ESSA 1

  1966-008A

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The next operational Tiros to be launched was Tiros OT3, at 0741 on 1966 Feb 3. Reaching orbit successfully at 0755, it was renamed ESSA I (Environmental Survey Satellite) to mark the Environmental Science Services Administration's funding and control of the operational weather satellite program. ESSA I orbited at 702 x 845 km x 97.9 deg. Replaced as primary satellite by ESSA 3 on 1966 Oct 2, it continued transmitting until 1968 Jun 13. 

Based on the post-third-stage-burn orbit, on the first orbit at the time of the burn, ESSA 1 was travelling southbound over the equator at 83W, over the coast of Ecuador, after a 7.5 min coast from Delta SECO.

First, I try and reconstruct assuming the documented 8.4 deg yaw (GSFC X-480-66-2) declared to be typical of a TOS launch. Final V2 is 7.526 km/s at flight path angle -0.36 deg, azimuth 188 deg, with the satellite at 722 km high descending toward perigee. This corresponds to a velocity vector of ( -1.021, -7.456, -0.047) km/s in coordinates (east, north, radial out). Impulsive dV is 2.114 km/s at pitch -47 deg, yaw -8.4 deg. Those angles are relative to the attitude of the stage, not to its velocity vector. We can assume the initial attitude is roughly the same as the SECO inertial velocity vector which would have been pitched up, perhaps 25-30 deg or so, but we don't know it in detail; the yaw is then relative to the SECO orbital plane. Let's assume that the actual X-258 burn was horizontal, which would be most efficient if they had freedom to arrange the preburn vector. Then we just have (ignoring the 0.05 km/s of radial velocity) V1 = ( V1 cos i1, V1 sin i1, 0 ) and dV = ( dV cos (i1+yaw), dV sin ( i2+yaw), 0 ), and given dV and yaw we can solve for V1 and i1. For small values of yaw of 8-16 degrees we get prior inclinations of around 94-97 deg, in which much of the burn goes into changing the southward velocity. In particular, 8.4 deg implies prior orbit of about -3860 x 722 x 95. This puts the Delta at 80W 20N at SECO time, a moderately plausible location south of Cuba.

ESSA 1
Date	Time	Event	Orbit
1966 Feb 3	0741:23	Launch by Delta C	CK LC17A
		T+1:30 Begin yaw 61.9 deg, roll -35.3 deg, pitch -8.7 deg
		T+2:10 End dog-leg
	0743:48	T+2:25 Thor S/N 20112 MECO
	0743:52	Delta S/N 20104 burn, 2:42
	0743:54	Begin 4.16 deg yaw
	0744:00	End yaw
	0744:06	Begin -2.6 deg pitch
	0744:08	End pitch
	0745:12	Fairing
	0746:34	Delta SECO
	0746:50	Pitch -47.21 deg
	0748:40	Yaw -8.36 deg
	0753:43	Stage 3 spinup
	0753:45	Stage 2 sep
	0753:56	X-258-C4 RH-88 burn, 23s
	0754:20	T+12:57 X-258 burnout
	0754:20	Coning begins
	0755	X-258 sep	702 x 845 x 97.9
	0755	Stage 3 weights sep
	0802?	ESSA despin weights sep
1966 Oct 2		Replaced by ESSA 3
1968 Jun 18		End of ops