[ntpwg] draft minutes from Vancouver NTP WG meeting

[Rob Seaman]

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.

> 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.

Rob Seaman
National Optical Astronomy Observatory