S-band ground station prototype for low-earth orbit nanosatellite missions
TELECOMUNICAŢII ● Anul LII, nr. 2/2009 69
Table 3.5
GOLIAT nanosatellite downlink budget
Downlink Data Budget
Spacecraft
GOLIAT
(Elliptical; 71 deg. inclination; 357 x 1447 km Altitude)
Parameter Units Value
Elevation angle degree 15 25 45 65
Spacecraft Transmitter Power Output watts 1.0 1.0 1.0 1.0
dBW 0.0 0.0 0.0 0.0
dBm 30.0 30.0 30.0 30.0
Spacecraft Total Transmission Line Losses dB 1.0 1.0 1.0 1.0
Spacecraft Antenna Gain dBi 2.2 2.2 2.2 2.2
Spacecraft EIRP dBW 1.2 1.2 1.2 1.2
Downlink Path
Propagation and Polarization Loss dB 3.0 3.0 3.0 3.0
Propagation Path Length km 2224.2 1726.8 1202.3 980.0
Path Loss dB 167.0 164.8 161.7 159.9
Isotropic Signal Level at Ground Station dBW -168.9 -166.7 -163.5 -161.7
Ground Station (EbNo Method)
Ground Station Antenna Pointing Loss dB 0.5 0.5 0.5 0.5
Ground Station Antenna Gain dBi 35.4 35.4 35.4 35.4
Ground Station Total Line Losses dB 0.5 0.5 0.5 0.5
G.S Effective Noise Temperature K 585 585 585 585
Ground Station Figure of Merrit (G/T) dB/K 7.2 7.2 7.2 7.2
G.S. Signal-to-Noise Density (S/No) dBHz 66.5 68.7 71.8 73.6
System Desired Data Rate bps 9600 9600 9600 9600
dBHz 39.8 39.8 39.8 39.8
Data System Eb/No for the Downlink dB 26.7 28.9 32.0 33.8
Demodulation Method Seleted GFSK GFSK GFSK GFSK
System Allowed or Specified BER Rate 1.0E-05 1.0E-05 1.0E-05 1.0E-05
Demodulator Implementation Loss dB 1 1 1 1
Telemetry System Required Eb/No dB 13.5 13.5 13.5 13.5
Eb/No Threshold dB 14.5 14.5 14.5 14.5
System Link Margin dB 12.2 14.4 17.5 19.3
Our simulations has shown that a reliable com-
munication between Goliat and our ground station
prototype is feasible even in worst condition scenario.
The link budget may suffer further improvements.
3.5. Ground station installation and first tests
Interference is an important problem, since the
amateur radio service uses the relatively unregula-
ted ISM band. The widespread of devices which
take advantage of the ISM service has resulted in a
high level of noise through Cluj-Napoca region. Even
though, the ground antenna has a very tight 2.9º
main beam width, it will still receive these signals
through its side and back lobes. Signals received in
those lobes, will be more powerful than the heavily
attenuated signals from a nanosatellite more than
1000 km away, and therefore be sufficient to inter-
fere with effective modem operation.
(20 paginas)
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