E and B Experiment (EBEX)

Ebex members: Amber Miller, Will Grainger, Britt Reichborn-Kjennerud, Vedant Misra, Ethan Dyer

The E and B EXperiment (EBEX) is a NASA funded, balloon-borne CMB polarization experiment. It will observe with bolometric detectors in four frequency bands from 150 to 450 GHz. EBEX will measure CMB polarization over a range of scales with enough sensitivity to measure or place an upper limit on the polarization signal generated by inflationary gravitational waves and from lensing due to large scale structure. The test flight is expected to be launched in the fall of 2007 and the science flight is expected to fly over Antarctica in December of 2008. Our lab will build and implement the attitude control system (ACS).

For background information on EBEX and the CMB click on the links below:

ACS Development at the Miller Lab

Electronics Block Diagram

Columbia's role in EBEX is to develop and implement the attitude control system (ACS). The ACS consists of two parts: the pointing, which outputs an orientation of the telescope as a function of time, and a feedback loop, which controls the motors so that the desired area of the sky is covered at the appropriate time as designated by the scan strategy. The pointing entails building hardware and electronics to measure the orientation of the gondola, and developing software to collect the pointing data, run the pointing sensors, and perform both real-time and reconstruction pointing solutions which combine data from a number of the pointing sensors.

A variety of sensors is necessary to achieve both real-time and reconstruction pointing solutions for two reasons: first, a redundancy is desirable whenever possible since we are unable to fix anything on the payload once it is launched, and second, no single sensor is absolute, highly accurate, and may be read on the timescale of the detector time constant. The figure above shows a block diagram of the pointing electronics. Our reconstruction pointing requirement is 48'', 1/10 th our smallest beam, however our real time requirement is much less stringent since we are not looking for point sources but rather merely require a reasonable number of hits per pixel so that the sky coverage is well distributed. For our real-time pointing solution we will use two redundant star cameras at the turnaround points in our scan that provide precise and absolute pointing, and we will interpolate with two redundant sets of three fiberoptic gyroscopes which provide rate data, using the star camera data for the integration constant and the inherent gyroscope offset. In our reconstruction pointing solution we may also use data from the other sensors if an unexpected failure occurs with both star cameras or gyroscope sets.

The photos below show the test setup we have built for the ACS components. It allows for simultaneous operation of the gyroscopes, encoder, GPS, clinometers and magnetometer, where the encoder is used to reference and characterize the signals from the other sensors.

The photos below show the EBEX gondola being delivered from SSL to Nevis and the EBEX gondola suspended.

Go to the official EBEX page here.

For a list of EBEX collaborators, click here.

EBEX Internal Site here.