Emily Lakdawalla continues her excellent blog coverage in this article, which does a great job of explaining some of the reasons why this image was especially difficult to take. Along the way, she includes a tutorial on TDI (Time-Delay-Integration), written by one of the engineers that helped build the instrument. TDI is the method HiRISE uses to gather lots of light into its CCDs, and it’s one of the reasons we get such high signal-to-noise in our images. It’s a complicated concept, but it’s an important one for understanding HiRISE’s incredible imaging abilities, as well as its limitations.

From her blog post:

This is a fascinating story showing how necessary it sometimes is to have a deep understanding of an instrument in order to understand the data that comes from it. …It can be dangerous to read too much into space images until you have studied how the cameras really work.

It’s a great post – she deserves a cookie!

MRO did a special imaging sequence to slew over to where the Phoenix spacecraft was plummeting down through the atmosphere, and it WORKED! I can’t believe what an engineering feat this was – the MRO spacecraft team’s pointing was right on, and Phoenix was exactly where they thought it would be.

When I left last night, we hadn’t gotten down the channel that included the parachute. The rest of the image is pretty low signal (and it’s a HUGE image), so we were searching through it for hours, trying to separate out cosmic ray hits and bright patches of ice. They had only given us a ~20% chance of getting it in our field of view, so I thought we had missed it. I finally went to bed feeling pretty frustrated, but woke up to find that, overnight we received additional channels of the image, and Richard Leis and some others here at HiROC had found THIS!

You can see the parachute itself, AND the lander encased in the heat shield dangling below it – AND you can see the STRINGS attaching them! This is the first time a spacecraft has ever been photographed as it descends through the atmosphere of another planet. Everyone here is incredibly excited about this image.

However, we’re too busy poring over the image we took after this one to spend too much more time on this. Hopefully soon we’ll be able to show you the lander itself, on the surface!

Go, Phoenix!

NASA press release: http://www.nasa.gov/mission_pages/phoenix/news/phoenix-20080526.html