Comments on: More evidence that the rim of Shackleton crater is valuable real estate

By: James Fincannon

James Fincannon — Fri, 17 Dec 2010 15:11:36 +0000

This overlay/composite image is derived from the LRO WAC images, not the NAC ones. The WAC resolution is around 50-100 meters/pixel. NACs are around 0.5 to 5 m/pixel. So yes, this image cannot give slopes, but WACs really aren’t intended to do so. You can just take alot more images covering a large area with the WAC than you can the NAC and this helps do a time study of illumination. But the NAC resolution is good enough for understanding the slope, seeing boulders, fissures and deriving good stereo height models. Also, I think you could do a illumination overlay at this site using the NAC since the orbit causes alot more passes of the poles than elsewhere. But I tried overlaying just two NAC images with Photoshop and it brought my computer to its knees… they are just too big.

The LRO LOLA laser data can give some slope data too for where the laser hits (it cannot hit everywhere of course).

As to the activity being moot, not so. This kind of data was really needed at the beginning of Constellation and its lack slowed down our work. Without this kind of data, more conservative vehicles/bases needed to be designed and this may have made the architecture too heavy. Knowing the minimum continuous eclipse period helps size the energy storage mass, a significant part of the launch mass. So the data will be useful in the future if we restart this activity or if others choose to do so.

By: Kelly Starks

Kelly Starks — Fri, 17 Dec 2010 14:40:01 +0000

I’ld also add that a composit like this doesn’t tell you much about if there are large flat surfaces to land on. I expect you could have pretty serious bolders slops etc and have them not show up on this.

Though given we dumped all our plans to put a research station there its kind of moot?

Certainly I can’t see even more distent commercial lunar bases wanting to set up a base here?

By: James Fincannon

James Fincannon — Thu, 16 Dec 2010 19:43:52 +0000

Beautiful image and will be useful and helpful. From 1700 images over 6 months, that’s about 1 images every couple hours!

Some issues that need to be considered are:
1) Light at the poles (this is the South Pole) is coming in nearly horizontally for a lot of the year. The surface dirt of the tops of hills or rims of craters may not be illuminated much (being nearly parallel to the Sun’s rays) even though light would fully illuminate an astronaut standing there or a solar array pointing at the Sun. The overlay method used to generate this image cannot address this issue. Look carefully at the image and you can see where this might be happening especially around the Shackleton Rim.
2) Dirt color. What if some of the dirt has different reflective properties than other parts? This would mess up the assumption of illumination. They assume some threshold of brightness to mean it is fully illuminated for the time step when generating this illumination map image.
3) Partial Sun blockage by terrain. The images cannot in any way quantify the low Sun on the horizon (for the polar regions this is of particular concern) being partially blocked by distant or nearby terrain. Just because it is lit up by their definition does not mean you are getting 100% Sun. Maybe only 25% Sun. Is the entire region or parts of it getting full Sun or half Sun? No way to know with these LRO snapshot images.

In summary, this illumination data must be taken with the above caveats and used in addition to the LRO laser altimeter digital elevation data and the LRO stereo imagery-derived digital elevation data to get the best assessment of illumination.