MOST

     Microvariability  &  Oscillations of  Stars Microvariabilité et  Oscillations STellaire

Mi

Mi

Canada’s first

space telescope

Peering into the hidden hearts of stars

Finding and exploring exoplanets

Reading stellar life stories

               AT A GLANCE

Scientific Goals  (in astro-jargon)

•  Asteroseismology of acoustic and gravity-mode oscillations in Sun-like stars, magnetic (rapidly oscillating Ap or roAp) stars, cool giants, pre-main-sequence delta Scuti pulsating stars,  massive O and B stars, and other stellar classes, to probe uniquely their internal structures and evolutionary states
•  Analyses of the transits and eclipses of exoplanets around Sun-like stars and red dwarf stars,  to reveal their sizes, atmospheric compositions, magnetic fields and other properties
•  Measurement of the turbulent variations in massive evolved (Wolf-Rayet) stars to understand how they add gas to the interstellar medium
•  Measurements of structure & variability of gas and dust disks around pre-main-sequence stars

Scientific Goals  (in plainer English)

Can we understand our Sun in the context of other stars? By putting a birth date on the oldest stars in the solar neighbourhood, can we set a limit on the age of the Universe? How do strong magnetic fields affect the physics of other stars and our own Sun? What are mysterious planets around other stars really like? How did the atoms which make up our planet and our very bodies escape from stars in the first place?

What MOST does?

It performs ultra-high-precision photometry (measurements of the brightness variations to a level as small as 1 part per million) of stars down to the naked-eye limit of visibility (visual apparent magnitude 6) for up to two months without major interruptions. (To put the sensitivity of MOST in perspective, look at a street lamp 1 km away and then move your eye 0.5 mm closer to it. The street lamp is now about 1 part per million brighter to your eye.)  MOST is also capable to performing extremely precise photometry of stars as faint as magnitude 16.

The instrument

An optical telescope with a collecting mirror only 15 cm across, feeding a CCD camera with a Marconi 47-20 frame-transfer device for collecting science measurements and for tracking guide stars for satellite attitude control. The Instrument contains a single broadband filter which selects light in the wavelength range 350 - 700 nanometres (nm).

The camera is equipped with an array of Fabry microlenses which project a large stable image of the telescope pupil illuminated by target starlight, which is key to the highest photometric precision of MOST. For low cost and high reliability, the instrument has no moving parts. The structure automatically maintains the same focus across a wide range of temperatures, and exposure times are controlled by rapid frame transfer of the CCDs. The CCDs are cooled by a passive radiator system.

The spacecraft

The Instrument is housed in a suitcase-sized microsatellite (65 x 65 x 30 cm; mass = 54 kg) powered by solar panels and oriented by a system of miniature reaction wheels and magneto-torquers. The attitude control system keeps the telescope pointing to better than 1 arcsecond (less than 1/4000th of a degree) of the desired target position 99% of the time. This is an improvement of three orders of magnitude over previous microsatellite pointing capability.

Launch and orbit

MOST was carried aloft aboard a Russian three-stage Rockot (a former Soviet ICBM now being put to peaceful service) on 30 June 2003, from a launch site in northern Russia (Plesetsk Cosmodrome). MOST was injected into a low-Earth polar orbit (820 km altitude; period ~ 101 minutes) in a Sun-synchronous mode remaining over the terminator (dividing line between day and night) of the Earth. From that vantage point, it has a Continuous Viewing Zone (CVZ) spanning declinations from about −19 to +36 degrees, in which a selected target star will remain observable for up to 60 days without interruption.

Communications

Three S-band stations with 2.5-metre dishes are located in Toronto, Vancouver, and Vienna to allow the MOST team to send commands and receive data from the microsatellite. We are in direct contact with MOST for up to 40 minutes per day per ground station, during which commands are uploaded at 9,600 kB/s and data downlinked at 38,400 kB/s.