MIT Envisions ‘Guide Star’ Satellites to Stabilize Giant Telescopes

MIT Envisions ‘Guide Star’ Satellites to Stabilize Giant Telescopes
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Missions like the Kepler Space Telescope and the newer Transiting Exoplanet Survey Satellite (TESS) have revealed thousands of exoplanets out there among the stars, but we know surprisingly little about them. To get up close and personal, we’re going to need extremely precise space telescopes. MIT scientists have proposed an innovative way to make sure those instruments remain calibrated and capable of peering at distant exoplanets. They suggest designers incorporate a smaller secondary satellite that can act as a “guide star” for the telescope.

Space researchers are anxious to get new super-sized telescopes in space because the equipment we have right now is only adept at finding planets and relaying basic information. Most exoplanets in the database were discovered via the transit method, which watches for dips in brightness as planets pass in front of their home stars. From this, we can often discern a planet’s size, orbit, and approximate temperature. To get detailed data about its atmosphere and composition, we need telescopes like the upcoming (and chronically delayed) James Webb Space Telescope.

Webb will offer much greater imaging prowess than Hubble because its primary mirror is larger, composed of 18 hexagonal segments with a total diameter of 6.5 meters. In the coming decades, space telescopes could reach 15 meters with as many as 100 mirror segments. Such telescopes would have a coronagraph, an instrument capable of separating the intense light of a star from the faint light of an exoplanet. If this measurement isn’t perfect, the telescope would be unable to resolve the details on a planet.

The MIT team estimates that a disturbance as small as 10 picometers could distort the coronagraph in such a telescope. MIT’s solution is the inclusion of small companion satellites that would go along with the telescope to shine a laser at the mirror. This bright, local reference point could be used to calibrate and maintain the instruments.

The Webb telescope’s segmented mirror.

This approach would not be without precedent. Astronomers have been using actual stars in the sky as guides to stabilize ground-based telescopes; they were used like signposts to compensate for imperfections in tracking mechanisms. In the late 20th century, scientists began using lasers to create artificial guide stars. The satellite proposal is simply sending a similar system into space with your telescope. This has the advantage of working no matter where you position the instrument, even if it’s far away from Earth.

The team is currently developing designs that rely on CubeSats, small shoebox-sized satellites that fit inside standard enclosures. NASA recently tested a pair of deep space CubeSats with the InSight lander — they made it all the way to Mars and relayed some of the lander’s data back to Earth. The MIT project could lead to a small network of guide star satellites that help stabilize telescopes as you survey far-flung parts of the sky. Guide star satellites may even make designing future telescopes cheaper and easier; that’s certainly been a problem with the Webb Telescope. 

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