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LIDOS (Large Inclination Doppler Only Satellite), also known as STP P68-1, was a geodesy mission carrying a Doppler radio beacon without a navigation signal.

In the late 1960s, the Navy asked APL to build a geodetic-research satellite called Low-inclination Doppler-only Satellite (LIDOS) "Doppler only" meaning that it was intended to be tracked by the Doppler method, similar to Transit. It was decided later to place the LIDOS satellite in a high-altitude, near-polar orbit; its name was changed to "Large" inclination Doppler-only Satellite" to keep the same acronym. LIDOS was launched on 16 August 1968, with nine other satellites, on an Atlas-SLV3 Burner-2 vehicle, but the heat shield failed to open and all the satellites were lost.

The spacecraft was built on a Transit-O navigational satellite bus. LIDOS was gravity gradient stabilized by deployable boom with tip mass an was powered by four small deployable solar arrays. LIDOS was to be ejected as Burner-2 crossed the equatorial plane and spun to provide attitude control. A perigee kick and plane change rocket motor (VIP) mounted on the forward end of the satellite was to be fired, placing the satellite and bus in a new orbit with an inclination of 91.8, a perigee of 741 km, and an apogee of 1019 km. The spin-oriented LIDOS plus final injection motor (TE-M-537) were to coast to apogee where the apogee kick and plane change motor mounted on the bus aft end woujd inject LIDOS and the bus into an orbit 96 inclination, a perigee of 1019 km, and an apogee of 4447 km.

Nation: USA
Type / Application: Geodetic-research
Operator: USAF STP (Space Test Program)
Contractors: JHU/APL
Equipment: Doppler radio beacon
Configuration: Transit-Bus
Propulsion: VIP motor, TE-M-537 motor
Power: 4 deployable solar arrays, batteries
Mass: 55 kg
Orbit: 1019 km × 4447 km, 96 (planned)
Satellite COSPAR Date LS Launch Vehicle Remarks
LIDOS (P68-1) 1968-F07 16.08.1968 Va SLC-3E F Atlas-SLV3 Burner-2 [VIP + TE-M-537] with Orbiscal 1, OV5 8, Gridsphere 1, Gridsphere 2, Mylar Balloon, Rigidsphere, LCS 3, RM 18 & UVR, Radcat, SECOR 11, SECOR 12
Further STP missions: