ISS Tissue Equivalent Proportional Counter (TEPC) Description and Failure Chronology
Background
According to the NASA Life Sciences Data Archive: “The Tissue Equivalent Proportional Counter (TEPC) system is an automatic microdosimetry system. Each TEPC system consists of two main components, the spectrometer unit and the detector unit. The spectrometer unit contains a powerful computer that allows real-time analysis of the data and provides calculations of total dose, total dose equivalent, incremental dose, etc, as a function of linear energy transfer (LET) and time, for penetrating radiation in space. The detector unit is attached directly to the multi-channel analyzer (MCA) card in the spectrometer. Different size detectors can be attached to the TEPC depending on the desired task. The radiation data that is measured can be stored inside the spectrometer unit for later analysis or communicated via RS-232 to a host computer. The TEPC is filled with a low pressure gas and produces gain stability for more than a year. The TEPC is calibrated in terms of lineal energy, by exposing it to fission neutrons and 137Cs sources.”
According to the NSBRI the TEPC “provides an efficient method of determining radiation dose and dose-equivalent in complex (mixed) radiation fields. It records the linear energy spectra for determining dose-equivalent exposures.”
References
- Shuttle radiation dose measurements in the International Space Station orbits, Radiat Res. 2002 Jan;157(1):69-75.
- Space radiation absorbed dose distribution in a human phantom., Radiat Res. 2002 Jan;157(1):76-9
- Related documents
TEPC Failure Chronology
ISS Flight 7 Soyuz Stage Operations Readiness Review, Certification of Flight Readiness, Presented at the SLSD 7S SORR, 9/24/03, Space and Life Sciences Directorate
Environmental Monitoring: Radiation
– Both TEPC units hard failed beginning Expedition 5
—- Limited energy transfer data
—- No alarm capability (most important during LOS)
– Potential that ground-tracked radiation data and forecasting from satellites will be reduced or eliminated in FY04 (NOAA)
– Lack of TEPC monitoring data and alarm capability for ALARA
– Manifest TEPC to ISS on 14P
ISS Flight 7 Soyuz Stage Operations Readiness Review, Certification of Flight Readiness, PRELIMINARY, Presented at the SLSD 7S SORR, 9/9/03,Space and Life Sciences Directorate
TEPC waiver through March 2004 no LET measurement on ISS, No radiation alarm capability. Acceptable for flight. Total radiation exposure prediction is within flight limits.
Requirements that have not been met and have not been waived – Radiation Monitoring
- Loss of in-flight capability of radiation dose rate alarm- MORD 5.5.3.2.1.1.2, USOS 3.7.30.8
- Radiation exposure monitoring shall measure dosages during high dose rate events. MORD 5.5.4 USOS 3.7.30.3.8.3
- Support radiation exposure monitoring of external charged particle radiation environment in 3 directions. USOS 3.7.4.3.41
Integrated Risk Management Application (SA) Matrix and ISS Risk Tracking
ISS Watch Item: 4718 Summary Report
Open Date: 3/18/2003
Status as of 9/9/2003
ECD: 1/30/2004
Description: Loss of radiation area monitoring and TEPC due to constrained up/down logistics resources. Increases potential for crew health issues.
Impact/Consequence: Lower ability to measure radiation levels in particular spacecraft locations. Lower radiation levels because of relationship to Solar Min, and other radiation dosimeters, sch as Crew Personal on 6S manifest, will have to suffice.
Current Status:
- 9/9/03 — TEPC is being prepared for launch on 14P
- 8/5/03 — SA requested manifesting the TEPC on 13P. The TEPC waiver will expire Nov 03.
- 5/27/03 — The TEPC waiver will expire 1/04. SA is requesting TEPC be available on orbit 1/04 to start evaluating radiation prior to Solar Min. TEPC was removed from 12P due to the cost of certification for launch on a Russian vehicle. CPD is the only radiation monitor in use for Inc 7.
- 5/9/03 — Risk accepted for 11P. TEPC funding from OB was cut from 3 EP to .75 EP for FY03 and FY 04. Impact of the cut is being evaluated. TEPC has been placed on the 12P manifest as a mandatory item. TEPC needs to be on ISS and functioning by 12/03 to start analysis as we enter into Solar Min.
NASA Space Station On-Orbit Status 3 Jul 2003
All three USOS/CHeCS radiation counters are currently down, unable to dump their accumulated file data. [TEPC (tissue equivalent proportional counter), IVCPDS (intravehicular charged particle directional spectrometer), EVCPDS (extravehicular charged particle directional spectrometer).]
ISSP Vehicle Health 6 Dec 2002
TEPC (real-time radiation monitor) – Determined failed. Returned on 11A. Long-term plan in work.
ISS On-Orbit Status 29 Nov 2002
After extensive troubleshooting of the TEPC (tissue equivalent proportional counter) by the ground remained unsuccessful, the instrument was declared failed and will be returned on 11A. Rebuilding it is expected to take 1-2 months, in time to refly it on ULF-1/STS-114 (NET 3/1/03). [TEPC (“tee-pick”), registered radiation at the zero dosage level on 11/17, then at an abnormally reduced level. Even without TEPC, there is redundant radiation monitoring on board.]
ISS On-Orbit Status 19 Nov 2002
A second item added to the task list by MedOps is a test to isolate a grounding fault of the CHeCS TEPC (crew health care systems/tissue equivalent proportional counter) radiation spectrometer, with a due date of 11/22. If successful, this test, which uses an ohmmeter to check resistance values at various pins of the TEPC power/data connector, will lift the current restriction on relocating the TEPC.
ISS On-Orbit Status 3 Nov 2002
Peggy Whitson was requested by the MCC-H radiation experts to install the TEPC (tissue equivalent proportional counter) spectrometer in the TESS (temporary sleep station), her private bunk in the Lab. [The TEPC measurements are important for determining the shielding properties of the radiation bricks used in TESS, in order to support additional shielding of this type for all crewmembers.]
