Andy McGarry ESA Ulysses Spacecraft Systems Engineer Kourou operations during the Ulysses Nutation anomaly in

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Outline of talk (Assumes background knowledge of Ulysses & Nutation Anomaly) Why we need Kourou support Nutation operations requirements Differences in Nutation from DSN low elevation Tx operations Important terms used by the DSN / JPL S/c and Kourou g/s contingencies Questions / comments.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Nutation Operations Goals Maintain s/c safety Try to prevent Nutation starting Keep any Nutation which does start as low as possible

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Basic g/s requirements for Nutation operations Continuous (24 hr) ground station coverage providing: Steady uplink (TX) as beacon for s/c CLC Telemetry (TM) to monitor critical s/c parameters Telecommand (TC) capability to respond to contingencies High resolution Doppler data (from DSN stations only) to provide additional ARGOS monitoring of Nutation levels.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Antenna coverage High latitude Solar Polar orbit =>gaps in DSN coverage. ESA providing Kourou station to fill in gaps in DSN coverage from 1 Feb - 31 Mar Unique orbit geometry causes scheduling and tracking problems.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Effect of Ulysses Solar Polar orbit on antenna tracking 6 deg limit (RISE / SET) 10.x deg limit (Tx ON/OFF) Antenna path Typical s/c track No uplink Ulysses Nutation track during high latitudes No uplink Continuous view, but large gap in uplink

Kourou fills in gaps in DSN coverage

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Important dates 6 Sep Jan 2001 Second South Polar Pass (Solar Latitude > -70°) Sep 2000Start Kourou MRTs, Nutation operations training Nov 2000Nutation operations training at JPL and Canberra 1 Dec 2000Begin Nutation operations 1 Feb - 31 Mar 2001Kourou antenna provides Nutation support 23 May 20012nd Perihelion (1.34 AU) 25 May 2001Ecliptic crossing 26 May 2001Maximum value of NFF 31 Aug - 10 Dec 2001 Second North Polar Pass (Solar Latitude > 70°) 1 Dec 2001End Nutation Operations 31 Dec 2001End of Second Orbit 1 Jan 2002Begin Ulysses Third Orbit

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Detailed g/s requirements for Nutation operations DSN antennas required. Kourou has –lower U/L power (noisier Conscan measurements) –lower TM rates (reduced monitoring) –no Doppler (cannot support ARGOS) Preferable to use as few stations as possible. –simpler s/c operations => fewer errors –simpler g/s operations => fewer errors –fewer breaks in s/c CLC => maximum Nutation damping TM essential for monitoring Nutation levels, s/c health & safety. TC capability frequently used to control Nutation & respond to contingencies.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Antennas suitable for Ulysses Nutation support Notes: FFULL Can support Nutation Operations standalone. PPARTIAL Can provide part of Nutation Operations requirement. EEMERGENCY Uplink beacon only. *Maximum during nutation period. **Available Feb-Mar Noisier Conscan, no Doppler, reduced TM rates.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Important terms used by Ulysses / DSN / JPL personnel Uplink transfer 2 sec overlap between uplink of incoming & outgoing stations to enable s/c to maintain receiver lock. 1-waydataDownlink frequency is driven by s/c oscillator. 2-waydataDownlink frequency is coherent with uplink signal (from same ground antenna). 3-waydataDownlink frequency is coherent with uplink signal (from different ground antenna). CLCClosed-loop Conscan. McElrath manoeuvreContingency manoeuvre which depoints the s/c, then re-enables CLC, to trigger a series of Nutation damping CLC thruster firings. Wide deadbandCLC control deadband set to 0.23 o Narrow deadbandCLC control deadband set to o

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Nutation ops depend on steady, continuous uplink When CLC is disabled, Nutation can grow. To provide maximum Nutation damping, CLC is continuously enabled. CLC only disabled during scheduled U/L disturbances e.g. U/L transfers, U/L sweeps, CMD MOD On/Off. We must carefully schedule all ground and s/c operations to avoid U/L transients affecting Conscan measurements,or producing erroneous thruster firings.

Avoiding U/L transients during U/L Transfers U/L Txfer Canberra view Kourou view CMD MOD CLC TC TT CLC disabled for mins

Avoiding U/L transients when there is a gap in coverage CLC disabled for mins + duration of gap Kourou view Canberra view TCTT CLC TT CLC CMD MOD U/L X X 15 mins mins GAP

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Note increased size of Conscan “cloud” Kourou AGC ~ -136 dB Typical Kourou Nutation support

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Note small Conscan “cloud” with nominal antenna Subreflector problems cause spurious Rx lock, & numerous wrong Conscan measurements Effect of subreflector problems on CLC

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Differences in Nutation Compared to the following points are different: NFF greater, Earth drift rate lower => greater ops challenge. NFF is continuously high for one year - no break in Nutation ops. Metal fatigue - wire booms have accumulated ~15months of flexing vs ~3 months before Kourou is a shared resource. Used for XMM-Newton & LEOP support. Kourou will provide lower bitrates => reduced monitoring capability. Kourou is operated remotely from ESOC - any considerations?

ESA Ulysses Flight Control TeamUlysses Nutation September Nutation Forcing Function is greater Peak value of NFF is 34% greater Nutation ops nutation threshold nutation threshold

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Tx elevation waiver requests DSN antennas supported Ulysses Nutation operations in with uplink down to 6 o. Since then, station upgrades have resulted in hardware & software changes limiting transmission to above 10 o elevation. 10 o elevation limit caused large gaps in Tx coverage Low elevation Tx Waiver requests submitted to DSN complexes in March-May Radiation surveys performed at all sites & waivers granted

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Nutation Coverage without Tx ops at low elevation.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Waiver requests fill the gaps in Nutation Coverage.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Tx elevation waiver implications for Kourou ops Kourou passes will begin and end with DSN stations uplinking at low elevation. These low elevation periods significantly help to reduce the tracking conflict with XMM at Kourou. Only Canberra will have end-to-end tested the modifications prior to operational use. The first time that Goldstone and Madrid use the low elevation limits while transmitting to Ulysses, will be in Feb/Mar 2001! Any operational problems, the antennas will not Tx below 10 o

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Contingencies S/c contingencies. Must be able to command at any time to respond to high Nutation levels or other platform or payload contingencies Kourou g/s contingencies. If all local redundancy options have been exhausted, since no other DSN resource is available, then the emergency Santiago U/L support must be requested (by JPL).

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Wide to Narrow CLC deadband Narrow d/b selected Nutation buildup

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 McElrath Manoeuvre Note small Conscan “cloud” McElrath performed here McElrath Manoeuvre shrinks Conscan “cloud”, & Nutation level Note increased size of Conscan “cloud” Nutation buildup

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Santiago experience with Ulysses Qualified in 1994 at U/L powers of 2.5, 5 & 10kW Downlink carrier successfully acquired via 12m VLBI antenna. Used on 27 October 1994 to support real-time ops for 4.75 hours. Santiago is not scheduled - on standby only for Dec July 2001.

ESA Ulysses Flight Control TeamUlysses Nutation September 2000 Current status of Nutation preparations Kourou data flow tests completed 6 Sep 2000 Santiago uplink stability confirmed on 29 Aug, 6 Sep, 11 Sep. Kourou Mission Readiness Tests underway ( Sep). DSN antenna coverage allocated through March Work has commenced on h/w & s/w modifications for DSN Low elevation Tx (available for testing at Canberra on 1 Nov 2000). 2.5 month Fuzzy Logic study (PHAEACIAN) commenced 11 Sep Will assess feasibility of FL techniques in analysing Nutation, and in recommending corrective action.

Latest Nutation information is available at Questions