MatterBeam

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About MatterBeam

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  1. Hi! I recently discovered an accurate-to-life hand-drawn animation of the Falcon Reusable booster and the Skylon concept, with explanations of the benefits and challenges spaceplanes face. Enjoy!
  2. After discussion: -Expanding the gas to hypersonic velocities is not desireable. Using a very-high-pressure, sub-Mach flow is much more efficient. -A radiator will be needed at the end of the Brayton cycle to remove the residual waste heat. At low temperatures, this radiator will be huge. Therefore a much lower temperature difference is needed between the reactor and the second nozzle, to be compensated for with a large pressure difference... much like actual nuclear reactor. -A similar concept has been tested. -Overall, this concept will be more effective due to the direct-cycle involving the nuclear reactor shooting directly into the turbine, rather than because of the possible temperature difference.
  3. Ha! They even chose the same coolant (nitrogen) as I did! Thanks for the find. Well, regarding reliability, I have started discussing this design elsewhere, and found that a hypersonic gas flow at the first nozzle was too optimistic and could cause huge drag losses. Mach 0.85 is the optimal gas flow velocity, because then we can use ultra-reliable, ultra-efficient turbofan designs from modern aviation. Turbofans run for thousands of hours without a hitch.
  4. I thought this would be slightly different. Modern reactors create a loop of high temperature isobaric coolant that loses heat through an exchanger. It is limited by the temperature limits of its various components. The Expansion part allows for a lot more energy to be put into the gas, while only subjecting the blades to moderate temperatures. The condensation at the end allows for us to 'cheat' the brayton cycle by allowing an arbitrarily high pressure drop across the turbine. I think it is a brayton cycle. At 90% or so efficiency at each step, the waste heat to be removed is quite low. In space, mass is at a premium. I think a single-loop reactor that operates at high reactor temperatures and yet has low temperatures at the turbine end might end up having very high specific power (kW/kg).
  5. Hi. I've been thinking about this configuration of a nuclear reactor, a set of nozzles and a turbine generator. The Expansion-Condensation Closed-Cycle Nuclear Turbine Generator. A nuclear reactor heats a coolant such as nitrogen to high temperatures and pressures, like a nuclear thermal rocket. Efficiency 90%. The coolant is expanded through a nozzle to moderate temperatures, low pressures and high velocity, like a propulsive nozzle. A multi-stage turbine converts the gas's energy into mechanical energy. This slows down the gas. Efficiency over 80%. Electric generator converts turbine motion into electricity, efficiency 90%. Second expansion nozzle condenses and liquefies the gas. This creates near-vacuum pressures, reducing back-pressure at the first nozzle. The liquid coolant is collected and pumped back into the reactor. Overall efficiency is 65% to 80%. Nuclear reactor can have GW/ton specific power. Turbine can have several dozen MW per ton specific power, coupled with electric generator. Can this work? Will it compare favourably to Stirling engines and thermocouples? Is the concept sound? Is there something I am missing as to why direct-cycle nuclear turbines have not been used for power generation? In space, specific power is very important, especially when several MW of power is needed for electric rockets, such as VASIMR. So far, concepts have described thermocouples or Stirling engines for electric power. Can this concept compete with current designs? After discussion: -Expanding the gas to hypersonic velocities is not desireable. Using a very-high-pressure, sub-Mach flow is much more efficient. -A radiator will be needed at the end of the Brayton cycle to remove the residual waste heat. At low temperatures, this radiator will be huge. Therefore a much lower temperature difference is needed between the reactor and the second nozzle, to be compensated for with a large pressure difference... much like actual nuclear reactor. -A similar concept has been tested. -Overall, this concept will be more effective due to the direct-cycle involving the nuclear reactor shooting directly into the turbine, rather than because of the possible temperature difference.
  6. Last year, I was searching for RSS/x6.4/x10 mission logs after attempting to do my own. I was not successful in keeping up, which is why I'm doubly amazed by @UnusualAttitude's persistence and constant quality.
  7. I think we should keep it all here. I mean, we're only at 20 pages, no need to disperse ourselves.
  8. I think you are confusing the Heat Exchanger Laser Thermal Rocket with the Lightcraft/Pulsed Laser Plasma Rocket. The HX-LTR has to have a hot piece of metal that acts an an intermediary between the laser's energy and the propellant. Temperatures are limited to the melting point of the heat exchanger. Like a nuclear thermal rocket, this is about 3500K maximum. A PLPR does not have a laser receiver or any element that heats up. It is a mirror surface that focuses a laser into a small torus under the vehicle. Air caught in that focal point is heated to plasma, then the plasma quickly absorbs the laser energy and reaches thousands of degrees Kelvin. There is no upper limit. The PLPR's mirror surface actually only reflects a relatively weak beam, of about a few dozen solar intensities (10kW/m^2 or more) and extremely low total joules per square meter. It has been tested, and it works. Blue-violet flashes indicate 10000K+ temperatures.
  9. I just caught up with the story. This is... amazing. Impressive.. no, incredible! Astounding! That 'shuttle as booster stage' is the kind of science-based ingenuity that made The Martian so much fun to watch. I can't wait to read future instalments. Count me in as one more 'Liked this' on all of your next posts
  10. Quite right!
  11. This is very interesting relative to the space warfare posts on my blog, where it is stated that 'The Laser Problem' becomes significant at shorter laser wavelengths. Free Electron Lasers can able to produce such wavelengths.
  12. That's my point: it's tested, readiness 1 technology that just needs more money for more powerful lasers. I noted that powerful lasers were being dragged alongside smaller microchip scales, and that the tech industry might be the indirect benefactor for laser launch technology that might be more reliable or faster than military research. That is true for the Heat Exchanger laser thermal rocket design. There are ways to slightly push past this limit, such as using liquid hydrogen active cooling. The higher Isp designs directly heat an independently floating piece of propellant. In ablative or 'pulsed plasma' designs, the propellant never interacts with the nozzle or any other parts of the engine while being heated. This allows for 10000K+ temperatures that do not damage anything. After the heating is completed, which takes between a nanosecond and a millisecond, you end up with a rapidly expanding ball of propellant. Gasses cool down as they expand (PV=nRT). If it starts out as a 1cm sphere, and expands to a 10cm sphere before bouncing off the nozzle walls, it would have cooled by a factor 1000. Suppose we take a 1 gram squirt of liquid hydrogen. We heat it up to 280000K using about 12kJ. It starts out as a blog 3cm in diameter. After heating, it explodes at about 25.5km/s. Within 2.6 microseconds, it has expanded to a ball of plasma about 13cm wide. By this time, it has cooled down to less than 1000K. This is easily handled even by small, metallic nozzles. In other words, there are ways to generate incredible exhaust velocities. The lightcraft operates similarly. Air is superheated to tens of thousands of kelvin by a pulse of laser, thrust is generated by its expansion, then the air is replenished and the next pulse arrives. At higher velocities, airflow is faster and the pulses can cycle quicker... but there is less air. The maximum quaoted in one of my referenced studies was Mach 10. Beyond that point, it became very difficult to generate enough thrust to match the drag. If the air is superheated to 10000K, then its initial temperature accounts for 0 to 10% of the total energy. At 100000K, it is 1%. At the several million Kelvin quoted as possible, the initial temperature of the air can simply be ignored.
  13. Hi! From this post. Laser Launch to Orbit In this post, we will look at laser launch systems, how they would look like and perform, and how they might be applied to reach orbit and beyond. The advantages of laser launch 140GHz is microwave. A typical rocket engine does two things: deliver propellant and heat it up using an energy source. In a chemical-fuel rocket, the propellant is combustible and is burned in a combustion chamber. The resulting heat and gasses serve both as propellant and an energy source. In a nuclear thermal rocket, the propellant is inert and nuclear material is used to heat it up. An electric rocket uses internal power, derived from a nuclear reactor or solar panels, to accelerate inert propellant using electrostatic or electromagnetic effects. What temperature do you think the gasses inside the nozzle are at? The performance of a rocket is limited by how much energy can be delivered to the propellant. This is how much energy is released by the combustion of fuels such as liquid hydrogen or kerosene, how much heat is released by a nuclear core of how much electricity is delivered to an electric rocket. However, rocket fuel is only so energetic, and there are strict limits on how hot a nuclear core can get before it starts melting down or has to be designed larger and heavier. Electric engines are rather low on specific power, and the more the rocket consumes, the more mass has to be dedicated to producing energy. Liquid fuelled rockets are a mature technology that have pretty much reached the limits of chemical performance. For example, the SSME Plus was designed for an Isp of 467 seconds (4580m/s exhaust velocity), and the Rocketdyne AEC engine with 481 seconds (4718m/s exhaust velocity). This is very near the theoretical maximum for liquid hydrogen and liquid oxygen (about 500s). Going slightly further requires impractical fluoride oxidizers. Nuclear rockets can push the envelope, but testing of solid-core designs delivered low Isp at high thrust levels, or high isp but low thrust in vacuum. Gaseous core rockets can provide both high thrust and high isp, but they require decades of research. Electric rockets have similar problems. Nuclear reactors in space are very heavy, and solar panels do not provide enough energy to lift off the Earth. The solution is to separate the energy source from the spaceship. A Skylon variant where energy for heating the hydrogen propellant is provided by laser beam. Laser beams can deliver the output of a several-thousand-ton power plants on the ground to the engine, at no extra cost. Although the specifics depend on the designs being used, the performance of laser-powered rockets ranges from 700 to 10000 seconds, with no upper limit except for laser power levels. A combination of high Isp and powerful engines that do not require on-board reactors, nuclear materials or volatile chemicals makes for small, cheap and safe rockets. The price per kilo in orbit can be made manageable at $1 to $100 per kg, therefore opening up access to space. The problems to solve Naturally, a rocket going into space cannot carry along an electrical wire to the ground to deliver energy. A power plant on the ground generates electricity, which is used to power a laser generator. The beam is then focused onto the spaceship, where an engine uses the laser energy directly, or absorbs it as heat indirectly. Four rough approaches to using laser power in a rocket The intermediary steps between the power plant's electrical energy and the spaceship's engine create efficiency losses. The biggest loss is in the laser itself. Laser generators are quite an inefficient piece of technology. Conventional lasers, such as solid-state lasers, have an efficiency of about 25%. Pure diode lasers can reach over 60% efficiency, but cannot generate intense pulses. Pulsed lasers have to rely on flash-pumping technology, which gives mediocre 0.1% to 5% efficiency. Fibre laser configuration from a cutting machine. Fibre lasers, where hundreds of tiny beams are joined through optical fibres into a larger beam, have both high efficiency, high resistance to heat and high pulsed power output, so are the best solution for a laser launch system. Another source of losses is from the laser beam travelling through the atmosphere. Some of it is absorbed. The best wavelengths for focusing a laser on a spaceship, such as ultraviolet (<400nm wavelength) do not travel far through the atmosphere. Optical wavelengths (700 to 400nm) and infrared to microwave wavelengths (700nm to 1cm) have narrow 'atmospheric windows' where they can travel through air without being quickly absorbed. Even so, a few percent is lost when the laser beam traverse dozens of kilometers of water vapour and various gasses. The 'atmospheric window' wavelengths If there is a heavy cloud cover, optical wavelengths will not go through. Microwave beams are the only solution, as they are the least affected by clouds and water vapour. A lot of power is needed to launch rockets on laser. Generating a multi-gigawatt laser beam requires expensive hardware, and a lot of it. You'd also need to build ground facilities such as custom power storage, a miniature electrical grid, a large laser focusing array and so on before the first rocket is even launched... this is a level of up-front investment that may be difficult to find people or organizations willing to pay for. In comparison, conventional rockets only need to built one booster per mission. The costs are specific to the task they need to complete. Ground installations are minimal in comparison to those of a laser launch facility. Some laser-powered rocket designs require that a laser pulse strike a small target in precisely the right time and location, with the correct amount of joules. While the fine targeting can be done using on-board mirrors, the ground focusing array is still required to track the spaceship across a wide range of altitudes and velocities. The biggest problem is that lasers do not strictly travel in straight lines through the air due to atmospheric distortions. Adaptive optics and some sort of guide laser and feedback loops are required, which are complicated to set up and might fail to achieve the desired accuracy. A depiction of a laser launch facility. To summarize, a laser launch capability must compensate for the various losses from equipment inefficiencies and atmospheric absorption. It must produce a high quality beam that strikes the target in all situations, through atmospheric distortions and weather effects. During this time, electrical power supply and cooling must be managed. These imply enormous up-front costs due to the quantity of expensive equipment required. Reference design and comparisons Reaching space is hard. Depending on the flight profile, a deltaV capacity between 9.5 and 11km/s is required to reach Low Earth Orbit. Due to the extreme variety in ways to achieve this amount of deltaV, we will use a reference design that we can compare the laser launch methods to. Our objective will be 10 tons in orbit. Estimating engine mass is hard, as more thrust means a heavier engine with required more propellant which leads more thrust. Estimating tank masses is even more complicated, as they scale with volume. To remove the need for hundreds of hours of iterative calculations, we will retro-actively convert the necessary amount of payload mass into structural, tank and engine masses once the propellant requirements have been calculated. A chemical-fuels rocket using Kerosene-Oxygen at 300s Isp in the lower stage and Liquid Hydrogen-Oxygen at 420s Isp in the upper stage can reach orbit using 23.6 tons of LH2/LOx and 121 tons of Kerolox. Total mass is 155 tons. Upper stage deltaV is 5000m/s, lower stage deltaV is 4500m/s for a total of 9500m/s. Overall mass-ratio is 15.5. Laser-powered rockets must achieve orbit using a much lower mass ratio to be competitive. The designs [...] Continued here.
  14. I'll try to be clearer next time. Both generating aerodynamic lift and using buoyancy forces is difficult on Jupiter. 'How to Live on Other Planets' is a series on the blog which tries to describe colonisation of the solar system without looking through the lens of Earth. It is more useful that way for SF writers or worldbuilders that have very different plans for what happens to our planet. I agree that Jupiter is a bad choice for colonisation, it was one of the central conclusions of the post. If it were necessary, and a main base had already been established elsewhere, then it could still be done. Low Jupiter Orbit is tough, especially when high TWR engines are required. If we start at a TWR of 1.2, Earth-equivalent TWR would be something like 3! Unless the setting has access to high-erformance nuclear engines, it would have to be achieved by chemical rockets. However, the latter have a poor exhaust velocity of 4.5km/s, and LJO is 40km/s, so about 42km/s deltaV is required. Mass ratio 11371. Obviously impossible. If we limit ourselves to a mass ratio of 100, then an exhaust velocity of 9km/s, which is achievable by hydrogen-propellant nuclear rockets. Aerodynamic heating is an issue, so ascent profile will likely be very steep, with the majority of the horizontal acceleration being done outside of the atmosphere.