RADIOASTRON LINK BUDGETS FOR HIGH ORBIT L. D'Addario, 2 July 1998 Astro Space Center is now considering placing the RadioAstron spacecraft in a much higher orbit than was planned when the earth station was designed [1]. If adopted, the new orbit will have an apogee of about 300000 km and a variable perigee of 10000 to 80000 km. To accomodate the much larger maximum range (3.06e8 m vs. 8.0e7 m), ASC now plans to upgrade the on-board radio link complex (Russian acronym "VIRK") as follows [2]: Old value New value Data downlink transmitter power 10 W 40 W Data downlink antenna gain (15 GHz) 37 dB 40 dB Reference link antenna gain (up, 7.1 GHz) 23 dB 26 dB Reference link antenna gain (dn, 8.4 GHz) 24 dB 27 dB Reference link receiver noise 1000 K 100 K Here the antenna gains are minimum specifications as measured at the VIRK interface, and thus include all transmission line and pointing losses. Note that Lavachkin Association is responsible for meeting this specification, whereas ASC is responsible for VIRK (via their contractor, Russian Institute for Space Device Engineering). In this report, I calculate link budgets for the Green Bank earth station based on the new maximum range and the new VIRK specifications. The tracking station specifications are the same as those assumed in the detailed design report [3], except that the Demodulator efficiency is degraded slightly to the value achieved in later laboratory tests [4]. Similar link budgets have been computed for the DSN stations by Springett [5]. The results are given in tables on the following pages. I have not provided a budget for the reference downlink because the permitted long integration time (0.1 sec) implies a very large margin under all conditions (see [1]). In summary, the margins are slightly worse than originally planned, but still positive except under the worst planned atmospheric conditions (3 dB loss at 15 GHz). The latter are not expected to occur except at very low elevations during moderate to heavy rain. REFERENCES [1] L. D'Addario, "Radioastron communication link parameters," OVLBI-ES Memo No. 2, 27 May 1990. [2] B. Kanevsky and V. Andreyanov, presentations and discussions at meetings in Moscow, 16 Dec 1997. [3] L. D'Addario et al., "OVLBI Green Bank Earth Station Project: Report on the detailed design phase." NRAO internal report, available on request, 9 Oct 1992. [4] L. D'Addario, "Summary Of Demodulator Tests, July 1996," in Green Bank file '~ovlbi/doc/demodulatorTests796.txt'. [5] J. Springett, spreadsheet printouts dated 28 April 1998 and distributed at meetings in Pasadena 28-29 Apr 1998. RADIOASTRON HIGH ORBIT LINK BUDGETS -- GREEN BANK EARTH STATION 1. DATA DOWNLINK ================= General parameters: Frequency 15.062 GHz Max range 3.06e8 m Nominal Worst systems Worst systems Clear weather Worst weather --------------- --------------- --------------- Spacecraft Transmitter power, dBW 16.0 15.6 15.6 Antenna gain, dBi 40.0 40.0 40.0 (includes transmission line, polarization, and pointing losses) Medium Propagation loss, dB -225.8 -225.8 -225.8 Atmosphere loss (5d elev), dB -0.7 -0.7 -3.0 Atmospheric noise, K 43.2 43.2 144.7 Earth Station Antenna gain, dBi 62.7 62.2 62.2 Pointing loss, dB -0.2 -1.3 -1.3 Feed and optics loss, dB -0.3 -0.5 -0.5 Polarization mismatch, dB -0.2 -0.4 -0.4 Receiver noise, K 31.0 40.0 40.0 Ohmic loss noise (290K), K 19.4 31.5 31.5 Scattering and spillover, K 38.0 38.0 38.0 SNR Calculation Received power, dBw -108.5 -110.9 -112.8 System noise temperature, K 131.5 152.7 265.2 Noise PSD, dBW/Hz -207.4 -206.8 -204.4 Bit rate, dBHz (144Mb/s) 81.6 81.6 81.6 ------ ------ ------ SNR, dB (Eb/N0) 17.3 14.3 10.0 ==== ==== ==== Margin Calculation Required SNR, ideal condx, dB 9.9 9.9 9.9 (BER=1e-5, diff enc QPSK) Allowances for non-ideal condx: Spacecraft (modulator, filter) 1.0 1.0 1.0 Earth station (demodulator) 1.5 2.0 2.0 ----- ----- ----- Required SNR, practical, dB 12.4 12.9 12.9 ==== ==== ==== AVAILABLE MARGIN, dB +4.9 +1.4 -2.9 ==== ==== ==== RADIOASTRON HIGH ORBIT LINK BUDGETS -- GREEN BANK EARTH STATION 2. REFERENCE TONE UPLINK ========================= General parameters: Frequency 7.215 GHz Max range 3.06e8 m Nominal Worst systems Worst systems Clear weather Worst weather --------------- --------------- --------------- Earth Station Transmitter power (2W), dBW 3.0 0.0 0.0 Antenna gain, dBi 58.0 57.2 57.2 Pointing loss, dB -0.1 -0.3 -0.3 Feed and optics loss, dB -0.3 -0.5 -0.5 Polarization mismatch, dB -0.2 -0.3 -0.3 Medium Propagation loss, dB -219.3 -219.3 -219.3 Atmosphere loss (5d elev), dB -0.3 -0.3 -1.0 Background noise temp, K 270.0 270.0 300.0 Spacecraft Antenna gain (incl losses) dBi 26.0 26.0 26.0 Receiver noise, K 100.0 100.0 100.0 Ohmic loss noise (est.), K 100.0 150.0 150.0 SNR Calculation Received power, dBw -133.2 -134.5 -135.2 System noise temperature, K 470.0 520.0 550.0 Noise PSD, dBW/Hz -201.9 -201.4 -201.2 Bandwidth (PLL), dBHz 30.0 30.8 30.8 (1.0--1.2kHz) ------ ------ ------ SNR, dB (Eb/N0) 38.7 36.1 35.2 Margin Calculation Required SNR, dB 33.7 33.7 33.7 (0.996 coherence at 22 GHz) AVAILABLE MARGIN, dB +5.0 +2.4 +0.5 ==== ==== ====