LCROSS en route |
LCROSS en route |
Jul 15 2009, 03:08 PM
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#1
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Junior Member Group: Members Posts: 87 Joined: 9-November 07 Member No.: 3958 |
While we're waiting for Those Pictures, here are a couple of shots of LCROSS from our campus observatory last night (0221, 027 UT on 15 July). 4 minute exposures tracking expected motion from the Horizons ephemeris, within 20 degrees of the southern horizon and fighting summertime haze as well as city lights. I wanted to catch it before its inclined orbit takes it too far south, after which it spends a week or so as a predawn object. The range was about 563,000 km, and the Centaur is no bigger than a CSM/LM combination, so this is a more difficult target than spotting an Apollo enroute was. (On the other hand, nobody had CCD imagers in 1969).
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Oct 5 2009, 08:10 AM
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#2
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Newbie Group: Members Posts: 16 Joined: 30-March 08 Member No.: 4078 |
As I understand it, the lower concentration of water in the new target area is offset by better viewing of the results. No, that's not true unfortunately. This document (http://www.nasa.gov/pdf/386497main_target-selection_web2.pdf) shows that the new target crater Caebus has *far* worse viewing conditions than Caebus A. Caebus A Sun Mask Height: 630m, Caebus A Earth Mask Height: 330m Caebus Sun Mask Height 1420m, Caebus Earth Mask Height 3070m This is quite bad news -- they're sacrificing a lot of water sensitivity due to the sunlight/Earth masking. There must have been something seriously wrong with Caebus A to warrant this, as the mask heights at Caebus A are absolutely perfect for an experiment like this. I'm guessing that new LRO data must have either indicated a very uneven distribution or lack of water in the old target. |
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Oct 5 2009, 03:34 PM
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#3
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Senior Member Group: Members Posts: 2173 Joined: 28-December 04 From: Florida, USA Member No.: 132 |
This document (http://www.nasa.gov/pdf/386497main_target-selection_web2.pdf) shows that the new target crater Caebus has *far* worse viewing conditions than Caebus A. The September 5 paper you link to has been superseded by a September 28 release. Based on new data, there are advantages both in certainty of hydrogen signal and viewing geometry for the new site. "The general consensus of lunar experts led by the LCROSS science team is that Cabeus shows, with the greatest level of certainty, the highest hydrogen concentrations at the south pole. Further consideration of the most current terrain models... was important in the decision process. The models show a small valley in an otherwise tall Cabeus perimeter ridge, which will allow for sunlight to illuminate the ejecta cloud on Oct. 9, and much sooner than previously estimated for Cabeus. While the ejecta does have to fly to higher elevations to be observed by Earth assets, a shadow cast by a large hill along the Cabeus ridge, provides an excellent, high-contrast, back drop for ejecta and vapor measurements." |
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