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Report published in issue 249 of the magazine Informacions (February 2012)

A foot on Mars with Curiosity

After nearly seven years’ work, the Curiosity rover of NASA’s Mars Science Laboratory (MSL) mission is on its way to the planet aboard an Atlas rocket launched on 26 November from the Kennedy Space Centre in Cape Canaveral, Florida. Curiosity, the best equipped vehicle NASA has ever sent to the Red Planet, is carrying technology developed at the Barcelona School of Telecommunications Engineering.

If everything goes according to plan, Curiosity will reach its destination in August after having travelled millions of kilometres. The aim of the MSL mission, a scientific laboratory on Mars, is to study the surface of the Red Planet using instruments on Curiosity, which include the Rover Environmental Monitoring Station (REMS), the Spanish contribution to the mission. The REMS will measure air and ground temperature, atmospheric pressure, ultraviolet radiation, humidity, and wind speed and direction.

In addition to contributing to a better understanding of the Martian climate, the data recorded will help scientists achieve the mission’s main objective: to determine if conditions on Mars are favourable for supporting microbial life.

The station includes a wind sensor equipped with a silicon chip designed and manufactured in the clean room lab of the Micro and Nanotechnologies Research Group, which is attached to the Universitat Politècnica de Catalunya. BarcelonaTech (UPC)’s Department of Electronic Engineering. Etched into the surface of the chip on a micrometric scale are the names of the five researchers who developed the component: Lluis Castañer, Vicente Jiménez, Manuel Domínguez, Lukasz Kowalski and Jordi Ricart.

The Martian atmosphere is composed mainly of carbon dioxide (95.32%), the average temperature is −63 °C, and atmospheric pressure varies between 600 and 1,000 Pa. These are harsh conditions for any instrument to withstand. “Such a low atmospheric pressure (on Earth it’s over 100,000 Pa) makes it very difficult to study the properties of the air, because it limits interaction between molecules in the environment and any device,” says Castañer, a researcher with the Micro and Nanotechnologies Research Group and head of the scientific team that designed the chip.

The landing site selected for the mission by NASA is the Gale crater, which is about one hundred kilometres in diameter and has a 5-km-high central mound. “It’s a crater about the size of the Grand Canyon in Colorado. The exploration zone is very uneven, so wind flows are particularly strong,” says Castañer.

The age of Mars exploration began in 1960 with the Russian Korabl 4 mission, which was followed by the Mariner 9 in 1971, the Mars Global Surveyor and Mars Pathfinder in 1997, and the Phoenix Mars Lander in 2008, among others. In total, some 40 missions have been sent to the Red Planet. Some of these missions have included vehicles equipped with instruments for measuring wind speed. Most of the data we have about the surface of Mars was collected by instruments carried aboard NASA’s Viking landers, which travelled to the planet in 1976.

The system developed by researchers at the Barcelona School of Telecommunications Engineering to measure the Martian wind is based on a technique known as hot-wire anemometry. In the traditional method, applied successfully on previous occasions, an electric current is used to heat a wire made of platinum (commonly used in electronics because its resistance is temperature-sensitive), and the temperature change the wire undergoes when it is cooled by the wind is measured. The wind speed can then be determined based on the difference in temperature. “Instead of using a platinum wire or film, we’ve used semiconductor volumes that are heated with the help of resistors deposited on the surface of the chip,” says researcher Vicente Jiménez.

A more energy-efficient device
The key distinguishing feature of the system developed by the UPC team, though, is not the method used to measure wind speed, but rather the use of different volumes at a constant temperature. “This isn’t the usual approach. What we’ve done is fix the temperature with an increment (10° or more) above the air temperature. Then, by calculating the power needed to maintain the temperature, we’re able to deduce the wind speed,” says Vicente Jiménez. This approach makes the sensor more energy-efficient than existing devices.

A basic requirement for any instrument on a space mission is functionality. Instruments must be shown to work under the environmental conditions that will apply—in the case of Mars, at a low temperature and low pressure—and pass tests that prove their ability to withstand vibration, impacts and heat stress. These conditions were reproduced in a low pressure chamber, the MarsLab-UPC, at the facilities of the UPC Research and Innovation Park, in the K2M building of the North Campus in Barcelona.

The chip was tested under the supervision of the Jet Propulsion Laboratory in California. But passing the tests was no easy matter. “In the first demonstration with the prototype, we put the chip in a Martian atmosphere, turned on the motors to generate wind, and obtained the first graphic measurements, which showed that the design worked, but up until that point no one had much faith in our models and calculations,” recalls scientist Lukasz Kowalski.

The UPC first became involved in the project in 2004, when the Centre for Astrobiology (CAB), based in Madrid, approached the Micro and Nanotechnologies Research Group because of its experience in measuring flows of wind and water. “But that didn’t guarantee our participation in the mission. First, you have to pass a lot of tests and examinations. And if you don’t, there are other competitors that move ahead of you,” says researcher Manuel Domínguez.

The consortium that developed the REMS is funded by the Ministry of Science and Innovation through the Spanish Centre for the Development of Industrial Technology. The other participants in the consortium are the CAB, the Spanish company CRISA, the space division of the European Aeronautic Defence and Space Company, and Complutense University of Madrid.

Instruments developed for a space mission also need to respect strict limits on weight and power consumption. “This is a critical point. In order for the sensor to be sensitive to the wind speeds expected, power must be supplied to heat the chips that are in contact with the environment,” says Domínguez. “To avoid exceeding the power limit established for this device, we had to use very strict control strategies,” he concludes. In fact, the wind sensor draws just 100 milliwatts (mW), not even enough power to light up a bulb.

High-value technology
When space instruments and components need to withstand extreme conditions, in addition to being sophisticated they have to be robust; in most cases repairs are not feasible. As well as gaining visibility, the partners involved in a high-profile NASA project like the Mars Science Laboratory have an opportunity to demonstrate that they can meet all the requirements the agency establishes for its equipment.

The UPC engineers can confidently claim that the technology developed is highly valuable, because it has already been approved for a space mission. Their participation is a seal of quality that puts them in a strong position in the competitive world of space missions.

Moreover, knowledge generated is generally carried forward from one mission to another; technology that has worked well becomes a candidate for future missions. This is precisely what has happened in the case of the Micro and Nanotechnologies Research Group, which has signed a three-year contract for another project to develop a wind sensor for use on Mars. The project will be a joint mission involving Spain, Russia, Finland and China. The aim is to launch a network of 16 meteorological stations that will send data to an orbiting spacecraft. Once in place, the network will provide global data on the Red Planet.

A simplified Earth

Mars is within a region of our solar system known as the habitable zone. Microbial life can only develop if liquid water exists on a planet’s surface. If a planet is too close to its host star, any water evaporates; if it is too far away, the water freezes. The fourth planet in our solar system is of enormous interest to astrobiologists, who study the origin and evolution of life. If the MSL mission can tell us once and for all whether there is liquid water on Mars, it will be a success. But this is not the only reason scientists are interested in the Red Planet.

Mars is the most similar planet to the Earth in terms of its geological characteristics. The rocky planet is composed mainly of minerals containing oxygen, silicon and iron. Its diameter is approximately half that of the Earth (6,794 km); it has a quarter of our planet’s surface area, and a tenth of its mass. The Martian solar day is similar in length to our own—24 hours and 41 minutes—but a Mars solar year is twice as long (686 days) because the planet is farther from the Sun. Understanding how the climate of Mars works could answer questions about the climate model of the Earth.

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