Motors

The UMBC Observatory relies on many moving parts. Broadly, these drive the following: the observatory dome azimuthal motion as well as the upper and lower door shutter motion, the four primary mirror doors, the right ascension motor, the declination motor, the telescope focus, the guide-probe, the main and secondary filter wheels, the translating stage, and the translating stage mirror.

 

Dome

The azimuthal motion of the dome moves the dome window into alignment with the telescope so we can see out into the sky. The azimuthal position of the dome needs to be synchronized with the azimuthal position of the telescope. In this way, the telescope and the dome window can move in unison to allow for long uninterrupted observations of celestial objects. Ensuring that the motor that drives this azimuthal motion responds reliably to the reporting of the azimuthal position of the telescope by control computer is paramount. Without this, all dome movement must be done “by-eye” and changed by manually engaging the dome azimuthal motor when the dome window and the telescope fall out of azimuthal alignment.

 

The upper and lower shutter doors of the dome cover the dome window when the telescope is not in use. These shutter doors nestle into each other so that the wonderful Maryland weather doesn’t make its way into the dome. Therefore, these two shutter motors need to activate at different times so that they can open and close properly. The control computer needs to be able to issue commands to these shutter motors so that they be reliably opened and closed. Without this, the dome shutters must be manually opened and closed for each observing session.

 

Telescope

There are four nested mirror doors that protect the primary mirror from dust and other debris that may settle on it when it is not in use. These four mirror doors must respond reliably to open and close commands issued by the control computer so that they can allow light to fall onto the telescope and allow us to capture images of the universe!

 

The telescope is mounted equatorially. This means that — for us in the Northern Hemisphere — the telescope mount is parallel to the celestial equator. The mount is therefore inclined at an angle dependent on our exact latitude. It was¬†built specifically for the location of the UMBC Physics Building. The mount also encloses two motors that determine where the telescope is aimed in the sky. One governs the motion parallel to this equatorial plane (motion along the right ascension celestial coordinate) and the other governs the motion perpendicular to this plane (motion along the declination celestial coordinate).

 

Pursuant to the Cassegrain Reflector design, the telescope collects light with its primary mirror and focuses it — with the help of the secondary mirror — down to the instrument box below the primary mirror. The exact place where this light is perfectly focused is modulated by a motor that moves the secondary mirror very slightly with respect to the primary mirror. It is important we understand this motion and how it is affected by environmental factors, different instruments, and aging of the telescope.

 

Instrument Box (a.k.a. the GAM)

The instrument box houses the guide-probe which is used for auto-guiding. This guide-probe collects unfocused light that is on its way to the detector and uses it to update the telescope position very slightly so that objects don’t “trail” through the images we take. This guide-probe needs to be carefully locked-on to a guide-star. There are two motors that govern the movement of this guide probe in the X-Y plane of the guide image. For this reason, the instrument box is sometimes called the Guide Acquire Module (or GAM) by the cool kids.

 

Inside the instrument box there are also two filter wheels. The on-axis filter wheel is “on-axis” (duh). This means that the light that goes directly through the telescope will interact with filters installed into this filter wheel. The on-axis filter wheel can hold six filters. We switch between them by issuing commands from the control computer to rotate the filter wheel to a certain filter position. Another motor is used to rotate the south filter wheel which holds eight smaller filters.

 

The instrument box also houses a translating stage that “translates” (meaning it moves along a well-defined line). This translating stage is usually “stowed”. This means that the translating stage lets the light move directly through the instrument box and down through the on-axis filter wheel and finally through the bottom port of our instrument box. If the translating stage is moved into its “on-axis” position, it blocks the light from this port on the bottom of the instrument box. The light instead falls onto a slanted mirror that redirects the light through any of the four additional ports in the sides of the instrument box. These ports are aligned with the cardinal directions, North, South, East, and West. This mirror can be rotated to direct the light it receives out through any of these ports. When it directs this light through the South Port, the light can interact with the filters in the south filter wheel. The linear movement of the translating stage and the rotation of this mirror are driven by two separate motors.

 

Modernization Project

All of these motors need to be tested and some need repairs. Further, their communication with the control computer needs to be understood so that we can ensure we have reliable control of the system of moving parts that allows us to explore the sky.