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The Japan Aerospace Exploration Agency (JAXA) launched new research aiming at realizing low resource and frequent space science mission. We report the development activity for realizing miniaturization of onboard equipment using SpaceWire. The technology development target is the miniaturization of onboard units, which are small enough for deploying interplanetary mission with small rockets as Epsilon Launch Vehicles. Since SpaceWire interface consists of full digital circuitries and its communication protocol enables hardware implementation, Large Scale Integration (LSI) technology, surface mounting technology (SMT), and ceramic ball grid array (CBGA) packages are exploited for the miniaturization of onboard equipment with communication interfaces. The preliminary result shows that one half and/or one third in scale and mass can be realized.

We developed a rewritable field programmable gate array (FPGA) using NanoBridge® that exploits atom switch technology. NanoBridge® is newly developed copper wiring technology with dynamic connection capability. Programmable circuitry with SpaceWire interface is realized without configuration memory cells for storing circuit connection information. It prevents single event effect caused by radiation and provides remarkably low power consumption. The first demonstration of the NanoBridge® FPGA on orbit by JAXA's program is planned in 2018.

SpaceWire is valuable because it facilitates the development of spacecraft subsystems such as payload instruments, mass memory, and onboard computers. On the other hand, it takes much time and effort for developers to configure an initiator of the SpaceWire network because they have to take account of the entire SpaceWire network in a spacecraft. As the target network becomes larger, the path addressing and the packet collision-free timeslot allocation are harder for the developers to configure. Furthermore, the configuration tables of the initiator should satisfy various constraints, such as the bandwidth limitation and priority of specific packets. These constraints are different in each spacecraft. In order that the developers can design the large-scale SpaceWire network efficiently, automatic configuration table generation under the constraints is indispensable. This paper presents a constraint-based configuration table generator (CTG) that automatically provides reliable redundant path routing and collision-free timeslot allocation for required transactions in the target topology. We apply a constraint solver to the CTG to set many kinds of user-defined constraints in the network. For example, the bandwidth limitation, priority of the packets, and other various constraints can be easily inputted into the CTG. The CTG automatically generates configuration tables satisfying these constraints. Additionally, the CTG reports network topology views with bandwidth utilization ratios. This helps developers to verify whether a generated configuration is just as designed. The CTG can also notify developers that their requirements cannot be solved. In this paper, we show the feasibility and effectiveness of this tool through evaluation using a large-scale SpaceWire network case.

The ASTRO-H, which will be launched in 2015, is the sixth in a series of Japanese X-ray satellites. It is an international mission led by JAXA in collaboration with NASA and ESA, aiming to observe astrophysical objects in the X-ray band from 0.5 to 600 keV. One of the important scientific goals is to understand physical processes in the extreme environments of active and variable astrophysical objects, such as black holes, neutron stars, binary star, and active galactic nuclei. Therefore, a fast timing capability is a key requirement for the mission. According to numerical estimates of scientific performance, absolute times of X-ray events are required to have an accuracy of 300 µs to achieve minimum scientific goals and an accuracy of 30 µs is desired as a goal. The satellite carries a GPS receiver to get the accurate time information, which is distributed from the central computer on board through the large-and-complex SpaceWire network. Distributions of time information are shared in the same lines used for communications of telemetry and commands, and thus propagation delays and jitters affect the timing accuracy of the payload instruments. Further six items are identified as sources of timing errors and are measured on ground to be used in the calibration by off-line software. The time-assignment tasks in the off-line software packages are designed to be common for all the scientific instruments, although the hardware designs for finer timing resolutions are different by the instruments. Measurements of propagation delays in the flight configuration on ground and in-orbit calibration plans are described. The detail description will be submitted to the IEEE TNS paper in near future. This work demonstrates a good example of care points for space-use instruments in the hardware-and-software designs and calibration measurements in order to achieve a fine timing resolution at the micro second order with the middle-sized satellites using the SpaceWire (IEEE1355) network.

SpaceWire-R is a protocol that provides onboard applications with reliable high-speed data transfer services over SpaceWire links especially for mission data transmission between sensors and data recorders. Independent implementations on different hardware with reference to the draft specification have been succeeded in interoperability test, which resulted in consolidating the protocol. The final specification document has been under preparation by JAXA. The present paper describes a result of interoperability test and evaluation of SpaceWire-R performed from 2013 to 2014.

Conventional protocols have been integrated with SpaceWire through service oriented approach with reference to SPACECRAFT ONBOARD INTERFACE SERVICES (SOIS). The design framework is based on the definition of determinism provided by SpaceWire-D draft standard in order to keep established services inherited from previous satellite projects. The implementation result is under evaluation in order to establish the consistency with the draft standard of SpaceWire - Plug-and-play protocol. This paper describes the integration approach and the evaluation of implementation experience.

A new SpaceWire router architecture with packet segmentation and multiplexing capability is presented. The aim is to resolve a blocking phenomenon, or an increase of packet transfer latency, that can happen in a SpaceWire network formed by ordinary SpaceWire routers. To resolve the blocking of packet transfer in a router caused by worm-whole routing of a preceding packet, we designed, implemented, and tested, a non-blocking packet transfer mechanism that uses the SpaceWire-R protocol for segmentation of packets, acknowledgement, multiplexing of segments, and management of an end-to-end communication channel. The mechanism is implemented as an extension to an existing SpaceWire router. The SpaceWire-R part is implemented as an extension module to the existing SpaceWire router VHDL IP core, and we do not modify SpaceWire router specification at all. Details of the architecture, implementation result, and performance evaluation result are shown in the present paper.

Thermal infrared imager system is developed for HAYABUSA2, which is planned to be launched in 2014 and aims at sample-return from a C class near-Earth asteroid 1999JU3 considered to contain organic or hydrated materials. The system consists of a thermal-infrared imager (TIR) and a digital electronics, which is used not only for the scientific investigation of physical properties of the asteroid surface, but also for the assessment of landing site selection and safe descent operation onto the asteroid surface with in situ measurement. Since round trip communication time between the asteroid and the Earth is more than thirty minutes, onboard automatic data processing function and high speed data recording capability are provided to exploit the limited downlink capacity which is up to 32kbps. TIR adopts an uncooled bolometer with 320 x 240 effective pixels. Image operations as multiple images summation, dark image subtraction, and the compensation of dead pixels are processed onboard. A processing module is connected to sensor interfaces through SpaceWire in order to provide deterministic processing time. Data compression is also provided to reduce restriction on storage capacity and operation time, which provides the equivalent compression ratio as JPEG2000 in 1/30 processing time in average. A high speed data recorder is also connected through SpaceWire in 50Mbps in order to record TIR data in parallel with other sensor data. The modularity of SpaceWire enables to use as built devices for TIR and inherits the same design as the long-wavelength infrared imager developed for the Venus climate orbiter Akatsuki.