{"id":22783,"date":"2026-08-07T12:22:40","date_gmt":"2026-08-07T16:22:40","guid":{"rendered":"https:\/\/www.purdue.edu\/newsroom\/?p=22783"},"modified":"2026-08-07T13:58:31","modified_gmt":"2026-08-07T17:58:31","slug":"a-smarter-way-to-track-satellites-beyond-earths-orbit","status":"publish","type":"post","link":"https:\/\/www.purdue.edu\/newsroom\/2026\/Q3\/a-smarter-way-to-track-satellites-beyond-earths-orbit","title":{"rendered":"A smarter way to track satellites beyond Earth\u2019s orbit"},"content":{"rendered":"\n<p class=\"wp-block-paragraph\">WEST LAFAYETTE, Ind. \u2014 Most current space activities operate close to Earth in what is called near-Earth orbit. However, as more satellites and other infrastructure begin to extend beyond that region, maintaining situational awareness of those objects will be crucial.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Purdue University engineer Keith LeGrand is developing methods to track the location and movement of objects in cislunar space \u2014 the area around Earth extending to just beyond the moon\u2019s orbit, which encompasses upwards of 300,000 miles, or roughly 12 times around the Earth\u2019s equator. His work will help to secure and defend U.S. national and economic interests in space.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Although there are far fewer objects in the cislunar region compared to near-Earth orbit, a variety of factors make it difficult to operate and maintain awareness of objects in cislunar space. These factors include poor visibility from contrast and glare, extreme distances and difficult-to-predict orbital behavior from the sun-Earth-moon system \u2014 what is known as a restricted four-body problem.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cIncreasing numbers of small satellites are launched into cislunar space, and given the area\u2019s complex and chaotic environment, it can be difficult to keep track of them,\u201d said LeGrand, assistant professor in Purdue\u2019s School of Aeronautics and Astronautics. \u201cWe need to develop the right tools and infrastructure to ensure that these objects don\u2019t get lost in space.\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">LeGrand specializes in space situational awareness, enabling intelligent sensing and decision-making in complex orbital environments. His research focuses on better characterizing when an object in cislunar space may have moved or altered course and what that move looks like. His team develops algorithms that determine how uncertainty about an object\u2019s position evolves over time.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Predicting motion in cislunar space<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Imagine you just blew on a dandelion and released its seeds from the stem. At that moment, you know the approximate location of those seeds, but you want to try to predict where they\u2019ll end up tomorrow. You know the wind will push them around, but the wind\u2019s direction isn\u2019t always predictable. As time passes, your guess about the location of the seeds will become less certain.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">LeGrand\u2019s algorithms capture this problem in the complex gravity environment between the Earth and the moon.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cWhat we\u2019re really capturing is how confidence fades over time,\u201d LeGrand said. \u201cBy understanding exactly how and when uncertainty grows in these complex environments, we can make better predictions, respond earlier to potential risks, and ultimately operate more safely and efficiently in space.\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">The method LeGrand uses to determine uncertainty is called Gaussian mixture approximation. Traditional Gaussian models are typically used to describe data that often clusters around an average and spreads out smoothly on both sides, like a bell-shaped curve. These models use this data to help make predictions, recognize patterns, model measurement errors, or filter noise from signals like GPS or sensors. Gaussian models work well for linear systems \u2014 ones that behave predictably and scale proportionally. But most engineering systems, including orbital mechanics and satellite motion, are nonlinear.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cNonlinear systems don\u2019t follow proportional cause-and-effect relationships,\u201d LeGrand said. \u201cSmall uncertainties don\u2019t stay small, and tiny differences can grow dramatically over time. This produces chaotic behavior and uncertainty patterns that might look more like bananas or spirals rather than neat bell curves.\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Other approaches used to predict this uncertainty have been either efficient but not accurate, or highly accurate but expensive and time-consuming. LeGrand says neither of those options work for the types of systems that are launched into cislunar space.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cThese smaller satellites are essentially running on a processor with the same capabilities as an older video game system. They don\u2019t have the performance that we\u2019re used to even on our laptops,\u201d LeGrand said. \u201cTherefore, we need to dedicate computational power where it matters most to be able to generate algorithms that stand a chance at running both quickly and efficiently while in space.\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">LeGrand\u2019s new method uses Gaussian mixtures \u2014 collections of bell-curve distributions \u2014 to represent uncertainty and splits them into multiple, smaller distributions when they are no longer accurate enough.<\/p>\n\n\n\n<figure class=\"wp-block-image size-full\"><img loading=\"lazy\" decoding=\"async\" width=\"876\" height=\"493\" src=\"https:\/\/www.purdue.edu\/newsroom\/wp-content\/uploads\/2026\/08\/LeGrand-secondary.jpg\" alt=\"Keith LeGrand talks with students and points to equations on a dry-erase board.\" class=\"wp-image-22780\" title=\"\" srcset=\"https:\/\/www.purdue.edu\/newsroom\/wp-content\/uploads\/2026\/08\/LeGrand-secondary.jpg 876w, https:\/\/www.purdue.edu\/newsroom\/wp-content\/uploads\/2026\/08\/LeGrand-secondary-300x169.jpg 300w, https:\/\/www.purdue.edu\/newsroom\/wp-content\/uploads\/2026\/08\/LeGrand-secondary-768x432.jpg 768w\" sizes=\"auto, (max-width: 876px) 100vw, 876px\" \/><figcaption class=\"wp-element-caption\">LeGrand and his team of graduate students have built algorithms that can help to predict an object\u2019s movement as it travels through space. These algorithms dedicate computational power where it matters most, saving time and energy. (Purdue University photo\/Kelsey Lefever)<\/figcaption><\/figure>\n\n\n\n<p class=\"wp-block-paragraph\">The challenge is ensuring that the distribution is split as efficiently as possible while retaining accuracy. Efficient splitting and minimizing the number of smaller distributions are critical as too many mixture components can make computation slow or impossible.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cThink of splitting as adding detail only where needed,\u201d LeGrand said. \u201cAs uncertainty evolves in chaotic environments, it gets stretched and distorted. By splitting one distribution into smaller Gaussian pieces, each piece can be tracked more accurately, and simpler equations that take less computational power work much better on those smaller parts.\u201d<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Modeling uncertainty with efficiency and accuracy<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">LeGrand has developed a <a href=\"https:\/\/ieeexplore.ieee.org\/document\/11244272\" target=\"_blank\" rel=\"noreferrer noopener\">framework<\/a> for splitting these distributions to ensure that the results are more accurate and faster to compute.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">First, the framework includes a splitting method that preserves the overall average and spread of uncertainty. In other words, the method ensures that, even after the distribution is broken into smaller pieces, the big picture doesn\u2019t change. It also introduces new methods for choosing the best way to split based on how the system behaves.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Additionally, LeGrand has created an <a href=\"https:\/\/ieeexplore.ieee.org\/document\/11373892\" target=\"_blank\" rel=\"noreferrer noopener\">algorithm<\/a>, Higher-Order Tensor-Based Deferral of Gaussian Splitting (HOTDOGS), which takes that framework into account and creates rules for when to split a distribution.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Instead of immediately breaking up a distribution into many small pieces, HOTDOGS starts with only a few splits and watches how they change over time. It will then only split when it starts to stretch or distort too intensely. In other words, the algorithm waits until splitting is necessary and then follows each smaller piece separately to stay accurate while remaining efficient.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cThe key idea behind HOTDOGS is not doing more work than necessary,\u201d LeGrand said. \u201cBy letting uncertainty evolve and the algorithm only stepping in when it truly starts to break down, we get the same level of accuracy with far less computation. That balance is essential if we want reliable predictions without slowing everything down.\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">Rather than treating uncertainty as a static problem, LeGrand\u2019s approaches adapt as conditions change, adding detail only where it is truly needed and directly supporting safer space navigation, improved situational awareness and better decision-making.<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">\u201cThe goal of our work is to make uncertainty prediction both smarter and more efficient,\u201d LeGrand said. \u201cAs cislunar space grows more crowded and complex, we hope we can provide a clearer picture of all the activities happening throughout the region.\u201d<\/p>\n\n\n\n<p class=\"wp-block-paragraph\">LeGrand\u2019s research is sponsored by the <a href=\"https:\/\/midwesthub.afresearchlab.com\/\" target=\"_blank\" rel=\"noreferrer noopener\">Air Force Research Laboratory (AFRL) Regional Network \u2014 Midwest<\/a>, a science and technology ecosystem in which partners from universities, industry and government help the AFRL drive innovation, and the Air Force Office of Scientific Research\u2019s Young Investigator Program.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">About Purdue University<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\">Purdue University is a research institution ranked among the top 10 public universities in the United States. More than 106,000 students study at Purdue across multiple campuses, including more than 57,000 at our main campus locations in West Lafayette and Indianapolis. As a land-grant university committed to affordability and accessibility, Purdue\u2019s main campus has frozen tuition 14 years in a row, enabling more students than ever to graduate debt-free.<\/p>\n\n\n\n<h2 class=\"wp-block-heading\">Papers<\/h2>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Nonlinearity- and Uncertainty-Informed Moment-Matching Gaussian Mixture Splitting<br><\/em>IEEE Transactions on Aerospace and Electronic Systems<br>DOI: <a href=\"https:\/\/doi.org\/10.1109\/TAES.2025.3632242\" target=\"_blank\" rel=\"noreferrer noopener\">10.1109\/TAES.2025.3632242<\/a><\/p>\n\n\n\n<p class=\"wp-block-paragraph\"><em>Higher-Order Tensor-Based Deferral of Gaussian Splitting for Orbit Uncertainty Propagation<br><\/em>IEEE Transactions on Aerospace and Electronic Systems<br>DOI: <a href=\"https:\/\/doi.org\/10.1109\/TAES.2026.3662318\" target=\"_blank\" rel=\"noreferrer noopener\">10.1109\/TAES.2026.3662318<\/a><\/p>\n\n\n<div id=\"note\" class=\"post-content__attribution \">\n    <div class=\"columns\"> \n                    <div class=\"column\"> \n                <p class=\"post-content__source\">\n                    <strong>Media contact:<\/strong> Lindsey Macdonald, <a href=\"mailto:macdonl@purdue.edu\">macdonl@purdue.edu<\/a>                <\/p>\n            <\/div>\n                    <\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>WEST LAFAYETTE, Ind. \u2014 Most current space activities operate close to Earth in what is called near-Earth orbit. However, as more satellites and other infrastructure begin to extend beyond that region, maintaining situational awareness of those objects will be crucial.<\/p>\n","protected":false},"author":25,"featured_media":22778,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"footnotes":""},"categories":[524],"tags":[],"department":[],"source":[29],"purdue_today_topic":[],"coauthors":[207],"class_list":["post-22783","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-space","source-purdue-news"],"acf":[],"_links":{"self":[{"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/posts\/22783","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/users\/25"}],"replies":[{"embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/comments?post=22783"}],"version-history":[{"count":2,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/posts\/22783\/revisions"}],"predecessor-version":[{"id":22785,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/posts\/22783\/revisions\/22785"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/media\/22778"}],"wp:attachment":[{"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/media?parent=22783"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/categories?post=22783"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/tags?post=22783"},{"taxonomy":"department","embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/department?post=22783"},{"taxonomy":"source","embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/source?post=22783"},{"taxonomy":"purdue_today_topic","embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/purdue_today_topic?post=22783"},{"taxonomy":"author","embeddable":true,"href":"https:\/\/www.purdue.edu\/newsroom\/wp-json\/wp\/v2\/coauthors?post=22783"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}