Gravity Assist vs Direct Burning

[HoloYolo]

What do you prefer? A slingshot or a Direct Burn? Me? Direct burns.

[tntristan12]

Care to provide more context? If we are talking about leaving the Kerbin system, there is almost no benefit to using a slingshot, as performing course corrections along the way will quickly eat up any savings. However, Duna is an excellent place to use gravity assists, because of the high mass and orbital speed of its moon, Ike. I nearly always use gravity assists coupled with aerobraking to drastically reduce the delta-v required to close an orbit around Duna.

[Deutherius]

To me, pulling off a successful gravity slingshot is one of the most satisfying things in the game. Getting from LKO to Jool in under 1200 m/s dV spent was one of my best moments so far.

(Not saying that I'm a slingshot god, or anywhere near consistently good, but when the planets align (pun intended) and you get it right, it's just the best)

[HoloYolo]

Care to provide more context? If we are talking about leaving the Kerbin system, there is almost no benefit to using a slingshot, as performing course corrections along the way will quickly eat up any savings. However, Duna is an excellent place to use gravity assists, because of the high mass and orbital speed of its moon, Ike. I nearly always use gravity assists coupled with aerobraking to drastically reduce the delta-v required to close an orbit around Duna.

I'm saying this for anywhere, hence why I didn't state a specific place.

[Francois424]

I always plan my launches to use the moon for that extra dV saving.

However the Kerbol system is so small that I seldom go beyond a moon assist.

If the system was 4x the size (new outer planets of relevant distance like our Solar System !) I might plan a Jool gravity assist to save even more dV.

[Brotoro]

Gravity assist is great for payloads arriving in the Jool system. It can also help in leaving the Jool system...but I tend to be too lazy to wait for the right configurations for that, and just use direct burns.

I tried to see if I could use Ike to get a gravitational capture at Duna, but I was unsuccessful at that.

[Brainlord Mesomorph]

I had assumed slingshots were better.

But after things were explained to me in the forms, I lernt that direct transfer is better, esp w/ the stock kiddie-sized solar system, IRL the numbers are different.

EDIT:

When I first started, for interplanetary flights I would first do a spoon out around the Mun, either prograde or retrograde, and then float in interplanetary space until it had a transfer window to the target. – but it was explained to me that I was giving up all of the "gravity assistance", more accurately Oberth benefit of the planet Kerbin. It is one of the biggest things of the solar system. – you can maximize that benefit using perigee kicking (see the tutorial in my sig)

In our real solar system the Moon is much larger and further away, which changes that.

Edited March 23, 2015 by Brainlord Mesomorph

[Guest]

Never bothered. The stock solar system is so small, the craft are so easy to pile up delta-V on, there's no fuel boil-off to worry about, and the planets have so little mass (even with their unrealistic densities) that you can't get a good slingshot going anyway. Bouncing off Jool could work, but in stock you can just Hohmann everywhere.

Now, in RSS, yeah, I would definitely consider using gravity assists off the inner planets to meet the outer ones because they would work much, much better.

[Xavven]

It depends on the situation. If you're talking about visiting Moho, Eve, Dres, or Eeloo, I tend to burn directly from LKO.

But I use Ike to help my orbital insertion into Duna, and I use Tylo to help my orbital insertion into the Jool system. For about 50-100 dV, you can get an Ike or Tylo intercept tangent to your hyperbolic escape trajectory in the counter-clockwise direction, and then you're effectively using the gravity from both the host planet and its moon to speed your orbit relative to the sun (Kerbol).

And gravity assists are great for getting around the Jool system because the inner moons have a lot of mass and a short orbital period. You don't have to wait long to get a free boost!

Since gravity assists vs. direct burns is a tradeoff between delta-v and time, everywhere else it's usually not worth the time you have to wait to get the intercept. I can easily build in an extra 1000 dV and just not have to bother with gravity assists, especially when doing manned missions where I try to keep them out of cancer-causing solar wind as much as possible (for roleplay reasons).

[Musil]

To me, pulling off a successful gravity slingshot is one of the most satisfying things in the game. Getting from LKO to Jool in under 1200 m/s dV spent was one of my best moments so far.

(Not saying that I'm a slingshot god, or anywhere near consistently good, but when the planets align (pun intended) and you get it right, it's just the best)

That.

[StrandedonEarth]

Yesterday was pretty sweet. I was able to use Tylo on my way up the well from Laythe to Bop. Used just enough dV to reach Tylo, burned maybe 7m/s at Tylo Pe, then only needed a 5m/s correction at the Dn to be on a Bop intercept. I don't remember how much I saved though, I think a few hundred m/s

[Superfluous J]

I do it every time I go to Jool, and sometimes while bouncing around it. I also use Ike if it happens to be available.

The only time I really plan for it is when coming into jool though. I hit Laythe just right to get into a nice orbit right in with the inner 4 moons without mucking about with all that aerobraking. I find it EASIER than the alternative.

[theJesuit]

Two things. First: I think I'd prefer to use slingshots for awesomeness, but don't because I am unsure whether I'd get it right.

Secondly a question: Is there a calculator anywhere that to work out interplanetary slingshots?

Peace.

[Gerandar]

I dont see the point in wasting time slingshotting around when its needlessly easy to get the delta v to go anywhere into LKO.

[Deutherius]

Secondly a question: Is there a calculator anywhere that to work out interplanetary slingshots?

Yep.

[Cdr_Zeta]

Hello,

Grav assists, slingshots, all that good and kool schtuff that 'real' spaceships use; plus it looks kool...

Just playing with d/v and TWR is too lazy when the numbers are right in front of you...there is more to KSP than just going up, so why not use it !

Cmdr Zeta

[Taki117]

I use direct burns simply because of the time requirements. Real life spacecraft can take years to reach their destination whereas in KSP a direct burn is much faster, and we don't have the weight requirements.

[klgraham1013]

I've done both, but for the most part, just direct burn.

[keeper]

Havn't a clue on how the "slingshot" thing works, never mind working out planet alignments aswell. Not a clue.

Direct burns will do just fine. All the way.

[federicoaa]

I use Tylo to get into Jool orbit from time to time, if I can get a good alignment.

Also once I used a Mun assist to capture an asteroid. I made a perfect U shape around Mun, it was beautiful.

Gravity assists are those things in KSP that give you a great feel of accomplishment.

[lajoswinkler]

If you want A or B or C, then you shouldn've have used inclusive poll options. It will skew your results.

I use optimal approach. If Mun can be used in an optimal manner, I use Mun. Same goes for other bodies.

[magnemoe]

Gravity assist is great for payloads arriving in the Jool system. It can also help in leaving the Jool system...but I tend to be too lazy to wait for the right configurations for that, and just use direct burns.

I tried to see if I could use Ike to get a gravitational capture at Duna, but I was unsuccessful at that.

Yes, I arived at Jool with 900 m/s dV, This was enough to land me on Pol, Jool aerocapture, Laythe gravity turn, followed by an Laythe aerocapture who did not but me in Laythe orbit but raised my Pe followed by an Tylo gravity assist to raise Pe outside Val and Ap at Pol orbit, just minor corrections outside of this, landed with over 100 m/s left.

[Hannu]

I like to calculate and plan orbits and have tried slingshots. But unfortunately there is no much use for slingshots in the game. It is easy and cheap to get enough dv to go to anywhere, even with massive manned ships. I use TAC life support and roleplay so that manned missions can not wait tens of years. When I have larger activity around Jool or modded outer planets, I want to get supplies there in reasonable time.

[Red Iron Crown]

I had assumed slingshots were better.

But after things were explained to me in the forms, I lernt that direct transfer is better, esp w/ the stock kiddie-sized solar system, IRL the numbers are different.

Size is not really a big factor. A well-done gravity assist will be more efficient than a direct transfer even in the tiny Kerbin system.

EDIT:

When I first started, for interplanetary flights I would first do a spoon out around the Mun, either prograde or retrograde, and then float in interplanetary space until it had a transfer window to the target. – but it was explained to me that I was giving up all of the "gravity assistance", more accurately Oberth benefit of the planet Kerbin.

Gravity assists and the Oberth effect are two entirely different things, though they are often combined. A maximally-efficient transfer would complete the burn from a low Kerbin periapsis (maximizing the Oberth effect) and grab a gravity assist from the Mun on the way out. The timing is a bit tricky, though, so I usually just do a direct transfer burn.

[AmpsterMan]

Closest thing I've done to a gravity assist is a free return trajectory of some Mun and Minmus probes. Otherwise, i haven't learned the math required properly align a gravity assist and therefore have never bothered.