Mercury-Atlas 4
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The launch of Mercury-Atlas 4
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| Mission type | Test flight |
|---|---|
| Operator | NASA |
| Harvard designation | 1961 Alpha Alpha 1 |
| SATCAT no. | 183 |
| Mission duration | 1 hour, 49 minutes, 20 seconds |
| Distance travelled | 41,919 kilometers (26,047 mi) |
| Orbits completed | 1 |
| Spacecraft properties | |
| Spacecraft | Mercury No.8 |
| Manufacturer | McDonnell Aircraft |
| Launch mass | 1,224.7 kilograms (2,700 lb) |
| Start of mission | |
| Launch date | September 13, 1961, 14:04:16 UTC |
| Rocket | Atlas LV-3B 88-D |
| Launch site | Cape Canaveral LC-14 |
| End of mission | |
| Landing date | September 13, 1961, 15:53:36 UTC |
| Orbital parameters | |
| Reference system | Geocentric |
| Regime | Low Earth |
| Perigee | 149 kilometers (80 nmi) |
| Apogee | 240 kilometers (130 nmi) |
| Inclination | 32.5 degrees |
| Period | 88.38 minutes |
| Epoch | September 13, 1961 |
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Project Mercury
Mercury-Atlas series |
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Mercury-Atlas 4 was an unmanned spaceflight of the Mercury program. It was launched on September 13, 1961 at 14:09 UTC from Launch Complex 14 at Cape Canaveral, Florida. A Crewman Simulator instrument package was aboard. The craft orbited the Earth once.
At this time, NASA was getting increasingly frustrated with the Atlas's poor launch record. Of four Mercury-Atlas flights so far, two (MA-1 and MA-3) had been total failures. One (Big Joe) had been a partial success and the otherwise completely successful MA-2 had experienced propellant slosh problems. In addition, the Atlas had not performed well in unmanned programs either as three Atlas-Able lunar probe launches in 1959–60 had all failed. The Air Force was also experiencing problems with military launches as a MIDAS early warning satellite and a SAMOS photoreconnaissance satellite launched with Atlas‑Agenas both failed to orbit during 1960. Only a few days before the flight of MA‑4 in September 1961, an Atlas‑Agena carrying a SAMOS satellite fell back on the launch pad at Vandenberg AFB, producing a spectacular explosion. Atlas ICBM tests at this time were still routinely failing as well.
These incidents produced a series of confrontations between NASA and Convair, the builders of the Atlas. As August 1961 ended, there had been 14 Atlas space launches (SCORE, Big Joe, the three Atlas-Able flights, Midas 1-3, Samos 1-2, Mercury-Atlas 1, Mercury-Atlas 2, Mercury-Atlas 3, and Ranger 1). Of these, eight were total losses and one had been a partial failure, yielding a 30% success rate. Convair argued that many of the failed Atlas space launches were due to faults of the upper stages or payload rather than the Atlas itself and on this point were correct. Only Big Joe and MA-3 could be directly blamed on a malfunction of the Atlas and the former's problems still did not preclude the mission from carrying out most of its goals. In any case, Atlas was hardly alone in reliability issues; the other workhorse of the US space program, Thor, had a launch record that was scarcely better.
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