Curiosity’s Secrets: The Hidden Features of NASA’s Mars Rover
Aug 29, 2012 09:30 am | admin
NASA’s newest Mars rover, Curiosity, is an awesome scientific machine. By now, you probably know all about its rock-blasting laser and its 17 amazing cameras.
But here and there, Curiosity is hiding a few secrets. Scattered around its body are little mostly unknown bits and pieces. You might have noticed them in images and said, like we did, “Huh, I wonder what that is.”
Well, here we take a very close-up and detailed look at the rover to answer some of those questions. Some of these features helped Curiosity pull off a flawless landing on the Martian soil. Other bits are there to assist in the day-to-day science collecting that will allow the rover to figure out the history of water on Mars and whether the planet was ever capable of sustaining life.
Curiosity’s engineers seem to love pyrotechnics even more than Burning Man enthusiasts do. During the spacecraft’s harrowing entry, descent, and landing sequence, it fired off 76 blasts to separate the pieces of the plummeting probe. Some of the pyrotechnics (which are essentially very controlled fireworks) had the energy of a box of matches while others contained the explosive force of a dynamite stick.
Just before Curiosity entered the Martian atmosphere it fired 10 pyrotechnics within five milliseconds – Pow! Pow! Pow! — some of which released miniature guillotines to cut connecting cables while the rest actually separated the entry capsule and the cruise stage. Other blasts released the spacecraft’s tungsten ballast weights (which were later spotted by the Mars Reconnaissance Orbiter satellite). The biggest boom was responsible for unfurling the rover’s supersonic parachute, the largest ever used on an interplanetary mission.
Even on the ground, the rover still had a few more bangs to go. Engineers needing to remove the cameras’ dust-blocking lens caps turned to — what else? — small pyrotechnic devices.
Descent Stage Unibody
Quick quiz: How is the Curiosity’s descent stage like a MacBook Pro? Answer: They both rely on a unibody.
The descent stage consisted of three large panels that had to connect to dozens of components, including fuel tanks, cabling brackets, telecommunication lines, avionics boxes, and the spacecraft’s backshell. Rather than bolting together a bunch of different pieces, which were more liable to break apart, engineers machined each of these panels from one solid piece of aluminum.
Because the pieces were so intricate and unique, they each took 11 months to complete, said engineer Benjamin Thoma from JPL, who led the rover’s assembly, test, and launch operations. The extra-long time was worth it, making the descent stage both more mass efficient and more structurally sound, and helping pull off Curiosity’s stressful dive to the Martian surface with near-perfect precision.
Heavy Hydrazine Lines
As Curiosity neared the ground, its descent-stage rocket engines were sucking up tremendous amounts of hydrazine fuel. To help them drink their fill, engineers needed to install very thick fuel lines.
These lines were so large and stiff that they actually started to provide structural support for the descent stage components, said engineer Benjamin Thoma. This caused a problem, he added, since jolting or pushing on some part of the descent stage might cause the load to travel through the tubes instead of the intended support elements.
Had the tubes bent or broken during Curiosity’s plunge, the entire mission would have been lost. To make up for this, the rover’s engineers placed giant crazy-straw-style loops in the hydrazine lines that prevented them from bearing too much of a load.
Image: The Curiosity rover inside its descent stage. NASA/JPL-Caltech
Curiosity’s six 20-inch wheels are a marvelous sight, dwarfing previous generations of Mars rovers. Each is controlled by its own motor and can be spun while the other wheels stay in place in order to dig shallow trenches in the Martian soil.
The black wheels might look like normal car wheels but they aren’t made out of rubber, which would have cracked in the extreme cold of outer space and possibly degraded from Martian dust. Instead, they are cast from anodized aluminum, which is a soft enough metal to give the rover some cushioning. Inside the aluminum are titanium spokes, curved to make them act like big springs and provide shock absorption.
When Curiosity begins driving around Mars sometime this week, it will be the first time that its wheels have even been used. The rover was tested on separate wheels back on Earth and the current wheels were the last piece of hardware placed on Curiosity. Engineers took this precaution because the wheels will be in constant contact with the Martian soil and therefore have the highest capacity to pass Earthly bacteria to the Red Planet.
The wheels on Curiosity have one of the geekiest surprises hidden in plain sight. Three lines of holes on each wheel spell out the letters J-P-L in Morse code so that when the rover travels over the Martian soil, it will leave behind the imprint of its makers.
This will actually be used for some important science – the tracks will help researchers count the number of steps the rover has taken. The odometry feature was first used on the previous rovers, Spirit and Opportunity, which had a small hole in their wheels through which ran a bolt that attached them to their platforms. When scientists looked back at the peculiar tracks that the rovers left, they realized the hole’s usefulness.
Curiosity didn’t need to be bolted to a platform through its wheels, so its holes are there for cosmetic and scientific reasons.
Many people have noticed the tiny QR-code-looking plaques sitting on Curiosity’s backside. These are actually augmented-reality tags that will be able to pass special information about the rover’s mission to a smartphone.
These tags are not expected to start their intended part of Curiosity’s project until the rover gets up and running. NASA has released very little information about them so far, simply stating that the tags will “allow the public to have an immersive experience of discovery as it happens” on their website.
Image: One of the rover’s two AR tags can be seen in the lower part of this image. NASA/JPL-Caltech
Curiosity’s actuators are meant to let engineers know how much its different parts have moved. But NASA folks generally like to be double sure about its measurements and so the rover is studded with many small, circular black-and-white fiduciary markers.
The rover’s cameras image the small icons — which look like circles sliced into quarters — before and after a move. This way, engineers can compare how much Curiosity’s arm has shifted to the left or how far its wrist has twisted clockwise. In this way, they can build a 3-D dataset of all the rover’s moving pieces.
Though plentiful, these fiduciaries are actually more of a backup system, said engineer Benjamin Thoma. Curiosity’s actuators should inform scientists about all the rover’s parts but the fiduciary markers offer a second opinion.
Image: Many small circular fiduciary markers can be seen around the rover in this test image taken back on Earth. NASA/JPL-Caltech/Malin Space Science Systems
Name to Mars
On the back of the rover, close to its UHF antenna, is a small repository of names. As NASA was building Curiosity, it collected nearly 1.24 million names from an online submission form and another 20,000 from visitors to JPL and Kennedy Space Center. These names were etched onto silicon chips with an electron-beam microscope and then stowed on the rover
As NASA puts it, the purpose of this is to “carry the hopes and aspirations of Earth’s peoples to Mars.”
Image: The silicon chips upon which millions of names are etched. NASA/JPL
Sticking up from the rover near the back right side is a tiny black knob – Curiosity’s sundial. A leftover bit from the previous rover missions, Spirit and Opportunity, which also carried sundials, this decoration has the word for Mars written in 16 languages on it.
In addition to keeping time, as you would expect of a sundial, the instrument is also used to calibrate Curiosity’s high-resolution 3-D color MastCams. Since Mars’ dusty atmosphere makes everything appear redder than it would on Earth, the cameras need to know what colors represent reality. Red, blue, yellow, and green bands on the sundial help the cameras attune to their surroundings.
The sundial also carries an inscription that will serve as a monument once the rover has finally bit the dust. “To Mars, To Explore,” it reads. “For millennia, Mars has stimulated our imaginations. First, we saw Mars as a wandering star, a bringer of war from the abode of the gods. In recent centuries, the planet’s changing appearance in telescopes caused us to think that Mars had a climate like the Earth’s. Our first space age views revealed only a cratered, Moon-like world, but later missions showed that Mars once had abundant liquid water. Through it all, we have wondered: Has there been life on Mars? To those taking the next steps to find out, we wish a safe journey and the joy of discovery.”
Image: A time-lapse covering approximately eight minutes as the sun’s shadow moves over the rover’s sundial. NASA/JPL-Caltech/Malin Space Science Systems/Wired Science