Friday, September 7, 2012

Curiosity online

The Curiosity rover, formally the Mars Science Laboratory, landed on Mars late on August 5th (or early on the 6th, depending on your time zone).

This was a major accomplishment.  Mars has a habit of eating space probes.  The majority have failed, sometimes quietly and sometimes spectacularly, at least once due to the kind of basic coding error that would send a regular geek cursing back to the keyboard.  Except when it comes to interplanetary travel there's generally no "next release".

The Curiosity landing was more complex than any Mars landing before it, and parts of it had never been realistically tested, much less the overall sequence.  This was not out of negligence or cut corners but a simple necessity.  Mars's atmosphere is much, much thinner than Earth's.  At its thickest it's equivalent to Earth's atmosphere at about 35 kilometers (about 20 miles, or about four times as high as the summit of Mount Everest).  Mars's gravity is about 40% of Earth's.  There's simply no practical way to re-create those conditions at the necessary scale anywhere near Earth.

This thin atmosphere is a real problem.  There's just enough of it you can't ignore it, but not enough for a parachute to take the lander all the way to the surface safely.  To land Curiosity, which is considerably larger and more massive than the Spirit and Opportunity rovers before it, NASA put together a landing sequence that Rube Goldberg might have appreciated:
  • The probe slams into the atmosphere, protected by a heat shield and pulling upwards of 10g of deceleration, possibly as high as 15g (This is from NASA's press kit from before the landing.  I don't know what the actual numbers were, but clearly it's not going to work with humans aboard.)
  • Once the the probe has slowed enough not to need the heat shield, the heat shield is jettisoned.
  • The probe then deploys a parachute, which slows it to about 300 km/h (about 180 mph).
  • The parachute is then jettisoned and a rocket-powered descent stage takes over, carefully avoiding the parachute and the back shell it's attached to.  If the rockets don't work, the probe will hit the surface, hard, in about 20 more seconds.
  • The descent stage lowers the rover on nylon cords while it slowly descends, since landing completely under rocket power risks kicking up enough dust to damage the rover.
  • While the descent stage is doing this, the rover gets its landing gear into place.
  • When the rover is safely on the ground, the cords are cut loose, using explosives, and the descent stage flies off to crash land some distance away.
What could possibly go wrong?  Mind, this is a simplified description (and any inaccuracies are mine).  The full details include several more maneuvers, through six different configurations in all, with 76 pyrotechnic devices, ballast jettisoned at various points and dozens of people sweating bullets in the control room and elsewhere.

"Seven minutes of terror", they called it.  Damn impressive engineering, I call it.

OK, so now that we've paused to admire NASA/JPL's chops, what does this have to do with the web? 

I'm old enough to sorta kinda remember Apollo and grainy black-and-white TV coverage.  And Tang.  Cool, and, it must be said, more culturally significant than today's missions, but technically not even close to what we have today.  This is true not only of the vehicle itself, but of the communications technology.  In the 70s we had grainy black-and-white video.  For better imagery you had to wait for the astronauts to bring back the film.

Now, using essentially the same technology as a cell phone camera, NASA is able to capture digital images and put them up on its web site for the world to see immediately (as many have pointed out, much more quickly than NBC saw fit to broadcast Olympic events).  The web gallery includes not only the pretty press-release pictures but also the raw frames they were made from, including pictures of Curiosity staring at its feet and other such that didn't make the cut.  There are plenty of other goodies as well.  I particularly like the "white-balanced" images, which have been post-processed to show what the same terrain would look like under sunlight on Earth.

And there are, of course, a Twitter hashtag (#MSL) and (obligatory plug) updates on NASA's Google Plus page.

As inspiring as it may have been to watch thrilling news coverage with Walter Cronkite narrating, there's something much more intimate about being able to visit a web site from time to time and watch the story unfold directly from the source.

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