You are not logged in.
In preparation for today's Google Meeting, I asked ChatGPT4o to "think" about ionization of hydrogen gas. VASIMR uses a complex electronics package to ionize gas for their ion drive. I wondered if direct solar heating could achieve the same thing with a lot less complexity and with greater output, but the answer appears to be no, due to the high temperatures involved. Here is a transcript of the discussion:
ChatGPT said:
Here's the summary of today's conversation, prepared using BBCode with your preferred formatting.Exploring Ionization of Hydrogen Using Solar Power
Introduction
Today, we investigated the feasibility of ionizing hydrogen gas directly using solar energy. The goal was to understand whether simple heat or other methods could be applied to achieve ionization, as part of our effort to use solar power efficiently for space propulsion.Can Heat Ionize Hydrogen Directly?
Thermal ionization of hydrogen requires extremely high temperatures due to hydrogen's ionization energy of approximately 13.6 eV.
This level of energy corresponds to temperatures exceeding 150,000 K.
Using the Saha ionization equation, it is established that achieving significant ionization at lower temperatures (e.g., around 10,000 K) is still difficult and energy-intensive.
Conclusion: Pure thermal ionization is impractical for our application.
Alternative Ionization Methods
Photoionization:
Using high-energy photons, particularly ultraviolet (UV) light from the Sun, to ionize hydrogen atoms.
Photons with energies exceeding 13.6 eV can ionize hydrogen directly.
Concentrating solar UV radiation or generating artificial UV sources could make this process more efficient.
Electron Impact Ionization:
Accelerating electrons to high energies and colliding them with hydrogen atoms to produce ionization.
This method is commonly used in plasma generators and can be powered by solar-derived electrical power.
Plasma Generation Techniques:
Using devices such as Inductively Coupled Plasma (ICP) or Electron Cyclotron Resonance (ECR) sources to ionize hydrogen.
These methods are effective and can be powered by the 20 MW of electrical power generated by our photovoltaic system.
Why VASIMR Uses Radiofrequency Systems
The VASIMR (Variable Specific Impulse Magnetoplasma Rocket) uses radiofrequency (RF) systems to ionize propellant because direct thermal ionization is inefficient.
RF systems allow efficient transfer of energy to gas particles, producing plasma without the need for extreme temperatures.
This approach allows for a controllable, efficient ionization process suitable for space propulsion, powered by electrical energy (like our proposed photovoltaic system).
Summary
Direct thermal ionization of hydrogen is impractical due to the high temperatures required.
Methods such as photoionization, electron impact ionization, and plasma generation are much more practical when powered by the 20 MW of electrical energy generated from solar power.
This analysis helps explain why the VASIMR system relies on RF-based ionization, which we may consider adopting or adapting to our own system.
Would you like me to prepare the next step in this project, where we design a suitable ionization system using the available 20 MW of electrical power?
(th)
Offline
Like button can go here
In this session, we looked at VASIMR, given the potential of 20 MW of electrical power from the Optical Plane.
As a reminder, 20 MW of waste heat can be used to accelerate propellant as a way of cooling the photovoltaic cells.
At 20 MW, the system could (apparently) produce 500 Newtons, which is 1/10 of the design goal of 5000 Newtons.
Thrust Estimation of VASIMR System with 20 MW of Electrical Power
Introduction
In this analysis, we estimate the achievable thrust of a VASIMR (Variable Specific Impulse Magnetoplasma Rocket) system when powered by 20 megawatts (MW) of electrical power. This energy comes from the photovoltaic conversion of sunlight as part of our hybrid propulsion system design.Performance Overview
The VASIMR engine's performance varies depending on the operational settings, particularly the specific impulse (I_sp), which measures how efficiently the engine uses propellant.
Higher I_sp values result in more efficient propellant usage but generally produce lower thrust.
Thrust Calculation
VASIMR engines operating at 200 kW of power produce approximately 5 newtons (N) of thrust.
This corresponds to a thrust-to-power ratio of 0.025 N/kW.
Extrapolating this ratio to our available 20 MW (20,000 kW) of power:
Thrust=0.025N/kW×20,000 kW=500N
Thrust=0.025N/kW×20,000kW=500N
Estimated Thrust: Approximately 500 newtons (N).
Power Allocation Considerations
The available 20 MW of electrical power must be divided among the following subsystems:Ionization of Propellant: Power required to ionize the hydrogen gas.
Plasma Acceleration: Energy used to accelerate ionized hydrogen to produce thrust.
Spacecraft Systems: Electrical power needed for other ship operations.
Specific Impulse and Mission Profile
The VASIMR system allows for adjustable specific impulse, making it suitable for various mission profiles.
High specific impulse settings are best for long-duration, efficient propulsion.
Low specific impulse settings provide higher thrust for short mission phases.
Conclusion
With 20 MW of electrical power, a VASIMR system could theoretically achieve 500 N of thrust, assuming optimal power distribution and efficiency.
This capability underscores the potential of VASIMR technology for efficient, adjustable propulsion in long-duration interplanetary missions.
Would you like me to help you expand this presentation with additional details to make it even more engaging and informative for your audience?
Bottom line ... there appears to be no shortcut using purely thermal energy to ionize gas.
(th)
Offline
Like button can go here
The question of blending the Optical Plane concept with VASIMR is on the agenda for this evening's Google Meeting.
The question of efficiency of solar cells will come up (since it has already come up).
I asked Google to look for reports about efficiency, and it found this one:
https://physicsworld.com/a/sunny-superp … fficiency/
The world record holder is rated at 44+%.
This system uses multiple layers to capture different wavelengths, and it uses concentration of sunlight.
I noted that the author writes that Silicon is unable to match this performance because (my understanding of this is limited) the layers available using Silicon are ? unable to align properly?
I noted that the author reports that the multiplayer chips do better in space than silicon as radiation does it's thing.
(th)
Offline
Like button can go here
Max efficiency by itself is a very misleading measure! It also has to survive extended operation at full soak-out temperatures, and for a duration that suggests a decent lifetime. The ones that meet those criteria have yet to exceed about 27% conversion efficiency. So says AAAS's "Science" Journal, which is peer-reviewed to a fault.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
Offline
Like button can go here
Thanks to GW Johnson for post #29....
As GW points out, the world record was set in a laboratory.
The 44% figure is aspirational. The 27% figure is more realistic for the near term. That means that instead of 56% of thermal energy available to accelerate hydrogen in a heating tube, we would have 73%.
The reason I am looking for an alternative to 100% thermal acceleration is that the 100% thermal acceleration option may be impossible to achieve with existing technology.
To prepare for this evening's meeting, I asked ChatGPT4o to compare the VASIMR magnetic ion accelerator to the Gerald R. Ford aircraft launcher. I recognize that the comparison is a stretch, but my objective is to show that the limiting factor for VASIMR is NOT the use of magnetic acceleration.
Comparison of Magnetic Acceleration Systems
Introduction
The comparison of magnetic acceleration systems between the Electromagnetic Aircraft Launch System (EMALS) on the USS Gerald R. Ford and the VASIMR engine reveals fundamental differences in operation, power use, and performance. This analysis aims to identify key factors limiting VASIMR’s performance and explore potential pathways for improvement in space propulsion systems.Comparison Breakdown
Feature: Mass Accelerated
EMALS: Up to 45,000 kg
VASIMR: ~100 to 250 mg/s (with krypton)
Feature: Acceleration Time
EMALS: ~3 seconds (short burst)
VASIMR: Continuous operation over extended periods
Feature: Power Source
EMALS: Stored energy (capacitors & generators)
VASIMR: Direct power generation (solar, nuclear)
Feature: Magnetic Field Use
EMALS: Linear Induction Motors
VASIMR: Magnetic Nozzle (plasma confinement & acceleration)
Feature: Purpose
EMALS: Short, high-power bursts
VASIMR: Continuous, efficient thrust for deep space
Feature: Thermal Management
EMALS: Not a major issue (short duration)
VASIMR: Major issue (sustained operation over long periods)
Feature: Power Consumption
EMALS: Extremely high for short bursts
VASIMR: High but requires sustainability over long durations
Key Insights
- The limitation of VASIMR is not due to magnetic force itself, but rather the available power supply and the efficiency of the plasma confinement and acceleration system.
- Unlike EMALS, which delivers energy in short bursts, VASIMR requires continuous power delivery and efficient thermal management.
- Achieving a mass flow rate of 1 kg per second would require a substantial increase in power generation, magnetic field strength, and thermal management capabilities.Next Steps
Would you like me to proceed by proposing an enhanced design based on this comparison? Additionally, I can estimate the power requirements to achieve a mass flow rate of 1 kg per second.
(th)
Offline
Like button can go here
The ability to model the behavior of gas heated by a long tube is a useful capability for planning the propulsion system envisioned by this topic. It appears that the tool needed to extend a mesh to create a heating tube is called "extrudeMesh". In preliminary testing in September of 2025, it appears this tool may be able to extend the intake to a mesh for the Merlin Engine.
(th)
Offline
Like button can go here
This post is about planning for physical implementation of heating in the Optical Plane vessel:
Thank you for both A and B scenarios! You and I can work on A. I'd like to offer B to our members and the larger audience. Please put B into BBCode as you did so masterfully a few days ago. I would like to encourage everyone to think about materials, and how they might be arranged.
Concept Note: “Half-Black Tube Bundle” Heater for Hydrogen
Plain-language idea
We heat hydrogen more effectively by running it through many small tubes. Inside each tube, one half of the inner surface is a very black, high-temperature absorber; the other half can be clear or reflective. We inject photons from both above and below so every tube sees light, the black halves soak it up, and the gas picks up heat by intimate wall contact and convection. This “unit cell” (a single half-black tube) can be repeated into a bundle, then scaled into rings around the intake.
Why this helps
[]Much larger hot surface area per unit flow → better convective heat transfer (higher h).
[]Shorter diffusion paths → the gas core warms, not just a thin near-wall film.Geometry is modular → easy to scale and service; lets us “tune” tube size, coating, and layout.
Candidate materials (pros/cons)
[]SiC (silicon carbide) tubes or inserts — high-temperature capable, good emissivity, robust; widely used in radiant heaters.
[]Graphite / carbon-carbon (C/C) absorbers — extremely high-T, ultra-black, light; must stay non-oxidizing (H₂ is fine). Watch erosion at high speeds.
[]Fused silica (quartz) windows/guides — great optics; structural use limited by softening temperature and thermal shock. Better for low-to-moderate T or as optical couplers, not the main hot absorber.
[]Sapphire / transparent ceramics — tougher windows at high T (costly), for where optical access must survive heat.Coatings — prefer integral “black” materials (textured SiC, graphitic surfaces). High-emissivity paints rarely survive >1000–1200 °C; avoid as primary absorbers.
How to arrange the tubes
[]Half-black interior: machine or line the inner wall with a semicylindrical black insert; the other half passes/redirects light downstream.
[]Two-sided illumination: split optics so every tube receives photons from above and below. Add cool baffles/reflectors to catch strays and re-aim onto black halves.
[]Bundle layout: square or hex close-packed arrays; consider slight staggering to promote cross-mixing while keeping pressure drop reasonable.
[]Manifolds: symmetric inlet/outlet plenums with flow straighteners; small orifices or calibrated restrictors at each tube for uniform distribution.Modularity: build “ring modules” that bolt around the intake; make absorber inserts replaceable for maintenance.
Fluid & thermal design knobs
[]Tube size (hydraulic diameter): a few mm to ~1 cm boosts surface-to-volume and heat transfer coefficient h.
[]Reynolds number: aim for transitional/turbulent per tube (within Δp budget) to raise Nusselt number Nu and h.
[]Length: long enough for target ΔT, but not so long that Δp or maldistribution dominates.
[]Interfaces: if you keep quartz for optics, let the absorber be a separate SiC/graphite insert so quartz isn’t the main hot path.Simple rules of thumb (text):
– Heat transfer: h ≈ k * Nu / D_h
– Momentum/thrust ceiling for a given jet power P_jet and mass flow ṁ: T_max ≈ sqrt(2 * P_jet * ṁ)Instrumentation for a bench article
[]Mass flow: Coriolis or thermal mass flow meter on H₂.
[]Pressure drop: Δp across the bundle to track regime and fouling.
[]Temperatures: fast thermocouples (or fiber sensors) at bundle exit; a few wall TCs embedded in absorber inserts; IR camera through a window for qualitative maps.
[]Power accounting: optical/electrical input vs. gas enthalpy rise (ṁ·c_p·ΔT) to estimate coupling efficiency and compare with CFD.Safety & longevity
[]Keep the hot absorber in a non-oxidizing environment (H₂ purge); carbon erodes/oxidizes if exposed to O₂ at high T.
[]Manage thermal shock: ramp up/down; compliant mounts for inserts.Protect optical windows with cooling and clean purge curtains.
Scaling thought experiment (text)
[]Suppose a subscale uses P_in = 40 kW and ṁ = 0.002 kg/s.
[]If 60% of power becomes jet kinetic power (P_jet ≈ 24 kW), then
T ≈ sqrt(2 * P_jet * ṁ) ≈ sqrt(2 * 24,000 * 0.002) ≈ 9.8 N.That’s measurable on a benchtop stand and lets us iterate tube size, coatings, and layouts quickly.
Open questions for the community
[]Absorber choice: SiC vs graphite/C-C for the hot “black” half—who has data on durability in high-speed H₂ and thermal cycling?
[]Tube diameter & count: what D_h and tube count strike the right balance between heat pickup (Nu) and pressure drop?
[]Coating / surface texture: proven high-emissivity textures or treatments that survive >1500–2000 °C in H₂?
[]Manifold uniformity: favorite tricks for equalizing flow (orifices, micro-channels, lattice infills)?
[]Windowing & optics: best materials and cooling schemes for in-coupling at temperature.
[]Fouling/erosion: how to monitor and mitigate surface changes over long burns.Suggested next steps
[]CFD: in our current model, redistribute the same 40 MW around the full perimeter and measure the change in jet power and thrust.
[]Bench coupon: build a small tube bundle with interchangeable absorber inserts (SiC, graphite), measure ṁ, Δp, exit T, and coupling efficiency.Scale-up module: assemble several coupons into a ring, validate uniformity, and refine manifolding before full circumference deployment.
Invitation: Please propose materials (grade/spec), tube sizes, textures/coatings, and manifold concepts. If you have relevant high-T data (even anecdotal from labs/industry), sharing it will help us converge on a durable, scalable “unit cell” for the flight-scale heater.
(th)
Offline
Like button can go here
The drawing at the link below shows a possible configuration of equipment for the heating system of the Optical Plane vessel.
http://40.75.112.55/phpBB3/download/file.php?id=95
If you cannot see the image and would like to while we wait for the solution kbd512 is working on, send your IP to newmarsmember at gmail.com
(th)
Offline
Like button can go here