The oil giant Shell has obtained what critics are calling a “protest-free zone” around a drilling vessel set to begin operations off Alaska’s Arctic coast later this month. The U.S. Coast Guard has granted Shell’s Noble Discoverer vessel “a 500-meter safety zone” that no demonstrators will be allowed to enter. The environmental group Greenpeace says it plans to defy the restrictions, despite the threat of penalties. Shell’s bid to begin exploratory drilling in the Arctic was approved last month over the objections of indigenous and environmental groups.