With the Hycon camera down, Roosa would have to step in and use a Hasselblad with a 500 mm lens, to take detailed photos of the Apollo 16 potential landing site. If Roosa did nothing else, he had to return to earth with pictures of Descartes that would be good enough to plan a lunar landing.
The first extended use of the Service Propulsion System engine on the Command and Service module was for the Lunar Orbit Insertion (LOI) burn.
Mitchell kept his plan a secret from NASA, knowing that the agency would be completely unreceptive to the idea. He said nothing about it to his crewmates. The test subjects had also agreed to keep quiet.
“The approaching dusk and the damp mistiness left by the now-departed rainstorm only enhanced the spectacular sight and the sound of the launch. Tentacles of flame erupted on either side of the bottom of the Saturn V, which seemed to sit in its own cauldron of fire momentarily before breaking free of its shackles, as four hold-down arms at the base of the launch pad and five access arms along the outside of the booster swung away.” (Smoke Jumper, Moon Pilot by Willie Moseley)