GSFC Experiment DUT Board for MPTB


INTRODUCTION
The Microelectronics and Photonics Testbed (MPTB) is a DoD-sponsored 
effort being developed by the Naval Research Lab intended to sponsor 
testing of microelectronics and photonics in a harsh radiation 
environment. GSFC proposes to provide an experiment DUT board to 
measure Bit Error Rate (BER) of emerging fiber optic data bus 
transceivers as well as to measure single event upset (SEU) response 
of devices previously flown on CRRES.

PRELIMINARY DESCRIPTION - fiber optic experiment

NASA/GSFC, jointly with the Naval Research Laboratory (NRL),  has been 
a leader in the development and/or implementation of fiber optic data 
busses in spacecraft systems. The success of the MIL-STD-1773 fiber 
optic data bus (or 1773 bus) on the Solar Anomalous Magnetospheric 
Particle Explorer (SAMPEX) spacecraft, launched in July of 1992, has 
paved the way towards the acceptance of fiber optics in the space 
environment. 

An extensive radiation ground test program was undertaken on the 1773 
bus components prior to flight. This collaborative NASA/NRL effort led 
to the formation of SEU models for fiber optic components as well as 
accurate predictions of SAMPEX in-flight performance. Further ground
testing on other fiber optic components have extended these technology 
and design-specific SEU models.

The 1773 bus, however, has its limitations. They include:
  - Albeit the 1773 bus has a maximum signalling rate of 1 Mbps, its 
    actual effective data rate is limited to around 400 kbps. Thus, the 
    1773 bus is useful for low-speed applications such as the collection 
    of housekeeping telemetry on most spacecraft. And,
  - The implementation of the 1773 bus on SAMPEX relies on SEU-sensitive 
    receiver design (both optically and electrically). Fortunately, a 
    combination of relatively low bus utilization (thus, allowing for 
    retransmission of unsuccessful messages) and protocol level error
    handling exists and allows for a robust system. However, at higher 
    data rates and/or higher bus utilization rates, the system does not 
    have the luxury of retransmitting every message in error.

There is a potential solution: MIL-STD-1773A is a dual-rate (1 and 20 
Mbps) fiber optic data bus that is emerging in many military, commercial, 
and aerospace programs. The 20 Mbps data transfer rate covers the 
requirements of >80% of spacecraft instruments. Additionally, two
separate transceiver designs exist (Boeing and Univ. of New Mexico NASA 
Space Engineering Research Center), both of whose designs are hardened 
to SEUs.

NASA/GSFC code 735.1, under NASA HQ/QW Research funding for emerging 
technologies as well as potential funding from DNA, is preparing to 
perform SEU ground tests on both transceiver designs before the end of 
the calendar year.

We propose to develop an experiment for the MPTB program that will 
perform in-flight BER measurements on both of the MIL-STD-1773A 
transceivers as well as the current 1773 bus components. This experiment 
provides validation of the fiber optic SEU models that have been
developed as well to provide further verification of the usability of 
fiber optic systems in spaceflight applications.

PRELIMINARY DESCRIPTION - CRRES devices

Numerous spacecraft experience unexplained performance anomalies and 
failures. It is suspected that many of these are due to the radiation 
environment. In order to address this problem, it is desirable to obtain 
reliable information from a controlled experiment about the impact of 
the environment on known parts. For this purpose, it is proposed to 
include the following part types on the NASA MPTB daughter board: 
HS1-6504RH and AM-93L422. The use of these parts is considered 
advantageous because extensive ground test data for TID and SEE is 
available, and because these parts have in the past  flown, and in some 
cases, are still flying on several satellites (HST, TDRS, CRRES, etc...). 
Thus, a controlled experiment with these devices provides a unique
opportunity to correlate the special data to be received from MPTB with 
past and current spacecraft performance histories.