n Entering Space, Allen describes the shuttle thrusters: "The forward primary thrusters sound like exploding cannons at thrust onset; and during their firing, jets of flame shoot out from the orbiter's nose. ...The orbiter reacts to the primaries' shove by shaking slightly and moving very noticeably. For the crew on board, a series of attitude changes using primaries resembles a World War I sea battle, with cannons and mortars firing, flashes of flame shooting in all directions, and the ship's shuddering and shaking in reaction to the salvos."

The lunar ascent module engine had a 15000 N (3500 lb) thrust. The attitude control thrusters for the Apollo C/SM and LM (which had four sets of quadruple thrusters) had 490 N (110 lb) of thrust each. In comparison, the 38 thrusters for shuttle orbit control each have a nominal thrust of 3870 N (880 lb), with a range from 3114 N to 5338 N. Why is the exhaust visible from the 3870 N shuttle thruster but not from the 15000 N lunar ascent module engine?

I have been unable to find any images or video footage of any visible flame or exhaust coming from any of the four quadruple clusters used for attitude control of the lunar module, or from the main engines of the ascent and descent modules.