Japan’s Mitsubishi Heavy Industries launched an H-IIA rocket on Saturday (05:30 UTC), carrying the third spacecraft for the country’s Quasi-Zenith Satellite System of GPS augmentation satellites. The H-IIA was scheduled to lift off from the Tanegashima Space Centre with QZS-3 a week ago, before an issue was found late in the countdown.
The QZS-3 satellite, which after launch will be named Michibiki No.3, will be placed into geosynchronous transfer orbit by the launch. It is part of a constellation of spacecraft intended to improve the accuracy of satellite navigation in built-up areas. The Quasi-Zenith Satellite System (QZSS) will initially consist of four satellites, broadcasting additional signals compatible with the US Global Positioning System (GPS).
A GPS receiver determines its position by using precise timing signals from a constellation of at least twenty-four satellites in Medium Earth orbit. The time signals are used to calculate the distance to each satellite, allowing a receiver to triangulate its position. In order to achieve a precise location, at least four satellites must be visible to the receiver.
QZSS is designed to help Japanese users overcome a shortcoming of the GPS constellation which causes receivers to become less accurate in cities where large numbers of tall buildings form urban canyons. Buildings can block line-of-sight to the satellites and can also reflect or scatter signals, resulting in a multi-path effect which can cause the receiver to miscalculate the distance to the satellite.
QZSS will provide additional signals from sources close to the zenith – or the point directly overhead – of users in Japan and its neighboring countries. This high angle allows receivers to pick up the signals without being obstructed or reflected by buildings.
Three of the four QZSS satellites will operate in a geosynchronous orbit inclined to the equator at 44 degrees, with their apogee slightly above and perigee slightly below geostationary altitude. This orbit gives a figure-eight ground track centered around a longitude of 135 degrees, which keeps at least one of the satellites within 30 degrees of the zenith from Japan at all times. The two satellites that have already been launched are in this orbit, with the fourth spacecraft expected to join them following a launch later this year.
The third satellite will go into a regular geostationary orbit. From a longitude of 127 degrees East the satellite will augment the inclined-orbit part of the constellation.
QZSS satellites broadcast several L-band navigation signals. The 1,575.42-megahertz L1C/A and L1C signals are compatible with the GPS constellation, while an L1S signal provides a messaging service and a sub-metre level augmentation service (SLAS).
The satellites also broadcast a 1,227.60 MHz L2C signal and an 1,176.55 MHz L5 signal, to complement the corresponding GPS signals. An experimental L5S signal, carried by all satellites except Michibiki No.1, is intended for further testing to augment GPS – providing a more precise position – while a 1,278-megahertz L6 signal is designed to provide a centimetre-level augmentation service (CLAS).
Michibiki No.3 is the first satellite in the constellation equipped to broadcast an additional L1Sb signal, a further augmentation signal which is expected to be rolled out around 2020.
Like the rest of the QZSS constellation, Michibiki No.3 was built by Mitsubishi Electric around the DS-2000 satellite bus. At a mass of about 4,700 kilograms (10,400 lb), it is some 700 kilograms (1,500 lb) heavier than its sister craft.
The extra mass is due to two additional antennae carried aboard the spacecraft to broadcast the QZSS Safety Confirmation Service, or Q-ANPI. This is an S-band system designed to transmit emergency broadcasts and evacuation instructions to compatible receivers in Japan, should the need arise.
The QZSS constellation is operated by Quasi-Zenith Satellite System Services Incorporated, a private company operating in partnership with Japan’s national space agency, the Japan Aerospace Exploration Agency (JAXA).
The first QZSS satellite, Michibiki No.1, was launched in September 2010 as a demonstrator in advance of the development of the remaining satellites. Michibiki No.1 was operated on its own as a proof-of-concept mission for over six years until Michibiki No.2 was launched this June. The fourth satellite is scheduled to launch in October.
Due to its additional mass over the other QZSS satellites, this launch will use an H-IIA 204 rocket instead of the H-IIA 202 which is being used to deploy the rest of the constellation. Compared to the H-IIA 202, which is the standard version of the H-IIA, the 204 configuration has two additional SRB-A3 solid rocket motors attached to the first stage, for a total of four.
The H-IIA is a two-stage rocket with both the first and second stages fuelled by liquid hydrogen propellant and liquid oxygen oxidizer. The SRB-A3 solid rocket motors burn hydroxyl-terminated polybutadiene (HTPB).
This launch was the thirty-fifth flight of the H-IIA, and was designated H-IIA F-35. It was conducted by Mitsubishi Heavy Industries, the rocket’s manufacturer, on behalf of JAXA.
The H-IIA departed from Pad 1 of the Yoshinobu Launch Complex at the Tanegashima Space Centre. All of the H-IIA’s thirty-four launches to date have used this launch pad, which was previously used for seven launches of the earlier H-II and H-IIS rockets.
Yoshinobu is a two-pad launch complex which serves Japan’s H-II family of rockets, replacing the nearby Osaki launch complex that was used by the N-I, N-II and H-I vehicles and later the short-lived J-I. The second pad at the complex, despite originally being built for the H-IIA, has only ever been used by the larger H-IIB.
The Yoshinobu Launch Complex makes use of an assembly building away from the launch pad for final integration of the rocket in a vertical configuration. In preparation for the launch, the H-IIA was rolled out overnight atop a mobile launch platform.
Seconds before the countdown reached zero the H-IIA’s LE-7A main engine ignited, followed at the zero mark in the countdown – termed X-0 by JAXA – by the four SRB-A3 solid rocket motors. H-IIA F-35 ascended from the launch pad, flying East over the Pacific Ocean.
The first major flight event after liftoff was the burnout of the solid rocket motors, about 115 seconds into the mission. The spent boosters separated in pairs eleven and fourteen seconds later, leaving the core vehicle to continue on towards orbit.
Three minutes and 45 seconds into the flight, the payload fairing separated from around QZS-3 at the nose of the rocket. The fairing which was used for this launch was the 5S model, with a diameter of 5.1 meters (16.7 feet). F-35 was the first H-IIA to sport a five-meter fairing since December 2006, with the additional space needed to accommodate the satellite’s emergency broadcasting antennae.
The H-IIA’s first stage burned for six minutes and thirty-eight seconds before main engine cutoff, or MECO, took place. Eight seconds later the spent stage separated with second stage ignition expected after a further six seconds. The second stage made two burns of its LE-5B engine during this launch.
The second stage’s first burn was four minutes and 31 seconds to set up an initial parking orbit. Following a twelve-minute, sixteen-second coast the stage restarted for a further 250 seconds, injecting QZS-3 into geosynchronous transfer orbit. Spacecraft separation occurred fifty-one seconds after the second burn’s conclusion, at 28 minutes and 40 seconds mission elapsed time.
This launch was the fourth H-IIA launch of 2017, and the fifth overall for Japan including January’s unsuccessful attempt to place a small satellite, TRICOM-1, into orbit with a modified SS-520 sounding rocket.
Japan’s next launch is currently planned for October, with an H-IIA 202 to deliver the fourth member of the QZSS constellation into orbit.
(Images via JAXA)