in conjunction with the canadian Alouette 2 satellite. It was instrumented to make direct measurements of selected ionospheric parameters at the spacecraft.

The DME satellite carried seven experiments:

  • a thermal ion experiment,
  • a thermal electron experiment,
  • an electrostatic probe,
  • an electron temperature probe,
  • a spherical mass spectrometer,
  • an energetic electron current monitor, and
  • a magnetic ion-mass spectrometer.

Since the spacecraft had no tape recorder, data could be observed at the spacecraft only when the spacecraft was in sight of the telemetry station and when commanded on. Experiments were operated either simultaneously or sequentially, as desired. The satellite was spin-stabilized with the spin axis perpendicular to the orbit plane. The spin rate and spin axis were controlled by an onboard magnetic torquing system. The attitude and spin rate information were observed by a sun sensor and a three-axis magnetometer.

Satellite performance was satisfactory except for a partial power failure in May 1966, which reduced data acquisition time to about half the nominal amount. Some difficulties were encountered in obtaining attitude information that was necessary for the reduction of the experiment observations. On 1 July 1969, the satellite data observations were terminated with five of the seven experiments operating. Responsibility for standby monitoring of the satellite was given to the ESSA telemetry station at Boulder, Colorado, on 8 July 1969. During this standby operation, experiment data were collected only once on 1 October 1969, for 9 min from the electrostatic probe for use in studying a red arc event. On 15 January 1971, no response was received from a variety of satellite commands, and the satellite was abandoned.

Nation: USA
Type / Application: Ionosphere Research
Operator: NASA Goddard Space Flight Center, Greenbelt, Maryland
Contractors: Applied Physics Laboratory of The Johns Hopkins University (APL)
Propulsion: None
Power: Solar cells, batteries
Lifetime: 1 year (design);
Mass: 99 kg
Orbit: 502 km × 2857 km, 79.8
Satellite COSPAR Date LS Launch Vehicle Remarks
Explorer 31 (DME A, ISIS X) 1965-098B 29.11.1965 Va 75-1-1 Thor-DM21 Agena-B with Alouette 2


Further Explorer missions: