That contradicts earlier denials by the country's fourth-biggest airline.
Northwest is the second carrier to be identified as secretly passing traveler records to the government. In September, JetBlue Airways said it turned over passenger records to a defense contractor, later apologizing to its customers.
Northwest's participation in the project was first reported by the Washington Post for its Sunday editions.
A privacy rights group in Washington, D.C., says the airline violated customers' privacy rights.
The Electronic Privacy Information Center plans to file a lawsuit this week in federal court in San Jose.
The group wants NASA to release more documents about the security project.
Northwest told the Washington Post that it took part in the NASA program after the terrorist attacks to help the government improve security.
"Northwest Airlines had a duty and an obligation to cooperate with the federal government for national security reasons," the airline said in a statement.