[FPSPACE] FGB ports

[Bart Hendrickx]

David Anderman wrote :

>Thanks for the information, which implies that the FGB contains 3 different
>docking systems - APAS, to connect to the Unity Node - Probe and Cone at
>the nadir port to connect with Progress, and Hybrid, to connect with the
>Service Module.


>Does anyone know why the Service Module's nadir port is Hybrid, but the FGB
>nadir port is Probe and Cone?


I think that in the original ISS plans both nadir ports were supposed to be
hybrid. Before the arrival of add-on modules to permanently occupy these
ports, Soyuz was to dock *only* to the nadir ports (both hybrid) and
Progress *only* to the Zvezda aft port (probe-cone).

However, in 1997 design changes were made to the FGB, which allowed it to
fly without the Service Module for much longer than originally planned. One
of those changes was to make it possible for the FGB to receive Progress
vehicles, so that it could be directly refuelled by them (and not via the
Service Module or Universal Docking Module). That seems to have necessitated
a switch from hybrid to probe-cone, although I'm not sure what the exact
technical reason for this is. Apparently, refuelling through a hybrid system
is problematic. Exactly the opposite modification was made to Zarya's "aft"
port (the one where Zvezda attaches). This was supposed to be probe-cone,
but one of the other changes made in 1997 was to turn that into a hybrid.
This made it compatible with the Interim Control Module should the need have
arisen to launch it.

By the way, there is un update on the Russian segment in the latest issue of
"Novosti Kosmonavtiki". The Docking and Stowage Module has been cancelled
and there is a good chance that the same fate will befall the Universal
Docking Module (UDM) if the Russian government doesn't come up with any
money soon. The only modules likely to fly are the commercial ones, the
Khrunichev/Boeing Commercial Space Module (CSM) and the Energiya/Spacehab
Enterprise module. The Commercial Space Module (to be launched by Proton) is
likely to be ready first because it will be based on the already-built Zarya
back-up ("FGB-2"). The Enterprise (to be launched by Zenit) is yet to be
built. If the UDM is cancelled, that would solve the problem of where the
commercial modules are to be docked, because both the Zarya and Zvezda nadir
ports would become available.

All this does raise the question if the functions of the UDM and the Docking
and Stowage Module can simply be taken over by the commercial modules. For
instance, it is not clear now where the gyrodins for the Russian segment
will be installed. Originally, they were supposed to be mounted on the power
platform, then on the UDM and according to the latest plans on the Docking
and Stowage Module, which has now been cancelled. It is also clear that one
of the two modules should have some kind of multiple docking adaptor on the
aft section.

Bart Hendrickx