Comet 73P/Schwassmann-Wachmann 3 (73P) has been observed to fragment on multiple occasions, however the cause of its fragmentation remains poorly understood. Using mostly unpublished archival Hubble Space Telescope data taken in 2006, we analyzed about 120 images and studied the properties of the fragments of 73P in order to understand its fragmentation mechanism. We studied fragments 73P-C (the nucleus), 73P-B, and 73P-G. In this work, we will present the results of the analyses of secondary fragments 73P-B, which was discovered in the 1995 apparition, and 73P-G, which was subsequently discovered in the 2006 apparition. The archival data show hundreds of tertiary fragments in 73P-B and 73P-G, on which we used careful photometry to accurately measure the luminosity distribution of fragments (as a proxy for their size). We also made measurements of the relative motions of these fragments in order to determine their speed and acceleration on the plane of the sky. This will allow us to determine whether the fragmentation process was staggered over time or impulsive. Our preliminary results show the relative speeds of the fragments of 73P-B are a few m/s, implying a break up date about 11 days prior to the observations. We also find that the breakup of 73P-B was impulsive rather than staggered over time. We will comment on break-up mechanisms consistent with the new data.