Japan’s H-IIA rocket launched the second navigation satellite in the country’s Quasi-Zenith Satellite System in the first of three launches scheduled for Thursday. Liftoff for the Michibiki-2 satellite took place from the Tanegashima Space Centre, on schedule, at 09:17 JST (00:17 UTC).
The payload of Thursday’s launch, Michibiki No.2, is the second member of Japan’s Quasi-Zenith Satellite System (QZSS). Once complete, the QZSS constellation will initially consist of four satellites: three in inclined geosynchronous orbits and one in geostationary orbit.
The satellites will be operated by a private company, Quasi-Zenith Satellite System Services Incorporated, in partnership with the Japan Aerospace Exploration Agency (JAXA). The program’s aim is to provide additional navigation signals, compatible with the US Air Force’s Global Positioning System (GPS) satellites, which will allow for more accurate navigation in Japan’s built-up cities.
The orbit used by QZSS is unusual in that it is geosynchronous, but not geostationary. Three of the initial four satellites, including Michibiki No.2, will operate in orbits inclined at 44 degrees to the equator, with perigees slightly below and apogees slightly above geostationary altitude. This gives the orbit a figure-eight ground track centered around a point on the equator at a longitude of 135 degrees east.
With three satellites evenly spaced around this orbit, at least one spacecraft will always be within 30 degrees of zenith – or the point directly overhead – for any users in Japan or neighboring countries. The system will also include one satellite – expected to be Michibiki No.3 – in a regular geostationary orbit.
A satellite navigation receiver uses time signals from multiple satellites to triangulate its location. In cities, urban canyons can prevent signals propagating correctly – both by blocking line-of-sight to satellites and by reflecting signals – resulting in a multi-path effect that may cause the receiver to misidentify its position.
QZSS will provide additional signals to help improve accuracy; having a satellite close to the receiver’s zenith helps to ensure that signals are not blocked or reflected. QZSS broadcasts L1C/A, L1C, L2C and L5 navigation signals compatible with the US Global Positioning System, with additional L1S, L5S and L6 signals also available.
The QZSS system is expected to become operational in 2018 with the initial four-satellite constellation. By 2024, Japan aims to increase the number of satellites to seven.
The launch of Michibiki No.2 came almost seven years after that of the program’s first satellite, Michibiki No.1. That satellite, which was launched on 11 September 2010, has served as a demonstrator for the constellation but will also form part of the initial operational system.
Michibiki No.2 was built by Mitsubishi Electric and is based on the DS-2000 satellite bus. With a mass of around 4,000 kilograms (8,800 lb) the satellite measures 6.2 by 2.9 by 2.8 meters (20.3 by 9.5 by 9.2 feet) stowed. Ordered in 2013, Michibiki No.2 incorporates upgrades over Michibiki No.1, including an increased design life of fifteen years.
Power to the satellite is provided by twin solar arrays, with a span of 19 meters (62 feet). These are designed to generate 6.3 kilowatts of power at the end of the spacecraft’s design life.
The satellite carries a space environment data acquisition (SEDA) package – consisting of a particle detector and a magnetometer – intended to return data about the satellite’s environment and aid diagnostics in the event of a malfunction.
Michibiki No.2 was launched by Mitsubishi Heavy Industries’ H-IIA rocket. H-IIA Flight 34 (F-34) will use the rocket’s 202 configuration, a two-stage vehicle augmented by a pair of SRB-A3 solid rocket motors.
The 202 configuration was originally the lightest version of the H-IIA, with the 2022 and 2024 versions adding two and four Castor-4AXL motors respectively and the heavier H-IIA 204 using four SRB-A motors. Incremental upgrades – including the replacement of the original SRB-A boosters with the higher-specification SRB-A3 – have improved the H-IIA 202’s performance, with the 2022 and 2024 configurations having since been retired.
The 202 configuration is the most-launched version of the H-IIA, accounting for twenty of the rocket’s thirty-three launches before F-34. Since its maiden flight in August 2001, the H-IIA has completed thirty-two of its launches successfully, with the only failure being of an H-IIA 2024 on the rocket’s sixth flight – which was left unable to achieve orbit after one of its SRB-A boosters failed to separate.
The H-II family of rockets launch from Japan’s Tanegashima Space Centre and its Yoshinobu Launch Complex. Consisting of two launch pads, this complex was constructed for the original H-II, which flew in 1994. The second pad was built in the early 2000s to provide for additional H-IIA launch operations, but has never been used by the H-IIA. Instead it is used by the larger H-IIB.
Rockets are assembled vertically in the complex’s vehicle assembly building and rolled to one of the two launch pads atop a mobile launch platform. For H-IIA F-34, rollout occurred around 19:00 local time (11:00 UTC) on Wednesday, with the rocket arriving at the launch pad by 19:25.
Thursday’s countdown proceeded towards X-0, Japan’s designation for the time of launch. Seconds before the count reaches this point, the first stage’s LE-7A engine ignited, with ignition of the two SRB-A3 solid rocket motors and liftoff timed for X-0.
Both stages of the H-IIA burn cryogenic propellant – liquid hydrogen oxidized by liquid oxygen – while the solid rocket motors use hydroxyl-terminated polybutadiene (HTPB).
The boosters provided thrust to augment the H-IIA’s first stage for the first 98 seconds of flight. Burnout, defined as the point at which the boosters’ thrust drops below 2%, was followed ten seconds later by the separation of the spent booster casings. At booster separation, the rocket was at an altitude of approximately 54 kilometers (34 miles, 29 nautical miles) and traveling at a velocity of 1.5 kilometers per second (0.93 miles per second, 3,400 mph).
After booster separation the first stage continued to burn, powering H-IIA F-34 towards orbit. The rocket’s payload fairing separated from around Michibiki No.2 at the nose of the rocket four minutes and ten seconds after liftoff, with the rocket having climbed to 151 kilometres (93.8 miles, 81.5 nautical miles) – clear of the dense lower regions of Earth’s atmosphere that the fairing acts to protect its payload from.
Six minutes and thirty-eight seconds after liftoff, Main Engine Cutoff (MECO) occurred. Having burned its propellant, the first stage shut down. Stage separation took place eight seconds later. A further six seconds after staging the rocket’s second stage ignited to begin the first of two planned burns.
The H-IIA’s second stage is powered by a single LE-5B engine. Its first burn was expected to last five minutes and 42 seconds, placing itself and Michibiki No.2 into an initial parking orbit. Following a twelve-minute coast phase the stage began a three-minute burn to inject Michibiki No.2 into a high-inclination geosynchronous transfer orbit.
Spacecraft separation occurred fifty seconds after the end of the upper stage’s second burn; at twenty-eight minutes and 24 seconds mission elapsed time.
The launch of Michibiki No.2 was the first of three scheduled for Thursday. The second launch of the day is targeting an instantaneous launch window at 21:55 UTC; twenty hours and thirty-eight minutes after the H-IIA lifted off. This will see a SpaceX Falcon 9 vehicle deploy a Dragon spacecraft to begin the CRS-11 resupply mission to the International Space Station. The third launch of the day is expected to be of an Ariane 5 with the ViaSat-2 and Eutelsat 172B communications satellites, during a one-hour window opening at 23:45 – an hour and fifty minutes after the Falcon.
The H-IIA launch was the thirtieth of 2017 worldwide and the fourth of the year for Japan – three of which have used H-IIA vehicles. It is unclear when Japan’s next launch will be, with several undated H-IIA missions due before the end of the year. These include two further spacecraft for the QZSS constellation, the Global Change Observation Mission – Climate (GCOM-C) Earth science satellite and a new Information Gathering Satellite (IGS) reconnaissance spacecraft.
(Images via JAXA)