The mode that Apollo would use to land on the moon was the most studied, analyzed, and debated decision made for the lunar landing program. There were four main choices Direct-ascent, Earth-Orbit Rendezvous, Lunar-Orbit Rendezvous, and Lunar Surface Rendezvous.
President Kennedy proposed the manned lunar landing as the focus of the US space program but, at the time of his address, only one American, Alan B. Shepard, Jr. had been into space, on a suborbital lob shot lasting 15 minutes. No rocket launch vehicle was available for a lunar voyage and there was no agreed upon method for placing any kind of spacecraft safely on the lunar surface and getting it back to the earth. Nor was there agreement within NASA itself on how it should be done.
Astronauts leave the spacecraft to investigate the lunar surface.
The return vehicle takes off from the moon.
The reentry vehicle begins to enter the atmosphere after jettisoning the propulsion unit.
The objectives of the Mercury Project, were as follows:
1. Place a manned spacecraft in orbital flight around the earth.
2. Investigate man’s performance capabilities and his ability to function in the environment of space.
3. Recover the man and the spacecraft safely.
After the objectives were established for the project, a number of guidelines were created to insure that the most expedient and safest approach for attainment of the objectives was followed. The basic guidelines that were established are as follows:
1. Existing technology and off-the-shelf equipment should be used wherever practical.
2. The simplest and most reliable approach to system design would be followed.
3. An existing launch vehicle would be employed to place the spacecraft into orbit. 4. A progressive and logical test program would be conducted.
“The designers made the Little Joe booster assembly to approximate the same performance that the Army’s Redstone booster would have with the capsule payload. But in addition to being flexible enough to perform a variety of missions, Little Joe could be made for about one-fifth the basic cost of the Redstone, would have much lower operating costs, and could be developed and delivered with much less time and effort. And, unlike the larger launch vehicles, Little Joe could be shot from the existing facilities at Wallops Island.”