National Astronomical Observatory of Japan Yusuke Kono VSOP-2 Link System National Astronomical Observatory of Japan Yusuke Kono

Outline Onboard Link system update Frequency selection General over view Ka-band OBS frequency changed Frequency selection Downlink 37.5GHz or 26GHz? The common design of Tracking station

Observation System × × × × × × Observation Frequency Q-band: 41 - 45 GHz K-band: 20.6- 22.6 GHz X-band: 8.0 - 8.8 GHz Intermediate 6.6- 8.8 GHz Base Band 1.3 GHz Q-band (R) LNA × LO (36/34GHz) ～ Q-band (L) LNA × K-band (R) LNA × × ADC DF MOD IF-SWITCH (6 to 2 ) LO (29.2GHz) ～ Synthesizer Ka-TX K-band (L) LNA × × ADC DF 1024Mbps Synthesizer VLBI DATA Rate: 512/256 Msps Bit: 1/2 bit Channel: 2 ch X-band (R) LNA X-band (L) LNA GRT: 512Msps(2bit) or 256Msps(2bit) expected

Ka Antenna Diameter 80cm Efficiency 70 % WaveGuide&Rotary Joint TWTA(20W) inside 60W power consumption radiated through a heat pipe to space

Link frequency selection : Frequency Allocation Uplink Three Space Research bands in 13~17GHz are hopeless (JAXA Frequency room) 13.25-14.3 GHz , 16.6 - 17.1 GHz ,17.2-17.3. GHz Uplink is 40 GHz Downlink 26GHz and 37.5 GHz possible 26 GHz band will be heavily used by the time that VSOP-2 is launched. Many missions are being planned for this band including NASA's Lunar Exploration Missions, some L1 and L2 missions like JWST, and some wideband low Earth orbiters like NOAA's NPOESS.  Most of these missions will receive higher priority than VSOP-2 if there is a need for coordination. 37.5 GHz is wide open and there won't be any need for coordination or worries about interference to VSOP-2 or from VSOP-2 to other missions.

Link frequency selection : Ionoshphere VSOP-2 OBS/link simulation (by Dr.Asaki) Software: ARIS MS-TID (Medium Scale Traveling Ionospheric Disturbance) ~0.2TECU Zenith TEC bias error~6 or 60 TECU Conclusion Ionosheric effect of 37.5GHz is smaller than 26GHz Tropospheric error in fringe phase of VLBI observation is outstanding. 40/26 and 40/37.5 GHz system possible

Onboard Lo-Phase (Zenith TEC Bias : 6 TECU) 40GHz/26GHz 40GHz/37GHz 43GHz: 15.0 deg 22GHz: 7.9 deg 43GHz: 1.9 deg 22GHz: 1.0 deg Black: 43GHz Red: 22GHz

Space-VLBI Fringe Phase (MS-TID , Zenith TEC Bias : 60 TECU) 60 min (Tropospheric and Ionospheric Errors) 40GHz/26GHz 40GHz/37GHz Black: 43GHz Red: 22GHz

43GHz Coherence No difference 22GHz Coherence No difference

Link frequency selection : Link margin ------------------------------------------------------ Link design 26GHz 37.5GHz d(26-37.5) TX Gain dB 45.2 48.4 -3.2 Feed Loss dB -4.2 -5.5 1.3 Space LossdB -210.3 -213.4 3.2 Rain Loss dB -4.6 -8.1 3.5 Atm Loss dB -1.7 -2.2 0.5 RX Gain dB 64.9 67.2 -2.3 (AE 34, 42%) Tsys dB -23.7 -24.6 0.9 Total dB 3.9

Rain condition of UDSC One-hour rainfall data at Usuda deep space center Nov.9,2005- Nov.9,2006 Time (2mm/h) is 2% of time!

Interference of 26GHz to K-band LNA Less than -60 dBm (Tx 20W, Off-beam interference, space loss) < LNA saturation level +9dBm

Technical easiness 26 / 40GHz Wider frequency range than waveguide and waveguide Rotary joint frequency specification (26.5-40 GHz) More complicated Ka-ant system Setting TX-HPA at the top of the boom is not good for thermal control

Link frequency selection: summary The downlink of 26GHz has several attractive merits comparing with 37.5 GHz. But, It is too severe to get the 26 GHz band allocation 40/26GHz link will increase complexity of the onboard system Construction cost of the s/c same 40/37GHz link is also feasible The downlink of 37.5 GHz proposed

AE of UDSC

The common design of Tracking station Based on Halca method NRAO GB project book

Functional requirement 1 Radio links to s/c Astronomical data downlink Time transfer uplink Time transfer downlink Realtime signal Processing Astronomical data Time transfer

Functional requirement 2 Interface From mission operation From orbit determination center To correlation center To orbit determination center To mission operation

Functional requirement 3 Automation Normal operation Recovery from link dropout Recovery after station power failure

System design 1 Main antenna Feed and Optics RF subsystem Wideband data subsystem Two way timing Reference distribution Control and monitoring

System design 2 Design principles Compact design Careful choice of reference signals Wideband design Avoidance of ALC loops Use of exiting design whenever possible Built-in test facilities and monitoring

System design 3 Link budget Downlink

System design 4 Link budget two way timing

System design 5 Required Dynamic range Packaging and cabling

Required basic function of Onboard link system Data transmission 1024 Mbps QPSK, Diff.Enc 37.5 GHz, 20 Watt (-2dB Backoff) EIRP 83.9 dBm 80cm HGA, RHCP TLM (bitrate TBD) data merged Coherent transponder Uplink carrier receiver

Required basic function for tracking station 1 Standard clock transfer Uplink transmission Carrier of 40GHz, EIRP 93.5 dBm, RHCP Downlink carrier recovery Carrier of 37.5GHz, RHCP Measurement of phase difference between up and downlink DeltaT correction file output Doppler compensation by prediction

Required basic function for tracking station 2 Data downlink demodulation 37.5 GHz QPSK, RHCP Required BER 1E-2 Data and carrier recovery Data storage Data Storage 1024Mbps, 11 T Byte / 24h VSI-H&S compatibility (for correlators) Realtime/quasi-realtime TLM QL

Principles of BER The cross-correlation SNR or sensitivity of the spacecraft data (with transmission errors) against ground telescope data (no quantization bit errors) is degraded by the BER loss factor VSOP is designed for BER = 5E-4, so its factor is negligible. The calibrated sensitivity loss for the best ground radio telescope is taken to be 2% (0.980). Correspondingly, BER = 1E-2. Designing for BER = 1E-2 is a strictly worst-case condition. Most of the time the BER will be much lower. Springett 2002

~ VSOP-2 Ground System Antenna Room Operation Center Feed U/C O/E E/O TX GEN ~ LOGEN O/E E/O Doppler Cntr / meas. Feed D/C O/E E/O Demodulator Antenna Room Operation Center

~ ~ Operation Center TX GEN D/A DIFF ENC DATA GEN D/A Demodulator A/D 1.54GHz+fud 1.5GHz 1.5GHz REF GEN LPF D/A 100MHz E/O SW BPF ~ NCO Fo (nominal) DIFF ENC DATA GEN 5MHz 5MHz STD CLK LPF D/A GPS 1.5GHz Doppler Control Meas. DOP CONT UP Fup (PREDICT) 1pps TIME DEC E/O 100MHz Time DOP CONT DW Fdw (PREDICT) Doppler Control PC Copper Count Dop.Cnt Demodulator Control PC 1.5GHz NCO Remote station LPF A/D TI COUNT 1.54GHz+fdd O/E BPF ~ NCO PD BIT SYNC DIFF ENC FRAME SYNC VSI I/F Storage BER MEAS LPF A/D 1.5GHz

Antenna Room HPA Translator LNA Antenna Room ATT BPF BPF O/E O/E Feed POWER METER 4.388+fud GHz 1.54+fud GHz ATT BPF BPF O/E 40.288 + fud GHz HPA 2.848GHz 35.9 GHz 100MHz 2.848GHz X 2828 /1000 O/E Feed DIP BPF HYB X 359 Translator 37.440 + fdd GHz 35.9 GHz LNA 1.54+fdd GHz BPF BPF O/E Antenna Room

ASTRO-G Ka-Band Link Simulations Uplink / Downlink 40GHz / 26GHz 40GHz / 37GHz Effects of the onboard local phase due to the ionosphere ARIS simulations MS-TID (Medium Scale Traveling Ionospheric Disturbance) Zenith TEC bias error

Discussion TLM Header Mobile TX simulator Phase Detection method Realtime/Quasi-realtime Mobile TX simulator Phase Detection method VLBI Data storage VSI I/F MarkVB RVDB of Japan Data transportation PM TEST and schedule

2-way Link: the effect of the ionosphere Δφion N : TEC [el./m2] fobs : Observing frequency [GHz] fup : Uplink frequency [GHz] fdown:Downlink frequency [GHz] c : Velocity of light [m/s]

Ka Tracking Simulations Black : Usuda Red : Goldstone Blue : Tidbinbilla Pink : Hart Yellow: Malind

Onboard Lo-Phase (Zenith TEC Bias : 60 TECU) 40GHz/26GHz 40GHz/37GHz 43GHz: 62.5 deg 22GHz: 45.8 deg 43GHz: 17.9 deg 22GHz: 9.3 deg Black: 43GHz Red: 22GHz

Onboard Lo-Phase (Zenith TEC Bias : 6 TECU) 40GHz/26GHz 40GHz/37GHz 43GHz: 15.0 deg 22GHz: 7.9 deg 43GHz: 1.9 deg 22GHz: 1.0 deg Black: 43GHz Red: 22GHz

Space-VLBI Fringe Phase (MS-TID , Zenith TEC Bias : 60 TECU) 60 min (Tropospheric and Ionospheric Errors) 40GHz/26GHz 40GHz/37GHz Black: 43GHz Red: 22GHz

43GHz Coherence No difference 22GHz Coherence No difference

Principles of Link Design But extremes for these conditions are very rarely concurrent, so most of the time there will be a substantial excess of performance (a positive link margin of many dB). This is excessive design, a waste of link resources. A statistical link design methodology reflects the fact that temporal variation of the parameters rarely results in simultaneous worst-case extremes. Springett 2002