<div dir="ltr">So then the irony is that the same mathematics used to error correct the data transmissions from Voyager II can't be used to verify the integrity of the backups for said data.</div><div class="gmail_extra"><br><div class="gmail_quote">On Wed, Oct 28, 2015 at 8:29 PM, Alex Carver <span dir="ltr"><<a href="mailto:agcarver+ale@acarver.net" target="_blank">agcarver+ale@acarver.net</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><span class="">On 2015-10-28 13:42, Jim Kinney wrote:<br>
> On Wed, 2015-10-28 at 14:46 -0400, James Sumners wrote:<br>
>><br>
>> I am glad I do not work where you work. Redundancy doesn't imply<br>
>> corruption mitigation. And refusing to allow such to be implemented<br>
>> because the tool isn't "old" is asinine.<br>
>><br>
> It's not that things are refused because they are new. It's rather they<br>
> are refused because they are not yet "well understood" and "mature".<br>
> Mil-Spec work is _always_ like that.<br>
> Often, there are areas where software is never upgraded or changed<br>
> because the systems are never networked. Thus any problem can never be<br>
> fixed and the process that machine exists for _MUST_ be up at all<br>
> times. So, no "new hotness allowed". Imagine being stuck in a world<br>
> where "new" was RHEL 5.<br>
<br>
</span>I'll give a real world example that's happening right now. One of the<br>
projects here is Voyager (you know the one with the two probes that<br>
exited the solar system and are now in interstellar space). The last of<br>
the original project members (the project manager) has announced his<br>
retirement at 83 years old.<br>
<br>
Voyager wasn't expected to be operating past ten years after launch<br>
(long enough to reach the primary targets Jupiter and Saturn). It was<br>
launched in 1977 but design and construction would have started in the<br>
very early 70's (mission concept, design and construction of this class<br>
is typically 6-10 years) which means the Voyager documents are now over<br>
40 years old. It's also still classified as an active mission because<br>
it is still returning science data which means making sure the computer<br>
and instruments on board stay running. Voyager's code is assembly with<br>
64 kilobytes of total operational program storage space on board (data<br>
is recorded to an 8-track tape).<br>
<br>
During the flights of the two Voyagers, many modifications to the code<br>
had to be made. This involved, among other things, knowing very<br>
specific details about the instruments on board each one which turned<br>
out to have very subtle differences. The code has to be rewritten from<br>
scratch every time because of the limited space. It gets written on the<br>
ground, verified, then uploaded.<br>
<br>
Unfortunately, the data retention policies at the time were not very<br>
stringent. Since the mission was expected to last only about 10 years,<br>
many documents were not updated and archived properly. Engineers kept<br>
details in their heads because they would likely still be working beyond<br>
the end of the mission. As the mission continued past its original<br>
endpoint, this quickly became a problem when changes needed to be made.<br>
Many of the engineers have died taking secrets about the spacecraft<br>
with them. In other cases files have been lost to time because the were<br>
written in formats that no one knew how to interpret (work is ongoing to<br>
recover much of that data). There's even a working replica of the<br>
computer in the mission office today where code is tested before upload.<br>
It has been running since 1979 and still needs to be maintained.<br>
<br>
It was because of this and other early projects (Explorer, Mariner,<br>
etc.) that the data usage, retention and archive policy was tightened.<br>
That included what software could be used and how generated data could<br>
be stored. The entire intent is to maintain an accessible, functional<br>
history for scientists and engineers in the event we need to go back to<br>
old data for anything. That happens very often.<br>
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</div></div></blockquote></div><br><br clear="all"><div><br></div>-- <br><div class="gmail_signature"><div dir="ltr"><div><div dir="ltr"><div>James Sumners<br><a href="http://james.sumners.info/" target="_blank">http://james.sumners.info/</a> (technical profile)</div><div><a href="http://jrfom.com/" target="_blank">http://jrfom.com/</a> (personal site)</div><div><a href="http://haplo.bandcamp.com/" target="_blank">http://haplo.bandcamp.com/</a> (band page)</div></div></div></div></div>
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