kbd512 Postings

tahanson43206 · 2025-04-09 17:11:58

For kbd512...

Thanks for looking at the specs for the optical plane.

Your comment revealed an (understandable) impression that the AI picked 1000 as the solar flux I wanted to design for. That is not correct. I told it from the beginning that I wanted to use 1000. If we design for 1000, and get more, then the system will perform better. On the other hand, if we plan for 1000 and fly out to a distance where 1000 is normal, then the system will perform as designed.

***
Thanks for additional details about how metals might help at some point in the project. I've decided to just go with the recommendation to use carbon, based in part on the great number of examples you provided. In my next session with ChatGPT4o, we'll dive into the challenge of heating the hydrogen through a 240 meter long carbon tube. At this point I don't know what diameter to start with or what increases to make along the 240 meters, but I'm hoping we can figure that out as we go along.

The optical input from the wings will be 6000+ watts per 38 mm, and that input will be supplied for the entire length of the pipe.

ChatGPT4o seems to think that 40 MW can heat 1 kg/s of hydrogen from 300 K to 3000 K, so tomorrow I hope to see how that would happen in the long heating tube.

I'll also be interested to see what pressure ChatGPT4o comes up with as we proceed. GW was looking for something in the range of 3.5 to 7 bar, and apparently if we can provide that he can deliver .93 force-tons (point nine three).

(th)

tahanson43206 · 2025-04-12 16:35:28

For kbd512 re graphite as a candidate material for Heat Pipe...

GW wrote about graphite in the context of heat shields and rocket nozzles.

My guess is he is not up to date with all the new materials you have found that feature carbon.

Graphite is just one form of carbon.

If you have time, please prepare a review of carbon based materials for Sunday evening.

https://newmars.com/forums/viewtopic.ph … 41#p231041

Graphite is both a poor insulator and a poor conductor of heat.

(th)

tahanson43206 · 2025-04-14 19:48:54

For kbd512 re Optical Plane vessel...

There is a need to be able to focus either the optical devices individually, or the entire wing to stay in the Sun's view as much as possible.

I am starting to work on navigation, and we may not be able to guarantee 100% perpendicular orientation for the space tug when attached to a payload.

Can you help by doing a bit of research to find out how much flexing fiber can stand? We're not talking about much but most fiber never moves after it is installed.

(th)

tahanson43206 · 2025-04-15 09:32:07

For kbd512 re Optical Plane vessel...

I'm working on a program to combine heat pipe and nozzle.

I looked for carbon pipe but only found carbon steel.

If you can spare a moment, please see if you can find pipe of about 25 cm diameter or 9 inches or a bit more.

The heat pipe needs to be larger than the nozzle throat, but this seems to be a chicken-egg problem so I thought a reasonable approach would be to see what size pipe is available.

(th)

kbd512 · 2025-04-16 04:32:05

tahanson43206,

Graphite heat exchanger tubing and shells are available in a very wide variety of sizes and shapes, because it's a sintered and then hot-pressed material formed using molds or 3D printing. I don't know think there are any Graphite tubes 240m long, but there are certainly 5m to 10m long tubes with flanges for connection to additional lengths of Graphite tubing. Heck, we even make Graphite and RCC bolts / nuts / studs / gaskets for connecting flanged piping.

If you require a 240m long heat pipe, that would imply 24 of the 10m long tubes, and possibly some sort of exterior support structure using stranded Carbon Fiber acting sort of like the suspension bridge cable-stays, which can natively survive high temperatures since they're made from pure Carbon as well.

complex pure Graphite components such as this jet mixer are also possible:

The components in some of these chemical processing plants are of considerable size because they run the Sulfuric acid through one set of pipes while they run water outside the pipe to absorb heat from the chemical reaction taking place inside the smaller diameter Graphite tubing. These chemical processes run at modest pressures but can and sometimes do achieve high temperatures.

tahanson43206 · 2025-04-16 06:11:19

For kbd512 re #255

Thanks for additional information about graphite tubes and related products!

Thanks too, for thinking ahead to mounting the heat pipe inside the cylinder of optical output devices.. The forces at work during flight will be primarily experienced along the length of the pipe, but keeping the pipe centered in the heating cavity is important, and your suggestion of a tension network instead of a compression system should save weight.

The hint I pick up from your post is to ask Google to look for chemical plant suppliers and for graphite tubing.

As reported earlier, the diameter of the heat pipe appears to be a significant factor in design of the nozzle, so I'm hoping to find a commercially available pipe suitable for this application.

(th)

tahanson43206 · 2025-04-19 19:22:03

for kbd512 re Registration message....

I put a reminder in Housekeeping, as you suggested.

I ** think ** that since you are an Administrator, you may have the ability to update that message in the database.

SpaceNut would ordinarily take care of something like that, but he's been out of touch since his wife died, and he started the house remodel.

(th)

tahanson43206 · 2025-04-20 19:58:30

For kbd512 ....

First, thanks for updating the Registration Information Line !!!

Second, re https://newmars.com/forums/viewtopic.ph … 40#p231240

Holy Moley!

Third... I was able to take a picture of the Merlin engine outline:
https://newmars.com/forums/viewtopic.ph … 39#p231239

(th)

kbd512 · 2025-04-20 21:55:16

Blackbody Definition
A blackbody is a theoretical object that absorbs 100% of the radiation that hits it. Therefore it reflects no radiation and appears perfectly black. In practice no material has been found to absorb all incoming radiation, but carbon in its graphite form absorbs all but about 3%.

Stefan-Boltzmann Law
P = σAT4
P = Power (energy per unit of time)
σ = Stefan-Boltzmann constant (5.67 x 10^-8 W/m^2K^4)
A = surface area of the blackbody (in square meters)
T = temperature (in Kelvin)

A = 1m^2
T = 3,000K
P = (5.67 x 10^-8 W/m^2·K^4) * (1m^2) * (3,000K)^4
P = 0.0000000567 * 1 * 81,000,000,000,000
P = 4,592,700 Watts per square meter, or 459.27W/cm^2

40,000,000W = total collected input power available from the solar concentrating array for heating of the Hydrogen propellant

40,000,000W / 4,592,700W/m^2 = 8.709m^2 <- Maximum receiver surface area which can be heated to 3,000K by the solar concentrator array

For this Graphite heat pipe (more of a soda straw) to be 240m in length, it needs to be 11.54mm in diameter. On the bright side, it could be flexible enough to bend like a fishing rod for easy storage / transport to LEO. On the downside, coupling the power into something that small could present a bit of a challenge. However, I think I finally understand what you're trying to tell me about why it has to be built that way. It's related to getting the power out of the collector array and focused onto the receiver tube assembly, as I understand it. I'm not trying to argue, merely understand what you're telling me. If that's how it has to be built to keep the weight of the collector array in check, as well as the complexity and thus cost of the tech used, then so be it. I can envision some structural advantages to the 240m tube vs a much more compact receiver. After all, that gigantic solar concentrator array has to be connected to something.

The emissivity of Graphite is not equal to 1 (Graphite is not a perfect black body), so we would need to modify the equation used to arrive at the actual Watts of power input required to heat the receiver tube assembly to 3,000K. However, this places an upper limit on the surface area and volume.

What are we connecting the LH2 tanks to, so as to keep them well away from the receiver tube?

We seem to have a rather complex vehicle geometry to keep the imparted forces low and the structures light, but I'm trusting your judgement on this arrangement so as to ensure we remain within tolerable mass limits because you have more sophisticated tools at your disposal than I do, specifically the AI and OpenFOAM simulation tools.

tahanson43206 · 2025-04-21 10:50:44

For kbd512 re #259

Thanks for this post, with what appears (at first scan) to be a helpful summary of data about the heat tube.

It will be a bit of a while before I can get back to it, but I'll put a search term here so it's easy to find: SearchTerm:Graphite

Void just posted about 3D printing of carbon structures. I don't know if it applies to the Optical Plane vessel, but the idea of 3D printing the entire heat tube in one operation is attractive.

https://newmars.com/forums/viewtopic.ph … 46#p231246

Update later....

If it is possible to 3D print a tube 240 meters long on Earth, then it should be possible in LEO. That would be a ** very ** nice way to solve the assembly-on-orbit problem. If it is possible to 3D print a tube, then it should be possible to print the spars and ribs of the Optical Plane wings, if they can be made of carbon, which seems like a reasonable idea to me.

***
In post #259 (if I am remembering correctly from my first scan) you brought up the important point of the keel design, to keep the propellant away from the hot tube at the same time as keeping the propellant away from the Sun. One advantage of the ship design is that there will be plenty of electricity available to keep the propellant cool while preparing for thrust events.

I suspect that some metal will be required for the keel, because the engine thrust is going to be carried up to the payload from the nozzle, according to GW's latest iteration of the design. If you have not been following along, the nozzle cannot swivel, so the most attractive option right now is to swivel the docking adapter.

(th)

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