What are the disadvantages of the Soyuz-type 3 module system?

[bobskythecanadianguy]

I just read on Wikipedia about the new Russian-ESA manned spacecraft, and it doesn't look like it will have a Soyuz-style orbital module. What are the advantages of this single capsule type system over a 3-module one? Isn't Soyuz much lighter than similar craft (ie Apollo) while having more room and life-support capabilities? Why drop the orbital module from the design?

[B787_300]

bob it is a bit more complicated than that

An apollo style capsule has 3 connection locations, the hatch on top, a side data and life support connection, and the structural connection under the heatshield

an soyuz style capsule has 5 connection points , the hatch on top the orbital module, a data power and LS connection between the OM and the LM, the hatch ontop of the LM, the power and LS connection from the LM to the SM, and the structure under the heat shield.

Also apollo had more interior space than the soyuz and they soyuz pilots are really cramped in the LM, but there is a lot of open space in the OM.

[Kibble]

There are almost no disadvantages that I know of, except if the Orbital Module fails to separate before reentry, it'll be aerodynamically unstable, and will almost certainly be...catastrophic</3 Thats why for the first several Soyuz flights they jettisoned the OM before deorbiting, until it was judged to be more unsafe to not have docking capability, in case the rocket engine fails to ignite. Its just as unlikely as any other mission-ending failure though.

Don't worry, PPTS is almost certainly going the way of Buran, Kliper, CSTS, and all the other proposed Soyuz replacements.

[Kryten]

Failure to seperate from the OM would be fatal during an abort in most phases of the flight.

[Bill Phil]

Soyuz has a lot less volume than Apollo. At least in the capsule. Very uncomfortable.

Soyuz is better for on orbit operations, while Apollo style is good for missions to the moon. Apollo style as in very heavy...

Soyuz and Apollo are similar, but Soyuz has been around for a while.

[Nibb31]

The advantage of the Soyuz layout is that the smaller descent module can be much lighter, which means that it requires a lighter heatshield, lighter parachutes, and lighter retro rockets, making for a much lighter overall spacecraft for a larger internal volume than Apollo (Soyuz has 6m3 + 4m3 of pressurized volume, Apollo had 6.2m3)

The drawback is that it requires more separation events, which means that more things can go wrong. In fact, there have been several occurences of failing explosive bolts on Soyuz, leading to some very scary reentry situations. None of them ended in disaster, because they were extremely lucky.

Complexity is the enemy in spaceflight, so a cm+sm design is simpler than a om+dm+sm design and therefore more reliable.

Edited February 14, 2015 by Nibb31