As a joke following Apollo 13's successful splashdown, Grumman Aerospace Corporation pilot Sam Greenberg (who had helped with the strategy for re-routing power from the LM to the crippled CM) issued a tongue-in-cheek invoice for $400,540.05 to North American Rockwell, Pratt and Whitney, and Beech Aircraft, prime and subcontractors for the CSM, for "towing" the crippled ship most of the way to the Moon and back. The figure was based on an estimated 400,001 miles (643,739 km) at $1.00 per mile, plus $4.00 for the first mile. An extra $536.05 was included for battery charging, oxygen, and an "additional guest in room" (Swigert). A 20% "commercial discount," as well as a further 2% discount if North American were to pay in cash, reduced the total to $312,421.24. North American declined payment, noting that it had ferried three previous Grumman LMs to the Moon (Apollo 10, Apollo 11 and Apollo 12) with no such reciprocal charges.
