A Low Cost Portable Telemetry
and Telecommand Station For The Brazilian
Data Collecting Satellites
Mário Eugênio
Saturno Carlos Eduardo
Santana Jânio Kono
saturno@dea.inpe.br santana@dss.inpe.br kono@dss.inpe.br
National
Space Research Institute (INPE)
São José dos Campos - SP -
Brazil
Phone:
55-123-25-6186, Fax: 55-123-25-6225
Abstract
The first Data Collecting Satellite Brazilian, developed by the National
Space Research Institute (INPE), has completed three and half years of
successful operation in orbit. The launching characteristics required INPE to
develop a Portable Telemetry and Telecommand Station (TTS). The hardware
developed is distributed in two boards installed in an IBM-PC compatible
computer. The TTS can also retransmit telemetry data to another station through
a common telephone line and a pair of modems. The TTS software was designed so
that system reconfiguration is done easily using a text editor and was
implemented very fast, in four months, mainly due to the use of Pascal language
and reuse of existing modules. Besides all the Satellite Functional tests done
in the launch Campaign, the TTS was also used to control the satellite during
the first three orbits. This success encouraged INPE to develop a new TTS based
on DSP technology and notebook computer.
1 - Introduction
The Brazilian National Space Research Institute (INPE) developed the
first Data Collecting Satellite (SCD-1). The SCD-1 is a low earth orbit spin
stabilized satellite, 25 degree inclination and 750 km altitude. It is a
dedicated satellite to the collection of environmental data emitted by Data
Collecting Platform (DCP) distributed over Brazilian territory. The DCP is
small automatic, unattended earth station which collects weather and other
local environment data for transmission to satellite in short intermittent
bursts[1].
The SCD-1 Service Telecommunication (TMTC) and On-Board Supervision
subsystems are composed by S-band antennas, transponder, TC decoder, TM encoder
and an On-Board Computer. The TM and TC frames follows the ESA format [2,3].
The SCD-1, launched by the Pegasus launcher at February 9, 1993, has completed
three and half years of successful operation in orbit. The next satellite, the
SCD‑2 is similar to the first, it is ready and a launcher is being
procured.
During the SCD-1 Assembling, Integration and Testing activities, a
conventional check-out system based on HP‑1000 minicomputer, a telemetry
receiver and a telecommand generator equipment was used. This type of check-out
system is heavy, big, complex, and needs air-conditioning. The launching
characteristics of Pegasus required SCD-1 check-out tests to be performed in
several and adverse conditions, including at the airport runway before the
launch with the launcher integrated in the aircraft. This requirements includes
portability, simplicity, use of an IBM-PC compatible computer, high level
language, software reconfiguration facilities.
2 - Portable Telemetry and Telecommand
Station general requirements
INPE had to develop a Portable Telemetry and Telecommand Station (TTS)
to support all the Satellite Functional tests done in the launch Campaign. The
TTS requirements are:
1) be portable;
2) distribute the hardware in ISA boards;
3) use an IBM-PC like as platform;
4) receive and store telemetry;
5) visualize telemetry in real time;
6) export telemetry data to a file;
7) display TM parameters out-of-limits;
8) transmit On/Off and On-Board Computer telecommands and make a log;
9) retransmit TM to a remote station through phone line;
10) and reconfigurate using a text editor: telemetry screens, calibration
curves, telecommand sequences.
3 - System description
INPE had already developed a test equipment to test the On-Board
Computer based on an IBM‑PC compatible computer. The hardware could send
NRZ‑L telecommands and receive PSK modulated telemetries[4]. The TTS was
upgraded to send PSK modulated telecommands. The software already developed
comprises of receive and store TM and send TC. The TTS software was upgraded to
monitor real time TM requiring a good user interface. Figure 1 shows the TTS.
TC Video (PSK) Umbilical TM Video (PSK) 
Figure
1 - TTS
3.1 - TTS Hardware
The Portable Telemetry and Telecommand Station was developed using an
IBM‑PC compatible computer as platform. The hardware developed to send
telecommands and receive telemetries is distributed in two boards. The TC bit
rate is 2000 bit/s, the modulation is BPSK, the code is NRZ-L, ouput level from
0.5 to 8.0 Vp (adjustable) and impedance 50 W. The TM bit rate is 2048 bit/s, the modulation is BPSK, the code is
Bi-phase-L, input level from 0.5 to 5.0 Vp and impedance 50 W.
The telecommand generator is composed of an NRZ data encoder and a PSK
modulator. The Telemetry Receiver is composed of a Bi-Phase decoder, PSK
demodulator, and a bit synchronizer. Figure 2 presents the TTS Hardware Block
Diagram. The TM reception is implemented using interruption.
