IRIS Primary Payload

The IRIS system consists of two units, Electro-Optical Unit (EOU) and Processing and Control Unit (PCU). Figure 1. shows the simplified preliminary system block diagram.

EOU consists of the Telescope and the Focal Plane Assembly (FPA). The Telescope is made of various optical and structural components. FPA houses three linear detectors and the front-end electronics (FEE). Within FEE, low-level video signal conditioning and clock pulse generation are performed. Within EOU, there are two survival heaters for Telescope and FPA. These heaters are under direct control of the spacecraft bus.

PCU consists of four electronics modules in a single mechanical box. The Power Supply Module (PSM) generates electrical power supplies for other modules from the unregulated bus power of +24 ~ 32 V. The Signal Processing Module (SPM) processes and digitizes video signals and transmits the digital image data to the Control Module (CM). As the heart of the IRIS system, CM performs the management of the overall system through a serial communication link with the command and data handling subsystem of the spacecraft bus. It also performs the maintenance of the stored image data. It can transmit either quick-look image data or stored image data through the transmission subsystem of the bus in high speed.

Figure 1 Preliminary System Block Diagram of IRIS

The preliminary specifications of the IRIS system are listed in the following table: These figures are subject to change as the development progresses and in accordance with the development of interfaces with the spacecraft bus.

 

Item	Specification	Remarks
Spectral bands	0.52 ~ 0.60, 0.63 ~ 0.69, 0.76 ~ 0.89mm	Nominal
Ground sample distance (GSD)	10m	@ 685 km & nadir
Swath width	³ 50km	@ 685 km & nadir
Modulation transfer function (MTF)	³ 15%	@ pixel Nyquist frequency for all bands
Signal-to-noise ratio (SNR)	³ 100	For ρ = 0.25, θz = 60 °
Signal Quantization	10 bits	8 bits used
Signal Gain	Programmable
Data Storage capacity	8 Gbits	@beginning of life
Power Consumption	<25 W	Peak Value
Dimensions (mm)	EOU: f180 ´ 530 PCU: 320 X 210 X 150
Mass	< 12 kg	Total Value
Data Transmission	TBD

The preliminary hardware component breakdown structure for IRIS is shown below:

Figure 2 Preliminary System H/W Configuration

The key features of EOU and PCU are shown in below tables:

EOU	Feature	Remarks
Spectral Bands	0.52 ~ 0.60, 0.63~0.69, 0.76 ~ 0.89mm	Nominal
Pixel Pitch	7mm
Active pixels	³ 5,000	Per Band
IFOV	14.6 mrad
Aperture	120 mm	Diameter
FOV	4.6 °
EFL	480 mm
F-Number	4
Distortion	0.5%
Band Registration	< 0.5 pixel
Obscuration	0.25	Area
MTF	44% : Optical Design 55%: FPA 15%: System	@ 71.4 cycles/mm
SNR	³ 100	For ρ = 0.25, θz = 60 °
O/P Data Rate	³3.4M pixel per second	Analog per band
Natural Frequency	³ 100 Hz
Dimension (mm)	< f180 ´ 530
Mass	<7.3 kg

 

PCU	Feature	Remarks
Signal Gain	Programmable
Offset Correction	Automatic + Programmable
Input Voltage	+24 ~ 32 V	Regulated or Unregulated
Power Consumption	<25W	Including FPA
I/P Data Rate	³ 3.4M pixel per second	Analog per band
I/P Data I/F	3 coaxial cables
Micro-processor	TSPC68360
Bus Communication	UART Serial Link
FPGA	Radiation-tolerant ACTEL Series
Storage capacity	8 Gbits	@ Beginning of life
Quick-look data	Supported
O/P Data Rate	30 Mbps	Baseline (TBD)
O/P Data I/F	I, Q, Clock	Baseline, TTL for QPSK
Natural Frequency	³ 100 Hz
Dimension (mm)	< 320 X 210 X 150
Mass	< 4.5kg

Summary (as at April 06)

The IRIS modules (EOU and PCU) has been subjected to thermal tests and random vibration tests in Dec 05, and its preliminary findings were that the EOU can withstand the anticipated launch environment although its optical performance (MTF) was found to be below specifications. The EOU would be re-manufactured and the entire modules are scheduled to be delivered by Jun06.

The above pictures show the EM/QM EOU (Left) and PCU (Right).