POLAR / TIMAS Interface Anomaly Status and Recourse Plan

1
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan
BACKGROUND

• On October 29, 1999, all instrument telemetry
  reported from TIMAS became invalid (zeroes).
• Subsequently, valid TIMAS telemetry has been
  sporadic, with extended intervals during several
  periods of low spacecraft temperature
• December, 1999
• January, 2000
• June 17 to July 15, 2000

• The fault appears to be located at the interface
  between TIMAS and the GGS Telemetry Module 1
  (GTM1) and is loosely temperature dependent.
• The TIMAS instrument itself is operating
  properly commands are received and executed by
  the instrument regardless of the telemetry
  reporting state.
• CURRENT STATUS TIMAS is on and enabled. TIMAS
  has not received valid TM since July 15, 2000.

2
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan
RECOURSE

• The POLAR spacecraft is equipped with fully
  redundant telemetry modules, GTM1 and GTM2. If
  the TIMAS telemetry fault resides on the GTM1
  side of the TIMAS/spacecraft interface, a switch
  to GTM2 can be expected to restore full telemetry
  reporting.
• Rational that the TIMAS serial interface problem
  could be corrected through a successful swap to
  GTM2
• such a swap would introduce a new serial
  interface within the GTM as well as a unique set
  of conductors through the harness out to the
  TIMAS connector. Much of the signal path resides
  on the GTM side, and therefore much of the new
  signal path will be unique to GTM2.

3
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan

• RATIONALE FOR FAULT LOCATION
• Evidence that the interface anomaly lies in the
  redundant GTM spacecraft circuits through the
  cable harness to the TIMAS interface circuit
• It appears the shift of data from the TIMAS data
  processors is working normally.
• TIMAS serially shifts three 8-bit telemetry words
  at a time to the GTM. The spacecraft generates a
  telemetry enable and clock to TIMAS to gate each
  byte. A hardware counter generates an interrupt
  to the TIMAS processor after the third telemetry
  enable. At the interrupt, the processor fills the
  shift registers with three more bytes from the
  telemetry queue. If the telemetry enable is not
  received, data words are not shifted to the
  registers and an error generated indicating that
  the processor is unable to maintain pointers to
  the telemetry. This symptom has not occurred and
  indicates that the telemetry enable signal and
  shifting of data words is working normally.
• The problem may lie with the telemetry clock or
  data output circuitry.
• The operation of the data processors are
  independent of the telemetry clock signal from
  the spacecraft to TIMAS and the data output
  signal from TIMAS to the spacecraft. If either
  of these circuits are intermittent, the serial
  data to the spacecraft would be corrupted or
  nonexistent (zeroes).

4
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan
STATUS OF INVESTIGATION

• Later this week, the POLAR Flight Operations Team
  (FOT), with input from the Lockheed-Martin
  spacecraft development team, is expected to
  deliver a final, detailed risk analysis regarding
  the switch from GTM1 to GTM2.

PROCEDURE

• Early next week, the ISTP and POLAR project
  scientists will issue a recommendation regarding
  the switch based on the value of the TIMAS data
  to the POLAR science objectives and the risk
  analysis provided by the FOT.
• Assuming a switch is recommended, the POLAR
  instrument Principle Investigators will be
  provided all relevant study material for
  comments.
• The ISTP and POLAR project scientists will assess
  the responses and forward a recommendation to
  the appropriate GSFC and HQ management.

5
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan
Comparison of the ion instruments on POLAR
TIDE 2D 0-500eV ions
TIMAS 3D 15 eV/q - 32 keV/q ions, full
composition
HYDRA 3D 2-35 keV/q protons
CAMMICE 6 keV/q - 60 MeV ion composition
CEPPAD 3D 20 keV/q - 1 MeV protons

• TIMAS MEASUREMENTS
• Energy Range 15 eV/e 32 keV/q
• Mass Range 1 32 AMU/q
• Angular Resolution 11.25 x 11.25 deg.
• Time Resolution 2-D 0.375 sec / 3-D 3 sec

CEPPAD gt10 MeV protons
POLAR carries the full range of instrumentation
necessary to resolve details of the field and
particle interactions leading to particle
acceleration throughout the inner magnetosphere
TIMAS is an important part of that instrument
complement.
6
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan

• ISSUES
• All instruments on POLAR interface to both GTM1
  and GTM2. Only one GTM can be active. A switch
  to GTM2 affects all instruments on POLAR.
• Because it is not known whether the interface
  anomaly exists on the spacecraft side or TIMAS
  side, it is not known whether the switch to the
  backup telemetry system should solve the
  interface problem with TIMAS.
• Commanding of the switching is done blindly.
  GTM1 is first commanded off and telemetry is then
  lost. Commanding to GTM2 occurs without
  confirmation of success until telemetry from GTM2
  is received. If no telemetry is received the
  state of the spacecraft is unknown. An attempt
  would then be made to command on the original
  GTM1.
• A multi-tree operations plan must be developed to
  handle unexpected anomalies that may or may not
  occur during the switch and during the immediate
  few days thereafter as the science instruments
  return to full science collection modes.

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POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan

• NON-ISSUES
• A TIMAS power supply anomaly resulted in a lower
  operational mass spectrometer pre-acceleration
  energy. In-flight calibration operations are
  waiting completion to refine the measurement to
  physical parameter calculations.
• The POLAR fuel supply will be depleted in late
  2002 or early 2003. The fuel is used to
  re-orient the spacecraft for optimal auroral
  viewing. The in-situ instruments on POLAR are
  primarily 3D and will continue to provide the
  particle and field parameters critical to SEC and
  LWS theme objectives. Auroral viewing will be
  less ideal.

8
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan

• ADDITIONAL INFORMATION TIMAS Science
  Objectives
• The science objectives of the Toroidal Imaging
  Mass-Angle Spectrograph are to investigate
  
• the transfer of solar wind energy and momentum to
  the magnetosphere,
• the interaction between the magnetosphere and the
  ionosphere,
• the transport processes that distribute plasma
  and energy throughout the magnetosphere, and
• the interactions that occur as plasmas of
  different origins and histories mix and interact.
  

9
POLAR / TIMAS Interface AnomalyStatus and
Recourse Plan

• ADDITIONAL INFORMATION TIMAS Instrument
  Characteristics
• TIMAS measures the full three-dimensional
  velocity distribution functions of all major
  magnetospheric ion species with one-half spin
  period time resolution.
• H, He, He, O, O, N.
• TIMAS is a first order double focusing (angle and
  energy), imaging spectrograph that simultaneously
  measures all mass per charge components from 1
  AMU/e to greater than 32 AMU/e over a nearly 360
  by 10 degree instantaneous field-of-view.
• Mass per charge is dispersed radially on an
  annular microchannel plate detector . The
  azimuthal position on the detector is a map of
  the instantaneous 360 degree field of view.
• With spacecraft rotation, TIMAS sweeps out a 4 pi
  solid angle image each half spin period.
• The energy per charge range of 15eV/e to 32 keV/e
  is covered in 28 non-contiguous steps spaced
  approximately logarithmically with adjacent steps
  separated by about 30.