Complex sentence: Data are retrieved remotely by a shipborne acoustic modem without the need for lander recovery until the planned mission end date, whereupon acoustic release of a rope canister on each lander is triggered for recovery by ship.
Split into simpler sentences: Data are retrieved remotely by a shipborne acoustic modem without the need for lander recovery until the planned mission end date. Then the acoustic release of a rope canister on each lander is triggered for recovery by ship.