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There are quite a lot of spacecraft that have been up there a while and a lot of them have star cameras for attitude determination and for attitude control. Space telescopes (both heavenly and Earth-observational) need to point carefully and these may have especially nice star cameras.

Those integrated years of observation makes them potentially attractive candidates for secondary science observations, though not all of their systems may allow for extraction of scientifically useful images.

Question: With all of those eyes intently trained on the stars, are spacecraft star cameras ever used as scientific instruments for research?

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    $\begingroup$ I'm sure its been discussed and pilot studies conducted though I think the starting point is not the camera itself but the on board processing and/or data downlink and this, I've been told, limits their use. Probably worth looking for papers from Jena Optronic. $\endgroup$
    – Puffin
    Jan 20 at 12:52
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    $\begingroup$ Information that may aid in researching this question: Crew-oriented Space Shuttle reference materials referred to the subject cameras as "star trackers." We used to joke in the crew office that nobody really much understood how these things worked. They were, however, quite important operationally. I'm guessing that any images obtained by the star trackers (not even sure if this is possible) would be extremely low res and probably not of much scientific interest... $\endgroup$
    – Digger
    Feb 20 at 16:03
  • $\begingroup$ @Digger Ha! I'm confident that no astronaut in the history of spaceflight has ever imagined themselves as a celebrity, not even for a nanosecond. :-) For the purposes of this question Hubble's Fine Guidance Sensors will count. (1, 2) $\endgroup$
    – uhoh
    Feb 21 at 2:35
  • $\begingroup$ If a spacecraft is launched in order to catalog the stars and that information is then subsequently used in almost all star trackers flying today ... does that count? cosmos.esa.int/web/hipparcos/catalogues $\endgroup$
    – ChrisR
    Mar 19 at 0:30
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    $\begingroup$ @ChrisR ha, well I think in that case the star camera itself was not "used as scientific instruments for research" as much as it was used as an engineering instrument. In a laboratory we might question if a hand-held volt meter used to check if voltages and currents is "used as scientific instruments for research" or if it's more like one of many general purpose tools in the lab used to support the thing that's really the "scientific instruments for research". But if you post such an answer I won't complain! $\endgroup$
    – uhoh
    Mar 19 at 0:42
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The nasa.gov featured news item NASA’s Juno to Get a Close Look at Jupiter’s Moon Ganymede mentions two cameras whose purpose is to look at stars will be used to count high energy electrons, though this is not using the camera as an imaging device per se (the camera's lens is not used to produce a real image):

Normally, Juno’s Stellar Reference Unit (SRU) navigation camera is tasked with helping keep the Jupiter orbiter on course, but during the flyby it will do double duty. Along with its navigation duties, the camera – which is well shielded against radiation that could otherwise adversely affect it – will gather information on the high-energy radiation environment in the region near Ganymede by collecting a special set of images.

“The signatures from penetrating high-energy particles in Jupiter’s extreme radiation environment appear as dots, squiggles, and streaks in the images – like static on a television screen. We extract these radiation-induced noise signatures from SRU images to obtain diagnostic snapshots of the radiation levels encountered by Juno,” said Heidi Becker, Juno’s radiation monitoring lead at JPL.

Meanwhile, the Advanced Stellar Compass camera, built at the Technical University of Denmark, will count very energetic electrons that penetrate its shielding with a measurement every quarter of a second.


enter image description here

Juno's Radiation Monitoring Investigation collected this image of Jupiter's moon Io with Juno's Stellar Reference Unit (SRU) star camera shortly after Io was eclipsed by Jupiter at 12:40:29 (UTC) Dec. 21, 2018. Io is softly illuminated by moonlight from another of Jupiter's moons, Europa. The brightest feature on Io is suspected to be a penetrating radiation signature. The glow of activity from several of Io's volcanoes is seen, including a plume circled in the image. CREDIT NASA/JPL-Caltech/SwRI

Stellar Reference Unit (SRU) Image (IMAGE) Southwest Research Institute source

From CNN's NASA's Juno mission captures first closeup images of Jupiter's largest moon in a generation

This image of the dark side of Ganymede was taken by Juno's Stellar Reference Unit navigation camera during its June 7 flyby of the moon

This image of the dark side of Ganymede was taken by Juno's Stellar Reference Unit navigation camera during its June 7 flyby of the moon.



Video linked in this answer to Does Juno's UVS have any chance to spot Europa plumes? showing Juno's Stellar Reference Unit being used to track showers produced by high energy charged particles incident on the camera.


From Space.com's Auroras, Lightning and Rings of Jupiter Amaze in Surprising NASA Juno Photos:

Its main job is to spot the stars, but an ultrasensitive navigation camera on NASA's Juno spacecraft is returning amazing images of Jupiter's rings, auroras, lightning, and even its moonlit dark side.

Scientists discussed the results from the camera alongside other Jupiter revelations during a briefing Dec. 12 at the American Geophysical Union's annual meeting in Washington, D.C. Juno is approaching the halfway point on its primary mission, with its 16th science pass by the planet set for Dec. 21.

That camera is called the Stellar Reference Unit, or SRU for short. According to Heidi Becker, Juno's radiation monitoring investigation lead at NASA's Jet Propulsion Laboratory in California, the camera's "day job" is to cut through interference from the intense radiation surrounding Jupiter to spot the stars, comparing them to a database to figure out Juno's precise location and orientation during its 53-day, elongated orbits of the gas giant.

This is the first view ever taken from inside Jupiter's rings, snagged by Juno's Stellar Reference Unit camera during its first science encounter with the planet on Aug. 27, 2016. The three stars of Orion's Belt can be seen in the lower right, and Betelgeuse shines just above the rings. (Image credit: NASA/JPL-Caltech/SwRI)

This is the first view ever taken from inside Jupiter's rings, snagged by Juno's Stellar Reference Unit camera during its first science encounter with the planet on Aug. 27, 2016. The three stars of Orion's Belt can be seen in the lower right, and Betelgeuse shines just above the rings. (Image credit: NASA/JPL-Caltech/SwRI)

The Stellar Reference Unit camera, which helps Juno navigate during its mission at Jupiter, snapped this close-up view of the northern aurora on the planet's dark side — the closest visible-light view of the phenomenon ever taken. (Image credit: NASA/JPL-Caltech/SwRI)

The Stellar Reference Unit camera, which helps Juno navigate during its mission at Jupiter, snapped this close-up view of the northern aurora on the planet's dark side — the closest visible-light view of the phenomenon ever taken. (Image credit: NASA/JPL-Caltech/SwRI)

"This is another first: This is the closest view of Jupiter's aurora that has ever been made by a visible[-light] camera," Becker said. "It's an amazing complement to what Juno is already bringing back in the ultraviolet and in the infrared. And, again, we're seeing amazing structure because of the high resolution of the camera and Juno's close flight to the camera."

This image also reveals another dot of lighting, in the lower right, and the squiggles of high-energy electrons beaming off the planet's poles — "so SRU was doing three kinds of science when it took this picture."

"It's really exciting to see what we can see out of an engineering camera, and we're really erasing all the boundaries between who or what can make a contribution to engineering or science or art," Becker added.


Nature: Small lightning flashes from shallow electrical storms on Jupiter readable here.

[...]All previous optical observations of Jovian lightning have been limited by camera 36 sensitivity, proximity to Jupiter, and long exposures (~680 ms to 85 s) hence some measurements were likely superimposed flashes reported as one. Here we report optical observations of lightning flashes by Juno’s Stellar Reference Unit with energies of ~105 -108Joules, flash durations as short as 5.4 ms, and inter-flash separations of tens of milliseconds. The observations exposed Jovian flashes with typical terrestrial energies. The flash rate is ~6.1×10-2 flashes/km2/yr, more than an order of magnitude greater than hitherto seen. Several flashes are of such small spatial extent they must originate above the 2 bar level, where there is no liquid water.

See also Possible Transient Luminous Events Observed in Jupiter's Upper Atmosphere

note: These two images are from Juno's ultraviolet spectrograph and are of supplementary interest only.

Figure 1.  A spatial map of Juno ultraviolet spectrograph measurements during a single spacecraft spin at PJ26 (10 April 2020).

Figure 1. A spatial map of Juno ultraviolet spectrograph measurements during a single spacecraft spin at PJ26 (10 April 2020). The color scale shows the number of photons counts measured. The shape of the instrument slit is shown in yellow in the lower right corner (widths of the both the wide and narrow slits increased by a factor of 5 for clarity). A bright flash is highlighted by the yellow circle. This flash is also shown in Figure 2j

Images of 11 bright flashes observed by Juno ultraviolet spectrograph.

Figure 2. Images of 11 bright flashes observed by Juno ultraviolet spectrograph. The labels relate the images to the bright flashes described in Table 1. The color scale shows the number of photons counts measured. Each image has dimensions 1° × 1° on the sky. Panel (j) shows the same bright flash as Figure 1.

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