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2. The KITSAT-3 Ground Receiving Station
To begin with, let us describe the KITSAT-3 satellite
briefly. A technical detail of this satellite can be found in
the references (Kim et al., 1995a; Kim et al., 1995b). The
KITSAT-3 is the third series of experimental small
satellites by Satellite Technology Research Center at
Korea Advanced Institute of Science and Technology
(KAIST). This satellite is circulating an sun synchronous
low earth orbit with an altitude of 870 km from the ground
and producing high quality remote sensing images. This
has four scientific instruments-High Energy Particle
Telescope, Radiation Effect on Micro-Electronics,
Electron Temperature Probe, and Scientific
Magnetometer-and an imaging instrument (Kim et al.,
19953).
The imaging instrument has three channels and the
resolution of image is 17m. A standard scene (3456 x
3456 pixels) covers 59 x 59 km in the ground. The
pointing accuracy of this satellite is relatively low (0.5
degree) cause this satellite is “experimental” but the
platform can maintain its stability (0.014 deg/sec drift rate)
during the image capture. The size of a scene is about 36
Mbytes. The image data captured by the camera is stored
onboard solid-state mass memory devices (-20Gbytes).
These image data are transmitted to the ground receiving
station in X-band with a transmission rate of 3 Mbps.
Table 1 summarizes the system specification of the
KITSAT-3 and its camera system.
Table 1. System specification of the KITSAT-3 and its
camera system.
KITSAT-3 Weight 100 Kg
Power 100 Watt
Dimension 45x45X60 (cm)
Altitude 870 km
Pointing Accuracy ~0.5 degree
Attitude Stability 0.014 deg/sec
Camera Resolution 17-m
Pixel number per line 3456
Swath 59 Km
Compared with conventional remote sensing satellites,
the transmission rate of the KITSAT-3 is relatively low.
This makes the development of the ground receiving
system easier and less expensive. There is no need to
hire a dedicated high speed hardware to handle high
speed data. Cheap and conventional moderate speed
(in the order of several MHz) devices can be used. In
particular, such speed can be handled by a PC hardware.
This also gives a great opportunity to simplify the task of
the development of the ground receiving station as PCs
are normally easier to control.
The following picture is a block diagram of the KITSAT-3
ground receiving station.
Data from
Satellite
= e Down High Speed Exabyte Archiving
Receiving Convertor Recorder Driver Exabyte
Sheehan & Bit Sync. (Computer) Tapes
Frame op stn
Sync. Display Laz further,
Figure 1. A block diagram of the KITSAT-3 ground receiving station.
KITSAT-3 transmits data (image data + auxiliary data) to
the ground receiving station. The selected download
frequency for the KITSAT-3 is a X-band frequency. As
this signal has already been modulated on the satellite,
this undergoes a procedure of down conversion,
demodulation, and bit-synchronization. After this
procedure, a series of bit stream is created. This input
stream should be recorded using an appropriate device.
In case of commercial remote sensing satellites with very
high frequency, an appropriate device can be a High
Density Tape Recorder (HDTR), which is very expensive.
However, in case of the KITSAT-3 with the speed of 3
Mbps, it is possible to record the incoming stream using
less expensive devices.
A new concept of recorder has been developed. As the
85
speed of incoming bit stream is not very high, a dedicated
hardware (such as HDTR) can be replaced by a
commercial devices. The core of this new concept is the
use of a Personal Computer (PC) as a recorder; the
incoming stream is recorded in the hard disk of a PC. The
use of PC reduces the cost of the total ground receiving
station greatly as a PC is a lot cheaper than, for example,
a HDTR. Moreover, the use of PC reduces the complexity
of the development of the ground receiving station as a
PC is easier to control (than, for example, a HDTR).
A PC can be used as a recorder by using a PC interface
card to convert incoming stream into a writable word for
PC. The technique for designing a PC interface card is
well-known and not very complicated. As there are built-in
I/O routines for a PC, the development of (dedicated)
software can be done without great difficulties. When the
International Archives of Photogrammetry and Remote Sensing. Vol. XXXI, Part B1. Vienna 1996
