The first communications satellite dedicated to support Japanese military forces will launch Tuesday on top of an H-2A rocket on the way to a perch more than 22,000 miles above Earth.
The advanced spacecraft carries an X-band communications payload to relay messages and serve the command and control network of the Japan Self-Defense Forces.
A Japanese H-2A rocket, built and operated by Mitsubishi Heavy Industries, will launch the powerful DSN 2 communications satellite from the Tanegashima Space Center in southern Japan at 0744 GMT (2:44 a.m. EST) Tuesday.
The launch window, which opens at 4:44 p.m. Japan Standard Time on Tuesday, extends for 74 minutes, and the weather forecast calls for favorable conditions.
The rocket rolled out of its 265-foot-tall (81-meter) assembly building around 1800 GMT (1 p.m. EDT; 3 a.m. Japan Standard Time), approximately 14 hours before the appointed launch time. Riding a mobile launch platform, the H-2A rocket reached its launch pad 1,600 feet (500 meters) from the assembly structure for fueling and other final flight preps.
Standing 174 feet (53 meters) tall, the H-2A rocket will fly in the rarely-used “204” configuration with four strap-on solid rocket boosters. Most H-2A missions take off with two of the solid-fueled motors, but the DSN 2 spacecraft mounted aboard the rocket for Tuesday’s mission requires the power of four boosters.
Tuesday’s launch will mark the 32nd flight of an H-2A rocket, and just the third to fly with the launcher’s most powerful version.
Once the rocket arrived at the launch pad at Tanegashima, the launch team planned to switch on the H-2A’s computer and navigation systems, test the rocket’s range safety mechanisms, and fuel the two-stage launcher with cryogenic liquid hydrogen and liquid oxygen propellants.
A computer-controlled sequencer will take charge of the final minutes of the countdown, switching the rocket to internal battery power and pressurizing its propellant tanks before igniting the first stage’s hydrogen-fueled LE-7A main engine at T-minus 4.7 seconds.
The four boosters mounted around the base of the rocket will ignite about four seconds later to propel the H-2A into the sky.
Riding 2.5 million pounds of thrust, the H-2A rocket will fly east from Tanegashima over the Pacific Ocean, dropping its four boosters into the sea around two minutes after liftoff. At the four-minute point, with the H-2A above the dense lower layers of the atmosphere, the clamshell-like nose fairing at the top of the rocket will jettison to reveal the DSN 2 spacecraft, also known as Kirameki 2.
The launcher’s LE-7A main engine will continue firing with nearly 250,000 pounds of thrust until around T+plus 6 minutes, 36 seconds, when the first stage will shut off and drop away. The second stage’s LE-5B engine will fire for the first of two burns to inject the DSN 2 satellite into the mission’s targeted orbit.
In a break in protocol from most H-2A flights, Japanese officials have not released a second-by-second timeline of Tuesday’s mission, possibly because of the payload’s military nature. If the flight profile follows the track of a typical H-2A launch, the DSN 2 satellite should be deployed from the rocket’s second stage around a half-hour after liftoff.
The size, mass, capabilities and operating position of the DSN 2 spacecraft also have not been revealed.
The satellite will be released into an egg-shaped geostationary transfer orbit, with a high point at, or above, an altitude of more than 22,000 miles (35,000 kilometers). DSN 2’s own rocket engine will maneuver the spacecraft into a circular geostationary orbit over the equator, where its communications antennas will reach military units patrolling by land, sea and air across the Asia-Pacific.
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