Lately we’ve been working hard dealing with a LOT of extra data. Because Mars is getting closer to the Earth (you can visualize that in this view of the solar system), we are approaching the peak data rate for the entire primary mission. Not that we’re complaining! This just means the Targeting Specialists are planning many more images, and we’re making those images as big as we can.

Unfortunately, we can’t just make them all the largest size the instrument is capable of taking, because our camera will get too hot. If it overheats, the instrument will shut itself off in order to prevent any damage to the electronics. So we have to be careful, and only plan images that won’t overheat HiRISE. In order to predict those temperatures, we use a tool called HiTemp (of course!). Here’s what it looks like (click on the image to see a bigger version).

This program reads in our planning files, and then models the temperatures of two key spots on the focal plane of the camera. It’s our job to make sure we don’t go above the dotted red line – this gives us a comfortable buffer below the scary solid red line. That’s when HiRISE would shut off, or safe. We know from experience by now that this is a big pain in the neck – a lot of work is required to get us back up & running, and we miss observations while we’re turned off. So we watch our HiTemp plots!

Last week we had a rare event: HiRISE turned off! We call this safe mode, because it’s a safety measure built into the instrument’s software. Whenever any of the sensors starts going out of bounds, like temperatures or voltages, the instrument powers down to prevent damage to the electronics. In this case, one temperature sensor went over its upper limit of 35 degrees Celsius. It’s pretty disconcerting when something unexpected like this happens, but at least we know the instrument is protected.

We had the difficult detective job of figuring out what went wrong. It was clear early on that the instrument overheated, but we couldn’t figure out why. Our tool that predicts the temperatures (”HiTemp”) didn’t predict anything that hot. We didn’t take a really large image, which would heat us up (at least, nothing bigger than normal! ). The local operations team worked with the health & safety people, the spacecraft engineers at LMA, and some of the software developers at Ball Aerospace that originally designed HiRISE. Together we all investigated the problem.

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The raw HiRISE image data needs to be cleaned up, and the HiCal pipeline is where this work is done. Now that the raw image data has been converted to a *.cub file format, ISIS tools can be used. These include hiclean, hipical, and hidestripe.

Hiclean does just what is says. Noise introduced into the image data by spacecraft electronics is corrected. Noise can show up as vertical and horizontal lines in the raw image and other periodic manifestations.

Hipical is a newer tool that performs calibration on the image data. For example, flatfield and gain corrections are performed by hipical. Hipical will be upgraded as we learn more about our instrument in its environment around Mars.

Hidestripe corrects a known striping pattern in HiRISE images.

We use other tools to collect even more statistical data about the newly calibrated image data. The HiCal pipeline will continue to be upgraded as our software matures. New statistics will be collected while corrections are added or improved.

After cleanup has been completed and a new *.hical.cub channel product created, HiCal creates a variety of jpeg browse and thumbnail images. The cleaned up channels are large, and for quick previews, these smaller jpegs come in handy.

Finally, HiCal lets the next pipeline – HiStitch – know that cleaned up channels are ready to be stitched together into CCD products.

Below is an example of raw data, prior to going through the HiCal pipeline. This image sample was taken from TRA_000873_1780; “Victoria Crater” at Meridiani Planum.

Below is the same image sample after going through the HiCal pipeline (notice that the bright vertical line in the center and the faint vertical lines throughout the image have been correctly removed by HiCal):