1. Andy McGarry ESA Ulysses Spacecraft Systems Engineer x3-0906, andrew.mcgarry@jpl.nasa.gov Planning, scheduling & training requirements for operating Ulysses through the Nutation anomaly in 2000-2001

2. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Outline of talk Introduction to Ulysses The Nutation anomaly What is the impact of the Nutation anomaly? How do we control Nutation? Nutation operations requirements The unique demands of Nutation operations

3. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Outline of talk (cont’d) Lessons learned from Nutation operations in 1994-5 How is Nutation in 2000-1 different from 1994-5? Preparations for 2000-1 Nutation operations Nutation tracks and operations are different! Present concerns / Q & A

4. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Introduction to Ulysses Introduction title page

5. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Ulysses mission Launch: 6 Oct 1990 on Shuttle STS-41 Discovery. First Orbit: Oct 1990 - Sep 1995. Jupiter Flyby: 8 Feb 1992. Second Orbit: Oct 1995 - Dec 2001. Third Orbit: Jan 2002 - Sep 2004.

6. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Dimensions Length 3.2 m (booms stowed) Width 3.3 m Height 2.1 m Weight Total Spacecraft 370 kg Scientific Payload 55 kg Stabilization Spin-stabilized 5 rpm Spacecraft

7. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Science payload Suite of 9 instruments Fields, particles & waves Radio Science No camera!

8. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Perfect timing! The first set of Solar Polar Passes in 1994 and 1995 occurred at a period of low sunspot activity. This allowed scientists to view the Sun in its quietest state. The second set of Solar Polar Passes will occur close to the predicted Solar maximum, thus allowing a direct comparison of the Sun’s two extremes of behaviour. Courtesy ESA Science website.

9. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 The Nutation Anomaly The Nutation Anomaly title page

10. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation Anomaly First occurred in 1990 Caused by solar pumping of axial boom + underperformance of passive nutation dampers Returned in 1994-5 - successfully controlled Returning in 2000-1

11. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Cause of Nutation NFF is a function of solar range (heat input) & solar aspect angle (shadowing of axial boom). NFF is a function of SAA and 1/R 2.

12. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation Forcing Function Peak value of NFF 2000-1 is 34% greater Nutation ops

13. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 What is the impact of the Nutation Anomaly? What is the impact of the Nutation Anomaly? title page

14. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Effect of Nutation s/c wobbles => spin axis wobbles =>large off-pointing wire boom flexing uncertain attitude => science impact

15. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Impact of Nutation If left uncontrolled => wire booms wrap around s/c or detach damage or loss of s/c if left uncontrolled data loss due to s/c off-pointing

16. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 How do we control the Nutation Anomaly? How do we control the Nutation Anomaly? title page

17. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 The s/c Closed-loop Conscan (CLC) function Continuous U/L from Earth provides beacon Conscan electronics calculate s/c off-pointing error and thruster firing phase CLC provides damping component Process repeats until s/c spin axis is inside Earth off-pointing deadband (0.125 o or 0.23 o ) Conscan very sensitive to U/L disturbances t s/c AGC t spin DC bias

18. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 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. To avoid U/L transients affecting Conscan measurements,we must have: S/c CLC off for 20mins around U/L transfers. S/c CLC off for (35mins+gap), around gap in coverage.

19. Example of daily Nutation Operations Narrow d/b selected Nutation buildup S/c Conscan operations

20. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation in 1994-5 Nutation kept low Max Nutation of 0.7 o half-cone No damage to s/c Science data return excellent

21. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation operations requirements Nutation operations requirements title page

22. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation operations Goals Maintain s/c safety Try to prevent Nutation starting Keep any Nutation which does start as low as possible

23. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Basic requirements Continuous (24 hr) ground station coverage providing: Uplink (TX) as beacon for s/c Conscan 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.

24. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Detailed requirements DSN antennas preferred. 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 Conscan => maximum Nutation damping TM essential for monitoring Nutation levels, s/c health & safety. TC capability frequently used to control Nutation & respond to contingencies.

25. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 The unique demands of Nutation operations The unique demands of Nutation operations title page

26. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Antenna coverage High latitude Solar Polar orbit => gaps in DSN coverage. ESA providing Kourou station to fill in gaps in Canberra coverage from 1Feb - 31Mar 2001. Santiago station requested as backup (uplink only) in case of DSN / Kourou failures from Dec 2000 - July 2001. Unique geometry causes scheduling and tracking problems.

27. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Continuous view at high solar latitudes 6 deg limit (RISE / SET) Antenna path Ulysses antenna track during high latitudes Antenna path Typical s/c track Antenna Elevation always > 6 deg. In view Out of view Out of view

28. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Kourou antenna description Picture courtesy of XMM-Newton Website Kourou Diane 15m antenna. Located in French Guiana at 5.25 o N, 52.8 o W 15m above sea level Tropical climate, highest rainfall March (!) - June.

29. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Kourou experience with Ulysses Qualified in 1994 at U/L powers of 0.4, 1 & 2kW TM tested from 64bps - 1024bps. 512bps used operationally (cooled LNAs). Supported nutation ops from Aug 1994 - Mar 1995.

30. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Santiago antenna description Picture courtesy of International Listings,Inc. University of Chile at Santiago 9m antenna. Located at 33.2 o S, 70.7 o W, 723m above sea level Staffed 12 hrs per day (1200-2400 UTC), otherwise 3 hrs response. Logo (above) & picture (below) courtesy of Universidad de Santiago de Chile website.

31. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 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 2000 - July 2001.

32. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Available Antennas for Nutation support Notes: FFULL Can support Nutation Operations standalone. PPARTIAL Can provide part of Nutation Operations requirement. EEMERGENCY Uplink beacon only. *Available ~Feb-Mar 2001. Noisier Conscan, no Doppler, reduced TM rates. Testing required.

33. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Continuous tracking High latitude Solar Polar orbit => Ulysses can be continuously in view. Good for s/c Conscan (no break in uplink) Bad for maintenance, predicts (both frequency and pointing data), cable wrap, keyhole problem. Also stressful on Flight Team, especially ACEs.

34. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Problems arising from continuous view. 6 deg limit (RISE / SET) Antenna path Large azimuth range => cable wrap problems Keyhole problem at high antenna elevation?

35. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 DSN Uplink powers during Nutation operations 2000-1

36. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Effect of DSN Tx elevation restriction 6 deg limit (RISE / SET) 10.x deg limit (Tx ON/OFF) Antenna path Ulysses Nutation track during high latitudes Antenna path Typical s/c track No uplink Continuous view, but large gap in uplink

37. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Impact of Tx elevation restriction U/L unavailable for longer periods from DSN antennas => longer Kourou use (cost impact) DSN antennas preferred => better Conscan, Doppler data for ARGOS support, higher TM bitrate Nutation support from Goldstone and Madrid must start later. Increases conflict with XMM-Newton at Kourou

38. Example of S/c Conscan operations via Kourou Noisier Conscan Kourou Pass S/c Conscan operations via Kourou

39. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Lessons learned from 1994-1995 Nutation Lessons learned from 1994-1995 Nutation title page

40. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Lessons learned from 1994-1995 Nutation Continuous tracking:~7-day tracks with 4 hour maintenance period in between. Cable wrap:If not correctly initialized before beginning of long pass, possible to wrap antenna cabling beyond limit. The pass, and s/c Conscan, would have to be interrupted to correct the problem. Keyhole problem:Ulysses reached high elevations & required tracking through the antenna zenith. S/c Conscan had to be disabled for 10-20 minutes either side of zenith. Antenna predicts:Antenna pointing predicts lost their accuracy during the 7 day passes. Uplink frequencies:U/L frequencies traditionally optimized for passes < 24hrs. Thus U/L frequency had to be calculated for a 7-day pass.

41. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 How is Nutation in 2000-1 different from 1994-1995? How is Nutation in 2000-1 different from 1994-1995? title page

42. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Differences in 2000-1 Nutation Compared to 1994-5 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. Kourou is a shared resource. Used for XMM-Newton & LEOP support Kourou will provide lower bitrates => reduced monitoring capability. Most operations personnel have moved on => training required. Some g/s equipment or capabilities changed / removed e.g. 26M cmd. It was a long time ago => all staff need refresher training

43. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation Forcing Function Peak value of NFF 2000-1 is 34% greater Nutation ops 1994-5 nutation threshold 2000-1 nutation threshold

44. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Differences in 2000-1 NFF Comparison of NFF in 2000-1 with 1994-5: Peak value of NFF 2000-1 is 34% greater NFF 2000-1 is higher than peak value of NFF 1994-5 from April - July 2001. Highest Nutation increase rate in 1994-5 was 68% per hour. Highest Nutation increase rate in 2000-1 predicted at 115% per hour.

45. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Preparations for 2000-2001 Nutation operations. Preparations for 2000-2001 Nutation operations title page

46. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Important dates Summer 2000Upgrades, testing, training for Nutation operations support 6 Sep 2000 - 16 Jan 2001 Second South Polar Pass (Solar Latitude > -70°) 27 Nov 2000Maximum South Solar Latitude (-80.2°) 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 19 Jul 2001Minimum Earth range (1.34 AU) 31 Aug 2001 - 10 Dec 2001 Second North Polar Pass (Solar Latitude > 70°) 13 Oct 2001Maximum North Solar Latitude (+80.2°) 1 Dec 2001End Nutation Operations 31 Dec 2001End of Second Orbit 1 Jan 2002Begin Ulysses Third Orbit

47. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation operations preparations S/c power and thermal strategy for Nutation preparations & operations Schedule antenna coverage Review and update s/c & g/s operating procedures Upgrade / refurbish ground equipment for Nutation support? (Kourou / 26M network only?) Revalidate command interface with Kourou Arrange comms & data links with Kourou & Santiago Produce support products (predicts, etc) & delivery to DSN / Kourou / Santiago Test new & upgraded equipment Train & familiarize all operations personnel

48. Kourou implementation

49. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation operations training Nutation background training will be given by 3 methods: Presentations Ulysses Mission Operations Homepage at (available Mar 2000?) http://ulysses-ops.jpl.esa.int/ By e-CD (business card sized CD-ROM) - available late May 2000. In addition operations training will take place: During real-time testing and validation tracks e.g. using Kourou and Santiago Nutation operations could begin ~2 weeks early, to gradually phase in to continuous Nutation operations.

50. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation tracks and operations are different. Nutation tracks and operations are different title page

51. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation ops depend on ground ops Compared to current Ulysses operations, Nutation operations are: More complicated - many events, stations More time critical - s/c & ground events precisely scheduled More sensitive - s/c Conscan very responsive to U/L power

52. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Routine s/c and g/s operations - simple SFOS

53. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation s/c and g/s operations - complex SFOS

54. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Nutation ops depend on steady Uplink Must not use ground Conscan => “duelling Conscans” S/c Conscan depends on steady uplink power. Conscan measurement strongly affected by –Power level:U/L must be smooth and stable for as long as possible. Watch for power drift. –Command modulation:Only switch ON or OFF when scheduled or requested by ACE –Polarization:U/L must be RCP. Wrong polarization is very, very bad!!! –Antenna tracking: Problems with subreflector or tracking quickly gives erroneous Conscan measurements.

55. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 What if there’s a problem? Maximum Allowable Nutation => 0.5 o half-cone is max. operational level of Nutation The MAGIC number. Maximum Allowable Gap in Coverage defined as time to go from 0.25 o to 0.5 o nutation. MAGIC number used as guideline in determining when to declare a s/c emergency in order to secure additional resources to cope with g/s problems. For example if MAGIC = 1 hour, but problem will be fixed in 45 minutes, then OK.

56. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Use of Santiago U/L for Ulysses Criteria for use No other suitable DSN or ESTRACK resources available. Declaration of s/c emergency by Ulysses FCT? Santiago provides U/L only support. If situation deteriorates, may view TM carrier using VLBI antenna.

57. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Current concerns. Question & Answer session. Current concerns title page

58. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Current concerns Elevation limit of 10.x o or 6.0 o at DSN stations? Possible coverage conflict with NEAR at Canberra in Jan 2001 Conflicts with XMM-Newton at Kourou in Feb-Mar 2001 Loss of TC capability over 26M network in late 2000.

59. ESA Ulysses Flight Control TeamUlysses Nutation Operations 2000- 2001 Prepared Sept 2000 Effect of DSN Tx elevation restriction 6 deg limit (RISE / SET) 10.x deg limit (Tx ON/OFF) Tx ON between 6deg and 10.xdeg Continuous Tx view No uplink or Rx view Continuous Antenna view Break Antenna view Tx ON between 6deg and 10.xdeg