Tag Archives: Soyuz 2-1a

116th cargo mission to the ISS is underway: Progress MS-06 launches

The Progress MS-06 spacecraft has been placed into orbit by a Soyuz 2 1-A rocket out of Baikonur Cosmodrome.  It carries 2450 kg of cargo, including 705 kg of propellant, 50 kg of air, and 420 kg of water.  (The ISS has a water reclamation system, but it is not able to provide 100% of the crews’ needs as yet.)  Among that cargo is a set of four nanosatellites which will be hand-launched by cosmonaust during a spacewalk.  Progress MS-06 will dock with the Zvezda module’s aft compartment, allowing it to transfer propellants into Zvezda’s tanks.

Progress MS-06 was originally slated to dock with Pirs, which it would then carry with it for disposal at the end of its mission, freeing a docking port for the Multipurpose Logistics Module “Nauka”, which has faced numerous delays going back years.  Unfortunately, Nauka encountered more delays and is no longer scheduled to launch before 2018.  Therefore, Pirs will remain at the ISS when Progress MS-06 departs.  Pirs does double duty as both a docking compartment and an airlock for EVAs mounted from the Russian segment; Nauka is equipped with an airlock as well.  Even if there is no Russian airlock, there is of course the Quest airlock on the US segment, but it is generally preferred to use the closest airlock to a given worksite.

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Russian rocket mishaps solved?

The investigation went deeper than previous ones, since the previous hadn’t actually resulted in any improvement, and what they found was surprising to me.  It wasn’t just quality control issues in manufacturing, as had previously been suspected; there are honest-to-gosh design defects in both the Briz-M upper stage for the Proton, and the upper stage of the Soyuz 2-1a.

The Soyuz 2-1a is a new model of the venerable R-7 family.  Being quite new, it’s perhaps unsurprising there’s a problem, but what’s interesting is that the design flaw only shows up with the Progress as payload.  (Presumably, it could also happen with Soyuz, which shares its service module entirely with Progress.)  This explains why it never had a problem on any of its other flights, but the defect must be fixed before it can carry Soyuz or Progress into orbit.

The Proton defect is a bit more worrisome, because it’s been in the system for decades without anyone noticing — despite multiple failures with similar characteristics and multiple investigations.  A small vernier engine used for steering the vehicle during third stage flight has a design defect which makes it extremely easy to unbalance.  And when it becomes unbalanced, it experiences increasingly violent vibrations until it undergoes what rocket scientists dryly refer to as an “unscheduled disassembly”.  The good news is that existing engines can be reworked with a different rotor shaft in their turbopumps to prevent the problem happening again.  Also, it’s back to flight now, having been cleared for all non-Progress/Soyuz flights, placing a military satellite (possibly a Kobalt or Persona spy satellite) into orbit:

So, good on you, Russia, for finding these defects!  Hopefully the design change and rework will do the trick, and keep Proton flying safely.  Alternately, I’d be happy with them replacing it; Proton’s one of the last flying launch vehicles to use hydrazine and nitrogen tetroxide in the first stage.  Nasty stuff to release into the atmosphere.

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