home

Solrad Satellites (8, 9 and 10)

The Solrad satellites were developed in the 1960s by the Naval Research Laboratory (NRL) to measure solar X-ray emissions — an issue for naval communications. These satellites were spin-stabilized with the spin axis oriented perpendicular to the satellite-Sun line so that each of the X-ray photometers rung around the satellite equator would point at the Sun once a revolution. However, the useful lifetime of these satellites was limited because the residual magnetic dipole within them interacted with the magnetic field of the Earth and caused the spin axis to drift from its desired orientation. A slow decay in the spin rate was a secondary issue.

In 1963, Aeronutronic won a competition for a control system to correct both problems for the forth-coming Solrad 8 satellite. I was responsible for the analytic design and modeling of the control system. Others were responsible for the hardware including the ammonia-vapor reaction control, electronics and sun sensors. Solrad 8 was designed to operate autonomously, without ground control. Aeronutronic also designed the attitude control or the Solrad 9 and 10 satellites, though for these satellites the NRL built the hardware in-house. Solrad 9 had a cylindrical shape but from a control standpoint functioned like Solrad 8, while Solrad 10 the X-ray photometers pointed parallel to the spin axis, which required a redesign of the Sun sensors and how they functioned. Solard 8, 9 and 10 performed as planned.


  • Solrad 8 (Explorer 30)
    Launched November 19, 1965
  • sat-spin
    Spin-Attitude Control System
    Launched February 15, 1965

  • Solrad 9 (Explorer 37)
    Launched March 5, 1968
  • solar
    Solrad 10 (Explorer 44)
    Launched July 8, 1971