{"id":20611,"date":"2026-03-26T08:20:23","date_gmt":"2026-03-26T12:20:23","guid":{"rendered":"https:\/\/www.purdue.edu\/newsroom\/?p=20611"},"modified":"2026-03-26T08:20:25","modified_gmt":"2026-03-26T12:20:25","slug":"limiting-space-junks-threat-by-predicting-its-mess-in-the-earth-moon-neighborhood","status":"publish","type":"post","link":"https:\/\/www.purdue.edu\/newsroom\/2026\/Q1\/limiting-space-junks-threat-by-predicting-its-mess-in-the-earth-moon-neighborhood","title":{"rendered":"Limiting space junk\u2019s threat by predicting its mess in the Earth-moon neighborhood"},"content":{"rendered":"\n

WEST LAFAYETTE, Ind. \u2014 Debris from moonbound spacecraft has left craters on the lunar surface since the U.S. Apollo missions<\/a>. But the moon is not used to being surrounded by debris.<\/p>\n\n\n\n

With an expected resurgence in lunar missions in the coming years, such as the U.S. Artemis II test flight<\/a>, Purdue University engineer Carolin Frueh<\/a> is researching how to track the likely increase in spacecraft debris and minimize its impact in the area between the moon and Earth, called the cislunar region.<\/p>\n\n\n\n

In the next decade, at least 30 missions<\/a> could be launching to the cislunar region.<\/p>\n\n\n\n

\u201cEverywhere humans have gone in space, we have left behind space debris. The fewer debris pieces we are creating, the better the problem in the end,\u201d said Frueh, Purdue\u2019s Harold DeGroff Associate Professor of Aeronautics and Astronautics<\/a>.<\/p>\n\n\n\n

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Preparing for how new technology \u2014 and space itself \u2014 could change debris<\/h2>\n\n\n\n

Frueh\u2019s research considers how the latest spacecraft technology could affect the formation of space debris. Unlike other spacecraft the moon has seen before, for example, rockets for upcoming lunar missions could have nuclear thermal propulsion systems to be more fuel-efficient. But if rockets with these systems collided or exploded, their radioactive contents could disperse and become debris.<\/p>\n\n\n\n

Frueh and her students have modeled the consequences of radioactive debris in the cislunar region, finding that nuclear-contaminated fragments from a nuclear thermal propulsion system could emit radiation up to a half-mile away<\/a> from an impact site on the moon. Their models also indicate that these radiation levels could stay elevated for at least a year, threatening a lunar base if built nearby.<\/p>\n\n\n\n

\"Carolin
Purdue associate professor Carolin Frueh, left, and PhD student Masashi Nishiguchi discuss their findings on how fragments could spread from the breakup of a spacecraft in the cislunar region. (Purdue University photo\/Kelsey Lefever)<\/figcaption><\/figure>\n\n\n\n

On the other hand, radioactive debris could float in other directions around the moon and have less impact.<\/p>\n\n\n\n

\u201cThere are better and worse locations for fragmentation. The pieces could hit a moon colony \u2014 or not. But we still need to be careful because it\u2019s not obvious where fragments will congregate,\u201d Frueh said.<\/p>\n\n\n\n

A \u201cbetter\u201d mess is still problematic because space doesn\u2019t stay the same, and telescopes on Earth currently aren\u2019t able to view the whole cislunar region to track where fragments and spacecraft go. Frueh and her students are working to remove these blind spots by creating comprehensive \u201cvisibility maps\u201d that indicate where telescopes on satellites should be placed in cislunar space to observe as much of the region as possible.<\/p>\n\n\n\n

\"Two
Carolin Frueh\u2019s research group has created maps to inform where telescopes should be put in cislunar space to improve visibility of the region. The two maps in this figure show how the visibility rate for a constellation of 10 telescopes could increase from 10%, left, to 80% when using certain orbits over a 30-day period. (Figure provided by Surabhi Bhadauria and Carolin Frueh)<\/figcaption><\/figure>\n\n\n\n

To consider the always-changing nature of space, Frueh\u2019s lab generates these maps using models that average out the orbits a telescope might use over a 30-day period and incorporate the constant movement of the Earth, moon and sun. The approach is more efficient than other mapping methods, which must rerun a model for each condition that would affect a telescope\u2019s orbit and overall viewing geometry at each instance in time.<\/p>\n\n\n\n

In a paper published in The Journal of the Astronautical Sciences<\/a>, Frueh\u2019s research group used their maps to show possible ways to increase visibility rate success from 10% to 90% for a constellation of up to 10 telescopes in cislunar space. She and her students also demonstrated that a method they developed could help test and improve trajectories a telescope may use to travel between regions of optimal visibility.<\/p>\n\n\n\n

Using AI to evaluate if space objects might hit each other<\/h2>\n\n\n\n

While working on solutions for the cislunar region, Frueh\u2019s research also extends to low Earth orbit, the messiest region in space.<\/p>\n\n\n\n

Most organizations have satellite operators available 24 hours a day year-round to monitor satellites and prevent collisions between them. But as the number of satellites in space increases, it will get much harder to watch them all. Each satellite operator also evaluates collision risk differently according to their organization\u2019s policies, even when given the same data, Frueh\u2019s lab observed in a study<\/a>.<\/p>\n\n\n\n

Frueh and PhD student Pavithra Ravi surveyed how satellite operators across five organizations decided whether to relocate satellites at risk of collision for 30 scenarios in low Earth orbit. The researchers then trained a machine learning model on two sets of data. One dataset had more than 300,000 physics-based simulated events closely mimicking reality, and the other set had 8,000 real confirmed collisions and misses in low Earth orbit.<\/p>\n\n\n\n

They tested the model on the same 30 scenarios the satellite operators had evaluated. Frueh and her students found that the machine learning model was able to mimic the decision-making of each satellite operator with high reliability, correctly detecting probable collisions most of the time and prioritizing safety in deciding if satellites should change position.<\/p>\n\n\n\n

\u201cThe idea would be to reduce the workload of analysts looking at all these cases while maintaining a given organization\u2019s priorities. The model could either make decisions about satellite maneuvers completely autonomously or give the analyst some guidance,\u201d Frueh said.<\/p>\n\n\n\n

\"Carolin
Carolin Frueh and her students like Luke Fortner, left, aim to find the best ways to optically track all objects in the cislunar region. (Purdue University photo\/Kelsey Lefever)<\/figcaption><\/figure>\n\n\n\n

Diagnosing problems with satellites before they create a mess<\/h2>\n\n\n\n

When a satellite gets stuck in space because it malfunctioned or lost communication with its operator, finding out how the satellite is oriented can help with getting it unstuck before it becomes debris. The orientation could reveal if the satellite is rotating, tumbling or stable, for example.<\/p>\n\n\n\n

Frueh is one of the few researchers in the world working to improve a technique<\/a> that uses sunlight to estimate the orientation of a satellite or its fragments.<\/p>\n\n\n\n

Most satellites are constantly illuminated by the sun and can be seen as white dots with a telescope. The technique Frueh uses tracks changes in the brightness of these dots over time, which form \u201clight curves\u201d on a graph.<\/p>\n\n\n\n

This method would be less expensive than radar and provides information about a satellite no matter how far away it is from Earth as long as the satellite reflects some light toward the telescope on the ground. Radar, although more detailed, is typically limited to satellites at low altitudes because of energy constraints.<\/p>\n\n\n\n

\u201cWith light curves, we\u2019re not seeing any detail \u2014 just a bright dot. Changes in information about the object\u2019s orientation, shape and reflectivity are all embedded in that dot,\u201d Frueh said.<\/p>\n\n\n\n

However, information from that white dot is often ambiguous. Frueh, PhD student Liam Robinson and others in her research group have developed an algorithm that provides all the possible orientations of a satellite given the information available. They have shown with measurement data of real space objects<\/a> that the algorithm can reliably determine a satellite\u2019s orientation, overcoming a major challenge in making light curves practical for use.<\/p>\n\n\n\n

The light curves method could also be useful for actively removing space debris.<\/p>\n\n\n\n

\u201cThe better we know about the pieces we\u2019re dealing with \u2014 what\u2019s the shape, how much rotation they have \u2014 the better we can execute missions to remove those pieces,\u201d Frueh said.<\/p>\n\n\n\n

Frueh\u2019s work on these studies is primarily supported by the U.S. Air Force Office of Scientific Research and the European Space Agency.<\/p>\n\n\n\n

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