SS 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, January, June 17 to July 15, 2000 POLAR / TIMAS Interface Anomaly Status and Recourse Plan 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, BACKGROUND:

SS 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. RECOURSE: POLAR / TIMAS Interface Anomaly Status and Recourse Plan

SS POLAR / TIMAS Interface Anomaly Status 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).

SS POLAR / TIMAS Interface Anomaly Status and Recourse Plan 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. STATUS OF INVESTIGATION: 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. PROCEDURE:

SS TIMAS MEASUREMENTS: Energy Range: 15 eV/e – 32 keV/q Mass Range:1 – 32 AMU/q Angular Resolution:11.25 x deg. Time Resolution: 2-D: sec / 3-D: 3 sec 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. POLAR / TIMAS Interface Anomaly Status and Recourse Plan TIDE: 2D 0-500eV ions HYDRA – 3D 2-35 keV/q protons CEPPAD – 3D 20 keV/q - 1 MeV protons CAMMICE: 6 keV/q - 60 MeV ion composition CEPPAD: >10 MeV protons TIMAS: 3D 15 eV/q - 32 keV/q ions, full composition Comparison of the ion instruments on POLAR

SS POLAR / TIMAS Interface Anomaly Status 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.

SS 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 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. POLAR / TIMAS Interface Anomaly Status and Recourse Plan

SS POLAR / TIMAS Interface Anomaly Status 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.

SS POLAR / TIMAS Interface Anomaly Status 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%.