Target Craters

[MoonThumper]

I have uploaded a file from LCROSS PI Tony Colaprete that details the
current list of target craters. The file is "LCROSS-SP-
Targets-071009.ppt" and is in the file area for this group. A few
notes about the data:
Target Designation = LCROSS specific target designation
Pole = North or South Crater Name = USGS name
Slope(P/F) = target area slopes meets criteria? Pass = P Fail = F
Roughness (P/F) = Target area meets roughness criteria? Pass = P Fail
= F
Mean WEH (%) = Mean value, greater than/less than 1%, for the
estimated Water Equivalent Hydrogen in target area
Topo Mask, To Sun = Topographical mask along line of site between
target area and sun
Topo Mask, To Earth = Topographical mask along line of site between
target area and Earth
Centaur Target Location = Latitude and Longitude coordinates for
Centaur impact point

[cano...@yahoo.com]

Thanks Brian. - Kurt

[Jim Mosher]

Brian,

Thanks for posting this information.

I wish the LCROSS mission well, but having followed this mission since
November 2008, I must say two recurring characteristics of the
operation that I have noticed are cryptic communications and lack of
attention to detail. The present release of target data, although
helpful, reinforces those impressions for me.

Is this presentation an attempt to document specific locations under
consideration within craters, or only intended as a vague indication
of the craters being considered (without specifying where, within
those craters, the impact point might be)?

I am honestly unable to tell because the "masking" information
presented in Slide 2 suggests the former, but everything else about
the presentation suggests the latter.

The shaded relief IAU/USGS nomenclature map used as the background for
Slide 3 seems an odd choice for showing the target positions since it
was obviously never intended to be topographically precise: note, for
example, the clearly incorrect placement of the south pole:

http://the-moon.wikispaces.com/South+Pole

in relation to the rim of Shackleton.

As a result, it is unclear to me if the target symbols in Slide 3 are
intended to show the relationship of the possible LCROSS impact points
to recognizable (but imprecisely placed) features; or if the target
dots have been plotted at their selenodetically correct positions on
the coordinate grid irrespective of how the surface topography is
depicted at that point.

The latter does not seem to be the case, because the dots in Slide 3
do not always seem to be plotted at the coordinate positions mentioned
in Slide 2. As a random example, the coordinates of the Faustini
impact point ("SP_A") are listed in Slide 2 as 89°E/87.2°S, but the
symbol is plotted in Slide 3 at what looks like 82°E/87.5°S. My first
guess would be that the coordinates specified in Slide 2 are (as they
say they are) the intended Centaur impact point, but that the dot had
to be shifted in Slide 3 to give a better impression of where that
point falls relative to the (incorrectly placed) crater rim.

However, the alternative interpretation does not work either, because
some of the locations mentioned in Slide 2 fail to make sense as
selenodetically correct positions. For example, Slide 3 seems to be
showing that LCROSS target point "SP_G" is intended to fall on the
Earthward side of the floor of a 20-km diameter crater to the west of
Malapert. Slide 2 gives its coordinates as 1°E/84.3°S. That's in
reasonable agreement with the map grid, but, when plotted on a
selenodetically correct map, it yields a point that lies outside the
crater on its sunlit north side. That seems an unlikely target for a
mission seeking water ice.

Also indicative of the lack of attention to detail is that on Slide 3
one finds a target point "SP_E" plotted inside Shackleton, but no such
target point is listed in Slide 2. Is Shackleton a potential target
or not?

--

To clarify these comments, the attachments show where the coordinate
positions listed in Slide 2 fall on four maps of the Moon's south pole
thought to be more selenodetically correct than the USGS/IAU shaded
relief nomenclature map.

1. Clementine_v2 is the "version 2" ULCN2005 warped Clementine basemap
from Map-a-Planet

http://the-moon.wikispaces.com/Map-a-Planet

2. Kaguya is their Laser Altimeter data set:

http://www.sciencemag.org/cgi/content/abstract/323/5916/897

3. Cornell_Smithsonian_Radar_2005 is a data set obtained using the
Arecibo radar transmitter:

http://ltvt.wikispaces.com/Radar+Maps

4. RadarCon2008 is from a presentation about a 2006 Goldstone radar
interferometric data set:

http://www.nasa.gov/mission_pages/exploration/mmb/022708.html

The maps have an identical scale and orientation with the red/blue
lines representing the theoretical terminator position at 2009 Oct 09
at 11:30 UT, and the light blue line at the bottom representing the
theoretical limb seen from Mauna Kea, Hawaii (the view from Earth will
be from the top, perpendicular to this line). The white lines are the
meridians at 0/180° and +/-90°, intersecting at the south pole.

These show (as Kurt Fisher's earlier plots have already demonstrated)
that the "SP_G" position listed in Slide 2 is obviously not an
intended target. Whether the others targets are where they were
intended to be, or just more equally random dots, is hard to say.

I don't know if this PowerPoint presentation was circulated internally
with additional notes explaining what it was intending to show, but
(if not) I sincerely hope the LCROSS team can get its act together
before impact. It seems to me that considerably more attention to
detail will be required if the spacecraft is expected to impact close
to its intended target.

-- Jim Mosher

P.S.: What does "Topo Mask" mean?

I would have guessed it means you draw a line from the target point on
the surface to the center(?) of the Sun or Earth and ask "What is the
highest elevation encountered above this line?" But if that were
correct, negative values would not be possible, yet negative values
are listed for the "Topo Mask to Earth" of SP_B and SP_CB. Is it
possibly the height of the "nearest" (defined in some way) crater rim
relative to this line?

[cano...@yahoo.com]

Jim, There is a further explanation on the "mask" columns in Kelly
Beatty's ST online article:

Kelly Beatty (Sky & Telescope). July 14, 2009. LCROSS Crater
Candidates Announced. http://www.skyandtelescope.com/observing/highlights/50623927.html
(last accessed 7/14/2009).

Clear Skies - Kurt