U.S. military warning sentinel attached to Atlas 5 rocket at Cape Canaveral

The U.S. Space Force’s fifth SBIRS GEO early warning satellite — encapsulated inside the Atlas 5 rocket’s payload shroud — arrives at the Vertical Integration Facility on May 7. Credit: United Launch Alliance

United Launch Alliance crews at Cape Canaveral have topped off an Atlas 5 rocket for liftoff Monday with the U.S. military’s next infrared sentinel to join a satellite fleet designed detect missile launches around the world.

Ground teams at ULA’s Vertical Integration Facility installed the U.S. Space Force’s fifth Space Based Infrared System, or SBIRS, satellite on top of the Atlas 5 rocket May 7. Since then, ULA personnel have performed a series of tests to verify mechanical and electrical connections between the rocket and the SBIRS GEO 5 spacecraft encapsulated inside the Atlas 5’s payload shroud.

The preparations set the stage for rollout of the 194-foot-tall (59-meter) rocket from the vertical hangar to pad 41 at Cape Canaveral Space Force Station this weekend. The Atlas 5 will ride on its mobile launch platform along rail tracks for the 1,800-foot (550-meter) trip to the launch pad.

After connecting the rocket with ground systems — such as propellant fluid lines — at the launch pad, ULA will kick off the countdown early Monday to target a launch time of 1:35 p.m. EDT (1735 GMT).

The launch Monday will be the first Atlas 5 mission of the year, and ULA’s second flight of 2021 overall, following the successful launch of a Delta 4-Heavy rocket from California on April 26 with a classified U.S. government spy satellite.

The SBIRS GEO 5 satellite. Credit: Lockheed Martin

The Atlas 5 launcher that will deliver the SBIRS GEO 5 spacecraft to orbit will fly in the “421” configuration with a 4-meter and two strap-on solid rocket boosters supplied by Aerojet Rocketdyne. A single RL10 engine from Aerojet Rocketdyne will power the Atlas 5’s Centaur upper stage.

The launch will mark the eighth flight of the Atlas 5-421 variant, and the 87th launch of an Atlas 5 rocket since its debut in 2002.

ULA crews at Cape Canaveral began stacking the Atlas 5 rocket on its launch table inside the VIF last month. The bronze first stage booster was raised vertical and positioned onto the launch mount April 21, a few weeks after the stage arrived at the Florida launch base from ULA’s rocket factory in Decatur, Alabama.

Twin AJ-60A solid rocket boosters from Aerojet Rocketdyne were installed on the side of the Atlas first stage April 23 and 24. The strap-on motors will give the rocket an extra boost off the launch pad, firing alongside the first stage’s kerosene-fueled RD-180 main engine.

Ground teams hoisted the rocket’s cryogenic Centaur upper stage and its Aerojet Rocketdyne RL10 engine on top of the Atlas first stage April 26. The Centaur was integrated with the rocket’s interstage and the bottom segment of the payload fairing inside a nearby processing facility before teams lifted the entire unit on top of the first stage.

The build-up of the Atlas 5 rocket was completed Friday, May 7, with the stacking of the 45-foot-tall (13.7-meter) payload fairing inside the VIF.

The Atlas 5 payload fairing containing the SBIRS GEO 5 satellite is raised inside the Vertical Integration Facility. Credit: United Launch Alliance

Workers encapsulated the SBIRS GEO 5 satellite inside the payload fairing at a clean room facility at the spaceport. The spacecraft arrived at Cape Canaveral on March 18 on a U.S. Air Force cargo plane from California, where Lockheed Martin built and tested the satellite at a factory in Sunnyvale.

Once at Cape Canaveral, the spacecraft was loaded with its supply of hypergolic hydrazine and nitrogen tetroxide propellants for in-space maneuvers.

SBIRS GEO 5 is follows four previous SBIRS satellites launched into geosynchronous orbit since 2011 to replace the military’s aging Defense Support Program missile warning spacecraft, the last of which launched in 2007. All of the SBIRS satellites in geosynchronous orbit rode to space aboard Atlas 5 rockets.

The Atlas 5 rocket launching the SBIRS GEO 5 mission will head east from Cape Canaveral. The launcher’s two solid rocket boosters will consume their pre-packed propellant in about a minute-and-a-half, then jettison to fall into the Atlantic Ocean at T+plus 2 minutes, 9 seconds.

The first stage’s Russian-made RD-180 main engine will shut down at T+plus 4 minutes, 10 seconds, followed by stage separation six seconds later. The hydrogen-fueled RL10 engine on the Centaur upper stage will ignite at T+plus 4 minutes, 26 seconds, for the first of two firings to place the SBIRS GEO 5 spacecraft into an elongated transfer orbit.

The Atlas 5 payload fairing containing the SBIRS GEO 5 satellite is raised inside the Vertical Integration Facility. Credit: United Launch Alliance

After cutoff of the Centaur’s first burn at T+plus 15 minutes, 6 seconds, the rocket will deploy two suitcase-size secondary payloads for the U.S. Air Force Academy. A second RL10 engine burn will begin at T+plus 31 minutes, 6 seconds, to maneuver into an orbit closer to the SBIRS GEO 5 spacecraft’s final operating position.

Separation of the Space Force’s new missile warning satellite is expected at T+plus 42 minutes, 46 seconds.

The Atlas 5’s guidance computer will aim to release the spacecraft in an orbit ranging in altitude between 575 miles (925 kilometers) and 22,216 miles (35,753 kilometers), with an inclination angle of 21.14 degrees to the equator.

The SBIRS GEO 5 spacecraft’s on-board propulsion system will steer the satellite to a circular geosynchronous orbit that is continuously at an altitude of nearly 22,300 miles over the equator. In that orbit, the satellite’s velocity will be fixed with the rate of Earth’s rotation, giving the craft’s infrared early warning sensors a constant view of the same part of the planet.

The new satellite differs from the first four SBIRS GEO satellites, introducing an upgraded spacecraft design Lockheed Martin calls the “combat bus.” Lockheed Martin built the fifth and sixth SBIRS GEO satellites using its new LM 2100 platform, which the company says is the result of an “internally-funded, multi-year modernization initiative.”

The Atlas 5 payload fairing containing the SBIRS GEO 5 satellite is raised inside the Vertical Integration Facility. Credit: United Launch Alliance

According to Lockheed Martin, the LM 2100 combat bus is designed to provide improved resiliency and hardening against cyber threats, along with additional spacecraft power, and enhanced propulsion and electronics. The modular design incorporates common components to streamline manufacturing, and can more easily accommodate new types of sensors to respond to innovation and new military requirements.

The LM 2100 combat bus will also be used by the next generation of missile warning satellites Lockheed Martin is building for the Space Force to replace the SBIRS fleet. The next generation of GPS navigation satellite, due to begin launching in 2026, will also use the combat bus platform.

The final SBIRS GEO satellite, GEO 6, is scheduled of launch on an Atlas 5 rocket in 2022. The military’s contracts with Lockheed Martin for the final two SBIRS GEO satellites are valued at about $2.2 billion, according to financial data published by the Pentagon in previous years.

Northrop Grumman builds the infrared sensors on the SBIRS satellites. The instruments can detect and track super-hot exhaust plumes from rocket motors, informing military officials of foreign missile launches. The information gathered by the SBIRS fleet could help defense units intercept an incoming missile before it strikes its target.

The Atlas 5 payload fairing containing the SBIRS GEO 5 satellite is raised inside the Vertical Integration Facility. Credit: United Launch Alliance

The SBIRS constellation includes a minimum of four SBIRS craft stationed in geosynchronous orbit and at least two infrared payloads in elliptical orbits aboard top secret National Reconnaissance Office spy satellites, providing polar coverage. The final two SBIRS satellites set for launch this year and next year will replenish the fleet.

Each infrared instrument package on the geosynchronous satellites includes staring and scanning sensors designed to provide visibility over an entire hemisphere, while allowing ground operators to focus the craft’s gaze on hotspots like North Korea.

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