NavList:

Most of the article is behind a paywall---does it happen to say what the current thinking is about the size of antenna needed?  I guess in space, the system noise temperature can be very low indeed.

A competing technology, XNAV, uses periodic x-ray sources for navigation, so essentially the same idea but in the x-ray part of the spectrum.  I seem to remember numbers being tossed around in the few-km range.  Quite impressive.

Well.  Thought I'd glance at Wikipedia's XNAV page for any updates, and there's a reference to something called Project SEXTANT.  Yep, you guessed it:  it stands for "Station Explorer for X-ray Timing and Navigation Technology".  Apparently it's an XNAV testbed that will go up to the ISS soon.

Cheers,

Peter

ps: the fragment of the article not paywalled mentions New Horizons, and seems to imply that the reason it wasn't an orbiter mission was because the nav wasn't accurate enough.  Good heavens.  There is no delta-V for Pluto orbit insertion---the whole mission was structured as a flyby from the very beginning!  Orbiters are possible, of course, but much more expensive.  The nav is/was more than good enough either way.