1958-001
Explorer I was launched on 1958 Feb 1 by a Jupiter C (Juno I) rocket from the Air Force Missile Test Center at Cape Canaveral. It reached orbit 7 min 8 sec after liftoff. Explorer I transmitted radiation data until Mar 15; the last transmission from the satellite was around Apr 1. Explorer I reentered on 1970 Mar 31.
The Redstone rocket separated 2 min after launch after burning out at an altitude of 100 km. It reached an apogee of 360 km and impacted 1400 km downrange. The upper stages fired roughly horizontally to increase payload speed; stage 2 impacted 2040 km downrange, stage 3 at 3092 km downrange.
The cluster gave slightly higher velocity than expected and the insertion angle was 0.9 deg higher than planned. Planned orbit was 352 x 1904 x 34.1 deg.
The satellite was 2.0m long and 0.15m in diameter. The rocket nozzle was 0.20 m long, the cylindrical rocket motor itself was 0.91 m long. The cylindrical part of the payload was 0.61m long, and the nosecone was 0.30 m long. Mass was 13.9 kg, with 5.7 kg for the rocket and 8.2 kg for the payload. The largest part of the payload was the SUI cosmic ray and micrometeorite experiment package, with the high power transmitter below it. Micrometeorite erosion gauges were carried on the aft part of the rocket motor casing, which also served as part of the low power antenna system. Temperature measurements were also transmitted.
The internal satellite temperature ranged from 0 to 35C, with the outer shell ranging from -25 to 75C. The cosmic ray count at perigee was about 30 to 40 events per second over California, but at apogee over the South Atlantic the count rate saturated at over 35000 counts per second - this was the discovery of the Earth's trapped radiation belts. The micrometeorite experiment indicated lots of hits, but these were probably spurious.
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| Explorer I |
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| Date | Time | Event | Orbit |
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| 1958 Feb 1 | 0347:56 | Launch by Juno I | CC |
| | 0350:32 | Redstone cutoff T+2:36 |
| | | T+2:42 Redstone sep, 105 km |
| | 0354:39 | Stage 2 burn T+6:43, 362 km | -5873 x 363 |
| | 0354:46 | Stage 2 cutoff T+6:50 | |
| | 0354:48 | Stage 3 burn T+6:52 |
| | 0354:54 | Stage 3 cutoff T+6:58 |
| | 0354:58 | Redstone apogee 364 km |
| | 0354:58 | Stage 4 burn T+7:02 |
| | 0355:04 | Stage 4 burnout T+7:08, 367 km | 359 x 2542 x 33.4 |
| 1958 Feb 13 | | High power transmitter failed |
| 1958 Mar 15 | | Last radiation data |
| 1958 Apr 1 | | End of transmissions |
| 1970 Mar 31 | | Reentry |
Payload:
- Cosmic ray package, Geiger counter
