Blog

08.28.2019

WHAT ARE CISLUNAR SPACE AND NEAR RECTILINEAR HALO ORBITS?

By: Mary Kathryn Fritz, Multimedia; Scott Tilley, Program Technical Director, Power and Propulsion Element; Ty Lee, Lead Systems Engineer, Power and Propulsion Element


Read Time: 4 minutes

Whether the world is celebrating the 50th anniversary of the lunar landing or looking forward to a return to the lunar surface with the NASA-led Gateway, there's a lot of focus on the moon these days. And that's a good thing, because, let's face it, going to the Moon is pretty exciting and is a necessary precursor to a human mission to Mars. We have a lot to learn along the way, and one place to start is with the orbit.

Artist’s concept of the NASA-led Gateway. Image: NASA

Maxar is a leader in designing and building communication satellites that reside in geosynchronous orbit (GEO) and imaging satellites that call Low Earth Orbit (LEO) home. But now it's time to take a look at a new neighborhood: Near Rectilinear Halo Orbit (NRHO).

The NRHO is a highly inclined orbit around the moon and is considered to be in cislunar space. Cislunar is Latin for "on this side of the moon" and generally refers to the volume between Earth and the moon. Cislunar space includes LEO, Medium Earth Orbit, GEO, as well as other orbits, such as Low Lunar Orbit and NRHO, the intended orbit for the Gateway.

The NRHO is a seven-day cycle, taking the Gateway as close as approximately 1,600 km (1,000 miles) and as far away as about 68,260 km (42,415 miles) from the lunar surface. Consequently, roughly every seven days, the lunar lander can depart the Gateway to travel to the lunar surface. Because the Gateway can sit in this halo orbit, almost like it’s held in place by the gravity of Earth and the moon, it requires little energy for stationkeeping or to maneuver into other cislunar orbits. The orbit is called a "halo" orbit because the tracked orbit looks like a halo around the moon.

The L2 family orbit (shown in green in the picture to the left) is the baseline orbit that the Gateway will use. The moon's south pole is the primary region of interest for initial future missions to the surface of the moon due to the presence of significant quantities of water ice in shaded craters. With a southern-oriented orbit, the spacecraft spends the vast majority of its time over the southern regions, allowing for more continuous communications with objects near the south pole, as well as allowing for the Gateway to act as a communications relay for the astronauts on the lunar surface to communicate with the Earth Mission Control. The Shackleton crater is in the southern region of the moon and is a strong candidate for future lander missions to the crater rim.

The Maxar-built Power and Propulsion Element of the Gateway, however, has the flexibility to maneuver between any of the orbits as the NASA mission changes. For example, if the lunar north pole becomes more attractive due to potential ice, minerals and science research, the orbit can be changed to make the north pole easily accessible. Maxar's highly efficient solar electric propulsion system allows multiple orbit changes because the amount of propellant used is minimal. Such an orbit change would be less feasible with a purely chemical propulsion system.

Moreover, learning how to leverage different orbits is critical to support a future human mission to Mars. Similar to early nautical explorers that had to learn how to use trade winds, we need to gain experience with using different orbits in cislunar space to carry America and all of humanity to the moon and Mars.

Back to Blog

Email Subscription