The House’s chief overseer of NASA on Wednesday blamed mismanagement for two failed Mars missions but stopped short of calling for changes in the space agency’s leadership. An independent review of the missions, which both failed in 1999, concluded last month that they failed because of inadequate testing, inexperienced staff, poor communication and insufficient funds. But Rep. James Sensenbrenner Jr., R-Wis., said those problems could have been avoided had management paid more attention to tests, employee training and budget management.