In the "previous episode" focused on Perseverance (we recommend you recover it by reading our first look at the Perseverance rover) we talked extensively about the mission MARS 2020, of the objectives that NASA scientists hope to bring to fulfillment and above all we talked about the technology that is hidden behind a nice six-wheeled robot.
Today we will complete the speech, we will understand what is hidden behind his "hearing" and behind the communication system installed on board, concluding with a look at how the rover will collect samples and move everything only on Mars.
Microphones
Hearing is the last of the five senses to arrive on the Red Planet. The robots that have "inhabited" Mars in recent years, have been able to make use of almost all the sensory experience of a human being: the cameras for sight, grippers and robotic arms have replaced the touch and thermal and chemical sensors they replaced taste and smell.
When the Perseverance rover arrives on Mars can use two microphones. This addition will finally allow you to hear the sounds of Mars. It is not the first time that NASA spacecraft travel to Mars carrying two microphones. For example in the mission of the Mars Polar Lander, which unfortunately failed, and in that of the Phoenix Lander, which had a microphone on the descent camera of the spacecraft, which never came on.
Hear on Mars
The engineers have equipped Perseverance to make him a good listener. It has microphones Entry Descent and Landing (EDL) which will record the landing sounds. The chambers on board the rover are equipped with a series of microphones that will help study the rocks and soil of Mars. And the engineers may, in particular conditions, be able to hear the sounds of the rover itself.
The Mars 2020 Entry Descent and Landing (EDL) system is similar to the Mars Science Laboratory (Curiosity), but it is equipped with a more powerful microphone, with which to record sounds in the descent phases. This microphone records audio as Perseverance drops to the surface and could record sounds like friction of the atmosphere and the dust moved during the landing.
The sounds of a laser
When Perseverance fires a laser on a rock, a small amount of it vaporizes into a hot gas (the plasma we talked about earlier), and the heat and vibrations create a shock wave that emits a "crackling" sound. The microphone hears the "burst" while the laser strikes the rock several meters away from the rover and it is precisely the intensity of the sound that gives information such as the hardness of the rocks and therefore on the geological context in which they were formed. For example, the hardness of the rock can help determine if it formed in a lake or was eroded by the wind.
The main microphone can listen for about 4 minutes at a time. This gives the rover the opportunity to hear the sounds of Mars, such as the high-pitched noise of the grains of sand hitting the vehicle, the wind whistling around Perseverance or sudden gusts of wind, in addition to the coring operations of the rocks and the wheels that they creak against the surface. In some cases, sound can help the team diagnose the state of wear of the rover's internal mechanisms or tools.
Battery operated
The rover simply needs electricity to function. Perseverance is equipped with a radioisotope feeding system and placed in the back of the frame. This power supply system produces a constant and stable flow of electricity by using the "fuel" heat from radioactive decay of plutonium. In short, an energy conversion takes place within the power supply system, the final product of which is electrical energy.
The power source is called "Multi-mission thermoelectric generator with radioisotopes "or MMRTG for short. And it is the MMRTG that converts the heat from the natural radioactive decay of plutonium into electricity. This power system takes care of charging the two main batteries of the rover (two rechargeable lithium-ion batteries ) and the heat from the MMRTG is additionally used for keep the instrumentation and the entire rover at the appropriate operating temperatures.
In the image below, you can admire the multi-mission radioisotope thermoelectric generator, in a phase prior to installation on the main body of the rover.
Perseverance's power supply system is essentially very similar to that used on the Mars Science Laboratory's Curiosity rover. NASA has been using similar power systems for decades, following the "horse that wins does not change". An example? The Apollo missions on the Moon, the missions like Pioneer, Voyager, Ulysses, Galileo, Cassini and New Horizon, all have the same power system in common. Where the heat formation process occurs, there are several layers of protective material resistant to high temperatures.
Among these there is even a type of material used in the "tip" of some rockets designed by NASA, which had to withstand the high temperatures that were generated when returning to the Earth's atmosphere. Furthermore, the radioisotopic fuel is present in "ceramic" form, and this with a very specific purpose: a ceramic-type material resists breakage and is difficult to reduce to small pieces, in this way it is possible to reduce the possibility that the material (which is obviously toxic) may leak during tests, during the launch phase or during the mission to Mars.
In the unlikely (but still possible) event of an accident at the launch site, the maximum estimated dose that a nearby operator could receive is 210 millirems. A US resident receives an average of 310 million radiation annually from natural sources, such as those generated by radon and cosmic rays from space.
In conclusion, this feeding system introduces some advantages. The MMRTG has an estimated operational life of 15 years, therefore it extensively covers the estimated duration of the Perseverance rover mission (which will last approximately 3 Earth years). It will offer the rover a lot of freedom of movement, being small in size. And the Perseverance instrumentation has benefited: there is now more space for the on-board computer, for the test tubes and the "laboratory" where the various tips for the robotic arm drill are kept.
Perseverance wheels and legs
The Perseverance rover has six wheels, each equipped with its own individual engine. The two front wheels and the two rear wheels are slightly different because they are equipped with individual steering motors. This steering capability allows the vehicle to perform a full turn on the spot and the four-wheel steering system allows the rover to bend very precisely.
The "legs" are made of titanium tubes formed with the same process used to create high quality mountain bike frames. These extensions allow the rover to overcome high obstacles 78 centimeters. The wheels are made of aluminum, with curved elements in titanium, to obtain an elastic behavior. They measure 52.5cm in diameter.
A little slow
By land vehicle standards, the Perseverance rover is very slow. For those Martians however, Perseverance is one of the fastest ever. The rover has a maximum speed on flat ground of 4.2 centimeters per second, or 152 meters per hour.
But to explore Mars, speed is not a fundamental factor, nor the most relevant one. For this type of mission, the energy expenditure of each action taken by the lander is assessed, and the slow pace of advancement is energy efficient and consumes less than 200 watts for each movement.
First step: collection of samples
The rover's main job is to collect rock and soil samples. These will be sealed in test tubes and left in a well-identified place, or more than one place, on the surface of Mars. Detailed maps will be provided for future missions that will land on Mars to collect these samples.
The rover's belly houses all the equipment and test tubes needed to collect the samples. It contains a rotating carousel, which is a wheel with different types of points. Beside this there are 43 test tubes waiting to be filled.
While the rover's large arm stretches and pierces the ground, the rover's belly houses a small robotic arm that acts as a "laboratory assistant". The small arm collects and moves the rocky elements to be sampled by transferring them to the containers. Once filled, these containers end up in a special space where they are sealed and stored.
Don't get dirty, thanks
Perseverance must comply with the strict cleanliness regulations required Office of Planetary Protection of NASA. These measures are in place to avoid contaminating Martian specimens with terrestrial contaminants that could inadvertently be brought to Mars.
Basically, strict rules have been drawn up which limit the amount of inorganic, organic and biological materials to be used during the construction of the rover.
In the future, if the Perseverance champions were to be recovered and brought to Earth to be analyzed, it will be the task of the test tubes to clearly show all the samples contaminated by terrestrial agents: the test tubes contain particular "witness" agents, that is substances capable of detecting molecular and particulate contaminants. This will help scientists establish which elements inside the tubes are of terrestrial origin and which are not.
Second step: memorization
After collecting a sample, the test tube is transferred back to the rover's belly. Here it is delivered to the small internal robotic arm and moved to the inspection and sealing section (like a small internal factory, in short). Once the test tube is hermetically sealed, nothing can enter or exit. The tubes are stored in the rover's belly until the team decides the time and the place to drop the samples on the surface.
The samples are finally deposited on the surface of Mars in a point designated by the team as "sample cache depot". The location or locations of the repository must be well documented from local landmarks and precise coordinates obtained through orbital measurements. They will remain in that position until a new robot lands on Mars to pick them up and bring them here, to Earth.
Three antennas
Perseverance has three antennas that act as both "voice" and "ears". They are located on the back of the rover and each has a specific task. Many times, Perseverance will use its approximately 400 megahertz Ultra-High Frequency Antenna (UHF) to communicate with Earth through NASA orbiters that will orbit around Mars.
Since the antennas of the rover and the orbiter are close to each other, they act a bit like walky-talkiescompared to long range telecommunications with Earth provided by low and high gain antennas.
Typically, it takes 5 to 20 minutes for a radio signal to travel the distance between Mars and Earth, depending on the positions of the planet. Using orbiters to forward messages is beneficial because they are much closer to the rover than the Deep Space Network (DSN) antennas on Earth. The rover can reach high data transmission speeds: up to 2 megabits per second a short distance to the orbiters.
The high gain antenna is adjustable so that it can point its radio beam in a specific direction. The advantage of having a swiveling antenna is that the entire rover does not need to change its position to communicate with Earth, that is constantly moving in the Martian sky. Like turning your neck to talk to someone next to you rather than turning your whole body, the rover can thus save energy by avoiding moving in its entirety.
The rover will use its low gain antenna mainly to receive signals. This can send and receive information in any direction; that is, it is said to be "omnidirectional". The antenna transmits slow data to the Deep Space Network on Earth.
Since there is no need to orient them to communicate, they represent a sort of "emergency channel" to always be in contact with the rover. And with all this shrewdness in building it, we are sure that NASA have no intention of losing it the first Martian sandstorm.
