How to Travel to the Moon

Plan for each phase of the mission. Unlike the straightforward space missions often depicted in science fiction, traveling to the Moon is a complex process divided into several stages: reaching Earth's low orbit, transitioning to the Moon's orbit, landing on the Moon, and then reversing these steps to return to Earth.

• Some science fiction stories offer a more realistic depiction, where astronauts first travel to an Earth-orbiting space station, from which smaller rockets take them to the Moon and back to the station. However, given the competition between the United States and the Soviet Union, this approach was not feasible. The Skylab, Salyut, and International Space Station were all decommissioned after the Apollo program ended.
• The Apollo program used the three-stage Saturn V rocket. The first stage lifted the spacecraft to an altitude of 68 km; the second stage placed the rocket in Earth's orbit; and the third stage pushed the spacecraft toward the Moon.
• NASA's Constellation program aimed to return astronauts to the Moon by 2018. It involved two different three-stage rockets. The first stage included Ares I, a crew-only rocket with a five-part launch vehicle, and Ares V, a larger version designed to carry both astronauts and equipment, featuring five rocket engines under a single fuel tank along with two additional solid-fuel boosters. The second stage for both designs used a single liquid-fueled engine. This launch system would carry both the Moon orbiting module and the lunar lander, which astronauts would use once the two rockets docked in space.

Prepare for the journey. Since the Moon lacks an atmosphere, you will need to bring an oxygen tank to breathe. While walking on the Moon, you'll also require a spacesuit to shield your body from the intense heat of a lunar day, which lasts around two weeks. In addition to this, you'll face radiation exposure and the risk of small meteoroids hitting the Moon due to the lack of atmospheric protection.

• You will also need food. Most space mission food is freeze-dried and concentrated to reduce weight and will require water to rehydrate before consumption. These foods must be high in protein to minimize waste from digestion.
• Anything you bring into space adds to the weight, which in turn increases the fuel required to launch the rocket. This means you can't carry too many personal items on the mission. Also, remember that rocks collected on the Moon will weigh six times more when they return to Earth than they did on the lunar surface.

Determine the spacecraft launch timing. This is the time frame from when the rocket is launched from Earth until it lands on the Moon in an area that has sufficient sunlight for exploration. The timing of the launch is determined in two ways: by month and by day.

• The month-based timing calculates the landing site's position on the Moon relative to Earth and the Sun. Because Earth's gravity forces the Moon to always show one side toward Earth, Moon landings typically occur on the side facing Earth to facilitate radio communications between the Moon and Earth. Launches are also timed to occur when the landing area on the Moon is illuminated by the Sun.
• Day-based timing takes into account factors such as the spacecraft's launch angle, the efficiency of the rocket boosters, and the presence of tracking stations at the launch site. In the past, daylight conditions for launches were crucial, as daylight helped monitor any issues during rocket takeoff or before the spacecraft entered orbit, while also enabling photographic documentation. However, with NASA’s increased experience in tracking spacecraft launches, the need for daylight launches has diminished. For example, Apollo 17 was launched at night.

Lift-off. Ideally, a lunar exploration vehicle would be launched vertically, taking advantage of Earth's rotation to reach orbital velocity. However, during the Apollo program, NASA allowed for a deviation of up to 18 degrees from the vertical, which did not significantly affect the launch process.

Achieve Low Earth Orbit. To escape Earth's gravity, two types of velocities need to be considered: escape velocity and orbital velocity. Escape velocity is the speed required to completely overcome Earth's gravitational pull, while orbital velocity is the speed needed to enter orbit around a planet. The escape velocity at Earth's surface is 40,248 km/h or 11.2 km/s. The orbital velocity from Earth's surface is about 7.9 km/s. The spacecraft will require more energy to reach escape velocity compared to the energy needed to achieve orbital velocity.

• Additionally, the further you travel from Earth’s surface, the lower the escape and orbital velocities become. Escape velocity is always 1.414 (the square root of 2) times greater than orbital velocity.

Move to the Moon's orbit. After entering Earth's low orbit and ensuring all spacecraft systems are functioning properly, it’s time to ignite the boosters and head toward the Moon.

• For the Apollo program, this was accomplished by firing the three-stage boosters one last time to propel the spacecraft toward the Moon. Along the way, the command/service module detached from the third stage, flipped around, and docked with the lunar module positioned atop the third stage.
• The Constellation program had a plan to send the crew and its command module into Earth’s orbit with the launch stage and lunar lander being carried into space by a cargo rocket. The launch stage would ignite the boosters to send the spacecraft toward the Moon.

Enter lunar orbit. Once the spacecraft enters the Moon's gravitational pull, the boosters are ignited to slow the spacecraft down and place it into orbit around the Moon.

Switch to the lunar lander. Both the Apollo and Constellation programs feature separate modules for orbiting and landing. Apollo’s command module required one of the three astronauts to remain in orbit while the other two descended to the Moon’s surface. The Constellation program’s orbiting module was designed to be fully automated, allowing all four astronauts the opportunity to descend to the lunar surface if they chose to do so.

Land on the Moon. Since the Moon has no atmosphere, rockets are needed to slow the lunar lander to around 160 km/h to ensure a safe landing and a smooth descent for the astronauts. Ideally, the landing area should be clear of large rocks and debris, which is why the Sea of Tranquility was chosen as the landing site for Apollo 11.

Explore. After landing on the Moon, it's time to explore. You can collect rocks and lunar dust to bring back to Earth for analysis. If you bring along a deployable lunar rover, as Apollo 15, 16, and 17 did, you can drive across the Moon's surface at speeds of up to 18 km/h. (However, you won't need to rev up the engine; the rover runs on batteries, and with no atmosphere on the Moon, you won’t hear the engine running.)

Pack up and head home. After completing the mission on the Moon, you will gather the samples and tools, board the lunar lander, and prepare to return to Earth.

• The Apollo lunar module was designed with two stages: the descent stage for landing on the Moon and the ascent stage for taking astronauts back to lunar orbit. The descent stage is left behind on the Moon (along with the lunar rover).

Dock with the command module. The Apollo command module and the Constellation orbital module were both designed to transport the crew from the Moon back to Earth. The items from the lunar lander are transferred to the command module, and the lunar lander is then separated to fall back onto the Moon.

Journey back to Earth. The primary engines on the Apollo and Constellation service modules are fired to escape the Moon's gravitational pull, and the spacecraft begins its trajectory toward Earth. Once entering Earth's gravity, the service module is ignited again to slow down the command module before being jettisoned.

Touchdown. The heat shield of the command module will deploy to protect the astronauts from the intense heat of re-entry. As the spacecraft enters the denser layers of Earth's atmosphere, parachutes will open to further slow the descent.

• In the Apollo program, the command module would splash down in the ocean, just like previous manned NASA missions, and be recovered by a Navy ship. The command modules were not reused.
• In the Constellation program, the plan was to land on solid ground, similar to Soviet manned space missions, with an alternate option to splash down in the ocean if land landing was not possible. The command module was designed for refurbishment, with the heat shield being replaced and reused.

• Private companies are gradually entering the lunar tourism industry. In addition to Richard Branson’s Virgin Galactic, which plans to offer suborbital spaceflights, a company called Space Adventures is in talks with Russia to send two tourists on a journey around the Moon aboard a Soyuz spacecraft piloted by an astronaut, with tickets priced at $100 million each.

• Note that most lunar missions require extensive testing of the equipment before launch. Before the Apollo 11 mission took Armstrong and Aldrin to the Moon, four crewed missions were conducted to test the command module (Apollo 7) and the lunar lander (Apollo 9 and 10), as well as the capability of transitioning from Earth to lunar orbit and back (Apollo 8 and 10). Astronauts also had to undergo regular physical fitness tests and receive training on how to operate the equipment. Additionally, three astronauts lost their lives in the Apollo 1 cabin fire.