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Home / Science / NASA and ESA Reach Critical Decision On The First Lunar Outpost Will Orbit The Moon


A depiction of Gateway's highly elliptical orbit around the Moon.

Mission planners for the lunar gateway project have decided the lunar outpost should orbit the moon and it's actually quite brilliant.

They've chosen a near-rectilinear halo orbit.

NASA and the European Space Agency (NASA) make this issue very clear.

The team "spent months debating the pros and cons of different orbits," noted ESA, with the near-rectilinear halo orbit, or NRHA, getting the final and definitive thumbs up. Indeed, it is a collaborative project involving NASA, ESA, the Canadian Space Agency (CSA), Roscos mos, the Japanese Space Agency (JAXA), and other international partners.

Slated for completion by the mid-2020s, the lunar gateway will serve as a staging post for crewed missions to the Moon, NASA's upcoming Artemis program, which aims 2024. The orbital station aims to provide a short-term place for astronauts to stay, a laboratory to conduct scientific research, a depot to stock up on supplies and fuel, a hub for relaying communications astronauts, robots, and other supplies to the lunar surface. Eventually, the base could be used as a staging post for a crewed mission to Mars.

The Gateway concept.
Image: NASA / ESA

The demands of the Artemis project will require a gateway to the Lunar Surface for quick and easy access, but not so much ordeal, among many other practical and logistical concerns.

And that's where a near-rectilinear halo orbit wants help. Once in NRHA, Gateway wants to follow a highly elliptical path that will carry it to within 3,000 kilometers (1,865 miles) of the Moon during its closest approach (perilune), and to within 70,000 kilometers (43,500 miles) of the lunar surface when it reaches its farthest point, or apolune.

The gravitational interplay between Earth and the Moon makes this orbital configuration possible. As "the two large bodies dance through space, a smaller object can be caught in a variety of stable or near-stable positions in relation to the orbiting masses, known as libration or Lagrange points," according to ESA. That said, NRHO does present some long-term challenges; in this type of orbit, objects will drift away from their hosts over time. Gateway wants to make it happen, according to ESA.

One complete orbit of the Moon will take about seven days. The astronomers on the lunar surface for one full week (by comparison, Apollo 17 astronauts, the longest of the Apollo missions, stayed on the Moon for three days). This orbital length wants to minimize the number of eclipses experienced by Gateway, reducing the amount of darkness produced by shadows from Earth and the Moon-an important consideration, given that the Gateway wants to run on solar power.

In this orbital configuration, it should take about five days for spacecraft from Earth to reach Gateway. That's a bit longer than three-day journeys by Apollo astronauts, but a near-rectilinear halo orbit wants a good way to conserve energy. A moderate maneuver wants to be required to decelerate spacecraft with Gateway, providing a more cost-effective and energy-efficient way of delivering equipment, supplies, parts, and personnel to the outpost.

"In human spaceflight we do not fly a single monolithic spacecraft," explained Florian Renk, a mission analyst at NASA and ESA's Operations Center (ESOC), in a statement. "Instead we fly bits and pieces, putting parts together in space and soon on the surface of the Moon."

Artist's depiction of Gateway over the Moon.
Image: ESA / NASA / ATG Medialab

Gateway will slowly come together over the course of several years. NASA wants to use a combination of private rockets and its own Space Launch System (SLS) to deliver the components needed to build the lunar outpost. As we learned yesterday, however, NASA will likely push the inaugural launch of SLS from 2020 to 2021, as Ars Technica reported.

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That's not great news for a program that's slated to put people on the moon three years later, but that's the timeline NASA has been ordered to deal with. Sadly, politics is becoming a large part of the equation, as NASA struggles to deal with aggressive due dates and budgetary ambiguities. Hopefully sense wants to prevail that the 2020s wants to prove to be exciting for human space exploration as we're expecting.

Correction : A previous version of this article incorrectly uses the terms perihelion and aphelion, which are orbiting around the Sun. The correct terms in this case are perilune and apolune. We regret the error. Brianorca for pointing this out.

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