Structural Subsystem

The spacecraft bus establishes the basic geometry of the spacecraft. It provides a place to attach components internally and externally, and to house delicate modules requiring the protection of an environment with a measure of thermal and mechanical stability. Contained within are the power electronics, spacecraft and instrument computers, transponder, gyros, reaction wheels, and torque rods. Attached to it are sun and magnetic field sensors, solar array panels and two antennas (located at the end of two array panels). The TRACE bus attaches to the telescope via two titanium adapter rings. Titanium was selected for its strength and ability to thermally isolate the telescope. The telescope must be kept at a constant temperature so that the optics will not distort and change the appearance of the images. The spacecraft bus also provides for radiator plates which act as cold sinks, pulling the heat from within the spacecraft into space. TRACE has one radiator panel to which the battery is attached and another beneath the spacecraft to which the CCD camera is attached.

Careful thought was given to the layout of subsystems within the bus, attempting to keep the distribution of mass equal about each of the three principal axes. Also, components which may electrically interfere with one another are spaced as far apart as possible, with shielding providing the remainder of protection. A good example is the location of the magnetometer relative to the torque rods. Since the torque-rods emitt electrical/magnetic fields, the magnetometer, which senses the Earth's magnetic field, is placed outside and on top of the bus. The remainder of interference is calculated and removed via software.

The structure also provides attachment points that allowed movement of the spacecraft during construction, testing, transportation, and launch. There are many lifting operations and numerous test fixtures.