MatterBeam

@PB666, @Mayer: Interstellar dust particles are deal killers when it comes to high transit velocities. No hull can withstand the energy released by a single impact, so withstanding years of impacts is out of the question... but there are smart ways to deal with the problem. A plasma shield is a type of shield where a plasma is held in front of the spaceship using magnetic fields. When the dust particle strikes ions in the plasma, it converts some of its energy into heat. This heat breaks up the particle, until you have a small, hot gas cloud travelling through the plasma shield. This gas strikes many more atoms, thereby converting most of its kinetic energy into random thermal motion. It reaches a high enough temperature to become a plasma... which becomes affected by the magnetic fields you are using to hold the shield in place. It can then be deflected out of the way or simply absorbed. Another option is to shoot out massive, thin disks ahead of the spaceship. Dust particles will run into these disks and annihilate themselves well clear of the spaceship.

Car crash levels of damage. Massive bruising, concussions, joints popping, ribs breaking, and at even higher levels, you get organ and blood vessel rupture. Its not pretty.

That periodic kicking I described in your thread is now the only option.

@UnusualAttitude I performed tests. Extreme physics warp won't work out ( Here is testing of a 0.026m/s^2 craft at x10000 physics warp. It seems that KSP just doesn't apply the thrust in between calculation steps at high warp, resulting in a 10x to 1000x reduction in effective thrust as you increase the physics warp multiplier.

Hello! I've been trying out the Better Time Warp mod, specifically its option to edit the Physics Warp settings to higher multipliers. I have incrementally increased the multiplier from x5 all the way to x10000. This is to test whether low-thrust spacecraft can perform 'spiralling orbits' in KSP. The test craft had only 4 parts, an initial mass of 12.7 tons and a thrust of 355 Newtons. Its deltaV is 16058m/s. It should have an acceleration of 335/12711: 0.02636m/s^2, which is equivalent to 2.6 milligee. This craft should have been able to reach the moon (3949m/s) in 1.7 days of continuous thrust. And yet, here it is 2 days later: It has barely produced 471m/s in the time it should have produced about 4710m/s! This is a 10x reduction in the acceleration it should have.

@Geschosskopf I've been thinking about the problem of long continuous burns in KSP and I've thought of two things we could try: Use a reference ship. This reference ship is composed of three parts: engine, drone core, propellant tank. You set the mass of the components so that you have the same mass ratio and acceleration as your full sized craft. Switch on the infinite electricity cheat, switch BetterTimeWarp to x50 or more, and start your burn. The reference ship should behave like the main ship, but with only three parts, you can comfortably achieve 50 times physics acceleration or better. A 20 hour burn becomes 24 minutes of real time... Once the burn is completed, use HyperEdit to place the ship on a Rendezvous with the reference ship. Or, use Hyperedit 'kicking'. Use the velocity modifier to add, for example, 10m/s at a time, then time warp until you spend an equal amount of time as the ship would have taken to produce 10m/s. For example, if you acceleration is only 0.001g, you would take 17 minutes. Add 10m/s to prograde, time warp 17 minutes, and repeat. This approximates a continuous burn... What do you think?

Exactly that! Also, launching up unmanned refueling shuttles to refill the InterLunar tug once it arrives.

Report 3:

Lovely designs and humor that we can rely upon.... but damn if that skybox doesn't make this look like Dante's Space Program: Journey through the seven orbits of Hell.

Report 2:

Thanks! The Dolphin is a joy to fly. I have Atmospheric Autopilot, so as long as the design is aerodynamically stable, there is no SAS flutter and jerky rolls and pitches to worry about. The large fuel tank is 7.5m in diameter, so in addition to the wings, it is very lightweight when empty relative to its surface area. This gives it phenomenal braking ability in the upper atmosphere and I get to descend to the lower atmosphere very gently. Real Fuels is a hassle I don't enjoy, so I cut it out. I have hydrolox fuels in this install too. The fuel payload is 20 tons, so it could theoretically be made much smaller. In fact, if I replace the central engine with a Mainsail and lower the payload to 2 tons, it can (and has) done SSTO missions. I'll try the runway...

For some reason, I thought it would be heading to Jupiter . Am I correct in understanding that you only needed 2.5km/s of deltaV to land on the Mun?

Hello. This is where I will post albums of missions, maneuvers and designs I design and fly in a custom Real Solar System install. To keep things clean, simple and to do things a bit differently than other mission reports, the albums will be wordless. All details will be shown through the HUD. There are no characters, no story or overarching objective, but I will respond to questions and engage in discuss after each report. Report 1:

You are doing the series justice. These look absolutely stunning. How did you get these renders?

It is possible. You'd need the 'grenade' to be shaped like a teardrop. The teardrop is filled with an chemical propellant with a high density and specific energy. It would produce a sharp shockwave. The conical tail of the teardrop is a wave shaping device. It bends the shockwave by using bubbles to alter the density of the medium the shock wave travels through. This focuses the shockwave down to a point. It is a shaped charge that is potentially powerful enough to detonate a fusion fuel. At bulbous end is the fission fuel. Fission has a minimum critical mass- for uranium, it is 52kg, for californium, it is 2.73kg. However, if the fission fuel is compressed by the aforementioned shockwave, and surrounded by a neutron reflector, then the minimum mass can be significantly reduced.

What is SKE? What is SPE? What is HMO? How much is 'markedly'? Why should we spend months using periapsis kicks when the deltaV penalty for doing a spiralling orbit is small for a Hohmann trajectory and tiny for an accelerated transit? Is the incredibly long mission time worth taking along a few percent more propellant?

@Ten Key That was pretty smart. I really like how you gave a KSC science run a fun narrative.

10e-19W/m^2 is for a telescope that sits undisturbed for weeks on end, with its data processed by supercomputers at NASA and pored over by scientists. A more realistic satellite in a combat environment would have much lower sensitivity, due to more noise, random flashes heating the sensor and shorter observation times (closer targets can sweep across the field of view in less than a second). 10e-17 or lower is likely what we'll get. This reduces the detection range of that hydrogen to less than 1km. The calculations I did were a simplification too. The hydrogen cloud would actually expand away from the nozzle, forming a sphere with increasing density towards the center. The actual emissions, averaged over the entire expanding volume, will be much lower than what I calculated at the 1 second mark. The low density of the expanding gas cloud also means that only a tiny fraction of the solar wind will actually collide with a hydrogen atom, and I used a worst-case figure of 750km/s when solar wind actually has a range of velocities from 400 to 750km/s. All in all, if a hydrogen steamer gets detected, it won't be because of the hydrogen gas.

The HiPEP produced a range of ISPs, 6000-9000s. I used 6000s because it is the only way it matched the numbers you came up with. A more sensible design would have a much lower Isp anyway, and a much better tank mass to propellant mass ratio. The 5600m/s... is for the entire mission. From Earth departure (3500m/s) to Mars arrival (2100m/s). I am concentrating on the first part. I have demonstrated that 'spiralling out' is not 'wasting' fuel. A spiralling trajectory does not circularize, it just reaches escape velocity and straight lines away from the planet

I can't follow you into your fantasies anymore. I've disproven every valid point you've raised, but you don't have any of those in here.

The leakage rate is negligible compared to the amount you will be using for cooling. IR detectors measure the photon hit rate on a Charge-Coupled Device. Once enough photons hit the CCD, the switch is tripped and an electron is let through, corresponding to one pixel lighting up. They have a certain noise rating, which is photons created by the device itself, an uncertainty in measurement and other factors which lead to a minimum amount of 'hits per pixel' to register the presence of a warm object in space, or else it cannot be distinguished from the 'noise floor'. This translates into Watts. For very sensitive cameras, signals as faint at 10e-19W/m^2 can be detected. Using larger collectors allows the IR detector to approach this minimum value, or the 'noise floor'. Trying to obtain a good probability of detection requires a large signal to noise ratio. The emissions of the target are subject to the inverse square law: it gets fainter at a rate of 1/distance^2. For a 10m^2 collector, and a 10e-19W/m^2 noise floor, and a 10:1 Signal-to-Noise ratio, we can detect a 300K object emitting 459W/m^2 at a distance (459*10/(10*10e-19))^0.5: 67.7 million km. For hydrogen being blasted by the solar wind, you'll have high temperatures. This shifts the spectrum of the emissions into the lower wavelengths.... but the total energy is very small. Using the above equation, and inputting 5.71e-10W/m^2 instead, we get a detection range of 75.5km. Quite right! The size of the Hydrogen Steamer will mostly depend on how long you want to hide it.

@PB666 I think you are approaching the concept of not being able to to continuously accelerate away from a planet incorrectly. You must first break down the interplanetary trip into three parts: the acceleration to escape velocity, the transit, and the insertion. For Earth, you can handle the climb from 7.8km/s to 11.2km/s by itself. All you have to make sure of is that the angle you leave from Earth from roughly points you at your target planet. During transit, you can further accelerate to first raise your apohelion to actually reach Mars, then shorten the trip with further acceleration above the lowest-energy trajectory that is the Hohmann trajectory. Since the transit times are measured in months, while the 'further acceleration' will be a week at most, this is not a complicated thing to optimize. Insertion just requires that the craft start decelerating early enough so that its velocity relative to the target planet falls below the planet's escape velocity. It needs enough distance and time to accomplish this. The part with which you seem to have an issue with is the first acceleration to escape velocity. You suppose that a craft can only accelerate along a tiny portion of its orbital period/angle. This is not the case! Solar-electric trajectories are notoriously hard to optimize, but they all use a continuous acceleration over the entire orbital period. They disregard the small benefit of the Oberth effect, but gain in the time it takes to reach the escape velocity. A good calculator is the General Mission Analysis Tool (http://gmatcentral.org/) that is free to download and has a tutorial to handle low-thrust missions between planets. The numbers you used for your reactor and engines are pretty good! 4kW/kg for the reactor, 2.5kW/kg for the engines. Assuming no other equipment, that's 1.53kW/kg for propulsion. Let me run your numbers (130t propulsion, 200t payload, mass ratio 1.115...) against a more ideal scenario. You did not define an exhaust velocity or Isp for the engines, so I'll assume it is 6000s, which has been demonstrated by HiPEP and would give enough deltaV for a Hohmann (minimum energy, 8.6 month) trajectory to Mars. You can accelerate at a rate of 0.0183m/s^2 initially (1.86 milligee), rising to 0.0204m/s^2. Let's take the average of 0.019m/s^2. What I got in GMAT. Continuous acceleration up to escape velocity. To climb from 7.8km/s to 11km/s (escape velocity at 140km altitude), you need to accelerate for 1.95 days. To reach Mars, you add another 300m/s, which is an additional 4.4 hours. For a Solar-Electric craft, you'll start only being able to accelerate on the sunny side of the orbit. As your altitude increases, less and less of the Earth's shadow blocks your orbit. It is known as the beta angle, and it becomes negligible to nil at high altitude.

In non-stealthy mode, you would handle the liquid hydrogen like any other propellant: insulated tanks. Whatever heat leaks through causes the liquid to evaporate, maintaining a temperature of at most 22K. It is the same reason why boiling water doesn't get hotter: evaporation rate matches heat input at constant temperature. This evaporative cooling creates gas. It can be collected, condensed by a heat pump, and recycled. This consumes power, but like every other system on the ship, it would be handled by conventional radiators. This ESA study describes how cooling down the liquid hydrogen directly allows for long-term Zero BoilOff storage of liquid hydrogen. In stealthy mode, the radiators are retracted, the heat pumps switched off and the liquid hydrogen starts circulating through heat exchangers. It cools down the hull, then a trickle of hydrogen is fed to the open-cycle cooling system to match the waste heat from sunlight absorption, habitats and other vital systems such as life support. As for the ejected hydrogen colliding with solar wind... I seriously doubt it will create any meaningful signature. For one, the hydrogen in vacuum with expand either quickly or very quickly. In the simple hydrogen steamer, hydrogen vapour starts at 22K and expands from a nozzle until it reaches 3K. Even without any expansion (straight pipe), the nozzle would allow the hydrogen to have a velocity of 523m/s (root mean square velocity). The gas would disperse very quickly, and the interaction between that gas and the solar wind would produce even less signature than the spaceship's hull. To give you an idea of how faint the signal you are thinking of is, consider a low-frontal-area spacecraft sitting at idle and producing 10kW of waste heat. This is much higher than is strictly necessary, but let's just assume that it is a warship with a large crew. 10kW of waste heat must be dealt with by 22grams of liquid hydrogen per second. That is 11 moles of hydrogen. If released out of a straight pipe, the hydrogen would expand into 598926392.5 times its initial volume in one second. If it starts from a liquid density of 70kg/m^3, it would expand from 3.14e-4m^3 to 188234m^3 in one second. So, after one second, the hydrogen forms a gas cloud 523m across, at a density of 1.168e-7kg/m^3. It would interact with 858881m^2 of solar wind, so it would absorb 1.965 milliWatts at most. Per square meter, this translates into 5.71e-10W/m^2 across the hydrogen sphere. For comparison, the spaceship's hull is emitting 1.3e-2W/m^2. The hydrogen's signature is ten million times lower.

Open-ended cooling means that your heat sink (the liquid hydrogen) is thrown out into space once you're done with it. The liquid hydrogen is a consumable item that grants a number of seconds of stealth for every kilogram you spend. Good point about the solar wind. It is not something I have considered. Solar seems to contain 5 million particles per m^2, mostly protons of mass 1.673e-27kg. At worst, they'll hit the stealth craft at a velocity of 750km/s. That's a kinetic energy of roughly 2.35 nanoWatts per square meter. I don't think it will significantly heat the spacecraft. The point of the hydrogen ship is not to have a hot side, and to not be picked up by J.Webb-like telescopes at all.

The simple hydrogen steamer just boils off hydrogen. The hydrogen gas evaporates at 22K, and is released into space as a form of open cycle cooling. No heat radiators involved. Good luck spotting a faint puff (tens of grams per second) sitting just above the temperature you are cooling your infrared satellites' instruments to! Inefficiencies are dealt with by throwing more hydrogen at the problem. The expansion-cooling hydrogen steamer takes this a step further. Hydrogen boils, and then is fully heated in steps to the temperatures of the components it is cooling. So 22K for the outer hull, 300K for the habitats, 3000K for your nuclear reactor. The resultant 3000K hydrogen gas has absorbed over 60MJ/kg. You then blow it through a nozzle to release it at 20K temperatures and 9km/s+. Imagine it as a regular nuclear-thermal rocket with a high expansion ratio, using preheated hydrogen as propellant. The hydrogen/helium steamer is the ultimate low-signature design. A helium heatsink cools down the hull to 3K. This is indistinguishable from the cosmic background temperature and is physically impossible to detect through emissions alone. The helium is then compressed through a heat pump to a 22K temperature so that it can boil off hydrogen and lose the heat it has absorbed. The heat pump increases power consumption. but like everything else, deal with more heat by throwing more hydrogen at the problem. The stealth ship is designed not to be detected at all instead of relying on it being mistaken for an asteroid after detection. Submarines today don't try to pass off as unusually large whales, they are just silent. The sides of the hydrogen steamer can also be coated with Vantablack. I'm not sure how an asteroid hitting Earth is relevant here. Cool, but nothing similar.