Alfred Worden—a NASA astronaut who took part in the Apollo 15 moon mission in 1971—has died at the age of 88, The New York Times reports. Worden’s family announced that he died in his sleep overnight in Houston, but provided no other details. During the Apollo 15 mission, Worden spent three days in his space capsule Endeavour orbiting the moon and taking photos, which remain some of the sharpest images ever taken of the moon’s surface. He also released a first-of-its kind “sub-satellite” to monitor the moon’s gravitational field, and took the first walk in deep space.

However, he and the two other astronauts aboard the Apollo 15 were accused of trying to profit off the flight by bringing aboard several hundred stamped and signed commemorative envelopes and allegedly plotting to sell them to a West German stamp dealer. When the deal became public, the men withdrew from the deal and NASA dropped them from flight status—with Worden and one other being reassigned to desk jobs while the third astronaut retired. In his 2011 memoir, Worden said he had “broken an unspoken trust” by taking part in the deal and was remorseful of his actions.