1. Ulysses Nutation anomaly in 2000-2001
Andy McGarry
ESA Ulysses Spacecraft Systems Engineer

2. 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 - ESOC & Kourou’s role
How is Nutation in different from ?
Preparations for Nutation operations
ESA Ulysses Flight Control Team
Ulysses Nutation

3. Ulysses mission Launch: 6 Oct 1990 on Shuttle STS-41 Discovery.
First Orbit: Oct Sep 1995.
Jupiter Flyby: 8 Feb 1992.
Second Orbit: Oct Dec 2001.
Third Orbit: Jan Sep 2004.
Note the unique Ulysses orbit. It is inclined approximately 70o to the ecliptic plane, allowing it to survey the Sun at Solar latitudes from 80oS to 80oN.
Contrary to ones first expectations, Ulysses is further away from the Sun than Earth! The distance from the Sun varies from approximately the orbital distance of Mars to that of Jupiter! The one way light time (OWLT) varies from less than 20 minutes, up to 53 minutes at maximum Earth range.
A Third Orbit has recently been approved and Ulysses is expected to operate until September The mission would therefore end before another period of Nutation would begin (approx )
ESA Ulysses Flight Control Team
Ulysses Nutation

4. Spacecraft Dimensions Length 3.2 m (booms stowed) Width 3.3 m
Height m
Weight
Total Spacecraft kg
Scientific Payload kg
Stabilization
Spin-stabilized rpm
ESA Ulysses Flight Control Team
Ulysses Nutation

5. Science payload Suite of 9 instruments Fields, particles & waves
Radio Science
No camera!
ESA Ulysses Flight Control Team
Ulysses Nutation

6. Nutation Anomaly
First occurred in 1990 after deployment of axial boom.
Caused by solar pumping of 7.5m axial boom + underperformance of passive nutation dampers.
Nutation Forcing Function (NFF) is function of SAA & 1/R2.
Successfully controlled in to < 0.7 deg half-cone.
Returning in
ESA Ulysses Flight Control Team
Ulysses Nutation

7. 72.5 m (~221ft) across wire booms
Impact of Nutation
Spin rate: 5 rpm
If left uncontrolled =>
wire booms wrap
around s/c or detach
damage or loss
of s/c
data loss due to s/c
off-pointing
72.5 m (~221ft) across wire booms
ESA Ulysses Flight Control Team
Ulysses Nutation

8. 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 (0.125o or 0.23o)
Conscan very sensitive to U/L disturbances t
s/c AGC
t spin DC
bias
ESA Ulysses Flight Control Team
Ulysses Nutation

9. 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 Team
Ulysses Nutation

10. 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.
S/c CLC off for 20mins around U/L transfers.
S/c CLC off for (35mins+gap), around gap in coverage.
ESA Ulysses Flight Control Team
Ulysses Nutation

11. 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 Team
Ulysses Nutation

12. 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 2001.
Unique orbit geometry causes
scheduling and tracking problems.
ESA Ulysses Flight Control Team
Ulysses Nutation

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

14. Kourou fills in gaps in DSN coverage

15. Antennas suitable for Ulysses Nutation support
Notes:
F FULL
Can support Nutation Operations standalone.
P PARTIAL
Can provide part of Nutation Operations requirement.
E EMERGENCY
Uplink beacon only.
* Maximum during
nutation period.
** Available Feb-Mar 2001.
Noisier Conscan, no Doppler, reduced TM
rates.
ESA Ulysses Flight Control Team
Ulysses Nutation

16. Differences in 2000-1 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 Team
Ulysses Nutation

17. 2000-1 Nutation Forcing Function is greater
Nutation ops
nutation threshold
nutation threshold
Peak value of NFF2000-1
is 34% greater
ESA Ulysses Flight Control Team
Ulysses Nutation

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

19. Nutation Coverage without Tx ops at low elevation.
ESA Ulysses Flight Control Team
Ulysses Nutation

20. Kourou support and waiver requests fill the gaps in Nutation coverage.
ESA Ulysses Flight Control Team
Ulysses Nutation

21. 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 2001.
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.
ESA Ulysses Flight Control Team
Ulysses Nutation

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

23. Latest Nutation information is available at
Questions
Latest Nutation information is available at