Explorer 4

  1958-005

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Explorer IV was launched on 1958 Jul 26 by Juno I from Cape Canaveral into a 110.2 min, 263 x 2213 km x 50.3 deg orbit. Its mission was to study both the natural radiation belts at high latitudes and the effects of the Argus high altitude nuclear explosions. It transmitted until Sep 19 and reentered on 1959 Oct 23.

Mass was 16.8 kg, including 11.7 kg for the satellite and 5.1 kg for the motor. The higher mass required a lower injection altitude and higher inclination.

The JPL Cluster used improved propellants in the third and fourth stages. The intended orbit was much more eccentric than previous launches, and used a different inclination. The intended orbit had been 288 x 2824 km x 50.8 deg.

Explorer 4
Date	Time	Event	Orbit
1958 Jul 26	1500:57	Launch by Juno I	CC LC5
		T+2:33 MECO
		T+2:40? Redstone sep
		T+6:02 Stage 2 burn
		T+6:10 Stage 2 cutoff
		T+6:10 Stage 3 burn
		T+6:18 Stage 3 cutoff	-3052 x 287
		T+6:18 Stage 4 burn
	1507:23	T+6:26 Stage 4 cutoff	257 x 2233 x 50.4
		T+10:58 Redstone impact 1475 km
		T+11:36 Stage 2 impact 2086 km
		T+13:36 Stage 3 impact 3317 km
1959 Apr 24			100.99 258 x 1352 x 50.2
1959 Jul 17			98.02 246 x 1080 x 50.3
1959 Oct 2			92.81 239 x 584 x 50.2