Junocam Images the Stars


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Between 20:23 and 20:56 UTC on 14 March 2012 (12:13 to 12:16 PM PST) Junocam took 21 images of the sky surrounding the spacecraft. At this time the Juno spacecraft was about 290 million kilometers from Earth. The primary purpose of the imaging sequence was to verify that operation of the Junocam instrument did not cause any electromagnetic interference for the rest of the Juno science payload. But it also allowed the Junocam team to assess the performance of their own instrument, especially its "Time-Delay Integration" (TDI) image stabilization mode.

Juno is spinning at 1 RPM during cruise, so normal exposures would have either had to have been highly blurred or extremely short (1/150 of a second or less). For this sequence an exposure time of about 0.5 seconds was used, allowing Junocam to detect stars down to about 4th or 5th magnitude. TDI electronically tracked the scene over about 80 image sensor lines as the exposure progressed, and each swath consists of about 40 individual frames covering 180 degrees of spacecraft spin.


Figure 1. The Big Dipper imaged by Junocam.
The Big Dipper as imaged by Junocam.
The field of view of Junocam is about 60 degrees, so only 60x360 degrees of the sky was covered, but this contained familiar star patterns (known as asterisms to astronomers) like the Big Dipper (Figure 1 and the lower section of Figure 2) and the "False Cross," and the bright stars Vega, Regulus and Canopus (the upper section of Figure 2; the False Cross is an asterism formed from stars in the southern constellations Vela and Carina, so-called because it is sometimes mistaken for the Southern Cross). About half of each image swath was washed out by glare from the sun, but this was anticipated by the Junocam team. An unlabeled version is available here. These images have been cosmetically processed. The raw image is also available here.

"An amateur astrophotographer wouldn't be very impressed by these images, but they show that Junocam is correctly aligned and working just as we expected", said Mike Caplinger, Junocam systems engineer.

Further analysis of the images will be used to refine the timing and pointing knowledge of Junocam.

TDI will allow Junocam to take high-quality color images in the dark conditions at Jupiter, which is over five times farther from the Sun than Earth. Long exposures enabled by TDI will also allow Junocam to take images in a near infrared methane band, enhancing its science return.

Launched in August 2011, the Juno spacecraft will arrive at Jupiter in July 2016 to begin a one-year campaign to study the composition and origin of the largest planet in the solar system.

Junocam was developed and is operated by Malin Space Science Systems in San Diego. NASA's Jet Propulsion Laboratory (JPL) manages the Juno mission for the principal investigator, Scott Bolton, of Southwest Research Institute in San Antonio. The Juno mission is part of the New Frontiers Program managed at NASA's Marshall Space Flight Center in Huntsville, Ala. Lockheed Martin Space Systems, Denver, built the spacecraft. JPL is a division of the California Institute of Technology in Pasadena.

More information about Juno is online at http://www.nasa.gov/juno and http://missionjuno.swri.edu. You can follow the mission on Twitter at http://www.twitter.com/nasajuno.


Figure 2 (below). The full 360x60 degree Junocam swath. The middle section of the image is dominated by glare from the sun. The upper section is of mostly southern sky, including the constellations Carina, Vela, and Hydra. The "False Cross" is to the left and slightly above Canopus. Note that the dark sections of the image have been contrast enhanced to bring out the stars. Click on the image for the full resolution version. The unlabeled is here and the raw version is here.
 The full 360 x 60 degree Junocam swath



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