The U.S. Navy and NASA are assisting in an international effort to track down an Argentine navy submarine with 44 crew members that has been missing for several days.

The lost vessel, the ARA San Juan, has been out of radio contact since Wednesday somewhere around the southern tip of South America in the Atlantic Ocean. However, late Saturday, the Argentine defense ministry said it detected several failed “satellite calls,” likely from the missing submarine, providing some hope that it would soon be found.