Ever since the launch of the first Mars rover, the Sojourner, in the mid-1990s, scientists all over the world have been working on more sophisticated rovers and drones, with much more advanced equipment and exploration modules to be sent to Mars. Amidst all of the 14 such successful attempts made to grasp at the possibilities on Big Red lies another rover, one slightly different and a little bit better than the rest, the rover Curiosity.
On 26th November 2011, NASA’s flagship ATLAS V-541 rocket launched carrying with it Curiosity to the Gale Crater on the Red Planet. It landed on Mars on 6th August 2012, thereby adding another feather to NASA’s rather fluffy cap. The rover is roughly the size of a car and weighs over 2000 pounds, making it the biggest rover ever sent in space. It was sent to study the geology of the Red Planet to find if life could ever have existed on Mars and also lay the groundwork for a future human mission there.
Curiosity was launched with the intent of serving as a backup for the now-dead rover, Opportunity which, lost power due to dust settling on its solar panels. However, Curiosity’s mission has proven to be quite the underdog-becomes-hero story, and its stay on Mars has been extended indefinitely. Now that we are all primed with curiosity (excuse the pun) let’s take a look at the science and engineering that makes the rover tick.
Powering the beast
Curiosity is around five times heavier, two times bigger, and the on-board scientific equipment weighs over 15 times more than any previous rover. One of the rover’s primary functions is to survey the landscape and study rock and soil composition with the help of a jackhammer drill on a massive 6-foot long robotic arm. The samples collected are then analyzed with some fascinating instruments such as the Alpha Particle X-Ray Spectrometer, Chemistry and Camera Complex, and the Mast Camera. So, where does the power come from to keep this rover up and running?
Curiosity is powered by a plutonium-based thermoelectric generator. This is a significant advantage for the rover over previous models because it avoids failure of the mission due to dust settling on the solar panels, and the long half-life of plutonium (a whopping 24,000 years!) means that it can be powered almost indefinitely.
Fig 2: Thermocouple
Fig. 1: MMRTG
Curiosity has a Multi-Mission Radioisotope Thermoelectric Generator (MMTRG), which contains a specially manufactured and fabricated form of Plutonium Dioxide whose natural decay gives off an immense amount of heat. This heat gets converted into useful forms of energy with the help of the thermocouples. The rover currently has about 4.8 kilos of Plutonium Dioxide, which provides 2000 Watts of thermal power and 120 Watts of electrical energy every second!
Fig 3: Gale Crater Fig 4: Deep Space Network
Curiosity receives its mission instructions from NASA’s command center in Houston. The ‘phone call’ home is nothing short of an engineering marvel!
Controllers on Earth have three ways of hailing Curiosity as it trundles around the Gale Crater. Two are direct links through NASA’s Deep Space Network, a worldwide collection of antennas. The Deep Space Network – or DSN – is NASA’s international array of giant radio antennas that supports interplanetary spacecraft missions, plus a few that orbit Earth. The DSN also provides radar and radio astronomy observations that improve our understanding of the solar system and the larger universe. The DSN is operated by NASA’s Jet Propulsion Laboratory (JPL), which also operates many of the agency’s interplanetary robotic space missions. This network provides both a fixed low-gain antenna(best for basic commands and emergencies) and a pointable high-gain antenna for complex commands. The DSN consists of three facilities spaced equidistant from each other – approximately 120 degrees apart in longitude – around the world. These sites are at Goldstone, near Barstow, California; near Madrid, Spain; and near Canberra, Australia. The strategic placement of these sites permits constant communication with spacecraft as our planet rotates – before a distant spacecraft sinks below the horizon at one DSN site, another site can pick up the signal and carry on communicating.
Curiosity also has a higher-speed ultra-high frequency (UHF) communications system that can send signals to spacecraft orbiting Mars, which in turn would relay them to Earth. To send back imagery, Curiosity must stay in touch with the Mars Reconnaissance Orbiter and Mars Odyssey spacecraft, two probes orbiting Mars that each can talk to the rover twice a day. “The high-gain antenna only gives us a moderate amount of bandwidth,” Ashwin Vasavada, an Indian scientist involved in the make of Curiosity, told SPACE.com. “We can transmit a series of commands every morning. But it’s not enough to transmit hundreds of images every day.”
Dissecting Curiosity’s Brain
Curiosity has two identical on-board computers, called Rover Compute Elements (RCE), which contain radiation hardened memory to protect it from the extreme radiation in space and to safeguard against failure due to power-off cycles. The rover has four single-core processors. One of them is a SPARC processor that runs the rover’s thrusters and descent-stage motors, which were active during the descent to the Martian surface. The next kind of processing element is called a PowerPC processor, which is the central processor and handles nearly all of the rover’s ground functions. Quite sensibly, this element has a backup. The final processor is another SPARC processor that controls the rover’s ground movement and is a part of the motor controller box. For navigation purposes, the rover has two guidance systems on board. These guidance systems include an Inertial Measurement Unit (IMU) that provides 3-axis information on its position, which helps in rover navigation. One of the guidance systems updates the rover about its position on the Red Planet, which is needed to find Earth in the sky and stay in contact with NASA. The other system calculates how close Curiosity is to rocks and other obstacles. Quoting Ashwin Vasavada, “For that system, we don’t care exactly where we are in the universe. We care about it if we can shoot at this rock with our laser or not.” Precautions against the failures of the previous rovers (Spirit, in particular) were also taken into account. Curiosity has sensors to sense if it’s slipping, and it will stop movement immediately if it drops beyond a certain threshold.
The rover’s computers are also continually self-monitoring to keep the rover operational, like regulating the rover’s temperature to keep sensitive scientific equipment working. Activities such as taking pictures, driving, and operating the instruments are performed in a command sequence that is sent from the flight team on Earth to the rover. Finally, a rather clever bit of engineering optimized the memory usage by the rover. The rover initially only had its flight and landing software installed before launch. Once it landed, it overwrote the operational software on top of the flight software. This helped reduce the cost and weight involved with including additional memory and compute elements. But, this also means that poor Curiosity is stranded on Mars forever.
Being the most modern and the most ahead of its time rover, Curiosity is still unparalleled in its capabilities. It still holds up humanity’s hope to find a suitable habitat other than our precious Earth. Its mission is always on, and somewhere all alone on that deserted planet lies the rover that might unlock many new pathways for our future.