Making Tracks on Mars

Home | About "Sojourner" | "Sojourner" Excerpts | "Sojourner" Contents | Rover Menagerie | About Me

This is a website about roving on Mars...

I was fortunate enough to be part of the team that designed, built, and drove the first Mars rover--Sojourner--on the surface of Mars during the Mars Pathfinder mission in 1997.

That story is chronicled in my new book, "Sojourner: An Insider's View of the Mars Pathfinder Mission."

I am again privileged to be a participant in the next Mars mission--called Mars Exploration Rover, or MER--that will land two rovers on the Red Planet in January 2004.

I will be periodically recording my observations as the MER rovers explore the terrain of Mars during the next few months...

Sunday, January 25, 2004

Ups, Downs...and Landing on Mars--Again!
It's been awhile since I've had time to post anything. The past week has been a rollercoaster of activities and emotion.

Spirit began its post-egress explorations of Mars on sol 12, analyzing the soil immediately in front of the rover. Everything was working great. We did our first drive to a rock the scientists had named "Adirondack;" we were going to analyze the rock with our instruments, and then RAT the rock, using our Rock Abrasion Tool, which should grind away a coin-shaped depression in the rock's surface. When this was done, we'd apply our robotic arm-mounted instruments to the hole.

Then, on sol 18, we couldn't get most of our command sequences to the rover. At first we thought that the thunderstorms at our transmitter in Australia were getting in the way of our commands. But as the day wore on, our ability get commands to the rover and see the right responses seemed to deteriorate. Sometimes the rover didn't answer when expected. The rover would miss communications sessions, and the team would try to develop an explanation. Then we'd get a report that lots of data was coming down from Spirit through one of our relay orbiters; the team would cheer with relief, only to discover minutes later that the content of the data was meaningless. What was going on? There had been no warning of a problem onboard.

Over the next sol or two we commanded Spirit to send us "beeps" that would prove it was listening to us. Sometimes these worked.

After one such attempt, we got no signal. The mood in the control room collapsed. The team forced itself into planning what to do next.

A few minutes later, their was a somewhat tentative, incredulous voice on the network: "Uh. Flight. Telecom. Station 63 is reporting carrier lock." Engineers around the room looked up in surprise. "They're reporting symbol lock...We've got telemetry lock." Spirit was back! The data coming down was garbled, but our girl was at least babbling at us...on her own. The mood in the room had transformed again.

From what little data we could get, it seemed that Spirit was booting up and reseting over and over, never fully waking up, never completely shutting down. If the rover was coming up long enough to begin communicating, it might reset in the middle of talking to us. And whatever was causing the resets was preventing Spirit from doing the rest of its tasks, like preparing data to be sent. The power and thermal engineers were particularly worried: Spirit was designed to shutdown each night. In its current state, it might never turn itself off. The result might be that the rover was overheating and draining its batteries down to nothing. On sol 20, an attempt to command the rover to shut itself down for the night failed. Spirit might be listening to us, but wasn't often doing what it was told.

I came back on shift as the anomaly Tactical Uplink Lead on the night of sol 20. The team decided that the objective for sol 21 would be to make Spirit shutdown. The software team had been meeting all day, coming up with scenarios to explain the rover's bizarre behavior. Their best notion was that the rover's main memory was corrupted, causing the rover to reset every time it tried to access data in that memory. So, the software guys proposed forcing the rover to wake up without using the main memory, like booting a computer without using its hard drive.

To get Spirit to boot up this way, the rover would have to accept a single command telling it what to do the next time it reset. So on the morning of sol 21 we sent this one command several times. We then commanded a reset (which seemed a bit redundant given what Spirit had been doing on its own), and after a while commanded Spirit to communicate with us. The rover started talking to us on schedule. We were getting data that made sense again! The rover appeared to be stable. The telemetry confirmed that we were in a low-power state. We sent a command to tell the rover to go to sleep until the next morning. This would give Spirit time to recharge its batteries. All the indications were that Spirit had listened to us this time.

We still have a lot of work to do. As it stands, we'll have to send the special command every morning to get Spirit out of its strange state and stable again. But at least we can now begin tracing the problem on a stable spacecraft.

In the meantime, Opportunity has been falling toward Mars. On Saturday night, those of us working on Spirit paused long enough to watch the landing events unfold. Waiting for a Mars landing is always nerve-wracking. (After Pathfinder and Spirit, this was my third time.) But everything went as perfectly as could be. Data came back from Opportunity pretty much the whole time, during descent, landing, and even bouncing across the Martian surface! And a few hours later, Odyssey relayed photos of our new landing site back to Earth that were amazing, even for Mars. There are no rocks! It looks like we rolled to a stop at the bottom of a bowl (probably a small crater). The soil is a grayish red, except where we've disturbed it with our airbags; there it looks like a deep pure red. There are imprints of the airbags in the soil in several places. And while there are no individual rocks, we seem to be partly encircled by a rock outcropping--bedrock. No one has seen this on Mars before. And it's only yards away. We'll probably spend weeks exploring it.

And thanks to landing on our side, and then needing to rotate the lander to be right-side up, there is no airbag at all in the way of driving forward off the lander. It appears that we have a perfectly clear path off the lander into an unexpectedly alien landscape...
4:06 pm pst

Thursday, January 15, 2004

Sol 12: Six Wheels on Dirt!
Spirit is now free of the lander!

The Vice President of the United Stated visited JPL yesterday to congratulate our Mars team on our success so far. Those of us working the Mars night shift to get the command sequence updates ready for driving off the lander had to keep working while the rest of the team and JPL employees listened to his speech. If we had taken a break for an hour or so, we wouldn't have been ready for the next Mars day's activities!

Mars time continues to be disorienting. During another sequence planning meeting for Spirit, a Congressman came by and was introduced to all of us. All I could think was, "What's he doing here in the middle of the night?" Well, it was two in the morning-Mars time. Only after the Congressman left did I remember that it was mid-afternoon Pacific time...

After delivering the commands for sol 12-drive off day-I took a break, tried to nap, and came back to hear the poll of the daytime team for "GO FOR EGRESS." When every subsystem reported "go," all of us crowded into the mission control area cheered and applauded. The Flight Director played the theme from "Rawhide"-and everyone applauded again.

Of course, we would now have to wait another hour and a half to hear back from Spirit how well egress from the lander had gone. All the rehearsals indicated it should go fine, but we were all tense anyway. Engineers are professional worriers. We imagine all the ways things can fail, so that we can design to prevent those failures from occurring. But even when we've done our jobs, and considered all the alternatives we can come up with, there is always some doubt...

I went back to my office and tried to sleep for an hour. I really should have gone home and to bed for the night, so I'd be fresh for my Mars-time shift tomorrow, which would start just after noon PST (but at 11 pm Mars-time). But I wasn't going to miss egress. So I slept on the floor-and I did sleep. Exhaustion can be conducive to rest.

I woke up again, and it was less than fifteen minutes until we should get a signal. I wandered back to the mission control area. Steve Squyres, our Principal Investigator, was finishing off an explanation of what our long term science plans were likely to be. It was now only a few minutes until we should hear again from Spirit. There were several different types of telemetry that would tell us if things had gone well. We weren't sure which would be the first source to arrive. The Flight Director pointed out that getting any signal at all would at least confirm that Spirit was still healthy.

Carrier lock! There was a signal. We waited for data to come through that signal. One subsystem reported that the rover had been tilted as much as 30 degrees during part of the past hour-just what you'd expect from driving down the ramp. People cheered. The mobility team said their data showed that the rover had rolled more than two meters. Applause. Then low-resolution pictures started to appear. There was the lander?behind us! We could see tracks in the dirt where Spirit had driven off. The front cameras showed nothing but soil Martian soil under-and on-our wheels. We were off! Engineers were cheering, applauding, and hugging each other. People were shaking my hand, telling me I now had a lot of work to do. The mission had just shifted from "Impact to Egress" to normal surface operations, and the operations process I had designed was about to kick into gear.

Time to go home. I have a big day tomorrow.
11:09 am pst

Sunday, January 11, 2004

Sols 6 and 7: Spirit Stands Up!
The day before yesterday, my wife came home with a new license plate frame for my car: "My other cars are on Mars." It replaces the one I've had since Mars Pathfinder that said, "My other car is on Mars." Between Sojourner and Spirit, I'm now up to two. I'll keep my fingers crossed Opportunity will land just as successfully.

I?ve been working Mars time for the past four days, and now finally have a couple of days off. The Mars day (called a "sol") is just a bit longer than an Earth day, at twenty-four hours and thirty-nine and a half minutes. Since the rover is solar powered, and wakes with the sun, its activities are coordinated with the Martian day. And so are the activities of the MER operations team. Part of the team works the Martian day, interacting with the spacecraft, sending commands, and analyzing the results. But those of us who build new command sequences for the rover work the Martian night, while the rover sleeps. Since the rover wakes up about 40 Earth minutes later every morning, so do we. It seems like sleeping later every day would be easy, but it can be disorienting. It's very easy to lose track of what time it is on Earth...

We've been struggling for the past few days to get the lander's airbags retracted far enough to drive straight off the lander onto the Martian surface. While it's possible that the rover could get tangled in airbag material during its egress from the lander, the bigger concern seems to be that the airbag might contact one of the rover's delicate solar arrays, tearing it or otherwise causing damage. The airbags all have internal cords that can be drawn in to the lander using airbag retraction motors. We've tried "lift and tuck" maneuvers with the lander, leaning back one petal to create clearance to make it easier to pull in the airbag under another petal. Some of the airbags have cooperated, but the one in our way is immobile. We've decided to turn 120 degrees to the right and drive off that way.

For the voyage to Mars, the rover was folded intricately into the volume of the lander, crouched down with its front wheels almost touching each other. Standing up the rover is a multi-step process--described by our Principal Investigator as "reverse origami--with careful checking all along the way. If any part of the standup is incomplete, and we go on to the next step, we could find ourselves unable to recover. On sol 6, we used the "rover lift mechanism" to raise the rover high enough that we could then rotate the front wheel "rockers" up and out to their full extension. The space is so tight that we have to steer the wheels out of the way during the rotation to keep from striking the solar array. After the wheels were deployed, the lift mechanism lowered the rover onto the wheels. The pictures came back and showed the wheels in the correct position. To confirm that the rockers were latched in place, the rover was raised again. There was no indication that either of the latches had failied...but...the telemetry didn't look exactly as the mechanical team expected.

So, on sol 7, we ran another version of the rocker latch test, just to be sure. Results looked good. So we extended Spirit?s rear wheels. With that completed, the rover is fully stood up on the lander! Once we cut the one remaining cable umbilical (the one that let's the rover move the petals of the lander around), Spirit will be completely independent of the lander and ready to drive off.

Egress should now be only about three days away. It's almost time to go exploring!
2:49 am pst

Wednesday, January 7, 2004

Starting to Live on Mars Time
The night of Sol 4-5

I just finished working the Martian night (which today happened to be daytime at JPL), planning Spirit's activities for Sol 5, the rover's fifth day on the surface. The uplink team is doing a great job of getting a lot done in a short amount of time. The rover seems to be getting more sleep than we do...

We've had lots of firsts the past few days, as we prove to ourselves that Spirit survived its bumpy landing in good shape. We've demonstrated that both orbiter relay links--MGS and Odyssey--are working, giving us multiple paths to get images and data down to Earth. Amazingly, both relays worked the first time we tried them out! Then we proved that we could relay commands, if the need arose, through the Odyssey orbiter. And we've been commanding the rover--and getting data back--every sol through the "low gain" antenna.

Spirit seems very healthy. Some of our team has been worried about our "high gain" antenna. This is the antenna on the rover that looks like a lollypop and tracks the Earth, sending back far more data than possible with the low gain. The first time we used the high gain antenna, it looked like one of the motors was noisier than it should have been--and working harder than it should be--but only when turning the antenna in one direction. We stopped using the antenna, while we studied the problem. But the antenna seems to be working fine now. The most likely theory is that there was some debris or maybe lumpy lubricant that got pushed out of the way the first time we swung the antenna around, and now everything is normal.

The rover has also been getting warmer than expected, forcing us to do a little bit less to avoid overheating. Spirit was designed to hold in the heat it generates, to avoid freezing overnight: Mars is a cold place, often getting down to -100 degrees C. But the weather at the landing site is balmy--at least for Mars. The lander seems to be insulating the rover from the cold ground better than we thought, and the "thermos bottle" we keep our electronics in may be even more efficient than expected. When we started developing Spirit and Opportunity, we knew that managing the thermal state of the rovers would require care throughout the mission. The fact that we're warm now may mean that we will survive for a long time as things get colder later...

The science team seems interested in investigating "Sleepy Hollow," what looks to be a small impact crater only about 50 feet from the lander. That may be our first destination once we finally driver off the lander, after Spirit is fully checked out and deployed. Then we may literally head for the hills. The hills might be a kilometer or more away, but in this terrain, we may be able to travel fast. We'll certainly be cautious at first. Time will tell...
10:03 pm pst

Sunday, January 4, 2004

Success! Spirit on Mars!
After all of the development, all of the worrying, and the nail-biting of the past few days, the Spirit rover has now successfully landed on Mars!

During the commentary being presented as Spirit approached Mars, I could not help but be struck that everything being described had actually already happened. The radio signals coming from Mars were only just arriving at Earth after traveling at the speed of light for nearly 10 minutes, so that at the moment that the commentator was confirming that the spacecraft had just contacted the Martian atmosphere, Spirit had actually already hit the surface.

Thanks to the radio tones the spacecraft transmitted every time a major onboard event occurred, we were able to follow the progress of Spirit all the way down to the surface. Then, immediately after the signals indicated the lander had hit the ground, contact was lost. Even though this was expected?the lander would be bouncing and rolling on Mars for half a kilometer or more before coming to rest, making communications difficult?everyone tensed up. Would we hear from Spirit again?

Ten minutes later, we got another signal. Spirit had survived! And had even landed upright, with its antenna pointed at the sky.

Amid all the cheering I was still worried. Several things still had to go right: the retraction of the airbags, opening of the lander petals, and then the critical step of getting the solar arrays deployed. Without health arrays, Spirit would be starved for energy, and would soon die. With them, we would have the time we needed to solve any problems that might crop up. Earth had set in the sky over Gusev crater, so direct communications with Spirit was no longer possible. The soonest we could know about the critical deployments would be when Odyssey?the science spacecraft in orbit over Mars we would use as a communications relay?passed over the landing site and sent back to Earth any data received.

The Odyssey data was coming in. People in the control area cheered this news: If any data was being downlinked, it meant that Spirit had succeeded in communicating with the orbiter on its first attempt?a very good sign. Then the engineering telemetry came in?the first picture?a shot of a calibration target?then more pictures from the surface of Mars!

None of us could believe our luck. The rover looked perfect, with its solar panels fully extended, and the camera mast fully deployed. All the engineering data looked nominal. There were no fault conditions?much better than any of our rehearsals! We wanted the lander to be level, to make it easier to drive off. We were tilted by?2 degrees!

In only a minute or two, the ground software had constructed a panorama from the individual images that had come down. We could see 360 degrees around the rover, to the horizon. The landing site looked flat, with small rocks. We can drive here!

It looks like I'll get a chance to do my job!

2:08 pm pst

2004.02.01 | 2004.01.01 | 2003.12.01

I'll make additions to this site as often as living on Mars time and exploring an alien planet permit...


Links to other Mars-related websites:

Mars Pathfinder Mission archive

Mars Exploration Rover Mission

Mars24: Keep track of Mars time at the MER landing sites