test the vehicle at higher wind loads and altitudes, flying to an altitude of one kilometer while testing the flight controls at the higher ascent and descent velocities before returning to a precise landing point. The ascent and initial portion of the descent was nominal, prior to the stuck throttle valve which resulted in the termination of the flight prior to the planned precision landing. Xaero-B Xaero-B was a follow up to Xaero with the ability to reach altitude with engine on throughout. Xaero-B was between 15 and 16 feet tall where Xaero was 12 feet tall. Xaero-B performed hot-fire testing and test flights. It would have been used for the bulk of research flights up to initial altitudes between to . The vehicle has now been retired due to damage on a test flight in April 2017. It flew 75 times. Xodiac The Xodiac was a VTVL rocket introduced in 2016. It featured pressure-fed LOX/IPA propellant, and a regeneratively cooled engine. Flights could simulate landing on the Moon or Mars. Video of Xodiac performing in-flight air flow tests Tuft strings. Xogdor Xogdor was a VTVL vehicle that Masten planned to introduce in 2023. As the sixth VTVL testbed developed at Masten, Xogdor would have improved upon the work done with Xodiac and tested descent and landing technologies at speeds up to . Xeus Xeus (pronounced Zeus) was a vertical-landing, vertical-takeoff lunar lander demonstrator. Xeus consisted of a Centaur upper stage (from United Launch Alliance) with RL-10 main engine to which four Katana vertical thrusters have been added. Production Xeus was estimated to be able to land on the Moon with up to 14 tonnes (revised to 10 tonnes) payload when using the expendable version or 5 tonnes payload when using the reusable version. The damaged Centaur on the demonstrator Xeus limited it to Earth flights. The production versions would have to have been manufacturing fault free and certified for space operations. Human rating might also have been needed. United Launch Alliance, supplier of the Centaur, referred to Xeus as an abbreviation for eXperimental Enhanced Upper Stage. Further details of the proposed design were given in the paper "Experimental Enhanced Upper Stage (XEUS): An affordable large lander system". Each of the Katanas used on a Xeus lander were likely to produce when performing a horizontal touchdown. In December 2012, Masten demonstrated their all-aluminum regeneratively-cooled engine, the KA6A. The talk in