Andy McGarry

1
Kourou operations during the Ulysses Nutation
anomaly in 2000-2001

• Andy McGarry
• ESA Ulysses Spacecraft Systems Engineer

2
Outline of talk

• (Assumes background knowledge of Ulysses
  Nutation Anomaly)
• Why we need Kourou support
• Nutation operations requirements
• Differences in 2000-1 Nutation from 1994-5
• DSN low elevation Tx operations
• Important terms used by the DSN / JPL
• S/c and Kourou g/s contingencies
• Questions / comments.

3
Nutation Operations Goals

• Maintain s/c safety
• Try to prevent Nutation starting
• Keep any Nutation which does start as low as
  possible

4
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.

5
Antenna coverage

• High latitude Solar Polar orbit
• gtgaps 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.

6
Effect of Ulysses Solar Polar orbiton antenna
tracking
Typical s/c track
Antenna path
Antenna path
10.x deg limit (Tx ON/OFF)
6 deg limit (RISE / SET)
No uplink
Continuous view, but large gap in uplink
7
Kourou fills in gaps in DSN coverage
8
Important dates

• 6 Sep 2000 - 16 Jan 2001 Second South Polar Pass
  (Solar Latitude gt -70)
• 26 -29 Sep 2000 Start Kourou MRTs, Nutation
  operations training
• Nov 2000 Nutation operations training at JPL and
  Canberra
• 1 Dec 2000 Begin Nutation operations
• 1 Feb - 31 Mar 2001 Kourou antenna provides
  Nutation support
• 23 May 2001 2nd Perihelion (1.34 AU)
• 25 May 2001 Ecliptic crossing
• 26 May 2001 Maximum value of NFF
• 31 Aug - 10 Dec 2001 Second North Polar Pass
  (Solar Latitude gt 70)
• 1 Dec 2001 End Nutation Operations
• 31 Dec 2001 End of Second Orbit
• 1 Jan 2002 Begin Ulysses Third Orbit

9
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 gt fewer errors
• simpler g/s operations gt fewer errors
• fewer breaks in s/c CLC gt maximum Nutation
  damping
• TM essential for monitoring Nutation levels, s/c
  health safety.
• TC capability frequently used to control Nutation
  respond to contingencies.

10
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.

11
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-way data Downlink frequency is driven by s/c
  oscillator.
• 2-way data Downlink frequency is coherent with
  uplink signal (from same ground antenna).
• 3-way data Downlink frequency is coherent with
  uplink signal (from different ground
  antenna).
• CLC Closed-loop Conscan.
• McElrath manoeuvre Contingency manoeuvre which
  depoints the s/c, then re-enables CLC, to
  trigger a series of Nutation damping CLC
  thruster firings.
• Wide deadband CLC control deadband set to 0.23o
• Narrow deadband CLC control deadband set to 0.125o

12
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.

13
Avoiding U/L transients during U/L Transfers
14
Avoiding U/L transients when there is a gap in
coverage
GAP
CLC disabled for 30-35 mins duration of gap
15
Typical Kourou Nutation support
16
Effect of subreflector problems on CLC
17
Differences in 2000-1 Nutation

• Compared to 1994-5 the following points are
  different
• NFF greater, Earth drift rate lower gt 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 1994-5.
• Kourou is a shared resource. Used for
  XMM-Newton LEOP support.
• Kourou will provide lower bitrates gt reduced
  monitoring capability.
• Kourou is operated remotely from ESOC - any
  considerations?

18
2000-1 Nutation Forcing Function is greater
19
Tx elevation waiver requests

• DSN antennas supported Ulysses Nutation
  operations
• in 1994-5 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

20
Nutation Coverage without Tx ops at low elevation.
21
Waiver requests fill the gaps in Nutation
Coverage.
22
Tx elevation waiverimplications 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 10o

23
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).

24
Wide to Narrow CLC deadband
25
McElrath Manoeuvre
26
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.

27
Current status ofNutation 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 (26 - 28
  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 2000. Will assess feasibility of FL
  techniques in analysing Nutation, and in
  recommending corrective action.

28
Questions

• Latest Nutation information is available at
• http//ulysses-ops.jpl.esa.int/ulsfct/Spacecraft_o
  ps_index.html