In 1971, the Apollo 15 crew, David Scott, Alfred Worden, and James Irwin, carried approximately 400 unauthorized postal covers (stamped envelopes) to the Moon with the intention of selling them to a German stamp dealer. Wikipedia The covers were postmarked before launch and after splashdown, and were to be sold for around $7,000 each. Quoracatawiki.com This commercial scheme violated NASA's ethics rules, and the crew was removed from future flight assignments. Wikipedia