The Mainframe, also called the main structural component,
is the backbone of the instrument. All of the instrument’s
internal components are attached to the mainframe in some
way, supporting a total of 185 kg of weight while maintaining
its structural integrity at all orientations. While it is
in space, the instrument will not always face the Earth, therefore
structural integrity is especially important. MODIS and Aqua/Terra
are periodically required to change their orientation to view
the Sun, the Moon, or deep space, or to perform various maneuvers
that will change the location of gravitational pressure on
The Mainframe (Fig. 1, 2) is composed of a combination of
sheets and hot-pressed blocks of beryllium. There are a total
of 50 parts making up the whole of the Mainframe, all of which
are bolted and bonded together to provide precise mounting
surfaces for the various internal components, such as:
The Scan Mirror
The Passive Radiative Cooler
Four calibration assemblies
Three anti-contamination doors
Three kinematic mounts which anchor the Mainframe to
The three primary load-carrying bulkheads are the Optical Bench
Bulkhead, the Calibration Bulkhead, and the Zenith Bulkhead.
The Optical Bench Bulkhead has machined features for
bolting the Main Electronics Module in a cold space view
direction and pseudo-kinematic mounts for the alignment
of the Optical Bench.
The Calibration Bulkhead precisely aligns and supports
the Scan Mirror Assembly, Blackbody, Spectroradiometric
Calibrator Assembly, and Solar Diffuser Stability Monitor.
The Zenith Bulkhead ties these primary bulkheads together
and provides a three-point mount for the Solar Diffuser.
The Mainframe fits within a dimensional cube that measures
1.2 m X 1.0 m X 1.0 m and weighs 43 kg.