1.0 Introduction
The MIL-STD-1773 optical fiber based communication bus has been qualified and successfully flown by GSFC on the SAMPEX (Solar Anomalous Magnetospheric Particle Explorer) satellite. The success of SAMPEX has led to acceptance of the MIL-STD-1773 data bus system in the XTE (X-ray Timing Experiment) satellite and on TRMM (Tropical Rainfall Measuring Mission). Each of these later projects have been able to improve on the SAMPEX bus design by modifying various parts of the system hardware. With the exception of the "453" connector and the M29504 optical termini that is described here (Figure 1 and 2), the basic passive optical components (the fiber, cable, star coupler1), have not changed.
The "453" - M29504 connection system can be used to replace multiple, individual, MIL-C-83522, SMA type, single fiber connectors. This approach should improve reliability and performance by decreasing the number of individually mating connectors and by introducing a physically contacting (PC) mate at the fiber ends. SMA connectors allow an air gap between the fiber ends which limits the performance to the air gap loss (typically 0.34 dB to 2.0 dB depending on the width of separation between the fiber ends). The M29504 termini are designed and polished to eliminate the air gap between the fiber ends.
The use of "453" connectors with several optical contacts provides smaller footprint and significant reduction in hardware weight. The XTE and TRMM busses use "453" connectors with four and sixteen optical contacts. SMA connectors are still used in these systems at the active device interfaces (transmitters and receivers).
1/ Part numbers for the optical components used in the MIL-STD-1773 fiber optic bus are listed in section 51 of the GSFC Preferred Parts List, PPL-21. Design changes have been made on the transceiver unit for the TRMM mission.
The "453" connector has a long history of use at GSFC
for electrical applications. M29504 contacts in MIL-C-38999 connectors
(military version of the 453) have been studied by such organizations
as NASA-JSC's Space Station group, the Air Force's F22/Comanche
Helicopter fiber optic development group and Martin Marietta Space
Systems in Denver, however the actual use of "453" connectors
in high reliability optical systems has been limited. These organizations
have reported good performance for the MIL-C-38999 - M29504 connector
with some uncertainty in the vibration area. To date, test data
has not been released by these organizations because the connector,
used as an optical device, is fairly difficult to test with respect
to accuracy and repeatability.
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