Explorer 51

 1973-101A

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Atmosphere Explorer C was the first of a new series of Atmosphere Explorers built by RCA for NASA-GSFC. The new AEs had their own propulsion system with two TRW hydrazine thrusters to allow major orbit changes and active spin control. The satellite was designed to probe the upper layers of the Earth's atmosphere, studying its structure and composition. It also carried instruments to measure the effects of solar radiation on the atmosphere.

AE-C was launched on 1973 Dec 16 at 0618 by a Delta 1900 from Vandenberg. The Thor stage separated at 0621 and the Delta second stage ignited to place AE-C in a 150 x 4263 km x 68.1 deg orbit. Initially the orbit perigee was at 13N; this moved up to 68N and then back down again.

In March 1974, the satellite began a series of maneuvers to dip down into the atmosphere for 24 hours and then raise perigee again to avoid decay. These maneuvers were carried out every two weeks; the first one was to a perigee of 140 km, the lowest to a perigee of 129 km. The effect of higher drag during these excursions was to rapidly decrease the apogee, and by 1974 Dec the apogee was only 600 km.

AE-C now entered the second phase of its mission, with a circularization maneuver to enter a 250 x 250 km orbit. This was soon boosted to 390 km altitude, and during 1975 the satellite was maintained between 390 and 250 km altitude. AE-C was deactivated from 1975 Sep 23 to 1976 Feb 20. Its last reboost was carried out on 1977 Mar 18, and it stopped operations on 1978 Dec 11, a day before it reentered.

Launch mass was 668 kg. 1.14m high 1.37m dia. 168 kg of hydrazine could be carried. Control from GSFC. Delta stage 2 mass was 5443 kg full including 4672 kg of prop.

AE-C orbital history
Date	Time	Event	Orbit
1973 Dec 16	0618:00	Launch by Delta 1900
		T+0:36 SRM 1-6 burnout
		T+0:39 SRM 7-9 on
		T+1:17 SRM 7-9 out
		T+1:36 SRM 1-9 sep
	0622:32	T+4:32 MECO
	0622:40	T+4:40 Thor sep
	0622:44	Delta SES-1 burn 5:33
	0622:48	Fairing sep
	0628:17	T+10:17 Delta SECO-1
		T+24:19 Spinup to 12 rpm
	0642:55	T+24:55 Delta sep
	0955		132.48 154 x 4305 x 68.1
1973 Dec 17	0800		132.46 157 x 4301 x 68.1
1974 Jan 7	1325		131.06 150 x 4186 x 68.1
1974 Feb 1	0219		129.67 152 x 4063 x 68.1
1974 Mar 2	1756		128.25 153 x 3939 x 68.1
1974 Mar 6	0516		128.10 153 x 3925 x 68.1
		Lower perigee
1974 Mar 7	0900		127.88 144 x 3915 x 68.1
1974 Mar 8	1034		127.72 136 x 3909 x 68.1
1974 Mar 13	0516		127.14 135 x 3859 x 68.1
		Raise apogee
1974 Mar 14	1307		127.55 138 x 3892 x 68.1
		Raise apogee
1974 Mar 15	1854		127.95 139 x 3925 x 68.1
		Raise apogee
1974 Mar 17	0921		128.30 140 x 3956 x 68.1
		Raise apogee
1974 Mar 19	0202		129.50 143 x 4058 x 68.1
		Raise apogee
1974 Mar 19	1710		130.35 144 x 4131 x 68.1
1974 Mar 26	1818		129.78 143 x 4082 x 68.1
		Raise apogee
1974 Mar 28	0502		130.19 145 x 4116 x 68.1
1974 Apr 9	0021		128.28 144 x 4037 x 68.1
		Raise apogee
	1526		129.74 146 x 4076 x 68.1
1974 Apr 15	0519		129.36 146 x 4042 x 68.1
		Lower perigee
	1815		129.14 129 x 4040 x 68.1
1974 May 1	1915		126.10 130 x 3772 x 68.1
1974 Jun 3	0532		120.27 128 x 3257 x 68.1
		Raise perigee
	2335		120.22 134 x 3247 x 68.1
1974 Jun 4	1336		120.15 134 x 3240 x 68.1
		Raise perigee
1974 Jun 5	2137		119.97 138 x 3221 x 68.1
1974 Jun 12	1502		119.09 135 x 3144 x 68.1
		Raise perigee
1974 Jun 12	1701		119.13 142 x 3142 x 68.1
1974 Jun 14	1638		119.24 145 x 3147 x 68.1
1974 Jun 19	2138		118.82 145 x 3110 x 68.1
		Raise apogee
1974 Jun 20	0736		119.26 147 x 3147 x 68.1
1974 Jun 27	0022		118.93 148 x 3117 x 68.1
		Raise apogee
1974 Jun 28	0010		119.16 148 x 3137 x 68.1
1974 Jul 10	2238		118.03 145 x 3039 x 68.1
		Lower perigee
1974 Jul 11	0036		117.94 136 x 3040 x 68.1
		Adjust perigee
1974 Jul 13	0537		117.65 139 x 3011 x 68.1
1974 Aug 2	0223		114.75 136 x 2751 x 68.1
1974 Aug 22	2339		111.33 139 x 2436 x 68.1
		Lower perigee
1974 Aug 23	0705		110.58 131 x 2375 x 68.1
1974 Aug 29	0322		110.19 137 x 2334 x 68.1
		Lower perigee
1974 Aug 31	1022		109.78 131 x 2301 x 68.1
1974 Sep 7	0418		108.47 138 x 2173 x 68.1
		Lower perigee
1974 Sep 9	1215		108.01 130 x 2139 x 68.1
1974 Sep 10	0238		107.88 130 x 2126 x 68.1
1974 Sep 11	0535		107.63 133 x 2100 x 68.1
1974 Sep 12	1538		107.35 129 x 2078 x 68.1
1974 Sep 28	0445		103.81 128 x 1749 x 68.0
		Lower perigee
1974 Oct 5	1201		102.36 124 x 1616 x 68.0
1974 Oct 11	1217		101.22 123 x 1509 x 68.0
1974 Oct 12	0806		100.96 126 x 1481 x 68.0
		Raise orbit
1974 Oct 12	1013		101.22 132 x 1500 x 68.0
		Lower perigee
1974 Oct 13	0806		100.96 126 x 1481 x 68.0
1974 Oct 17	2231		99.83 123 x 1376 x 68.0
		Lower perigee
1974 Oct 18	2007		99.57 118 x 1357 x 68.0
1974 Oct 31	1844		96.61 119 x 1073 x 68.0
1974 Nov 1	0600		96.51 116 x 1066 x 68.0
1974 Nov 12	2129		93.80 121 x 799 x 68.0
1974 Nov 26	2247		91.00 122 x 525 x 68.0
1974 Nov 27	0926		91.09 130 x 525 x 68.0
1974 Nov 30	1012		90.76 135 x 488 x 68.0
1974 Dec 9	0315		89.64 134 x 378 x 68.0
1974 Dec 10	0308		89.49 133 x 364 x 68.0
		Raise perigee
1974 Dec 13	0243		89.21 142 x 328 x 68.0
1974 Dec 15	0216		89.06 147 x 308 x 68.0
1974 Dec 16	1352		88.87 147 x 289 x 68.0
		Raise perigee
1974 Dec 17	1931		89.16 183 x 281 x 68.0
		Raise perigee
1974 Dec 18	1919		89.49 219 x 278 x 68.0
		Raise perigee
1974 Dec 19	1443		89.89 259 x 279 x 68.0
1975 Jan 1	0640		89.74 251 x 272 x 68.0
1975 Jan 30	1304		89.01 218 x 232 x 68.0
		Raise orbit
1975 Feb 1	0215		89.33 229 x 252 x 68.0
1975 Feb 12	0852		89.03 220 x 232 x 68.0
		Raise orbit
1975 Feb 14	0225		89.11 222 x 239 x 68.0
		Raise orbit
1975 Feb 16	0925		89.19 227 x 240 x 68.0
1975 Feb 26	0527		88.89 213 x 225 x 68.0
		Raise orbit
1975 Feb 26	2315		89.13 217 x 245 x 68.0
		Raise orbit
1975 Feb 27	1835		89.33 235 x 247 x 68.0
1975 Mar 14	1809		88.85 211 x 224 x 68.0
		Raise orbit
1975 Mar 18	0522		89.25 228 x 246 x 68.0
1975 Apr 8	1114		88.41 190 x 201 x 68.0
		Raise orbit
1975 Apr 10	1158		88.74 198 x 226 x 68.0
1975 Apr 11	1009		88.67 196 x 220 x 68.0
		Raise orbit
1975 Apr 12	1251		89.01 220 x 231 x 68.0
1975 Apr 22	1540		88.56 197 x 209 x 68.0
		Raise orbit
1975 Apr 24	0747		89.34 231 x 252 x 68.0
		Raise orbit
1975 Apr 27	0744		90.14 264 x 298 x 68.0
1975 May 15	0811		90.01 258 x 290 x 68.0
1975 Jun 2			89.64 236 x 276 x 68.0
1975 Jun 8	0223		89.57 233 x 272 x 68.0
		Raise orbit
1975 Jun 14	0538		90.66 302 x 311 x 68.0
1975 Jul 6	0155		90.61 299 x 308 x 68.0
1975 Sep 18	2354		90.31 285 x 293 x 68.0
		Raise orbit
1975 Sep 19	0558		90.53 291 x 309 x 68.0
		Raise orbit
1975 Sep 20	1341		90.68 303 x 311 x 68.0
1975 Sep 23		Deactivated
1975 Dec 7	1644		90.24 283 x 288 x 68.0
		Raise orbit
1975 Dec 11	2142		90.76 305 x 317 x 68.0
1976 Feb 20		Reactivated
1976 Mar 8	1119		90.48 293 x 302 x 68.0
		Lower perigee
1976 Mar 9	2200		90.26 267 x 306 x 68.0
		Lower orbit
1976 Mar 11	2038		90.05 254 x 299 x 68.0
1976 Apr 20	1121		89.52 238 x 262 x 68.0
		Raise orbit
1976 Apr 21	2140		89.85 261 x 273 x 68.0
1976 Apr 26	0929		89.80 259 x 269 x 68.0
		Raise orbit
1976 Apr 26	2129		90.17 278 x 287 x 68.0
		Raise orbit
1976 Apr 30	0652		90.50 293 x 304 x 68.0
1976 Jul 15	0952		90.20 280 x 288 x 68.0
		Raise orbit
1976 Jul 23	1055		90.49 292 x 304 x 68.0
1976 Sep 28	0729		90.22 279 x 291 x 68.0
		Raise orbit
1976 Sep 29	1504		90.43 280 x 301 x 68.0
1977 Jan 1	1054		89.69 256 x 261 x 68.0
1977 Jan 22	1257		89.40 239 x 249 x 68.0
		Raise orbit
1977 Jan 26	0155		89.68 257 x 260 x 68.0
1977 Feb 8	0930		89.46 246 x 248 x 68.0
		Begin orbit raising burns
1977 Feb 10	0804		90.71 295 x 322 x 68.0
	2311		91.34 320 x 359 x 68.0
1977 Feb 11	2333		91.46 328 x 364 x 68.0
1977 Feb 14	0153		91.46 328 x 363 x 68.0
1977 Feb 15	0234		91.58 331 x 372 x 68.0
1977 Feb 17	1822		91.83 355 x 372 x 68.0
1977 Feb 24	1236		91.80 356 x 369 x 68.0
1977 Mar 1	1958		92.31 383 x 391 x 68.0
1977 Mar 12	0953		92.35 387 x 391 x 68.0
1977 Mar 18		Last orbital adjust?
		Orbit raising complete
1977 Aug 2	0126		92.24 383 x 385 x 68.0
1978 Feb 6	0901		91.96 366 x 374 x 68.0
1978 Mar 16	0701		91.82 361 x 366 x 68.0
1978 Mar 23	1805		81.80 359 x 365 x 68.0
1978 Aug 30	1900		91.01 320 x 327 x 68.0
1978 Nov 27	2013		89.27 238 x 238 x 68.0
1978 Dec 10	1022		88.02 175 x 177 x 67.9
1978 Dec 11		End of transmissions
1978 Dec 12		Reentered

Payload:

• CEP Cylindrical Electrostatic Probe (GSFC/Brace)

• MESA Accelerometer (AFCRL/Champion)

• PES Photoelectric Spectrometer (APL/Doering)

• RPA Retarding Potential Analyser (UTD/Hanson)

• ESUM Extreme Solar UV Monitor (GSFC/Heath), 40-1220A

• EUVS Extreme Solar UV spectrometer (AFCRL/Hinteregger), 140-1850A, 24 monochromators

• OSS Open Source Neutral Mass Spectrometer (UMn/Nier)

• NACE Neutral Atmosphere Composition Experiment (GSFC/UM/Nace)

• NATE Neutral Atmosphere Temperature Experiment (GSFC/UM/Spencer)

• MIMS Magnetic Ion Mass Spectrometer (UTD/Hoffman-J)

• BIMS Bennett Ion Mass Spectrometer (GSFC/Brinton)

• LEE Low Energy Electrons (GSFC/NOAA/Hoffman-R)

• UVNO UV Nitric Oxide Experiment (Colorado/Barth)

• VAE Visible Airglow Experiment (UM/Hays)