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Japanese Data Relay Satellite JDRS-1

A relay satellite is an effective measure for increasing downlink availability in JAXA’s satellite grid. The downlink time window for most LEO satellites is 10 minutes to 1 hour. With a data relay satellite like JDRS, that time window can be expanded up to 9 hours, increasing the amount of data that can be downlinked from the original LEO satellite. With a time window increase also comes an effective position increase, allowing the LEO spacecraft to be out of range of its ground station but still able to communicate with the relay, and thus still able to communicate by proxy to its ground station. This greater site diversity has the potential advantage of not only reducing the complexity, weight and cost of equipment carried by JDRS, but also mitigating the attenuation effect of clouds on optical signals by routing traffic around it.

Japan successfully launched an H2A rocket carrying a new Japanese Data Relay Satellite JDRS-1 from the Tanegashima Space Center in southern Japan. It was the 43rd launch of this type of rocket. The launch took place at 4:25 p.m. on 29 November 2020. The rocket rose steadily and separated from its booster. It released the satellite 30 minutes after liftoff at an altitude of 300 kilometers as planned. It was confirmed that the rocket flew as planned and successfully separated the data relay satellite No. 1 and the optical data relay satellite.

The JDRS-1 will relay optical and radar data from Japan’s Information Gathering Satellites (IGS) and other data from science satellites to Earth. Few details of the satellite have been revealed due to the largely military nature of its mission. The satellite will transmit high-speed data and images of the Earth to a base station, as well as other data for the Cabinet Satellite Intelligence Center. The Cabinet Satellite Intelligence Center owns and operates the satellite, with JAXA responsible for the optical data relay function. The satellite used its own engine to enter orbit 36,000 kilometers above the equator.

On November 29, 2nd year of Reiwa, Prime Minister Suga Yoshihide stated "Today, the H-IIA Launch Vehicle No. 43 was launched from the Tanegashima Space Center, and the on-board data relay satellite No. 1 was put into the specified orbit. The government will make the best use of information gathering satellites including this data relay satellite No. 1 and will continue to make every possible effort for Japan's security and crisis management."

The satellite can transmit data for nine hours per day on average, or nine times more than the previous model. The JDRS-1 replaces the “Kodama” Data Relay Test Satellite (DRTS) launched in 2002 and operational through August 2017. By 2017 JAXA had initiated a new data relay satellite programme which adapts optical communication in the inter-orbit link. The program includes development of a data relay satellite and optical terminals both for GEO (i.e. the data relay satellite) and LEO, Ka feeder link system to communicate between the data relay satellite and ground stations and has data-relay service capability up to 1.8 Gbps.

The prior issues with this technology are different whether the transmission link lies in the vacuum or in the air, and the practical use began in the inter-satellite communication systems whose transmission link is ideal for the laser propagation. Japan follows similar scenarios, and planned to launch a data relay GEO satellite having Free Space Optical [FSO] system only for inter-satellite use in 2019, and another GEO satellite in 2021 with which the technologies for optical feeder link systems will be tested.

JDRS includes a Gbps-class laser communication system, further maximizing data throughput. Since the satellite is small and has low SWaP, multiple lasercom systems can be linked to it, allowing several LEO spacecrafts to use the relay at the same time. The laser operates at 1550nm, contains built-in error correction code, and can operate for GEO and LEO satellites. The total effective data rate is 2.5Gbps for a return link (downlink) and 60Mbps for a forward link (uplink). The designers of JDRS have planned to include WDM capability after the satellite has obtained orbit.