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By Emily Lakdawalla


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Nov. 21, 2009 | 08:26 PST | 16:26 UTC

Prepare for your jaw to hit the floor when you see these pictures of Enceladus


Wow, just wow. I didn't know what to expect from the second flyby of Saturn's geyser moon Enceladus in November, which happened yesterday. I knew the cameras were given control of spacecraft pointing during the closest part of the flyby, so that there should be some pretty cool photos of tiger stripes, but I have to confess I didn't expect anything tremendously different from the first high-res imaging flyby.

Well, I was wrong. Wrong, wrong, wrong. Cassini has sent back some of the most amazing images from the whole mission. I'm traveling now and not able to do much of my own image processing so I'm grateful to Gordan Ugarkovic for posting the following two stereo pairs of Cassini Enceladus images to unmannedspaceflight.com. They are both cross-eyed stereo: stare at the images, allow your eyes to cross so that the two images overlap in the center of your vision, then make your eyes focus on the overlapped pair, and it should (unless you are among the 10% of the population who are stereo blind) pop into 3D.

The first one is unimaginably amazing. I never, ever thought we would actually seen the plumes where they issued from the vents. But with the dramatic side-lighting of polar autumn sunset, we can actually see them. Tremendous. This one's a keeper.
Enceladus' plumes in cross-eyed stereo
Enceladus' plumes in cross-eyed stereo
Credit: NASA / JPL / SSI / stereo comparison by Gordan Ugarkovic
The other one shows the vents in really eye-popping 3D.
Tiger stripes near Enceladus' south pole
Tiger stripes near Enceladus' south pole
Credit: NASA / JPL / SSI
For many more amazing photos, visit JPL's raw images website.



Nov. 19, 2009 | 14:54 PST | 22:54 UTC

Encouraging motion on Spirit


UPDATE 7 p.m. PST: It seems there was a bit more downward motion than I detected. The JPL update says:
Spirit successfully completed the first step of its planned two-step motion on Sol 2090 (Nov. 19). After spinning the wheels for the equivalent of 2.5 meters (8.2 feet) in the forward direction, the center of the rover moved approximately 12 millimeters (0.5 inch) forward, 7 millimeters (0.3 inch) to the left and about 4 millimeters (0.2 inch) down. The rover tilt changed by about 0.1 degree. Small forward motion was observed with the non-operable right front wheel, and the left front wheel showed indications of climbing, despite the center of the rover moving downward. These motions are too small to establish any trends at this time. The drive plan had imposed a limit of 1 centimeter (0.4 inch) motion in any direction. The second step of the drive was not performed, because Spirit calculated it had exceeded that limit.
The update goes on to say that the downlink was better than expected, which means (my interpretation here) they'll be able to complete their analysis tomorrow. But I'm not sure if that means they'll be able to drive over the weekend; next drive may not be until Monday.


It really looks like the second attempt at driving Spirit out of the trap has had the hoped-for result: some forward progress (maybe about a centimeter), and no evidence for further downward sinking. The best views seem to be from the right-eye Hazard Avoidance Cameras, the belly-mounted fish-eye cameras that the rover uses to get a look at her own wheels. I'm going to give my preliminary analysis here -- I'll edit this post later with an update based upon JPL's end-of-day report.

Here's the view from the front (apologies for the large file size, but you need all the pixels to get a global view of what progress is being made).
Free Spirit progress as of sol 2090
Free Spirit progress as of sol 2090
This animation consists of four frames from the right eye of Spirit's forward belly-mounted Hazard Avoidance Camera, or Hazcam. The Hazcam gives a fisheye view of the world in front of the rover encompassing the ground between its front wheels, all the way out to the horizon, with Husband Hill in the background. The animation begins on sol 2078, with Spirit bogged down in dust at Troy, and covers the extraction efforts up to sol 2090, when a drive moved Spirit forward slightly, and more importantly, caused the horizon to drop very slightly, meaning that the rover was tipping upward. A full-resolution version of this animation (3 MB) may be downloaded here. Credit: NASA / JPL / animation by Emily Lakdawalla
And here's the rear view.
Free Spirit progress as of sol 2090
Free Spirit progress as of sol 2090
This animation consists of four frames from the right eye of Spirit's rear belly-mounted Hazcam. A full-resolution version of this animation (2 MB) may be downloaded here. Credit: NASA / JPL / animation by Emily Lakdawalla
Things I notice:
  • The right front wheel, which is the one that doesn't roll, clearly advanced forward along the ground. I think this is very good news, because it means the other wheels are getting enough traction to overcome the frictional force of that wheel dragging along the ground.
  • The left wheel clearly rolled, and it must have dragged some of the soil from in front of it as it rolled, because you can see that soil has cascaded or landslided from the top of the pile of soil in front of it, leaving a scar.
  • The forward view of the horizon didn't move a lot, but to the extent that it did move, the left side seems to have dropped just a tiny bit, which might mean that the front of the rover lifted up. Or it may mean that the back of the rover sank, which would be less good. Either way though, the motion is slight.
  • I think I can see the rear wheels lifting a bit, but I'm less confident of that.
  • However, there is definitely forward progress visible in the rear hazcam animation.
As a final gem, here's an animation of the Microscopic Imager views of the pointy rock underneath the rover, which has been some concern to rover drivers, as it's not obvious whether the rock is touching the belly of the rover. From this animation it appears that the pointy rock is receding into the distance. The images are very blurry because the Microscopic Imager was never intended to be used to view objects so far away from it -- it is very, very nearsighted. Rover driver Scott Maxwell mentioned to me a couple of days ago that these Free Spirit driving efforts mark the first time that Microscopic Imager photos have been included in the data stream with the high priority assigned to data products that are critical for mission planning.
Pointy Rock motion during Free Spirit efforts
Pointy Rock motion during Free Spirit efforts
From sol 2088 to sol 2090, the "pointy rock" underneath the rover receded slightly into the distance. Credit: NASA / JPL / USGS / animation by Emily Lakdawalla

All in all, it looks very, very encouraging, and I'm looking forward to the full report from the mission!



Nov. 19, 2009 | 12:49 PST | 20:49 UTC

Space Imaging II: Getting Started with MER and Cassini Raw Images now available for download


I probably crammed too much into today's class: an hour-and-a-half whirlwind tour through the cameras on the rovers and Cassini, how to access their raw images on the Internet, and some basic processing that you can do with each of them.

If you would like to see the recording of the class, go to the Space Imaging section of our website, to the Tutorials page, and follow the links to the WebEx recording, either streamed or downloaded. Before you do so, you will want to have either GIMP or Photoshop installed on your computer. For this class I did all the demonstrations in GIMP, but the operations are pretty similar in Photoshop.

It's interesting to compare the two software packages. I'm a Photoshop user myself, but I'm finding processing color images to be easier in GIMP than in Photoshop. Animations are easier to compose in Photoshop than in GIMP, however. And Photoshop includes a way-cool Photomerge automatic mosaic-stitching package that's not available in GIMP. But I may switch to GIMP to do my own color image processing work from here on out!

The next class will not be until some time after the Thanksgiving holiday. I'll start digging into the nitty gritty details of how space cameras work, and follow that with a class introducing the Planetary Data System.



Nov. 19, 2009 | 09:16 PST | 17:16 UTC

Hayabusa's still coming home: JAXA engineers come up with yet another creative solution


Ideally, you'd like to have a space mission that faces no problems. But in the real world, spacecraft run into trouble. Trouble has come time and again to JAXA's little Hayabusa asteroid sample return mission, yet the mission's engineers always come up with new and creative ways to solve problems.

Just last week, I reported on what seemed like a fatal blow to the mission, the failure of thruster D, one of only two still-functioning ion thrusters. With only one functioning thruster, it seemed unlikely that Hayabusa could perform the trajectory correction necessary to bring it back home.

They've solved the problem in a way I couldn't have imagined. To explain the solution, I need to explain a little bit about how ion propulsion works. In ion propulsion, a gas (usually xenon or some other noble gas) is ionized, stripped of one or more electrons, then accelerated electrically across a charged grid. This mechanism can accelerate the ions to very high speed, producing thrust more efficiently (per unit mass of propellant) than chemical thrusters, although ion engines can't match chemical thrusters for sheer thrusting power. But there's a charge balance problem here: if you ionized and then tossed away all those positively-charged atoms, you'd be building up a huge negative charge on your spacecraft, and pretty quickly your spacecraft would be attracting back all those positively charged ions (and I don't imagine an enormous negative charge would do great things for your electronics). So a key part of an ion engine is a neutralizer, which sits outside the ion engine and emits electrons that are gobbled up by the high-speed xenon cations, resulting in both propellant and spacecraft remaining neutrally charged.

The failure of thruster D was actually a failure of the neutralizer component. Thruster B failed for the same reason. Thruster C's neutralizer is on its last legs, but is still operable. Thruster A, however, has never been used; the engine was found to be "unstable" after launch.

The solution that the engineers have come up with is that they are somehow able to use the neutralizer from thruster A to neutralize the ion beam from thruster B. With this configuration, and the continued operation of thruster C, they have determined that they can maintain the schedule that has them returning to Earth in June of 2010.

Here's some further notes from the press briefing, contributed by unmannedspaceflight.com member Ishigame:
  • Engines A/B/D can no longer stand alone.
  • They won't use Engines A/B and C simultaneously. Engine C will be regarded as a back-up as long as possible.
  • Combining two engines has never been tested on the ground but it has been working for one week [in space] (180 hours). It has been managed thanks to an emergency circuit.
  • Combining two engines requires twice as much power/fuel as standards but Hayabusa has plenty resource. 5 kilograms of fuel will be required to gain 200 meters per second acceleration over 2000 hours, but Hayabusa still has 20 kilograms of fuel in reserve.
  • The acceleration will continue until mid March 2010.
  • The situation doesn't allow premature conclusions [by which I think he means Hayabusa is not out of the woods]. If more troubles happen, e.g. Engines A/B stop before the end of the year, the team will have to consider another plan about returning in 2013.
Go Hayabusa, go!
Hayabusa
Hayabusa
Credit: JAXA





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