Brian Thorn wrote in
:

On Sun, 07 Dec 2008 22:00:43 -0500, John Doe wrote:

Does it really reduce flight software complexity ?

Yes, but not very much.

Seems to me that you
still need precise guidance, ability to stop and station keep (more so
with HTV since it will need to station keep very close to the station.

Where would HTV berth ?

Probably Node 1 nadir now that Node 3 won't be there (Node 3 is now
baselined for Node 1 port, opposite Quest).

HTV was never baselined for Node 3. It will be berthed at Node 2 nadir -
just like it has always been planned to be.

And how far from its berthing point will it
need to station keep for the arm to go and grapple it ? couple of
metres ? 10 metres ?

10 meters is a good guess. Has anyone seen any hard data on HTV
approach and grapple?

10 meters is about right. HTV has a "berthing box" they must remain
within in order for the SSRMS to capture it. The velocity requirements
are probably harder to meet than the position requirements.

ATV/Soyuz/Progress use "targets" on the station to get Kurs to guide
their approach. Does the USA side have ay such targets to allow HTV
to guide itself to proper location an orientation to be grappled ?

ATV's approach can be aborted by a crew member on ISS, and ATV has an
auto-retreat system to get out of Dodge if the approach is botched.
Almost certainly, HTV will have the same setup, and can be aborted by
the crew member in the Cupola waiting to grapple it.

HTV has two laser retroreflectors on the nadir surface of the JEM PM.

Bottom line is, the GNC systems needed to achieve the HTV berthing box
are just as sophisticated as the systems required to achieve the
ATV/Progress docking conditions.

There is no significant difference in risk between the systems, and they
are all markedly higher risk than Shuttle or Soyuz, which have crew
onboard. (Remote abort does no good if the spacecraft isn't listening to
you.)