The probe going up is called SBIRS GEO-4, for Space Based Infrared System, and it's the fourth satellite of its kind to go into a high orbit around Earth.
ULA will provide a live launch webcast beginning at 7:32 p.m. EST (0032 GMT).
Tonight's launch is set to take off from Cape Canaveral Air Force Station in Florida sometime during a 40-minute window that opens at 7:52PM ET. There were no details available about which orbit the SBIRS payload would hopefully be delivered to on Thursday evening.
United Launch Alliance's Atlas V rocket is scheduled to launch from Cape Canaveral Thursday night (Jan. 18) carrying the Space Based Infrared System (SBIRS). Two other satellites, SBIRS GEO Flights 5 and 6, are expected to follow.
"SBIRS provides our military with timely, reliable and accurate missile warning and infrared surveillance information", Tom McCormick, vice president of Lockheed Martin's Overhead Persistent Infrared systems mission area, said in a November 28 statement when SBIRS GEO Flight 4 was shipped to its Florida launch site.
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The infrared payloads are provided by Northrop Grumman. The fourth will give the SBIRS fleet global coverage, replacing missile detection capabilities now provided by older, previous-generation Defense Support Program satellites.
The Air Force has ordered two more SBIRS satellites for launch in 2021 and 2022 to improve coverage, and eventually replace the first two SBIRS geosynchronous spacecraft.
Air Force Space Command operates the SBIRS system.
The flight of SBIRS GEO 4 is the first scheduled Cape launch for ULA's Atlas V rocket this year (2018).