ULA readies for U.S. Air Force SBIRS GEO 4 launch

Bart Leahy

CAPE CANAVERAL, Fla. — After a slight delay from late 2017, United Launch Alliance is readying an Atlas V 411 to launch the fourth geosynchronous element of the U.S. Air Force (USAF) Space Based Infrared Sensor (SBIRS) program. The launch, is currently set to take place from Cape Canaveral Air Force Station (CCAFS) Space Launch Complex (SLC) 41 on January 18.

The payload

The SBIRS GEO 4 spacecraft was delivered to CCAFS in December of 2017 and was certified to begin fueling operations. Once launched aboard Atlas V and on station, the 10,000-pound (4,536 kg) GEO 4 satellite will measure 49 ft x 22 ft x 20 ft (14.9 m x 6.7 m x 6.1 m) with all of its appendages deployed.

The GEO spacecraft bus is a militarized, radiation-hardened, three-axis-stabilized version of the Lockheed Martin A2100 spacecraft, which provides power, attitude control, command and control, and a communications subsystem.

The spacecraft’s instrument complement includes a scanning and staring sensor capable of looking at Earth using short-wave, mid-wave, and see-to-ground sensor chip assemblies, and short Schmidt telescopes with dual optical pointing. Its onboard navigation includes a GPS receiver with Selected Availability Secure Anti-Spoof Module. The satellite’s mass also includes two deployable, sun-tracking solar arrays for power and 430 lbs of fuel. The spacecraft is designed to have a 12-year service life.

GEO 4’s scanning sensor continuously scans the earth to provide 24/7 global strategic missile warning capability. Data from the scanner also contributes to theater and intelligence missions. The step-staring sensor is a highly agile and accurate pointing and control system, providing coverage for theater missions and intelligence areas of interest with fast revisit rates and high sensitivity.

The spacecraft was encapsulated into the Atlas V’s four meter payload fairing on Tuesday, Jan. 9, 2018, with the SBIRS GEO 4 satellite, safely ensconced in the nosecone, moved out to the Vertical Integration Facility on the following day (Jan. 10). From there it was mated to the Atlas V 411 launch vehicle in preparation for flight.

The spacecraft has now completed all major testing milestones required prior to the rocket leaving the pad.

The Mission

SBIRS GEO 4 represents the latest addition to the USAF’s follow-on program to the Defense Support Program (DSP). The overall program, designed to support missile early warning, missile defense, battlespace awareness, and technical intelligence, comprises a mix of satellites in geosynchronous orbit (GEO) and highly elliptical orbit (HEO) as well as a ground component.

Both the GEO and HEO infrared sensors gather raw, unprocessed data that are downlinked to the ground, so that the same radiometric scene observed in space will be available for ground processing. In addition to transmitting unprocessed raw data, the GEO sensors also perform onboard signal processing and transmit detected events to the ground.

The SBIRS sensors are designed to provide greater flexibility and sensitivity than DSP’s infrared sensor and to detect short-wave and mid-wave infrared signals, allowing them to perform more types of missions. The enhanced capabilities provide warfighters with improved prediction accuracy. The evolved ground system uses better mission processing software, improving event message accuracy, and reducing manpower for DSP and SBIRS support and operations.

To date, USAF has launched two HEO spacecraft (designated Trumpet) and three GEO satellites, the most recent being on January 20, 2017. The ground element integrates the HEO and GEO satellites plus currently operational elements from DSP. The launch of GEO-3 experienced delays due to a propulsion system issue prior to delivery and then sensor issues on the original date of launch.

The launch

ULA’s Atlas V 411 has a 40-minute launch window from SLC-41 on January 18 that is scheduled to open at 7:52 p.m. EST. Previous launches of the SBIRS GEO satellites used an Atlas V 401, indicating the increased size and capabilities of this newer spacecraft.

This will mark the first flight for United Launch Alliance that is scheduled to take place from Cape Canaveral under the 2018 launch manifest.