Hsieh, K. C., Zurbuchen, T. H., Orr, J., Gloeckler, G., & Hilchenbach, M. (2004). A collimator design for monitoring heliospheric energetic neutral atoms at 1 AU. Advances in Space Research, 34, 213-218. doi:10.1016/j.asr.2003.02.056.