26 Jan 2009
(Source: Jet Propulsion Laboratory)
OPPORTUNITY UPDATE: Post-Solar Conjunction Hangover - sol 1716-1742, November 20 - December 17, 2008:
As soon as Opportunity came out of solar conjunction - a period when the Sun passes between Earth and Mars and prohibits communication - engineers discovered that the rover's computer memory was a bit too full for comfort. They spent the first two days after conjunction minimizing data generation on Mars and planned to spend another two days doing the same. The purpose of the slowdown was to give Opportunity a chance to empty out some of the large number of "sent" data products.
In this case, the memory situation involved the data product limit, not the data volume limit. In the event of an excess of data volume, the rover automatically deletes data. An excess number of data products, on the other hand, can cause a rover fault. Such a fault occurred on Spirit, Opportunity's twin on the opposite side of Mars, shortly after landing. The potential for such a fault becomes a concern whenever the number of on-board data products is greater than 6,000. After solar conjunction, on sol 1740 (Dec. 15, 2008), the number of data products in Opportunity's computer memory was 6,448.
To prevent a potential fault, engineers postponed more scientific studies and adopted a plan to minimize data products. These plans permitted only one measurement per sol of atmospheric opacity or "tau"
(atmospheric darkness caused by dust) and an overnight measurement of atmospheric argon. The rover science team expects a pending deletion of about 3,000 "sent" data products on sol 1743 (Dec. 18, 2008) to alleviate the memory overload.
As soon as engineers confirm deletion of a sufficient number of data products from the rover's flash memory, Opportunity will resume studying the cobble nicknamed "Santorini." The name Santorini comes from a Greek isle once known as Thera that 3,600 years ago was the site of one of the most powerful volcanic eruptions ever seen. Remaining observations will include taking microscopic images and measuring elemental composition with the alpha-particle X-ray spectrometer.
Opportunity is healthy and all subsystems are performing as expected as of the downlink of data on sol 1742 (Dec. 17, 2008). Energy was around
594 watt-hours (almost enough to light a 100-watt bulb for six hours).
Tau, a measure of the amount of sunlight blocked by dust in the atmosphere, was 0.622, and the dust factor, a measure of the amount of sunlight penetrating dust on the solar arrays, was 0.6536.
Before, during, and after solar conjunction, Opportunity completed the following activities:
Sols 1716-1720: With only a few days left before solar conjunction, Opportunity scrambled to get as much interactive work done as possible.
Having successfully placed the robotic arm on Santorini, Opportunity began studying the mineralogy of Santorini with the Moessbauer spectrometer and acquired images of the rock with the panoramic camera.
Opportunity also used the panoramic camera to acquire a 360-degree panorama, take images of the rover's tracks, and monitor dust-related changes in the atmosphere. In addition, the rover surveyed the horizon, acquired time-lapse movie frames of the sky in search of clouds with the navigation camera, and measured argon gas in the atmosphere with the alpha-particle X-ray spectrometer.
Sols 1721-1722: Opportunity switched over to the master sequence of commands to be followed during the two weeks of solar conjunction. Plans called for Opportunity to study the mineralogy of Santorini using the Moessbauer spectrometer on all but two Martian days - sols 1726 (Dec. 1,
2008) and 1736 (Dec. 11, 2008) - when the rover was to measure argon gas in the atmosphere with the alpha-particle X-ray spectrometer. During conjunction, Opportunity was also to complete a photon-transfer measurement on each of the rover's cameras.
Sols 1723-1740 (Nov. 28-Dec. 15, 2008): While out of contact with Earth, Opportunity studied Santorini's mineralogy with the Moessbauer spectrometer, measured argon gas in the atmosphere with the alpha-particle X-ray spectrometer, and made remote-sensing observations.
On sol 1725 (Nov. 30, 2008), approximately 0.93 megabits of data transmitted to Earth was lost to solar interference. The following day, sol 1726 (Dec. 1, 2008), at least a third of the expected data volume from Mars was lost. After that, virtually all data was lost while the Sun blocked communications.
Sol 1741 (Dec. 16, 2008): Opportunity relayed data to Earth via NASA's Mars Odyssey orbiter, measured dust-related changes in atmospheric clarity with the panoramic camera, and measured argon gas in the atmosphere using the alpha-particle X-ray spectrometer.
Sol 1742 (Dec. 17, 2008): Opportunity measured dust-related changes in atmospheric clarity with the panoramic camera and recharged the batteries.
As of sol 1742 (Dec. 17, 2008), Opportunity's total odometry was
13,616.47 meters (8.46 miles).