Mars Exploration Rovers Update: Opportunity Braves Onset of Winter to Picture Perseverance

The Martian winter began to grip Endeavour Crater in September, slowing the pace of the Mars Exploration Rovers mission. But Opportunity braved the brutal cold in Perseverance Valley and followed her commands to visually document everything in sight with images, and even check out a couple of pebbles up close.

The veteran robot field geologist is on a small rise along the southern ‘wall’ or side of the valley, which cuts into the western rim of Endeavour at Cape Byron. Opportunity drove onto the slope, at the end of August. The second of seven planned science stops on a route that extends from the top to the bottom of the valley and the interior of Endeavour Crater, the site is about a third of the way down the valley. Known simply as station 2, it’s where the rover would spend the month of September.

“Winter is setting in and we’re getting cold,” said MER Chief of Engineering Bill Nelson, of the Jet Propulsion Laboratory (JPL), the NASA center that has produced all of the American Mars rovers.

Opportunity is producing enough energy to survive and to work, but she’s had to use a lot of that energy just to keep warm. The robot’s two rechargeable lithium ion [Li-ion] batteries, which provide energy for the rover when the Sun isn’t shining, are in effect her heartbeat. That heartbeat is being strained and the depths of the season are still ahead.

The winter solstice in the southern hemisphere of Mars where Endeavour and this rover are located won’t occur until November 19^th or 20^th depending on where you live on Earth. The day of the least amount of sunshine, what planetary scientists call minimum insolation, falls on Halloween. But that’s not as spooky as just how cold it is at Endeavour right now.

Mars has four seasons, just like Earth. But the seasons on Mars are about twice as long and during winter outside temperatures on the Red Planet in recent weeks have been plummeting from cold to “damn cold,” as MER Project Manager John Callas, of JPL, defined it. Model predictions of the rover’s external wall indicate Opportunity in September likely felt the freeze of minus-90 degrees Celsius [minus-130 degrees Fahrenheit], wind chill not factored.

It got so cold that the MER ops engineers huddled in September to come up with a plan to deploy a back-up, never-before-used battery heater to help out their robot colleague in the Martian field. Opportunity, true to her MER personality, pressed on.

“We are imaging and we have even looked at a couple of targets, pebbles within reach,” said MER Project Scientist Matt Golombek. “But things are slow going, because we’re approaching the dead of winter.”

The MER team’s science objective on this, its tenth extended mission, is to study the morphology or the shape and form of this valley. That translates, for the rover, into an imaging campaign. So, Opportunity’s objective is to take dozens of images at each stop along the route. At the end of the journey, the rover’s collection of image data will be used to produce a three-dimensional digital elevation model.

Then, using that model along with other data, the MER scientists will piece together clues and determine for once and for all what it was that carved this distinctive feature into the western rim of Endeavour billions of years ago.

Since it is winter, Opportunity is “hopping” from one energy-favorable slope – or "lily pad" to the next, as reported in last month’s MER Update. These lily pads are sites where the terrain is tilted sufficiently to the north to maximize the amount of Sun the solar-powered rover's solar panels takes in. The strategy, which has been used nearly every Martian winter since 2005, worked well through September, with the rover producing a little less than one-third her capability in 2004 on landing with clean solar arrays, enough to drive and work.

Despite the increasingly brutal cold, Opportunity was able to keep herself warm and work, at least a bit. But rove she did not. “The last drive was on 4836 (August 31, 2017) and we haven't moved since,” lamented Rover Planner Paolo Bellutta, who charts Opportunity’s paths. “We have plenty of power to survive, and to drive, it is just the combination of lack of flash [long-term] memory and the late [after sunset] Odyssey passes that are making things more difficult,” he said.

The realities cannot be ignored and now are part of the territory. In addition to the cold that is impacting the stamina of her battery power, the rover lost the use of her long-term memory, her Flash drive, nearly two years ago and is working in RAM mode. Since RAM is volatile memory, the data disappears when the rover shuts down, so the robot has to off-load all the work from each sol or Martian day to one of the Mars orbiters before she goes to sleep each night.

The challenge is that the Mars Odyssey orbiter, the rover’s primary communication link to Earth, circles by late in the Martian day, after sunset. That means the rover has to work and then stay awake until the orbiter comes into view. It all takes energy, especially in winter. So, when the rover must wait for Odyssey, she starts her workday later. The rub: late afternoon is not always a great time to be taking images.

All Martian winters tough and so it’s hard to say right now where this one ranks. Myriad factors are involved, though the reality that Opportunity is two years older than she was during the last Martian winter has to be considered. Nevertheless, the cold of this winter may be one for books.

“We’ll get through it,” assured Callas. “It will be a slog to get down to the deepest part of the winter, but after that, things will get better.”

There are good reasons for optimism the pace will pick back up soon. If all goes as designed and planned, the rover may soon turn on the battery heater. And, the mission has acquired more Mars Reconnaissance Orbiter passes, which come by much earlier in the day, enabling the rover to add to the workflow. And there’s more.

If Mars proves consistent, an October surprise or two could be in the offing. “By this time last Mars year, the dust on the solar panel was starting to be removed,” said MER Power Lead Jennifer Herman, of JPL. “We are hoping to see a cleaning trend sometime soon this winter. We've had no such luck yet, but I am hoping by Thanksgiving that we will be thankful for some Opportunity dust cleaning.”

Meanwhile, the images trickling in from Mars and Opportunity are not only a respite from the flow of news images from natural and manmade disasters flashing across TVs on Earth, “they’re great,” said MER Deputy Project Scientist Abby Fraeman, of JPL-Caltech. “We’re starting to see from the ground things we’ve been seeing in orbital images for years and I’m excited about what lies ahead, farther into the valley.”

“The morphology of the valley is quite interesting … there’s a little more diversity of rocks here than what I think we expected,” Golombek elaborated. “You never know what you’re going to get until you get there, but Ii looks like there are different things here. If there are other rock types, then maybe they can tell us something about the structure, the rim of the crater, and the erosion that’s occurred to preserve it.”

It will be up to the MER scientists to characterize all of it and to glean the clues needed to determine which one of the working hypotheses tells the story of how Perseverance formed. Was it a muddy debris flow? Could wind or ice have carved it? Or was it liquid water flowing over the crater rim edge? “We’re keeping an open mind,” said Golombek. “We have no particular timetable that we need to adhere to, so we can almost take as long as we want. We want to do the job right.”

Truth told, they’re in no rush, not yet anyway. This winter being what it is, Opportunity needs to stay on Sun-facing slopes probably for the next three to four months to maintain the energy needed to keep going. And in these parts on Mars, the southern wall of Perseverance is the only place where power friendly slopes can be found. 

“We’re taking our time, but that time is letting us get a lot of imaging done,” said Fraeman. “And that, this imaging of the morphology of the valley, is the centerpiece of this campaign.”

Given that it’s winter, September 2017 wound up to be the kind of work-and-recharge kind of winter month where no news is probably good news. The golf-cart-sized robot that has forever aimed to please just kept working as much as she could through the winter chill, succeeding, however slowly, in advancing the mission’s science objectives.

“Pancam imaging continues to go extremely well, cameras are healthy and calibration continues to hold,” reported Planetary Society President Jim Bell, Pancam Lead, of Arizona State University (ASU).

“Opportunity is still very capable,” added Nelson. “This rover has her aches and pains, but and with the Pancam, the Navigation and Hazard cameras, the Microscopic Imager, APXS [Alpha Particle X-Ray Spectrometer], we continue carrying out our science campaigns.”

On Earth, millions of Americans joined by millions of other people around the world paused on September 11^th to reflect on the 16^th anniversary of the terrorist attack in New York City that impacted the world. Although The MER Update has covered this in previous issues, given these unsettling times of both natural and “manmade” disasters on Earth, it’s worth a few paragraphs to reflect once again on the little memorials that both Opportunity and Spirit carry.”

On that Tuesday morning in 2001, members of a Honeybee Robotics team were arriving at the company’s building on Elizabeth Street in Manhattan to work on the MERs’ rock abrasion tools (RATs). The company’s founder and chairman, a member of the MER Science Team, Stephen Gorevan, was riding his bicycle to work. Just six blocks from the World Trade Center, he heard the airliner hit the first tower. For the rest of the day, he and the Honeybee workforce watched, feeling helpless, from the roof of their building, less than two miles away.

In the weeks and months following, trucks loaded with debris from the explosion rumbled through Lower Manhattan every day. Steve Kondos, then a JPL engineer working closely with the Honeybee team, wondered if it might be possible to include something, emplace something on Spirit and Opportunity as a kind of interplanetary memorial?

Gorevan reached out and a very cool collaboration began. On December 1, 2001, a parcel from the NYC Mayor’s Office arrived at Honeybee. Inside were twisted pieces of metal and a note confirming the pieces were debris from Tower 1 and Tower 2. 

Company engineer Tom Myrick proposed machining the aluminum into the cable shields for the tools that they were making for Spirit and Opportunity. Honeybee enlisted a machining shop in Round Rock, Texas that was working on other components of the rover rock grinders and Myrick flew there with the metal debris.

Back in New York, finished shields in hand, Myrick affixed an image of the American flag on each.

“The rovers and the memorials they carry truly represent the best of humanity,” said Fraeman, who was in the ninth grade that day, in a high school, just miles from the Pentagon. She would grow up with and onto the MER mission, first as a Planetary Society Student Astronaut working briefly on the start of the action, then as a grad student, when she served as the mission documentarian and part of the team responsible for capturing the now historical image of the flag-draped shield on Opportunity for the 10^th anniversary in 2011.

For the MER team, the shields, ingenious in the repurposing, remain deeply meaningful.

“Spirit and Opportunity are the products of teamwork, robot field geologists that could only be created and designed by hundreds, thousands of individuals working together to take us to another world to explore,” Fraeman reflected. “The best of humanity, the worst of humanity, and how despite the worst, it is the best that continues on – that juxtaposition is very powerful.” 

Next time you turn on the television and see images or hear news that makes your heart sink or your gut wrench, consider a thought experiment to another world where the best of humanity is still roving along. Get up a couple hours before dawn, go outside and take in a Marsrise. There, on that peaceful, desolate planet is an explorer from Earth created and built by some pretty thoughtful, caring human colleagues who designed this golf-cart-sized machine to simply go forth, explore new places, and learn something new.

Consider too the fact that the rovers and the little flag-draped, metal shields, the 9/11 memorials they carry, could remain in good “used” condition for many years after all of us on Earth now are long gone. Millions of years in fact. Millions of years after the trials and tribulations among the peoples of planet Earth in the early 2000s were somehow resolved.

Deep Dive into September 2017

When September 2017 dawned at Endeavour Crater, Opportunity, with 45.02 kilometers (27.97 miles) on her odometer, was beginning work at the second station or science stop on her journey through Perseverance Valley. She had just backed onto the slope at the end of August after driving right by it.

The plan for September at this site was the same as it would be for every one of the planned science stops Opportunity would make as she drove from the top of the valley to the bottom: take extensive color Pancam pictures and Navcam panoramas and, when power permitted, check out any interesting targets within reach with her Microscopic Imager and her chemical analyzing APXS.

Winter put the freeze on some of the robot’s work agenda though and Opportunity spent the first sols of September, from 4837-4839 (September 1-3, 2017) recharging.

On Sol 4840 (September 4, 2017), the robot woke up and got to work. She used her Pancam to take a Tau measurement to monitor the atmospheric opacity and to begin taking pictures toward the east for the digital elevation model project. The rover also used her Navcam to take a complete 360 panorama, as well as some images of the tracks she has left in the Martian terrain.

Opportunity worked through the first week of the month and into the second week on collecting more of the dozens of Pancam images she would take of the view eastward. She took a break Sol 4845 (September 9, 2017) to recharge and them got back to focusing her Pancam eastward or toward the bottom of the crater and interior of Endeavour Crater.

Positioned as she was on a 12-degree slope, the solar-powered robot was basking in the Sun and producing 285 watt-hours, a respectable amount of energy for wintertime given her solar array dust factor continued to hover around 0.507. The Tau did drop to 0.533, some of which was because of the recalibration that MER Science Team member Mark Lemmon, of Texas A&M University, did in August and some because the sky had cleared a bit, as happens during the winter season.

On Sol 4847 (September 11, 2017), Opportunity successfully conducted a robotic arm salute, raising her Instrument Deployment Device (IDD) in preparation for an attempt to place the APXS down on a ground target. Then the rover continued her imaging assignments. 

Opportunity took another day to recharge on Sol 4849 (September 13, 2017) and on the following sol wrapped the second week of September shooting part of a stereo panorama.

On Sol 4851 (September 15, 2017), the robot took the pictures needed for an MI mosaic and then used her IDD to set up for an early morning test of the APXS. The scientists wanted to see if the rover could glean chemical data in the early morning hours from a pebble the team named Albuquerque, after a stop on El Camino Real de Tierra Adentro (The Royal Road of the Interior Land). 

The MER team began the new naming theme when Opportunity entered Perseverance in July, and so the targets are each being named after stops along this old, 2,560-kilometer (about 1,591-mile) trade route between Mexico City and San Juan Pueblo, New Mexico.

Winter continued to constrain the rover’s activity as September wore on. Opportunity took another recharge sol on 4852 (September 16, 2017). The next morning, she put her APXS down on Albuquerque for a while, and then went back to recharging.

In the early morning 4854 (September 18, 2017), Opportunity took another early morning APXS integration on Albuquerque. “We ran that the test from 07:40 a.m., local Mars time to 12:20 p.m.,” said Nelson.

Opportunity spent the rest of her workday shooting more pictures for the Pancam stereo panorama and filling out a dataset that will go into the digital elevation model of this location in the Perseverance.

The APXS morning integration tests revealed that Opportunity could successfully collect good quality data during an early winter early morning and not just late at night when the robot has almost always completed these chemical analysis measurements of targets. However, there’s a wrinkle.

“In the early morning, we get, maybe, an hour of good data,” said Nelson. “We can get longer periods of integration and better signal-to-noise ratio at night. So it looks like the evening data is going to be better. It’s difficult with power limitations to do these integrations, so if we can integrate for three good hours at night versus one good hour in the morning, then we’re better off putting our efforts into integrating at night. That’s basically what we learned from the APXS morning tests.”

Opportunity spent sol 4854 (September 19, 2017) recharging and then took a nap while her APXS worked on the late night integration on Albuquerque. The rover’s computer or CPU [central processing unit] draws very little current while the APXS is busy working.

The following morning, September 20, 2017, the MER team read out the APXS data from the night before and then commanded the rover to conduct another post Odyssey integration. “That was a pretty light sol,” said Nelson.

Since the APXS can operate independently from rover’s CPU and since it has non-volatile memory in which it stores data collected, the team can operate the instrument when the rover’s computer is napping. They can also allow the rover to completely shut down and then retrieve the APXS analyses the next morning from the instrument’s memory, and move it to the rover’s RAM for downlinking to Earth. 

“As long as power is applied, we can turn the APXS on and off and we can apply power to the instrument even when the rover napping,” Nelson reminded. “This allows us to do integrations after the Odyssey pass, after sunset. When things start to get cold, we will turn on APXS power and while the CPU naps, the APXS is busy working. Then we will wake up between 8 p.m., and 11:30 p.m., the APXS stops integration and stores the data, and then the rover shut downs and goes into DeepSleep.”

The following morning the rover wakes up and her human colleagues read-out the data from the APXS. “We hold onto that data in the computer memory until the orbiter pass, typically the Odyssey pass that afternoon,” Nelson explained. “Once we’ve done these read-outs the APXS is available to do further observations.”

Opportunity ended the third week of the month on Sol 4856 (September 21, 2017), using her Pancam to take a Tau, reading out the previous evening’s APXS data, and then shooting close-ups of a ground target mosaics with her MI.

As the fourth week of September got underway, the robot put in another fairly full day on Sol 4857 (September 22, 2017), taking MI stereo images an off-set target, a little pebble the team named Bernalillo, after the New Mexico town, renowned apparently for its good chili, as the story goes. The robot then did another post-Odyssey-pass integration APXS on the same target.

“It’s a large pebble, but big enough that most of the APXS gets the rock and not the dirt around it,” said Golombek. “It was the largest and biggest pebble that was in the workspace that we could reach.”

Following another quiet day of recharging, Opportunity spent Sol 4859 (September 24, 2017) reading out APXS data and shooting some more pictures. The robot spent Sol 4860 recharging, and on the following sol did some light imaging and continued APXS analysis on Bernalillo.

The rover and her team read out the previous night’s APXS analysis on Sol 4862 (September 27, 2017), then Opportunity took some more mosaic pictures with the MI, and imaged some other nearby targets, including a half-frame uphill and half-frame of a target called Socorro, topping all that with another late night APXS integration on Bernalillo.

“We’re geriatric and amnesiac and we take naps and the only data we get back is the data we acquire just before a pass,” Golombek said in summing September. Despite the winter cold and the power issues however, Opportunity made respectable progress in surveying the valley from this, the second way station and the outlook is getting brighter.

Halloween and minimum insolation is just a month away, and winter solstice will follow that three weeks later, at 1:44 UTC November 20, 2017. Meanwhile, the MER mission succeeded in acquiring some additional communication passes with the Mars Reconnaissance Orbiter (MRO), which happen earlier in the Martian day. “That helps for power and image quality, because we can take images earlier in the day,” noted Bellutta.

“It’s been a challenge having to dedicate so many sols to recharging,” Callas admitted. “The added MRO passes though are already beginning to help. Previously, we had four recharge sols out of seven, and then this last week we only had two recharge sols out of seven,” he noted at month’s end.

Still, winter has arrived at Endeavour and, pointed out Callas, “it’s going to be like this for a while.”

Opportunity’s survival heater, which kicks in at minus-19 degrees Celsius (minus-2.2 degree Fahrenheit) and warms up the battery, has been automatically turning on “consistently” during the past week or two, said Nelson. “Our batteries are pretty cold,” he said. “And the colder the battery is the lower its capacity. Sometimes a battery may look like it’s got full charge and the voltage is high, but the moment you try to draw power out of it, it drops down to practically nothing. Our batteries are not that bad, buy they suffer from the same effect. The colder they are the smaller their capacity and so they discharge rapidly and don’t charge very efficiently.”

The MERs’ lithium-ion [Li-ion] batteries are rated down to about minus-30 Celsius (minus-22 degrees Fahrenheit). “They’re operating range is down to -20 (minus-4 degrees Fahrenheit) and the survival heater kicks on at -19 and we can go fairly close to that with much trouble.” 

This parallel Li-ion battery pack has been a true champion performing flawlessly as the heart of the MERs, just like almost every other part. However, like most everything else, including the rover herself, it is slowly degrading, like all batteries do.

“This battery is kind of the Dick Clark of batteries,” suggested Nelson. “It looks a lot younger than it is. Nonetheless, it is aging. And so we have lower capacity today than we did back during the winter at Greeley Haven when we were relegated to stay in a solitary place throughout the season. We’re also not getting as much energy as we’d like this winter, because Opportunity is really dusty.”

It’s hard to say if this, the MER mission’s eighth Martian winter will turn out to be the toughest one for Opportunity. “This is not the dirtiest our solar panels have been this time of – that was last winter,” said Herman. “This winter does not have the dustiest sky we've seen this time of year – this winter's sky is about as dusty as any winter's sky. Something I can say is true is that we are generating less array energy per sol this winter than we did last winter or the winter before. The last winter that we averaged 280 watt-hours per sol was in Winter 4 (2009) and Winter 5 (2011). But I cannot even say that this is the lowest our array energy has been, because there is a tie for the bottom between this winter, and Winters 4 and 5,” she noted.

In any case, the MER team is looking to assist their robot through this cold and difficult time. For the first time, the ops engineers are looking at the zero degree battery heater. “We want to warm up the battery and we’re looking at turning on the zero degree heater, also called the battery warm-up heater,” Nelson said. “It will kick in anytime the battery temperature drops below 0 degrees Celsius (32 degrees Fahrenheit) and warm it up to roughly +4 (32.9 degrees Fahrenheit). That will put it in a pretty nice range.”

Since Oppy’s Li-ion batteries have been running closer to -15 or so (about 5 degrees Fahrenheit), this battery heater “would bring the battery temperature up to roughly around 0 and keep the battery much warmer than it is,” said Nelson.

This battery heater won’t work when the rover is in DeepSleep, so the battery will still get colder when the rover shuts down. “But during the day, this heater should keep the battery fairly toasty and warm, and the result should be that we have much more capacity to do science observations,” said Nelson. “In so doing, it will also put heat back into the REM (Rover Electronics Module) and that should minimize the amount of heating we have to do on the battery.”

The heater could be turned on in early October, “but that's not guaranteed,” cautioned Nelson. “Even with that battery heater deployed however, the effects of the Martian winter will continue to challenge this veteran explorer likely through January 2018. “We have an unusual constraint in that we probably don’t want to leave Perseverance until after power starts improving, because the only place with north-facing slopes in the immediate area is in this valley,” said Golombek. Other than that, we’re going to do the right thing in this valley, and if the research here takes longer, then we’ll take longer.”

“It’s kind of in our best interests to be taking our time and slowly make our way down the valley,” summed up Fraeman.

During the final sols of September, the team discussed the next plans for Opportunity. One option under consideration is to send the rover back uphill to an area near the first way station where the MER scientists have spotted some interesting bedrock.

“It looks like two different colored, bedrock units in direct proximity,” said Golombek. “One area that we’re imaging shows that one side has rocks of a lighter tone and the other has a browner, darker tone and the two units appear to be separated by what could be a fracture zone or something. It’s all dirt, maybe broken up rock that’s been filled in by sand, or who knows? But when you have two different units right next to each other, then there is often information in that contact that tells you about what rocks are there and what the relationship is between them, whether one has been deposited on top of the other or how different they are, and what’s going on.”

The team members have also been discussing sending Opportunity farther east, down the valley about 12 meters, to what ostensibly be the next science stop. But the actual decision probably won't be made until after discussion at the "End-of-Sol" meeting on Tuesday, October 3^rd.

Although the team settled on the new target-naming theme when Opportunity entered Perseverance in July, they have not yet named the science stops. They did however talk about it, said Golombek. “That just came up and I think we may start doing that,” he said.

As September turned to October, Opportunity was still working on completing her imaging assignments at station 2 and APXS investigations into Bernalillo and an offset of that target and team members talked about what’s next.

“There are certainly some interesting things we’ll be seeing as we continue our way down the valley,” said Fraeman. “From orbit, we can kind of see what might be this anastomosing features that we’ll have a chance to look at up close. And, we’ve been seeing a lot of bedrock and carefully documenting it. We are still discussing what carved this feature. But we haven’t found the smoking gun yet.”

It seems a majority of the MER scientists still agree that whatever formed Perseverance, it probably happened 3 to 4 billion years ago during the Noachian Period on Mars. “A lot of us are pretty convinced that whenever this was done it was quite some time ago, because there’s just a lot of dirt on everything,” Golombek chuckled. “We haven’t seen anything that’s indicates it’s youthful although it’s not like you get there and it’s got this big ’N’ on it that says: ‘Formed in Noachian.’ You still have to use the surface data to figure it all out.”

Most of the scientists also seem to also still be leaning toward water as the force that carved Perseverance into Endeavour’s rim. ““A lot of us feel the information from the walkabout was semi-indicative of flow over the edge of this, water flow,” said Golombek. “There have been proponents who have suggested there are a variety of things that are consistent with that. We have seen Aeolian erosion, and I guess I would call it modification of some of the surface rocks. But I don’t think anybody’s talked about how you would carve such a valley, with what look like these channels that go back and forth, by erosion. We need to just get the rest of the data and put it all together.”

Perhaps the most important news this past month from Endeavour is that no one’s worrying about whether or not Opportunity will make it through winter – and the rover is admirably still working her little robot heart out.

“I think we can be very proud of our rover,” said Nelson. “We are by no means having to just hunker down and wait things out. We still have work that we are doing and once we get the 0-degree, battery heater running that should also help quite a bit.

Actually, there is that other reason for optimism – Mars itself. “We’re waiting with bated breath,” said Nelson. “Maybe if we all huff and puff really hard, we can make the wind blow on Mars…”