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This new topic is intended to fill an unmet need...
We had these topics:
Rotating Tank Cryogenic Liquid Pumping Method by tahanson43206
Science, Technology, and Astronomy 2 2024-10-31 11:52:47 by kbd512
Movable Partition Cryogenic Liquid Pumping Method by tahanson43206
Science, Technology, and Astronomy 1 2024-10-30 08:55:43 by tahanson43206
Cryogenic heat engines by Calliban
Science, Technology, and Astronomy 11 2023-02-17 09:11:25 by tahanson43206
Origami bladders for cryogenic propellant by Quaoar
Interplanetary transportation 4 2022-10-22 17:04:34 by SpaceNut
NASA tests composite cryogenic fuel tank by Mark Friedenbach
Single Stage To Orbit 10 2016-04-09 23:20:43 by SpaceNut
None of them addressed a serious concern raised by GW Johnson as he works on his Space Tug concepts.
In the topic created by Mark Friedenbach, GW listed the problems with existing technology.
Since the original topic was created, the engineers and scientists who designed and built and deployed the James Webb space telescope have proven conclusively that they can establish and maintain near-Zero Kelvin temperatures for extended periods of time. Those low temperatures are needed for proper operation of the infraread sensors that are the main payload for the telescope.
I've been trying to understand why this achievement is not more widely recognized, and I think I may have found an explanation.
In order for a deep space shade to work effectively to preserve cryogenic fluids, the entire storage container, piping and other hardware must be brought to just above Absolute Zero, along with the propellant.
Perhaps the problem is that cryogenic fluids are shipped to space in rocket vehicles that are only partially cooled, and in any case, the engine compartment gets blazing hot during launch. If a vehicle (such as a Starship) reaches orbit with tanks full of liquid propellant, the heat of the vehicle will inevitably find it's way into the propellant tanks, and those will experience sublimation of the liquid to gas.
In addition, until GW began work on his Space Tug project, there is no evidence (that I have seen) that ** anyone ** has conceived of a mission for which it is necessary to preserve liquid propellants for years at a time.
It seems to me the answer is deep space cooling of the entire structure that is holding the propellant.
Once the entire structure is cooled to just above Absolute Zero, and as long as the Deep Space shade continues working, the propellant will remain undisturbed for centuries.
This topic is offered for members to provide links to related research or actual projects, and to make comments appropriate to the problem.
for reference:
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The boiling points of nitrogen, oxygen, and hydrogen are:Nitrogen: -195.8°C (-320.4°F)
Oxygen: -183°C (-297.4°F)
Hydrogen: -252.87°C (-423.2°F)
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This post is reserved for an index to posts that may be contrbuted by NewMars members over time.
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This topic offers an opportunity for NewMars members to contribute to a collection of information about the problem of storage of liquid cryogenic materials.
At present, as GW Johnson keeps reminding me, humans have only one demonstration of keeping a gas liquid for an extended period of time, and that gas is Nitrogen. Nitrogen boils at a higher temperature than Oxygen or Hydrogen.
The James Web telescope is a working demonstration of the technology needed to keep nitrogen below boiling for (hopefully) years at a time, using a sun shield designed for the purpose.
This topic would be enhanced if someone can take the time to find out and post details about how the James Web telescope keeps nitrogen in the liquid state. Whatever that technology is needs to be extended to oxygen and hydrogen, so these materials can be transported with a space vessel that needs them to "dock" with a remote destination, and to return to Earth.
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There are active means and there are passive means, to keep sunlight from heating the tanks and boiling off the propellant inside too fast. The active means require some sort of power producer driving some sort of refrigeration equipment. I'm no expert on how that is done, but there is always a significant weight penalty, especially if the power producer is a heat engine (thermodynamics requires this).
Passive means involve interrupting the path of heat flow, which is always from hot to cold (again, thermodynamics). Shade the tank so the sunlight cannot reach it. Radiant energy is the thing to interrupt, in the vacuum of space with no other physical structures, conduction and convection are not an issue, but the radiant energy from a star surface at many thousands of degrees is. What you cannot forget is that your shade surface will get warm, and radiate in the infrared. You have to interrupt that too.
Many of the things you might do have both beneficial and adverse effects. You have to achieve a net balance in your favor. You interrupt the radiant heat from your warmed shade surface with insulation, on its shady side. The surface of that insulation still radiates, but it is cooler and radiates a whole lot less than the bare shade would. That is because radiation varies as the fourth power of absolute temperature. That is one huge effect you can manage!
You can make the sunlit side of your shade surface very reflective, so that most of the sunlight is reflected back to space. But not all of it, nothing is perfectly reflective. That will cool off the temperature of the sunlit side of the shade surface. But it will cool off a lot less effectively when it is shaded, because high reflectivity is associated with low emissivity, and that strongly impedes re-radiation cooling to space. Once warmed, it tends to stay warm longer even when in darkness.
You can mount a shade panel on some sort of extended arms, yes, but you still have to insulate its backside to interrupt the infrared from the warmed shade surface. There is a weight penalty associated with those mounting arms, as well as the shade panel and insulation itself. If instead you wrap the tank in a layer of low thermal conductivity insulation, and over-wrap that with a highly reflective metal foil, you get the same insulated shading effect at pretty much the same (or possibly less) shade panel and insulation weight, but without the weight penalty of the extended arms.
You do pay for this with a thermal conduction path through the insulation to the tank. However, the temperature difference through the insulation multiplies a very low conductivity and gets divided by a significant thickness, for a low heat flow value. Thickness divided by thermal conductivity (in mixed US customary units) literally is the R-value of the insulation. And if the shade is the highly reflective foil, that shade surface temperature is not very high. The colder your propellant, the higher the R-value of your insulation that is required. Simple as that!
If your fuel and oxidizer temperatures are greatly different, do not use a common bulkhead between the two tanks, even if insulated in some way. We already understand that to be a dominant heat leak path in the Centaur stage design, which limits the "stage life" to only hours to a day or so. Just accept the weight penalty of two bulkheads to completely interrupt that heat flow path.
The SpaceX idea of the header tank is the way to further interrupt heat flow from the heated shade material to the tank wall into the propellant, when you do it by wrapping the tank. You must correctly size the header, and it must be located nested inside the main tank, for this to work as a thermal control. Short-term, you burn all the propellant out of the outer main tank at the start of your mission. What you need for the rest of the longer-term mission is all in the header. Vent the outer tank to vacuum. That cuts off the conductive/convective heat flow through the propellant vapor, from the outer tank wall to the inner header tank wall. In effect, the outer tank wall and vacuum around the inner tank wall form a Dewar. The only possible heat flow path is infrared radiation from the outer tank wall, but that temperature will not be very high, so there is very little of that kind of heat to flow. We already know this Dewar technique works very, very well.
These suggestions, carried out properly, might get you a "stage life" measured in weeks or even a month or so, even with hydrogen! For years of "stage life", you might have to add the refrigeration equipment.
"Stage life" is the interval until there has been enough boiloff evaporation inside the propellant tank to raise its pressure dangerously, whereupon you either vent the propellant, or the tank bursts. This is a serious issue, and the source of a significant fraction of the space debris around the Earth.
Sorry, guys, there's no simple (one-issue) answer here. Thermal control is ALWAYS a very complicated tradeoff among many issues. You just have to do the necessary engineering, and you have to get it right. The answer will NEVER come from just plugging numbers into one single equation.
GW
Last edited by GW Johnson (2024-12-30 10:32:01)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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Our goal in this topic is to find a solution that will keep cryogenic materials intact for years, and certainly for months.
Today I asked Google's Gemini to look for information about the James Webb telescope. I now remember reading about the multiple layers of the shade that keeps sunlight away from the telescope. The layers are separated by vacuum, and each contributes to a cascade of cooling.
The equipment used to achieve 7 degrees Kelvin deserves further study.
The James Webb Space Telescope (JWST) employs a sophisticated combination of passive and active cooling systems to maintain its instruments at cryogenic temperatures. While it doesn't directly use liquid nitrogen for fuel, it does rely on it for passive cooling.
**Passive Cooling:**
* **Multi-Layer Insulation (MLI):** This consists of multiple layers of thin, highly reflective material (like Kapton) separated by thin spacers. It acts like a thermal blanket, minimizing heat transfer from warmer areas of the spacecraft to the colder instruments.
* **Sunshield:** A five-layer, kite-shaped sunshield blocks heat from the Sun, Earth, and Moon. Each layer is made of a thin, silicon-coated Kapton film that reflects sunlight and radiates heat away.**Active Cooling:**
* **Cryocooler:** The Mid-Infrared Instrument (MIRI) requires cooling to a much colder temperature (below 7 Kelvin) than can be achieved passively. A cryocooler, a mechanical device, actively cools MIRI to its operating temperature of 6.7 Kelvin. It uses a closed-cycle helium refrigeration system to achieve these extremely low temperatures.
**Liquid Nitrogen's Role:**
* **Passive Cooling:** Liquid nitrogen is used during ground testing to cool down the telescope and its instruments to their operating temperatures. It helps simulate the cold space environment and ensures that all systems function as expected before launch.
**Key Points:**
* JWST doesn't use liquid nitrogen as fuel.
* It relies heavily on passive cooling techniques like MLI and the sunshield.
* The cryocooler is essential for cooling MIRI to its extremely low operating temperature.
* Liquid nitrogen plays a crucial role in ground testing but not in the operational phase in space.**Finding More Details:**
To delve deeper into the specific engineering details of JWST's cooling systems, you can explore these resources:
* **NASA's JWST website:** [https://science.nasa.gov/mission/webb/](https://science.nasa.gov/mission/webb/)
* **Technical papers and publications:** Search for articles and papers on JWST's cryogenic systems in scientific databases like NASA Technical Reports Server (NTRS) or IEEE Xplore.
* **Books on space telescope engineering:** Look for books that provide in-depth coverage of JWST's design and technology.I hope this information is helpful!
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As a follow up, there is an opportunity for a NewMars member to look for more details about the design, and particularly for details of temperatures observed at each stage of the process. For example, there may be temperature readings taken at each of the five layers of the sun shade, and perhaps at other locations in the telescope.
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Post #5 contains a link to a NASA web site ... I entered a search for James Webb Cooling System and received back a long list of citations...
This one seems to have a bit of useful information in the context of a storage facility for cryogenic fluids...
https://www.nasa.gov/solar-system/webb- … mperature/
NASA’s James Webb Space Telescope will see the first galaxies to form after the big bang, but to do that its instruments first need to get cold – really cold. On April 7, Webb’s Mid-Infrared Instrument (MIRI) – a joint development by NASA and ESA (European Space Agency) – reached its final operating temperature below 7 kelvins (minus 447 degrees Fahrenheit, or minus 266 degrees Celsius).
Along with Webb’s three other instruments, MIRI initially cooled off in the shade of Webb’s tennis-court-size sunshield, dropping to about 90 kelvins (minus 298 F, or minus 183 C). But dropping to less than 7 kelvins required an electrically powered cryocooler. Last week, the team passed a particularly challenging milestone called the “pinch point,” when the instrument goes from 15 kelvins (minus 433 F, or minus 258 C) to 6.4 kelvins (minus 448 F, or minus 267 C).
“The MIRI cooler team has poured a lot of hard work into developing the procedure for the pinch point,” said Analyn Schneider, project manager for MIRI at NASA’s Jet Propulsion Laboratory in Southern California. “The team was both excited and nervous going into the critical activity. In the end it was a textbook execution of the procedure, and the cooler performance is even better than expected.”
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Pursuing the question of how NASA cools to 7 Kelvin, here is a link to a YouTube video that appears to be attempting to explain the process..
https://www.youtube.com/watch?v=FUH61gx149c
A detail that may be of interest: The mechanical pumps used for the helium heat pump cycle in James Webb are designed to avoid introducing vibration by working in opposite directions. The video animation shows what that looks like.
In the case of a fuel tank I don't think absence of vibration is necessarily a requirement, but it seems to me as though vibration is evidence of wasted energy, so it would make sense to use the balanced system now that it is invented, proven and working.
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I asked Gemini to "think" about the cooling problem facing GW Johnson in designing his deep space missions, and the refueling station in LEO.
I was able to detect and correct the influence of NASA mission planners who are constrained by budgets. One useful outcome of the discussion was the observation that the number of sun shade layers is not fixed at five. That is the number arrived at by the James Webb team, as sufficient to meet the mission objectives while at the same time fitting within the mass budget for the mission.
The gent I'm working with has created flight plans for a variety of systems for the Mars Settlement problem. The ISP provided by LOX/LH2 makes it attractive for flights to and from Mars, but it is necessary to preserve the propellant throughout the trip. We are impressed by the five layer sun shade developed for James Webb. That system would appear to be replicable, and it appears able to deliver about -183 Celsius conditions on the side opposite the Sun. There is an abundance of solar power available in the region between the Earth and Mars. It seems to me as though it should be possible to design a system able to remove thermal energy from an LH2 tank faster than it enters the tank. The system is designed to be reusable for many space flights between Earth and Mars. You may be influenced by the writings of those who are constrained by tight budgets. If you free yourself from those constraints, and think in terms of a massive transportation infrastructure that will slowly but surely grow in the Solar System over time, you will be less concerned about the immediate cost of a system, and more concerned with achieving the project objective.
You're onto something significant! The JWST sunshield demonstrates a powerful concept: passive radiative cooling. By effectively shielding a structure from external heat sources and maximizing its ability to radiate heat away into the cold of space, we can achieve incredibly low temperatures.
Here's a concept building on this for long-duration cryogenic propellant storage:
1. Enhanced Multi-Layer Insulation (EMLI):
Beyond JWST: Go beyond the JWST's five layers. Develop a more sophisticated, multi-layered system with:
Variable Layer Spacing: Adjust the spacing between layers dynamically based on the internal temperature of the propellant tank.
Radiative Cooling Fins: Incorporate thin, highly conductive fins extending from the tank's outer surface to enhance radiative heat transfer.
Advanced Materials: Explore novel materials with even higher reflectivity and lower thermal conductivity for the insulation layers.2. Active Radiative Cooling:
Deployable Radiators: Integrate deployable, high-emissivity radiators that can be oriented to maximize heat dissipation.
Pumped Fluid Loops: Circulate a low-temperature fluid (potentially a cryogenic fluid itself) through the tank walls and through the radiators to enhance heat transfer.3. Solar Power Utilization:
Refrigeration Cycles: Utilize abundant solar power to drive advanced refrigeration cycles.
Stirling Cycles: These engines offer high efficiency at low temperatures and can be well-suited for space applications.
Thermoelectric Coolers: Employ thermoelectric modules to directly convert thermal energy into electrical energy, which can then be used for refrigeration.4. Propellant Tank Design:
Optimized Tank Shape: Design the propellant tank with a spherical or near-spherical shape to minimize surface area and reduce heat transfer.
Superinsulation: Integrate advanced superinsulation materials within the tank walls to further minimize heat conduction.5. Integrated System:
Closed-Loop System: Create a closed-loop system where the refrigeration system removes heat generated by the propellant and any residual heat leaks, maintaining the propellant at cryogenic temperatures.
Key Considerations:
Micro-meteoroid and Debris Shielding: The delicate insulation layers must be protected from micrometeoroids and space debris.
System Redundancy: Incorporate redundant components and fault-tolerant design to ensure long-term reliability in the harsh space environment.
Continuous Monitoring and Control: Implement sophisticated sensors and control systems to monitor propellant temperatures and adjust the cooling system accordingly.Long-Term Vision:
This approach represents a significant investment in advanced cryogenic storage technology. However, within the context of a long-term, expanding space infrastructure, the benefits are substantial:
Reduced Propellant Losses: Minimize boil-off losses, significantly reducing the amount of propellant that needs to be launched from Earth.
Increased Mission Capability: Enable longer-duration missions and more ambitious exploration goals.
Reduced Launch Costs: Lower launch costs by reducing the amount of propellant that needs to be launched.
Enabling Technologies: Develop critical technologies for future space exploration, such as long-duration cryogenic storage for deep space missions and potential future space-based industries.This concept requires significant research and development, but the potential rewards for enabling human exploration of the solar system are immense.
profile pictureThank you for this encouraging overview of the situation we are addressing! I'll share it with our team.
You're welcome! I'm glad this information is helpful.
Remember, this is a complex challenge with no easy solutions. Continued research and development in areas like advanced materials, cryogenic engineering, and space-based power generation will be crucial for achieving the goal of long-duration cryogenic propellant storage in space.
I encourage your team to continue exploring these ideas and consider collaborating with researchers and engineers in relevant fields.
Good luck with your work!
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