Robots have replicated much of the human sensory experience on Mars. Cameras have given us sight; robotic hands, arms, and feet have supplied touch; and chemical and mineral sensors have let us taste and smell on Mars. Hearing is the last of the five senses yet to be exercised on the Red Planet.
When Perseverance arrives at Mars, it will have two microphones, making it possible for the rover to not only touch and taste, but finally hear the sounds of Mars.
Body and Brains
Perseverance is car-sized — about 10 feet long (not including the arm), 9 feet wide, and 7 feet tall. But at 2,260 pounds, it weighs less than a small car.
The rover’s body — the warm electronics box (WEB) — is a strong, outer layer that protects the rover’s computer and electronics (which are basically the equivalent of the rover’s brain and heart, respectively). The rover body keeps its vital organs protected and temperature controlled.
The WEB is closed on the top by the Rover Equipment Deck (the rover’s “back”), which turns Perseverance into a convertible, allowing a place for the rover mast and cameras to sit out in the Martian air, taking pictures with a clear view of the terrain as the rover travels. Its main job is to carry and protect the computer, electronic, and instrument systems.
The bottom and sides of the body are the frame of the chassis — the top is the Rover Equipment Deck and the bottom is the belly pan. To accommodate a new Sampling and Caching interior workspace, the belly pan is dropped soon after the rover lands. This exposes the workspace to the Martian atmosphere and makes more room for sample handling operations within that workspace.
Unlike people and most animals, the rover’s brain — its computer — is in its boxy body. There are actually two identical computers, or Rover Compute Elements (RCEs), in the body so there is always a spare brain that can be awakened to take over control and continue the mission.
The RCE interfaces with the engineering functions of Perseverance over two networks that follow an aerospace industry standard designed especially for the high-reliability requirements of airplanes and spacecraft. In addition, the RCEs have a special purpose: to direct interfaces with all of the rover instruments for exchange of commands and science data.
Just like the human brain, the rover computers register signs of health, like temperature and power levels, along with other features that keep the rover “alive.” This main control loop constantly checks systems to ensure that the rover is both able to communicate throughout the surface mission and that it remains thermally stable (not too hot or too cold) at all times. It does so by periodically checking temperatures, particularly in the rover body, and adjusting temperature control accordingly. It then records power generation and power storage data throughout the Mars sol (a Martian day) to decide what new activities can be started or completed. Finally, it schedules and prepares for communication sessions with Earth or with local Mars orbiters. Activities such as taking pictures, driving, and operating the instruments are performed under commands transmitted in a command sequence to Perseverance from the flight team back on Earth.
Perseverance generates constant engineering, housekeeping, and analysis telemetry and periodic event reports that are stored for eventual transmission once the flight team requests the information from the rover.
The rover’s driving software gives Perseverance greater independence than Curiosity had. This allows Perseverance to cover more ground without consulting controllers on Earth so frequently. Also, engineers have added a “simple planner” to the flight software. This allows more effective and autonomous use of electrical power and other rover resources. It allows the rover to shift the time of some activities to take advantage of openings in the daily operations schedule.
The rover’s “nerves” for balance and position are supplied by an Inertial Measurement Unit (IMU) that provides 3-axis information on its position, which enables the rover to make precise vertical, horizontal, and side-to-side (yaw) movements. The device is used in rover navigation to support safe traverses and to estimate the degree of tilt the rover is experiencing on the surface of Mars.
Rover Has 10 Million “Passengers”
NASA’s “Send Your Name to Mars” campaign invited people around the world to submit their names to ride aboard Perseverance. Some 10,932,295 people did just that. The names were stenciled by electron beam onto three fingernail-sized silicon chips that were attached to an aluminum plate on Perseverance. The three chips share space on the plate with a laser-etched graphic depicting Earth and Mars joined by the star that gives light to both. Affixed to the center of the rover’s aft crossbeam, the plate will be visible to cameras on Perseverance’s mast.
Arms and Legs
Engineers also redesigned Perseverance’s wheels — its “legs” — to be more robust due to the wear and tear the Curiosity rover wheels endured while driving over sharp, pointy rocks. Perseverance’s wheels are narrower than Curiosity’s but bigger in diameter and made of thicker aluminum.
Perseverance has six wheels, each with its own individual motor; the two front and two rear wheels also have individual steering motors. This steering capability allows the vehicle to turn in place a full 360 degrees. The four-wheel steering also allows the rover to swerve and curve, making arcing turns.
Perseverance uses a similar “rocker-bogie” suspension system that was used on previous Mars rovers. The suspension system is how the wheels are connected to the rest of the rover and control how the rover interacts with the planet’s surface. When driving over the uneven Martian terrain, the suspension system maintains a relatively constant weight on each of the rover’s wheels. The suspension also minimizes rover tilt as it drives, keeping it more stable; Perseverance is designed to withstand a tilt of 45 degrees in any direction without tipping over.
By Earth vehicle standards, Perseverance is slow. By Martian vehicle standards, however, Perseverance is a standout performer. The rover has a top speed on flat, hard ground of 4.2 centimeters per second, or 152 meters per hour. This is a little less than 0.1 miles per hour. For comparison, a 3-mile-per-hour walking pace is 134 centimeters per second, or 4,828 meters per hour. In the case of exploring Mars, however, speed isn’t the most relevant quality. The rover’s energy-efficient pace consumes less than 200 watts, compared with a 200-horsepower car engine that consumes nearly 150,000 watts.
The 7-foot-long robotic “arm” on Perseverance can move a lot like a human arm: it has a shoulder, elbow, and wrist “joints” for maximum flexibility. The arm lets the rover work as a human geologist would, by holding and using science tools with its “hand” or turret. The rover’s own hand tools extract cores from rocks, take microscopic images, and analyze the elemental composition and mineral makeup of Martian rocks and soil.
A new addition to Perseverance’s arm is a rotary percussive drill designed to extract rock core samples from the surface of Mars. A suite of interchangeable bits includes coring bits, regolith bit, and an abrader. The rover’s drill will penetrate into the Martian surface to collect samples. The coring and regolith bits are used to collect samples directly into a clean sample collection tube, while the abrader bit is used to scrape off the top layers of rocks to expose fresh, unweathered surfaces for study.
In the future, another space mission could potentially pick up about 30 of the sample tubes and bring them to Earth for detailed analysis. At a time and place of the team’s choosing, the samples will be deposited on the surface of Mars at a “sample cache depot” that will be well documented by landmarks and coordinates from orbital measurements. The cache of Mars samples remains at the depot, available for pickup and potential return to Earth.
Perseverance has several cameras focused on engineering and science tasks. Some serve as the rover’s “eyes” on the surface, enabling it to drive around.
The cameras for driving help human operators on Earth drive the rover more precisely and better target the movements of the arm, drill, and other tools that get close to their targets. A much wider field of view gives the cameras a much better view of the rover itself. This is important for checking on the health of various rover parts and measuring changes in the amount of dust and sand that may accumulate on rover surfaces. The new cameras can also take pictures while the rover is moving.
Perseverance carries six new Hazard Detection Cameras (HazCams) — four on the front and two on the rear of the rover body. HazCams detect hazards to the front and back pathways of the rover such as large rocks, trenches, or sand dunes. The front HazCams can see where to move the robotic arm to take measurements, photos, and collect rock and soil samples. When driving, the rover stops frequently to take new stereo images of the path ahead to evaluate potential hazards.
Two sets of color stereo Navigation Cameras (NavCams) help engineers navigate Perseverance safely, particularly when it operates autonomously, making its own navigation decisions without consulting controllers on Earth.
Located up high on the rover’s mast, these two sets of black-and-white stereo cameras can see an object as small as a golf ball from 82 feet (25 meters) away. Before Perseverance “drives blind,” the NavCams initially help ensure a safe path. Blind-drive mode occurs when engineers command the rover to drive a certain distance in a certain direction, and the rover’s computer calculates distance from wheel rotations without looking or checking for wheel slippage.
The new CacheCam is a single camera that looks down at the top of the sample cache. It takes pictures of sampled materials and the sample tubes as they are being prepared for sealing and caching. This helps scientists watch over the samples as they are being obtained and keeps a record of the entire process for each sample collected.
Voice and Ears
To communicate, Perseverance has three antennas that serve as both its “voice” and its “ears” and are located on the rover’s back. Having multiple antennas provides operational flexibility and backup options just in case they are needed. Most often, Perseverance will use its ultra-high frequency (UHF) antenna (about 400 megahertz) to communicate with Earth through NASA orbiters around Mars. Because the rover and orbiter antennas are within close range of each other, they act a little like walkie-talkies compared to the long-range telecommunications with Earth provided by the low-gain and high-gain antennas.
It generally takes about 5 to 20 minutes for a radio signal to travel the distance between Mars and Earth, depending on planet positions. Using orbiters to relay messages is beneficial because they are much closer to Perseverance than the Deep Space Network (DSN) antennas on Earth. The rover can achieve data rates of up to 2 megabits per second on the relatively short-distance relay link to the orbiters overhead. The orbiters then use their much larger antennas and transmitters to relay that data on the long-distance link back to Earth.
The high-gain antenna is steerable so it can point its radio beam in a specific direction. The benefit of having a steerable antenna is that the entire rover doesn’t need to change position to talk to Earth, which is always moving in the Martian sky. Like turning your neck to talk to someone next to you instead of turning your entire body, Perseverance can save energy and keep things simple by moving only the antenna.