Made for Mars

A silicon chip that can measure wind speed and direction on Mars will be a key component of a roving weather monitoring station due to be launched by NASA next year.

The Roving Environmental Monitoring Station (REMS) will be carried by NASA’s Mars Science Laboratory (MSL) rover on its scheduled mission to the Red Planet.

The station will spend an entire Martian year (about two Earth years) measuring and providing daily reports on atmospheric pressure, humidity, ultraviolet radiation, wind speed and direction, and air and ground temperature.

The new chip, designed by scientists at Universitat Politecnica de Catalunya (UPC) in Barcelona, is part of the REMS’ anemometer, a device used for measuring wind speed. It is a silicon-based version of a technology to collect wind data used by the Mars Pathfinder in 1997.

The previous technique, called hot wire anemometry, involved heating a platinum-iridium alloy wire then letting air cool it to vary its temperature. Calculations were then performed to relate heat convection to the wind speed.

In the case of the new chip, the hot point is not a wire but a piece of silicon.

Each silicon chip is 1.5mm thick, said Luis Castañer, co-ordinator of the Micro and Nano Technologies (MNT) Research Group at UPC. The silicon substrate is heated up to 25ºC above ambient temperature by sending a current to a platinum resistor deposited on top of it. The temperature changes are measured with a second platinum resistor.

Castañer said the problem with the previous hot wire technology was that the wire’s diameter was too small — only 65 micrometres — and it was difficult to get a good measure of the convection of heat. Also, he said the hot wire system was power hungry and his group believed it could design a more energy-efficient system with silicon.

Silicon is an excellent thermal conductor, said Castañer, which means convection of heat is almost homogeneous throughout the material. It is already well known and used as a substrate in the microelectronics industry.

Each wind sensor consists of four similar silicon chips placed together in close proximity. An additional chip that measures ambient temperature as a reference is located further out.

The REMS weather monitoring station contains three of these sensors in each of its two booms, which stick out from the station’s mast. The sensors are separated by an angle of 120 degrees.

The sensors will have 3D monitoring capability, said Castañer, which means that they will be able to record the horizontal and vertical components of wind speed.

This will allow scientists to clearly determine whether air flowing near the Martian surface has the velocity of a breeze or a dust storm. They will also learn more basic information, such as which direction the wind is coming from.

The chips were manufactured at the MNT group’s Laboratorio de la Sala Blanca in collaboration with the Centro de Astrobiología, EADS Astrium Crisa and the Centro Nacional de Microelectrónica in Barcelona.

Over the three-year development period, the sensors have been tested under Mars-like conditions in a low-pressure CO2 wind tunnel at Aarhus University, Denmark.

Castañer said the device demonstrated an ability to work at 6millibar pressure in a CO2 atmosphere and it could sense winds up to 60m/s with a one-second response time.

The REMS has already been incorporated into the MSL rover, and it is now undergoing further testing at the Jet Propulsion Laboratory in California, US.

Castañer said future exploration plans for Mars are putting greater pressure on scientists to acquire a fuller understanding of the planet’s atmospheric dynamics.

Referring to NASA’s plan to return astronauts to the Moon by 2020, he said the mission would be a stepping stone for manned trips to Mars and beyond.

Yet Castañer said a great deal more information is required before man puts his footprint on the Martian surface.

‘A manned mission to Mars is likely to be happening in the next decade and to know the landing conditions on the Mars surface is mandatory,’ he said.

Siobhan Wagner