Looking Ahead to the Lunar Gateway
No human being has set foot on the Moon since December 11th, 1972, when Apollo 17 last landed on our orbiting satellite. We've sent rovers, orbiters and landers since then, but no humans have made the 238,900-mile trip. That might change in the next few years, with NASA's Moon to Mars mission in full swing. When can we expect humans to reach the Moon again, and how will NASA stay in touch with the astronauts once they're there?
Moon to Mars
In 2017, President Donald Trump started to push us toward the Moon. In signing Space Policy Directive-1, he told NASA to return to its roots and start exploring again. The resulting Exploration Campaign has five goals:
- Transition U.S. human spaceflight activities in low-Earth orbit to commercial operations that support NASA and the needs of an emerging private sector market.
- Lead the emplacement of capabilities that support lunar surface operations and facilitate missions beyond cislunar space.
- Foster scientific discovery and characterization of lunar resources through a series of robotic missions.
- Return U.S. astronauts to the surface of the Moon for a sustained campaign of exploration and use.
- Demonstrate the capabilities required for human missions to Mars and other destinations.
The first stage of this mission requires private companies to increase their participation in low Earth orbit operations. SpaceX has already taken strong steps to accomplishing this goal, with the successful test flight of the Crew Dragon capsule early in 2019. NASA and U.S.-based companies aren't the only ones looking toward the Moon, however.
China's Chang'e Lander
In January 2019, China successfully put a lander and rover on the dark side of the Moon, something nobody has ever done.
In addition to its rover, the Chang'e lander also carried seeds and insect eggs to see if life could survive on the dark side of the Moon. Cotton seeds did sprout successfully, but they were unable to survive the brutally cold temperatures of the lunar night.
How are scientists able to communicate with a lander on the far side of the Moon?
Queqiao… and lots of testing.
Queqiao is a lunar relay satellite, and it's the first of its kind. It sits in an L2 halo orbit beyond the Moon. Messages from Chang'e are sent to the Queqiao relay then back to Earth. Because of its halo orbit, the satellite is always in range of the Chang'e lander but always has a clear line of sight to Earth.
This satellite, and others like it, undergo detailed testing on Earth before they ever make it into orbit. Each component of the satellite needs to function individually and with the entire machine before liftoff.
They're tested under simulated vacuum conditions, similar to those they'll experience in orbit to ensure they'll be able to survive the harsh conditions. Communications tests are also crucial for making sure the satellite can send and receive signals once it gets there. Satellites also undergo vibration testing to ensure they'll withstand the dramatic vibrations during launch.
Once in orbit, Queqiao went through more systems checks before the Chang’e launch. This process of “test, build, test, launch, test” before starting the mission is something all projects go through. One project currently in its early stages hopes to bring people back to the lunar surface.
NASA’s Gateway Station is still in its design phase, but when constructed, it could provide a permanent human presence in a lunar orbit as well as a quicker means of transportation and communication for astronauts and rovers on the ground.
The Orion Spacecraft, which had its first successful flight test in 2014, will likely carry astronauts to this station as early as 2024.
For the first time since 1972, humans will be going back to the Moon, but how will we be able to talk to them, especially if the Gateway's orbit carries it behind the Moon?
Right now, most communication to and from the Moon takes a few seconds. A radio signal from Earth will reach the Moon in 1.27 seconds, and take just as long to return. Most interstellar communication right now is carried on radio waves, and while it might still be used for non-mission-critical communications, it isn't fast enough if there is an emergency.
Laser communication, on the other hand, could beam data, photos, and video nearly instantaneously. NASA's Laser Communications Relay Demonstration, set to launch in 2019, will transmit data 10 to 100 times faster than today's fastest RF radios, because, as the space agency explains, "the wavelength of the laser light is orders of magnitude shorter than radio waves, meaning the energy is not spread out as much as it travels through space." With this satellite they plan to test transmissions encoding methods and improve tracking. In theory, it could even be used to receive and transmit data from Mars or even further out into the solar system.*
This system isn't without its problems, but since it is still in its testing and implementation phase, we've got plenty of time to sort them out. Cloud cover and smog could interfere with this form of communication, dispersing the lasers until the data is irretrievable. This may lead researchers to launch data buffers into orbit that can store the information until conditions are favorable to transmit it to the ground.
Becoming an Interstellar Species
NASA's Moon to Mars mission is a momentous step toward becoming an interstellar species. Communication will present a problem until laser relays or other similar technology become more readily available. As humans move out into the cosmos, quick and error-free communication won't just be valuable for science. In an emergency, it could mean the difference between life and death for the brave astronauts who choose to explore our solar system and beyond.
As it stands, we may become a two-planet species as soon as 2030. Plans are in place to hopefully have the Gateway Station in orbit around the Moon by 2024, and once that happens, we'll have a solid stepping stone for our journey to the stars.
*Section amended 4/10 to explain how laser communications can be faster than radio.