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Emily LakdawallaSeptember 30, 2008

Doug Ellison at Europlanet 2008: Kaguya update

All last week, Doug Ellison filed reports from the third European Planetary Science Congress, also known as Europlanet, taking place in Münster, Germany. Doug is the dictator-for-life of the online forum Thanks, Doug! --ESL

by Doug Ellison

On Friday Professor Manabu Kato, science manager for Kaguya gave an update on the mission (which it seems they still refer to as "Selene," given the layout of his Powerpoint slides). Most of you will have heard of and about Kaguya previously -- but a health report is certainly overdue!

Kaguya deploys its mini-satellites


Kaguya deploys its mini-satellites
Views from a small onboard camera show the successful deployment of the lunar orbiter Kaguya's two mini-satellites. Each mini-satellite is an octagonal prism one meter in diameter with solar cells covering its 0.65-meter-long sides; the satellites will be used in a radio interferometry experiment to map the Moon's gravity. The first satellite, Okina (also known as the Relay satellite or Rstar), was released on October 9, 2007 into an elliptical orbit 100 by 2,400 kilomters in size (first two frames). The second satellite, Ouna (also known as the VRAD satellite or Vstar), was released on October 12, 2007 into an elliptical orbit 100 by 800 kilometers in size (last two frames). Okina and Ouna, meaning "honorable elderly man" and "honorable elderly woman," refer to the old couple who adopted the moon princess Kaguya in the Tale of the Bamboo Cutter.
Kaguya launched on September 14 last year. After a flight to the Moon, orbit insertion, the release of two sub-satellites and checkout of the spacecraft and its instruments, it began steady science operations on December 21. In February it successfully survived its first lunar eclipse and to date they have had 9 months (or 9 lunar days ) of nominal science operations. They are fully expecting an extension from the end of the nominal mission in October for 7 to 8 months

Kaguya is probably most well known for carrying HDTV technology to the moon to record high definition video of flying over the lunar surface, and image Earth setting and rising over the limb of the Moon. To date, 60 minutes of HDTV footage has been downlinked. All the instruments except two are functioning well, the unspecified trouble being with the X-ray Spectrometer and Charged Particle Spectrometer.

Kato showed a global Gamma Ray spectra that showed very strong spikes in uranium, aluminium, potassium, silicon, thorium, oxygen, titanium, and iron (see this abstract for more details ). They have had interruptions on GRS use, so to date have about three months of good analysis, and will build better-resolution maps of elemental distribution as time allows.

Kaguya Earthset sequence


Kaguya Earthset sequence
Kaguya captured the blue marble of Earth setting below the Moon's north pole on November 7, 2007. This image is a still from a high-definition movie shot with Kaguya's telephoto HD camera. The Australian continent can be seen at the left center of Earth, and Asia to the lower right; because the view is across the Moon's south pole, Earth appears "upside down". The five frames were taken about 20 seconds apart.
The Terrain Camera has taken stereo imagery at a 10 meter-per-pixel resolution, with the footprint of the two stereo channels 60 kilometers apart. Kato showed elevation models of Pythagoras, Jackson and Antoniadi craters. With these in hand, they can correct the brightness of their images for the influence of topography, obtaining its inherent brightness independent of the slope it presents to the Sun. Using crater counting, they have concluded that the lunar far side stopped having active volcanic activity much earlier than the near side.

Their laser altimeter elevation data is at a coarser resolution, but they now have global coverage. This was demonstrated with both a single profile across a 2.5-kilometer-deep crater, and a stunningly sharp global elevation map. In a way similar to the radar sounding of Mars conducted by SHARAD on Mars Reconnaissance Orbiter and MARSIS on Mars Express, Kaguya is getting radar profiles of the lunar surface. This was actually done previously by the Apollo command and service modules, but only in a few small equatorial regions and at a relatively low resolution of three kilometers per pixel. Kaguya is getting profiles at 500 meters per pixel, and they are trying to calibrate to better understand the signals they are getting.

Kaguya deployed two sub-satellites while maneuvering into its final orbit, and by using Kaguya, the sub-satellites and the ground station as a four-way radio network, high-resolution gravity field maps have been produced of the near side and, uniquely, the far side. The gravity map showed some localized gravitational highs on the near side, but the far side is noisier, with highs at large crater rims. Apollo crater is a local gravity low, whereas Mare Serenitatis is a high gravity anomaly. The first of the sub-satellites will impact the moon next February, on the lunar far side. It is because of the slightly lumpy nature of the very gravity field it's designed to map that its orbit will decay.

Kaguya is clearly getting very, very good science, and as the first spacecraft of the International Lunar Decade, it's setting a high bar for the missions that have already followed, and are yet to join in. There is not a great deal of finished science to be drawn from

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Emily Lakdawalla

Solar System Specialist for The Planetary Society
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