Timeline of events during Epsilon rocket’s launch with the ERG mission

The ground track for the Epsilon rocket’s launch with Japan’s ERG mission. Credit: JAXA

An Epsilon rocket is set to send a Japanese space weather research probe into an orbit stretching more than 20,000 miles (33,000 kilometers) above Earth to investigate how the Van Allen radiation belts shrink and swell with variable solar activity.

The Exploration of Energization and Radiation in Geospace, or ERG, mission will last at least one year, collecting data on the composition, intensity and direction of particles, waves and the magnetic field inside donut-shaped bands of radiation hovering a few thousand miles above Earth.

The ERG spacecraft, weighing around 804 pounds (365 kilograms), will launch on the second flight of Japan’s Epsilon rocket. The launch will debut an upgraded version of the Epsilon with an improved second stage motor, simplified structures, a lengthened payload fairing, and a lighter power distribution system.

The rocket will blast off from the Uchinoura Space Center, a shoreline spaceport on the southern Japanese island of Kyushu, heading east over the Pacific Ocean to propel the ERG satellite into a highly elliptical orbit.

The timeline below chronicles the major events during the ascent.

T-00:00: Liftoff

The first stage’s SRB-A solid rocket motor ignites and propels the 105-ton Epsilon rocket away from the Uchinoura Space Center. The SRB-A motor produces 530,000 pounds of thrust in vacuum.

T+01:49: Stage 1 Burnout

The Epsilon’s SRB-A first stage, derived from boosters on the H-2A and H-2B rockets, burns out at an altitude of 44 miles (71 kilometers) and a speed of 4,700 mph (2.1 kilometers per second).

T+02:30: Fairing Jettison

The rocket’s 8.5-foot (2.6-meter) diameter payload fairing is released at an altitude of 71 miles (115 kilometers).

T+02:41: Stage 1 Separation

The Epsilon’s empty first stage separates moments before ignition of the rocket’s second stage motor.

T+02:45: Stage 2 Ignition

The M-35 second stage motor fires to begin a 128-second burn, generating around 79,000 pounds of thrust.

T+04:53: Stage 2 Burnout

The Epsilon’s M-35 second stage burns out after reaching a velocity of 12,300 mph (5.5 kilometers per second) at a downrange distance of 356 miles (573 kilometers) east of the launch site. The Epsilon rocket enters a nearly two-minute coast period, during which thrusters on the second stage spin up the vehicle for staging and ignition of the third stage.

T+06:38: Stage 2 Separation

The Epsilon’s M-35 second stage and KM-V2c third stages separate at an altitude of 142 miles (229 kilometers) ahead of third stage ignition.

T+06:42: Stage 3 Ignition

The rocket’s spin-stabilized KM-V2c third stage motor ignites to begin an 89-second burn.

T+08:11: Stage 3 Burnout

The KM-V2c third stage consumes its supply of solid propellant as the Epsilon rocket soars over the Pacific Ocean. The spinning stage aims to place the ERG spacecraft in an orbit with a perigee, or low point, of 136 miles (219 kilometers), an apogee, or high point, of around 20,600 miles (33,200 kilometers), and an inclination of 31.4 degrees to the equator.

T+13:27: ERG Separation

The approximately 804-pound (365-kilogram) ERG spacecraft deploys from the Epsilon rocket’s third stage to begin its research mission in the radiation belts.

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