This came up here, and it seems like it required another question.

I always assumed that the Torpedoes were 'sucked' in. Although thinking about it, the port is an exhaust port. Perhaps some complex pump system causes a pressure differential after exhausting waste gas.

Our candidates are: Heat, Gas, Solid, Liquid, Plasma.

What was the vent venting?

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    The weekly curry night was just before, and you know how it gets .... Jan 5 '12 at 21:18
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    Venting heat would be unlikely, since that would be handled with heatsinks.
    – Tango
    Jan 5 '12 at 21:18
  • @TangoOversway - To say nothing of the fact that the vacuum of space doesn't conduct heat. Unless the heat it's venting is radiant (like sunlight), this vent can't be of any use at all, as there are no atoms to convey heat energy in space.
    – Dan Ray
    Jan 5 '12 at 21:27
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    I think a better way to word the question would be, "How does a hole or port vent heat instead of a heat sink?" There's nothing there, just a hole. It's not possible to vent heat that way.
    – Tango
    Jan 5 '12 at 21:38
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    It wasn't an exhaust port, it was an aesthetic choice by the architect.
    – Anthony
    Jan 7 '12 at 0:37

My guess is that it vents heat by expelling superheated gases (not plasma). Everyone is right that the only way heat can escape a body in space is by radiation, so an "exhaust port" designed to expel pure heat the way a car's exhaust would wouldn't work very well.

HOWEVER, that's not the only way to remove heat while in a vacuum. A very effective way to cool heated surfaces such as heatsinks is to spray a liquid onto that surface, forcing conduction of the heat away from said surface, and then expelling the now-heated liquid or gas into the void. As the main source of heat in the Death Star would be its reactor core, should that core overheat, you can cool the entire system by simply expelling some of the coolant and replenishing it.

The original novel by Lucas states, as an extension to the dialogue heard in the movie, something along the lines of "the shaft would be rendered useless by particle shielding; however, it is completely ray-shielded". This further increases my confidence that the "thermal exhaust" consists primarily of matter and not energy. And, we know there's a main port that usually handles most of the station's cooling needs, but this port can likely be particle-shielded to protect it in an attack, leaving the auxiliary port to handle the cooling needs.

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    That last sentence is the clincher!
    – AncientSwordRage
    Jan 7 '12 at 11:09

Surely the fact that it's a thermal exhaust port indicates that it vents heat?

Thermal exhaust port

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    But through what medium?
    – AncientSwordRage
    Jan 5 '12 at 21:44
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    Exactly! Heat isn't just vented, it has to pass through matter. That's what a heat sink is for.
    – Tango
    Jan 5 '12 at 22:08
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    @TangoOversway - Slightly misleading statement, heat can pass through vacuum in the form of radiated light - witness the sun. A heat-sink whilst usually designed to remove most of its heat by convection, some will radiate too. That said, I understand what you mean - either this port radiates very little heat, or it would have to be glowing. Jan 6 '12 at 0:41
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    @iandotkelly: Maybe it was glowing, but in a non-visible portion of the EM spectrum (i.e. infrared).
    – gnovice
    Jan 6 '12 at 7:07
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    Things start glowing at around 400 Celsius, not 'couple thousand', so this would be ~670 Kelvin as the upper bound on the difference between the vent and space, which actually isn't that large a temperature difference. Evaporative cooling in the context of a vacuum means dumping a material into space. As @anthony-arnold points out - one explanation is that it wasn't venting at the time of the attack. Jan 6 '12 at 13:58

Radioactive particles

The issues that the exhaust port was intended to deal with are discussed in great detail in the Rogue One novelization. Basically, radioactive particles from the reactor core were causing it to overheat.

I also spoke to my team and we identified the problem. The reactor core modifications are resulting in radiation buildup, which in turn has the potential of interfering with the hypermatter annihilator.

The buildup is caused by the inner shield actively reflecting excess particles and metaphorically “cooking” the reactor core. Had the shielding team’s research not been so heavily compartmentalized this might have been avoided.

Rogue One: A Star Wars Story

The exhaust port was one of three proposed methods for dealing with the aforementioned problems.

Option three: construction of manual venting shafts and thermal exhaust ports. This should reduce particle buildup to within tolerances but not to a degree I find personally acceptable. In addition, adding venting shafts risks additional incompatibilities with noncritical systems.

Rogue One: A Star Wars Story

It’s probably worth noting that expelling massive radioactive particles would really be the only feasible way of reducing heat buildup in the core. Radiative heat loss (i.e. from electromagnetic radiation, which is to say massless particles) in space is quite inefficient.

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