During the rover's 83 Sol mission on Mars, it nearly circumnavigated the lander, staying within a 12 meter radius of the lander. Early APXS measurements were taken on rocks to the north of the lander (Barnacle Bill and Yogi) and a variety of soils near the end of the ramp and to the east of the end of the ramp (cloddy deposits between the ramp and Yogi, Scooby Doo, wheel-disturbed soil next to Scooby Doo, and soil next to Lamb).
The unusually high sulfur content of the rock analyses for Barnacle Bill and Yogi indicated that the APXS may have sampled weathered rock or rock covered by sulfur-rich dust or soil, so the rover was sent towards the 'Rock Garden' for more rock APXS analyses. This is an area to the southwest of the lander containing several large rocks, some of which have low red/blue ratios (less oxidized iron) and what appeared to be near-vertical rock faces (less likely to be heavily dust covered). En route, an APXS measurement was taken on the 'dune-like' feature called Mermaid Dune. The 'Rock Garden' terrain was difficult for rover driving and the loss of the rover battery on Sol 56 slowed down operations, but during the last 46 Sols, seven additional rock APXS analyses were obtained. Two analyses were taken on one rock (Half Dome), although the rover battery was alive for the first one and dead for the second one. Preliminary X-ray composition results for eleven APXS analyses (5 rocks and 6 soils) are given in [RIEDERETAL1997B].
An inventory of the 173 APXS_EDR data files is found in a table provided in three formats: APXS_INV.HTM (HTML), APXS_INV.ASC (formatted ASCII text), and APXS_INV.TAB (comma separated value ASCII). (The former two are found in the DOCUMENT directory on the MPRV_0001 CD, and the latter is in the INDEX directory of the same CD.) The inventory lists for each data file: APXS measurement number; rover command number; rover command sequence number; VICAR data file name; whether the file contains cumulative data, is the start of a new data collection, or is a re-read of old data from the memory; measurement start and stop times (in SCLK and Local True Solar Time); target; and measurement comments (including duplicate insurance readouts of the APXS memory, sequence requeue mistakes, electronics noise tests, and power problems).
Other parameters measured are the temperature of the X-ray preamplifier in the sensor head, the temperature of the alpha detector preamplifier in the rover's warm electronics box (in °C), and the sampling duration of the alpha, proton, and X-ray measurements (hh:mm:ss).
The APXS Experiment Data Records were created at the Multimission Image Processing Laboratory of the Jet Propulsion Laboratory.
Some data files are completely new starts, as indicated by ACCUMULATION_COUNT=1 in the file header, and these only contain temperature measurements at the beginning and end of the APXS measurement session. Other files are 'cumulative spectra' and consist of accumulations of multiple measurement sessions added together, and the number of sessions is indicated by the accumulation count. For cumulative spectra, temperatures at the beginning and end of each measurement session are recorded and counts for each detector are summed with those for previous accumulations. Up to 10 accumulations are possible.
Jet Propulsion Laboratory
Pasadena, CA 91109-8099
|X||Y||Z||Rock/Soil APXS Target|
|A-2||1.89||-1.95||0.31||soil off the end of the ramp|
|A-3||1.30||-2.45||0.18||Barnacle Bill rock|
|A-4||2.79||-2.64||0.28||soil near Yogi|
|A-5||3.29||-2.48||0.28||soil near Yogi|
|A-8||2.85||1.13||0.32||Scooby Doo indurated soil or rock|
|A-9||3.08||1.32||0.28||disturbed soil next to Scooby Doo|
|A-10||3.74||-0.43||0.28||dark soil next to Lamb|
|A-18||-4.81||-3.81||-0.54||Half Dome rock, first location|
|A-19||-4.82||-4.13||-0.59||Half Dome rock, second location|
The Mars Pathfinder Lander (L) Coordinate Frame
The Mars Pathfinder Lander is a tetrahedral structure. One of its faces, the one upon which it sits, is called the base petal and houses most of the lander equipment. The other three faces, or petals, open after surface impact to expose these systems. The rover is mounted on one of these petals. The Mars Pathfinder Lander Coordinate Frame, or 'L' Frame, has the lander base petal as its reference plane and its center coincident with the geometric center of the base petal. The YL-axis of this coordinate system passes through the geometric center of the rover petal, and defines the reference direction. The ZL-axis is normal to the reference plane and coincident with the nominal spacecraft spin vector. When the lander is upright on the surface, the ZL-axis is directed positively downward into the ground.
The Martian Local Level (M) Coordinate Frame
The Martian Local Level Coordinate Frame is a right handed, orthogonal, frame whose origin is co-incident with the origin of the Lander Coordinate Frame. The XM axis points north, the YM axis points east, and the ZM axis points down.
For more information on Mars Pathfinder coordinate systems, see the [MELLSTROM&LAU1996], [WELLMAN1996B], and [VAUGHAN1995] references. However, please note that as of the time this APXEDRDS.CAT file was written, [WELLMAN1996B] had not yet updated his discussion of elevation measurements to match that agreed upon by the Project. Where he used elevation ranges of 0° to 180°, the MPF Project used -90° to +90°.
|Address:||Planetary Data System, PDS Operator
Jet Propulsion Laboratory
4800 Oak Grove Drive
Pasadena, CA 91109
When measuring rock and soil samples, the desire was to obtain at least 10 integrated hours. Only 3 hours of nighttime measurement were needed for a good X-ray analysis. X-ray spectra obtained during the night, when ambient surface temperatures were low, were unaffected by electronics noise. Ten hours of measurement during the day or night provide good alpha and proton analyses. Shorter times still provide useful results. Actual spectral accumulation times (listed in the table below) for the rock and soil analyses on Mars range from 5 to 16 hours.
A summary of the 27 APXS measurements is shown in the table below.
|Measurement initial start
time and final stop time
(Local True Solar Time)
|A-1||Sol 1 07:17 - Sol 2 09:58||2.8||1.9||atmos.|
|A-2||Sol 2 14:53 - Sol 3 10:00||19.6||15.9||soil|
|A-3||Sol 3 15:00 - Sol 4 07:01||16.5||13.6||rock|
|A-4||Sol 4 16:59 - Sol 5 01:32||8.8||8.1||soil|
|A-5||Sol 5 16:01 - Sol 6 06:55||15.3||9.2||soil|
|A-6||Sol 10 09:01 - Sol 10 09:40||0.7||0.1||atmos.|
|A-7||Sol 10 14:17 - Sol 11 02:37||12.7||5.7||rock|
|A-8||Sol 14 14:03 - Sol 15 02:55||13.2||5.7||soil|
|A-9||Sol 15 14:04 - Sol 16 03:15||8.6||7.7||soil|
|A-10||Sol 20 14:03 - Sol 21 02:59||8.3||7.0||soil|
|A-11||Sol 22 15:23 - Sol 23 02:40||11.6||4.8||atmos.|
|A-12||Sol 24 17:07 - Sol 24 17:17||0.2||0.1||atmos.|
|A-13||Sol 24 18:01 - Sol 24 18:12||0.2||0.1||atmos.|
|A-14||Sol 25 00:06 - Sol 25 00:16||0.2||0.1||atmos.|
|A-15||Sol 28 14:05 - Sol 29 02:44||8.0||5.3||soil|
|A-16||Sol 37 14:07 - Sol 38 03:05||8.2||6.5||rock|
|A-17||Sol 52 14:18 - Sol 53 03:05||8.0||7.0||rock|
|A-18||Sol 55 14:06 - Sol 56 00:05||7.2||5.9||rock|
|A-19||Sol 58 12:08 - Sol 64 10:45||12.6||8.9||rock|
|A-20||Sol 64 12:04 - Sol 66 10:40||10.3||6.5||rock|
|A-21||Sol 66 12:04 - Sol 67 10:32||5.2||3.0||atmos.|
|A-22||Sol 67 12:04 - Sol 68 09:32||4.0||2.0||atmos.|
|A-23||Sol 68 12:05 - Sol 70 10:47||9.5||4.9||rock|
|A-24||Sol 76 12:09 - Sol 77 09:06||2.7||0.5||atmos.|
|A-25||Sol 77 12:08 - Sol 78 09:06||3.0||0.8||atmos.|
|A-26||Sol 78 12:03 - Sol 79 10:17||4.6||2.6||atmos.|
|A-27||Sol 79 12:08 - Sol 82 09:47||11.1||6.3||rock|
Measurement initial start and stop times were obtained from the SCLK times in the downlink telemetry for the acknowledgement of the exact commands that were issued to trigger the start and stop of each APXS measurement (usually Meas_Start, Meas_Stop, Reset, or Shutdown). SCLK times were converted to Local True Solar Time using the script sclk2ltmst (see Ancillary Data discussion). This time is only as accurate as the rover's clock, and is a close approximation to the exact initial start and stop time of each APXS measurement. In a few cases, the downlink was lost, and uplink predictions were used instead. Some of the cumulative APXS measurements were interrupted by other rover activities, in which case, the first accumulation start time and last stop time are indicated. Integrated measurement time, as indicated by ALPHA_SAMPLING_DURATION, PROTON_SAMPLING_DURATION, and XRAY_SAMPLING_DURATION in the data file headers, is always less than the accumulation final stop time minus the initial start time, because the sampling durations do not include quiet periods when the APXS was powered off and detector 'dead time.'
In 15 of the APXS_EDR files, the APXS spectra are filled with zeros. This is the case when rover command sequence 50520D was requeued by mistake on Sol 6, when there was not enough power to turn on the APXS (some of the A-19 measurements). The files filled with zeroes are indicated by N/A listings for measurement start and stop times in the inventory table of the 173 APXS_EDR data files (mentioned in the Data Set Overview).
One known discrepancy was found in the APXS time stamps, for A-2 rover command 2723. The ALPHA_SAMPLING_DURATION (and PROTON and XRAY) indicate a minimum duration between measurement start and stop time of 2 hrs 45 minutes, but the stop minus start time duration, as indicated by rover time stamps is 2 hrs 10 minutes. The cause of this discrepancy is unknown.
In addition, the rover clock was sometimes significantly in error when it wasn't synced up with the lander clock beforehand. Syncing usually occurred early each morning. The only way to check for this is to carefully examine the rover downlink telemetry. Timestamps for A-19 are the most uncertain of the APXS files, because the rover battery stopped working early in the morning of Sol 56 and the rover had difficulty powering back up in the first few days following this event.