Reply To: specific foreign languages ?

[zapkitty]

vansig wrote: ok, brainstorming here…

Yay! 🙂

vansig wrote:
refrigerant
isnt ammonia the more common coolant in space?
i hear that helium would be used to cool the DPF anode?

Ammonia is used in current external ISS radiators because it stays liquid at very low temps. But there is a drawback if you want to operate at higher power levels because ammonia is not quite so good as water at handling higher heat loads (although it’s better than anything else but water at the temperatures and pressures we currently deal with)

In fact the interior coolant loop of the ISS uses water in the hab modules, which dumps the heat to an outside ammonia loop via heat exchangers.

But engineering an ammonia loop to handle megawatts of heat at hundreds of degrees is not properly matching the coolant to the project and results in notable engineering inefficiencies. In fact even with the minimal fusion plant discussed here we’re pushing the limits for unpressurized water… but it’s a well understood tech and is both quicker and cheaper to implement than other, more robust options that will require research on orbit before they can even be used.

We are not escaping the eventuality of liquid metal coolants when it comes to fusion plants in space, but water cooling can keep our initial units running while we hash out the more advanced tech… and a lot of time and money will be saved by having an operational reactor in a genuine space environment ready and willing to test out new cooling ideas and systems.

btw, quite a few proposed nuclear spacecraft designs use water as well… so I’m not exactly apostate here 🙂

As for inside the DPF: I’ve been treating it as a black box that puts out electricity and heat. (also magnetic fields but that is another subject) The heat is supposed to be delivered from the reactor by a helium loop but my own little project stops there. Is the helium stored cryogenic? Is it liquified after heating? Are there sufficient hamsters to run the pumps? I don’t know.

I’ve just been told that a certain amount of heat will be delivered via helium gas at a certain temperature.
(well I presume it’s a gas at that temp, I think someone would have mentioned a high-pressure system otherwise… I hope…)

vansig wrote:
VASIMR
is the shape realistic?
pictures i’ve seen show the accelerators as longer cylinders

It’s a placeholder, not a miniature 🙂

And a serious note: I did the pics because others find them useful but I can’t really see very much of them at one time myself. They are just mass and volume estimations assembled as needed… the veriest epitome of the epithet “lego spacecraft” 🙂

The Bigelow modules use the exterior dimensions and wall thickness given by Bigelow.

The nodes are approximate in size based on the CBM hatches that Bigelow uses on all its modules and nodes. (Imperial NASA strikes back!)

The SLASR arrays use the 2.5x5m 4kw units developed by the SLASR people so they’re in the ballpark at least.

Dragon Crew and Dragon Cargo w/ extended trunk are copyright for all eternity by SpaceX.

The station radiator is an external ammonia loop radiator swiped directly from ISS… I wonder when they’ll notice it’s gone…

The arcjet propulsion module uses 4 commercial ammonia arcjets operating at 30kw for 2.37 newtons each at an Isp of 1012 seconds. The implementation thereof is a figment of my imagination.

The CMG box is something else that the inhabitants of ISS will notice is missing… sooner rather than later, I think…

The ISPR racks are done European style instead of the more curved style used elsewhere… (socialist science racks! 🙂 )

vansig wrote:
xenon propellant tank for VASIMR?

… xenon, argon… as long as it’s something easily distributed through the gas or fluid interfaces of the CBMs it doesn’t otherwise matter. LH2 is right out for the initial tests 🙂

vansig wrote:
if opposing nozzles, then each VASIMR engine would connect at about the centre of mass?

Rather, the center of mass of the axis of the station node that they are mounted on… they can be located most anywhere otherwise. I stuck them next to the fusion radiator.

vansig wrote:
can the VASIMR nozzles be positioned?
if they hinge/twist at or near the station’s centre of mass, then they could be
positioned quickly and effectively for acceleration in any direction

They are there to be tested and measured.

They are not there to be a part of station operations.

This is a good thing 🙂

vansig wrote:
mass of the modules?

Usually less than the mass of whatever is put in them… usually…

vansig wrote:
total station mass?

As above. I will have better estimations later on but this will do for a start. The only certainty is that this station will be quite a bit more massive than what Bigelow envisioned the original Sundancer assemblies as weighing in at, thus my substitution of the high-ISP arcjets for the Bigelow hypergolic propulsion module.