Silverchain

Takeoff... ...and circularising, who needs proper rockets? Random Skurj aerobraking into Eve orbit. I've got a ship at Moho which is waiting for a proper heavy lander after the spaceplane it was using there crashed trying to take off from a mountainside; once that's done I'm going to try for my first Grand Tour. Well, not so Grand Tour as I don't intend to visit Eve or Tylo with crewed landers, but I'll transfer the pilot from this rover to the lander en route to Gilly, and drop this rover to Eve surface uncrewed.

If you can get your speed high enough that your apoapsis is well outside the atmosphere then you'll need very little rocket fuel to circularise the orbit (and deorbit); some of my smaller planes use only a few of the tiny grey tanks and a couple of 48-7S engines.

Rule of thumb - if your craft has about three times as much fuel as it does payload then its delta-v is about 10 times the specific impulse of its engine.

"Join the Space Program, they said. See other worlds, they said..."

"My Mod, it's full of Kars!"

The spaceship in the foreground lifted with three modular fuel pods but has shed two and docked with another; in the background, a spaceplane has taken one of the other tanks on board and the third spins off into the distance. Being dim, I sent this one to Moho refueld in orbit but without the benefit of an attached fuel pod. It didn't make the deceleration, and is stuck in a fairly tight solar orbit that's going to be a bugger to rescue from. It's not so much that I have a one track approach as that I really like this model. I try others, but keep coming back... two or three dozen active. ^^

If it gets To Orbit in a Single Stage, it's an SSTO. Staying in one piece when it's up there isn't mandated.

That's a shame, 'cause it's mentioned in the description text for an Ike surface EVA.

I'm developing a real fondness for the swept wings.

I blatantly copied your design to give it a whirl and a tweak. I like those side mount pylons that hold the engine pods, though I had to add struts to keep them from wobbling. Replacing the Aerospike with an LV-909 gives a good performance increase, and I set the jet fuel tanks to only partly full (90 each, which was quite enough) using tweakables which also helps.

Can you get to orbit? When you're in orbit, wait until the moon appears just over the horizon in front of you, then burn directly prograde (forwards!). Watch on the map and provided you have enough fuel you should see your orbit extend until it intersects with that of the Mun and changes colour. Time accelerate until you get to the point where you enter the Mun's sphere of influence (the orbit path will change to blue, and be shown relative to the Mun instead of relative to Kerbin). When you get to the Mun, you will be on a flyby trajectory. Wait until you get to the periapsis point (it's marked on the orbital track) and burn retrograde (backwards!) until you see the orbital path change from a flyby to an orbit. Keep burning retrograde until the orbit is roughly circular. Landing is trickier - ideally you should start from a low orbit (say 20km x 20km) and burn retrograde until your horizontal velocity drops to zero; you're now falling towards the surface of the moon. Your velocity vector will start to point more or less straight down. You can bring your ship to a dead halt (hovering above the moon) but you should let it fall downwards at a steady rate. I'd say use your engine to keep your downwards speed about 50ms-1. When you see the landscape getting close (you may see your ship's shadow) slow the rate of descent down to about 20ms-1; when you're very close, bring the speed below 12ms-1 and as you get to the landing bring the speed down to about 1 or 2ms-1 only. It's easier done than said. A Poodle engine, or an LV-909 if you've got them, makes for a good simple Mun lander engine. You don't need huge amounts of fuel on top. Don't bother about ladders as your Kerbal pilot can use the suit's EVA fuel to fly back up to the pod. When you take off, fly up a little way then turn the nose over to point more or less at the horizon at 90 degrees (due East) as soon as you're going to clear any mountains that are in the way. Coming back from the Mun, wait until your rocket is on the "Kerbin" side of the Mun and accelerate prograde. It shouldn't take much before you will see your orbit leave Mun orbit and get back to orbiting Kerbin. Burn retrograde at apoapsis and you will see your periapsis drop to intercept Kerbin. Bring the peri down to about 20 - 30 km and when you get there your ship will reenter the atmosphere in a safe way and be slowed until it starts to fall to the ground; use parachutes when you need to.

I've done some testing to determine the tradeoff between loss from added mass and gain from using the Oberth effect from Kerbin orbit. Test craft Regenbogen Oberth in 150km x 150km LKO. It is fitted with five LV-Ns, four of which are discarded here to carry out a burn using only a single engine. (Strictly speaking, each LV-N has a docking port attached, so they're slightly heavier than normal; I could've discarded them but it's nice to have a stock in orbit!) By save-scumming I started it from more or less the same point each run (the orbit is near circular anyhoo), and flew the best path I could to raise the orbit to a close approximation to 40Mm x 40Mm, slightly inside the orbit of Minmus. I was flying manually, but it wasn't particularly complicated. It would be interesting to repeat with an autopilot. I made two runs for each config and chose the better. This is what happened flying with 1, 3, and 5 engines: 1 engine: used 1185 dV from a total budget of 7085 dV. 3 engines: used 1121 dV from a total budget of 6236 dV. (+64, -849 vs base) 5 engines: used 1109 dV from a total budget of 5576 dV. (+76, -1509 vs base) In short, while there is a saving to be made from the Oberth effect, it's eclipsed - for a ship of this type and for this run - by the loss of total dV budget entailed by the extra mass. You need less dV to get to the same place, but you have much less to begin with. I expect, though I won't try right away, that starting from a lower orbit (say 75km x 75km) would increase the gain from the Oberth effect more for the multi-engine rigs, and generally reduce the dV requirement to reach 40Mm x 40Mm for all configurations. I expect that starting with a more massive ship (say if I stick another Big Orange on the front) would do the same thing. I expect that starting from Eve or Jool orbit would do the same thing, and anywhere else would reduce the gain. Thoughts?

It would be interesting to do a practical investigation of the different delta v requirements to move a big ship from LKO to some high orbit using different numbers of nuke engines. Stick a couple of big oranges in 100x100 with a single central nuke and mounting arms for extra pairs of nukes. Fly (or in this case for consistency maybe let an autopilot do its best) up to ~Minmus orbit, check what dV is required. Restart and dock a couple more nukes, repeat the test. And so further. (Or do it the other way round, start with lots of nukes and jettison them before retrying) (if you're reading this and thinking "no need to do that, just get the different dV numbers from Kerbal Engineer / MechJeb / whatever" then I suspect you'll be surprised by the result ^^)

When changing orbit it's usually more efficient to do a single instantaneous burn than it is to do a series of small burns. Also orbital insertion from high speed. Basically, the loss of efficiency from having too little thrust can be worse than the loss of efficiency from adding more engines. And you may need multiple nukes to land a massive craft, should you wish to do so. Which I do. Or launch one. If you wanted to launch a five ton payload from Tylo's surface, for instance, then a craft with two nukes and the equivalent of 10 small fuel tanks is a good option.

Looks very nice.

They are very much harder to mount.

For a recent 5 ton SSTO I used 1 ram and 8 radial intakes. With that amount of intakes I could get the apoapsis above 200km, at which point the orbital insertion burn uses only a trivial amount of fuel. That's slightly less than numerobis' suggested ratio as two radials are less effective than one ram, but pretty close...

Duna. Though in absolute terms I've lost far more Kerbals on Kerbin and the Mun, it's the unreliability of parachute landings there that always gets me.

The single most important thing if you want to understand rockets is to learn what the rocket equation means in practice. In a nutshell: the more fuel you have, the bigger a change to the speed of your rocket you can make BUT it is subject to severe diminishing returns And: Each type of engine has an efficiency rating, its specific impulse. the bigger the specific impulse of an engine, the bigger a change to the speed of your rocket you can make ----------------------------- So - you have a rocket, and it can make a change of speed (delta v) of 2000ms-1, say. You put some more fuel on it. Now it can make a change of speed of 3000ms-1. You put a lot more fuel on it. Now it can make a change of speed of... 3500ms-1. You put vast quantities of fuel on it. Now it can make a change of speed of... 3700ms-1. Severe diminishing returns. And it handles like a pig because there's so much fuel. ----------------------------- You have a rocket. It has an engine with a specific impulse of 300. It can do 2000ms-1. You change the engine on the rocket for one with a specific impulse of 800. Now it can do 5330ms-1. You add another engine of the same type (specific impulse 800) to the rocket. It still does 5330ms-1. Actually a little less, because it's carrying another engine. You add ten more engines of the same type. It still does 5330ms-1... actually a lot less, because ten nuclear engines are very heavy. ----------------------------- When you're designing rockets to get off a planet, there's two other things to consider. You need to beat gravity (so you need enough thrust to be accelerating upwards) and you need to beat air resistance. The first is easy, if your rocket moves upwards faster than an arthritic snail then you're doing ok. The second is also easy; you can more or less ignore air resistance for now so long as your rocket is not glowing red hot with flames all around. If it does that you're going too fast. A third thing: you need to turn the rocket, when you're high enough, so that you're going sideways around the planet - so that you're in orbit - and not just boosting straight upwards. Usually people fly up to around 10km and then start slowly turning the rocket sideways, until by the time it leaves the atmosphere it is pointing towards the horizon.

Project Limpid Ginger in 160x160 Kerbin orbit. Nice looking, I think. It handles well in atmosphere and naturally leaps into the air from the runway. Doesn't have such niceties as a docking port, a parachute, electricity or !!Science!! bits yet, but it's carrying way more jet fuel than it needs so can be lightened to compensate. And there's totally room for another couple of radials on the nose. ...and the finished article, the Dearworthy A Wreckage Looks The Same in 205x205 Kerbin orbit. It gets up to about 2250ms-1 on turbojets and needs only a small orbital insertion burn; at this point it's got about 350ms-1 reserve, but it's carrying surplus fuel which can either be kept for a spin around Kerbin, dumped for better performance or exchanged for a small payload. Landing is fine on runways and flat surfaces though it does have a tendency to bounce into the air after the wheels first touch down. Landing on bumpy ground is... less advisable but doable. The parachute can usually be deployed at speed and with all engines on, which trashes the plane but keeps the pilot alive. It's really nippy for flying round at low level and at one point I was dragging it round the sky over KSC in a full out, sustained turn and it didn't spin out, which is a first for my planes... Dearworthy A.craft

Starting from a 100x100km orbit I try and get PE down to about 35-40km just beyond KSC; but it varies greatly depending on the orbit you're coming from, the steepness of the descent angle, the attitude and design of your plane and so on. I often end up frantically looking about for the nearest flat spot of land!

Skurj 23-V Channel Nine approaching Duna. You can't help but like Ike! After adding extra intakes to this model and flying a better ascent, it was up to 55km before the jets cut out.

You are always under the effect of the gravity of one body, that's the only major simplification in KSP. In vacuum, with engines off, your ship would keep going in a straight line. Gravity pulls it down towards the planet (or moon, or sun). When the pull of gravity downwards is enough to keep bending the path of your ship around the planet, you're in orbit. Gravity at a given radius is given by F = GMm / r^2. G is the gravitational constant. M is the mass of the large body. m can be set equal to 1kg and conveniently removed. r is the radius from the centre of the large body. For Kerbin its equatorial radius is r = 600000. Its mass is 5.29 * 10^22 kg. G is equal to 6.67 * 10^-11 thingummys. Which gives Kerbin surface gravity = 6.67 * 10^-11 * 5.29 * 10^22 / (6 * 10^5)^2 = 6.67 * 5.29 * 10^11 / (36 * 10^10) = 35.28 * 10 / 36 ~ 9.8 ms-2 Which is what you'd expect. For a spacecraft in a 100km altitude orbit, the new radius is 600km (Kerbin's radius) + 100km (the height) = 700km. Plug the numbers into the equation and we get: ~ 7.2 ms-2 At 200km, the radius is 800km... ~5.5 ms-2 At 1000km, the radius is 1600km... ~2.7 ms-2 And so on, until we reach a point a long way out where the game decides that the Sun's influence is more important than Kerbin's, and calculations are made relative to the Sun instead of relative to Kerbin. Basically, if you use your engines to come to a dead stop in space at some point near Kerbin, this is how strong gravity will be at a given height.

Unimaginatively, it's just "Kay Career." Career being quite the operative word. I did have a sandbox mode save for mucking about with, but got rid of it once I'd unlocked the tech tree.

I like Cal and his dog Napalm.