A.J.S. RaylNov 05, 2018

The Mars Exploration Rovers Update: NASA Green-Lights Team to Continue Opportunity Recovery Plan into 2019

Sols 5221-5251

October came and went without a beep from Opportunity, silence that was still no surprise for some, but a little discouraging for other members of the Mars Exploration Rovers (MER) team. 

“We're still waiting,” said MER Principal Investigator Steve Squyres, of Cornell University, summing up the month. 

But as ghosts and goblins prepared to haunt the streets around the world, NASA Headquarters delivered good news. The MER team now has the green light to continue “for the foreseeable future” its two-pronged strategy of actively listening and commanding to find Opportunity’s signal and passively listening on the Deep Space Network’s (DSN’s) most sensitive radio receivers to try and make contact with the rover.

Work in progress
Work in progress This is the color panorama Opportunity was working on right up to a few sols or Martian days before the planet-encircling dust event (PEDE) put a stop to all science operations and caused the robot field geologist to shut down and enter a sleep survival mode in June 2018. James Sorenson processed this image in true color. From the black sections, it’s clear that the rover was still working on it. “I hope when or 'if' Opportunity wakes up, that she could continue to finish it,” said Sorenson. “She still has work left to do!” There’s a team of scientists and engineers and MER followers around the world who wholeheartedly agree.Image: NASA / JPL-Caltech / Cornell / ASU / J. Sorenson

The announcement, which appeared on the MER mission’s home page October 29th, was the best “treat” the MER team could have hoped for Halloween, and it alleviates a huge amount of pressure. It means that the operations engineers will be able to continue searching for Opportunity through the dust-cleaning season when the Martian winds historically have cleaned the rover’s solar arrays.

“We know that the timeframe from November through January 2019 corresponds to an annual period of dust cleaning at the Opportunity site at Endeavour Crater,” said Squyres. “So active listening through January is a boost to our chances of hearing from the rover if the arrays are very dusty now.”

A monster storm – known as a planet-encircling dust event (PEDE) – caused Opportunity to stop all work in Perseverance Valley, shut down, and go into survival mode back in early June. Although officially declared over in September, the PEDE’s secondary or decay phase, wherein all the dust that was kicked high into the atmosphere settles back down to the surface, may still be lingering.

The atmosphere and the sky above Opportunity have cleared to almost normal, hazy summer levels. Even so, the rover continues to take on dust. “When you’re outside of the dust-cleaning season on Mars, then dust accumulates on the rover,” said MER Project Manager John Callas, of the Jet Propulsion Laboratory (JPL), original home to all of NASA’s Mars spacecraft.

There is no way of knowing unequivocally, but MER atmospheric scientists and members of the Power team are pretty certain that Opportunity is laden with dust, perhaps more so than ever before, and that the rover seriously needs some dust cleaning, as reported in previous MER Updates. If that is the case, the solar-powered rover would not be getting enough sunlight to produce the energy she needs to recharge her batteries, wake up, and phone home. 

“My feeling remains that it is likely a lot of dust was stirred up and fell locally,” said MER Athena Science team member and atmospheric scientist Mark Lemmon, of the Space Science Institute. “That is true for most of Mars. Curiosity was plastered with dust, and even vertical surfaces got dusty. It is especially true for Opportunity, at the epicenter of the storm.”

Curiosity, actually, got some dust cleaning sometime between September 14th and October 25th, during the time it had an anomalistic memory problem that required the Mars Science Laboratory (MSL) team to move from one computer back to another, MSL Deputy Project Scientist Joy Crisp confirmed. “What Curiosity saw was that a lot of fine material – grey powder from the shallow drill attempt and dark reddish brown loose regolith – was blown away at the location where we attempted to drill the target Inverness,” she said. “We don’t know when exactly the clearing happened in that time period, because we had very few images acquired during the rover anomaly.” 

An omen for Oppy?
An omen for Oppy? Curiosity suffered an anomalistic memory issue in mid-September and the Mars Science Laboratory (MSL) team didn’t see rover’s workspace and target, Inverness, for more than a month. “And there were some surprises in store for us!” Melissa Rice, a collaborator on MER, and an MSL Participating Scientist,wrote in the MSL blog. In the Mastcam images above, the rock was covered with gray-colored tailings, but when the team took another look on Oct. 25th, voila! The tailings and a lot of the dark brown soil and reddish dust were gone. “The winds have been moving, sweeping the workspace clean,” noted Rice, of Western Washington University. On the other side of Mars, Opportunity is waiting for winds to clear her solar arrays.Image: NASA / JPL-Caltech / Malin Space Science Systems

Although Curiosity is on the other side of the planet, her good fortune is a reminder that it is still summer and therefore still dust storm and dust-cleaning season in the southern hemisphere of Mars. And that rover’s images are evidence that the Martian winds are indeed kicking up here and there. 

Could it be an omen that the winds are already kicking up at Endeavour, and the dust-cleaning season will soon be blowing in soon at Meridiani Planum, the region where Endeavour Crater and Opportunity are located? Time and perhaps the rover will tell in coming weeks. 

The Martian winds and the coming dust-cleaning season were key elements in the MER team’s recommendation to agency officials that they be permitted to keep on keepin’ on, listening actively and passively for the rover as they have been since early September

During the last week of October, in a teleconference call, MER Mission Manager Matt Keuneke, stepping in for Callas who was on leave, presented a review of what the team has done so far and the ops engineers’ case for continuing their current strategy through January 2019. With Squyres, Deputy Principal Investigator Ray Arvidson, and MER Deputy Project Scientist Abby Fraeman also on the line, Director of JPL’s Mars Exploration Directorate Fuk Li, and Director of the Mars Exploration Program at NASA Headquarters Jim Watzin, listened and concurred. 

A few days later, the team learned it was granted NASA’s approval.“We’re glad that we will be continuing to make every reasonable effort to reestablish contact with Opportunity,” said Keuneke.

The go-ahead to continue reaching out and listening as they have been has boosted morale in a significant way. “It has really invigorated us,” said Spacecraft Systems Engineer/Flight Director Michael Staab, who has been working for months on various aspects of the MER ops team’s recovery strategy. “I think there’s a lot of dust on the arrays and the rover hasn’t been able to wake up and talk to us yet. We just have to wait for dust-cleaning season and now we’ll be able to do that,” he said.

“Obviously, we are pleased that NASA wants us to do everything we possibly can to try and recover this vehicle,” added Callas at month’s end. “If we hear from the rover, it will be fantastic. It will just be a phenomenal achievement and all of us will delight in that. Right now, we have no data,” he added, tempering his words. “We only have speculation, and it weighs on one’s confidence.”

It’s fair to say that everyone everywhere was hoping NASA-JPL would have heard the rover’s beep by now, even those who believe Opportunity’s solar arrays are thickly covered in the powdery Martian dust. “We were hoping to hear something and we haven’t heard anything at this point,” acknowledged Rich Zurek, Chief Scientist of the Mars Program at JPL, who is also Project Scientist of the Mars Reconnaissance Orbiter (MRO). “But there are still some things to try, and the dust-cleaning season should begin soon.”

The Who cheers MER, Mel Brooks inspired
The Who cheers MER, Mel Brooks inspired Opportunity and the MER team got some rockin’ support from The Who (right) and inspired the one and only Mel Brooks (left) in October. Brooks (left) is a filmmaker, actor, comedian, and composer extraordinaire whose movie Spaceballs motivated the MER ops engineers. The Who – Roger Daltrey, John Entwistle, Keith Moon, and Pete Townshend pictured here from a concert in 1975 in Chicago – started back 1964 in London and performed at Woodstock in 1969. Though Moon passed away in 1978, not long after the MER Update author celebrated Who Are You at a listening party with the band on the set of Battlestar Galactica at Universal Studios, and Entwistle passed away in 2002, Daltrey and Townshend continue to keep The Who on the road.Image: Angela George, (left); Jim Summaria (right), both via Creative Commons Wikimedia

Meanwhile, the whole world is watching – even The Who, one of rock’n roll’s preeminent and most influential bands, and the one and only, inimitable filmmaker-comedian-actor Mel Brooks. When Staab posted the team’s wake-up song for the sweep-and-beep commanding activity on October 20th– The Who’s classic, “I Can See For Miles” – the band responded two days later: “Wake up, Mars The Who are here!” 

And, as Staab, prepared to head in for active listening on October 24th, he was inspired by Brooks’ 1987 movie Spaceballs and re-dubbed the "Sweep, Beep, and Creep” just for fun on his Twitter account. Brooks responded promptly. He loved it.

The additional time that NASA has granted doesn’t mean the MER mission’s ops team can kick back and relax, even though the holidays are coming. Until the rover phones home, these team members will remain, effectively, in a state of heightened alert and readiness they call DUSTCON 1, a term they adapted from the U.S. military’s DEFCON system of five graduated levels of defense readiness.

“DUSTCON 1 is not an official designation,” underscored MER Power Lead Jennifer Herman, of JPL. “It’s just something that a few of us on the operations team made up for fun and inspiration, to remind ourselves to stay ready,” she said. “We haven’t heard from our spacecraft, so our tactical readiness is still on high alert. When we hear from Opportunity and return to nominal operations, then we can lower it.”

The rover and the mission’s fate may all be up to Mars. For now, for the team, it’s about continuing the preparation, keeping the faith, and believing in possibilities just like they have done from the very beginning. But team members miss Opportunity, the world’s longest-lived robot on Mars. “It’s pretty much a bummer,” said MER Project Scientist Matt Golombek. “It’s been an awful long time, and the rover is like part of our family.” 

Everyone agrees that hearing that beep from Mars and getting Opportunity back online and roving again would be a triumph like no other, and they’re doing everything in their power to make it happen. “We don’t want to throw up our hands and go: ‘Oh well, that was the dust storm, we tried,’” Herman said, echoing the sentiments of other team members as well as followers around the world. “No. We want her back!”

DUSTCON 1 When MER Power Team Lead Jennifer Herman suggested that the team having a readiness rating scale kind of like the U.S. military’s DEFCON, JPL Operations Engineer Brian Barker got creative and designed a graphic that turned up in Herman’s workspace the next day. “DUSTCON 1 is not an official designation,” noted MER Power Lead Jennifer Herman, of JPL. “It’s just something that a few of us on the operations team made up for fun and inspiration, to remind ourselves to stay ready,” she said. “Our tactical readiness is on high alert.”Image: JPL-Caltech, B. Barker

It’s been nearly five months since the MER team last heard from Opportunity and the telemetry she returned was jaw-dropping. In that downlink, which the team received June 10, 2018, the rover revealed she was only producing an astonishingly low 22 watt-hours of energy, and the atmospheric opacity was 10.8, the highest any surface mission on Mars has ever recorded. But there was not enough telemetry to determine the amount of dust on the solar arrays with the data in that June 10th downlink, said Herman.

This PEDE turned out to be the worst global storm on Mars since 2001, according to Bruce Cantor of Malin Space Science Systems, who has been observing Martian dust storms since then. The massive event finally entered its decay phase in late August and came to an end in September, as reported in the last issue of The MER Update.

During the decay phase of these PEDEs, all the dust that was lifted high into the Martian atmosphere comes back down, settling out across the planet’s surface. By the end of September, the skies had cleared substantially, but not completely. The Tau, what the team calls the measurement of dust in the atmosphere, bounced around the 1.1-1.3 range, and possibly a little bit higher in October, according to Cantor who uses imagery from the Mars Color Imager (MARCI) onboard the MRO along with models to make estimates. Although the skies are still hazy, those measurements are “typical for storm-free conditions” during the late spring and summers on the Red Planet,” he said.

Opportunity’s long and winding road
Opportunity’s long and winding road The gold line on the image on the left shows Opportunity's route from the Eagle Crater landing site to Cape Tribulation, which is north of her current location in Perseverance Valley. The base image for the map is a mosaic of images taken by the Context Camera onboard the MRO. Larry Crumpler, of the New Mexico Museum of Natural History and Science, provided the route. Right graphic shows the rover’s movements up to Sol 5100 (May 29, 2018) and her approximate location. Phil Stooke, author of The International Atlas of Mars Exploration Volumes 1 and 2, (Cambridge University Press), of the University of Western Ontario, Canada, documented this graphic with sol and site annotations. The base image was taken by the HiRISE camera also onboard MRO.Image: NASA / JPL-Caltech / MSSS / UA / add-ons L. Crumpler (left) / P. Stooke (right)

October proved to be a lot like September for MER in terms of the active sweep-and-beeps, listening and commanding to try and find Opportunity’s signal and get the rover to respond, and the passive listening over the Deep Space Network’s (DSN’s) global array of transmitters and receivers around Earth, explained in detail in the last issue of The MER Update

The ops engineers continued throughout the month experimenting with searching more of the DSN space and on different frequencies during the several sweep-and-beeps the engineers make during their hour of DSN time every day. “We have only one uplink session allotted per day, because the DSN is in high demand,” Staab said. “But when we’re doing the sweep-and-beeps, we’ll send multiple commands in a single session.”

They did try something new though in October, just in case there is a possibility that the engineers and Opportunity may not be communicating in the same wave configuration.

“There are two modes on the signals, what are called the left circular polarization (LCP) and the right circular polarization (RCP),” said Zurek. On the right circular polarization, the vector rotates in a right-hand sense with respect to the direction of the signal’s propagation, and left circular polarization in which the vector rotates in a left-hand sense. “Normally, we use the right circular polarization, because that’s what all the spacecraft use for commanding, and the DSN sets up for that routinely.”

However, there are some scenarios and fault modes wherein Opportunity may have tried to phone home on the right hand circular polarization and for some reason the engineers on Earth didn’t hear it, so the rover switched to the left circularization polarization of the wave and then began switching back and forth between the two. 

JPL Space Ops Mission Control
JPL Space Ops Mission Control This image shows a panoramic view of the Space Flight Operations Center at the Jet Propulsion Laboratory (JPL) in Pasadena, CA. This is where mission engineers and scientists communicate and keep track of their mission’s spacecraft via NASA’s Deep Space Network (DSN). The DSN is only international network of antennas that provide the communication links between the mission team on Earth and the spacecraft and rovers on Mars. The network is comprised of three deep-space communications facilities placed approximately 120 degrees apart around the world: at Goldstone, in California's Mojave Desert; near Madrid, Spain; and near Canberra, Australia, a strategic placement that allows for constant observation of spacecraft as the Earth rotates on its own axis.Image: NASA / RadioFan / Creative Commons Wikimedia

That’s why the engineers are switching to LCP for the sweep-and-beeps to try and see if they can elicit a response from the rover. “If Opportunity is on the opposite polarization, maybe that’s why we haven’t heard from it,” Staab said. 

The engineers must stay on one polarization during the sweep-and-beeps, so they have to plan ahead which tracks they’re going to command on LCP, and which one they will command on RCP, summed up Staab.

On Sunday, Oct 21st, with the DSN receivers and transmitters reconfigured, the team switched from RCP to the LCP for its sweep-and-beeps, said Staab, who during the process in his role as a flight director works with the engineers, known as Aces, who monitor and communicate with spacecraft over the DSN from JPL. “I’ve got a tracking spreadsheet of when we’ve been sending commands and most of our attempts are within that sweet spot of the window where we think the rover may be awake and so far we’re doing pretty well with the coverage. But again, it’s probably a little too early for it to wake up because of the amount of dust on the solar arrays,” he said. 

Moreover, according to Staab, Opportunity may only be awake “about an hour” each day. “That’s being optimistic if we are seriously not dirty,” he said.

That reality puts the odds of catching that one window, the hour where they might get a command in to the rover, at only about 10%, Staab estimated. “So the odds are very stacked against us right now in the current situation we’re in,” he said. “If we get cleaning, then the odds dramatically increase,” he said. 

But, it could be that Opportunity has not been able to wake up and stay up long enough to receive commands. “It just may be that Opportunity wakes up for two minutes and then shuts down, and that’s not enough time to get a command into it,” Staab said. “Right now, we may not even have any time to get a command into the rover. But that’s what we expect right now. All that dust that goes up comes down and it’s going to fall on the rover. The fact that we haven’t heard anything yet suggests to me Opportunity is really dirty.”

Listening for Opportunity
Listening for Opportunity In late October 2018, NASA Headquarters gave the MER team a green light “for the foreseeable future” to continue its two-pronged strategy of both actively and passively listening to find Opportunity’s signal. “It has really invigorated us,” said Spacecraft Systems Engineer/Flight Director Michael Staab, who has been working for months on various aspects of the mission’s recovery strategy.Image: NASA / JPL-Caltech

One thing the team is certain about now is that the rover has tripped three faults: a low-power fault; an up-loss timer fault; and a mission clock fault. “The mission clock is long gone, so the rover doesn’t know what time it is, and it could be waking up at unusual times, because of the way the algorithm works,” said Golombek.

Nevertheless, JPL’s Radio Science Team engineers and the MER mission managers and/or flight directors should be able to pick up Opportunity’s signal through the passive listening effort during the daylight hours on Mars. They look every day for the rover’s signal over a vast range of times and frequencies that are recorded by the DSN’s receivers, the most sensitive radio receivers in the world.“We are passively listening on virtually every DSN track going to Mars, and we would see the rover if it was trying to say ‘Hello,’ even if we weren’t actively listening,” Golombek reminded.

While the power models suggest there should be enough energy for Opportunity to occasionally wake-up, all the suppositions about the extreme dusty state of the rover suggest she needs a good gust of wind to clear off some of the accumulated dust from her solar arrays before she can phone home or respond to the sweep-and-beeps. For the MER scientists, October was a repeat of September. “We got the update from the engineers everyday and it was basically a template where only the sol number changed,” said Arvidson, of Washington University St. Louis.

There has been a lot of discussion about other possible reasons that Opportunity may not have phoned home yet beyond being laden with dust. Not surprisingly, ops team members, as well as people who have been following the mission from the beginning have wondered if the rover’s two linked batteries could be drained down or damaged in some way or worse, dead.

However, it is not likely that the batteries are completely dead, said Marshall Smart, a Principal Member of the Technical Staff in the Electrochemical Technologies Group at JPL. “The batteries are pretty robust. Even though the batteries may be drained and frozen for months, if they are warmed up properly and recharged, it is likely that they should display operational capability, although may be degraded,” said Smart, an organic chemist who, with Kumar Bugga, a Principal Member and Cognizant Engineer of the MER lithium-ion (Li-ion) battery, developed the electrolyte that goes into the cells of the batteries to withstand the brutal beyond-freezing temperatures on Mars. 

The batteries on Spirit experienced similar under voltage, to a lesser extent, when they were over discharged, because of the ‘flash memory anomaly’ within the first month of the rover’s primary mission, said Bugga. “But they recovered and performed admirably for a long time after that,” he said. “ Another low-voltage episode occurred with the protoflight batteries on Curiositywhere several cells were discharged to below 1 volt. Yet, the batteries recovered and supported the System Integration and Test operations, albeit with reduced performance, higher impedance and lower capacity,” he said.

Oppy’s body, brains, heart, and power pack
Oppy’s body, brains, heart, and power pack The diagram on the left shows the basic layout of the Mars Exploration Rovers’ suite of scientific instruments. The diagram on the right reveals the interior of the rover’s body, aka the Warm Electronics Box (WEB), which protects the rover ́s brains and heart and is located just below the solar array “winglets.” It shows the location of the RAD6000 computer that serves as the robot's brain. Along with the parallel lithium ion battery pack (lower left) that powers the rover and other electronics, it is housed in the Rover Electronics Module (REM), which sits inside the WEB protected from frigid Martian nights.Image: NASA / JPL-Caltech / Cornell

Accordingly, it is likely that Opportunity’s batteries will recover and be operational again once they receive adequate electrical charge from the solar arrays, Bugga said. “While there may be some performance loss because of their deep discharge, that loss may be expectedly less in their current ‘frozen’ state.” 

So, even though Opportunity didn’t have the energy to use her heaters to keep her batteries warm during the global storm, the batteries should still work. That is not to say that there isn’t any way they could be damaged. “If the batteries are really cold and you try to charge them too rapidly, that could be damaging to their health, for example by plating reactive lithium on the surface of the carbon anodes,” said Smart. 

“But this lithium plating is unlikely in a fully discharged battery; it’s more likely that the batteries just wouldn’t accept the charge because of their high impedance at these low temperatures. This can result in the battery self-heating to warmer temperatures, where charging is kinetically feasible,” Bugga explained.

If the battery voltage dropped too low however, that could reduce the battery capacity and performance, Smart said. “If the voltages of the batteries, and the cells within, are drained to very low values, a degradation mode can occur that will lead to permanent capacity loss and impedance growth.” 

Therefore, even if the batteries are heated up and charged gracefully, they may display degraded performance compared to their health prior to being drained and frozen, “as observed with the Curiosity protoflight batteries,” noted Bugga.

Could the mission clock have been working through part or even through the PEDE and constantly draining the batteries to the point of effectively killing them? 

MER batteries: a dynamic duo
MER batteries: a dynamic duo Despite some rumblings that Opportunity’s batteries may be dead or damaged beyond use, JPL’s own MER battery experts, Kumar Bugga and Marshall Smart, who developed the electrolyte that goes into the cells of the batteries to withstand the brutal beyond freezing temperatures on Mars, don’t think either scenario is likely. If the battery voltage dropped too low however, that could reduce the battery capacity and performance they say. But that doesn’t mean the rover couldn’t still rove on, once she is recovered and back to nominal status.Image: NASA / JPL-Caltech

“This is less likely because of the low currents required for the mission clock, which makes the under voltage effects less impactful, especially at these low temperatures,” said Bugga. Smart concurs: “I don’t think that scenario would result in the batteries being destroyed either. As mentioned above, allowing the batteries to drain to very low voltage is not healthy for the battery, and will likely lead to some performance loss. But this one time occurrence is not expected to be catastrophic. In addition, the harmful effects of draining the batteries to low voltage is not as dramatic at very low temperatures, since the rate of degradation, which involves the dissolution of the anode copper current collector, will be slower.”

There is also the possibility that something, somewhere on the rover broke. “We have to accept the fact that this is a 14-and-a-half-year-old rover,” said Callas. “Remember my analogy, it’s the difference between your 17-year-old nephew being outside without a jacket and your 97-year-old grandmother outside without a jacket. We’re the 97-year-old grandmother.”  

While there is no evidence for or reason to believe that something broke on the rover, there is just no way of knowing without any data from Opportunity. Barring a breakage or mission catastrophic failure, it all appears to come down to dust. Confounding things even more, there is just no way of knowing with any certainty just how much dust fell on this rover. Considering that the PEDE literally blanketed the entire planet though, it’s hard to fathom the rover wouldn’t be dirty with dust. 

“Yes, it was a giant dust storm and there was a lifting center right nearby, but how much of that actually falls locally versus globally getting mixed into the atmosphere is not known, so that may or may not have been a major factor,” said Golombek.“For there not to be enough power to at least charge the battery sufficiently for it to wake-up, there would need to be an extraordinary amount of dust on the solar arrays, probably more than we have ever seen in the past.”

That’s exactly what Lemmon, Herman, Staab, and others have been thinking for a few months now. “My thought is that unless something is broken, Opportunity’s solar arrays must be covered in lots of dust, so much that it’s blocking well over half the light that’s hitting them, maybe as much as 80% or 90%,” said Herman. 

“I think it’s more than half because of the results of some power simulations I ran,” Herman continued. The inputs were the known positions of the rover and of Mars, as well as Tau estimates from the orbiters. “I assumed various amounts of dust on the solar arrays, from enough dust to block 10% of the sunlight to enough to block 90% of the sunlight,” she said. “If less than half of the sunlight is blocked by dust, then the arrays should have produced enough energy to have allowed us to hear from Opportunity by now. So the only thing that makes sense – aside from something being broken – is that more than half of the sunlight hitting the arrays is being blocked by accumulated dust,” she said.

Actually, the storm may have kicked up large particles that could have settled on the rover’s arrays, and those large particles may be part of the reason the sunlight is being blocked, as reported in the last issue of The MER Update. “Many papers suggest this, and they show that the larger particles settle close to the lifting area,” Lemmon said. 

The curse and kiss of Martian winds
The curse and kiss of Martian winds Opportunity used her Pancam to take the self portraits above, in January 2014 (left), when her solar arrays was coated in the powdery Martian dust, and in late March 2014 (right) after the winds of Mars whisked off much of the dust from the arrays. As the Martian winds give, they also take away. Both a curse and a blessing, the winds of Mars have enabled the rover to live long and prosper. Just how dirty Opportunity is right now as a result of the fallout from the planet-encircling dust storm that churned up in June July, and August 2018, no one knows. But the Martian winds should start kicking up and blowing through Endeavour when the dust-cleaning season begins in mid-November.Image: NASA / JPL-Caltech / Cornell / ASU

Since Opportunity is believed to have been very close to a lifting area for days, if larger stuff was lifted as proposed by those atmospheric scientists, that stuff may well have settled on and around the rover. While this supposition is still in the 'model' area, not the 'data' area, “I think it is likely,” said Lemmon.

Another factor to consider is that “Opportunity has always needed and gotten dust cleanings around this time of the Martian year whether there was a dust storm or not,” said Herman, who did the historic dust-cleaning research that informed the team.

Without any incoming data from the rover on the ground, all the team has had to go on is the orbital HiRISE image taken in September. As to what can actually be determined from that image depends on whom you talk to. While some scientists on the MER team think the rover looks as dusty as its immediate surroundings, others disagree.

The High Resolution Imaging Science Experiment, or HiRISE, is a camera onboard the MRO. The 65-kilogram, $40-million instrument, built under the direction of the University of Arizona's Lunar and Planetary Laboratory by Ball Aerospace & Technologies Corporation, has been producing stunning imagery for more than a decade.

The HiRISE image of Opportunity in Perseverance Valley, which cuts the western rim of Endeavour, was acquired after the dust storm settled down and the Tau was around 1.5. “It shows that the top of the rover looks really bright,” said Arvidson. “But what’s interesting is that the surrounding areas don’t look particularly bright. The area actually doesn’t look much brighter overall pre and post-PEDE. Still, the deck itself looks really bright so it may have trapped more dust than the surrounding areas.”

Initially HiRISE Principal Investigator Alfred McEwen, of the University of Arizona, interpreted that most of the fallout from the storm settled at latitudes higher than Opportunity's coordinates. “Butsince then, we have seen evidence for extensive dust fallout in some equatorial regions as well, such as in Valles Marineris,” he said. 

“What is clear is that the dust deposition is very non-uniform, in spite of the fact that the atmospheric dust looked uniform at the peak of the PEDE,” said McEwen, who is a planetary geologist and director of the Planetary Image Research Laboratory (PIRL) at the Lunar and Planetary Laboratory, at the UA. 

When the sky first cleared
When the sky first cleared The MER team saw Opportunity for the first time in months when HiRISE, a high-resolution camera onboard NASA's Mars Reconnaissance Orbiter took this image in late September 2018, after the sky over Endeavour cleared from the monster global storm called a planet-encircling dust Event (PEDE). The image shows that the rover is still hunkered down at her site about halfway down Perseverance Valley, which cuts the western rim of Endeavour Crater. But to untrained and unknowing eyes, the golf cart size rover could be mistaken for a boulder. The square highlighting the rover is about one kilometer (a half-mile) across.Image: NASA / JPL-Caltech / University of Arizona

“The west rim of Endeavour Crater looks remarkably similar in color and albedo patterns as an image with similar lighting acquired before the PEDE, with the exception of some small streaks extending south from topographic knobs on the crater floor, McEwen added. “This suggests that some dust was deposited on the nearby crater floor, then removed by surface winds except where protected by topographic obstacles.” [See animated HiRISE gif in this report].

As for what the images tells us about Opportunity? “I don’t think we can say much about the brightness of the rover itself, given the unique photometric geometry of this image compared to previous images of the rover, and the fact that atmospheric opacity was still higher than normal,” McEwen said.

The rover’s solar arrays only occupy a few HiRISE image pixels. “So doing an analysis of how bright the arrays are relative to the surroundings is beset with problems associated with small numbers of samples, and therefore relatively large errors in estimates of the amount of dust on the panels relative to the surroundings,” Arvidson elaborated.

There are, however, plans for HiRISE to take another image. In fact, a shoot had been scheduled in late October as a ride-along with the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) observation that Arvidson, a CRISM co-investigator, proposed. But that was deferred because of troubleshooting a relay problem between MRO and Curiosity. 

October proved to be a tough month on Mars. In addition to Oppy’s situation and Curiosity’s memory problem, that troubleshooting required the MRO team to turn off MARCI, CRISM, along with other instruments onboard for a couple of weeks. “Because we’re troubleshooting this relay issue on the MRO, we’ve powered down the instruments temporarily, except for HiRISE, which doesn’t seem to have any of this interference,” said Zurek.“We have had some relay glitches as we were trying to work through with Curiosity, and we’re all getting ready for InSight because it’s not very far away and we’ll be landing shortly after Thanksgiving.”

The objective was to make the environment as quiet as possible as the engineers worked to resolve the anomalous interference with the MRO relay. “We’ll reschedule CRISM for after the InSight landing,” said Zurek.

While you can’t see even see the rover at all in a CRISM pixel, the MER scientists will be able to check out the scene around Opportunity. “With CRISM’s 18-meter per pixel spatial resolution, it is impossible to see the rover,” said Arvidson. “Instead the intent is to estimate the amount of dust that has accumulated on Endeavour Crater’s rim overall as another constraint on what may have accumulated on the rover’s solar arrays.”

Now you see the dust, and now you don’t
Now you see the dust, and now you don’t This gif shows that dust on the floor of Endeavour has been whisked away, indicating there is wind activity at least on the floor of the crater. Initially HiRISE Principal Investigator Alfred McEwen, of the University of Arizona, interpreted that most of the fallout from the storm settled at latitudes higher than Opportunity's coordinates. “But since then, we have seen evidence for extensive dust fallout in some equatorial regions as well,” he said.Image: NASA / JPL-Caltech / University of Arizona

So the MER team won’t have to wait for InSight to land for HiRISE to take another image. “We will probably try again for the cycle that executes between Nov 11th–24th, said McEwen. “This should be a much better image with clearer air, unless a regional storm kicks up before then, which is common in summer in the southern hemisphere of Mars.”

With NASA’s approval, the MER team is pressing on positively. Work will soon begin on the extended mission plan, beyond 2019. “It’s due in the second week of February,” said Arvidson. “We still have to submit a plan about the science we would do assuming the rover wakes up. We have to do it. It would be weird if on February 1stthe vehicle responds because the dust has been blown off and, despite being 15 years old, it’s survived on its own for nine months or so and us not have a proposal ready.”

The extended mission would essentially pick up where the PEDE stopped MER in its tracks. Opportunity would continue the science campaign in Perseverance Valley and then drive down into the crater. 

First, of course, the robot field geologist has to wake up and the team has to recover her, fix the faults that have been tripped and attend to anything else it would take to put the veteran robot back in the saddle. “Even if we reestablish contact with Opportunity, it will still take a month or more to get the rover under complete Earth control and back to business, and we have to have that in the proposal too,” Arvidson said. 

“There is a lot of hope that the vehicle can survive this long and not be communicating with us, because of the dust cover, and then the wind blows off enough dust and we get Opportunity up and running again – that’s the pro side,” Arvidson said. “The con side is – geessh, she’s going on 15 years old. I mean it’s not like we just bought the vehicle. But who knows? We all hope Opportunity comes back.”

Both Opportunity and her twin, Spirit, were “warrantied” for 90-day primary missions on the Martian surface. The expectation was that Mars’ extreme winters and dust storms would take them out. While Spirit, which landed in the harsher region of Gusev Crater, succumbed sometime in 2010, Opportunity has been like the energizer rover ever since, carrying on it seems with the power of two.

In the immediate future, the team will continue the routine of the last month and half. “I don’t suspect there will be much difference in what we do over the next few months,” said Golombek.

NASA hasn't set any deadlines for the mission. The only plan it seems now is that the team will appear before the Mars Program officials at JPL and the powers-that-be at the space agency again for a reassessment sometime in January 2019. “No one has mentioned deadlines recently,” noted Golombek. “Perhaps it’s because of the popularity of the rovers.”

“Until we hear”
“Until we hear” MER Mission Manager Scott Lever decided the day after the rover shut down to wait out the storm to begin growing a beard, and will continue to let it grow “until we hear from Oppy or give up trying.” The selfie on the left was taken shortly after the team lost contact. The one on the right was taken on Sep. 26, 2018, after 108 days of silence. The image on the right was snapped, after coiffing, at the end of October. Like everyone else on the team, he’s looking forward to getting that ‘phone call’ from Mars.Image: S. Lever

Grateful and relieved to have NASA’s approval to continue with both active and passive listening, the MER ops team is focusing all eyes and all efforts like a laser beam on the prize. “We will be much happier when finally hear from her,” said Keuneke.

Silent as Oppy was in October, with NASA’s go-ahead, the month of All Hallow’s Eve brought a welcomed kind of fall color to the team. “It’s great that NASA is continuing to use the best available tools for communicating with the rover through January,” said Lemmon. “If there is no signal by then, I'm not sure how we'd get a signal. But between now and then is when we expect the winds, and this is a time when it is still warm at Opportunity’s site.” 

Meanwhile, Staab has started to work on what the team calls Hail Mary scenarios, “our last-ditch efforts,” he said. “We’re trying to identify all the scenarios that could have happened, and then which ones we can actually do something about, and how we would actually go about commanding to rule out those scenarios have occurred.” [More on that next issue.]

Time however sets it’s own deadline. Summer will be transitioning into fall in the coming months and fall of course turns to winter. “As we move past summer, solar insolation will be decreasing and temperatures will be decreasing, and unless we get some dust cleaning, dust will continue to accumulate on the solar arrays,” said Callas. “Since the storm, dust has probably continued to settle out of the atmosphere and has probably accumulated even more on the rover, so it is concerning. We just don’t know. The rover hasn’t talked to us, and that is the thing that will tell us what’s going on.”

While the MER team members simply do not know the state of their rover, Opportunity is cherished, and many are choosing to believe, at least for now. That’s not surprising. Belief in themselves and in their rovers put this team into the history books again and again and again, and along the way they succeeded in taking the world on NASA’s first overland expedition of Mars.

These human Mars explorers have bonded with this “Little Miss Perfect” rover in a way that no previous robotic planetary mission ever has – and that is no doubt a key factor in how and why this 90-day mission has gone on for nearly 15 years. “If we could bring Opportunity back just with the strength of our emotions,” said Herman, “she would be back already.”

MER optimism prevails and with luck the mission’s lucky star is still shining. “There is no reason to think yet – we haven’t heard from Opportunity, that means it’s gone,” said Staab. “We’re not even to the point where cleaning season historically begins. So there’s no reason to give up yet. We’re not at that point yet.”

Not this day
Not this day Author and astronomy outreach educator, Stuart Atkinson, who has been following MER since the beginning used Google’s Aragorn meme generator to create this graphic. The images are from the 2003 movie version of J.R.R. Tolkien’s The Lord of the Rings: The Return of the King, directed by Peter Jackson. Atkinson frequently contributes images to The MER Update and has his own blog that has tracked Oppy’s travels since her journey to Endeavour Crater began. See his The Road to Endeavour.Image: S. Atkinson

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