The structure was completely covered with a Martin-developed ablative heat shield 0.75 to 2.75 in (19 to 70 mm) thick, and the nose cap was constructed of carbon phenolic material.

During an inspection fly-by of the descending parachute system it was seen that reefing cutters had failed to actuate.

Subsequently, the vehicle separated from its flotation "balloon" in the rough seas and, with the parachute, sank before a nearby ship could arrive to retrieve it from the ocean.

[1][2] The final PRIME mission was flown on 19 April 1967, and simulated re-entry from low Earth orbit with a 617 nmi (710 mi; 1,143 km) cross-range.

An inspection by a USAF-Martin team reported the craft "ready to fly again", although no later missions were carried out.