The Separator for Capture Reactions (SECAR) is a detector system that is optimized for direct measurements of thermonuclear reactions on radioactive nuclei that cause some stars to explode. SECAR will be the most sensitive device of its kind in the world. SECAR acts as an electromagnet lens to focus the products of rare (one-in-1-trillion) thermonuclear capture reactions into a detector for precision measurements. Consisting of a system of electromagnets and electrostatic plates, SECAR is over 20 meters long and will have a final sensitivity of 1 part in 10^17. ORNL plays a key role in the SECAR project. Currently under construction at the Facility for Rare Isotope Beams (FRIB) at Michigan State University, SECAR will enable measurements of many of the key reactions that influence the generation of energy and the creation of elements occurring in nova, X-ray bursts, supernovae, and other exotic astrophysical phenomena.