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TWINKLE will use a 0.45 meter telescope to record spectra of stars transited by their exoplanets. By looking at tiny changes in the spectrum as the planet's atmosphere moves in front of the star, they hope to characterize exoplanet atmospheres a few hundred systems in visible light as well as infrared out to about 4.5 microns in wavelength.

From New Atlas' Twinkle mission to take a closer look at exoplanet atmospheres:

When launched, Twinkle will be set in a polar low-Earth orbit on a three to five-year mission, during which it will study 100 exoplanets in our galaxy.

From Room's Twinkle - a mission to unravel the story of planets in our galaxy:

The Twinkle satellite will be built in the UK and launched into a low-Earth, sun-synchronous orbit by 2019, using a platform designed by Surrey Satellite Technology Ltd and a payload built by a consortium of UK institutes led by UCL.

From TWINKLE – A Low Earth Orbit Visible and Infrared Exoplanet Spectroscopy Observatory:

The platform must physically accommodate a payload assembly with an aperture of 52cm and length of 85 cm. The instrument includes cryo-coolers and a dedicated radiator to maintain the telescope to its required operating temperature < 200K. The total mass of the payload is 100 kg with an average power requirement of 100 W, including all margins. The mission will operate in a 600 to 700km sun-synchronous dawn-dusk orbit with the boresight of the telescope pointed within a 40° cone centred around the anti-sun vector.

Question: Why specifically a sun-synchronous orbit? Wouldn't staying out of the Sun be better for very sensitive spectral measurements?


Further reading:


Artist's concept of Twinkle, Source

TWINKLE Space Telescope

Another artist's conception, Source

TWINKLE Space Telescope

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    $\begingroup$ Don’t know about this mission’s planning, but a dawn-dusk orbit gives you more observing time in the directly-sunward direction, so I’d expect it to give you more anti-sunward time. Also, in an equatorial orbit you’d have to have a movable Earth shield for the cold optics (or do a repoint twice each orbit, with one being high precision) $\endgroup$ – Bob Jacobsen Jun 13 '19 at 13:29
  • $\begingroup$ @BobJacobsen that sounds so right that it's probably the answer. The required operating temperature of <200 K probably means there is a cooling system that needs constant power, so those solar panels pointing the opposite direction from the telescope would receive constant power in a dawn-dusk orbit as well. Consider writing it up? If nobody does I'll do it myself in a few days... $\endgroup$ – uhoh Jun 17 '19 at 12:32
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I don’t know about this mission’s planning, but there are some common considerations:

  • To maximize the observing time, you’d like an orbital plane that’s perpendicular to where you’re looking. That way you can keep looking one way, without Earth getting in the way. Not only do you lose observing time if Earth is in the way, you also (usually) have to either point away or have a shutter to protect optics.

  • if it’s compatible with what your looking for, a dawn disk orbit reduces your eclipsed time. This is good for power, and also makes thermal management a little simpler.

Twinkle is a search, i.e. isn’t staring at a specific target, so they could choose to point anti-sunward with a dawn-dusk orbit and get those advantages of 24x7 observing, stable pointing, and consistent thermal management.

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