Do different cargo carriers to the ISS generally have different profiles for their cargo composition, or is it basically just the number of tons that matter? Especially with respect to cargo which is expensive to replace, such as some spare parts and science experiments.

Many different spacecrafts have visited the space station: Proton, Soyuz, Shuttle, ATV (ESA), HTV (JAXA), Progress, Dragon, Cygnus. It was my impression that much more attention given to the experimental payload lost with the Antares/Cygnus Orb-3 failure in October 2014, than after the loss of Progress 59 (or M-29M) in May 2015. Didn't the Progress carry as much value per ton? Or is it maybe a national issue? American Cygnus carrying American payloads which are reported in English speaking media, while Russian Progress carries mostly Russian payloads which are harder to learn about for non-Russian speakers? What factors play into this, technically and policy?


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Progress is built around the same basic design as the Soyuz, three modules. Propulsion is much the same. The Orbital module at the other end, docks to the station and has cargo the crew removes. The middle module on Progress (where the crew would normally be during launch/landing) is redone to carry fluids. Water, fuel for the station, whatever. Thus Progress is optimized for fuel carriage. Dragon has recently been upgraded to allow carrying water to the station as well.

HTV has a large capacity (6000Kg total), and allows for a fairly large unpressurized cargo to be brought up (1500Kg). Dragon has similar unpressurized cargo but in smaller size (Max of 3310Kg combined pressurized and unpressurized). Thus Dragon and HTV have the better unpressurized external carriage.

Cygnus when fully expanded has pretty good internal volume and mass capability for payload.

So why the disparity in concern on lost 'things' between Cygnus and Progress? Probably the incidental nature of the specific payloads.

Progress carries food, water, fuel, etc. Basics. Cygnus just happened to be carrying experiments of interest on that flight. As well as basic food, supplies, etc.

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    $\begingroup$ Is Progress the only vehicle presently capable of transferring propellant? Somewhere I got the impression that Dragon and Cygnus can not. I have a recollection the ATV could, I don't know about HTV. $\endgroup$
    – Puffin
    Commented Dec 6, 2016 at 21:43
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    $\begingroup$ That is a good standalone question. :) The answer is that the plumbing to PUMP fuel and water into the station, is only available on the Russian ports, so Progress and ATV were the only possible vehicles. $\endgroup$
    – geoffc
    Commented Dec 6, 2016 at 22:19

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