Arvid Hammar recently defended his thesis as an industrial doctoral student at the Department of Microtechnology and Nanoscience – MC2 – at Chalmers. He has worked at Omnisys Instruments AB and the Terahertz and Millimetre Wave Laboratory and has been part of a team from Gothenburg that developed and built the payload* of MATS (Mesospheric Airglow/Aerosol Tomography and Spectroscopy) – Sweden's new satellite for atmospheric research.
MATS has been developed in collaboration between researchers at Stockholm University, Chalmers and KTH Royal Institute of Technology. From its orbit at 600 kilometers altitude, MATS will be used to study so-called gravity waves* in the atmosphere by detecting formations in clouds in the mesosphere at altitudes between 70 and 110 kilometers. Just like waves in the ocean, gravity waves in the atmosphere give rise to large-scale circulation and are important to study in order to improve current climate models, and to give a better understanding of the atmosphere as a whole. To make measurements on gravity waves, MATS will detect signals from noctilucent clouds in the ultraviolet wavelength range (270-305 nm) as well as emissions from oxygen molecules at infrared wavelengths (754-772 nm). This will be done using six separate image sensors and by combining information from a large number of images, three-dimensional structures and temperature distributions in the atmosphere can be calculated.
Exploded-view drawing of MATS showing the different parts of the satellite. Illustration: Swedish National Space Agency
Because the satellite itself was required to be relatively lightweight and compact– maximum 50 kilograms and not larger than a conventional dishwasher, 60×70×85 cubic centimeters (see picture below) – a single telescope had to be used to form images onto the six image sensors. In order to meet the scientific goals, MATS must be able to detect gravity waves with sizes down to 200 meters over a field of view of 250 kilometers in the atmosphere while disturbing signals – stray light – from, for example, the sun, and light from cities is efficiently suppressed.
"Combining these requirements in a single instrument is a big challenge that was driving the development of MATS telescope, which was the main focus of my thesis," says Arvid Hammar.
The telescope itself is a so-called off-axis telescope and is the first of its kind to utilize a new design method where linear astigmatism is eliminated to drastically enlarge the field of view while maintaining a high optical resolution. The fact that the field of view can be made larger is the key to a mission like MATS and cannot be done with classical telescope designs. The design utilizes three mirrors made of solid aluminum, which were fabricated using a special lathing process (diamond turning) that provides optical quality for the geometrically complex surfaces without any need for subsequent polishing.
The development of the payload has been made in a short time and with small resources, which has been a challenge for Arvid Hammar and his colleagues at Omnisys Instruments.
"It was therefore of great value to cooperate with Professor Soojong Pak and his group from Kyung Hee University in South Korea who have years of experience with this new telescope technology that is now used for the first time in a real application," says Arvid Hammar and continues:
"We are a small team that has worked with the development of the optical instrument, but at the same time this has enabled us to work in an efficient manner where the expertise has for the most part been found in-house."
In addition to design, the development of MATS has also implied extensive testing to ensure a functioning instrument in the challenging environment that space entails. The imaging quality of the telescope has been tested in a newly built lab that Arvid Hammar has set up and been responsible for as part of his work. In addition to optical resolution, stray light suppression has also been measured in the same facility.
"By utilizing a new extremely black material based on carbon nanotubes, the throughput of stray light has been minimized," says Arvid Hammar.
For about two years, MATS will be used to study the upper part of the atmosphere. The data produced will be used by researchers worldwide. The launch is scheduled for 2020 when several satellites are sent up simultaneously using the same rocket, including a larger Canadian satellite. The last time Sweden put a research satellite in space was in 2001 when Odin was launched. During its 18 years in orbit, Odin has traveled nearly 100,000 times around the earth, although it was also expected to last for two years. A copy of the research satellite Odin can be seen close by Café Canyon at MC2. To the left is the research satellite MATS in mounted condition at OHB Sweden in Kista, with visible contributions from Omnisys and Chalmers.
Arvid Hammar defended his research findings related to the MATS telescope in his thesis "Optics for Observation Instruments" on 12 April. The thesis also describes instruments operating at longer wavelengths for two other space-related projects. Professor Jan Stake, head of the Terahertz and Millimetre Wave Laboratory, has been Arvid's main supervisor together with Anders Emrich, technical manager at Omnisys.
"It is exciting to see how a solid thesis work can be an important part of a new Swedish research satellite, whose instrument will contribute to a better understanding of our atmosphere and global climate challenges. Arvid's work is also a brilliant example of successful applied research in close collaboration with companies," says Jan Stake.
Several other Chalmers researchers are involved in various aspects of the MATS project, primarily Ole Martin Christensen and Donal Murtagh at the research division Microwave and Optical Remote Sensing at the Department of Space, Earth and Environment.
Text: Michael Nystås
Photo: Swedish National Space Agency
Photo of Mats: Arvid Hammar
*The instruments you send up to space with a rocket or satellite is commonly called payload.
*The gravitational waves described in the article are not the same as the gravity waves predicted by Einstein's theory of relativity.
Scientific initiator of MATS is the Department of Meteorology (MISU) at Stockholm University. In addition to the Department of Microtechnology and Nanoscience – MC2, researchers at the Department of Space, Earth and Environment at Chalmers, and the Division of Space and Plasma Physics (SPP) at the KTH Royal Institute of Technology have contributed to the project. The satellite has been developed by OHB Sweden AB in collaboration with ÅAC Microtec, while the instrument was mainly developed by Omnisys Instruments AB. The initiative is being financed by the Swedish National Space Agency.
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Omnisys Instruments AB develops and manufactures measuring instruments for advanced research projects in satellite-based research and radio astronomy. The instruments are built from the ground up and include technology from many different areas such as microwave technology, electronics, mechanics, optics and software.