Soyuz design changes to address 'ballistic' re-entries

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Flight has obtained details of proposed changes to Rocket and Space Corporation Energia’s Soyuz spacecraft to address the likely cause of Soyuz TMA-11’s 19 April ballistic re-entry, the improper separation of its descent and equipment modules.

Sources working for the International Space Station’s participating space agencies have told Flight that an improper separation caused TMA-11’s ballistic reentry and that recent “improvements” to the spacecraft may have contributed to the last two landings’ problems.

TMA-11 was returning to Earth members of the International Space Station expedition 16 crew, NASA astronaut Peggy Whitson and Russia's cosmonaut Yuri Malenchenko, and the Russian trained guest astronaut, south Korea's Yi So-yeon.

Before TMA-11’s landing, TMA-10’s 21 October descent last year saw a damaged flight control panel wire cause an uncommanded ballistic re-entry.

Although that was the TMA-10 investigation’s conclusion, inadequate module separation was initially thought to be a likely cause. An incorrect separation did occur though for Soyuz 5 in January 1969.

These partial separations alter the descent module’s aerodynamics, as the equipment module is reentering with it, stopping this crew capsule from orientating correctly.

The proposed changes Flight has been informed could be made, to stop this inadequate separation are, for the next Soyuz launch, TMA-13, additional wiring for the separation system’s electrical connectors and for TMA-14, more cabling to provide two independent routes to the pyrotechnics.

While for the 8 April-launched TMA-12, which is currently docked to the ISS, additional checking of the pyrotechnics’ electrical connectors was added to the assembly and checkout process; despite the TMA-10 investigation officially concluding separation was not the cause.

The proposed changes were set out in a 29 April briefing given to NASA’s spaceflight training management office. NASA and Russia's Federal Space Agency were unavailable for comment.

To read more go to Flight technical editor Rob Coppinger's Hyperbola blog