Epsilon rocket launches Japanese ERG mission

by William Graham

Japan’s Epsilon rocket conducted its second flight Tuesday, orbiting JAXA’s ERG satellite to study Earth’s radiation belts. Liftoff from the Uchinoura Space Centre was on schedule at 20:00 local time (11:00 UTC), the opening of what was an hour-long launch window.

Epsilon-2 Mission:

The Exploration of Energisation and Radiation in Geospace (ERG) mission will be operated by the Japan Aerospace Exploration Agency (JAXA), studying Earth’s magnetosphere.

Also known as SPRINT-B, ERG is a 365-kilogram (805 lb) satellite based on JAXA’s SPRINT bus, which was demonstrated by 2013’s Hisaki – or SPRINT-A – mission. The spacecraft measures 1.5 by 1.5 by 2.7 meters (4.9 x 4.9 x 8.9 feet) in its launch configuration.

Once in orbit, ERG will deploy its instrument booms and solar arrays. With a span of 6.0 meters (19.7 feet) along the satellite’s x-axis and 5.2 m (17.1 ft) meters along its y-axis, the solar panels will generate over 700 watts of power for the spacecraft’s systems and instruments.

Following initial operation and testing, ERG is expected to operate for at least a year.

The ERG satellite carries instruments dedicated to the study of plasma, particles, waves and fields in Earth’s radiation belts.

Earth’s radiation belts were discovered by James Van Allen’s experiments aboard the first US satellite, Explorer 1, in 1958 although their existence had previously been theorized by other scientists. As a result, the belts are known as the Van Allen belts.

Earth has two permanent radiation belts, the inner and outer Van Allen belts, although NASA’s Van Allen Probes, or Radiation Belt Storm Probes (RBSP), which were launched in August 2012, showed that a third belt can form and dissipate.

ERG will join NASA’s two Van Allen Probes and three earlier Time History of Events and Macroscale Interactions During Substorms (THEMIS) spacecraft in making in-situ observations of the Van Allen belts. These will be joined by the UA Air Force Research Laboratory’s DSX satellite, currently scheduled for launch aboard SpaceX’s Falcon Heavy rocket next year.

ERG’s Plasma and Particle Experiment (PPE) instrument suite consists of electron and ion mass analyzers. The Low Energy Particle Experiments – Electron Analyser (LEP-e), Medium Energy Particle Experiments – Electron Analyser (MEP-e), High Energy Electron Experiments (HEP) and Extremely High Energy Electron Experiments (XEP) instruments will study electrons at increasing energies between 10 electronvolts and 20 megaelectronvolts.

Low Energy Particle Experiments – Ion Mass Analyser (LEP-i) and Medium Energy Particle Experiments – Ion Mass Analyser (MEP-i) are mass spectrometers which will be used to study the different types of ions present in ERG’s environment.

The Plasma Wave Experiment (PWE) will measure the Earth’s electric and magnetic fields as the satellite passes through them, up to frequencies of 10 megahertz and 100 kilohertz respectively.

This will be complimented by the Software-Type Wave Particle Interaction Analyser (S-WPIA), software aboard ERG’s computer systems, will attempt to quantify energy transferred between waves and electrons through the spacecraft’s observations of plasma waves and particles.

ERG launched atop JAXA’s solid-fuelled Epsilon rocket, which made its first flight in September 2013 and has not flown since.

A replacement for the earlier M-V rocket, which retired in September 2006, Epsilon is designed to provide a ride to orbit for Japan’s smaller satellites. Epsilon uses an SRB-A3 motor – used as a strap-on booster on the larger H-IIA and H-IIB rockets – as its first stage with upper stages derived from the M-V.

Epsilon launches from the Uchinoura – formerly Kagoshima – Space Centre, using the same launch pad from which the M-V flew.

Also used by earlier members of the Mu family of rockets – of which the M-V was the final member – the complex was originally constructed in the 1960s.

It consists of an assembly tower with the rocket mounted upon a movable launcher platform which is rotated into position ahead of launch. This was originally built as a rail launcher for the Mu series, however a pedestal has been added for Epsilon with the former support structure for the rail serving as an umbilical tower.

Tuesday’s launch was the first flight of the operational or “Enhanced Epsilon” configuration, introducing improvements to the upper stages over those used on the maiden flight.

The vehicle has been described as “Epsilon-2”, however it is presently unclear whether this name refers to the enhanced configuration, or to Tuesday’s launch being Epsilon’s second flight.

Epsilon’s launch began with first stage ignition and liftoff, when the countdown reached zero. The rocket flew in a south-easterly direction, along an azimuth of 100 degrees. Its first stage burned for 109 seconds, accelerating the vehicle to a velocity of 2.5 kilometers per second (5,600 mph). At burnout, Epsilon was at an altitude of 71 kilometers (44 miles, 38 nautical miles) and 75 kilometers (47 miles, 40 nautical miles) downrange.

After the end of the first stage burn, Epsilon entered a coast phase as it ascends into space. Around 41 seconds after burnout, at an altitude of 115 kilometers (71.5 miles, 62.1 nautical miles), the payload fairing separated from the nose of the rocket. Eleven seconds later the spent first stage was jettisoned.

Epsilon-2 had an M-35 second stage, in place of the M-34c used on the maiden flight. The new stage is larger than its predecessor and has a fixed nozzle instead of the extendible nozzle used on the M-34c. The M-35 generates 445 kilonewtons of thrust, an increase from the 327 kilonewtons generated by the M-34c, and burns for fifteen seconds longer.

The second stage ignited four seconds after first stage separation, burning for two minutes and eight seconds.

A second coast phase took place between second stage burnout and third stage ignition. One minute and forty-five seconds after burning out, the second stage separated with the third stage igniting four seconds later. During the coast phase the third stage was spun-up; spin-stabilisation was used to help it maintain attitude during its burn.

For Tuesday’s launch the third stage was also been upgraded, with Epsilon-2 using a KM-V2c instead of the KM-V2b that flew on the 2013 launch. This uses a fixed nozzle instead of an extendible one, but has no significant difference in performance. The third stage will burn for about 89 seconds.

Epsilon can fly with a liquid-fuelled fourth stage, the Compact Liquid Propulsion System (CLPS), which was used on its first launch. This is not required for Tuesday’s launch, so instead the rocket flew in its all-solid three-stage configuration for the first time.

Spacecraft separation occurred thirteen minutes and twenty-seven seconds after liftoff; five minutes and sixteen seconds after third stage burnout.

Tuesday’s launch was targeting an elliptical orbit with a perigee – the point closest to Earth – of 219 kilometers (136 miles, 118 nautical miles) and an apogee – or highest point – of 33,200 kilometers (20,600 miles, 17,900 nautical miles).

The orbit will have inclination of 31.4 degrees to the equator, with the satellite taking about 580 minutes – or 9.7 hours – to complete one revolution.

Tuesday’s launch was Japan’s fourth and last of 2016, following H-IIA missions in February and November which deployed the Hitomi observatory and the Himawari 9 weather satellite – and an H-IIB launch earlier this month with the Kounotori 6 spacecraft to resupply the International Space Station.

Japan’s next launch, currently scheduled for 11 January, will be an experimental flight which aims to use a modified SS-520 sounding rocket to orbit a single three-unit CubeSat. An H-IIA launch carrying the DSN-2 communications satellite is also scheduled for January.

The next Epsilon launch will carry the ASNARO-2 experimental radar imaging satellite. This is expected to occur during Japan’s 2017 financial year, which begins on 1 April.

(Image via JAXA).

Related Articles