metaphor

Try clicking on Jool's orbit instead of Jool itself. That usually works.

I don't really understand the disagreement here. A constant-altitude burn is a suicide burn, at least in the way me and EdFred defined it (burning at max thrust at the last possible moment so that speed reaches 0 right as altitude reaches 0). It's just that your thrust to weight ratio dictates how high above retrograde you have to burn. And it's a special case of a suicide burn where your trajectory is tangent to the body's surface. If your trajectory intersects the surface at an angle, it's no longer a constant-altitude burn since you start out with a vertical component of velocity, but it's still a suicide burn. Both of these are the most delta-v-efficient way to land when starting with their respective initial conditions. (If you start out in high orbit though, the most efficient way to get down is to get your trajectory tangent to the body's surface and then perform the suicide/constant-altitude burn.) It's not always done this way in practice since there's other considerations besides efficiency (can't compute the exact trajectory beforehand, safety issues, abort options, terrain obstacles, etc).

But if you're sending a telescope to 550 AU in a reasonable amount of time you have to send it fast. If you want it to get there in 20 years it has to be going about 100 km/s. Therefore if you want to stop at that distance (or orbit) you need another 100 km/s of delta-v. Orbiting is kinda useless, better to just stop it entirely, it's not going to fall a significant distance towards the Sun for hundreds of years. The fact that you can only look in a single direction seems like a huge downside. Kepler's field of view was 0.25 square degrees, while the size of the Sun from 550 AU is 8*10^-7 square degrees (and the field of view of a telescope there would be about the same). If you wanted to view something 0.1 degrees away, you would have to travel 1 AU.

Go ahead, let me know if you want any help. Is that instantiating Neptune from scratch somehow, using Planet Factory, or Kopernicus, or some other mod?

I think there's two different things being discussed here. How to most efficiently get down from a circular orbit (which is a retroburn so that Pe is at 0 followed by constant-altitude max-thrust burn at Pe), or how to most efficiently land once you're already on a trajectory intersecting the surface (which is a suicide burn, burning at max thrust and slightly above retrograde so that both your horizontal and vertical velocity reach 0 when your height reaches 0).

Starting from Jool's orbit, you can get a Kerbin intercept anytime pretty easily by just adding some radial in/out component to your burn. Radial in shortens the time until periapsis, and radial out lengthens the time until periapsis. Since Kerbin's orbit is so much smaller than Jool's, a small radial burn can change the time you encounter Kerbin's orbit (near solar periapsis) by a lot. By tweaking that time, you can always get a Kerbin encounter. (By the way, this also works in other situations like going from Kerbin to Moho.) If you're in orbit around Jool, an easy way to add a radial in/out component to your burn is to move the maneuver node forwards or backwards along your orbit. You want to exit Jool's SOI mostly going retrograde, but with some radial in/out (and maybe normal north/south) component. So assuming you're going counterclockwise around Jool, and make a maneuver node going straight towards solar retrograde, if you move that maneuver node a little forwards you're going to get a radial out component (lengthening the time until Kerbin encounter), and if you move the maneuver node a little backwards you're going to get a radial in component (shortening the time until Kerbin encounter). If you use a Tylo flyby, just make sure it's in the right position to take you out of the SOI in the right direction. It takes about a 1300 m/s burn from low Tylo orbit to encounter Kerbin, which is about 400 m/s above Tylo escape velocity, so make sure you have that amount of velocity as you pass Tylo periapsis.

Here's an Eve landing. I made different action groups for different sets of engines and only used one of them to get the right trajectory correction.

I think the payload also has to have a similar mass as the tungsten, or at least 90% of it. That means it needs to be dense, so would be a problem for blimps meant to be filled by a light gas (stored as a liquid).

Since it's allowed to use one space bar to land on the Mun, is that the case with landing on other planets as well?

That's probably what's going to happen. Another possibility would be buildings that are "buildable" on other planets/moons, kinda like the Extraplanetary Launchpads mod.

They're all there if you click on the arrows or scroll, it's just that the window appears very thin for some reason. You can see all the mods if you look at the "Reply With Quote" text. I have no idea what could be causing the problem though, my uneducated guess would be one of the parts mods.

Would a space telescope at 550 AU be useful at all? You could really only point it toward a single direction unless you wanted to burn massive amounts of fuel. And if it got there ballistically within a reasonable timeframe it wouldn't be within its operating range for more than a year or so. Anyway, it's certainly possible to send a probe toward Alpha Centauri at 50 km/s using only chemical engines (and 50 kg is tiny as far as space probes go). Without gravity assists: you could launch on an Altas V with a Star 48, which can take about 1 ton to solar escape velocity. Then you would spend several years/decades getting to a high apoapsis, and burning about 2 km/s to drop to a low solar periapsis. By that point your mass is about 0.5 tons. Then you could drop by the Sun (at the right inclination/ArP for Alpha Centauri) at about 4 solar radii (the original mission plan for Solar Probe+), and burn at periapsis for maximum Oberth effect. Assuming hypergolic propulsion and another stage, you could probably get about 6 km/s, which would result in a solar hyperbolic excess velocity of about 60 km/s. But it's much easier and shorter with gravity assists. The Atlas V can get a 5 ton payload to Earth escape velocity. You could go past Venus and use either VEE or VVE gravity assists to get to Jupiter, which would then be able to drop you to the Sun without any other burns (basically this trajectory). So with your 5 ton payload at 4 solar radii you could burn about 12 km/s (with hypergolic propulsion) and get a solar hyperbolic excess velocity of about 100 km/s. Of course, you could use a bigger launch vehicle, like the SLS, and an improved currently available mode of propulsion, like solar thermal or high thrust ion engines (since there's huge amounts of solar energy that close to the Sun). Using the gravity assist method, your ~60 ton payload could get to ~180 km/s solar escape velocity using solar thermal, or ~280 km/s using ion engines. If you have enough shielding on your spacecraft to get even closer to the Sun, like within 1 solar radius of the surface, you could get 300-400 km/s. That would get you to 550 AU in 6 years, and to Alpha Centauri in 3000 years.

What else could it have been? It was said from the beginning that it would be a minor but fun feature. It definitely looked a lot better than I expected.

You could start out with where the kerbals would put an ISS or Hubble equivalent. In other words, if the solar system looked exactly like the kerbal system, in what orbit would we put the ISS or Hubble? The ISS has the inclination it does since it has to be reachable by ships launched from the Russian space center, and it has the altitude it does so that it can stay above the atmosphere but low enough that debris nearby is deorbited relatively quickly. Since there is only one space center in KSP, and the atmosphere stops at 70 km, by following the same constraints the ISS in KSP would be in an equatorial orbit just above 70 km altitude (unless you had another space center you wanted to launch ships from). Hubble is as close to the Earth as it could be, to allow crewed repairs, but still outside of any significant atmospheric disturbances. So in KSP Hubble would also be right above 70 km in an equatorial circular orbit. For a communications satellite equivalent, the best orbit would be geostationary, so the KSP equivalent would be keostationary orbit at around 2800 km (whichever altitude has an orbital period exactly equal to the rotation of the planet).

So starting with an initial condition of your trajectory already intersecting the surface? In that case you can't really do a constant-altitude landing since you already have a large downward component to your velocity. But still, what you want to do is burn slightly* above retrograde at the last second with the highest thrust available so that you reach both 0 horizontal velocity and zero vertical velocity at 0 altitude. (*How "slightly" depending on your TWR, angle of incidence, velocity, etc.)

You can't really equate energy that way, since you have to take into account the gravitational potential energy and the kinetic energy of the fuel expended as well, instead of just the ship. Basically when you burn downwards the gravity field of the planet is cancelling out some of your ship's acceleration, and if you burn slower you lose a higher percentage of your acceleration to the planet's gravity, which means more delta-v used to achieve the same result.

I guess it depends what you mean by suicide burn then, and what the initial conditions are. I would say a constant altitude burn is what I described as a suicide burn, since you're burning at the last second at the highest available thrust. You could burn in a different direction, but that's a harder thing to compare since it's a 2D problem instead of a 1D problem.

Yes, I was assuming the ship was in a constant gravitational mass and didn't lose a significant mass, to make it simpler to get the point across. If you're landing on the Mun with an Isp of 350s, the changing gravitational field and the changing ship mass are negligible when calculating delta-v while falling from 1 km up. The ship losing mass over time doesn't actually matter at all, since that's equivalent to raising the thrust in a constant-mass ship. If you want, you can keep the ship at the same acceleration as it loses mass by continuously lowering the throttle. My point was that the most efficient landing is one where you use the highest thrust possible at the latest time possible. That is true whether or not the mass of the ship decreases (which is equivalent to increasing your maximum thrust) or the gravitational field increases (which means you lose a higher proportion of your effective acceleration at lower thrusts).

I find it kinda funny that 50-100 years ago people were ridiculed for suggesting that there were stars large enough that not even light could escape from them because it didn't make sense, and now it's the complete opposite (it doesn't make sense to not have black holes. Yes, from the point of view of an outside observer, it takes matter an infinite amount of time to fall into a black hole's event horizon. So from that point of view, black holes don't currently exist (but they would be observationally indistinguishable from "actual" black holes). Hawking radiation does take this into account, since this is a relativistic effect (time dilation). But this effect combined with quantum mechanics gives rise to things like the "firewall" theory. See this wiki page

All objects in the kerbal system have the same rotation axis (which is perpendicular to the plane of the "galaxy"), the inclination of their orbits doesn't matter. It's also kinda impossible to give an object axial tilt, even with mods, since that's hardcoded into the game.

Even though the orbital mechanics of the game are pretty much the same as real orbital mechanics, the length scales are completely different from the real world, and different from each other. The Earth is 10.5 times bigger than Kerbin in diameter. But Earth's atmosphere is only about 1.6 times thicker than Kerbin's atmosphere, so as a proportion of diameter, Kerbin's atmosphere extends 6.5 times further out than Earth's atmosphere. The Moon orbits 30 Earth diameters out from Earth, but the Mun only orbits 10 Kerbin diameters out from Kerbin. So all the proportions are off, and you can't really scale Earth orbits to Kerbin orbits and vice versa, something will always be wrong in proportion. As far as your second question goes, if you want equally spaced satellites in the same orbit you should pay attention to their orbital period and make sure it's the same. And you can use a single delivery vehicle for all the satellites. For example, if you want to put 4 satellites in an orbit with an 8-hour period, you could get your delivery vehicle into a 6-hour period, then deploy each satellite one by one at subsequent apoapses (and circularize each satellite by itself). That way each time you would arrive at apoapsis 2 hours ahead of the previous satellite, or 1/4 of an orbit, resulting in 4 satellites in an 8 hour orbit with 2-hour gaps between them.

I thought we were assuming that the initial speed is constant and straight up/down, and the spacecraft does not have any sideways velocity (so you're only moving up/down). In that case a suicide burn (burning at the last second at full thrust so that your velocity reaches zero exactly as your position reaches zero) is always the most efficient. For example, let's say you start out stationary 1 km up from a body that has a gravitational acceleration of 1 m/s^2. If you don't do anything, it would take you 44.7 seconds to hit the surface, and you would be moving at 44.7 m/s when you hit it. Let's say your spacecraft can accelerate at 4 m/s^2 at full throttle. Then while it is burning, its effective acceleration with respect to the ground is 3 m/s^2 upwards (since the acceleration due to gravity is 1 m/s^2). So starting at 250 m up, when its velocity is 38.7 m/s, it would burn full throttle for 12.9 seconds, ending up on the ground at 0 m/s speed. The total delta-v used by the engines is 12.9 s * 4 m/s^2 = 51.6 m/s. Now let's say we use the same spacecraft but instead of burning at full throttle we burn at half throttle, or 2 m/s^2. Then while it is burning, its effective acceleration with respect to the ground is 1 m/s^2 upwards. So it would have to start at 500 m up, at a velocity of 31.6 m/s, and burn at half throttle for 31.6 seconds, ending up on the ground at 0 m/s speed. The total delta-v used by the engines in this case is 31.6 s * 2 m/s^2 = 63.2 m/s. If the spacecraft has infinitely high TWR, then it can stop right when it hits the surface, with a delta-v of 44.7 m/s. If the spacecraft burns at 1/4 throttle or less, that means it has a TWR of less than 1 on this body and it will not be able to slow down. So the delta-v used has a minimum of 44.7 m/s (with infinitely high TWR), and goes up to infinity as you go down in throttle to 1 m/s^2 of acceleration. Equations used here: kinematic equations You can also think of a landing as being the same as an ascent going backwards in time. It's less efficient going lower than full throttle during an ascent from an airless body.

Good idea. That should just require changing a couple of names in the RSS config file. More planets/moons should be available to put into RSS when the Kopernicus mod comes out, then we can stop using Planet Factory for the extras. By the way, awesome job with the crewed missions to Callisto, Saturn's moons, and Mercury.

It's not a great coincidence that we discovered Sedna when it was close to its periapsis. Our current instruments can only detect objects like Sedna out to ~100 AU. Sedna spends approximately 1/80th of its orbit close enough to the Sun to have been discoverable. That means that there's probably ~80 more objects out there with orbits and sizes similar to Sedna's, but not currently close enough to the Sun in their orbits. So by the time we would send a probe to Sedna in the 2080s or so, there will probably already be a few more of these kinds of objects that are nearing their periapses (for example, 2012 VP113, which is half the size of Sedna and in a similar orbit, was recently discovered). Also by that time, our detecting capabilities will have probably progressed enormously, so we could detect such objects out to 1000 AU or more. If there's more objects like Sedna out there and they follow a normal size distribution, the largest one could be about the size of Mars. Now that would be an interesting object to send a probe to.

That's probably due to Planet Factory. PF used to have a bug with Ascension (the body that is used as Triton) where the surface would appear completely black from any angle. That bug was supposed to have been fixed a long time ago, but I guess not entirely. I'm not sure if this bug always existed or not in the RSS config... maybe you're just the first person to ever go to Triton.