Opportunity imaged Santa Maria crater and part of itself at foreground on its Sol 2454 enroute to Endeavour crater where it now is operating. Credit: NASA/JPL/Cornell/Marco Di Lorenzo/ Ken Kremer.com
The NASA Mars Exploration Rover Opportunity is beginning its 10th year roving Mars, completing nine years of "shocking" performance and historic discoveries that began with a bouncing airbag roll into tiny Eagle crater on Jan. 24, 2004.
"It's amazing, we never expected these kind of results!", says Pete Theisinger, the original MER project manager at the Jet Propulsion Laboratory in Pasadena. Calif. He also led JPL's Curiosity rover development in the same role.
Pete Theisinger, project manager for both the Mars Exploration Rovers and the Mars Science Laboratory, talks about Curiosity, NASA's most advanced mobile robotic laboratory, which landed on Mars in August, 2012. Credit: (NASA/Paul E. Alers)
There is no manager at JPL more measured and soft spoken than Pete Theisinger, but during only 20 minutes of discussing the nine years of Opportunity's engineering achievements, Pete was effusive.
Four times he evoked the word "very", twice using each of the adjectives "shocking", "amazing" and "remarkable", with "wondrous" and "neat" thrown in to boot!
Blessed with unexpected Martian bedrock barely feet away, it took just over a month for Opportunity's science team to make the paramount discovery that potentially life sustaining water had once existed on the Meridiani plains of Mars.
Dozens of Opportunity Microscopic Imager pictures revealed "smile" like ripple marks, which Dr. John Grotzinger's analysis showed was from shallow sea like conditions on Mars. Nine years later Grotzinger now leads the Curiosity rover science team. Credit: NASA/JPL/Cornell
Opportunity's five Cornell University managed "Athena" science instruments showed that the rover had come to a stop "on what was once the shoreline of a salty sea on Mars," Steve Squyres, MER Principal Investigator from Cornell said at the time.
Since then, "Oppy" has operated on Mars 36 times longer than its original 90 day specification and driven more than 22 mi. (35 km.) compared with a prelaunch specification of less than a half-mile (0.7 km.) of roving. Its Athena science instruments have operated equally well across nearly a decade on Mars.
Opportunity was the first built, but the second MER rover launched and landed.
Spirit and Opportunity combined cost about $850 million to develop, launch and operate and are identical rovers each weighing about 400 lb. They were built and tested at the Jet Propulsion Laboratory. A prelaunch wheel motor and rover mobility test is underway here at JPL. NASA/JPL
It is part of a MER pair that included the rover Spirit which after 6 years of its own water related discoveries, became stuck in a Martian sand trap in March 2010, entered hibernation and was declared dead in March 2011 after some 1300 electronic attempts to reestablish communication went unanswered. Had Spirit not gotten stuck, unable in winter to fully charge its batteries, JPL might well have had two rovers on opposite sides of Mars starting their 10th year of Martian operations.
During development "we felt the solar array [dust buildup] and the resulting electrical
power situation would probably not allow us to survive beyond the first deep winter," Theisinger told CuriousMars. "But the surprise dust devils which cleaned dust off the solar arrays and the policy of going to North [sun facing] slopes and hibernating through the winters has worked wonders," he said.
"It is the motors [on each of six wheels] that have really been shocking. During the development we went with brush motors and felt that was also a life limiting characteristic." Theisinger said.
Opportunity casts a long pre-winter shadow on Mars. Imaging has been led by Dr. Jim Bell.
He added that concern over the life limiting MER brush motors, that on Earth create friction wear on motor parts, is what led the Mars Science Laboratory program, that began shortly after Spirit and Opportunity landed, to opt instead for brushless motors in each of Curiosity's larger wheels.
"And yet on Opportunity the brush motors have done absolutely remarkably well," Theisinger said.
He noted that Opportunity does have a bad front wheel motor leading to often driving the rover backwards to avoid the troubled wheel's use for steering and an arm motor that is suspect, "but given the extremely cold conditions, that's not shocking," he said.
Mars Reconnaissance Orbiter image shows the about 3 billion year old Cape York ridge on the rim of Endeavour Crater more than 20 miles from where Opportunity landed. The rover working near the center of the ridge is now investigating clays formed in neutral or alkaline water possibly hospitable to ancient microorganisms. Credit: NASA/JPL/Arizona
"Its been nine years, that these things are out in the cold (as low as -112F/-80C) with thermal extremes going up and down, but yet they have done famously well. That is very, very remarkable", he told CuriousMars.
"The mission itself has been neat. The ability with such a long duration mission to get outside the landing ellipse is something we thought would never happen. From a science standpoint before landing we were always looking at what science was within the landing ellipse".
Opportunity specifically has been very, very gratifying to the engineering and science teams--"the troops," Theisinger said. "It is amazing that the first rover we built is the one still working. That is remarkable," he emphasized.
Oppy on Burns Cliff: A picture of Opportunity has been placed for scale to illustrate the size of Burns Cliff using a mosaic of rover images of the spectacular crater wall. Credit: NASA/JPL/Cornell
Spirit originally built second was launched first and landed 20 days before Opportunity, which was the first assembled and tested during 2002-2003.
"With a traditional brush motor you must commutate the current into the motor so that you are driving the motor the right way. You do that by having a brush on the rotating part which makes sure the current is always going the right direction," said Theisinger.
"On the other hand a brushless motor operates through the phasing of the windings using electronic switching so there is no friction wear on that part of the assembly".
"The issue with the brush motors is that there is wear, because there is no lubrication at all on Opportunity's motors. I do not think we expected the 6 millibar carbon dioxide atmosphere to provide any lubrication, but maybe it does," said Theisinger.
Using the Opportunity Honeybee Rock Abrasion Tool (RAT) grinder on El Capitan rock in Eagle crater was a key moment in the early search for evidence of water. The reddish tailings indicated ground up hematite, a mineral formed in aqueous conditions. Spherical "blueberry" concretions also formed in water also dot the images. Credit: NASA/JPL/Cornell
"It was common lore in the business that for a long duration rover, a brush motor was not the thing to do. The point I want to make is that we thought it was a life limiting characteristic for the MER rovers, but it did not turn out that way," he said.
For Curiosity, built as a long duration rover from the start, brushless is the way to go even with the addition of a larger electrical controller to manage the motor current, he said. "When MSL program started we had just landed Spirit and Opportunity, so it was not like we had the experience we now have."
"Curiosity should last a long time. Could it survive 36 times its original two year specification, no, but nobody would be surprised to see it go at least 5-6 years. Hell, I don't even know if I will last another 5-6 years," the veteran JPL project manager said.
Theisinger says that he is now getting the pre Phase-A Mars 2020 rover study underway for a spacecraft that will be largely identical to Curiosity and its Sky Crane landing system. A science definition team is being formed to define the 2020 mission's science objectives by this summer toward what Theisinger hopes will lead in the years ahead to a traditional Preliminary and Critical Design Review process for the instruments selected.
Cape Tribulation at Endeavour crater was imaged by Opportunity as it began to explore its current area of operations. Credit: NASA/JPL/Cornell
"There is a large part of the new 2020 rover that will use the same Curiosity type rover computing element and the same power switching electronics. We hope there is a lot of it we can "build to print" (from Curiosity's blueprints) and move out fairly quickly depending upon what kind of funding profile we get," Theisinger said. Curiosity this week is still being prepared to drill its first rock.
Meanwhile on the other side of Mars from Curiosity, the senior rover Opportunity is exploring the Cape York ridgeline of Endeavour Crater, where clays formed by neutral to alkaline water would have been more favorable to life than the evidence for more acidic water found earlier by both MER rovers (See CuriousMars article January 10, 2013).