Mir Electric Field Characterization (MEFC)

MEFC Hardware

Objectives

The primary objective of the Mir Electric Fields Characterization (MEFC) Experiment was to sample the Radio Frequency (RF) environment in low Earth, high inclination orbits. The secondary objective was to measure the electric field intensity in various Mir modules to get typical values of field intensity within a spacecraft.

Shuttle-Mir Missions
STS-76, STS-79, STS-81, STS-84

Approach
During STS-79 and 81, the objective was to sweep from 400 MHz to 18 GHz as quickly as possible while maintaining a minimum sensitivity of 0.5 V/m. The MEFC software configured the spectrum analyzer to consecutively sweep over three bands: DC to 2.9 GHz (low band), 2.9 GHz to 12 GHz (mid band), and 12 GHz to 22 GHz (high band). The spectrum analyzer's resolution bandwidth was set to 5 MHz so that the sweep time was minimized. Each band was measured in 2 seconds and the measurement cycle was repeated every 6 seconds. For STS-84, the software was modified to focus on active frequency bands with greater frequency resolution and amplitude sensitivity based on the results of STS-79 and STS-81.

Results
Preliminary results indicated that the frequency band below 2 GHz contains many strong signals. Specifically, the UHF band (200-400 MHz) and L-band (1.2-2 GHz), which are near the operating frequencies of the ISS Space-to-Space Communications System (SSCS) and Global Positioning System (GPS), contain strong signals. The final report will assess potential for interference affecting the operation of those systems. Preliminary results also indicate that the Mir's core and Priroda internal RF environments are relatively benign.

Data was collected during STS-79 and STS-81 that will be useful in characterizing the RF environment in low Earth, high inclination orbits. Active frequency bands are being identified and the field strength in those bands is being assessed and compared to the radiated susceptibility limits currently defined for ISS. Data collected aboard the Mir indicated that the Mir's internal environment is benign.

Earth Benefits
The effects of electromagnetic interference (EMI) can be very detrimental to electronic systems. EMI can cause anomalies or even failures of electronic systems. Military helicopters, such as the Blackhawk and Apache, have crashed as a result of EMI. Antilock Braking System systems have failed to operate correctly because of EMI. Even wheelchairs have been affected, going into a forward mode with no warning. Space systems can be as vulnerable as these other systems. Ensuring electromagnetic compatibility (EMC) can help avoid accidents and safeguard human life. (Source: Electronic System Failures and Anomalies Attributed to Electronic Interference, NASA RP 1374).

Publications
None available at this time.

Principal Investigators
M. A. Chavez
NASA/Johnson Space Center

G. D. Arndt

P. H. Ngo

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Page last updated: 07/16/1999

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