HN user
I'm a little late to the party, but I did a similar study on ridesharing's influence on DWI rates in Austin, TX before and after Uber and Lyft arrived and then exited the city, you can read it here: http://rpubs.com/ianwells/247645
Forward error correction can add significant overhead. From the specification of the RF subsystem posted earlier (http://www.boulder.swri.edu/~tcase/NH%20RF%20Telecom%20Sys%2...), 5/6 of the data returned is redundant.
New Horizons is using a 1/6 rate Turbo code for forward error correction, meaning 5/6 of the data returned is redundant. Previous discussion: https://news.ycombinator.com/item?id=9890476
Much faster data rates I suspect - you can spend some of that on forward error correction to compensate for rain fade.
Pretty much - call that antenna gain, it's much cheaper to put bigger and better hardware on the ground. Recall though that the signal still goes through a TDRSS satellite, which also has a bigger dish.
Other more obscure methods of communicating with the ISS include the Russian Lira and Regul systems as well as the Japanese Ka-band dish on the external lab.
Can't speak for S-band, but Ku-band data rates are 25 Mbps Earth-to-ISS and 300 Mbps ISS-to-Earth, which is the maximum supported by TDRSS Ku-band links. Data rates may drop a bit depending on the individual satellite involved, configuration, etc.
Elaborating on TDRSS a little bit - the ISS has allotments on both S- and Ku-band transponders (there are several per satellite) and hands off between satellites (TDRSS is geostationary) as it orbits, it's rare that another TDRSS customer has something important enough going on that the ISS gets no allocation at all for more than an orbit.
IMHO, the real application for laser communications is for high bandwidth inter-satellite links.
Try space-filling curves! http://www2.isye.gatech.edu/~jjb/mow/mow.html