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Japan -the sixth country with its own satellite navigation

PostPosted: Tue Jul 19, 2011 9:48 am
by spacesys
Japan made the first step towards building its own satellite navigation system, which would transform Japan into the sixth country owning this kind of applications.
Probably the best known is the American GPS system consisting of six orbital planes, each with four satellites (30 satellites being currently in operation). Similar systems are the Russian GLONASS system, using a different configuration (three orbital planes with eight satellites each, of which 21 are currently active), or the European Galileo system, still in the beginning phase, which will include until 2016 three planes of ten satellites each. Countries like China and India are also trying to secure their independence in this sensitive area of satellite navigation applications.

The Chinese Compass system will include five geostationary satellites and 30 satellites orbiting on MEO orbits, and will be operational by 2020.

India in turn has in plan to finish IRNSS (Indian regional navigation satellite system) until 2014- which includes three geostationary satellites and four MEO satellites.

Returning to JAXA’s program, its first satellite from the new QZSS (Quasi zenith satellite system) which will include two more platforms, is called Michibiki, a name chosen after an intensive PR campaign among the Japanese public and which could be translated as “guidance”.

The satellite is three axes stabilized, with a total mass of 4 tons in the form of a 2.9 x 3.1 x 6.2 m parallelepiped. It is powered by two LDAR (Large Deployable Antenna reflectors) solar panels with a span of 25.3 meters, generating 5 kW. It will operate for a period of approximately 10 years, in an orbit having an inclination of 45 degrees, with its apogee at 39.000 km and its perigee at 33.000 km.
Because of the orbit’s specificity, the satellite will move south or north, depending on the rotation of the Earth, ensuring seven to nine hours of visibility of the Japanese territory. Thus, a constellation of three satellites would provide a 24 hour a day visibility of Japan for local users. A 2D projection of the orbit would result in an ‘8’ type figure. In the end JAXA has chosen an asymmetric orbit which has the advantage of providing a bigger period in which the satellites would cross the Japanese territory and makes easier the signal transfer between satellites.
The satellite is built on an ETS-8 (Engineering test satellite) platform and will send four navigation signals in L1, L2 and L5 bands, compatible with GPS signals (the same central frequency, the same spectrum, the same structure of the message) but which will require special receivers from users, creating a local market for the standardization of such equipment.
Orbit or flight position correction maneuvers will be carried out with the help of one R-4D engine system, powered by N2O4/MMH and built by the Kasier Marquardt, a company which has a long history (their first model flew in the Apollo campaign, in 1966).
On board was a so-called "retro-reflector array” consisting of 56 retro-reflectors built in collaboration by Honeywell Technology Solutions Inc. and Instrumentation Technology Engineering Inc., reflectors which will allow fine measurements of the current orbit from the ground.
Additionally, the satellite is equipped with a TTS antenna used for calibrating two Rubidium Atomic Clocks, one L1-SAIF antenna which increases the power of the navigation signal, resulting in a positioning accuracy of less than one meter and finally a C-band antenna for bi-directional communication (telemetry and commanding).

The launch was done from Hangar One of Tanegashima Space Center, aboard a H-2A rocket. Launched Saturday, 11 September, at 11:17 GMT, the rocket successfully carried the satellite onto its orbit after a 28 minute and 26 seconds flight. The separation took place at 11:45 GMT, the first telemetry being provided by the ground station in Hawaii.
H-2A is a two-stage rocket capable of carrying a load of up to 10 tones on a LEO orbit (low orbit around the Earth) or equally cargo up to 3.8 tones to a GTO (geostationary transfer orbit) orbit.
53 m in length, weighing 289 tones, it is powered on the first stage by a LE-7A engine using liquid fuel; the engine provides a force of 1098 kN. The second stage is powered by a LE-5B engine, also fueled with liquid fuel and providing a traction force of 137 kN. Depending on the specific of the flight, a system of auxiliary “booster” engines which use solid fuel can be mounted on the rocket. The variants available for this purpose are SRB-A engines (with a traction force of 5040 kN) and SSB engines (with 1490 kN of traction force).
In this particular flight, named F18, the H2A202 version was used, meaning that two SRB-A type systems of “boosters” were mounted on the rocket.
A previous flight was conducted in May 2010, when several small satellites (Planet-C, Ikaros, K-Sat etc) were launched together.

So how does the new system really work? QZSS shouldn’t be seen as a stand-alone system, but merely as a complement to the American GPS. The first talks between US and Japanese representatives- which started targeting signal compatibility and interoperability of the two systems- began in September 1998 when the two administrations established the so called agreement "Joint Statement by the Government of the United States of America and the Government of Japan on Cooperation in the use of the Global Positioning System”.
As it is well known, for a complete determination of a position, at least four GPS satellites are needed.
However, in Japan, because the country’s specifics (mountainous terrain, agglomerate cities with tall buildings etc.) many obstacles tend to reduce signal quality or even lessen the amount of time in which satellite navigation is available.
For example, when using only the GPS signal, positioning accuracy is limited to 10 m while in case of simultaneous use of GPS and QZSS signals the accuracy will grow to 1 m in the first stage of the project (and even up to a foot in the future).
Availability will also increase from an average of 90% (when using at least four GPS satellites, which most of the time are available at an elevation greater than 20 degrees over Japan) to a value of 99.8% using the complementary QZSS system.
The power on time that electronic equipment needs to determine its position is expected to drop from 30 - 60 seconds now to only 15 seconds with the help of QZSS, while an abnormality in one of the navigation satellites (whether we are talking about GPS or QZSS) will be reported in less than 20 – 30 seconds.
Besides classical applications, the QZSS system will bring major improvements in other areas as well – for example, in the prevention of disasters. Here because of the increase of accuracy, the current tsunami warning buoys which are currently located at maximum 20 km away from the continental monitoring stations will be located at larger distances than today (meaning there will be a better reaction time and obviously better chances for local authorities to evacuate the population).