Aerospace and Electronic Systems - May 2019 - 26

Reconﬁgurable Wavelet Based Real Time Imaging System for Low Bit Rate Telemetry Space Missions
Table 2.

SPACE QUALIFICATION OF THE SYSTEM

Comparison R-D Performance and Various Code Block
Sizes with the (9,7) Filter-Bank
Rate
(bits/
pixel)

Average PSNR in dB

64 Â 64

32 Â32

16 Â 16

8Â8

0.0625

22.94

22.89

22.73

22.35

0.125

24.95

24.87

24.68

24.24

0.25

27.72

27.63

27.34

26.75

0.5

31.46

31.34

30.95

30.16

1.0

36.34

36.20

35.79

34.82

2.0

42.58

42.36

41.94

40.83

COMPRESSION RATIO
The compression ratio is appropriately selected to get
reasonably high-quality images. The color component is
subsampled and compressed to a higher level without
much visual degradation. The compression ratio can
be varied but it is kept fixed for a particular mission. It is
chosen depending on the available bit rate, an event to be
captured and available ground station visibility for transmission of the stored images. Compression Ratio has been
varied from 20:1 to 50:1 for various missions.

PROGRESSION ORDER
The order in which packets appear in the code stream is
called the progression order and is controlled by specific
markers. "Layer-Resolution-Component -Position"
progression order was selected for our application. The
compressed information is organized so that as more of the
compressed data stream is received, reconstructed images
of successively higher overall quality can be reproduced.

Video Imaging System is qualified to meet the anticipated
severe environments such as vibration, shock, temperature,
Electro Magnetic Interference (EMI) etc., radiation and
vacuum (for interplanetary missions) which the systems
will experience during different phases of the mission.
A fault tolerant, high-reliability system design is followed
to ensure the performance of the system under various
stressed conditions. Both component level tests, as well as
system level tests described below, are carried out in the
facilities at Vikram Sarabhai Space Centre, India.

COMPONENT LEVEL TESTS
For critical space applications where the success or failure
of a mission hinges on the lifetime and performance of a
single device, it is critical that all aspects of the reliability
and the various known failure modes and mechanisms be
addressed prior to the insertion of the component in the
application [11].
Selection of reliable components is an important factor
in ensuring the reliability of the system. A Failure Modes
Effects and Criticality Analysis is carried out to analyze the
potential failure modes, criticalities within the system for
classification by severity and determination of the effect of
failures on the system. The devices are subjected to a series
of electrical and environmental stresses so that the weak
devices are removed from the lot by subjecting each device
to failure detection tests such as visual inspection, environmental tests, hermetic tests, thermal cycling, etc.
For deep space missions, in order to ensure that the
systems do not affect other sensitive elements in the neighborhood by way of outgassing, total mass loss (TML) and
collected volatile condensable material (CVCM) are
measured. TML of 0.1% and CVCM of 0.01% have been
used as screening levels for rejection of spacecraft materials. The devices are wrapped with a thin sheet of tantalum
to further protect them against ionizing radiation.

SYSTEM LEVEL TESTS
REAL TIME DISPLAY AT GROUND
During the course of flight of launch vehicle or interplanetary probes through space, all measurement parameters
are sent through a wireless link to earth. Ground stations
located in different parts of the earth receive these signals.
Image data, which is a part of this telemetry, is stripped
from the total telemetry data and sent through optical
cables to the real-time display mission consoles.
The real-time decompression and display software
running in the console will decompress the data in real
time, create images, and display on the monitor. The
console is operated at Sriharikota, India.
26

The system experiences static and dynamic loads during
the flight of the launch vehicle. It also experiences temperature variations, thermo vacuum, and dynamic disturbances in the orbit. The environmental tests are designed to
ensure reliable performance of the system at the ground,
flight and on-orbit environments.
Thermo vacuum test provides assurance that component subassemblies will operate successfully in the
thermal extremes and vacuums of space. These tests will
ensure design margins in extreme temperature condition.
Vibration tests are carried out on the subsystem to eliminate the possibility of any workmanship defect, which
will deteriorate the performance of the subsystem. Shock

IEEE A&E SYSTEMS MAGAZINE

MAY 2019

Aerospace and Electronic Systems - May 2019

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