Japan’s Mitsubishi Heavy Industries launched an H-IIA (H-2A) rocket Tuesday (local time) carrying the country’s QZSS-4 navigation satellite. The rocket departed from the picturesque Tanegashima Space Centre on schedule at 07:01 local time (22:01 UTC on Monday).
QZSS-4, which will be known as Michibiki No.4 once in orbit, is the fourth member of the Quasi-Zenith Satellite System (QZSS), a constellation of satellites which Japan is launching to improve the accuracy of satellite navigation in its densely-populated cities.
QZSS broadcasts additional signals compatible with the US Air Force’s Global Positioning System (GPS), providing additional points of reference that a QZSS-enabled receiver can use to triangulate its position.
GPS, as well as its Russian and European counterparts GLONASS and Galileo, use constellations of satellites in medium Earth orbit. Each satellite carries highly-accurate atomic clocks and broadcasts signals that encode the exact time of transmission.
A receiver can use these signals to calculate the distance to the satellite from the difference in time between the signal being transmitted and received. By computing the distance to several satellites – whose positions are known from their orbit ephemeris – the receiver can triangulate its position.
A receiver must be able to pick up signals from at least four satellites in order to calculate its position accurately in three dimensions. In cities, tall buildings create urban canyons which can block, reflect or scatter signals from the satellites.
Signals that have been reflected can result in a multi-path effect if they are still picked up by a receiver; the signals will have traveled further than expected, so the receiver will compute that the satellite is further away than it is, and miscalculate its position.
The QZSS satellites operate in orbits designed to keep them as close as possible to being directly overhead – near to the zenith point of an observer’s frame of reference – of users in Japan for as long as possible. To achieve this, three QZSS satellites use highly-inclined geosynchronous orbits.
The Michibiki No.3 (QZSS-3) satellite, launched in August, compliments the constellation from an equatorial geostationary orbit. Once QZSS-4 reaches its operational orbit, the three inclined-orbit spacecraft will ensure that there is always a spacecraft within 30 degrees of the zenith as observed from Japan.
QZSS broadcasts several L-band navigation signals. The constellation’s L1C, L1C/A, L2C and L5 signals are designed to be compatible with GPS.
The spacecraft also broadcast an L1S signal to facilitate messaging and a sub-meter level augmentation service (SLAS), an L6 signal to provide a centimeter-level augmentation service (CLAS). An experimental L5S signal has been included on all satellites except for Michibiki No.1, which is also expected to enable more precise position determination.
The initial QZSS constellation of four satellites will be completed by Tuesday’s launch. A replacement for the constellation’s first satellite is expected to launch around 2020, with Japan planning to expand the constellation to seven satellites in the 2020s. The system is operated by Quasi-Zenith Satellite System Services Incorporated, in partnership with the Japan Aerospace Exploration Agency (JAXA).
The 4,000-kilogram (8,800 lb) QZSS-4 satellite was built by Mitsubishi Electric (MELCO), based on the same DS-2000 platform that has been used for all four first-generation QZSS satellites.
The satellite is identical to Michibiki No.2 (QZSS-2) which was launched in May, with both satellites incorporating upgrades over the Michibiki No.1 (QZSS-1) satellite that was deployed in 2010 as a pathfinder for the rest of the constellation. The geostationary Michibiki No.3 (QZSS-3) is similar in design to Michibiki No.2 and No.4, however it also incorporates an emergency broadcasting system payload.
QZSS-4 is expected to operate for at least fifteen years. After launch, the satellite will use its R-4D apogee motor to raise itself from the geosynchronous transfer orbit that it is expected to separate into, into its operational geosynchronous orbit.
The satellite’s orbit will be slightly eccentric, with its perigee slightly below and apogee slightly above geosynchronous altitude, at around 32,600 kilometers (20,300 miles, 17,600 nautical miles) and 39,000 kilometers (24,200 miles, 21,100 nautical miles) respectively. Inclined at 41 degrees to the equator, this orbit – shared with Michibiki No.1 and No.2 – will see the satellite move in a figure-eight pattern relative to the ground with its motion centered around a longitude of 135 degrees.
The QZSS-4 satellite was launched aboard Mitsubishi Heavy Industries’ H-IIA rocket, which is flying in its 202 configuration. The launch, designated H-II F-36, was the thirty-sixth flight of the H-IIA rocket. H-IIA, which first flew in August 2001, has completed thirty-four of its thirty-five flights prior to Tuesday successfully.
The only failure came on its sixth launch, in November 2003, when a solid rocket booster failed to separate resulting in the loss of a pair of reconnaissance satellites that had been aboard the rocket.
The two-stage H-IIA uses cryogenic propellants: liquid hydrogen oxidized by liquid oxygen. SRB-A3 solid rocket motors are attached to the first stage to provide additional thrust at liftoff, burning hydroxyl-terminated polybutadiene (HTPB).
Depending on the rocket’s payload and target orbit, two or four boosters can be used, with the third digit of the rocket’s configuration indicating the number of boosters. In the 202 configuration, which will perform Tuesday’s launch, two boosters are used.
H-IIA launches are made from Pad 1 of the Yoshinobu Launch Complex at Japan’s Tanegashima Space Centre. The Yoshinobu Launch Complex was first constructed in the 1990s for the H-II, the rocket that was replaced by the H-IIA.
It consists of two launch pads – Pad 2 was built in the early 2000s as a second pad for the H-IIA, but has been used instead by the larger H-IIB rocket.
H-IIA vehicles are integrated vertically away from the launch pad, atop a mobile platform which is used to transport it to the pad ahead of liftoff.
Shortly before the zero mark in Tuesday’s countdown, termed X-0 by JAXA, H-IIA’s LE-7A first stage main engine ignited. The SRB-A3 strapon boosters lit at X-0, and H-IIA F-36 began its ascent to orbit.
Ninety-one seconds into the flight, chamber pressures in the boosters drop off and the solids burned out, separating seventeen seconds later.
Following booster separation, H-IIA continued to fly under the power of its LE-7A engine. Four minutes and ten seconds after liftoff, with the rocket at an altitude of 151 kilometers (93.8 miles, 81.5 nautical miles), the payload fairing separated from around the QZSS-4 satellite at the nose of the rocket.
The first stage burn continued until main engine cutoff, or MECO, at six minutes and thirty-eight seconds mission elapsed time.
The spent first stage was jettisoned eight seconds after MECO, with the second stage igniting after a further six seconds. Powered by a single LE-5B engine, the restartable second stage made two burns to inject QZSS-4 into its initial transfer orbit. Its first burn lasted five minutes and 42 seconds, before the rocket coasted for twelve minutes.
At the end of the coast phase the LE-5B restarted for a second burn of three minutes duration. Fifty seconds after the end of the second burn, QZSS-4 separated into its geosynchronous transfer orbit.
Tuesday’s launch was the fifth of the year for Japan’s H-IIA rocket, and the sixth of 2017 overall for Japan. The country’s next orbital launch was scheduled to be of an Epsilon rocket with the ASNARO-2 satellite in mid-November. However, this has been delayed to resolve an electrical problem with the rocket.
The next H-IIA launch is expected to carry the Japan Aerospace Exploration Agency’s (JAXA) Global Change Observation Mission – Climate (GCOM-C) satellite, however a launch date has not yet been announced.
The QZSS launch will be the third orbital launch to be conducted in less than 24 hours, following China’s launch of the Venezuelan Antonio José de Sucre, or VRSS-2, satellite via a Chang Zheng 2D rocket and SpaceX’s launch of ten Iridium-NEXT satellites aboard a Falcon 9.
(Images via JAXA)