The EBEX Balloon-Borne Experiment - Gondola, Attitude Control, and
  Control Software
  The E and B Experiment (EBEX) was a long-duration balloon-borne instrument
designed to measure the polarization of the cosmic microwave background (CMB)
radiation. EBEX was the first balloon-borne instrument to implement a
kilo-pixel array of transition edge sensor (TES) bolometric detectors and the
first CMB experiment to use the digital version of the frequency domain
multiplexing system for readout of the TES array. The scan strategy relied on
40 s peak-to-peak constant velocity azimuthal scans. We discuss the unique
demands on the design and operation of the payload that resulted from these new
technologies and the scan strategy. We describe the solutions implemented
including the development of a power system designed to provide a total of at
least 2.3 kW, a cooling system to dissipate 590 W consumed by the detectors'
readout system, software to manage and handle the data of the kilo-pixel array,
and specialized attitude reconstruction software. We present flight performance
data showing faultless management of the TES array, adequate powering and
cooling of the readout electronics, and constraint of attitude reconstruction
errors such that the spurious B-modes they induced were less than 10% of CMB
B-mode power spectrum with $r=0.05$.
