[Spice_discussion] Long-term accuracy of the IAU_MOON frame

John Irwin john at jir1667.plus.com
Sun May 10 05:30:35 PDT 2015


The following observations may be of help.

Using the ME lunar orientation taken from DE430 (a successor to DE421 with a
longer time span) and comparing it with the IAU_MOON model between the years
1550 and 2000, I find there is a general increase in the angular difference
between these two models the further back in time you go. But at most the
linear difference is only 299 m on the lunar surface (sampling the
orientations at 1-day intervals).

Assuming the PA orientation taken from DE431 (a longer version of DE430) can
be converted to ME using the same offset as DE430, the difference in
orientation compared to IAU_MOON reaches 630 m going back to the year 1000.

Strictly speaking the ME offset for DE431 will not be the same as DE430
because of the slightly different modelling of the lunar orientation but I
cannot see them being vastly different. Unfortunately JPL have not
determined this offset for DE431.

So I would say the IAU_MOON model performs quite well over several hundred
years into the past, although it all depends on how far you want to go back
and whether the above errors are within your requirements. If not, perhaps
you can get NAIF to create a binary PCK from DE430 or DE431 over a longer
time span. I think the results should be compatible with the DE421
orientation used for LRO data.


> -----Original Message-----
> From: spice_discussion-bounces at naif.jpl.nasa.gov 
> [mailto:spice_discussion-bounces at naif.jpl.nasa.gov] On Behalf 
> Of Ernie Wright
> Sent: Sat 2015-May-09 04:09 PM
> To: spice_discussion at naif.jpl.nasa.gov
> Subject: [Spice_discussion] Long-term accuracy of the IAU_MOON frame
> I use SPICE to create renderings of the Moon's phases:
> http://svs.gsfc.nasa.gov/goto?4236
> I've been using DE 421 for positions.  For epochs near the present, I 
> use the DE 421-derived binary PCK and the MOON_ME frame for the 
> orientation of the Moon (the color and elevation maps come 
> from LRO and 
> are aligned to MOON_ME).
> I'd like to do something like this for epochs hundreds of 
> years in the 
> past, but the coverage of the binary PCK only goes back to 1900, so I 
> have to use IAU_MOON as the body-fixed frame.
> Does anybody have a sense of the long-term accuracy of IAU_MOON?
> The IAU report,
> http://astropedia.astrogeology.usgs.gov/download/Docs/WGCCRE/W
> GCCRE2009reprint.pdf
> says somewhat vaguely that the orientation equations that 
> IAU_MOON are 
> based on (see Table 2) are precise to about 150 meters, which is more 
> than good enough for what I need, but it doesn't say anything about 
> whether that holds up over long time spans.
> - Ernie
> -- 
> Ernest T. Wright                                
> ernest.t.wright at nasa.gov
> Scientific Visualization Studio                 
> http://svs.gsfc.nasa.gov
> NASA/Goddard Space Flight Center, Code 606.4      voice: +1 
> 301 286-1569
> Greenbelt, MD 20771                                 fax: +1 
> 301 286-1634
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