christok

Check the note right at the top of the post. I accidentally said 2000km instead of 2000m because I was tired and when I noticed I put a note there rather than edit the whole thing because, again, I was tired. The value then becomes 1.96J/kg - 1.05J/kg, hence the 0.9J/kg specific energy.

Edit: Oops, I wrote megametres instead of kilometres. That makes the numbers significantly different but the conclusion is the same: Your astronaut escapes the surface with about 0.9J/kg specific energy over and above that required for escape velocity. (Continuing the discussion here rather than in PM because it's relevant to everyone interested.) I may well be wrong about the 20cm/20in confusion. If a NASA scientist said the centre of mass jumps up by 20cm on average and only the feet go up by much, you should use their value rather than some guy on the internet's. We already know potential energy at the top of the jump in each case is equal to the kinetic energy at the bottom. However, there are two important caveats: 1) This is energy relative to the surface and not energy relative to the centre of the planet(esimal), which is what we'll be using for the orbit calculations. 2) g * m * h is an approximation which is only valid if the height is very small relative to the distance to the centre of the planet(esimal). We can use g * m * h for the jump on Earth because 0.2m << 6Mm. Instead of regular kinetic and potential energy, we can use specific energy which is the energy divided by the mass and completely ignore the mass of the astronaut. epsilon = specific energy = 0.5 * V^2 - mu / r, where mu = G * M. So at the starting point, epsilon = KE - mu / 2km on the comet where KE = g_earth * h_earth is the specific kinetic energy at the start of the jump and equals potential energy relative to the surface for the Earth jump. Thus epsilon = 1.96 J/kg - mu_comet / 2km = 1.96J/kg - 3.14 * 10E12 kg * 6.673×10^-11 m^3 s^-2 kg^-1 / 2km = 1.96J/kg - 1.05J/kg unless I made a mistake somewhere. Now we have a little shortcut. I did say energy makes it easy! You don't need to calculate the height you jump to. If (specific) orbital energy = 0, you have a parabolic trajectory. If it's < 0, you have an elliptical or circular orbit. If it's positive, the trajectory is hyperbolic and therefore we know that the astronaut escapes.

More problems with your analysis: - An average man jumps way higher than 0.2m, which is only 20cm. You may have misread 20in. Try this table for better values: https://en.wikipedia.org/wiki/Vertical_jump#Vertical_jump_norms - You need to account for solar tides, especially in borderline cases, so you will have a minimum and maximum value depending on where the body is located and where the person is standing. Nitpicking: - You should add a reasonable minimum mass for the spacesuit since it's significant relative to the mass of a man. (Including movement restrictions due to the suit would be difficult, so I recommend neglecting that on the basis that you may be using a more advanced form-fitting suit.) - Energy makes mechanics easy. Use energy instead of acceleration. Your centre of mass is accelerated over the same distance on Earth as on the asteroid, which is the distance between where you start crouched and the point where your feet no longer touch the ground. Work is force times distance and the force your legs exert is the same in both cases, so work is the same. By the work-energy theorem, (sub-)orbital energy gained is the same. Increase in E_specific ~= 0.5m * g on Earth, so E_specific = 0.5 * 9.8 = 4.9 J/kg is gained on the asteroid as well. Add that to the potential energy between the surface and the centre of the asteroid to work out how high your new apoapsis is.

3: A high albedo would certainly help. Oceans have a lower albedo than dry land, and dry sand higher than wet sand. Water is also a potent greenhouse gas. You can thus make your planet a little cooler by making it a little drier. Don't make it bone dry. That introduces all sorts of problems on geological timescales, mainly due to water binding atmospheric CO2 to minerals. To further increase the albedo, you can consider either making the crust richer in white minerals or look for something cloud-forming that would add a higher anti-greenhouse effect than greenhouse effect. 5: Volcanism requires a large partially molten metal core in the absence of tidal heating. This could be a little tricky to explain depending the ice sheet, as it should have rapidly grown into an ice giant out beyond the frost line. Perhaps a collision between an icy body and a rocky one would result in something reaccreting with a substantial icy crust, or perhaps its orbit could have been disturbed during formation? Or perhaps the hydrosphere is similar in size to ours, but frozen at the surface? Thin atmosphere and dangerous weather don't sound like a good combination to me. I'd rather make the atmosphere thicker, or subsitute things like toxicity/corrosiveness for dangerous storms. A bit of danger from a (possibly rare) thunderstorm is something you could fit in somewhere. How about a normal atmosphere Snowball Earth instead? 6: Your largest planet should form in the first position after the frost line. This looks fine to me. Volcanism is only really possible at the innermost moon or two unless they're ludicrously oversized. And out far from the planet, they likely won't be. Since this planet must have formed outside the frost line, expect mostly icy moons and captured asteroids outside of the volcanic ones. Subsurface oceans are likely common but very deep down. Smaller moons will be less completely differentiated so the more even mixture of rocky and icy material near the surface is probably more interesting--and more nutritious. 10: I'm thinking about all sorts of potental problems with getting it into that orbit depending what you mean. I think you're distracting from the story by adding too many planets. I'd probably lose at least 2 and 8-10 but it's your choice.

Let's not regard the matter of what we're going to grow as anywhere near settled. There are several options and we'll need to do a little research on all of them, as well as work out the thermal design, before we can make a final decision. My current status: I'm going through K^2's maths for the simulation. Expect it to take several days since I'm also reading up on some physics I'm not familiar with.

And arcjet is lame because it wears out quickly. Anyway, I mentioned resistojet simply as an example of one electric thruster that can use a wide variety of propellants. The main reason for using an arcjet is that it produces much more thrust than most electrical thrusters, which is not equally important for all applications.

Of course I won't mind f you use it. But if you put up a link you should probably say that it hasn't really started yet. Otherwise you'd get people excited and they would not come back to the project after the initial letdown.

I'm also against full sunlight but that's not something to worry about yet. The species hasn't been decided but we have asked for more info on which mosses are the commonly used model species.

There are three types of electric propulsion: - Electrothermal is a normal rocket except the propellant is heated electrically instead of chemically. - Electrostatic, AKA ion engines, accelerate electrically charged ions by means of electrostatic fields. - Electromagnetic engines, AKA magnetoplasma engines, accelerate a plasma using the interactions between electric currents and magnetic fields. Besides the important points MoparGamer and Ralathon raised about xenon for ion engines, these general principles apply: - You generally want the propellant to have the lowest possible molecular mass because you get higher exhaust velocity. This favours hydrogen and to a lesser extent helium and is the reason why some electric and nuclear designs use those fluids. - HOWEVER electrostatic thrusters require high voltage/low current electrical systems for high propellant particle masses and low voltage/high current systems for low particle masses. This strongly favours high atomic masses to the extent that there has been work on droplet-propellant ion engines to further increase mass. Xenon wins hands down over hydrogen or helium in this case. - Low density makes for bulky and heavy tanks. - At least in thermal engines you want the propellant to have as few internal degrees of freedom as possible because these suck out some of the energy that would otherwise increase speed. This favours noble gasses such as helium and xenon. - Cost. The ideal propellant is not the one with the highest delta-v per unit mass, it's the one with the highest delta-v per dollar spent. (The latter may tend to be the same as the former for especially later stages in the mission.) This favours, for example, hydrogen over helium. - Toxicity/corrosiveness/fire hazard. You want to make it as easy as possible to produce, store and launch the spacecraft and associated propellants. This tends not to be such a big problem with electric thrusters but favours noble gasses over hydrogen. Some thrusters, such as the (electrothermal) resistojet, can in principle run on almost any fluid. Don't we all dream of ISRU...

I started that. It's mentioned earlier in the thread but I don't blame you for not finding it The idea was to get some sort of outline going. There isn't anything to see yet, as you may have noticed. I also need to rewrite some stuff where I guessed wrong about how it's going to work and upload what I've done. Sorry, but I had a major project at work and have been on call, so I haven't done as much as I should have. (I.e. nothing.)

Sorry I've gone AWOL for a little while. Will get right back on it (work permitting).

Don't tell me someone has a malfunctioning neocortex and then claim that just means "stupid". Don't tell me mild neurosis means temporary anger. I'm not going to bother with this sort of argument anymore.

[citation needed] These do probably contribute to the problem but having several mild neuroses is normal. Unless you happen to be a psychopath, you almost certainly have them.

All of our brains work like that and failing to recognise it can lead you down the same path. The brain builds a complex framework for understanding the universe through everything you experience in your life. When one little fact seems to contradict a large framework covering a broad range of phenomena, it makes more sense (in general) to try and find a way to reinterpret the fact in terms of the framework than to rebuild the framework in terms of the fact. This is exactly the same thing we do when we see a claim about superluminal neutrinos: we assume there must probably be a mistake because it would invalidate to many things we think we know. You and I have had broader and better exposure to the topics at hand and have, as a result, built ourselves relatively decent frameworks for understanding the science and engineering behind spaceflight. Your typical "nutter" isn't so much insane as chronically ill-informed over a period of many years.

Personally, I think Squad is doing a lot for public education with this game. They created what all those stupid "educational games" were supposed to be. And I do not fault the game for simplification nor for being a little too easy--it's a stepping stone to greater understanding.