Why to orbit?

[Ghostexx7]

This is just curiosity (that is why not in the help forums)

why people before going to any other moon or planet they orbit kerbin? can't they just go directly?

i did that with Mun and Minmus (not orbiting )

is there some sort of benefit?

because you are technically wasting fuel.

[Moar Boosters]

This is just curiosity (that is why not in the help forums)

why people before going to any other moon or planet they orbit kerbin? can't they just go directly?

i did that with Mun and Minmus (not orbiting )

is there some sort of benefit?

because you are technically wasting fuel.

You're not wasting fuel by achieving orbit first. Once you're in orbit you're no longer fighting gravity.

You can test it yourself very easily. Build the biggest rocket you can...... point it directly at the mun, and see how far your rocket gets before it runs out of fuel and loses the battle with gravity.

[TeddyDD]

From stable orbits you can schedule more precise maneuver. Besides, nothing.

[Ghostexx7]

You're not wasting fuel by achieving orbit first. Once you're in orbit you're no longer fighting gravity.

You can test it yourself very easily. Build the biggest rocket you can...... point it directly at the mun, and see how far your rocket gets before it runs out of fuel and loses the battle with gravity.

the maneuver to get to orbit wastes fuel, included with the maneuver to reach Planet1 from Orbit that also wastes fuel, how can you be sure that it benefits yourself?

[G'th]

Direct ascent takes good timing (or, absurdly precise timing if you want any kind of specific orbit once you get there) and doesn't leave a lot of margin for error. Free returns also become harder with direct ascent.

[Franklin]

Easier to setup rendezvous, more room for error, more accurate rendezvous from orbit, able to use 'kicks' to save fuel with further bodies, etc.

[Franklin]

And while the moon's a larger target to hit, try this B-line approach for a rendezvous with your space station, or anything outside of Kerbin's orbit, like Duna.

[Superfluous J]

The single most fuel-efficient straight-up burn to Mun will waste more fuel than a fairly sloppy get-into-kerbin-orbit-first maneuver.

You're not wasting fuel getting in to orbit first, you're SAVING it.

Next up: Why do we thrust forward to slow down?

[magnemoe]

From stable orbits you can schedule more precise maneuver. Besides, nothing.

This, add that if something goes wrong you can launch an follow up mission to refuel or even add modules.

You get time to do an second launch if the first fail, you can also launch kerbals later if the launcher design is untested.

The 2-300 m/s you save can easy be lost if anything goes wrong.

Tips: real world missions is done this way for a reason, they don't have the option to launch followup resupply mission either.

They also don't have the option to return the core stage with the expensive engines and huge tanks to space center after reaching orbit who is smart in 0.24.

Edited August 14, 2014 by magnemoe

[Greenfire32]

This is just curiosity (that is why not in the help forums)

why people before going to any other moon or planet they orbit kerbin? can't they just go directly?

i did that with Mun and Minmus (not orbiting )

is there some sort of benefit?

because you are technically wasting fuel.

Because once you're in orbit, you're no longer fighting against gravity. Once you've put yourself in a stable orbit, doing more burns requires much less fuel as opposed to just going straight there. An example would be: changing 5m/s while on Burn-To-Target costs you 5 units of fuel. Changing 5m/s while in stable orbit costs you 2 units of fuel.*

And then there's the issue of launch windows and rendezvous. If you don't leave at the right time or if there's more crafts coming with/docking to you, then you need time to set all that up. Plus, if the mission is more complex (like say you're launching a "mothership" that will do flybys and leave smaller satellites in orbit around various planets), you'll need more time to calculate maneuver nodes and such.

*Numbers arbitrary in the case of this example. While the exact numbers aren't correct, the concept is.

i did that with Mun and Minmus (not orbiting )

As long as you waited for the correct launch windows, it is possible to achieve the same fuel efficiency as going to orbit first. But by and large, its easier to launch when it's convenient to the player, not the planets, and that's another reason why we go to orbit first.

the maneuver to get to orbit wastes fuel, included with the maneuver to reach Planet1 from Orbit that also wastes fuel, how can you be sure that it benefits yourself?

Because of the Oberth effect. Putting yourself in a stable orbit means you have an Apoaps and Periaps. Burning at Periaps (point closest to planet) means it will take less energy to raise your Apoaps (because you're already at your fastest at Periaps) and by extension, less fuel.

The 20 extra units of fuel it takes to get into stable orbit will actually save you the 100's of units of fuel you're wasting by burning-to-target. The idea is to get to the mun (or any target) with as much intertial assistance as possible. If you burn-to-target, you get zero help by means of gravity and are acting 100% on the internal power of your craft and aren't using your fuel reserves as efficiently as you could be.

TL;DR

Players like time to plan out missions and it's actually more fuel efficient in the long run to get to orbit first.

[merendel]

the maneuver to get to orbit wastes fuel, included with the maneuver to reach Planet1 from Orbit that also wastes fuel, how can you be sure that it benefits yourself?

How can you be sure it does not? Many of us have tested this ourselves, not just takeing the word of others. Judgeing by your comments so far you have not.

The quick and dirty explanation of it is when you burn strait up your fighting gravity, when you burn sideways you are not. Every second of vertical flight the force of gravity is countering your acceleration as if you had a rocket on the nose of your ship pushing you backwards by 1g. Aiming for orbit you minimize the time fighting gravity and every bit of acceleration you apply to your ship is being stored up as kenetic energy instead of being robed by gravity.

[lucusloc]

For the edification of the op: Oberth effect. It is better to go to orbit first.

As long as you waited for the correct launch windows, it is possible to achieve the same fuel efficiency as going to orbit first. But by and large, its easier to launch when it's convenient to the player, not the planets, and that's another reason why we go to orbit first.

This assumes you are following an ascent profile that does the majority of the burn horizontally, which would have left you in orbit if you cut short anyway. If you do not follow the proper profile, and you burn for altitude instead of speed you will be less efficient. Basically, you burn for orbit, but time you launch so that you can go launch->orbit->transfer burn all in one go, so you could argue you skipped the orbit stage.

Edited August 14, 2014 by lucusloc

[Javster]

Not to mention, if you run out of fuel, a rescue mission is actually possible, instead of watching your spacecraft plummet to the ground.

[Ruthgar]

Tips: real world missions is done this way for a reason, they don't have the option to launch followup resupply mission either.

They also don't have the option to return the core stage with the expensive engines and huge tanks to space center after reaching orbit who is smart in 0.24.

This is somewhat incorrect as obviously the ISS gets resupplied all the time(food, life-support, thruster fuel, etc...), and when the shuttle was around part of the maintenance they did on the satellites they worked on in orbit (Hubble for example) was to resupply the onboard fuel (usually either tank swap, or transfering a pre-calculated amount). However the main reason why resupply missions aren't done to most satellites (aside from the shuttle being retired) is that currently it's cheaper/easier to just launch a new satellite when the old one de-orbits/goes offline.

[Renegrade]

Because once you're in orbit, you're no longer fighting against gravity. Once you've put yourself in a stable orbit, doing more burns requires much less fuel as opposed to just going straight there. An example would be: changing 5m/s while on Burn-To-Target costs you 5 units of fuel. Changing 5m/s while in stable orbit costs you 2 units of fuel.*

Actually no. 5m/sec change always requires 2 units of fuel, regardless of where it is (assuming it's the exact same rocket with the same starting level of fuel, otherwise Tsiolkovsky gets involved with fuel consumption).

The point is actually that it takes more or less than 5m/sec acceleration to get to a particular orbit depending on how you handle or mishandle gravity.

KSP's delta-v countdown is actually a bit of a lie due to it's self-adjustment.

[Ghostexx7]

Whoa, never heard of Oberth effect

and no, i never tried to orbit to go to something (like a moon), that is why the discussion.

edit pd: so sad i delta-v is too advanced for me, making "get a delta-v of xxx to reach stable orbit around Duna or blah blah blah" chinese.

Edited August 14, 2014 by Ghostexx7

[Superfluous J]

Whoa, never heard of Oberth effect

and no, i never tried to orbit to go to something (like a moon), that is why the discussion.

edit pd: so sad i delta-v is too advanced for me, making "get a delta-v of xxx to reach stable orbit around Duna or blah blah blah" chinese.

Until you're ready to think in terms of dV think in terms of fuel used for your ship. It's not exactly 1:1 or anything but it's visible.

Launch any ship from KSC to orbit around Mun or land on it, and do the launch straight up. Put that craft file up somewhere where I can download it and tell me how much fuel you had left once done. Screenshots of the trip would be nice. I guarantee you: I will be able to do the same thing (either orbit or land on Mun) cheaper (with more fuel left) by orbiting Kerbin first.

[merendel]

And thats even with 5th's tendency to get talking while recording a launch and forgeting to stage off side boosters or start the gravity turn on time

[SRV Ron]

Try this test with three rockets of the exact same size.

1. Do a straight up burn at dusk until you reach Duna orbit. Note the fuel left.

2. Burn to orbit, then do an escape burn prograde to Kerban to a Duna orbit intercept.

3. Burn to orbit, then burn to Kerban escape, then burn to a Duna orbit intercept.

The results;

1. Extremely inefficient.

2. Most efficient of all since little extra fuel is needed once escape has been reached using the Oberth effect to intercept the Duna orbit. However, you need to know that the intercept window is available at launch in order to get a Duna intercept.

3. Not as efficient due to more fuel is needed to intercept once you have escaped Kerbal to a solar orbit. However, it is the most common method used in the sim for interplanetary missions.

[cantab]

This comes up from time to time. Indeed burning straight up is inefficient.

Burning with a normal pitchover directly to your Mun transfer orbit, on the other hand, can be slightly more efficient than establishing a parking orbit first, because you can then use a transfer orbit with a lower periapsis. However stopping in a parking orbit is just plain easier.

IRL, the parking orbit is time to check the spacecraft systems, and you can do that in KSP too - give your ship a look over to make sure you haven't forgotten any parts.

[Master Tao]

IRL, the parking orbit is time to check the spacecraft systems, and you can do that in KSP too - give your ship a look over to make sure you haven't forgotten any parts.

I've also used it in casese where things have already gone wrong. During one launch, one of four boosters exploded shortly after liftoff, but the rocket still reached orbit. Once there, I realized I still had enough dv to complete the mission, so I didn't have to relaunch.

[The Jedi Master]

Is it even possible to do the straight point-at-Mun-and-burn strategy? I've never seen it done, and I've tried.

[r4pt0r]

Is it even possible to do the straight point-at-Mun-and-burn strategy? I've never seen it done, and I've tried.

thats how i always did it in the beginning. set mun as target and launch when mun is half way to the center of the navball.

edit: so its not exactly "straight at mun" as 5th horseman points out.

[Superfluous J]

Is it even possible to do the straight point-at-Mun-and-burn strategy? I've never seen it done, and I've tried.

Well you don't point *at* Mun per se, but in front of it a bit. It's the same idea as the "burn at munrise" trick that was used before maneuver nodes existed, and you still notice on every burn that Mun is rising right as you're doing the burn. Like that, there's a specific place where Mun is in the sky when you burn, that you'll encounter Mun when you and it both get to the same location.

I don't know offhand were in the sky Mun should be to make that work, but that's only because the "burn straight up" technique is so inefficient that I'd never bother to learn how to do it.

[G'th]

I've burned for the Mun when it was overhead before. You can in fact, get an encounter doing it this way, but the thing is is that it won't be the typical fly-by type trajectory. It'll most likely be a literal straight line through the Mun's SOI and on to solar orbit.