MatterBeam

Hi! How are you balancing the engines? Do you use kW/kg as a balancing factor?

I really like how you used multiple control surfaces to fit the wings. I think that the X-29's wings weren't supposed to resist bending through the use of ultra-tough materials, but to have a negative AoA behaviour that prevented stalling as they twisted.

Yes, I am. How soon? About ten years. It would take about 10x the development cost of the Falcon 9, so about 10-20 billion. The problem is that absolutely no-one wants or needs a first generation fusion spaceship. By first-generation, I mean it relies on fission-ignited fusion pulse units for propulsion. It is the most accessible technology.

I'm sorry to hear that.

Oh there's no tradeoff. The two concepts use the same mechanism to start a fusion reaction, but the version I posted here is a propulsion method while the fusion bullets I will post about is a weapon.

I don't understand. Could you elaborate?

Oh what a coincidence: Kinetic impact ignited fusion projectiles is third on my list of topics.

@sevenperforce You are right that it is practically impossible to contain a nuclear explosion. However, generating electricity does not need a sustained, contained nuclear explosion. What all pulsed nuclear fusion designs use is a waste heat reclamation system. The simplest versions exploit the fact that much of the fusion reaction's energy becomes x-rays and neutrons. A magnetic bottle cannot deflect pure energy or neutral particles. So, these products slip through the magnetic fields into space. Some of these radiations are blocked and absorbed by the physical drive components, causing them to heat up. Electricity can be generated from this heat. This process is incredibly inefficient, but even 0.01% of a fusion blast's energy is enough to ignite the next one. More efficient methods use the magnetohydrodynamic effect of charged particles moving through a magnetic field. These generate electricity directly from the magnets by slowing down the particles slightly. For your question: Casaba Howitzers Nuclear Shaped-Charge projectiles.

Sorry, I just did a quick calculation. If we wanted to be more precise, the tower would stand 1069km from the center of rotation. Duna's atmosphere is very thin and the orbital velocity lower than Kerbin's so aerodynamics won't be a big issue for railgun-launched payloads. The real mass penalty is the aerodynamic package you need to create enough drag to slow down for a soft landing. As for the specificities of deltaV comparisons between Dres and Duna... well, you're the one with the modded solar system! I can only guess

What do you mean by 'recirculating enough of the heat.?

Sorry. I though 'break even' referred to the commonly used 'Q-factor', which is the ratio of fusion energy to ignition energy.

Very creative write-up for Dres! Here's a few thoughts: Dres' low gravity means that building towers is extremely easy. Like, simple steel becomes 10x the effective strength as here, on Earth. If we have access to CO2/NH3 from inner planets or comets, we can build aramid fibres with an effective strength 100x greater than here on Earth. Visualize truss towers over 1000km tall around Dres' equator. The planetoid only needs to be spun up to very low velocities to create significant centripetal force at the tip of these towers. At 0.016RPM, we can get 0.3g at the top of a 1000km tower. Dres, at 13km diameter, would only feel an acceleration of 0.00195g, which is barely 1.4% of its surface gravity. Win-win. Commercial use would depend on the answer to the following question: For a spacecraft in low Duna orbit, is it cheaper to lift up propellant from the surface, or to send down propellant from Dres? Don't forget that Dres has several advantages, such as allowing the transport ship to use low-thrust engines all the way down to Duna and never needing a heatshield and parachute to be recovered. Another point I'd like to make is that asteroid mining would like a distributed resource collection system (mining asteroids) but a centralized resource processing and handling system (refineries and factories on Dres). It might be cheap to haul bulk quantities of rock from asteroids to Dres. If you cut out all the useless dirt and extract pure nickel and magnesium, you reduce the number of trips you have to make down to the inner planets and save money overall. Dres could become a resource processing center of local asteroids. Of course, in space, local means that it takes little deltaV to get from A to B. By that definition, Duna is closer to Dres than Kerbin is to the Mun, because it takes less deltaV (I think ).

I... really like that you're going straight for 10m diameter designs. Build them big! Get your economies of scale! If I were you, I'd mod the fairing mass in the .cfg settings to be much lighter than they currently are. Also, don't forget to autostrut them in the VAB so that they don't pop off on physics loading.

If you don't break even, then you might as well directly heat an inert (non-fusion-fuel) pellet of hydrogen. You'd get the same thrust and Isp with better efficiency. These alpha particles can be very slightly slowed down by magnetic fields. If you slow them down by just 1%, you can power a magneto-hydrodynamic generator to create electricity out of the fusion explosion. If the MHD is 50% efficient, you can extract as much as 0.5% of the fusion yield. 0.5% of a terajoule blast is 500MJ. Current attempts at igniting fusion are using pulses in the 100kJ to 1MJ range, so powering the fusion ignition device should never be a problem.

@qzgy Good job! How does it fly in KSP?

There's another, much simpler than Z-pinch, concept for initiating fusion. Gun Fusion. Excerpt: What is proposed here is a method to ignite fusion using well-understood technologies, requiring only minimal power inputs yet remaining well adapted for use in propulsion. Gun-fusion configuration The design is composed of two railguns, each accelerating a specially configured bullet, to be launched at each other with the intention of igniting fusion within a solid propellant cylinder. It involves a 5 step process: -Launch. The bullets contain three elements: a thin (100nm) faceplate of gold, a chamber containing a gas mixture of deuterium, tritium and hydrogen, and a solid 'tail'. They are launched using a railgun to velocities of 20-100km/s depending on configuration. The basic bullet configuration -Impact. Upon impact, the gold faceplates vaporize as kinetic energy is converted into thermal energy (10% efficiency). The heat radiated by the impact raises the temperature of the gas mixture (1% of bullet mass) to 3.125 million K. This lowers pressure requirements for ignition by a factor of 100000. Diagram of impact: 2) Gold plate. 3) Gas mixture. 4) Optional backing plate (solid fusion fuel). 6) Point of impact 7) Radiated energy. 8) Vaporizing backing plate. -Compression. The momentum of the tails makes them act as pistons. Their movement compresses the gas mixture to over 80 million atmospheres. Temperatures rise to over 50 million K. A fusion reaction is ignited. Diagram of compression: 3) Gas mixture being compressed. 4) Optional backing plate (solid fusion fuel). 5) Tail pieces. -Propulsion. The impact takes place under a half-sphere of polyethylene or other suitable propellant. The energy released by the fusion reaction vaporizes and ionizes the propellant. The momentum of the propellant is captured by electromagnetic or mechanical means. Configuration for gun-fusion drive This 'gun' fusion has several clear advantages over the aforementioned methods of igniting fusion. Railguns are simpler than electromagnets cooled to superconducting temperatures or petawatt lasers using heavy, bulky supercapacitors. While the total energy involved is equal to or greater than that of inertial confinement fusion, the power levels are much lower and vastly more manageable. The fusion fuel does not have to be handled at cryogenic temperatures either. With today's technologies, railguns are lighter than particle accelerators or Tokamaks. They are also more efficient than petawatt lasers, and the fusion mechanic is more robust. In the special designs discussed below, they can be replaced by even lighter methods of accelerating the bullets. Another important characteristic for fusion propulsion is that the fusion equipment can be placed arbitrarily far away from where the fuel is ignited. This lowers shielding requirements.

I have this same issue. I think it is a mistake in the 1.3 patch document... but it is a very minor annoyance. It shows up as 'Earth' correctly on contracts.

It is a tradeoff. You can increase the mass of the skyhook and make it longer, or increase the velocity of the aircraft instead. A first-attempt skyhook would probably pick up a payload from a first-stage rocket booster, so that the hook capture can happen entirely outside of the atmosphere. This prevents the tip of the hook from having to undergo re-entry every few minutes.

I'm enjoying these! A note I'd like to make: A laser thermal rocket is materials limited to the same degree as a solid-core NTR. In this blog post, I worked out the performance of laser launch systems. Remember, the laser can come from the ground, but also from a station in orbit.

Hello. I'm un-sure how you handle requests, but I'd love it if you added this beautiful plane to your to-do list, complete with its drop tank: F-5E Tiger II.

You said commercial exploitation was a meaningless buzzword, so I gave you the dictionary definition I was referring to. Who pays? NASA, ESA, SpaceX, anyone with an interest in space really. Why? Orbital re-fuelling allows for beyond LEO rockets to become three to ten time smaller on the ground for the same payload. Who pays? China, India, US, EU. Why? Asteroid and lunar mineral resources dwarf land availability of those same resources, allowing for cheap expansion of high tech industries without rare element restrictions. Who pays? BP, Shell, Exxon, Total. Why? Solar satellites build in orbit can become cheaper than land-based, rare-metal-restricted panels and are the future of energy. The reasons are numerous, the possibilities endless... the first hurdle is paying for the development program. That's an investment in the future that does not answer to simple economics, and will be made by the same people who put money into fusion research and exo-planet hunting. The point of 3D printing in space is not to turn a colony into a closed eco-system. It is to prevent having to load up rockets on Earth with simple things such as bricks, spades and hammers. It represents enormous mass savings if you only have to ship up lightweight items such as microprocessors and MEMS. I didn't understand you emphasis on exploitation in the last line of your comment.

Methane? CH4. Ammonia. NH3. Ammonia is hard to use as a fuel. It has 6.3 times less energy per kg than hydrogen and needs a catalyst to burn in air. That's normally possible in a rocket... but not at hypersonic speeds where the catalyst will melt. Although... maybe having the ammonia sperheated by the nuclear reactor beforehand might make this a non-issue. The fact that the reaction products of an ammonia-oxygen flame are similar to the atmosphere at the engine inlet doesn't quite matter - the only thing which affects Isp is temperature, molar mass and proper expansion. An ammonia/oxygen flame mixed with with atmospheric gasses will burn colder and have higher molar mass than the same with hydrogen instead of ammonia. The small disadvantage in atmospheric flight becomes a massive one in the exoatmospheric regime, where ammonia's molar mass of 17 is compared to hydrogen's 2. If we factor in dissociation of ammonia, the picture still isn't pretty. Complete dissociation of 1 mol ammonia gives us 1 mol of nitrogen and 3 mols of hydrogen, for an average molar mass of 4.25. This means and exhaust velocity less than half that of hydrogen. When the NTTR breaks out of the atmosphere at Mach 10, it might still have to produce 6km/s of deltaV to reach orbit. With dissociated ammonia at 3000K, it will have an exhaust velocity of 4.2km/s and needs a mass ratio of 4.18. With hydrogen at 3000K, it has an exhaust velocity of 8.65km/s and needs a mass ratio of 2. Ammonia will mean you need a rocket twice as massive! If we consider pebble-bed reactors at 4500K, the mass ratios are reduced to 3.2 and 1.76, which is still pretty much means the ammonia rocket is twice as heavy as the hydrogen rocket. However, further research shows that ammonia dissociates into N2 and H2 at about 600K, however N2 only completely dissociates at 30000K and H2 at 10000K. The real dissociated molar mass of an ammonia gas at 3000-4500K temperatures is very likely to be between 8.5 and 4.85 g/mol, leading to frankly terrible exhaust velocities of 2.9km/s at worst and 3.9km/s at best (3000K). Use this calculator: http://calistry.org/calculate/kineticTheoryVelocityCalculator Why would hydrogen give a low TWR?

I don't really mind. Its still a lot of great work.

I don't understand why you would switch from hydrogen to ammonia. Hydrogen is being used as a fuel here. A majority of the NTTR's thrust at lower velocities comes from combustion of hydrogen in an oxygen atmosphere. Since oxygen propellant would mass 9x the hydrogen propellant but you are getting it free from the atmosphere, there is a massive saving in propellant fraction. Ammonia would not allow these gains. Why do you mention a lightbulb, as in a closed-cycle gaseous core nuclear engine? A pebble bed reactor might allow core temperatures to rise from about 3000K to 4500K. Solid materials cannot survive any higher. According to this Root Mean Square calculator, if we take the completely dissociated H2->H atoms at 1g/mol, then at 3000K a NERVA would reach 8.65km/s exhaust velocity while a pebble-bed would increase this by 22% to 10.6km/s. This is not a significant enough increase to consider moving away from hydrogen because it is 'overkill'.

By commercial exploitation, I use the definition 'the development and use of a resource for business'. These resources are things which can only be obtained from space or are much cheaper if obtained from space. It includes propellants for in-orbit refuelling, asteroid resources such as rare metals or even common materials such as basalt fibres and iron alloys for building spaceship components in vacuum, instead of lifting heavy parts such as propellant tanks and pressure hulls from Earth's surface. The use of these resources defines the need for them, but its a circular questions that escapes the original post's question of what would be lifted on super-heavy launchers. Now, onto your other statements. Mining colonies do not have to cost trillions of dollars. This is not 70's era extraterrestrial colonization, where we need to set up self-sustaining habitats for dozens to hundreds of people with every nut and bolt launched from Earth. We only need to land a set of robots that can use local resources to 3-D print the remaining equipment. Space exploration is not about economics. If it were, we'd never spend a dime on expensive projects such as the Kepler telescope or Curiosity. Those things don't make money, and belittling the billion dollar price tags and the millions of man-hours of effort on those things cost as 'fanboy fantasies' is disingenuous. If we do pay for commercial exploitation of space, it will be initially to make the 'fanboy fantasies' less expensive than they currently are.