[ntpwg] draft minutes from Vancouver NTP WG meeting

[Danny Mayer]

Rob Seaman wrote:
> On Dec 23, 2007, at 11:38 AM, Danny Mayer wrote:
> 
>> Consider the Interplanetory Internet for example. Sending a packet  
>> from a spacecraft orbiting Mars to a station on Earth, for example,  
>> has very long delays AND asymmetry since the  returned packet will  
>> be returned from a different location on Earth than when it arrived  
>> AND the position of the spacecraft will have changed.
> 
> This is a different problem regime.  The light time delay is highly  
> predictable, whether or not it is asymmetric.  The general issue of  
> "world coordinate systems" and space-time coordinates is quite active  
> in the astronomical computing community - you can benefit from side  
> channel information about the relative positions of the endpoints of  
> each link.
> 

Very true. My Master's degree is on General Relativity by the way so I'm
well aware of the issues. I am also interested in the work that NIST is
doing where they are already needing to incorporate general relativistic
principles to measure time and frequency accurately. Yes side channel
information is helpful here though I don't know how accurate the current
technology is. I haven't tried to keep up.

>> I realise that this is an extreme example (well today it is,  
>> tomorrow it will be commonplace) but it gives you an idea of what we  
>> have to struggle with.
> 
> The Earth-bound challenges are likely to dwarf any spacecraft issues.   
> The relative complexity is opposite to what you suggest.  Also, just  
> as Jetson transport never took off commercially, so it is unhelpful to  
> assume that we'll be nonchalantly zipping around the solar system in  
> the coming century.
> 

No, but I expect many more spacecraft out there.

Danny

> Rob Seaman
> National Optical Astronomy Observatory
> 
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