Day in the Sun

Opportunity Navcam
Opportunity’s rear hazard camera looking back up the steep wall of Endurance Crater, Sol 208
Credit: JPL/NASA

The Spirit rover is now in a safe place to continue daily science observations automatically throughout its solar conjunction period when engineers and scientists will be unable to send commands reliably to the rover. The planned gap in sending daily plans runs for about 12 days beginning Sept. 8 for Spirit and Sept. 9 for Opportunity.

An 18-day period began a transition into solar conjunction on sol 241, when the Sun partially obscured the communications path between Earth and Mars, making communications sessions unreliable. Engineers were able to successfully command Spirit on sol 241, and they had partial commanding success on sol 242.

From sol 244 through sol 255, sequences already safely on board will perform a set of science activities on a daily basis. No movements of the wheels or the robotic arms are in the conjunction-period plans, but the camera masts may move for making observations. The rovers also will continue communicating daily with NASA’s Mars Odyssey orbiter and will also attempt to communicate directly with Earth. On sols 256 through 258, the last three days of conjunction, the rover team will attempt normal operations again.

On sol 242, engineers sent Spirit a set of coordinated commands to use the miniature thermal emission spectrometer and panoramic camera for observations of possible future science targets. A new set of 12 conjunction master sequences was also transmitted successfully to Spirit. This new set of conjunction master sequences will use less energy than previous sequences.

Opportunity tire track through dune
Opportunity tracking through sand dunes and hematite concretions
Credit: JPL/NASA

For the conjunction period, the rover team has placed the Mössbauer spectrometer on one of the two magnets on the rover deck. Spirit will activate the Mössbauer instrument every day during conjunction in order to characterize the dust that has collected on the magnet. However, a wrinkle has developed in this plan. Before placing the Mössbauer spectrometer on the magnet, Spirit placed it on the soil in front of its current location. That soil touch was done to leave a soil impression that would be studied after conjunction for changes. Images taken after the touch indicate that Spirit inadvertently picked up some soil and likely sandwiched that soil onto the magnet with the Mössbauer. It’s the team’s first inadvertent sample acquisition.

Engineers and scientists decided to leave the Mössbauer in place on the magnet and will evaluate the status and effect of the dirt clod after conjunction. The dirt does not pose any threat to the rover from an engineering perspective.

Since Spirit arrived at its solar-conjunction resting place, its science activities have focused on gathering data from the surrounding area for use in planning post-conjunction sols. Navigation camera images in Spirit’s drive direction have been used to develop traverse maps. These maps show areas that allow Spirit to maintain a north-facing tilt; these areas will provide significantly more solar energy and will therefore be favored as the team plans the traverse to Spirit’s next science target.

"Based on experience with other spacecraft, we expect that when the Mars-Sun-Earth angle is 2 degrees or less, the ability to successfully communicate degrades rapidly," said JPL systems engineer Scott Doudrick, who has been organizing conjunction operations for both rovers. "To be cautious, we’re allowing three days on either side of that period."

During conjunction, Spirit will transmit five-minute "beep" tones, and engineers will send "No-operation" commands to the rover to characterize effects that the conjunction has on radio transmissions between Mars and Earth.

Opportunity fine-scale wind dunes
Opportunity fine-scale wind dunes.
Credit: JPL/NASA

For the Opportunity rover, a newly downlinked navigation camera mosaic, created from images taken on sols 115 and 116 (May 21 and 22, 2004) provides a dramatic view of "Endurance Crater." The rover engineering team carefully plotted the safest path into the football field-sized crater, eventually easing the rover down the slopes around sol 130 (June 12, 2004). To the upper left of the crater sits the rover’s protective heatshield, which sheltered Opportunity as it passed through the martian atmosphere.

The Mars rover, Spirit, landed in the Gusev Crater on Jan. 4. Opportunity, its twin, landed on the Meridiani Planum on the opposite side of the planet Jan. 25. Both rovers still are under operation by NASA and returning science data, although over about two weeks, the rovers are out of reach as the Sun moves between Earth and Mars. Both have each conducted more than four months of bonus exploration and discoveries after successfully completing their three-month primary missions on Mars.

"The science team gets some time off from the daily planning cycle, but we will have a full spacecraft team every day, so we will be able to respond quickly if the rovers communicate a problem to us and there’s a good reason for emergency commands," Doudrick said.

Related Web Pages

Astronaut’s View of Mars
Conjunction Junction
Life on Mars: A Definite Possibility
Mars Rovers JPL
Mars Berries Once Rich in Iron-Water
NASA’s RATs Go Roving on Mars

Water Signs
Microscopic Imager
Gusev Crater
Pancam– Surveying the Martian Scene
Mössbauer spectrometer
Alpha Proton X-ray Spectrometer