Saturday, November 26, 2011
I saw a spaceship go to Mars today. It was very exciting.
Like a sunset or a southwest canyon, a rocket in launch is not something that can be captured losslessly in photographs or video. Images can convey something of the events that occur, but the richness of the time and place is muted relative to truly witnessing the launch. You really need to go see something like this for yourself, but maybe my words can add something to the many pictures and videos you can find. Watching the Atlas V and her Mars rover cargo Curiosity take flight this morning felt something like this.
First, the tension.
The Atlas V 541 is the second-largest launch vehicle offered by the Lockheed Martin branch of United Launch Alliance. It's actually misleading to call it a vehicle, since there are six machines, each composed of many parts, sitting on the pad at launch time. Four solid rocket boosters surround a kerosene-burning core stage, all topped by a hydogen-burning Centaur upper stage. Add to this the payload fairing which must separate (failures do happen) to let the Centaur burn and all the other separation events which must proceed on schedule (solids from core, Centaur from core, spacecraft from Centaur), and you have some sense of the complexity of the events that must unfold with perfection for a successful launch.
Things happen. Nuts corrode. Separation bolts fail to fire. Motor cases burn through. Valves leak. Fuel sloshes. Software bugs surface at the most inappropriate times. Debris clogs fuel lines. All of these are nontrivial, and have ended launches in the past. Failure is the most obvious option of all in launch vehicle operations, and is only thwarted through enormous effort to the contrary. If the Atlas had failed on her ride to Mars, it would've been much more than a few rockets and a rover going to the bottom of the Atlantic. $2.5 billion and countless hours of blood, sweat, thought, design meetings, and tears have gone into this program over nearly a decade. Atlas needed to work, and while the program had been reliable in the past, there was no guarantee she would. Such is the tension of launch day.
Second, the motion.
On TV, rocket launches take on a regal sort of spectacle. The engines light, the hold-down bolts slice, and the rocket gently tugs its way up into the air. Watching the Atlas claw her way off the pad this morning looked anything but gentle. For an hour before the launch, the rocket and the three lightning towers stood together across the bay, as immobile as the buildings and blockhouses of Kennedy Space Center that have stood for decades. Suddenly the Atlas jerked loose, poking up past the lightning towers, faster and faster, until just after clearing them it lurched drunkenly to the side. This is all as intended, of course, lining up on the proper inclination to head toward Mars, but the effect is nauseating to look at. All those hours of dedicated work slew into the raging Atlantic wind shear under the command of a flight control system barely able to keep up with the momentum piling out of the solids and the core. The effect is a baroque and terrifying dance of one computer and a few servos against the fury of nature.
Third, the fire.
For whatever reason, the light of solid rocket motors never looks right on video. It's probably just too bright, and the white-hot glowing particles of soot just peg out any CCD that tries to look at them. Your eye can do better. From three miles away, the light of four solids and a core hurt to look at through my polarized sunglasses. The intensity of the flame makes vivid the numbers of temperature and pressure and velocity that escape imagination, though they describe the rocket faithfully. White, white beyond imagination, the solids blazed, pushing Curiosity up first, then east.
Fourth, the smoke.
The central Florida coast is peppered from Daytona Beach to Patrick Air Force Base with cameras of every size and type to monitor the ascent of all rockets launched form Cape Canaveral. While they capture a mountain of good data from each launch, they all fail to capture the context that your eye sees intuitively watching the Atlas climb. Watching later on video, the rocket seems to be a self-contained unit moseying along up up and away. Watching in the moment, the smoke trail traces the Atlas's path all the way to the lightning towers across the bay. Just past the tip of the fire, the smoke billows, jutting down with surreal quickness and eventually tangling into the familiar fractal puffs of clouds. A new cloud is born, arcing up and east, first to Africa, then to Mars.
Fifth, the sound.
Until I took an aerodynamics class in college, I never appreciated just how different things can be depending on whether you're moving faster or slower than the speed of sound. Crossing Mach 1, the physics of fluid dynamics fundamentally changes. Shapes that once slowed flow now accelerate it, which among other things explains why narrowing the exit of a garden hose increases exhaust velocity (the hose flow is subsonic), and the widening exit of a rocket nozzle also increases exhaust velocity (the rocket exhaust is way, way supersonic). Rocket engines are built to do one thing: take propellant and turn it into blazing hot gas moving as fast as humanly possible back toward Florida. The exhaust wails with the sound of the physics of the fast colliding head-on with the physics of the slow. Radically supersonic water vapor and carbon dioxide rips the ocean breeze into curtains of noise, and that ripping, rumbling, vibrating sound fills your ears and your stomach from three miles away, while the Doppler shift of the accelerating rocket gradually drops the pitch until only a barely-present shaking of the bleachers remains. No electronics yet built is sophisticated enough to bottle this feeling. It's like hearing a whole formation of F-16s tearing up and away while a gentle earthquake hums at your feet.
Within five minutes it was over. The westbound breeze was strong this morning, and it tugged the rocket's contrail apart quickly. By the time the Centaur's first burn was done, the only evidence that anything had happened at all was the empty pad nestled between the lightning towers. The palm fronds bucked in the wind, and the buzzards circled through the updrafts, just as they had before launch. The alligators have lazed in the swamps for millions of years before the launch pads were built, they'll be happy to do it as long as rockets keep flying away.
Yet something is different now the Curiosity is on her way to Mars. After all those hours, all those intense arguments over funding priorities, all those heartbreaking setbacks and euphoric completions, this machine will never again rest on Earth. She was built lovingly by human hands, but is now a creature of deep space, and soon will be a creature of Mars. Hopefully, one day, she'll feel a human's touch again, but that person will be a creature of Mars as well. If you're up late enough, you can see Mars in the sky tonight, a twinkling orange pinprick in the black. But machines like Curiosity have given us a visceral since of the reality of Mars. It's not just a point of light, it's a whole place, a world. We live in a time when we send our robotic envoys to live and march and sift the sands of alien worlds. Please set the bickering and grim tone of today's news and politics aside for a moment, and just think about that. What a wonderful time this is.