X-Sat

X-Sat is a microsatellite developed and built by the Nanyang Technological University (NTU) in collaboration with Defence Science Organisation (DSO) Singapore. The satellite was launched by ISRO's PSLV-C16 on 20 April 2011 from Satish Dhawan Space Centre FLP in Sriharikota, India. The satellite was launched along with Indian ResourceSat-2 and Indo-Russian YouthSat.

The objective of the X-SAT mission is to demonstrate technology in support of high-resolution imaging capabilities and to analyse and implement onboard parallel-processing algorithms, thereby demonstrating improved mission achievements for generally downlink-limited small satellite imaging missions.

Objective

• Earth observation and imaging for environmental applications such as monitoring of forest fires and ocean red tides, with a 10 m resolution multispectral (three spectral bands in the visible and near infrared spectrum) instrument as a primary payload.
• Satellite-based data acquisition/distribution and messaging using mobile terminals.

Payloads

The satellite carries three payloads, namely the imaging system IRIS, the communication platform ADAM, and the Parallel Processing Unit (PPU) for image processing. Further research experiments using the communication and navigation instruments on-board will be conducted to investigate atmospheric question and communication related issues.

IRIS

The camera is built by SatReCi and designed as a push-broom scanner with three individual scan lines in the green (520 nm – 600 nm), red (630 nm – 690 nm), and near-infrared (760 nm – 890 nm) wavelength range. The three linear detectors consist of 5000 active elements each, which were all manufactured on the same wafer and subsequently coated with different interference filters to select the appropriate spectral characteristic. The design provides a high degree of band-to-band alignment, i.e. 0.1 pixels. The provided spatial resolution will be 10 m for the nominal altitude of 685 km, thus enabling a swath width of 50 km. The optics were designed as a variant of the Mangin telescope with a primary and secondary mirror as well as two correction lenses and has an aperture diameter of 120 mm. Internally the IRIS is equipped with a redundant signal processingand control module, which pre-processes the image data for the storage in the 8 Gbit large memory module. This bulk storage module is entirely under the control of the IRIS.

ADAM

The instrument is a two-way low-data-rate communication link using Ultra high frequency (UHF) to acquire oceanographic data, e.g. temperature, salinity, and water pressure, from autonomous, operating buoys that drift in the open sea. Further applications are in aeronautics, search-and-rescue missions, as well as in land-based data collection. For the downlink of the gathered information to the individual ground receiving station the satellite's S band transmitter is utilised.

Parallel Processing Unit

The third payload is the PPU that will provide processing of acquired imagery on a parallel architecture. The objective is to increase the mission's benefits by enabling unsupervised data processing in space and therefore easing the bottleneck of transmission to the ground receiving station. The computer consists of four fully connected radiation-hardened Xilinx Virtex FPGAs (Field-programmable gate arrays) with each of it hosting four processing nodes (PN). In addition, spare processor nodes are kept available in case a regular PN will become inoperative due to the environmental conditions. Every node comprises a StrongARM processor that is clocked at 100 MHz and 64 MByte of local memory (SDRAM). The choice for this processor was determined through its 0.35 mm manufacturing process, i.e. the relatively small sensitivity to radiation, and the provided performance energy ratio of 115 MIPS / 200 mW.

External links

• NSSDC ID: 2011-015C
• Homepage
• A few photographs of the development process
• Academic paper discussing the design of the X-Sat PPU
• The X-Sat PPU: designed to be the first Beowulf cluster in space