TERRESTRIAL FIELD TESTS
With programs
such as MIDP and ASTEP, and Mars Fundamental Research, NASA recognizes
that testing of instruments in terrestrial analog environments is essential
to determine the utility of these instruments on Mars and other planetary
surfaces. LIBS has been involved in a number of field tests.
As part of the Mars Instrument Development Program between 1998 and 2001
the LIBS team participated in two field tests. The first test was
a joint rover exercise held at Black Rock Summit, NV in May, 2000.
The exercise tested the ability to use two rovers synergistically.
One rover, K9--outfitted with remote sensing instruments—was to act as
the scout rover, directing the FIDO rover—outfitted with in-situ instruments—to
locations where the most decisive in-situ measurements could be made.
Our prototype LIBS instrument was integrated into the K9 rover, with the
laser and telescope on the mast (see photo) and the spectrograph, detector,
and electronics in the body. Unfortunately, a wild fire which destroyed
some 200 homes in Los Alamos kept most of our team from reaching the field
site. As a result, we had to settle for making laboratory measurements
of rocks returned from the field, of course using our portable LIBS prototype.
The results are described in Wiens et al. (2002). This paper explores
the advantages of using both passive spectroscopy and LIBS on the same
samples, showing how LIBS distinguishes between the bulk rock composition
and surface weathering which can complicate passive spectroscopy observations
even on terrestrial samples.
The LIBS team participated in a second field test in 2001 in which our team operated in an arroyo adjacent to the FIDO team, near Baker, CA. For this test the LIBS instrument was stand-alone, mounted on a tripod. The relatively low-resolution moveable-grating spectrograph was replaced with a compact echelle spectrograph which allowed coverage of the entire spectral range of 200-800 nm at a resolution of l/Dl ~ 2500. Overall, we have found that LIBS is especially useful in providing immediate screening information which can be followed up with in-situ measurements if so desired. For example, in the field test at Baker, CA, the FIDO rover team, using imaging and an IR point spectrometer, was not able to identify the composition a white-colored alteration product. The team wanted us to find out if it was caliche—a calcium carbonate alteration product--or a high-silica replacement. With essentially a single LIBS shot we were able to determine that the white-colored substance in question was calcitic, not a high-silica alteration product.
LIBS testing has also included other field tests sponsored by organizations other than NASA.
NASA AMES K-9 Rover during field test at Black Rock Summit, Nevada
in May of 2000. Images courtesy NASA Ames Research Center.