On Feb 9, 2:11*pm, "Eddie Lyons" wrote:
Docking hasn't gotten harder. The trajectory is optimised for fuel
efficiency. There's no particular rush to get there so why waste fuel just
to get there quicker?

I don't see how a perfectly executed one hour ground to docking flight
plan would use any more or less fuel than a four day chase. Why would
a slow continual-thrust spiral be more efficient than raising the
apogee to station orbit in one burn, then raising the perigee to
station orbit on another burn 45 minutes later? It's not like a
planetary proble that is sent on a circuitous path around the solar
system to pick up multi-planet slingshots.

The down-side of a four day chase is that one is burning lots of
consumables. CO2 canisters and food on the crew, hydrogen and oxygen
for the fuel cells. That's a significant amount of mass on a vehicle
like the shuttle which does not have solar panels or recycling.

The upside of a four day chase is that one has tons of time to tweak
the orbit (but if Armstrong managed to get it correct on the very
first attempt in the 60s, it can't be that hard to do with modern
computers). Time to do OBSS inspection is certainly put to good use
(but FD-3/FD-4 rendezvous predates STS-107, so that can't be the
reason). Glen suggests that it allows for elimination of space
sickness during docking (but according to Wikipedia, "In most cases,
symptoms last from 2–4 days" which would mean a FD-1 rendezvous would
be far preferable).