Satellite Structural Design - Finite Element Analysis for Satellite Structures - page 74

Fig. 3.31 Basis unit case

Strut

Basis plate

Bracket of
star sensor

3.5.3 Basis Unit Case

The basis unit case consists of a basis plate and four wall frames connected
together and reinforced with the help of two struts. It contains also the star sensor
bracket. The plate, frame, bracket, and struts are made of aluminum alloy AMg6.
General view of the basis unit case is shown in Fig. 3.31 .
Basis plate is a 25 mm height milled plate made of aluminum alloy AMg6. It
has L-shaped and rectangular cross-section stiffeners. Selection of the modules
cross-sections is made to provide design rigidity for the plate to satisfy the
requirement of high-accuracy relative position of the MBEI and ADCS sensors.
Stiffeners are oriented as shown in Fig. 3.32 . These stiffeners are milled as
follows:

• L-shaped cross-section stiffeners—along lines between holes for eight studs of
the satellite case fastening and four holes intended for fastening of the plate with
the basis frame;
• Rectangular cross-section stiffeners—along the perimeter of plate, and between
installation seats of the satellite components.

Thickness of the skin is 1.5 mm. Outer and internal stiffeners of the basis plate
have 2 mm thickness and 13.5-23.5 mm height. The basis plate provides
mounting seats for MBEI, bracket of star sensor, bracket of magnetorquers,
Z-direction reaction wheel, Z-direction gyro, bracket of skewed gyro, interface
unit of skewed gyro, and magnetometer. It contains a circular hole working as a
window for the MBEI. Mass of the basis plate is 2.66 kg.
Basis frame (230 mm height) consists of four milled walls connected together
by rivets as shown in Fig. 3.33 . The basis frame has a square cross-section with
outer and inner dimensions equal to 565 and 503 mm, respectively. The basis
frame walls are made of aluminum alloy AMg6. Stiffeners of the basis walls have
rectangular cross-section, and are oriented along the perimeter of each wall and
between installation seats of the satellite components. Stiffeners height of the basis
frame is 10-16.5 mm. And thickness of the skin is 1.5 mm.