A visit with Curiosity
Posted by Emily Lakdawalla
11-07-2011 14:32 CDT
I had an amazing opportunity back in April: an invitation to go inside the fabled Spacecraft Assembly Facility at the Jet Propulsion Laboratory to see the next Mars rover up close. There hadn't been enough notice of the date that this was going to happen to invite out-of-towners, so it was just a couple of dozen local TV, radio, print, and Web media who were given this privilege.
I wrote briefly about my visit when it happened, two months ago, and have been too busy to write about it. But now I'm going to take my time and go through all the details I remember. You may want to go get a cup of coffee before you start reading!
Bill Nye, Mat Kaplan, and I trooped to JPL together. Mat planned to film and record audio of Bill for the Society website and Planetary Radio; I was technically there not for the Society but instead for Sky & Telescope, researching the article I wrote for them on Curiosity's mission to Mars. We were met at Visitor Control by Guy Webster, Veronica McGregor, and Jia-Rui Cook, all from JPL's public information office. As we got our temporary badges and followed them through the campus to the Spacecraft Assembly Facility (referred to by acronym-happy JPLers as "SAF," pronounced "saff"), they told us that they'd be taking us to the public viewing gallery first, where we could chat with mission personnel like Project Manager Pete Theisinger. But, they said, don't waste too much time there; what you really want to do is get downstairs and into the "high bay," the cavernous clean room that's seen the assembly of so many great robotic spacecraft.
Following Guy's suggestion, we didn't linger in the viewing gallery, and followed him straight down to a locker room. It amused me to see lockers just like the ones in my high school (a bit cleaner, though) in such an advanced facility as SAF -- but that's what they were. Inside the locker room were a couple of engineers, already suited up to enter the clean room. (I assume that anybody dressed in a white suit that day was either an engineer or a member of the media.) They helped us suit up in the white outfits, which are called "bunny suits" by those in the know.
The engineers sized us up and started distributing clothing. There were paper shoe covers and hair nets, and a paper surgical-type mask, one size fits all. Then came the cloth gear, each piece of which was individually wrapped in plastic. First was a one-piece, footless, white cloth coverall that zipped in front, like kids' pajamas. Next, a pair of cloth boots, with non-slip soles. I was wearing shoes with tall heels (actually a practical choice of dress -- it is rarely a bad thing to be tall at media events), and the first pair of boots I was given, with pink straps; couldn't fit over them; I was given the next size, with yellow straps. I mention this because I think I was the only one in the room wearing boots with yellow straps, which makes it easier to pick me out in the photos of the media event that were shot from the viewing gallery. I tucked the pants of the coverall into the boots; they fastened tightly around my calves with snaps at the top and Velcro straps across the instep, like a pair of gaiters.
Next, the hood, which totally covered the hair net, and extended into a collar that reached to my shoulders; we were instructed to tuck the collar into the coverall. Last came a pair of vinyl gloves. At least I think they were vinyl; they certainly weren't latex. Bill asked if he could tie his bow tie on top of the white suit, and was told no, he couldn't. Once we were all dressed, the only way to tell us apart from the engineers was the little anti-static devices they wore, small black devices with coiled cords, which they draped around their necks.
While we were suiting up, another engineer was swabbing and wiping the cameras and other doodads we'd brought in with us. Then we were directed, in pairs, into a closet-sized airlock. The doors were clear glass, ceiling to floor; the sides had an array of little air jets, probably a hundred or so on each side. As soon as the door from the locker room closed, those air jets blasted away at us for maybe a minute. Then we could open the second glass door, which led into a vestibule. From there we could retrieve our cleaned cameras, which had been passed through their own little glass-doored airlock cabinet, adjacent to the one for humans.
My camera is special. It's not the highest-quality camera ever, but it shoots in 3D -- it has two lenses spaced about 10 centimeters apart, and two CCDs, so it takes simultaneous left- and right-eye images, just like a Mars rover. If you want you can download all my 3D images here in their native MPO format; there's free software available to open and view these as red-blue or cross-eye stereo or convert them to two separate left- and right-eye images. My favorite way that I've found so far to view these is in Piku-Piku view, where the two images are processed into an animation that shifts back and forth. Here's my entire photo album in piku-piku form, and I've embedded some of them here. Sometimes the Piku-Piku processing makes a hash of the 3D; if you click on the images to go through to the website you can view them in your favorite mode, either red-blue or as crossed-eye stereo.
Once we'd all collected in the vestibule -- three engineers, me, Mat, Bill, and a couple of other people, including someone representing CNN -- they opened the very tall double metal doors into the clean room. It had been neatened up for this event, and the different pieces of hardware -- rover, backshell, and descent stage -- were parked behind red ropes. The cruise stage was tucked in a corner, mostly beyond view. Here's the video that Mat shot of me and Bill, in which it takes me a little while to overcome my speechlessness and start talking sensibly:
I walked in reverently, as though entering a cathedral. It's a hugely tall room, brightly white. It's ringed with tool cabinets and armatures and all kinds of other electronic looking stuff that was really very visually confusing -- it was hard to take it all in. Clearly, though, the most important thing in it was the rover, so I carefully approached it.
I recognized it, of course, yet it looked kind of unfamiliar. When you see the rover from a distance, from the viewing gallery, or in a computer simulation, it's easier to see it as a whole. From so close, it was hard not to see it as a confusing pile of parts. Bundles of wires crawl all over the place. Various moving parts have bull's-eye shaped black-and-white markings. The turret at the end of the arm is much bigger than I had remembered it, and I had a hard time wrapping my head around how the turret was divided into its five instruments and tools. And the whole thing is just so big. It was tall enough that even with my tall heels I couldn't really see down onto the rover's "back."
There was one engineer assigned to each of the components on display -- rover, descent stage, and backshell -- plus a couple more floating in the center of the room to answer questions. It was kind of disconcerting to make conversation with people in these bunny suits. With only their eyes visible to set them apart from each other, I found myself making more continuous eye contact than felt comfortable. I suspect though that if I actually worked in there day in and day out, I'd learn to recognize my peers from their shrouded shapes, their posture, and their way of walking.
Anyway, I started quizzing the engineer standing by the rover about various parts. I asked him to walk me through the parts on the turret, and I found that the two instruments that were facing us were the sample acquisition mechanism (CHIMRA) and the Alpha Particle X-Ray Spectrometer (APXS). Coming out the bottom was the percussive drill bit, with its two contact probes. On the front of the rover there's a bit box containing two spare bits in case one wears out or gets stuck in a rock; but the engineer assured me that no bit had gotten stuck in any of the rocks they'd tested. The drill isn't really like a wood drill that twists into its target; it's more like a jackhammer, banging a rock and powdering it as it bores downward. I couldn't really get a good look at the other two parts on the turret, the microscopic imager MAHLI or the brushing tool.
Someone else asked about the bull's-eye marks. These are center-of-gravity marks to help the rover get a visual check on the positions of its arm joints and wheel pivots. The rover has electronic sensors that should tell it how each of these is positioned and oriented, but the center-of-gravity marks will give it a backup source of information.
A prominent feature of the side of the rover that faced me was a thick bundle of orange, kapton-wrapped wires that terminated in a black frame on the front left corner of the rover. I asked what those were going to, and he said that the black frame was a bulkhead, where the ribbon-style wire that runs down the robotic arm was plugged in and converted to the copper, kapton-wrapped wiring. That juncture is also there because it's part of what permitted the arm to be developed and tested as a unit distinct from the rover itself; it is designed to be removable and replaceable more or less by plugging it into the rover cabling at that bulkhead, like a peripheral device being plugged in to a computer. The rover was assembled and disassembled several times during its development, so it was helpful for it to be modular like that.
Another media person asked why the wheels were painted black. The engineer said there were two main reasons. The first is that the matte black color wouldn't throw any glinty reflections at the cameras. The second is that, as they roll kilometers across Mars, it'll be easy to spot the wear patterns on the treads as they become lighter-colored spots on the wheels.
Looking up at the camera bar, I noticed that there were two pairs of circular lenses on each end. I asked if there were two pairs of Navcams, and the engineer said yes, they were fully redundant; there's also two sets of Hazcams in front and in back. Spirit and Opportunity have only one set. But Spirit and Opportunity were designed for only 90-day missions, maybe double that at the outside; failure of the cameras was considered unlikely enough that it wasn't worth the mass to put extra pairs on. Curiosity's prime mission is 687 Earth days long, and it should last much longer; that means there's much more time for systems to fail with age. So critical things like avionics and the engineering cameras are all fully redundant and independent of each other.
I was struck by how large the tubular "legs" of Curiosity are. They were kind of spindly on Spirit and Opportunity; they are thicker than my arm on Curiosity. They also vary in thickness depending on the weight they have to support: the front legs are the thickest, then the back leg and rear part of the bogie is medium in thickness, and the skinniest tube is on the part of the bogie that goes to the middle wheel.
While researching Curiosity I'd noticed that its wheelbase is about exactly long as it is wide, which is another way in which its design differs from Spirit and Opportunity. I asked about that, and the engineer said that the main reason for this difference has to do with the launch configurations of the two rovers. The origami-like fold of the Mars Exploration Rovers within their tetrahedral landers resulted in a wheelbase narrower than it is long. Curiosity will hardly fold at all to get inside its aeroshell -- it basically just squats -- so the shape of its wheelbase reflects the circular cross section of its aeroshell. In fact, the middle wheels jut out a bit farther than the corner ones. This makes all six wheels much closer to being co-circular (if that's a word) when the rover toes in front and back wheels for turning in place, which might be a nice driving feature.
One light bulb that went off in my head as I examined Curiosity from up close was an answer to why the RTG tilts down into the rover's rear end. The real RTG won't get installed on the rover until just before launch, because it will be so hot (both in the temperature and radioactive senses). The rover will be all packed up inside its aeroshell, stacked onto the tip of its launch rocket before they install it through a hatch that opens up on the sloping side of the aeroshell. The slope of the RTG's angle into Curiosity's butt has to do with that installation process -- it's perpendicular to the aeroshell wall, so that it can be inserted straight through the hatch to hook it up to the rover.
I asked about what was evidently an access panel on the rear left side of the rover. I was told that it was a panel to allow access to DAN. In general, it is very easy for engineers to access all the internal parts of the rover. Everything's mounted onto the underside of the top panel; they take off the belly panel and easily reach in to access the instruments and electronics. Making everything very accessible was a lesson they learned the hard way, on MER, where they had to dig in to the rover's internal workings just days before launch, to replace (if I remember correctly) a blown fuse.
It was getting late and time for us to go, but of course Bill had to bring up the Sundial with the engineers. The one that's on Curiosity now is the same as those on Spirit and Opportunity, a flight spare that had sat on Jim Bell's desk since the assembly of Spirit and Opportunity was complete. ("Flight spare" means that it was built to the same design and tolerances as the ones that actually flew on the spacecraft, it just wasn't selected to be one of the ones actually sent to Mars.) Bill asked the engineers if they'd read the text on it, and a couple of them hadn't; they walked over and peered at it to read the text up close.
It was truly a thrill to be in there. And I have to say that how I feel about Curiosity changed completely after seeing her up close. In the past, I've tended to regard her as a bit of a monstrosity -- she's huge and squat and asymmetrical and horribly, horribly expensive and it seemed impossible that she could ever occupy the place in my heart that Spirit and Opportunity do. But after meeting her face to face, I have to admit that it was love at first sight. And I immediately switched from calling the rover "it" to calling it "she." (I'm having a debate with rover driver Scott Maxwell about whether Curiosity is male or female. Scott insists it's male and calls it "George." My position is that anything with a butt that big must be a chick.)
I asked one of the engineers how many people on his team refer to Curiosity as "she" and how many as "it." He said that maybe a third of them refer to the rover as "she," but he predicted that that would change with time as the rover begins to develop a personality. "She doesn't have one yet, but she will," he told me. If you're wondering how a rover can have a personality, just search Scott Maxwell's blog on "Spirit" and "Drama queen."
Curiosity won't replace Spirit and Opportunity. Hers will be a totally different mission, with a totally different personality. Hopefully more like Opportunity's charmed child one and less like Spirit's drama queen one. Provided, of course, that she gets to Mars safely. I'm going to be much, much more apprehensive now at her launch and landing.