The MOST advanced microsatellite that has ever been launched into space was substantially designed and built at the Space Flight Laboratory (SFL) at the University of Toronto Institute for Aerospace Studies. Onboard is a satellite so sensitive it can detect variations in reflected light from planets outside our solar system.
“We designed, built, integrated and tested four of the six subsystems for the satellite, including the structure, thermal, computer and communication subsystems,” explains Professor Robert Zee, manager at the SFL and leader of the MOST (Microvariability and Oscillation of Stars microsatellite) project. His team also worked on satellite integration and system level testing, and even assembled a complete spacecraft in their lab.
The attitude-control system, used for positioning the satellite, is so precise that the onboard telescope points with an accuracy of between 10 and 20 arcseconds (an arcsecond is 1/3600 of a degree, or 1800 times smaller than the moon’s diameter), and is sensitive enough to detect one part per million changes in brightness.
The engineering marvels of this mission allow for scientific research of equal excitement. “The primary objective was to perform long duration stellar photometry [measurements of the properties of light] in space, staring at a star for a long period of time and collecting information on how the [apparent] brightness of that star varies over time,” explains Zee.
The oscillations in apparent brightness can give valuable information on the properties of the star. “The reason the star would oscillate is because of sound waves travelling through the interior and causing the gaseous body of the star to vibrate, not unlike a musical instrument,” says professor Jamie Matthews of the department of Physics and Astronomy at the University of British Columbia and Mission Scientist for MOST.
“The paths of the sound waves are refracted by the varying conditions of the gas in the interior. This is how the surface vibrations allow us to probe the internal structure [composition of the star], akin to using earthquake waves to probe the Earth’s core.”Additionally, since the internal composition of the star changes during its lifetime, data on the age of the star can also be estimated.
“This is the first time that this type of science is being done from space…atmosphere, weather, day and night cycles of the earth, when you go to space all of that disappears and you can use a fairly small aperture [the mirror or lens that collects the light] telescope to do this science, so it’s actually cheaper to go to space than to do the science on earth,” comments Zee.
The capability of such high precision measurements has led to another discovery explains professor Zee. “Within the last year the astronomy team has determined that they can get bonus science out of this mission…determining whether there’s an orbiting exoplanet around a given star.” An exoplanet is a planet outside the Earth’s solar system.
But there’s more than that. “Depending on which phase of the orbit the planet is in, it will reflect different amounts of light from the star,” says professor Zee. This variation in the brightness measurement can be correlated with properties of the planet. “The amount of light a planet reflects from its parent star back to an observer depends on its size and the detailed composition and other properties,” Professor Matthews says. These other properties also include details of the atmosphere of the planet.
MOST will mostly be used to learn details about known exoplanet systems impossible to determine by any method that has up until now been used. These include the stars 51 Pegasi and tau Bootis, where the Doppler evidence confirms the existence of exoplanets. The Doppler shift, whereby a star moving towards or away form an observer has it’s light spectrum shifted, can be used to measures the wobble of a star due to the presence of a companion planet.
There is one last exciting mystery that may have some light shed on it by the MOST mission. “We are looking at metal-poor subdwarfs [slowly decaying first generation stars] because they are believed to be amongst the oldest stars in the Galaxy…by measuring the ages of these stars, we hope to set a firm lower limit on the age of the Universe,” professor Matthews says.
The satellite was launched June 30, 2003 from Plesetsk, Russia and is currently still in the commissioning stage, during which performance calibration takes place prior to starting true scientific observations.
Back at the SFL more missions are underway. While a microsatellite is defined by having a mass under 100 kg, the SFL engineers are not stopping there. Along with MOST they sent CANX-1, one of the first ever nanosatellites. “A nanosatellite is under 10kg, CANX-1 was a 1 kg satellite, you could actually hold it in your hand,” said Professor Zee with pride.
The CANX (Canadian Advanced Nanospace Experiment) program involves teams of graduate students building their own satellites for the purpose of experimenting with enabling technologies that could be used in space, such as computer, imaging and attitude-control systems. The CANX-2 project has already begun with a new group of ambitious students.
