|Mission type||Earth science|
|Launch mass||45.8 kg (101 lb)|
|Start of mission|
|Launch date||21 December 1964, 09:00:03UTC|
|Rocket||Thor Delta C|
|Launch site||Cape Canaveral Launch Complex 17A|
|End of mission|
|Last contact||26 May, 1967|
|Perigee altitude||171 km (106 mi)|
|Apogee altitude||8,545 km (5,310 mi)|
Explorer 26 was a spin-stabilized, solar-cell-powered spacecraft weighing 45.8 kilograms (101 lb). It carried five experiments: Solid-State Electron Detector, Omnidirectional and Unidirectional Electron and Proton Fluxes, Fluxgate Magnetometers, Proton-Electron Scintillation Detector, and Solar Cell Damage. The Solar Cell Damage experiment was intended to quantify the degradation of solar cell performance due to radiation, and evaluate the effectiveness of glass shields at preventing this degradation.  A 16-channel PFM/PM time-division multiplexed telemeter was used. The time required to sample the 16 channels (one frame period) was 0.29 s. Half of the channels were used to convey eight-level digital information. The other channels were used for analog information. During ground processing, the analog information was digitized with an accuracy of 1/800th of full scale. One analog channel was subcommutated in a 16-frame-long pattern and used to telemeter spacecraft temperatures, power system voltages, currents, etc. A digital solar aspect sensor measured the spin period and phase, digitized to 0.036 s, and the angle between the spin axis and sun direction to about 3-deg intervals.
Explorer 26 was launched from Cape Canaveral Launch Complex 17A on a Thor Delta C rocket on 21 December 1964 at 09:00:03. The spacecraft systems functioned well, except for some undervoltage turnoffs, until May 26, 1967, when the telemeter failed. The initial spin rate was 33 rpm, and the spin axis direction was right ascension 272.8 deg and declination 21.5 deg. The spin rate decreased with time to 2 rpm on September 9, 1965. For the balance of its life, the spacecraft was coning or tumbling at a rate of about 1 rpm.