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Emily LakdawallaSeptember 5, 2008

Rosetta on target, no further rocket firings needed

The rocket firing that Rosetta performed yesterday has targeted the spacecraft to within two kilometers of the planned position, an accuracy that the navigation team deems is good enough to cancel the final opportunity for a trajectory correction this morning. In fact, according to the Rosetta blog, the engineers seem to be almost jubilant over the accuracy of their targeting.

Some of you might be asking: if they had the chance to fix that last two kilometers, why not do it? My answer to you is that one of the most frequently quoted aphorisms I hear from spacecraft engineers is "better is the enemy of good enough." The current target position is only a quarter of a percent off from the target miss distance. They didn't say this but I assume that that's well within whatever tolerances they set when they were planning their science observations. Why take the risk of something going wrong with an unnecessary firing of the rockets? Let the spacecraft coast on in and do its work without any further fiddling.

Here's an updated animation of navigation camera images showing Steins getting brighter as Rosetta approaches.

Rosetta approaches Steins

ESA

Rosetta approaches Steins
Ten Rosetta Navcam images show asteroid 2867 Steins brightening in Rosetta's forward view as the spacecraft approached for its September 5 flyby. In fact, the images were taken with exposures set for Steins, so they have been processed to make the brightness of stars constant, which makes Steins appear to brighten over time. Steins remained an unresolved dot of light throughout this period.
Finally, I'll mention that the ESA press office has announced that they will be streaming the post-encounter press briefing on Friday live on the Web. Hallelujah! -- sort of. The briefing is happening at 11:55 European summer time on Saturday, September 6. That's 02:55 my time. Yikes. But I've been having some trouble with insomnia lately, so I might be awake. If you are awake, tune in to this page. (If you tune in now you can hear some lovely 'hold' music.)

We're now just about an hour away from closest approach!

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Emily Lakdawalla

Senior Editor and Planetary Evangelist for The Planetary Society
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Emily Lakdwalla
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