From spencer Wed Oct 25 11:22:42 1995 From spencer Wed Oct 25 11:22:42 1995 To: oleroemer Subject: Memo from Galileo Project X-Sun-Charset: US-ASCII Content-Length: 4136 X-Lines: 91 Status: RO Greetings: This is a memo from Bill O'Neill and Torrence Johnson to the Galileo community this morning. It is pretty emphatic about no Io science being done during the December flyby. As I understand it, any particles and fields data that might be recorded would be done *after* the Io flyby, on the outbound passage through the torus at a large distance from Io itself. (Again, I'm sending this to a subset of the IJW mailing list, including those most concerned with Io and excluding media people) John. ________________________________________________________________________________ 25 October 1995 Refer to: 950-TVJ:vp-95-024 TO: Galileo Science Community FROM: T. V. Johnson, W. J. O'Neil SUBJECT: Status of Galileo Tape Recorder Anomaly and Near-Term Plans As you know, we have been very busy since the 11 October tape recorder (DMS) anomaly on the spacecraft. This is a brief status report to let you know where we are in our investigation and what to expect in the near future. Status of Tape Recorder - Commands sent to the spacecraft 20 October successfully moved and read a small portion of the tape. - This test apparently rules out failure modes involving a broken negator spring, as well as a hard electrical fault or broken tape. - The most likely cause of the anomaly seems to be tape slippage - the cause TBD. - The JPL investigation team is working with the manufacturer (Odetics) to understand the problem and recommend a course of action to operate the DMS reliably. Near-Term Actions - We will attempt to record the full Probe descent data as planned in the Critical Engineering Sequence. - We will increase the amount of Probe data stored in the CDS solid state memory - up to 70 minutes if possible. - We will not use the present concurrent science sequences nor attempt to recover any approach remote sensing observations. - We will investigate whether it is safe to record some amount of fields and particles (LPW) data during encounter and how best to return it. Plans for the Orbital Mission - No Tape Recorder Contingency Mission: We are developing a functional design for a no-tape recorder contingency capability (called "Phase 3" internally). This design relies on using CDS memory currently used for record and playback control to provide an increased buffer size in the CDS to provide real time imaging and PPR capability and expanded real time capability for other instruments. If required, an excellent mission could be flown with this design, including the return of hundreds of hi-resolution Jupiter and satellite images. The phase 3 requirements and point design will be completed by 3 November. We are completing this functional design now in order to have a head start if the recorder fails during the tour. - Tape Recorder Mission: At the moment we expect to proceed with the tape recorder-based orbital mission after return of Probe data. We expect that there will be new and revised rules for operating the DMS and some TBD limitations on the ways we use it. We do not know yet the extent to which we will have to revise existing tour sequences to deal with the DMS. A very preliminary schedule is: - Mid-November: Assessment of tape recorder condition and recommended course of action for future use - Mid-December (post JOI) - 1 January '96: Develop plan for modified tape recorder usage and sequence updates - Uplink new capabilities in time for G1 (July 4, 1996) We would like to thank all of you for your positive and timely response to the DMS anomaly. There will certainly be some disappointments and lots of hard work ahead of us but we remain committed to achieving the Probe mission, getting into orbit, and working with you to perform a wonderfully exciting orbital exploration of the Jovian system.