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Telescopes in space have a huge advantage over those on the ground: they can see the universe more clearly. The Earth\u2019s atmosphere, weather conditions, and low-flying satellites don\u2019t obscure their view. But space telescopes have a disadvantage too. They can\u2019t be repaired, at least not since NASA\u2019s Space Shuttle program ended in 2011.<\/p>\n
But next-generation telescopes are being planned with robotic servicing missions in mind. And not just in low earth orbit, where the Hubble Space Telescope received repairs and upgrades five times during its lifespan from space shuttle crews. Today\u2019s engineers are preparing for ways to repair telescopes in deep space, including at the Sun-Earth Lagrange point L2.<\/p>\n
<\/p>\n L2 is the current home of the James Webb Space Telescope (JWST) and ESA\u2019s Gaia mission. In this position, the Earth is kept between the Sun and the telescopes, giving them pristine conditions for observing the universe.<\/p>\n \u201cWhile neither Gaia nor JWST were explicitly designed to be serviceable, next-generation space telescopes now in development include serviceability in their baseline designs,\u201d write the authors of a new paper from a team at the Grainger College of Engineering, University of Illinois Urbana-Champaign.<\/p>\n Service spacecraft could attach themselves to derelict telescopes, bringing extra fuel, working reaction wheels, or even repairing damaged mirrors and other key components.<\/p>\n But it isn\u2019t an easy task.<\/p>\n The University of Illinois team, including Professor Siegfried Eggl and Ruthvik Bommena, used Gaia and JWST as test subjects to design a feasible service mission.<\/p>\n \u201cGaia is like a rotating cylinder with a solar panel. It is encapsulated, so it hasn\u2019t been damaged, but after a decade out there it\u2019s running low on fuel,\u201d said Eggl in a press release. \u201cRuthvik Bommena designed a novel concept to add a sort of spider-looking attachment that can extend its life without impeding its data collection. Gaia will be decommissioned soon, so there isn\u2019t enough time to reach it, but the James Webb might still be a possibility because it will be operating for several more years and they may decide to prolong its mission.\u201d<\/p>\n JWST\u2019s exposed mirrors have already been struck by micrometeorites multiple times, affecting the quality of its observations.<\/p>\n \u201cWe\u2019re trying to stay a step ahead so there is a plan to replace broken mirrors, for example. If we don\u2019t, it\u2019s like buying an expensive sports car, then like throwing it away when it runs out of gas,\u201d says Eggl.<\/p>\n One of the most significant barriers to long-distance servicing missions is designing a trajectory for rendezvous with the target.<\/p>\n \u201cA spacecraft sent to repair or refuel a telescope needs to brake when it reaches it,\u201d Bommena said. \u201cUsing the thrusters to slow down would be like pointing a blowtorch at the telescope. You don\u2019t want to do that to a delicate structure like a telescopic mirror. How do we get there without torching the whole thing?\u201d<\/p>\n In addition, the team is working to optimize both fuel efficiency and cost for such a mission.<\/p>\n As Professor Robyn Wollands, another author on the paper explains, \u201cgetting there is doable because of some hidden highways in our solar system. We have a trajectory that is optimal for the size of spacecraft needed to repair the JWST,\u201d she said.<\/p>\n These \u2018hidden highway\u2019s are geometrically optimal paths that take advantage of orbital mechanics to make rendezvous safe and cost-efficient. The team have developed a new way to calculate and evaluate these optimal paths.<\/p>\n \u201cAfter we create a map of initial solutions, we use optimal control theory to generate optimal end-to-end trajectories,\u201d said PhD student Alex Pascarella. \u201cOptimal control allows us to find trajectories that depart near Earth, and rendezvous with our space telescope in the least amount of time. The initial sampling of the solution space is fundamental\u2014optimal control problems are notoriously difficult to solve, so we need a decent initial guess to work with.<\/p>\n \u201cThe novelty is in how we brought together two separate approaches to trajectory design: dynamical systems theory and optimal control theory,\u201d Pascarella added.<\/p>\n With teams like this one laying the groundwork, the lifespan of space telescopes might be extended long past their original best-before date, and that\u2019s good news for astrophysicists and space programs worldwide.<\/p>\n Learn More:<\/strong><\/p>\n Alex\u00a0Pascarella,\u00a0Ruthvik\u00a0Bommena,\u00a0Siegfried\u00a0Eggl,\u00a0Robyn\u00a0Woollands, \u201cMission design for space telescope servicing at Sun\u2013Earth L2.\u201d Acta Astronautica.<\/p>\n \u201cA mission design for servicing telescopes in space.\u201d EurekAlert.<\/p>\nLike this:<\/h3>\n