Usage of IGS TEC Maps to explain RF Link Degradations by Spread-F, observed on Cluster and other ESA Spacecraft

Transcription

1 Usage of IGS TEC Maps to explain RF Link Degradations by Spread-F, observed on Cluster and other ESA Spacecraft J. Feltens, J. Dow, G. Billig, D. Fornarelli, S. Pallaschke, B. Smeds, H.-J. Volpp, P. Escoubet, H. Laakso IGS Workshop & Symposium, Berne, Switzerland, 1-5 March IGS 10 th Anniversary Workshop & Symposium

2 Contents Introduction Problem description The Spread-F phenomenon Applicability of Spread-F to observed link anomalies Operational consequences for Cluster Possible consequences for future ESA spacecraft and missions Conclusions 2 IGS 10 th Anniversary Workshop & Symposium

3 Introduction RF link anomalies were observed on the Cluster spacecraft in autumn and spring 2001, 2002 and 2003: Sudden variations of the received RF signal power. The duration of these disturbances ranged from 10 minutes to 4.5 hours, occurrence mostly in the local evening hours. Maspalomas and Villafranca are the nominal tracking sites. A cross-disciplinary working group of experts at ESOC and ESTEC started investigations in January 2003: Spread-F could be identified as the source. IGS TEC maps played a key role to relate the observed phenomena to Spread-F. Recommendations for the operations of Cluster and other ESA missions. 3 IGS 10 th Anniversary Workshop & Symposium

4 Problem Description Characteristics of the Cluster Mission (1) The The 4 Cluster spacecraft were were launched in in July/August Highly eccentric polar polar orbits with with heights ranging between km km and and km, km, line line of of apsides initially in in the the ecliptic plane. Ideal Ideal tetrahedron constellation in in one one orbital position, the the inter-spacecraft distance ranged from from km km to to km km up up to to now. now. The The argument of of perigee increases by by about 5 degrees per per year year due due to to Moon and and Sun Sun attraction, causing the the apogee to to move southward. The The orbital period of of about hours results in in an an average visibility from from one one ground station in in the the order of of hours, subdivided into into 2 3 passes of of typically hours length, for for all all 4 spacecraft per per orbit. 4 IGS 10 th Anniversary Workshop & Symposium

5 Problem Description Characteristics of the Cluster Mission (2) All All science data data acquired during non-visibility periods are are stored on-board and and dumped to to ground during the the visibility periods. Initially, Villafranca was was the the only only nominal ground station. Maspalomas became the the second nominal ground station in in September Nominally SC1 SC1 and and SC2 SC2 are are tracked from from Villafranca, SC3 SC3 and and SC4 SC4 are are tracked from from Maspalomas. The The Telemetry & Telecommand uplink frequency is is MHz, the the downlink frequency is is MHz. 5 IGS 10 th Anniversary Workshop & Symposium

6 Problem Description Observed phenomena (1) The The uplink/downlink RF RF signal power is is monitored via via the the receiver Automatic Gain Gain Control (AGC) on-board resp. resp. at at the the ground station. The The AGC level level of of the the satellite receiver shows strong and and fast fast fluctuations as as increasing and and decreasing signal strength. The The AGC level level of of the the ground station receiver shows the the same same behavior. If If the the variations are are too too strong-, data data dump has has to to be be stopped to to avoid data data losses. It It is is vital vital that that enough time time is is available to to downlink the the data data stored on-board before they they get get overwritten. 6 IGS 10 th Anniversary Workshop & Symposium

7 Problem Description Observed phenomena (2) events were were registered until until May May at atvillafranca, no no event was was observed at atredu from from May May September Of Of a total total of of passes for for SC3 SC3 and and SC4, SC4, have have been been affected between mid mid September and and end end of of October at at Maspalomas. From September December events were were observed at at Villafranca and and events at atmaspalomas. All All passes with with fluctuations as as seen seen from from Maspalomas were were in in a window with with an an elevation <60 <60 degrees and and an an azimuth range between degrees, i.e. i.e. into into the the southern direction. 7 IGS 10 th Anniversary Workshop & Symposium

8 Observed phenomena (3) AGC Problem Description dbm -80 Fluctuations DOY / 18 October SC4 over MSP -90 SC1 over VL1 SC2 over VL % 91% of of the the documented events occurred SC3 over MSP -100 in in the the September --December period, -105 and and they they appeared during late late evening -110 hours -115 between 19:50 to to 02:00 UT. UT Due Due to to the the Cluster orbit orbit and and position of of -130 apogee relative to to the the Sun, Sun, most most of of the the pass RX 1 AGC 3H_103 DBM RX 1 AGC 1H_103 DBM pass time time in in autumn is is in in the the late late RX 1 AGC 2H_103 DBM RX 1 AGC 4H_103 DBM afternoon up up to to early early morning. The The inspection of of recent tracking data data indicates enhanced presence of of RF RF link link disturbances at at Maspalomas also also for for September December :00 18:10 18:20 18:30 18:40 18:50 19:00 19:10 19:20 19:30 19:40 19:50 20:00 20:10 20:20 20:30 20:40 20:50 21:00 21:10 21:20 21:30 21:40 21:50 22:00 22:10 22:20 22:30 22:40 22:50 23:00 23:10 23:20 23:30 23:40 23:50 00:00 00:10 00:20 00:30 00:40 00:50 01:00 8 IGS 10 th Anniversary Workshop & Symposium

9 The Spread-F phenomenon Creation of Spread-F Upwelling flux flux tubes of of reduced plasma density plasma bubbles above the the geomagnetic equator, their their diameter is is km. km. After reaching the the apex apex height in in the the geomagnetic equatorial plane around post-sunset, they they move on on either side side of of the the geomagnetic equator and and break into into small patches. Around 18:00 LT LT there there can can be be a strong increase in in the the east-bound E-vector, causing the the F-layer to to move upwards due due to to Lorentz force. Around 21:00 LT LT the the E-field reverses and and directs to to west. west. Lorenz force force causes the the F-region now now to to come down, and and it it can can then then become unstable. * Effect on on radio radio links: steep steep variations of of the the signal strength (scintillations).( 9 IGS 10 th Anniversary Workshop & Symposium

10 The Spread-F phenomenon Spread-F requires Well-developed eastward E-field at at the the geomagnetic equator. Sharp raise raise of of the the F-layer s height around sunset (above ~ km). km). Geomagnetic storms (induced by by Sun). The The european longitude sector is is stronger affected than than others. Spread-F occurs within ~ ±15º ±15º lat. lat. of of geomagnetic equator between km km altitude, primarily between 20:00-23:00 LT, LT, but but also also in in the the post post midnight sector during high high geomagnetic sub-storms (induced by by Earth). 10 IGS 10 th Anniversary Workshop & Symposium

11 Applicability of Spread-F to observed link anomalies Cluster (1) IGS IGS TEC TEC maps were were used used to to find find out out whether the the affected RF RF links links passed through potential areas areas of of Spread-F. For For the the majority of of the the reported anomalies this this could be be confirmed. 11 IGS 10 th Anniversary Workshop & Symposium

12 Applicability of Spread-F to observed link anomalies Cluster (2) Maspalomas 17:00 19:00 Maspalomas 17/10/2002, SC4 pass from 17:59 21:24 UT, fluctuations from 19:45 UT to pass end. Maspalomas 21:00 12 IGS 10 th Anniversary Workshop & Symposium

13 Applicability of Spread-F to observed link anomalies Cluster (3) 19/03/2003 Villafranca SC1 SC2 Fluctuations 20:40 21:00 UT on SC4. Villafranca Maspalomas SC3 SC4 13 IGS 10 th Anniversary Workshop & Symposium

14 Applicability of Spread-F to observed link anomalies MSG-1 06/10/2002 Maspalomas 21:00 23:00 Fluctuations 21:00 22:30 UT on both days. 07/10/2002 Maspalomas 21:00 23:00 14 IGS 10 th Anniversary Workshop & Symposium

15 Applicability of Spread-F to observed link anomalies XMM 18/03/2002 Kourou 01:00 03:00 Fluctuations 01:30 02:30 UT on both days. 20/03/2002 Kourou 01:00 03:00 15 IGS 10 th Anniversary Workshop & Symposium

16 Operational consequences for Cluster The most practicable consequences: Usage of another nominal ground station than Maspalomas, e.g. Perth (conflicts with other missions) or 2nd antenna at Villafranca. Reduction of the Cluster perigee by 7 9 degrees during the next constellation change manoeuvres. Possible consequences for future ESA spacecraft and missions Some of the most important consequences: Usage of X-band rather than S-band in future missions. Preferably usage of non-equatorial tracking sites. Installation of an ionosonde at Maspalomas (at other sites?)? 16 IGS 10 th Anniversary Workshop & Symposium

17 Conclusions The Cluster spacecraft suffer from seasonal link degradations up to complete signal loss. A working group of experts from ESOC and ESTEC could identify Spread-F as source of the problem. + Several proposals were made by the working group to handle the Spread-F problem in routine operations of the Cluster spacecraft. + Recommendations were made how to take care about Spread-F in future missions planning and design. + The installation of ionosondes at selected ESA tracking sites for Spread-F forecasts is considered. + The relevance of Spread-F for new navigation satellite systems, namely Galileo, should be investigated. IGS TEC maps played a key role to relate Spread-F appearance to observed satellite link disturbances at Cluster and other ESA spacecraft. 17 IGS 10 th Anniversary Workshop & Symposium