The Power of the "Humble" Space Telescope

MOST is 16 times smaller, by dimensions, than its cousin, the Hubble Space Telescope, earning it the nickname of "Humble" Space Telescope. So exactly how powerful is it? For that, we need to briefly go over some information from MOST technical papers, abridged for your convenience of course!

Anatomy, Trajectory and Optical Properties

A side-viewing Rumak-Maksutov telescope with a 150mm aperture feeds two CCDs, one for tracking and one for science. Both CCDs are capable of a maximum resolution of 1024 x 1024, with an intrinsic pixel size of 13 microns (10^-6 metres). Thus, one pixel covers about 3 arcseconds of sky, and the whole CCD covers about a degree. There is a 300nm wideband filter centered at 525nm, and the short wavelength cutoff is at 380 nm. The long wavelength cutoff starts at 600 nm and decreases to 50% at 700 nm. Microlenses in the telescope project Fabry images of brighter target stars onto the science CCD, while fainter stars are focused elsewhere on the CCD.

This microsatellite setup results in a telescope with a relatively fast f/6 focal ratio and a focal length of 897 mm.

Proposal Tip: MOST follows a low-Earth, Sun-synchronous, polar orbit. This means that the declination range for viewable stars is -19 degrees to +36 degrees. These stars can be viewed continuously for up to 60 days (the Continuous Viewing Zone or CVZ). Remember this when you decide on a target star for your proposal.

What are MOST's Viewing Limitations? - IMPORTANT!

There are two major limitations on what is observable by MOST.

The first is whether or not the desired target is contained within MOST's Continuous Viewing Zone (CVZ). If an object is within this region, MOST can observe it for a complete orbit without the object passing behind the limb (edge) of the earth. The maximum time an object can be within the CVZ is 58 days.

The second limit is referred to as the Sun Sensor limitation. The angle between the opposing face to the entrance to the telescope and the Sun must always be within around 30 degrees for two reasons. The first is that the majority of the solar panels on MOST are on this face of the telescope. Ensuring that it is always pointing near the Sun provides power. The second reason is that the Sun is used for coarse pointing information.

Fabry Microlenses and Fabry Images

The Fabry imaging technique is the backbone of MOST's success. Fabry microlenses are etched into the glass window, which is also the window for the CCD. They produce pupil images on the science CCD.

Proposal Tip: Suitable primary MOST targets for Fabry imaging lie in the V = 0.4 - 6.0 (apparent visual magnitude) range. The total time base for a set of observations is the dwell time in the CVZ, with the maximum possible being ~60 days. However, we will decide the duration of observations based on your target star's characteristics.

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