On Dec 2, 4:42*am, "Brian Gaff" wrote:
You know, after hearing a bit about how the Japanese *cargo vehicle is
supposed to be docked to the station, I cannot help wondering if this is
actually safe.

I mean, it has no automatic docking, it just comes to the station, and
station keeps very close while the *arm from the station grapples it and
mates it rather like the mplm to a spare port.

If anything *goes out of line during the grapple, the vehicle could surely
twist, and with its mass be very hard to stop before it hit something vital.
The mplm, after all is *in a rigid mount when grappled, but the htv will be
free floating albeit attitude controlled one assumes. This sort of control
if it uses thrusters rather than gyros could also cause plume damage.

I've not read any discussion about all this and wondered if anyone had
brought it up previously.

All those failure modes and more can happen just as easily with
Progress, Soyuz or ATV. The HTV and future spaceraft like SpaceX's
Dragon only need to approach with the grapple range area of the SSRMS,
and hold still rather than continue to close in order to accompish a
docking. Once grappled, the spacecraft is inert and can be berthed on
a CBM port at the leisure of the station crew. So it seems to me to be
a far safer mode of docking a craft to the station, not less so. It
also confers a weight savings (no docking mechanism) and reduction in
systems complexity. Both good things, plus we retain the ability to
move station racks and other bulky cargo through the large CBM
hatches. A capability that will be lost sadly when shuttle and the
MPLMs are retired.
-Mike