Originally Posted by blackshire

Even Surveyor 1, launched on Memorial Day, 1966, was given only a 1-in-10 chance of succeeding (NASA would have been satisfied if its radar had simply detected the Moon and triggered the spacecraft's descent sequence). This small hope diminished even more when one of its two low-gain antenna booms failed to extend after launch, as some engineers feared that its off-center mass might prevent the lander's control system from keeping the spacecraft stable during powered descent. JPL was very pleasantly surprised