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1968: Apollo 5 (NASA)

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Published on Apr 25, 2008

The Apollo 5 mission was intended to test the Lunar Module in a space environment, in particular its descent and ascent engine systems, and its ability to separate the ascent and descent stages. The descent engine would become the first throttleable rocket engine fired in space.

The mission was also intended to perform a "fire in the hole" test - as depicted in the mission's insignia - whereby the engine of the ascent stage would be fired whilst still attached to the descent stage. This would simulate the conditions experienced in an abort during descent to the lunar surface.

It had been planned to launch Apollo 5 in April 1967 and so delivery at the Cape was hoped for around September 1966. But delays kept occurring. Although the lunar module was fully designed, there was trouble fabricating the custom made parts. The all important engines were also having problems. The descent engine was not burning smoothly and the ascent engine was having fabrication and welding difficulties.

The launch vehicle for Apollo 5 was the Saturn IB, a smaller rocket than the Saturn V but capable of launching an Apollo spacecraft into Earth orbit.

On 22 January 1968, eight months after the planned launch date, Apollo 5 lifted off just before sunset. The Saturn IB worked perfectly, inserting the second stage and LM into a 163 x 222 km orbit. The Lunar Module separated 45 minutes later, and after two orbits started a planned 39 second burn of its descent engine. This was curtailed after four seconds by the onboard guidance computer, which detected that the engine's thrust was not building up rapidly enough. This was due to a software bug; the propellant tanks were only partially pressurised, and it took longer than the programmed four seconds to reach full acceleration.

The ground controllers moved to an alternate plan. They turned off the guidance computer and started an automatic sequence programmed into the onboard computer. This fired the descent engine two more times. It then performed the "fire in the hole" test and another ascent engine burn.

After four orbits the mission was over, and the two stages were left to decay into the Pacific several hundred kilometres southwest of Guam on 12 February.

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