The Bush administration is rebuffing a congressional challenge to the Department of Homeland Security’s new satellite surveillance system. Last week, Democrats threatened to shut down the program unless privacy concerns could be addressed. The satellite program is designed to provide federal, state and local officials with extensive access to spy satellite imagery to assist with emergency response and other domestic security needs. But critics say the Bush administration hasn’t created legal safeguards to ensure that the program won’t be used for domestic spying. In a letter to lawmakers, Chertoff said the system poses no civil liberties concerns and will be slowly activated in the coming weeks.