Apollo 5 was the first unmanned flight of the Apollo Lunar Module, which would later carry astronauts to the lunar surface. It lifted off on January 22, 1968.Objectives
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.
Flight
Lunar Module 1 during ground testing
Apollo 5's Saturn IB on the launchpadThe 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. The Saturn IB AS-204 that was used on Apollo 5 was the one originally intended for Apollo 1. It had been undamaged in the fire at Launch Complex 34 and was reassembled at Launch Complex 37B for the Apollo 5 launch.
The windows of LM-1 were replaced before the flight with solid aluminum plates. To shorten delivery time for the Lunar Module, it was decided to do without the module's legs. Without a crew or even a CSM, there was no need for the launch escape system. As a consequence the assembled rocket was only 55 meters tall.
On January 22, 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 pressurized, 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 fall into the Pacific several hundred kilometers southwest of Guam on February 12.
The Apollo 5 LM ascent stage (1968-007A) decayed January 24, 1968. The LM descent stage (1968-007B) decayed February 12, 1968.
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