This week on SPEXcast we continue 'Mars May' with Jet Propulsion Laboratory (JPL) engineer Joel Steinkraus to discuss two CubeSats hitching a ride with the InSight mission, which launched from Vandenberg Air Force Base on May 5th. Mars Cube One (MarCO) is comprised of a pair of 6U CubeSats which will each relay signals from the InSight lander back to Earth during while it enters the Martian atmosphere. We ask Joel about the technology behind MarCO and the challenges of designing two interplanetary CubeSats. You can check out additional links and references at https://blog.spexcast.com/marco-joel-steinkraus .