Focused Solar Power Propulsion

tahanson43206 · 2024-12-14 11:51:07

This topic is inspired by recent work by kbd512.

It is created as a separate topic because it seems to be subtly different from the 30 other topics with the word "propulsion" in the title.

We will lead off in post #3 with an image created by GW Johnson showing one possible example of what such a craft might look like.

Substantial mathematics exploring this concept are available for study in topic "kbd512 Postings".

This topic is available for NewMars members who might wish to move beyond hand waving and onto Real Universe achievement.

This forum has 20+ years of hand waving in the archive, and some of it is ** really ** impressive!

GW Johnson is hard at work designing a Space Tug infrastructure for the Earth-Moon system, and the Solar Powered Propulsion idea recently brought back into focus by kbd512 has the potential to provide a way to push deep space vessels from the Moon out further in the Solar system.

Update: This topic is not about using solar power to generate electricity using solar panels or solar collectors to heat fluid to generate electricity.

The intention for this topic is to attempt to collect information about use of solar power to heat propellant, and to encourage design and construction of space vessels which will use this technology.

(th)

tahanson43206 · 2024-12-14 11:51:34

This post is reserved for an index to posts that may be contributed by NewMars members over time.

Post #3: GW Johnson: Model of spherical Focused Solar Power vessel
Post #5:
Post #6:
Post #7:
Post #8:
Post #9: kbd512: Latticed asymmetric resistojet thruster engine core design: << compare turbulent flow for heating to laminar

(th)

tahanson43206 · 2024-12-14 11:53:08

GW Johnson created an image that shows one of many possible ways to design a space vessel that would generate propulsion by collecting solar radiation for heating purposes.

Here is some text that arrived via email:

The definition says that 1 N = 1 kg * 1 m/s^2. Here on Earth, the standard acceleration of gravity is not 1 m/s^2 but instead pretty near 9.80667 m/s^2 (it actually varies a little with primarily latitude, and altitude. That says at sea level on a standard day near 45 degree latitude north, the weight of 1 kg is 9.80667 N. Divide through by 9.80667 and you find that 1 N = weight you feel of 1/9.80667 kg = 0.10197 kg = 101.97 grams. Which says your 102 gram's Earth weight really is 1 N. You got it right.
As for the thrust producible, the physics of that are just a lot more complicated. The thrust coefficient CF is set solely by the nozzle area expansion ratio for a vacuum rocket device. That's standard compressible flow analysis applied to expansion nozzles, which most people think is not simple. The thrust is F = CF Pc At, set by the definition of thrust coefficient, where Pc is the chamber pressure within the solar receiver, and At is the throat area. At low Pc, At must be large, for a given thrust, which means all the other chamber and nozzle dimensions must also be large, in turn meaning your equipment core must be very big and very heavy. You must use a high Pc to get a small At for a given thrust, to get your engine T/W down. Sunlight is a diffuse energy source, and can be concentrated only so far, because spherical mirrors do not focus. That means the receiver has to be physically large anyway. You are not free to choose those two effects independently.
As to the rest of the solar rocket idea, the problem faced will be the inherent slowness of the heat transfer processes. Heating 1 kg of anything through a temperature rise of 2700 K in only 1 sec is not going to be possible at the energy/area of even concentrated sunlight. It will just take longer than that, thus limiting the massflow for the size of mirror you can build. That third effect is also not independently set from the other two. See sketch attached.
GW

I note that this is one of ** many ** possible designs. It has the feature/drawback that the flight must be scheduled so that the Sun is at 90 degrees to the desired dV addition to the trajectory. For a boost from the Moon to Mars (for example) there should be plenty of opportunities when the needed conditions apply.

(th)

GW Johnson · 2024-12-14 15:19:49

If you can steer the spherical balloon collector relative to the core axis, the 90 degree thing is no longer a requirement. There are still angles that won't work, but there will be a majority that will work. But you get what you pay for: you must hold onto the balloon, and steer it to face where you need, and STILL get the rocket nozzle through the side of the balloon. That is NOT AT ALL easy! It will be heavy. Inherently!

GW

tahanson43206 · 2024-12-14 16:25:30

For GW Johnson!
Thanks for adding Post #3 (via email) and adding clarification with post #4.

From my perspective (not knowing the orbital mechanics) I would think that planning a flight path that keeps the Sun square abeam should be feasible. We may need to master GMAT to be sure. Or we can enlist someone like James Miller who has experience plotting courses for deep space missions.

***
For kbd512 re tomorrow's meeting ...

I'd like to (at least try to) encourage you to think about a solar trough a kilometer long,built using the ideas from GW's model, but extended in the longitudinal axis for as far as makes sense.

The basic model GW has provided is a hydrogen (or other propellant) tank in front, a heating element/pressure chamber in the middle, and the exhaust bell at the back.

I'm hoping you can perform the math needed to see if that configuration would deliver the 1000 tons of thrust I'm looking for.

Or 8 million Newtons if you prefer.

(th)

kbd512 · 2024-12-15 00:17:25

I'll describe what I was thinking of doing, even though it's very different than what GW was thinking of doing.

I used NERVA as my "how to build a solar thermal reactor" guide:
NUCLEAR THERMAL ROCKET/VEHICLE CHARACTERISTICS AND SENSITIVITY TRADES FOR NASA’s MARS DESIGN REFERENCE ARCHITECTURE (DRA) 5.0 STUDY

A NERVA-derived engine uses a "graphite matrix" material fuel element (FE) containing the U-235 fuel in the form of uranium-carbide (UC2) microspheres or as a dispersion of uranium and zirconium carbide (UC-ZrC) within the matrix material, referred to as "composite" fuel. The typical NERVA FE has a hexagonal cross section (~0.75" across the flats), is 52" long and produces ~1 megawatt of thermal power. Each FE has 19 axial coolant channels, which along with the element's exterior surfaces, are CVD coated with ZrC to reduce hydrogen erosion of the graphite. Composite fuel, with its higher exhaust temperature range (Tex ~2550-2800K), was the preferred fuel form at the end of Rover/NERVA program, and is used here. The performance characteristics for the 25klb-f NTR baselined in this study include: Tex ~2650–2700 K, p ch ~1000psi, ε ~300:1, and Isp ~900-910s. At Isp ~900s, the LH2 flow rate is ~12.6kg/s. The thrust-to-weight ratio for a dual TPA, expander cycle 25klb-f engine is ~3.43. The overall engine length is ~7.01m, which includes an ~2.16m long, retractable radiation-cooled nozzle skirt extension. The corresponding nozzle exit diameter is ~1.87m.

In the "Orbital Mechanics" thread, I described an engine primarily constructed of graphite (Carbon), generating about 1/30th the input thermal power and thrust of NERVA XE PRIME, with Hydrogen flow channels protected by Zirconium Carbide (ZrC), just as they were by the end of the NERVA program.

NRX A6 - November 1967
Avg Core Power: 1,199MWth
Tpropellant (chamber): 2,406K
Tpropellant (exit): 2,558K
Pchamber: 4,151kPa
Flow Rate: 32.7kg/s
Isp: 869s

NERVA XE PRIME - March 1969
Dry Mass: 18,144kg
Avg Core Power: 1,137MWth
Tpropellant (chamber): 2,267K
Tpropellant (exit): 2,400K
Pchamber: 3,806kPa
Flow Rate: 32.8kg/s
Isp: 841s
Thrust: 246,663N

My Solar Thermal Rocket (STR) engine uses a different heat transport mechanism because the thermal power is being dumped into the core via its exterior. I specified Supercritical Argon or Xenon for heat transport through the core.

Specific Heat Capacities of Hydrogen, Argon, Xenon, Graphite, Zirconium Carbide, and Tungsten
Hydrogen: 14,300J/kg°K
Argon: 312.2J/kg°K
Xenon: 158.32J/kg°K
Graphite (Carbon): 710J/kg°K
Zirconium Carbide: 334J/kg°K to 368J/kg°K
Tungsten: 134J/kg°K

At 175K, Hydrogen requires 13.02kJ/kg of thermal energy input to raise its temperature by 1K. At 2,700K, Hydrogen requires 18.06kJ/kg of thermal energy input to raise its temperature by 1K. Thus, the heat transfer rate is not a linear constant, between 20K and 2,750K. However, 14kJ/kg is close enough to gauge the thermal power that must be dumped into the Hydrogen to raise its temperature to the required value to produce the required exhaust velocity.

45.8X less thermal energy input is required to raise the temperature of Argon by 1°K, in comparison to Hydrogen, or 90.3X less for Xenon. Another way of looking at this is that the 40MW of thermalized input photonic power from the Sun will raise the temperature of 53.05kg of Argon from 393K (the ambient temperature in space at 1AU in full sunlight, or the temperature to which materials exposed to direct sunlight will increase to, above absolute zero), to 2,750K, given by:

39,039,000J is the heat transfer rate into the core from the solar array.

39,039,000J / ((2,750K - 393K) * 312.2J/kg of Argon) = 53.05kg of Argon
39,039,000J / ((2,750K - 393K) * 158.32J/kg of Xenon) = 104.62kg of Xenon
39,039,000J / ((2,750K - 393K) * 134J/kg of Tungsten) = 123.6kg of Tungsten

The supercritical Argon or Xenon will be contained in Tungsten heat pipes on its exterior, very similar in appearance to the KiloPower fission reactor. KiloPower used a lower temperature capability Iron-based superalloy that would melt long before achieving 2,750K, hence why I have specified Tungsten heat pipe tubing vs the Haynes superalloy used by the KiloPower demonstrator. The Tungsten heat pipes are filled with Argon or Xenon at supercritical pressures. The graphite core acts as a heat spreader device to increase the surface area in contact with the Hydrogen flowing through it. The Zirconium Carbide surface coating or cladding protects the graphite heat spreader elements from Hydrogen erosion. Since there is no nuclear fuel in my STR core, the thermal power density should be higher.

KiloPower Heat Pipes:

All that equipment you see the heat pipes leading to, above the core region, in the image shown above, is required to convert thermal power into electrical power using gas turbines. My core design doesn't have any of that equipment, meaning the heat pipes circulate Argon from the outside of the core, where they absorb heat from the concentrated sunlight impinging on them, to the inside of the core, where the thermal power is imparted into the Hydrogen and subsequently removed by the Hydrogen as it exits the core. This is effectively an inversion of the NERVA core design.

After the core has been heated to 2,750K by the concentrated sunlight it's bathed in, the mass of materials responsible for keeping the core temperature at 2,750K must be capable of replacing the heat dumped into the Hydrogen gas flow through the core, which removes heat at a rate of 39,039,000 Joules per second, given a 1kg/s flow rate, or else the core starts to cool down and propulsive efficiency is lost. This is in addition to the normal radiative heating loss to space. The STR core is being heated to the point that it's quite literally "glowing". The color temperature of an incandescent lightbulb is 3,000K for comparison purposes.

The materials used to construct the core can be both heated and cooled at a much faster rate than the Hydrogen propellant. This is a good thing, because the heat lost to the propellant must be replaced faster than it's removed. I specifically mentioned using supercritical Argon or Xenon as my thermal power transfer fluid for that reason.

NERVA's core flow velocity was approximately 130m/s, so for a similar-length core, we should expect similar heating rates, a similar chamber pressure, etc. The fuel element length was 1.32m and the fueled region was 0.91m in length. Since my core has a greater thermal power density owing to the fact that there is no Uranium in it, thermal power density is even higher.

GW seems worried about the solar concentration factor, but that's not an actual problem, except possibly for the design he came up with. I'm far more concerned about not melting the core, because whereas NERVA's core power density was 2-3MW/L thermal power density, in the STR design we have megawatts of power focused onto square centimeters of surface area.

At 1,000W/m^2, there is only 0.1W/cm^2. Most solar concentrator systems operate between 10,000X and 20,000X, with some as high as 30,000X. For 20,000X concentration, merely a "middle-of-the-road" system, that means the thermal flux is 2,000W/cm^2. A flight-weight prototype would be closer to 30,000X. NERVA was nominally 1.2GW core, so 1,200,000,000W divided by 3,000W/cm^2 is 400,000cm^2, or 40 square meters. A sphere 3.6m in diameter has a surface area of 40.715m^2. A sphere of that size made from pure Graphite would weigh about 54,967.5kg, although a lot of the core would need to be hollow in order for Hydrogen or any other gas to flow through it.

I'm not too worried about trying to match NERVA's core power density or flight weight because HEU is not available for civil applications. Whatever civilians could potentially achieve using HEU fueled NTRs is irrelevant to reality, because we're never getting any HEU. President Trump has stated that there will be no weapons grade nuclear materials used by our civil space program. If someone changes his thinking on this, then great, but there is zero political appetite for the use of weapons grade reactor fuels for civil applications, here in America or anywhere else. Certain qualified organizations may be able to obtain HALEU, perhaps suitable for NTRs, perhaps not. All NTR testing in America and Russia used HEU.

kbd512 · 2024-12-15 00:36:00

Solar Concentrator Design
As for the solar power collector design, I'm specifying 10m diameter parabolic dish concentrators used to couple the received photonic power into short fiber optic "pigtail" cables. The cables do not carry the concentrated photonic power all the way back to the reactor core, but they do de-couple the pointing of the solar concentrators dishes from their ability to point received power back at the reactor core, and only require a singular design regardless of distance from the reactor core. Therefore, the actual fiber optic cable lengths will only be sufficient to provide vehicle-concentrator-target independent pointing capabilities, in addition to initial solar power concentration from 1 Sun to 1,600 Suns. These pointable fiber optic "pigtails" create "hot spots" by focusing the power from the pigtail at a specific spot on the surface of the reactor core.

78.53982m * 1,224.9W/m^2 (at 1AU) = 96,203W per 10m diameter solar concentrator
96,203W * 416 concentrators = 40,020,448W of total input photonic power

All 416 concentrators will be arranged in concentric rings around the 10m diameter space tug Hydrogen tank.

Power Pointing Pig Tail Design
25mm diameter Silica-based fiber optic cable
2W/mm^2 is the input power limit for Silica-based fiber optic cable (higher concentration is achievable with shorter cable lengths)
490.87385cm surface area * 100,000cm (1km) length = 49,087,385cm^3 per 1km of 25mm thick fiber optic cable
49,087,385cm^3 * 2.2g/cm^3 = 107,992,247g = 107,992.247kg per linear kilometer of 25mm thick fiber optic cable
Edit: Pigtail mass should read 1,079.92247kg/km, NOT 107,992.247kg/km; decimal point mistake

Pig Tail Power Density:
96,203.646W from 10m concentrator / 0.049087385m^2 fiber optic cable surface area = 1,959,845W/m^2 or 1.959845W/mm^2

Initial Power Concentration:
1,959,845W/m^2 from 10m concentrator / 1224.9W/m^2 (1 "Sun") = 1,600 "Suns" of solar power concentration

416X "hot spots" are independently focused onto the reactor core, each with a power density of 195.9845W/cm^2

10m Diameter Parabolic Solar Concentrator Dish Arrangement
232m diameter outer circle, 10m diameter inner circle
Solar concentrator counts by ring position around the 10m diameter core stage:
1st - 6
2nd - 13
3rd - 19
4th - 25
5th - 31
6th - 38
7th - 44
8th - 50
9th - 57
10th - 63
11th - 69

Last edited by kbd512 (2024-12-15 01:29:26)

kbd512 · 2024-12-15 02:43:33

Pigtail Design Expansion #1
Each pigtail connects to a TIR (Total Internal Reflection) lens. Distance from the reactor core may or may not require different lens designs, in order to maintain a tightly focused beam of photonic power. Over the very short distances involved here, I would say that it's probably not required. To scale this system up to achieve substantially greater total core power, different TIR lens geometries will likely be required.

A TIR lens is an optical lens built on the principal of total internal reflection (TIR). TIR lenses collimate light, sending out a concentrated beam of full intensity. They are used in a wide variety of applications, including collimating the beams from high power LEDs.

MagLite TIR Lens

Theoretically, smaller TIR lenses of perhaps 1m to 2m in diameter could be used to increase packing density. This means the much larger and somewhat unwieldy 10m diameter parabolic dish concentrators could be replaced with a greater number of smaller TIR lenses to receive input power from the Sun, a short pigtail to concentrate and redirect power, with second smaller TIR lenses on the opposite end to further concentrate and direct the photonic power onto the reactor core.

Each 10m diameter parabolic dish concentrator couples its received photonic power into the pigtail, each pigtail independently focuses its concentrated power onto the core over a fairly short distance, and each pigtail is independently mechanically steered to deposit its "hot spot" onto a specific location around the circumference of the reactor core. The use of TIR lenses ensures that nearly all of the power is very tightly focused. It's not a laser beam, but well over 90% of the power. The TIR lenses could also further increase the concentration of the photonic power, if so desired or required. Each TIR lens must have a direct shot at the core, but that was the entire reason for using a fiber optic pigtail. Each parabolic dish can be moved independently of the vehicle it's attached to using its limited adjustment range, each pigtail has a far greater adjustment range, and if power is lost from a few of the concentrators, each hot spot can be readjusted to provide optimal overlap on the core.

ITV and STR Space Tug Vehicle Control Scheme
To keep the engine design as simple as possible, the engine will not gimbal. The entire vehicle's attitude will be adjusted by the considerable mass of the ITV's four habitation rings / reaction wheels, which provide gross X and Y pointing capability. Control in the Z plane, along the vehicle's direction of travel, is manipulated using thrust from the STR engine. When the STR Space Tug is detached from the ITV, its own onboard CMGs will provide X and Y pointing capability. The combination of the gigantic habitation ring reaction wheels up front and the considerable lever arm for the CMGs to act upon will provide gross and fine attitude control, respectively.

Design Imperatives
The major design goals here are to keep the parabolic dish array support structure and parabolic dish concentrators very light, and to keep the pigtails short since they get very heavy very quickly, especially when you displace the decimal point, as the math in my previous post shows, and to keep the core volume as low as practical so that it heats up to operating temperature very rapidly.

Solar Thermal Reactor Core Design
I need some expert advice on whether or not a graphite core is even necessary. Graphite in NERVA was used as a medium in which to deposit the Uranium fuel particles, as well as acting as a neutron moderator. I don't have either of those reqirements for a STR. However, graphite was also used to evenly distribute heat through the core. My initial thinking on the core design involved maximizing heat spreading to avoid core damage from hot spots, which proved troublesome during the NERVA program. There's enough photonic power being focused onto the surface of the core to rapidly melt most alternative materials. However, Tungsten is a notable exception with excellent thermal conductivity. To rapidly bring the core up to operating temperature, a pure Tungsten core with a Tungsten Carbide coating to resist erosion from the hot flowing Hydrogen may be substituted. Unfortunately, Tungsten is also a very heavy metal, so a Tungsten core would need to be kept very small, perhaps too small when compared to Graphite or other Carbon-based materials, such as Reinforced Carbon-Carbon (RCC) composite.

Graphite's tensile strength at room temperature is only around 5ksi, but rather interestingly, tensile strength doubles up by about 2,773K, then rapidly drops to zero as the material nears its sublimation point. If there's a way to properly seal the thermal power transfer channels within the core to prevent the Argon or Xenon from escaping, then the core and nozzle could be made from a monolithic material, such as RCC.

I don't know what will prove best. Tungsten, being a metal with good thermal conductivity and considerable tensile strength, even at 2,750K, would likely be far easier to fabricate than RCC. RCC is most notable for its thermal shock resistance. In-plane thermal conductivity can be even higher than Tungsten, but through-thickness thermal conductivity is rather poor, and is likely insufficient to permit rapid engine warm up. However, even if it proves fairly cheap to 3D print the Tungsten engine, I question whether or not the surface area will be sufficient.

Nozzle Design
NASA has conducted very recent testing of passively cooled RCC rocket engine nozzles for LOX/LH2 engines with excellent results. LOX/LH2 combustion temperatures reaches 2,985K, slightly hotter than the nominal 2,750K exhaust temperature from a NTR or STR. Radiative cooling of the nozzle was sufficient to permit multiple back-to-back engine runs with no repair or refurbishment between runs. Zirconium Carbide or other UHTC coatings may enable long duration firing of the engine without significant thermal damage or Hydrogen erosion. RCC is very light, at 1.96g/cm^3, making it an ideal nozzle material.

If there's a realistic way to 3D print most of the engine as a monolithic piece of material, from either RCC or Tungsten, then that would be most desirable. Despite the high cost of both materials, an engine that only flows 1kg/s is still tiny. RCC would be my preference because that minimizes weight and affords extreme thermal shock resistance. Carbon is ultimately easier to come by than Tungsten. However, I'm willing to use both materials. If Tungsten proves to be a better core material than RCC, for both absorbing heat and rapidly spreading it, then so be it.

kbd512 · 2024-12-15 03:48:09

Alternative Solar Array and Engine Configurations
It may be highly desirable, especially for very heavy vehicles with low acceleration rates, to use an asymmetric solar array mounted above or below the vehicle being accelerated. The primary reason has to do with optimization of the support structure that the concentrators / power collectors are mounted to, particularly the results of having a good number of them mounted too close to the engine core, resulting in the fiber optics having to adjust the output at unfavorable angles. It's still "doable", but you need longer pigtails or you have to use a non-planar array.

The above image shows the radar from the E-3 Sentry AWACS aircraft. Imagine for a moment that all those shiny radar emitter elements are solar concentrators. Said array could be side-mounted to the giant Hydrogen propellant tank and then the photonic power could be much more easily focused onto the engine.

Asymmetric Engine Core Geometry
Unlike a NTR, which virtually requires a symmetrical cylindrical core to achieve its power density, a STR core design could greatly benefit from being asymmetric, especially when used in conjunction with an asymmetric solar array.

Asymmetric turbulent flow resistojet:
Resistojet%201.png?width=903&name=Resistojet%201.png

Asymmetric turbulent flow resistojet test article:
Resistojet%20Hotfire%20Test.jpg?width=400&name=Resistojet%20Hotfire%20Test.jpg

The above image from Benchmark Space Systems shows a fairly new asymmetric resistojet engine design intended for use aboard micro satellites as an Isp upgrade from typical cold gas thrusters. Resistojets work on the principle of electrical heating of a propellant. The turbulent flow through its core enables the propellant to pick up more heat from the electrical heating elements over shorter distances. In this case, the scaling of the engine's input power and physical size precludes the use of a "straight through" laminar flow design, as shown in the left portion of the image for comparison purpose, because laminar flow has very poor thermal power transfer characteristics. What you're looking at is heat flux dumped into the propellant. The laminar flow design on the left does a relatively poor job when compared to the turbulent flow design on the right.

Latticed asymmetric resistojet thruster engine core design:
aerospace-11-00714-g003.png?1725245738

We can apply this same design concept to our STR's engine core to improve the heating rate of its Hydrogen propellant.

Edit:
Soviet / Cold War era efforts towards a flight-ready NTR design also employed turbulent flow, using twisted fuel elements, similar in appearance to a drill bit, to dump more heat into the Hydrogen propellant. The Soviet NTR engine design was likewise intended to support their own Mars exploration efforts.

1-s2.0-S100702140770038X-gr2.jpg

Similar engine solutions were arrived at by completely different interested parties (NASA and ROSCOSMOS in this case), because engineering solutions tend to converge on what the basic math and physics says will work, not necessarily because "one group copied the work of another". America and Russia both knew they needed high-Isp nuclear powered Hydrogen engines to undertake manned Mars missions in a practical way. That was the only tech sufficiently advanced at the time to do that.

Last edited by kbd512 (2024-12-15 15:05:07)

kbd512 · 2024-12-16 09:05:13

One of the principles employed by the optical pigtails at the center of each parabolic reflector dish, which is ultimately used to transmit power back to the solar thermal reactor, is that of the TIR (Total Internal Reflection) lens. A pair of TIR lens, one on each end of a short fiber optic cable, is used to first couple the photonic power from the reflector into the fiber optic pigtail, and then redirect its "hot spot" back onto the exterior of the solar thermal reactor core.

There are two different optical principles at play here. The first is reflection from the parabolic collector dishes. The second is refraction, which is what happens inside a TIR lens.

kbd512 · 2024-12-16 09:29:36

tahanson43206,

I found something very interesting last night that was, to me at least, quite astonishing. I had no earthly idea that such tech existed in a lab, let alone something that manufacturers are mass producing for industry. Apparently, we have flexible Silicone TIR lenses and even optical quality aerogels capable of acting as optical waveguides. I had no inkling that such tech existed, or that they were already commercialized products.

Flexible Silicone TIR Lenses:

The optical quality aerogels were developed by a pair of ladies working at MIT who were looking to use them in solar thermal power plants because the aerogel would be optically transparent to incoming photonic power from the mirrors, but would trap the heat inside a solar power tower.

MIT News - Making a remarkable material even better - Aerogels for solar devices and windows are more transparent than glass

This significantly alters the materials I would like to use, because you once asked me to come up with a kilometers-long collector array, so then I thought to myself... but how? How could I actually do that in a realistic way?

I guess we really can do this, and wrap the material around a core section (like new palm tree fronds / buds), so we would have a "solar tree" that collects the incoming light and runs it all the way back to the solar thermal reactor core. Anyway, this is a superior design my first thought about how to collect the photonic power, because it could be inflated using gas from the core stage and "unfurled", quite literally like palm fronds.

tahanson43206 · 2024-12-19 10:49:01

This post is intended to show a drawing attempt using Blender and a Wacom tablet.

The subject matter is kbd512's vision of a way of capturing solar energy in a plane of optical devices designed to feed photons into optical fiber cable.

If the vision is fully realized, the traditional cassegrain mirror concept will not be needed.

If the visions is fully realized, photons that arrive perpendicular to the plane will be deflected 90 degrees so they enter an optical fiber cable and proceed to a desired end point.

(th)

tahanson43206 · 2024-12-19 19:28:30

Here is an attempt to sketch what an individual optical bucket in an optical capture plane might look like...

Rendered in Blender using Wacom tablet - saved in Pinta as jpg and delivered via imgur.com

Note: This vision is aspirational. What kbd512 has shown us so far is what exists today, and is (apparently) in wide use.

Existing installations employ a solid light gathering device that delivers photons to a fiber optic cable that is connected to the base of the light gathering device. The 90 degree bend occurs in a section of the cable.

This implied one optical cable for each light gathering device.

The aspirational version shown above would incorporate the 90 degree bend into the light gathering device, and join the flow of photons so that only one optical fiber cable is needed per row in the platform.

(th)

tahanson43206 · 2024-12-20 22:12:29

The Blender default workspace color is dark, so that lines of various colors will stand out during design. I looked at changing colors, but decided there are too many factors to take into account for it to be worth while. Instead, I decided to investigate a program called Pinta, which is said to be similar to Paint for Microsoft computers. This is an early version of a drawing using Pinta.

The intent is to show in the simplest possible terms what an optical plane would look like, if such a thing is possible.

While the entire concept was inspired by work by kbd512 to design a solar powered propulsion system, it seems to me the concept would work on Earth as well as in space. Solar panels are planes that accept photon input and deliver electron flow. This concept, if realized, would consist of planes that accept photons and deliver thermal energy in a fluid.

It is not clear at this point if the materials needed to make such planes would be as common as silicon on Earth, or some other common material, but at this point it is not even clear it is possible. What ** is ** clear is that solid objects exist that can accept photons from the Sun and deliver them via fiber optical cable to destinations some distance away from the collection point.

(th)

kbd512 · 2024-12-22 20:26:16

Q: Can light strike a surface and turn 90 degrees?
A: Yes, light can technically "turn 90 degrees" when it strikes a surface, but only under specific conditions, most notably when it undergoes "total internal reflection" at a critical angle, where the angle of refraction reaches 90 degrees, causing the light to bend sharply and change direction significantly; this typically happens when light moves from a denser medium to a less dense medium at a specific angle.
Refraction and critical angle:
When light enters a different medium at an angle, it bends, a phenomenon called refraction. The critical angle is the specific angle of incidence where the refracted light would bend at 90 degrees.
Total internal reflection:
If the angle of incidence exceeds the critical angle, the light completely reflects back into the denser medium, effectively "turning 90 degrees".
Example:
A light ray traveling through water hitting the water-air boundary at a large angle can experience total internal reflection, causing the light to bend sharply and seemingly "turn 90 degrees".

tahanson43206 · 2024-12-22 21:07:49

For kbd512 re post #15

Thanks for this helpful addition to the discussion.

I followed up by asking Google for help, and it came back with a suggestion to look at Wikipedia's article on Snell's law (Snell-Descartes) or the ibn-Sahl law.

In the case of the proposed flat plane solar power collector we are discussing, it seems to me most likely that refraction is involved at the interface between the arriving photon in vacuum, and the optical fiber cable. Whatever that interface turns out to be, the photon is entering a denser material from a less dense environment. The desired output direction of the photon is toward the center of the space ship framework. What I am imagining is something like a sawtooth structure for the interface, so that photons arriving perpendicular to the plane are refracted by the interface medium so they enter the fiber optic cable at an angle that allows them to proceed along the cable toward the energy delivery port.

This topic is about Focused Solar Power Propulsion, and as Lead for this topic, you are rightly concerned about the delivery end of the fiber, where the magic will happen to drive the space ship.

I am not here to support that part of the system at this time, because we do not yet have the photon feeder working. I'll be interested in what you do with the photons after you have some photons to work with.

As we discussed in the meeting, if we are looking at a new concept for photon collection, and if it is not obvious to a practitioner of the art, then the concept can be patented, and if this particular concept is patented, it will be competing with solar panels to collect solar energy. Solar reflectors will be left in the dust, because they require complex machinery and tons of metal framework and man years of maintenance for a large system.

The key patentable element of the proposed system (as I understand it) is a tiny component made of common material that accepts light photons and delivers them into a optical fiber cable in such a way that the photons do not attempt to escape, but instead obediently proceed toward the exit point you have offered them.

In our meeting today, we discussed the physical layout of the light collection plane.

I am imagining the Light Collection Plane as a set of 1 millimeter diameter optical fiber cables mounted next to each other in a plane that is 100 meters wide and kilometers long, and there is one of these panels on either side of the central power collecting pipe (whatever it turns out to be).

Update to clarify: The individual fiber optic cables would be 100 meters long. They would stretch across the plane and collect photons over that distance.

The fiber would be supported by an ultra-lightweight, ultra-strong set of carbon fiber girders that stretch out 100 meters on either side of the center line, and run for kilometers along that center line, for as far as the funders can afford to take them.

We have a goal to achieve to produce 1 ton of thrust from an array 100 meters wide on both sides of the center line, and 1 kilometer long.

When you have time, please see if you can make the numbers work. Don't worry about cost of anything at this point. We need to find out if physics will support the concept, before we worry about asking someone to pay for it.

How much thrust can you get out of the proposed array? Does it need to be longer?

(th)

tahanson43206 · 2024-12-23 13:12:28

For kbd512 re side coupling to fiber optic cable....

I asked ChatGPT4o to look at the question, and it found several references that seem to include study of several alternatives.

The primary driver of research appears to be communications rather than solar concentration.

Hello! It's great to collaborate with you again. Your project to capture and route sunlight through optical fibers from multiple collection points is both innovative and challenging. Let's explore the key aspects and potential solutions for efficiently coupling sunlight into optical fibers, especially when considering multiple input points.
**1. Coupling Sunlight into Optical Fibers:**
Coupling light into optical fibers involves aligning the light source with the fiber's core to maximize transmission efficiency. This process can be complex due to factors like the light's divergence, the fiber's numerical aperture, and alignment precision. For sunlight, which is a broad-spectrum and incoherent source, specialized coupling optics are essential to focus and direct the light into the fiber effectively.
**2. Techniques for Side Coupling into Optical Fibers:**
Introducing light into an optical fiber from the side (broadside coupling) is less common than end-face coupling but can be achieved through various methods:
- **Side-Polished Fibers:** By polishing the side of the fiber to create a flat surface close to the core, light can be introduced laterally. This technique has been explored for coupling external light sources into the fiber.
- **Imbedded V-Grooves:** Creating V-grooves in the fiber's cladding can facilitate side coupling. Research has demonstrated high-efficiency side-coupling using such structures, particularly in double-cladding fibers.
- **Grating-Based Couplers:** Implementing gratings on the fiber's surface can diffract incoming light into the core. This method has been studied for broadband optical concentration, making it suitable for coupling sunlight.
**3. Combining Multiple Light Sources into a Single Fiber:**
To merge light from multiple collection points into a single optical fiber, consider the following approaches:
- **Wavelength-Division Multiplexing (WDM):** If each light source operates at a distinct wavelength, WDM can combine these wavelengths into a single fiber. However, for broad-spectrum sunlight, this method may be less applicable unless the spectrum is divided into narrower bands.
- **Optical Couplers and Combiners:** These devices can merge light from multiple fibers into one. For instance, a tapered fiber bundle can combine several inputs into a single output fiber. Designing such a system requires careful consideration of coupling efficiency and loss minimization.
**4. Practical Considerations:**
- **Alignment Precision:** Accurate alignment of the light sources with the fiber is crucial to minimize losses, especially when coupling from multiple sources.
- **Numerical Aperture (NA):** The fiber's NA determines its light acceptance angle. Ensuring that the incoming light's divergence matches the fiber's NA is essential for efficient coupling.
- **Loss Management:** Each coupling interface introduces potential losses. Employing anti-reflective coatings and optimizing the coupling optics can help mitigate these losses.
**5. Research and Development:**
While several studies have explored side coupling and combining multiple light sources into a single fiber, the specific application of routing sunlight from multiple collection points into one fiber is relatively novel. Further research and experimentation will be necessary to develop a system that meets your inventor's requirements.
In summary, while the concept of side coupling and combining multiple light inputs into a single optical fiber presents challenges, existing research provides a foundation upon which to build. By leveraging techniques like side-polished fibers, grating-based couplers, and optical combiners, and by addressing practical considerations such as alignment and loss management, it's possible to develop a system that efficiently channels sunlight from multiple sources into a single fiber.
I hope this overview assists you in your project. If you have further questions or need more detailed information on any of these aspects, feel free to ask!

(th)

tahanson43206 · 2025-02-16 20:48:10

This post is intended to bring the topic back into view, following the Google Meeting of 2025/02/16...

kbd512 has been working on (researching) the use of optical fiber to collect and route photons from a large flat collecting area.

This work is in direct competition with the more familiar solar panels technology that is well established, and the less developed but still practical solar mirror technology that might be developed some day in space. Solar mirror technology is well established on Earth, but recent news reports seem to indicate it is losing the economic competition with photoelectric panels.

http://newmars.com/forums/viewtopic.php … 21#p229821

The link above points to a post by kbd512 in which he provides detailed numbers for use of optical fiber to transmit power.

Transmission of power by optical fiber is distinctly different from communications.

In the case of the proposed solar powered space tug that is the focus of this topic, the system we are considering would have solar collection wings that extend 100 meters to the side of the central shaft, and reach 1 kilometer or more in length.

The idea is to collect every photon that falls on the collecting area, and to to deliver it (with very little loss) to a propulsion system of some kind.

In the post at the link: http://newmars.com/forums/viewtopic.php … 21#p229821

kbdt12 considers the typical case of a row of the light collection sail. The row would be 1 centimeter across, and it would extend for 100 meters.

A similar sail would extend on the opposite side of the central shaft.

Each row would collect (on the order of) 1 kilowatt of power when operating near Earth. The purpose of the exercise is to collect:

1 kilowatt per row on one side of the array
2 kilowatts per row for the system taken as a whole
1 centimeter per row so 100 rows per meter
1000 meters for a model system
2 kilowatts * 100 rows per meter * 1000 meters >> 200,000 watts available for propulsion.

Actual power collected would be greater than the example when the system is flying closer to the Sun, and less further out.

It is possible that this system is the most efficient for collecting solar power for any purpose, when compared to photovoltaic systems or mirror based systems.

(th)

tahanson43206 · 2025-03-03 20:42:05

This post is intended to bring this topic back into view after the Google Meeting of March 2nd, 2025.

kbd512 has been continuing to research the use of solar power for propulsion.

It appears that a solar energy collection platform that collects photons and routes them to a single point via optical fiber is not only feasible but everything needed has already been done on Earth for various applications.

It appears that a collecting system a kilometer long, 200 meters wide and a meter thick could deliver 2000 Megawatts to a single point.

kbd512 has published an estimate that the 2000 Megawatts could deliver 5 tons-force while consuming 5 kilograms per second of hydrogen.

5 tons is not a lot of force.

From https://en.wikipedia.org/wiki/Rocket_engine

Jet or rocket engine Mass Thrust Thrust-to-weight ratio (kg) (lb) (kN) (lbf)
RD-0410 nuclear rocket engine[10][11] 2,000 4,400 35.2 7,900 1.8
J58 jet engine (SR-71 Blackbird)[12][13] 2,722 6,001 150 34,000 5.2
Rolls-Royce/Snecma Olympus 593
turbojet with reheat (Concorde)[14] 3,175 7,000 169.2 38,000 5.4
Pratt & Whitney F119[15] 1,800 3,900 91 20,500 7.95
RD-0750 rocket engine, three-propellant mode[16] 4,621 10,188 1,413 318,000 31.2
RD-0146 rocket engine[17] 260 570 98 22,000 38.4
Rocketdyne RS-25 rocket engine[18] 3,177 7,004 2,278 512,000 73.1
RD-180 rocket engine[19] 5,393 11,890 4,152 933,000 78.5
RD-170 rocket engine 9,750 21,500 7,887 1,773,000 82.5
F-1 (Saturn V first stage)[20] 8,391 18,499 7,740.5 1,740,100 94.1
NK-33 rocket engine[21] 1,222 2,694 1,638 368,000 136.7
Merlin 1D rocket engine, full-thrust version 467 1,030 825 185,000 180.1

The only engine that delivers under 5 tons-force (50 kiloNewtons) is the RD-0410 nuclear rocket engine

On the other hand, the 2000 Megawatts is available essentially without sensible limit.

The consumable in this scenario is hydrogen, and I assume that would be liquid hydrogen since that is what all rockets that burn hydrogen consume.

I'm hoping NewMars members with the appropriate skills and the time and energy to take this on will investigate to see what the space tug kbd512 has imagined can actually accomplish.

FYI... the mass of the photon collection system would include:

Carbon to make a honeycomb-like framework for the platform.
Silicon to make the photon collectors and optical fiber
(to be defined) to make the propulsion unit
(to be defined) to make the LH2 tanks

(th)

tahanson43206 · Yesterday 12:00:14

This post points back to a post by kbd512 in which an example of a device for collecting photons is shown.

http://newmars.com/forums/viewtopic.php … 70#p228570

Design of an Optical Plane Deep Space vessel would include deployment of devices such as these to collect solar output and feed it into an optical fiber cable.

The area needed to collect one watt of solar power (assuming 1000 watts per square meter) is 10 square centimeters. The side of a square of area 10 centimeters is 3.2 centimeters (rounding to the nearest 10th).

A photon capture device able to collect one watt would thus be 3.2 centimeters on a side, taking into account space needed for mounting in a frame.

Update:

Worksheet for Optical Plane
Goal is 40 MW (for kbd512 design)
Estimate size: 200 meters by 200 meters collecting area
3.2 cm is the side of a square able to capture 1 watt
1 meter has 100 centimeters so a square meter has 100*100 or 10,000 square centimeters
A square of 10 square centimeters would fit 1000 times into a square meter.
40000 square meters * 1000 watts >> 40,000,000 watts
40,000,000 watts = 40 MW
***

And since one photon collector produces one watt, the system will require 40,000,000 photon collectors.

Each photon collector could be mated to an optical fiber at the factory.

The collectors could be shipped to LEO in lots.

The elements of the frame are envisioned as ultra strong ultra lightweight carbon able to assemble into wings 200 meters by 100 meters by 1 meter.

Update: Due to space needed for mounting, the number of 1 watt devices that would fit inside a square meter is 976 (with .5625 left over)

To achieve the full desired power level of 40 MW, the array would need to be increased in size slightly.

As is, the device would produce 40,000 * 976 watts (39 MW and change)

(th)

tahanson43206 · Yesterday 13:00:22

This post is a follow up to #20

The concentration for this post is the TIR lens that kbd512 identified as a candidate for consideration for the Optical Plane Deep Space vessel.

I asked Google to round up some information about TIR lenses, and it found ** a lot !!! ** ... In light of the hypothetical need for 40,000,000 of these lenses, I am glad to see that there are multiple suppliers and that existing volume of production is significant.

Search Labs | AI Overview
Learn more
You can buy TIR lenses from Brightlx, Convoy, and Shanghai Optics.
Where to buy TIR lenses
Brightlx: Offers custom LED lenses for spot lights, warning lights, and more
Convoy: Sells TIR lenses for flashlights
Shanghai Optics: Sells TIR lenses that use total internal reflection to concentrate light beams
What is a TIR lens?
GUIDE TO TIR LENSES - LEDiL
A TIR lens is an optical lens that uses total internal reflection (TIR) to create a concentrated beam of light. TIR is an optical phenomenon that causes light to reflect back into a denser medium when it passes from a denser to a less dense medium.
TIR lens applications
TIR lenses are used in a variety of applications, including collimating beams from high power LEDs. Most optical fibers also use TIR as the guiding principle.
TIR Lens - Shanghai Optics
A TIR lens is an optical lens built on the principal of total internal reflection (TIR). TIR lenses collimate light, sending out a...
Shanghai Optics
20MM TIR lens for 5050 LED (SST40,XML2,etc) - Convoy flashlight
20MM TIR lens for 5050 LED (SST40,XML2,etc) - Convoy flashlight.
convoy flashlight
30 Degree LED TIR Lens - Brightlx
Trust Brightlx and choose us as your led lens manufacturer to provide high-quality custom led lenses that contribute to safer and ...
Brightlx
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Universe Optics
https://www.universeoptics.com
Designed For Medical Imaging, Surveillance, Night Vision, Machine Vision & More, Call Now!
GUIDE TO TIR LENSES
LEDiL
https://www.ledil.com › support › guide-to-tir-lenses
For you
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Feedback
60 Degree TIR Lens - 21.2mm x 13mm
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(th)

tahanson43206 · Yesterday 13:10:35

This post concentrates on supply of 32 mm TIR lenses ...

As a reminder, a 32 mm square area can collect one watt of solar power if insolation at a site is 1000 watts per square meter.

I asked Google to look for vendors that offer 32 mm TIR lenses, and once again, it came back with a substantial collection:

Search Labs | AI Overview
Learn more
GUIDE TO TIR LENSES - LEDiL
You can buy 32 mm TIR lenses from Auer Lighting and Vyoptics.
Suppliers
Auer Lighting: Sells a 32° TIR lens for LED "Quad" Cavity 3 mm
Vyoptics: Sells a 32 mm glass half dome lens
What is a TIR lens?
TIR Lens - Shanghai Optics Shanghai Optics
A TIR lens is an optical lens that uses total internal reflection (TIR) to concentrate light into a beam. TIR lenses are used in many applications, including collimating beams from high power LEDs.
How does a TIR lens work?
TIR lenses and reflectors have similar working principles, but TIR lenses have more control over light. With reflectors, much of the light doesn't touch the reflector and can't be controlled.
TIR lens applications
TIR lenses are used in a variety of applications, including collimating beams from high power LEDs.
TIR Lens for LED "Quad" Cavity 3 mm, 32 - Auer Lighting
TIR Lens for LED "Quad" Cavity 3 mm, 32°: Auer Lighting.
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I note that some of the lens on offer have circular cross section instead of square. If it turns out that a circular style is better for this application (for whatever reason) then the area needed for the array will increase somewhat from the 200 by 200 meter square area used here as a template.

The idea is to match the photon collection device to the power carrying capacity of the optical fiber. it appears that standard single strand optical fiber used for communications on Earth in 2025 is able to carry one watt of power without overheating.

(th)

tahanson43206 · Yesterday 13:35:40

It appears that a 36 mm diameter lens is needed if our goal is to collect 1 watt at the presumed insolation of 1000 watts per square meter.

Happily, it appears that TIR devices are available in this size.

Deep Space Solar Collection Concept
Objective:
We are exploring a novel propulsion concept for a deep space vessel, where sunlight is collected over a large area and directed toward a propulsion unit. Instead of relying solely on traditional solar panels, the design leverages Total Internal Reflection (TIR) lenses to efficiently capture and channel sunlight into optical fibers.
Key Design Parameters:
The collection plane is approximately **200 meters × 200 meters**, covering **40,000 square meters**.
Solar power available in space is assumed to be **1000 W/m²**.
Each unit in the system must collect **1 watt**, requiring **10 cm²** of collection area.
Standard optical fibers can carry **1 watt of power**.
TIR Lens Sizing Calculation:
If only circular TIR devices are available, we need to determine the diameter of a lens that can subtend **10 cm²**.
Using the area formula for a circle:
A = π × (d/2)²
Solving for diameter (d):
d = 2 × √(10/π) ≈ 35.7 mm
Thus, we should look for circular TIR lenses with a diameter of approximately 35.7 mm.
Next Steps:
We will now search the market to see if TIR lenses of this size are available. Adjustments may be required if commercial options differ in size.

(th)

tahanson43206 · Yesterday 13:40:34

In this post, we adapt the concept to use circular TIR devices. It appears the 40 MW can be achieved with sides of 240 meters.

Updated Solar Collection Plane Dimensions
Objective:
To determine the required dimensions of the solar collection plane that can generate **40 MW** using Total Internal Reflection (TIR) lenses. Each lens captures **1 watt** of solar power at **1000 W/m²**, and we assume a **2 mm separation** between adjacent lenses.
Key Parameters:
Total power required: **40,000,000 W** (40 MW)
Power per TIR device: **1 W**
Diameter of each TIR lens: **36 mm**
Separation between lenses: **2 mm**
Step 1: Calculate the Effective Spacing per Device
The total width occupied by each lens, including separation:
Effective Spacing = 36 mm + 2 mm = 38 mm = 0.038 meters
Step 2: Determine the Total Number of Devices
Since each device collects **1 watt**, the total number of devices required:
Number of Devices = 40,000,000 / 1 = 40,000,000 devices
Step 3: Compute the Side Length of the Collection Plane
Assuming a square grid arrangement:
Side Length = √(40,000,000) × 0.038
Side Length ≈ 240.3 meters
Conclusion:
With **36 mm TIR lenses and 2 mm separation**, the collection plane must be approximately **240.3 meters × 240.3 meters** to generate **40 MW**.

(th)

tahanson43206 · Yesterday 15:27:13

IN this post, I've enlisted Gemini, Google's enhanced search engine. I had hoped it would perform a search on the Internet, but instead it perform analysis and evaluation of the Optical Plane Deep Space vessel concept. The result appears to be a reasonable set of guidelines for a vendor search. The photon capture device for this application may not exist at present, but there may be devices that come close, and which would be suitable for testing in Real Universe situations.

Conversation with Gemini
Hi Gemini! Thank you for your assistance with many previous questions. Today I am hoping you can help with a shopping question. The product I am looking for may not exist, but if it does, I'm hoping you can help me find the vendor. There is a category of optical devices called TIR (Total Internal Reflection) lenses. We have found lens in the size we need of 36 mm diameter, but not in the configuration we need. The purpose of the lens for our application is to take in photons that arrive from the Sun dead on, and to deliver those photons to an optical fiber that is the standard diameter for a communications optical fiber. By any chance, can your search tools find a product that fits that description?
Okay, I understand. You're looking for a 36mm diameter TIR lens specifically designed to:
Capture direct sunlight (photons arriving "dead on").
Focus that light into a standard communications optical fiber.
This is a very specific requirement, and as you suspected, an off-the-shelf product that perfectly matches this might be difficult to find. However, let's break down the search and explore potential avenues:
Challenges and Considerations:
TIR Lens Design Complexity: Designing a TIR lens for efficient sunlight collection and fiber coupling requires precise control over the lens's geometry. The lens needs to:
Maximize the capture of incident light.
Minimize losses due to reflections and absorption.
Match the numerical aperture (NA) of the optical fiber for efficient coupling.
Accommodate the specific diameter of the optical fiber.
Sunlight Concentration: Sunlight is a very intense light source. The lens must be able to handle the thermal load associated with concentrating it, especially when coupled to a delicate optical fiber.
Fiber Coupling: The lens must precisely align the focused light with the fiber's core.
Standard Communications Fiber: The diameter of standard communication fibers is very small. This means the lens must have a high level of precision.
Potential Search Strategies and Vendors:
Specialized Optics Manufacturers:
Edmund Optics: They offer a wide range of optical components, including TIR lenses. While they may not have an exact match, they could potentially provide custom solutions.
Thorlabs: Known for their expertise in photonics and optical components, Thorlabs might have relevant products or be able to assist with custom designs.
Carclo Optics: Carclo specializes in LED lenses, including TIR lenses. While their focus is often on illumination, they might have relevant expertise.
Fraen Corporation: Fraen also specializes in LED optics.
Asphericon: They specialize in aspheric optics, which are often used in TIR lens designs.
Custom Optics Design Firms:
If you cannot find an off-the-shelf solution, consider contacting firms that specialize in custom optical design. They can create a lens tailored to your specific requirements.
Search Terms:
When searching online, use specific keywords such as:
"36mm TIR lens solar concentrator"
"TIR lens fiber coupling"
"High NA TIR lens"
"Custom TIR lens design"
"Optical fiber concentrator lens"
"Photonic concentrator"
Universities and Research Institutions:
Researchers in solar energy and photonics may have developed similar optical systems. Searching for academic publications and contacting relevant research groups could be beneficial.
Recommendations:
Contact Edmund Optics and Thorlabs directly: Explain your specific requirements and inquire about custom solutions.
Prepare detailed specifications: Before contacting vendors, create a document outlining your lens requirements, including:
Lens diameter (36mm)
Fiber type and diameter
Numerical aperture (NA) of the fiber
Desired concentration ratio
Wavelength range of the sunlight you are trying to capture.
Thermal requirements.
Consider a two-stage approach: If a single TIR lens is insufficient, you might need to use a combination of lenses or other optical elements.
I hope this helps!
Thank you for your willingness to tackle this unusual request, and for the comprehensive set of suggestions you provided for how to proceed. One detail I would like to clarify since you mentioned it... There should be NO risk of damage due to the intensity of solar radiation at the location where the application is to be used, because we have sized the device specifically to collect no more than one watt. The optical fiber we are interested in using can accept up to one watt without risk of overheating. Thus, our proposal seeks to avoid the risks you have identified.
Excellent clarification! Knowing that you've already addressed the heat dissipation and power handling aspects significantly narrows the search and makes it more focused on optical performance. That's a critical detail that simplifies the potential design.
With the 1-watt limit in mind, here's how we can refine the approach:
Refined Search and Considerations:
Emphasis on Optical Efficiency:
Since heat isn't the primary concern, focus on maximizing the optical efficiency of the TIR lens. This means minimizing losses due to:
Fresnel reflections (use anti-reflection coatings).
Absorption within the lens material (use high-quality optical glass or polymer).
Scattering (ensure smooth surfaces and precise manufacturing).
The lens must efficiently transfer the collected light into the fiber's acceptance cone (defined by its NA).
Fiber Coupling Precision:
The alignment between the focused light and the fiber core is crucial. Even small misalignments can lead to significant power losses.
Consider using fiber coupling adapters or mounts to ensure precise alignment.
The lens should be designed to produce a focused spot size that closely matches the fiber core diameter.
Wavelength Range:
Specify the wavelength range of the solar radiation you're interested in. This will help vendors select the appropriate lens material and coatings.
If you're only interested in a specific portion of the solar spectrum, you can use optical filters to further refine the light entering the fiber.
Vendor Communication:
When contacting vendors, emphasize the following:
The 1-watt power limit.
The importance of high optical efficiency.
The need for precise fiber coupling.
The wavelength range of interest.
That the lens is to be used for solar collection.
It may be useful to provide a drawing or sketch of your intended optical system.
Simplified TIR Lens Design:
Because the heat load is not a concern, the lens design may be able to be simplified.
This may make it easier to find a company willing to create a custom design.
Key Points to Communicate to Vendors:
"We are developing a solar energy collection system with a 1-watt power limit."
"Optical efficiency and precise fiber coupling are our primary concerns."
"We require a 36mm diameter TIR lens to couple sunlight into a standard communication optical fiber."
By emphasizing these points, you'll help vendors understand your specific needs and provide more relevant solutions.
Thank you (again) for your thoughtful assessment of the situation in light of the low power levels involved. I noticed another detail in your reply, and am hoping your will allow me to impose a bit more on your generosity... We are needing all the energy we can secure from the Sun. The application is propulsion of a space vessel, and the effectiveness of the system will depend upon our success in capturing as much energy as we can. Please consider the implications of ** that ** requirement for our vendor search.
Ah, maximizing energy capture for space vessel propulsion changes the game significantly! This adds a layer of extreme optimization to your requirements. Here's how that impacts the vendor search and design considerations:
Implications of Maximizing Energy Capture for Space Propulsion:
Broadband Spectral Response:
You need to capture as much of the solar spectrum as possible. This means:
Wideband Anti-Reflection Coatings: Coatings that minimize reflection across the entire solar spectrum (or at least the widest possible range).
Lens Material Selection: Materials with high transmittance across the relevant spectral range. Fused silica or specialized optical polymers might be preferable.
You will need to provide a spectral analysis of the light that is available in space, as this will have a large impact on the materials used.
High Numerical Aperture (NA):
A higher NA allows the lens to capture light from a wider angle, maximizing the amount of sunlight collected.
This is critical for space applications, where the sun's angle relative to the spacecraft might vary.
Precise Optical Design and Manufacturing:
Any imperfections in the lens design or manufacturing can lead to significant energy losses.
You'll need to work with vendors who have expertise in high-precision optics and advanced manufacturing techniques.
Consider aspheric lens designs to minimize aberrations and improve focusing.
Radiation Hardness:
In space, optical components are exposed to harsh radiation environments.
The lens material and coatings must be radiation-hardened to prevent degradation over time.
This adds a significant constraint, and will limit the available materials.
Minimizing Losses:
Every percentage point of energy loss matters.
Pay close attention to:
Surface Quality: Ultra-smooth surfaces to minimize scattering.
Material Purity: High-purity materials to minimize absorption.
Precise Alignment: Minimize losses at the fiber coupling interface.
Total Internal Reflection Efficiency: ensure that the TIR is maximized at all angles.
Lightweighting:
Spacecraft components must be lightweight.
Consider using lightweight materials like optical polymers or thin-film coatings.
Optimize the lens design to minimize its volume and mass.
Vendor Selection:
Specialized Space Optics Companies: Companies that specialize in optics for space applications will have the expertise and experience to meet your requirements.
High-End Optical Design Firms: Firms that have experience in designing complex optical systems for demanding applications.
Companies that provide radiation hardened materials and coatings.
Key Vendor Communication Points:
"This lens is for a space-based solar propulsion system, where maximizing energy capture is critical."
"We require a broadband spectral response, high NA, and radiation-hardened components."
"Weight and efficiency are paramount."
"We need vendors who have experience in designing and manufacturing high-precision optics for space applications."
Additional Considerations:
Consider the effects of micro-meteoroids on the lens.
The lens will need to operate in a vacuum.
Thermal cycling in space will place stress on the lens.
By focusing on these points, you can significantly improve your chances of finding a vendor who can provide the optimal solution for your space propulsion application.
Thank you for this comprehensive evaluation of our proposal! While I'm away, best wishes for similar success as you try to assist your many other customers!
You're very welcome! I'm glad I could provide some helpful guidance. Best of luck with your space propulsion project! It sounds like a fascinating endeavor.

Gemini brought up radiation impinging upon the material making up the TIR devices. I have no idea how serious a problem that might be. Certainly cosmic rays are going to be arriving from all directions and at all times, and occasionally bursts of particles from the Sun will arrive if the vessel does not adjust attitude to avoid direct exposure.

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