Yury Vinokurov

STARS: a software application for the EBEX autonomous daytime star cameras

The E and B Experiment (EBEX) is a balloon-borne telescope designed to probe polarization signals in the CMB resulting from primordial gravitational waves, gravitational lensing, and Galactic dust emission. EBEX completed an 11 day flight over Antarctica in January 2013 and data analysis is underway. EBEX employs two star cameras to achieve its real-time and post-flight pointing requirements. We wrote a software application called STARS to operate, command, and collect data from each of the star cameras, and to interface them with the main flight computer. We paid special attention to make the software robust against potential in-flight failures. We report on the implementation, testing, and successful in flight performance of STARS.

First implementation of TES bolometer arrays with SQUID-based multiplexed readout on a balloon-borne platform

EBEX (the E and B EXperiment) is a balloon-borne telescope designed to measure the polarisation of the cosmic microwave background radiation. During a two week long duration science flight over Antarctica, EBEX will operate 768, 384 and 280 spider-web transition edge sensor (TES) bolometers at 150, 250 and 410 GHz, respectively. The 10-hour EBEX engineering flight in June 2009 over New Mexico and Arizona provided the first usage of both a large array of TES bolometers and a Superconducting QUantum Interference Device (SQUID) based multiplexed readout in a space-like environment. This successful demonstration increases the technology readiness level of these bolometers and the associated readout system for future space missions. A total of 82, 49 and 82 TES detectors were operated during the engineering flight at 150, 250 and 410 GHz. The sensors were read out with a new SQUID-based digital frequency domain multiplexed readout system that was designed to meet the low power consumption and robust autonomous operation requirements presented by a balloon experiment. Here we describe the system and the remote, automated tuning of the bolometers and SQUIDs. We compare results from tuning at float to ground, and discuss bolometer performance during flight.

Software systems for operation, control, and monitoring of the EBEX instrument

We present the hardware and software systems implementing autonomous operation, distributed real-time monitoring, and control for the EBEX instrument. EBEX is a NASA-funded balloon-borne microwave polarimeter designed for a 14 day Antarctic flight that circumnavigates the pole. To meet its science goals the EBEX instrument autonomously executes several tasks in parallel: it collects attitude data and maintains pointing control in order to adhere to an observing schedule; tunes and operates up to 1920 TES bolometers and 120 SQUID amplifiers controlled by as many as 30 embedded computers; coordinates and dispatches jobs across an onboard computer network to manage this detector readout system; logs over 3 GiB/hour of science and housekeeping data to an onboard disk storage array; responds to a variety of commands and exogenous events; and downlinks multiple heterogeneous data streams representing a selected subset of the total logged data. Most of the systems implementing these functions have been tested during a recent engineering flight of the payload, and have proven to meet the target requirements. The EBEX ground segment couples uplink and downlink hardware to a client-server software stack, enabling real-time monitoring and command responsibility to be distributed across the public internet or other standard computer networks. Using the emerging dirfile standard as a uniform intermediate data format, a variety of front end programs provide access to different components and views of the downlinked data products. This distributed architecture was demonstrated operating across multiple widely dispersed sites prior to and during the EBEX engineering flight.

Star camera system and new software for autonomous and robust operation in long duration flights

The E and B Experiment (EBEX) is a balloon-borne telescope designed to probe polarization signals in the cosmic microwave background. It completed an 11 day flight over Antarctica in December 2012 / January 2013. EBEX requires 10 arcsecond accuracy on attitude determination for post-flight data analysis, and 30 arcminute accuracy for real-time attitude control during flight. The primary pointing sensors employed to achieve these pointing requirements are two redundant star cameras and two redundant sets of orthogonal gyroscopes. This paper is focused on the star cameras. The EBEX star cameras must be robust against multiple classes of challenges that may arise in the long duration balloon-borne environment. These challenges include daytime sky brightness, bright polar mesospheric clouds, uncataloged satellites, thermal effects on the camera focus, and the potential for abnormal inputs from other on-board subsystems. Real-time monitoring and manual intervention by the user is limited by the low communication bandwidth on long duration flights. Each star camera consists of a pressurized vessel containing a digital camera, an embedded computer, a hard disk, and various supporting electronics, along with an optical baffle to limit reflections and reduce atmospheric noise. We developed a dependable, thread-safe, C++ software application that can tackle potential issues with the images and defend against failures in other subsystems. It employs a wide selection of features with robust and efficient algorithms to best prepare for the long duration environment, and was developed with a focus on reliability. The features range from relatively novel to well-established, and many of them ultimately proved critical in the recent EBEX flight. We will report on the design, implementation, testing, and successful in-flight performance under challenging conditions of the EBEX star cameras and their associated custom-written software.