In checking back over my files from my employment at the NASA Johnson Space Center, regarding my review of Russian safety documents from the point of view of Orbit Design, I came across this interesting memo. The section on "collision during docking" tried to point out what I thought was an inadequacy in the Russian assessment of the danger of this type of accident. Recent events, in hindsight, give perspective to this long-ago and long forgotten memo of mine. --

Jim Oberg

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Memo
Oct 12, 1994
To: G. Schrage
From: Oberg/R16C/282-4351
CC: K. Repa; C. Manno
memo.270
Re: Review of Russian Report on Service Module Hazards

Per your request I reviewed the document "Analysis of Off-Nominal Situations Associated with the Service Module (SM) of International Space Station Alpha", September 1994, from NPO Energiya, as part of the Russian Service Module Hazard Report Review process (DM contact is M. Donahoo). I paid particular attention to FD&D issues such as space debris and prox ops, which comprised a significant subset of the 38 contingencies specifically listed and described.

My overall impression is that the NPO Energiya document covered the 'classic' hazards associated with FD&D, but provides incomplete and misleading documentation of actual flight experience in the Soviet program regarding many of these types of failures. This withholding of relevant safety-related flight data is distressing and should be a topic for future discussion with the Russian side.

The following specific comments provide more details.

Pressure Hull Rupture during docking: Failure RS-02 discusses impact during nominal approaches, and states that since the R-dot is usually less than 0.3 m/sec, "probability of penetrating the SM shell is rather small". If so, why do Mir crews retreat to the Soyuz module during such dockings? The term "rather small" still allows Russian practice of preventive and other contingency measures. Further, this is an incomplete contingency since a sensor/control failure during prox ops [‘proximity operations’, or flying one vehicle near another vehicle] can lead to a higher approach rate with consequent higher danger of hull rupture.

The point to be made here is that contact/rupture and sensor/control failure are NOT independent contingencies to be only considered separately, since the former can be a direct result of the latter. Information on the maximum allowable impact forces, and associated contact rates, should also be estimated and provided here.

Historical Soviet prox ops contingencies have resulted in close fly-by near misses with rates in the 3-5 m/sec and greater range, and should be documented explicitly.

Vehicle-Generated Debris Recontact: The list of failures does not include any discussion of the volume of vehicle-generated objects jettisoned deliberately or accidentally during flight, with potential recontact. The danger of recontact is less a penetration of the pressure hull than a jamming of exterior mechanisms. Salyut/Mir vehicles generate a significant amounts of debris, and on at least one occasion one such piece (a trash bag) jammed a docking port and required a contingency EVA to clear it. Such contingencies are not covered by this document, but should be.

(deleted)

Conclusions: This survey of contingencies provides details on most 'classic' threats, although it omits threats from SM-generated debris. More significantly, this Russian report provides incomplete and misleading documentation of actual flight experience in the Soviet program regarding many of these types of failures. This withholding of relevant safety-related flight data is distressing.