Curiosity

by Rod Pyle

  He continued: “It's like we had already taken an SAT [Scholastic Aptitude Test], and are waiting for the results—you've taken the SAT, you are done. Nobody tells you the score right then, you have to wait. We know that we have done everything that we can do, for many years now, so how did the exam go? So you're nervous, and something happening could change the outcome of your life. I don't have kids, so it's not like I can compare it to sending my kids off to college or something like that. Besides, at this point there is no way for the spacecraft to phone home and ask us for help, like ‘Hey, Dad, can you send more money?’ It is just doing what it is going to do.”

  AL CHEN: A year after landing, Chen admitted in a press conference that he had experienced a heart-stopper early in the EDL sequence: “I had two guidelines: don't say anything stupid and report everything you see. It's that second part I didn't do very well.

  “We had two types of telemetry coming back from the vehicle.” At this point, this is the main data coming back from MSL. “These 256 tones that Curiosity would send back tell us what was going on. That's all we had for about 14 or 15 minutes, from cruise stage separation until we got into the atmosphere. After that we started picking up data from Mars Odyssey.

  “Things were looking pretty good, we had ten minutes of pretty boring heartbeat tones, my blood pressure was up but it was just starting to calm down….” Heartbeat tones tell the controllers the condition of the spacecraft.

  “Then shortly after we hit the atmosphere we got a tone, called ‘Data Catastrophic.’ It's usually bad when you get these tones coming back that say catastrophic,” he chuckled nervously, then continued: “We had intended that tone to tell us that we were about to lose the vehicle…. I almost had a heart attack when I saw that. If it was true, it meant either that the vehicle was tumbling or it was not heat shield forward….

  “So I thought about it for a second…I thought, if we are about to lose the vehicle, I'd better not say anything dumb, going back to guideline one. I thought, this should happen right when we hit the atmosphere, there should not be much error at that point. Do I really believe this? Is there more going on there than what I was thinking about? The computer was subtracting the readings from two sensors up there, trying to compare pressures, so I thought, let me just sit on this for a minute….

  “We were about to hit peak deceleration and peak heating, so it will become obvious if we are about to lose the vehicle in a minute or two…so I sat on it. Luckily it turns out that the instrument was working fine, we just had a calibration error. If I was not already sweating then, I sure was after that.”

  +01.25: Peak heating was reached on the heat shield. It was pointed the right way.

  +01:36: Peak deceleration occurred, straining the spacecraft at eleven times Earth's gravity. MSL was still gliding on its heat shield, steering itself toward Gale Crater.

  +04:00 to +04:10: The remaining weights were jettisoned, and MSL settled back to its natural balance, base centered downward.

  + 04:19: The 52-foot supersonic parachute was deployed at about 800 mph, or Mach 1.7. It supported 5,293 pounds of rover, aeroshell, and heat shield (minus the weight of the parachute itself).

  ROB MANNING: Manning agrees with Chen that testing parachutes is not like testing computer circuits or rockets. They are soft and somewhat unpredictable, and a real PITA. “Parachutes are always a problem. The soft bits are the difficult part. Unlike metal for example—you can test metal, when you pull it, it will break under a given amount of force. You can't do that with fabric, though, it just doesn't cooperate. Fabric has a much more empirical trial-and-error aspect. So with the parachute it was a bit more trial and error. For MSL we tested the parachute at the wind tunnel up at Ames [Research Center, a NASA field center in Northern California]. One of the problems is when you mortar launch a parachute on Mars, the supersonic flow opens the parachute from the front to the back. On Earth it opens up from the back to the front, just because of the thickness of the air. For these tests we don't really care how it opens but that once it gets to its full state [fully open] that it doesn't break.”

  +04:39: The heat shield was dropped free. The MARDI camera began imaging the landscape below, catching a few shots of the heat shield as it departed.

  ADAM STELTZNER: “We were now looking with the MARDI imager at the surface of Mars in a new way. We saw black sand dunes underneath us, and the red iron-rich soil that gives Mars its natural color. The attitude we have is governed by the trim angle of attack of the parachute.” As MSL descends, the parachute swings a bit, allowing the camera to do pan around. “That gave us a sort of a tour of the neighborhood where we would be landing.”

  AL CHEN: “The landing radar was a concern here—with the enormous heat shield, and uncertainties about how it would wear, and the wear patterns affecting its aerodynamics, what would it do once set free?” Would the radar lock on the falling heat shield instead of the ground? “That was something we had to figure out—is the heat shield going to fall away fast enough so that all your radar won't get locked up on it?” It fell away fine, and the radar saw the ground just as planned.

  +04:44: The landing radar began feeding information about the remaining distance to the ground.

  AL CHEN: Al relates that landing radar was a critical development for MSL. Such radar had been used before but needed to be far more accurate for this mission. “If you don't know how fast you are going, certainly if your velocity is one meter per second, good luck landing at those speeds, because you have no idea where you are going. That was a big developmental hurdle. We accepted the fact that we would have to go off and develop radar that could give us very good velocity data down to the 10th of a meter per second level.”

  ROB MANNING: “We tested the radar with a helicopter but we also tested it with an F-18 jet. We used the helicopter to simulate the descent stage with the rover dangling below and the radar on.” It worked. “The amazing thing is the only time we actually hung the rover from the descent stage was in the ceiling at JPL. We only did that once or twice because it was an expensive test, and you got everything you needed to know from one test. There is very little variability in the system.”

  ADAM STELTZNER: “We were concerned about our landing radar. We had six beams on that radar, but we restricted ourselves to using only two when we separated the rover from the descent stage. Since we were only measuring two directions, but controlling for x, y, and z [three directions], we had to estimate one of them, and that was z. we were confident that we understood [the] surface gravity of Mars [and] that we could use that as an estimate for the z-axis.” Z-axis in this case means down, the direction of travel.

  “But it turns out that there is a gravity anomaly at Gale Crater not present in any of our models. That meant that there was less gravity, by 400 micro g's, at the surface of the landing site than we had anticipated. As soon as we separated and went to two beams, we started to slow down. We had set our throttle to handle what we had anticipated as the surface gravity, but the anomaly meant that we were slowing down.

  “That was actually convenient because landing slower is usually thought of as better than landing faster, but it was sheer luck that the anomaly went the direction it did. If it had gone the other direction…I think we would have been fine, but every time something went wrong with the rover for the rest of the mission, the guys would turn around and say, ‘It's because you EDL guys landed us too hard.’ We got lucky. We need to remember that in the future.”

  +05:00: At this time, Earth was out of radio contact so the “heartbeat” tones Al Chen referred to earlier could not be sent home to be heard fourteen minutes later, but this was expected. It would be sweaty-palms time nonetheless.

  +06:00: The landing rockets were primed and made ready.

  +06:16: Backshell separation—the protective aeroshell, as well as the parachute, were left behind to drift away, their work done. The landing rockets were ignited and throttled up to 20 percent. The rockets also guided MSL off to the
side in what is called a “slew maneuver,” maneuvering about one thousand feet to get it out of the way of the parachute and backshell, which continued to fall.

  ADAM STELTZNER: “This is the divert maneuver, we are getting out of the way of the parachute and backshell. We slew first to one side, then the other.” The lander reoriented to move straight down at the completion of the maneuver.

  +06:18: The landing rockets were throttled up to full.

  +06:40: Powered approach—all rockets were firing as MSL neared the surface.

  +06:43: MSL decelerated further to lose speed.

  +06:50: Four of the landing rockets throttled down, and the remaining four were shut off.

  +06:53: The rover began to rappel down from the rocket pack, descending on nylon cords. The front wheels were released to fall into position for landing.

  +07:01: The “bogie” was released, completing the wheel-suspension-system preparation to act as landing gear.

  ADAM STELTZNER: “We liked that we were using the wheels and suspension system, which had been designed from the beginning to conform to uncertain terrain. Slope-related disturbances would not affect the vehicle. Even if the rover could not rove, due to the steepness of the slope, the landing would be successful.”

  +07:02: The computer enabled “touchdown logic,” the software that was needed to complete landing.

  +07:11: Touchdown on Mars.

  +07:12: The rover's onboard computer confirmed that all wheels were on the ground and stable.

  ADAM STELTZNER: “It was decided not to measure the landing event, but to measure the state of the vehicle.” What's the difference? “We wanted to avoid the fate of the Mars Polar Lander, which had a false indication, noise in the system, which it interpreted as a landing, shut off the rocket motor and fell the last 80 meters.”

  +07:12: The flyaway command was sent to the rocket pack, telling it to go crash on its own somewhere else, at least 2,100 feet away. The “bridle,” or nylon cords along with the wires leading up to and throttling the rocket pack, were cut.

  ROB MANNING: “When the wheels made contact, the rocket pack continued coming straight down, slowly, so it never hovered [prior to touchdown]. When the rover sensed ground contact, the computer realized that the rockets were using less power to stay up in the air. The computer then says ‘I must be on the ground.’ So it sent the command up to the rocket pack to say ‘Stop and hover,’ so now the descent stage begins to hover. It slowed to a stop and finally the computer cut the cables. Before it cut the last electrical cable, it said, ‘Okay were done, go ahead and fly away!’ in one second the descent stage replied ‘Right—copy that.’” He said this last part in a cute British accent. I wondered when the rover started talking like a Spice Girl, but didn't ask. The important thing was that it had landed safe and sound.

  About fourteen minutes later, on Earth, the whole drama was played out for humans to hear. A bit over seven minutes after this delayed transmission had indicated entry interface, Al Chen confirmed touchdown. The control room was jubilant, as were three million viewers.

  Ferdowsi summarized his feelings after landing, which doubtless applied to many in the room that night: “I was super happy once we had landed——it was exciting to share it with everyone else, you know how hard everyone has worked up to that point. What surprised me was how leading up to that I had felt like I was getting tired, you've worked these long hours and done all these things. But the moment we landed my first thought was: ‘Let's do this again! I'm ready, let's go and launch another rover now!’”

  A very tired Adam Steltzner wrapped up the night with a press-conference statement that further inspired: “Great things take many people working together to make them happen. That is one of the fantastic parts of human existence. I'll be forever satisfied if this is the greatest thing that I have ever done…. This nation is a truly great representation of a piece of humanity that reaches out and explores and conquers and engineers. We are toolmakers, agriculturalists, and pioneers…and that is reflected in the activities and actions and results of tonight.”

  Well said.

  Fig. 17.2. JOY: After the landing, the generally restrained engineers cheered and wept with joy—a decade of work had paid off brilliantly. Adam Steltzner embraces Al Chen in lower left. Image from NASA/JPL-Caltech.

  In a swath of suburban bedroom communities hugging the foothills of northeastern Los Angeles, people began to notice odd things. These normally quiet and pedestrian communities—La Crescenta, La Canada, Flintridge, and Pasadena, are not places where people generally act out much, and disruptions of routine are noticed. These are towns where teenagers’ parties are often shut down by the cops at 9:00 p.m. But what the neighbors were seeing looked like a low-budget slasher movie, where the neighbors just aren't quite right and you probably should begin to worry and round up the kids before they are trapped and cooked. People who normally worked a pretty steady 8:00-to-6:00 schedule were coming and going at odd hours. When home, they were drawing heavy black shades across their windows. Sometimes entire families, even young children, were seen having barbeques complete with ribs and beer (for the adults, of course) at 7:00 a.m. Something was not right. It was all a bit The Hills Have Eyes.

  But there was at least one non-JPL local who knew what was up. Garo Anserlian, a jeweler in nearby Montrose, was helping these folks to maintain their bizarre new schedules. For besides being a jeweler, he was also a part of a rapidly vanishing breed, a watchmaker. And he was creating some very odd timepieces for a number of folks at the lab.

  Starting with Pathfinder, it became clear that early-stage operations of landed rovers worked best if the engineers and scientists responsible for wringing the most out of the machines lived on a Martian schedule. Mars days, or sols, are much like Earth days, lasting 24 hours…and 40 minutes. So if you spent three months on Mars Time, as they had on the Mars Exploration Rovers, your schedule shifted pretty quickly. You lost about five hours per week.

  Keeping track of this became a major pain in the neck, so a couple of engineers on the MER project had decided they wanted watches devoted to keeping the oddball time properly. But what digital chip maker would design something for the few dozen people who might spend a couple hundred dollars for such a timepiece? The answer was none.

  The engineers approached Anserlian, as he was one of the few locals who could even fix a watch, much less make one. He said he'd check it out. He consulted other watchmakers, including some acquaintances in Switzerland, and they said forget it, it's too hard, don't get mixed up in it. Fortunately, he was an inveterate tinkerer and ignored them, spurred on by the challenge.

  Starting with a mechanical watch, he added weights to the balance mechanism and adjusted the spring, and soon he had a workable 24-hour, 40-minute watch. The JPL’ers gobbled them up, and many were still in use when Curiosity landed. New ones were still available at a price. Many of the watches even had red Mars logos on the face.

  None of the neighbors thought to ask Anserlian what was going on, but they should have. He would have told them about Mars Time with great pride.

  But buying a Mars watch was the easy part. Shifting one's circadian rhythms—even at the slow rate of forty minutes per day—threw one's system out of whack. Some tried pharmaceuticals, most just dealt with it. None were unaffected.

  And it's not as if this was a simple eight-hour workday. Most people on the mission labored from twelve to fourteen hours because that is what it took. That alone can disrupt a regular schedule—adding almost an hour to each day made it even tougher.

  Most JPL’ers I spoke to said, however, that very strong bonds formed during Mars Time. The LA-based people already knew each other pretty well, having for the most part worked together for years, but the others from faraway cities and other countries were brought to JPL for the three-month duration of primary operations in Mars Time. So, although the days were drifting continuously, everyone was working together on long but synchronized shifts.

  Rebe
cca Williams, a participating scientist on MSL, now works on the mission out of her home in Wisconsin. So, in addition to the Mars Time shift, she had the time zone change to deal with as well. Or perhaps that already gave her an edge when she came to Pasadena? She spoke to me from her chilly basement office just outside of Madison.

  Fig. 18.1. MARS WATCH: One of Garo Anserlian's Mars timepieces. They come in many styles, but all have in common the 24-hour, 40-minute Martian sol time measurement. Image from NASA/JPL-Caltech.

  “In the beginning there's a lot of engineering check outs, but it was really a fortuitous thing that we all got to live and work together for three months. You develop important relationships, and it makes it much easier to do the telecommunications that we do now on a daily basis. You know whom to contact and you've developed that relationship so you feel more comfortable. It also increases the efficiency of doing it, which was really amazing. Of course, it was already a bonding experience to be exploring this amazing area on Mars, but doing it on Mars Time so you're all jet lagged…that's when you really get to know people.”

  It sounded to me as if it had been slightly easier for her to adjust, as she was already shifting her time to accommodate the West Coast clock.

  “Those three months were among the best I had ever experienced. It's kind of like the most idealized summer-camp experience you've ever had. It's as if you're synched with the people you most admire and you're all experiencing something amazing together for the first time.” Her voice almost quavers with rich memories of the early days of the mission. “One of my favorite experiences, and I still can't get over this, was when we had data coming down and everybody would gather around and watch as the new images flickered up the screen. You would look at a rock and you think you understood it, then the person next to you had a completely different interpretation. So you are going back to your first principles as to why you think you are interpreting a rock a certain way. We all saw them simultaneously for the first time. It was a lot of fun.”