Avoiding traffic accidents on the way to the moon

Purdue engineers aim to protect upcoming lunar missions from space debris

WEST LAFAYETTE, Ind. – With dozens of missions headed to space between Earth and the moon over the next 10 years, there’s bound to be plenty of traffic.

To prevent those spacecraft from crashing into each other, Purdue University engineer Carolin Frueh is working on how to observe and track all man-made objects and predict the effects of potential damage. hidden in this Earth-moon neighborhood, known as the cislunar region.

According to Frueh, associate professor of aeronautics and astronautics at Purdue University, the reality is that the solutions for space traffic in the cislunar region will be moving targets. The methods she is developing are intended to adapt to this area as traffic changes.

“There really will never be a final answer to the problem of space traffic management because as the commercial sector evolves and the capabilities and types of vehicles you have change, so will the problems. follow,” she said. «So when we think about the techniques we want to use, we also have to make sure that what we have in mind can evolve over time.»

The economic potential of the cislunar space is estimated to be more than 30 billion dollars over a 20-year period, taking into account government investment, demand for space telecommunications services, and other factors.

At 238,900 miles, the distance between the Earth and the moon is 18 times longer than the Great Wall of China. That seems like enough room for spacecraft to move around without hitting each other, but the cislunar region is much less understood than near-Earth orbits, which extend 24,000 miles beyond Earth’s surface to a » «sweet spot» known as the geosynchronous region allows the satellites to catch up with the Earth’s rotation. The orbits near Earth are home to most of the satellites. Notable residents of that area include the Hubble Space Telescope and the International Space Station.

Even with more knowledge about near-Earth orbits, there’s still about 130 million space debris surrounding Earth. Much of this debris has broken off from exploding satellites or colliding with other objects. Debris reached the moon: A rogue booster crashed onto the lunar surface last March.

frueh-debrisThis animation shows man-made space objects cataloged by the US Space Force. The red objects are in near-Earth orbit. The green object is in the cislunar area. (Purdue University/Carolin Frueh image)

To address the incoming traffic in cislunar space, Frueh drew from his research on how spacecraft become debris. She works with space agencies around the world to improve databases of space objects.

Doing the same for cislunar space would be difficult if that much larger region could not be seen. For near-Earth orbits, telescopes in space, and to a limited extent, telescopes on Earth are among the «traffic cameras» for satellites. But there aren’t any telescopes in the cislunar area because there’s still not much satellite activity to observe. Space-based telescopes are better at tracking cislunar satellites when many of them reside in that area because ground-based telescopes can only detect one satellite of interest in cislunar space if the satellite, moon and Earth align exactly.

Together with his student, Surabhi Bhadauria, Frueh is developing a way to create a «visibility map» that will show the best areas that telescopes should use to find and track objects. man-made objects in cislunar space – including active satellites, dead satellites, and satellite debris.

Compared with other approaches, these maps better address a major challenge in cislunar area monitoring: the ever-changing space. The constantly moving positions of the Earth, moon, and sun affect what the telescope sees at any given time and what orbits it can use to see the spacecraft clearly. Current mapping methods have to rerun a model for each condition that will affect the telescope’s orbit and overall viewing geometry at each point in time, which requires a lot of computation.

map fruehThe «visibility map» could show where to place telescopes in cislunar space to improve detection and monitoring of man-made objects, helping to prevent satellite collisions. This visibility map considers all the limitations that will affect the orbits that telescopes should use to capture as many areas as possible over a 30-day period. The map shows areas of lower visibility (pink) and higher visibility (yellow) independent of the direction of view. (Purdue University/Surabhi Bhadauria and Carolin Frueh’s photo)

Frueh’s visibility maps run on models that show where the telescopes should go to see as much of the cislunar region as possible and faster. Maps allow more areas to be seen by averaging all the orbits that a telescope can use instead of integrating each orbital change over time like other mapping methods Must perform. Frueh’s method also does not require any additional computation time to indicate which satellites can be observed under what conditions from different positions.

«It’s like planning a road trip. Right now, we’ve identified interesting spots in the cislunar area for telescope observations, but we haven’t figured out a route to that yet. put the telescope there,» Frueh said.

Even if the telescopes do eventually get into the cislunar region, the satellites will likely look like white dots or streaks in the images these telescopes capture. But Frueh was used to gleaning meaningful information from these shapes in satellite images taken from telescopes in near-Earth orbits. She’s working on a method that would allow researchers and mission planners to discern the orbit a satellite is using to carry out its mission. This method will be designed to work in a wide range of situations – even if there is very little information about the satellite.

Since a traffic accident in cislunar space is inevitable, Frueh is also thinking ahead about how to estimate the damage an accident could cause. If there is a collision or explosion, where will all the pieces be?

Her research shows that fragments from a fragmented satellite can travel long distances in a relatively short period of time. She and her student, Ariel Black, recently presented a study at the 2023 AAS/AIAA Space Flight Mechanics Meeting showing that these pieces can travel easily back to Earth from​ deeper into cislunar space.

frueh-fragmentationIn this graph, the debris of a spacecraft that exploded near the moon is predicted to scatter millions of miles away in just a month’s time depending on the orbit where the explosion took place. The length of each colored line in this graph shows how far debris can spread in 30 days from an explosive point in the Lyapunov family of orbits around a location known as the second Lagrange «L2» point. two. These orbitals are being considered for cislunar missions. On each orbit, the explosion point is said to align with the Earth and Moon. (Purdue University/Ariel Black and Carolin Frueh photo)

“We are laying the groundwork that we believe will shape how spatial traffic management issues are addressed in the cislunar region,” says Frueh.

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