(j3.2006) (SC22WG5.5760) RE: RE: Units of measure

Tom Clune Thomas.L.Clune
Fri Jul 8 07:19:17 EDT 2016

I?m now curious how similar/dissimilar the processes at JPL are to those at GSFC.    I?m inside the science/research side of the house which is far less concerned about reliability (see note below), but the spaceflight side of the house would appear to be very concerned about it.   I?ve never heard of any issues with units in this regard but it would appear indirectly that there is a cohort at Goddard that is internationally recognized for leadership in software reliability.   (And none of this is manned spaceflight,which is a whole other level of concern.)

On the science side of things, I?ve worked with a very wide variety of codes over the last 20 years at NASA, including some (SAR) from JPL.   I have very rarely seen quality implementations, and am not infrequently severely disappointed.   But, having said that, I?ve also very rarely uncovered a bug that caused wrong answers in practice.   A major reason for this is that the Earth scientists have a huge amount of data against which to compare their results.    It is a very expensive debugging technique, but it has enabled them to eliminate bugs in code that I would have given up on.   The flip side is that the implementation of new features is incredibly expensive.

I will continue to float the idea of incorporating units into the language when the right opportunities arise.   Thus far (again on the science side) I have not gotten any strong feedback.  Certainly the scientist developers that I?ve discussed this with are not opposed to the concept.     Van seems to represent a more interesting group in that they actually see the standard as something whose path can be impacted.   Here I mostly see developers regard the standard as a ?force of nature?, and spend their time coming up with ?clever? (TM) workarounds.

> On Jul 7, 2016, at 11:39 PM, Van Snyder <Van.Snyder at jpl.nasa.gov> wrote:
> On Thu, 2016-07-07 at 21:43 -0500, Dick Hendrickson wrote:
>> ...
>> On Thu, Jul 7, 2016 at 9:02 PM, Van Snyder <Van.Snyder at jpl.nasa.gov>
>> wrote:
>>        ...
>>> 3.  You implied that JPL has an absolute lock on reliability
>>        requirements.  If providing units checking is so trivial and
>>        so important, why hasn't JPL built or contracted to be built
>>        such a checker?
>>        The "lock on reliability requirements" depends on how
>>        mission-critical
>>        the software is.  On-board flight software, such as the 1/3
>>        million
>>        lines of Ada in orbit around Saturn is the most critical.  The
>>        software
>>        I work on, data analysis after download, is much less critical
>>        because a
>>        mistake can always be corrected and the data reprocessed,
>>        without losing
>>        the entire mission.  It's not free, but it doesn't compromise
>>        an entire
>>        mission.
>>        The reason we haven't been able to get funding for these kinds
>>        of
>>        software tools is that the bean counters don't know which end
>>        of the
>>        software to plug into the wall and which end to use to melt
>>        solder.
>>        Whenever we ask for software tools beyond compilers thay ask
>>        "Huh? Why
>>        do you need that?"  They appear to think that labor is free,
>>        but
>>        software tools are too expensive to tolerate.  
>> Times have changed, but back in the late 60s there never was enough
>> time/money to do it right, but there was always enough to fix it
>> later.
> Times haven't really changed that much, even though Dan Goldin is no
> longer the NASA administrator.
>> Dick Hendrickson 
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