How Did Apollo 11 Return to Earth?

After 21 hours on the Moon, Armstrong and Aldrin returned to their lunar module, known as Eagle. They disconnected it from the command module that would remain orbiting above, before undocking Eagle from Eagle itself and dismounting from it.

Armstrong made history when he took “one small step for man, one giant leap for mankind”. But astronauts weren’t done yet.

The Ascent Module

The Lunar Module’s ascent stage engine kicks on when astronauts are ready to return home from the Moon and use liquid hydrogen and oxygen fuel cells to generate 33 million newtons of thrust.

The ascent stage also houses LM’s electrical power system. Seven silver-zinc batteries supply operating current to its EPS DC section, which in turn powers several subsystems that manage electrical commands from its command module. Other batteries supply power for explosive device activation or operate portable life support systems.

On the lunar surface, crew spend anywhere between one and three days, performing one EVA per day. While on the Moon’s surface, LM remains docked to CSM which circumnavigates every two hours; when astronauts return, the ascent stage jettisons LM’s descent stage and they rejoin both modules in lunar orbit for docking back together again.

Armstrong and Aldrin were prepared to exit the LM after several days of quarantine, having sealed up their spacesuits and venting all of the air out through a series of handles. Finally they crawled out through the hatch feet-first down the ladder to Earth – only for 21 days more would Earth not appear again!

Once again, astronauts re-entered their spacecraft, which now had to burn its fuel for their return journey home. To do this, they fired the LM’s ascent engine using its descent stage as launch pad – burning for only seven minutes to reach lunar orbit and meet with CSM in rendezvous orbit.

The CM then separated from the LM, which was reconfigured into heat shield-forward position to parachute through Earth’s atmosphere and land safely. Although its decompressant was intended to decompress into the ocean, its RTG reactor (a tube of Plutonium) did not survive reentry and broke apart upon impact – any remnants that reached ocean floor were likely headed towards Marianas Trench, an unbearably deep canyon in Pacific Ocean.

The Service Module

The Service Module (SM) of Apollo spacecraft orbited above Earth. It contained instruments for providing astronauts with power, video data processing and transmission as well as relaying commands and information from and to Lunar Module. As part of its function, CSM also contained the lunar landing spacecraft adapter used to dock with Lunar Module (LM). Once separated from CSM, once LM separated it would align its drogue mechanism on top with probe inside SM to be captured by 12 automatic latches for docking with Lunar Module. From there, the drogue could be directed by reaction control engines until it would engage with the CSM’s drogue port and engage it for deployment. After short course corrections from RCE systems, CSM could slowly rise to dock with LM.

SM was constructed with aerodynamically efficient attachment ports designed to safely break apart upon reentry into Earth’s atmosphere, enabling it to safely reenter without colliding with or ruining reentry of Command Module.

Once the LM had successfully landed on the moon and Armstrong and Aldrin had boarded it, they would use its adapter to connect to an orbiter waiting in space and return home using it as their only means.

Starting from behind the Moon, Mission Control carefully orchestrated a two-and-a-half minute burn from the SPS engine that sent LM on its journey homeward. Mission Control had no way of knowing whether or not their SPS engine had worked until they received confirmation via signal from LM’s telemetry data that all had gone smoothly.

The Lunar Module never returned intact to Earth; however, some portions may have survived reentry without being consumed by atmospheric pressure and burned up by fireballs. Only two parts – Command Module (which housed crew) and Lunar Module itself – actually made it back. The rest of its rocket assembly counterpart – part of which the LM was composed – was scattered throughout space.

The Command Module

The Command Module was the vessel used to transport astronauts back home after landing on the moon, constructed at North American Aviation in Downey, California. North American Aviation had just received their contract for the Apollo program months prior to launch and were quickly hiring engineers and technicians from around the country – one being Chuck Lowry who moved with his family from Ohio to Downey – a former farmland that had become a hub of space technology by then.

Lowry was an expert in parachutes, which would be used to slow the command module’s descent upon reentry. He was also an excellent quality tester; making sure all its parts would function harmoniously if successful mission completion depended on it.

As soon as the Lunar Module (LM) docked with the Command Module (CM), Commander Neil Armstrong and Lunar Module Pilot Edwin “Buzz” Aldrin emerged to take their historic first steps onto the Moon in Eagle. Their tanks still contained about 30 seconds of fuel when they took those historic first steps upon our moon!

After landing, when the Command Module and Service Module separated they performed a series of thrust maneuvers to alter their flight paths in order to prevent the Lunar Module (LM) from accidentally reentering Earth’s atmosphere as it passed over lunar surface.

Risky as it was, the crew knew this decision would be their best bet. Although it would add 215 miles to their flight path, they believed it to be preferable than risking crashing in the Pacific Ocean during a severe thunderstorm.

On July 20, Armstrong and Buzz Aldrin launched their LM’s descent engine and dropped them into an orbit approximately 114 by 116 miles – almost exactly paralleling what they had practiced during Apollo 10’s dress rehearsal two months earlier. Later, as they entered final descent toward Moon surface, they fired it again as part of their final descent plan; soon thereafter they had successfully touched down there within hours.

The Lunar Module

Armstrong and Aldrin would typically spend about two-and-a-half hours conducting experiments and collecting photos and samples of the lunar surface during each landing mission. Once their work was complete, they returned to the Lunar Module (LM) for their return home.

Before their return to Earth, the Lunar Module and Command/Service Module (CSM) met up. Astronauts utilized the CSM for travel between Earth and the Moon; its structure prevented it from flying alone through atmospheric pressure; so its Lunar Module was attached to CSM for transportation into lunar orbit.

As it traveled toward the Moon, the LM was fuelled with liquid oxygen and hydrogen fueling its main rocket engine and also providing atmospheric reentry power. The engine fired for 756.3 seconds while traveling roughly 300 miles uprange from lunar surface – during this period its landing radar detected waves reflected off lunar surface that bounced back toward it; its computer then calculated how close to surface LM was and adjusted its landing trajectory accordingly.

Once they had arrived on Earth, astronauts lived inside the LM for approximately three days after landing, eating, sleeping and accomplishing mission objectives as planned. Progress reports were often provided using instruments similar to what sailors used centuries earlier — such as telescopes and sextants.

LM was comprised of two sections: an upper ascent stage and lower descent stage. The ascent stage housed the crew compartment, system displays and controls, S-band antennae, radar antennae and reaction control system while the descent stage stored equipment used by astronauts for surface exploration along with a descent rocket engine and fuel/oxidizer tanks.

As it came time for their return journey, astronauts prepared their LM for ascent by disposing of its descent stage and using it as a launchpad to place it into orbit around the moon. Finally, docking occurred between it and CSM before being returned back home with astronauts aboard.