Emily LakdawallaSep 11, 2007

Cassini went into safe mode, but everything is OK

EDIT: Sorry, I made a mistake on the timeline earlier and reported the news as worse than it was in the second paragraph.

According to a release that was just posted by JPL, the Cassini spacecraft went into safe mode 21 minutes into its first post-flyby data downlink. As a result of the spacecraft going into safe mode, the playback of the data was messed up, and the rest of the sequences on the spacecraft were canceled. That's the bad news.

The good news is that I've been assured that there's nothing wrong with the spacecraft; the safing event was caused by "a solid state power switch that was tripped due to a galactic cosmic ray hit," or, in layman's terms, sheer bad luck. Normal commanding has been recovered. Even better news is the timing of the safing event -- it was just 21 minutes after Cassini had finished executing and saving all of its highest-priority, highest-resolution data from the closest approach it will ever get to Iapetus. If you read my timeline, the safing event happened right about 15 hours after closest approach, after all the highest-res observations. Nothing after the September 11 05:10 mark of the timeline was executed, which is too bad, but all the good stuff is there -- everything up until Iapetus shrank to less than one narrow-angle camera frame in size.

And there's even better news; due to careful preplanning and rapid action after the safing event, it looks like very nearly all of the data that Cassini captured up to that point will be returned to Earth. It'll take a few days longer than originally planned to get it all on the ground, but it will all be here. New images should start showing up on the raw images page any minute now.

Just another object lession in how space exploration is hard. I think this is an appropriate time to share the text of a video greeting that Arthur C. Clarke sent to JPL, which was played at an event they held for their staff this morning (which I was, to my sadness, not permitted to attend). I don't have the video, but if I can get my hands on it I'll post it.

Video greeting to NASA JPL to mark the Iapetus flyby of Cassini spacecraft: 10 September 2007

ello! This is Arthur Clarke, joining you from my home in Colombo, Sri Lanka.

I'm delighted to be part of this event to mark Cassini's flyby of Iapetus.

I send my greetings to all my friends -- known and unknown -- who are gathered for this important occasion.

I only wish I could be with you in person, but I'm now completely wheelchaired by Polio and have no plans to leave Sri Lanka again.

Thanks to the World Wide Web, I have been following the progress of Cassini-Huygens mission from the time it was launched several years ago. As you know, I have more than a passing interest in Saturn...

And I was really spooked in early 2005, when the Huygens probe returned sound recordings from the surface of Titan. This is exactly what I had described in my 1975 novel Imperial Earth, where my character is listening to the winds blowing over the desert plains overhead.

That was perhaps just a foretaste of things to come! On September 10, if everything goes according to plan, Cassini would give us our closest look at Iapetus -- one of Saturn's most interesting moons.

Half of Iapetus appears as dark as asphalt, and the other half is as bright as snow. When Giovanni Cassini discovered Iapetus in 1671, he could only see its bright side. We had a better glimpse when Voyager 2 flew past in August 1981 -- but that was from almost a million kilometres away.

In contrast, Cassini is going to come within a little over one thousand kilometres of Iapetus.

This is a particularly exciting moment for fans of 2001: A Space Odyssey -- because that's where the lone astronaut Dave Bowman discovers the Saturn monolith, which turns out to be a gateway to the stars. Chapter 35 in the novel is titled

Let’s Go Beyond The Horizon

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