What kinds of problems can be encountered while building a satellite like IMAGE?

During August 1997, a 'Mission Critical Design Review' was held to go over the program status, the mission schedule and how well we were on track for a January 2000 launch, and an overview of the Request For Actions problems or 'RFAs' uncovered by the CDR process to date. Below is a table that indicates the number of RFAs that have been identified for each spacecraft component, and which must be addressed and solved in time for delivery of the spacecraft to the Southwest Research Institute (SwRI) in January 1999.

Function Date of CDR RFAs Filed
FUV 24-25 July 37
EUV 22-23 July 36
HENA 9-10 July 31
MENA 15-16 July 29
LENA 29-30 43
RPI 5-6 July
CIDP/SCU 16-17 July 18
Spacecraft 13-14 August 90
Ground Segment 28 July 17
The list looks intimidating, but NASA Project Scientist Bill Gibson noted that some of these RFAs are duplicative, and are actually finished or 'closed-out' issues, but an RFA was filed just to make certain that a paper trail existed for the particular issue to show that the IMAGE team was aware of it, and to show how the issue was settled to everyone's satisfaction.

Problems Found

Common CDR problems included management insufficies, missing parts lists, lack of detailed software requirements, incomplete structural or thermal analysis, and issues related to power supplies.

FUV was identified as being on the so-called 'Critical Path' which is a timeline of activities and technology development issues that are seen as controlling whether IMAGE can make its launch date or not.

The entire spacecraft and the commands for running it remained undefined and this means that the Ground Segment Team in charge of telemetry and commanding the spacecraft cannot as yet begin to develop the GS system in detail. The main holdup is that the individual experiment groups have not yet decided exactly what features of their experiments they want to be commandable and exactly which functions will be needed when IMAGE is operational. Although the specific observing modes are understood and defined, the specific list of commands to activate these modes are not as yet finalized. The specific telemetry requirements, packet sizes and formats and telemetry word lists were still lacking. There will be a workshop on Thursday August 21, 1997 to go over the telemetry issues.

Electromagnetic Interference from RPI

The top IMAGE risk areas were identified and these will be discussed at length today. The most serious one was the RPI electromagnetic interference (EMI). The radiated EMI levels for RPI at PEAK power are well above the levels being tested for in the other instrument test criteria. The RF pulses produce energy which can leak into the interor of the instrument and possibly interfere with the workings of the other experiments. One recommendation is to seal all openings, gaps, seams, screw holes etc that could possibly provide access by the RF energy into the interior of the spacecraft. The cost for this sealing is rather high and estimated to exceed $300,000 and about 1 month of the reserve schedule time would be needed, and only WIC and MENA would not be safeguarded in this way because they may not need this sealing. Also, it is not yet known from the RPI instrument whether it will be operating at peak power on a routine basis. A number of solutions were discussed including building each instrument inside its own Faraday cages, taping the 1.5 millimeter edge joints with copper tape, or even ignoring the problem because not enough RF energy would enter the spacecraft to really matter. The 'EMI Working Group' was setup to look into how severe this problem is and how much time and money should be allocated to insure that the other instruments still operate within their design specifications with RPI working. One estimate suggested it would 'cost' about 500 grams of payload weight to fill all the gaps. Since there are currently 97 kg mass margin, this is not a serious mass increase. There was also the labor and cost issue because Lockheed, who is now fabricating the spacecraft outer shell, would have to be told to 'stop work' on the current gap-filled shell and make the required changes. They could have to scrap what they have just built and start from scratch which would be very expensive and could delay the IMAGE mission. So, the EMI Working Group has to determine how severe the EMI problem is and what the least-costly solution to it is.

There are now over 170 pages in the master schedule. Bill Gibson summarized the current mission timetable and noted that there were only about 2 weeks left of leeway in getting to the planned launch date on time. As of June 1997 Bill Gibson stated we no longer have 'positive margins' on all instruments with FUV showing no remaining reserves for a January 1999 delivery to SwRI. HENA also has a very small reserve. Schedule slips are usually associated with cost problems. Any launch delays could be very costly because it costs about $1 million per months to keep the full IMAGE team active.

Other problems are typically identified and resolved, but there is tremendous pressure to resolve all identified problems that come up as fast as possible to meet the launch schedule.


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