Friday, December 7, 2012

Your Descendents Will Likely Never See Your Digital History

I've written before about the risks of digital storage for family archival material.  The IEEE Spectrum has published a story that leads me to believe that I was probably too optimistic when I wrote that.  The main topic in the story is that a group of people appear to have solved the Pioneer deceleration anomaly.  The part of the story that interested me was how hard it was for that group to put together the data necessary to do the necessary analysis.

First, some background.  Pioneer 10 and 11 were unmanned deep-space probes launched in 1972 and 1973 respectively.  Both traversed the asteroid belt and made fly-bys of Jupiter.  Pioneer 11 used a gravity slingshot maneuver around Jupiter to enable a fly-by of Saturn as well.  After passing those planets, the Pioneer spacecraft became essentially ballistic objects headed out of our solar system, with their courses determined only by the effects of gravity from the sun and planets.  By 1980, however, measurements showed that the probes were slowing more than could be accounted for by gravity alone.  The anomaly was announced in 1998, and hundreds of papers proposing explanations for the slow-down were subsequently published.

In order to conduct a detailed analysis of one of the possibilities, it was necessary to have access to as much of the Pioneer navigation data as possible.  That data was originally stored on various media.  From the Spectrum story:
"As luck would have it, most of the Pioneer 10 and 11 telemetry data had been saved and were available for study. Although there was no requirement that NASA properly archive these records, it turned out that systems engineer Larry Kellogg, a contractor and former Pioneer team member at NASA Ames Research Center, had been informally preserving all the Pioneer data he could get his hands on. Kellogg already had nearly all of the two probes’ master data records, binary data files that contained all the Pioneers’ science and housekeeping data.
Kellogg had taken care to copy those records, which in total took up just 40 gigabytes of space, from soon-to-be obsolete magneto-optical discs to a laptop hard drive. When we decided to work with the telemetry data in earnest, in 2005, one of us (Toth) had already been in touch with Kellogg, working on new software that could extract useful information from the master data records without the need for an old, decommissioned mainframe.
Procuring additional Doppler data that could help solve the mystery turned out to be a bit trickier. The JPL team had already collected all the radio-science data files that were easy to find and work with, but we knew that we needed more measurements. It took some time, but we were able to find additional files on the hard drives of JPL navigators’ computers and the archives of the National Space Science Data Center. We even found magnetic tapes stuffed in cardboard boxes under a staircase at JPL. Some of the files were in a rather sorry state, corrupted while they were converted from one storage format to another over the span of three decades."

 Despite their best efforts, the authors (and others) recovered only 23 years worth of data for Pioneer 10 and 10 years worth of data for Pioneer 11.  The whole process illustrates exactly the problems that I suggested put family digital archives at risk: (1) will someone preserve the digital media, (2) will it be possible to extract the bits from the media, and (3) will there be software that understands the coding used for the data?  If NASA keeps magnetic tapes with the data from two extremely valuable space probes in cardboard boxes under a staircase, how many of my descendents are going to do any better?

NASA apparently did better with paper records.  The authors were able to obtain the original blueprints for the Pioneer craft -- designed in the days before computer-aided drafting -- for use in constructing a detailed thermal model of the vehicles.  Even with access to blueprints, it was necessary to consult retired engineers from the firm that built the Pioneers to obtain some details.  In addition to distrust of my descendents storage conditions, there's also a question of whether they could afford the same kind of recovery effort as the authors (funded in part by the Planetary Society, a nonprofit space-advocacy organization).  I'm going to have to rethink my preservation "strategy."  Encode the files simply.  Get copies into as many hands as possible.  And find someplace safe to store a paper version.

Oh, and the deceleration anomaly?  No new physics, I'm afraid -- it appears to be simply asymmetric heat radiation from the on-board plutonium-fueled electric generators.

Photo credit: Slava G. Turyshev

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