kbd512 Postings

tahanson43206 · 2025-03-10 10:55:39

For kbd512 ...

Thanks again for your participation in Sunday's Google Meeting!
***
As a follow up ... I just scanned a collection of posts that FluxBB found with the words "photon" and "trap"....

I didn't find the post you gave us showing the optical device that collects light for shipment indoors via optical cable.

If you have time please remind me of that post.

However, the reason for ** this ** post is that in one of the posts in the collection, in which you and Louis were talking about solar panels on Mars, the spectrum came up briefly.

An advantage of the all-thermal system you are working on is that the full solar spectrum is potentially available for the system, and not just the optical spectrum.

The infrared wavelengths might be (somehow) adapted to feed into the fiber, and perhaps ultraviolet photons might be stepped down to travel the same path.

I'm wondering now if the 1350 watts of solation that Wikipedia reports per square meter on Earth might be limited to the visible spectrum.

I found a graph showing the spectral distribution of solar energy reaching Earth, and the bulk is in the Visible range. However, longer wavelengths are present in significant amounts.

(th)

tahanson43206 · 2025-03-20 06:26:15

For kbd512...

Glad you're feeling better!

Thanks for taking a look at the Optical Plane topic.

It is possible you haven't noticed that I did not hear back from Edmund Optical. I'm disappointed but not surprised.

The optical TIR device may not be available off the shelf, although lens of the required dimensions definitely are.

Edmund Optical is probably a distributor and not a manufacturer.

***
The next stage of development appears to be design of a test rig for the heating system. GW has drawn from earlier work and extended it to apply to the present concept, and I hope to have his latest work posted today.

Here's something for you to think about ....

A test rig could use hydrogen as the test gas, but hydrogen is dangerous. Nitrogen might work as well for the purpose of testing materials for the hot core. Are you aware of any reason nitrogen would not be acceptable as a substitute for hydrogen?

***
I've lost track of the performance data you provided...

We have a system size of 40 MW as a firm specification.

I'm a bit less sure of the material flow rate. I ** think ** that is 2 kilograms per second of LH2.

The desired ISP is 800 (matching NERVA?)

The associated temperature is 3000 Kelvin?

The possible thrust is 1/2 force-ton.

That 1/2 force ton is available as long as the LH2 holds out.

GW suggested carrying propellant in the keel under the optical deck.

Such a keel would provide the strength needed by the system to perform push operations, as appropriate for a space tug.

It ** should ** be possible to use the ordinary rocket equation to determine system performance, since we have ISP and propellant flow rate.

Half a ton-force is not much, but it could amount to something if it runs long enough. The mass of propellant is a variable that can be adjusted. I'm wondering what a graph of performance would look like if we plotted the variables in play.

Variables in play include the mass of the propellant, and thus the duration of thrust, as well as the mass of the vehicle and the customer vehicle.

(th)

kbd512 · 2025-03-20 09:43:30

tahanson43206,

Yes, testing can be performed with N2 vs H2. This is fairly common. The safety equipment required for using H2 as the test propellant dictates some fairly extreme equipment costs. Only a well-equipped university labs or NASA ion engine test facilities would have that kind of equipment. Performance values can be extrapolated.

H2 mass flow rate (mdot) was anticipated to be around 1kg/s. I think I originally empirically derived H2 flow rates obtained from NERVA documentation.

Target / desired Isp was 1,000s, which is how the 40MWth input figure was derived.

I believe 3,200K corresponds with a 1,000s Isp using H2 as the propellant, NOT the 2,750K I originally used.

Target thrust level was 10 kiloNewtons vs the 1kN I kept referencing. My memory is not what it used to be. Apologies.

Thrust = g0 * Isp * mdot
9,806.65N = 9.80665 * 1,000s * 1kg/s

mdot = Thrust / (Isp * g0)
1kg/s = 9,806.65N / (1,000s * 9.80665)

Isp = Ve / g0
1,000s = 9,806.65m/s / 9.80665

That all seems to check out.

We'll use 14,300J/kgK as the Specific Heat Capacity of Hydrogen gas, but the real input energy is here:
NIST - Hydrogen Specific Heat Capacity

14,300J * 3,200K = 45,760,000J/s of input thermal energy

1 Watt = 1 Joule per second

45,760,000J/s = 45,760,000W/hr

45.76MW <- Closer to actual input energy requirement

I think I remember what I initially did wrong. I miscalculated the temperature required. I think I used 2,750K or something like that.

14,300J * 2,750K = 39,325,000J/s <-- That was indeed my mistake

So...

45.76MW / 0.95 CoP = 48.168MW <-- This is closer to our true input optical power requirement, after accounting for 5% losses in the optical array. There will be some additional power losses involved with heating of the core. We need GW to tell us what those might be.

tahanson43206 · 2025-03-20 10:05:09

For kbd512 re Post #228

Thanks for adding details and clarifying as needed.

May I offer a suggestion? Please consider working with the system as it has evolved. 240 meters on a side is a very large array. It appears that temperature is a significant variable here, but GW has concerns about how the temperature will be achieved if we try to pass photons through quartz. He has proposed using hydrogen to cool the quartz facing the hot core.

You provided a number to work with of 40 MW, and the system as it stands reflects that value.

If we can confirm all the numbers for that size system, we can increase whichever parameters make sense.

I am hoping to find a supplier for the photon capture devices (TIR lens). The current proposed diameter is 36 mm with a 2mm border to allow for expansion when installed in a frame. That size leads to the 240 meter dimensions of the array.

***
Thanks for clarifying that Nitrogen is an acceptable substitute for Hydrogen for the test cell.

A number of materials are on offer for the heating fins.

The number of photon ports is to be determined, with a starting number of two.

There may be tradeoffs as the numbers of ports and fins are increased.

A value that would be of interest is the pressure that is going to be recorded inside the heating chamber. That pressure is going to be felt throughout the entire 240 meter length of the heat pipe.

The quartz windows must be able to withstand that pressure.

Cooling will be critical in this application. Failure of cooling at any of the quartz windows would lead to failure at that point, with possible loss of hot gas under extreme pressure. The frame is proposed to be made of carbon, so 3000 Kelvin gas would do some damage.

Perhaps the quartz windows could be designed to fail safe, by blocking the arriving photons at that location, but otherwise holding pressure.

(th)

kbd512 · 2025-03-20 11:55:50

tahanson43206,

The optical / thermal power input must increase slightly to achieve thrust closer to 10kN (for a 1kg/s propellant flow rate). I used the wrong temperature for achieving 1,000s Isp, but that was my target Isp for the design, because it reflected the maximum temperature that the engineers who worked on Project Timberwind believed was attainable using then-known ceramics.

I agree with GW about using the H2 propellant as regenerative engine coolant.

I don't think a 240m long quartz window heat pipe is very practical, so maybe I'm missing something, but you need purpose-built photon collectors and then you need a purpose-built rocket engine to dump the thermal power into the propellant to generate thrust.

tahanson43206 · 2025-03-20 12:46:05

For kdb512 re #230

This is a very interesting technical challenge, in any case.

I agree that GW's concept for a 240 meter long quartz tube looks difficult to fabricate as one piece, but perhaps there is a way to build this heat transfer system in smaller chunks.

I'd like to see what we can achieve with the 40 MW design. It turns out adjusting the power collected just amounts to arithmetic. The project needs stability, or nothing will ever be achieved.

As you predicted long ago, the optical part of this system is a (relatively speaking) easier part of the system than the heat exchanger.

If you are able to spare a bit of time looking, it would be helpful to learn if anyone has attempted anything like this in the past.

GW found documentation for a hypothetical solar balloon system, but (apparently) that was never developed beyond the conceptual stage.

***
Regarding the rocket engine length ....

That is up for adjustment. I proposed that as a logical consequence of the layout of the photon collection system. The shortest runs for fiber are horizontal along the ribs to the spine where the heat pipe could be located.

By distributing the heating over the entire 240 meters, the heat input at any one point is the same as everywhere else, so the components can be the same at every location in the structure.

(th)

tahanson43206 · 2025-03-24 13:07:12

For anyone searching for the post in which kbd512 shows an example of a chamber designed to heat gas passing through the device...

https://newmars.com/forums/viewtopic.php?id=10959

This is Post #9 of topic: Focused Solar Power Propulsion

Asymmetric turbulent flow resistojet test article:

(th)

tahanson43206 · 2025-03-27 17:21:49

For kbd512 re reactor images in post in Focused Solar topic...

The images you posted looked familiar...

https://newmars.com/forums/viewtopic.ph … 31#p229731

I had reported on a Canadian company that has been developing mechanically induced fusion.

The reactor you showed us looks a lot like one of their machines.

The idea they are pursuing is to use mechanical pumping to bring plasma to a density sufficient to support fusion for a brief interview.

Update: and here's a link to the web site for the company, with a nice animation showing how their system is supposed to work.

https://generalfusion.com/

(th)

tahanson43206 · 2025-03-29 06:11:19

For kdb512 re https://newmars.com/forums/viewtopic.ph … 53#p230653

in Focused Solar.

Congratulations for finding this important citation!
And! Congratulations for finding much needed support for the validity of your idea!

As a small note for further study .... the idea of adding small thrusters is a good one, but they cannot (and will not) substitute for directing the force of the main engine through the center of gravity of the vessel.

(th)

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