On sol 192, Opportunity drove down slope in "Endurance Crater" to reach a rock dubbed "Axel Heiberg." The rover arrived in position to approach a particular point for work in this area with its instrument deployment device (the rover arm). Favorable geometry for an overnight communications pass with Mars Odyssey motivated the team to keep the rover out of deep sleep mode and take advantage of the pass. About 115 megabits of data were returned in this overnight pass.
The rover started sol 193 with some cloud imaging at about 8:45 a.m., local solar time. This required some heating of the camera mast motors and bearings. The observations were acquired, though one of the heaters apparently did not heat as planned. Engineers believe a thermostat controlling that heater had already opened. This rendered the heating circuit inoperable so that even though the heater switch was commanded on and off correctly, the heater itself never got powered. This probably resulted in use of the mast actuator at lower-than-intended temperatures. Rover team members are investigating this, and in the meantime they will not command the rover to perform mast activities at that time of morning.
After the early morning activities, the rover was commanded to approach a target on Axel Heiberg for grinding with the rock abrasion tool. The drive was designed and executed to compensate for slip, and the result was very precise. The rover also made additional remote-sensing observations, then it went into a deep sleep for the night to save energy.
On sol 194 the rover took microscopic imager pictures of a spot on Axel Heiberg, and then performed a grind with the rock abrasion tool to get access to subsurface chemistry. The grind went well, but the targeting was a little off (the hole was about 6 centimeters - about 2.4 inches - to the left of the intended target.) After some investigation it was determined that there is an error in the way one of the ground tools represented the commanded position. This error has existed previously, but the team has never detected it to be this large. It is now being fixed. The exact positioning of the rover and the arm, and the nature of the activity all combined to make the error particularly large in this instance. After the grind, the rover placed the alpha particle X-ray spectrometer on the hole to measure the rock's elemental composition early the next morning.
On sol 195, which ended on Aug. 11, the rover acquired post-grind microscopic images and placed the Mossbauer instrument on the hole to take a reading all afternoon, plus an additional reading after wakeup on the morning of sol 196. The rover also made remote-sensing observations, including images to help assess where it might drive next.