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In Kerbal Space Program, I finally managed to build a rocket that would actually do something other than explode on the launch pad.

So far I've been fairly consistent in making it into orbit. Sadly, I eventually get pulled back down to earth. I suppose I should have used a parachute in preparation for that... R.I.P. Bill Kerman... Anyway, I'd really like to just let them drift off into space. Maybe find a wormhole or something and end up on a planet taken over by apes.

Can I escape Kerbin's gravity? If so, at what height?

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what-if.xkcd.com/58 will help understand why you did not go to space today. –  Shadur Dec 30 '14 at 16:48

6 Answers 6

up vote 15 down vote accepted

Technically, you can escape Kerbin's gravity at any height, as long as you're going fast enough.

To orbit the planet at any given altitude, you only need to be travelling at the corresponding horizontal speed, as shown in the table below. The only reason that you can't orbit the planet consistently at low altitudes is that it's difficult to maintain your orbital velocity in the presence of atmospheric drag.

For example, to enter an orbit at 100km above the surface, you need a horizontal speed of 2245.8 meters per second.

Kerbin's atmosphere tapers off at approximately 68-70 km above the surface. Any orbit below this altitude will require corrections due to atmospheric drag, or else your ship will begin losing orbital speed and eventually deorbit. You can also do this intentionally if you want to deorbit your spacecraft - reduce your speed enough to drop below the minimum horizontal speed given in the table, and your spaceship will begin to descend.

I've snipped portions of this table to save space. The full thing can be found on the Kerbal Space Program Wiki:

Altitude (m)    Horizontal Speed (m/s)  Orbital Period (min)
35000                2357.9                   28.20
40000                2348.7                   28.54
45000                2339.6                   28.87
50000                2330.6                   29.21
55000                2321.7                   29.54
60000                2312.8                   29.88
65000                2304.1                   30.22
70000                2295.5                   30.56
75000                2287.0                   30.91
80000                2278.6                   31.25
85000                2270.3                   31.60
90000                2262.0                   31.94
95000                2253.9                   32.29
100000               2245.8                   32.64
110000               2229.9                   33.34
120000               2214.4                   34.05
130000               2199.2                   34.76
140000               2184.3                   35.48
150000               2169.6                   36.20
160000               2155.3                   36.93
170000               2141.3                   37.66
180000               2127.5                   38.39
190000               2114.0                   39.13
200000               2100.7                   39.88
300000               1980.6                   47.59
400000               1879.0                   55.73
500000               1791.5                   64.30
600000               1715.3                   73.26
700000               1648.0                   82.61
800000               1588.0                   92.32
900000               1534.2                   102.39
1000000              1485.5                   112.79
2,868,378            1008.9                   6 hours
8,140,000             635.4                   24 hours 
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Related: what-if.xkcd.com/58 –  Shadur Dec 30 '14 at 16:47
Also note that below 60 kilometers or so, atmospheric drag will slow you down if you aren't under constant thrust, so if you want a semi-permanent stable orbit you should be looking at 65 klicks, minimum. –  Shadur Dec 30 '14 at 16:49

Once you hit roughly 100 km above Kerbin, the effect that gravity plays on your ship is minimal. Problem is, once you leave the planet's sphere of influence, the sun will continue to exert it's influence on you.

It is (remotely) possible to leave the solar system, but most of it just involves adding as much fuel as you can, and building the most momentum possible. Once you run out of fuel, just turn up the game speed, and perhaps you got enough to leave the solar system. If not, your Kerbal is doomed to orbit the sun. Forever.

For an amusing twist (since Kerbals are all about fun), if you manage to fail spectacularly enough, it's possible to have it orbit the planet, and you can leave him up there if you so choose. He then becomes a navigation hazard for subsequent launches.

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If you're 100 km above Kerbin, it's gravity is still dominating your ship--the gravitational acceleration of astronauts in Earth orbit is still about 9 m/s**2. –  Nick T Mar 8 '13 at 17:36

Just as a side note about the last post talking about orbit. It's never optimal to go full blast out off the earth once oyu have the capability of using liquid fuel over solid fuel boosters. 300m/s to 15,000m, then 45* at the same speed till 50,000m. You will practically be in a full orbit by that point and you will need to make anywhere from a 5-20 second burn depending on how well you executed the launch. But more engines and more speed is almost never better in KSP.

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You may be correct, in theory. However in practice the Orkish method has never steered me wrong. It has threatened to melt my computer on occasion, but it has always pushed my massive payloads into orbit. –  Trent Hawkins May 19 '14 at 2:48

once you have good parts and high t/w ratio (1.5-2), you should start your gravity turn at 5km, and slowly turn so that you are at 45 degrees at 10km. then, slow down your gravity turn so that you are at 30 degrees at 20km. then, keep going this way until your apoapsis is at 80km or so. with this method your orbital completion burn is minimized, and you can take advantage of the oberth effect since your primary orbital burn is close to kerbin (30km or so). i can get into orbit with ~4000 dv this way with stock aerodynamics.

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What I did, and was fine for getting into orbit, was: I went straight up until I got to 10,000 and then cut engines while lining myself to 40 degrees on the orange side (the side facing down). Then burned until the orbit map showed a good orbit. Then I cut the engines and let it drift around and around the planet.

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I found it easy to go straight up until your apoapce is around 60,000 m. Then go at a 45time degree angle until your apoapce is roughly 100,000 then shut off engines. Wait until your craft is almost at apoapce, and go at 90a degrees until you get in orbit.

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