Now boarding' … 240,000 miles from Earth, at the moon's first airport — Phys.org

RESOLVING THE LEDGER

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Add as preferred source The moon's getting its first airport, and it's about to get busy. Within the next two decades, NASA's planned Gateway —humanity's first lunar spaceport—may become a bustling hub for Orion crew capsules, lunar landers, cargo vehicles and astronauts traveling between Earth, the moon and, eventually, destinations in the deep unknown.

But this airport won't have concrete runways crowded with airplanes, flashing taxiway lights or a crackling voice over an intercom announcing, "Your gate has changed." Instead, Gateway will operate along an invisible highway, where traffic patterns are written in elegant mathematical rules that trace the gravitational crossroads of Earth, the moon and deep space.

Someone has to direct the traffic, and that's where celestial air traffic control comes in.

A team of engineers from Texas A&M University, NASA's Johnson Space Center and Purdue University developed algorithms and operational strategies to manage spacecraft loitering scenarios and orbital traffic operations around Gateway.

In other words, the researchers lay out the mathematical flight manual and orbital "rules of the road" for multiple spacecraft to safely share one of the most challenging environments ever considered for human exploration—giving future missions a safer, more predictable traffic system around the moon.

Their findings, published in Acta Astronautica , balance fuel efficiency and operational demands while reducing the risk of spacecraft colliding during space missions.

"The future of lunar exploration depends as much on the traffic management as it does on the rocket science," said Dr. Diane Davis, associate professor of space engineering at the Texas A&M University College of Engineering, and an author of the study.

Building a lasting human presence around the moon won't simply depend on getting there first; it will depend on creating the infrastructure that allows spacecraft to safely share the same invisible highway carved by gravity itself.

For Gateway and visiting spacecraft, that celestial highway is called a near-rectilinear halo orbit, or NRHO.

"The Gateway NRHO is a nearly stable and highly elongated orbit around the moon that provides an uninterrupted line of sight for communications to Earth and requires little propellant to maintain," Davis said.

The catch? Gateway and space vehicles traveling along this egg-shaped orbit will be locked into a relentless gravitational tug-of-war, following the shifting pulls of Earth and the moon.

And the orbit itself is unlike anything humans have used for crewed spacecraft before, swooping within 1,000 miles (1,600 kilometers) of the moon's north pole before swinging back out again nearly 40,000 miles (64,000 kilometers) beyond its south pole.

For a single space station, occasional thruster burns are enough to stay on course. But when you add an arriving Orion crew capsule, an uncrewed cargo ship and a massive lunar lander all trying to dock or park in the same neighborhood, the challenge is making sure everyone and everything stays safely out of each other's way.

"Collisions and serious damage could happen. To ensure crew safety and mission success, effective traffic management in the NRHO is crucial," Davis said.

Effective traffic management boils down to a deceptively simple concept: loitering, or the careful choreography of spacecraft positioning.

"Loitering in space means maintaining a spacecraft relative to a specific orbit or trajectory without executing an immediate maneuver," Davis said.

Think about it like a busy airport. Some airplanes sit at the gate, others hold on the taxiway and some circle overhead waiting for clearance.

Around Gateway, the idea is similar. Before docking or departing, space vehicles may need to wait hours, days or even weeks until a port becomes available or another mission is complete.

The difference is that there is no tarmac, nothing stays still, and the stakes are far higher.

"Every spacecraft is constantly moving," Davis said. "It's a Goldilocks zone of keeping 'parked' vehicles far enough from each other to be safe, but close enough to their destination so that resources are used efficiently."

Finding that sweet spot is at the heart of the team's study.

Using thousands of computer simulations, the researchers tested strategies for keeping vehicles carefully spaced around Gateway while accounting for realistic navigation errors, thruster imperfections and even small disturbances expected during future Artemis missions.

They found that modest increases in station-keeping maneuvers allowed spacecraft to stay significantly closer to their intended positions, requiring only small changes in propellant use.

"Greater positional accuracy means mission planners can better predict where every spacecraft will be, preserving valuable fuel," Davis said.

That predictability makes docking schedules easier to coordinate, rendezvous operations easier to plan and crewed and robotic missions safer.

"Every maneuver has a cost," Davis said. "Just like air traffic control on Earth, spacecraft need predictable positions and paths to safely coordinate their movements."

Predictability also makes the intricate choreography of arriving and departing spacecraft far easier to manage.

So, rather than wandering independently, visiting spacecraft would loiter at carefully calculated intervals behind or ahead of Gateway until it's their turn to dock or depart, lining up in what the researchers describe as a "string of pearls" formation.

"Similar to the arrangement of pearls on a string necklace, spacecraft would arrange themselves naturally along the lunar orbit and relative to Gateway," Davis said. "Maintaining the loitering vehicle relative to Gatewa...

Now boarding' … 240,000 miles from Earth, at the moon's first airport — Phys.org | AIPROPX