Moho...A step too far

[Kasuha]

I wouldn't say they're not worth it, even Ike can help

http://i.imgur.com/jaKryR9.jpg

I can't remember exactly how much DV this save me, but it was significant enough.

The thing is, you were already moving rather slow at that point, you were clearly not much above Ike orbital speed. The effect can be very strong under such conditions. But at interplanetary transfer/intercept speeds (~2 km/s) Ike is not strong enough to give you noticeable kick.

[Vicomt]

The thing is, you were already moving rather slow at that point, you were clearly not much above Ike orbital speed. The effect can be very strong under such conditions. But at interplanetary transfer/intercept speeds (~2 km/s) Ike is not strong enough to give you noticeable kick.

Granted this was at Duna Orbital speed, but telling people not to use them except for certain bodies is a bit OTT. In some cases slingshots and other gravity assists can be the difference between getting your kerbals home safely and them never getting home at all.

[Kasuha]

If you read the discussion, you'll realize it was about using gravity slingshots to reduce dv for inteplanetary travel. And sorry but I insist that Duna is not very useful in that regard and most of moons aren't as well.

[The_Rocketeer]

If you read the discussion, you'll realize it was about using gravity slingshots to reduce dv for inteplanetary travel. And sorry but I insist that Duna is not very useful in that regard and most of moons aren't as well.

You can insist if you like, but you'll still be wrong.

As I'm sure you're aware, and as I repeatedly explain in this forum, delta-V isn't just about speed. Moon's/small planetoids like Gilly, Ike and Moho can all contribute a lot a desired change in speed AND direction, especially if you're lucky enough to catch a synergy between Duna/Eve and Ike/Gilly by using their combined gravities to amplify the force exerted on your craft. A slingshot around Ike/Mun can throw you clear of Duna's/Kerbin's gravity, that's not a change in velocity to be sniffed at.

I opened onto this discussion by mentioning an S-shape maneuver I made between Eve and Gilly. I could have further explained that I lacked the required fuel to lower my orbit far enough to pass close (within 5M meters) to Kerbol for a low-orbit EVA etc. However, by intercepting Eve and Gilly, and arranging this maneuver, I was able not only to lower my periapsis, but in the same maneuver I could modify my trajectory to bring me very close to Moho after I had passed Kerbol. With another slingshot then to again change my escape trajectory, I was able to line up on Kerbin at my apoapsis and return all 3 crew alive after a single orbit. THAT's the power of gravity-turns, regardless of the strength of the gravity field - proximity and speed translate to magnitute of turn, lower speeds yielding higher changes in direction.

[Kasuha]

You can insist if you like, but you'll still be wrong.

As I'm sure you're aware, and as I repeatedly explain in this forum, delta-V isn't just about speed. Moon's/small planetoids like Gilly, Ike and Moho can all contribute a lot a desired change in speed AND direction, especially if you're lucky enough to catch a synergy between Duna/Eve and Ike/Gilly by using their combined gravities to amplify the force exerted on your craft. A slingshot around Ike/Mun can throw you clear of Duna's/Kerbin's gravity, that's not a change in velocity to be sniffed at.

I opened onto this discussion by mentioning an S-shape maneuver I made between Eve and Gilly. I could have further explained that I lacked the required fuel to lower my orbit far enough to pass close (within 5M meters) to Kerbol for a low-orbit EVA etc. However, by intercepting Eve and Gilly, and arranging this maneuver, I was able not only to lower my periapsis, but in the same maneuver I could modify my trajectory to bring me very close to Moho after I had passed Kerbol. With another slingshot then to again change my escape trajectory, I was able to line up on Kerbin at my apoapsis and return all 3 crew alive after a single orbit. THAT's the power of gravity-turns, regardless of the strength of the gravity field - proximity and speed translate to magnitute of turn, lower speeds yielding higher changes in direction.

Okay, then. A nearly optimal arrival speed from Moho to Eve is about 1000 m/s. Now please show me a gravity slingshot around Gilly at that speed if you're that sure I am wrong.

[The_Rocketeer]

A nearly optimal arrival speed from Moho to Eve is about 1000 m/s.

I have absolutely no idea what that means.

In your last post you

insist that Duna is not very useful in that regard and most of moons aren't as well

and in this one you jump right to Gilly, the smallest body in the whole system - by a long, long way. Gilly's gravity is 0.5% of Kerbin's. Even so, that means that over the same time/distance, it will have 1/200th the effect of Kerbin, which in small terms isn't much, but in a large orbit might make the difference between an intercept and a complete miss.

I'm sorry, but you're not strengthening your point by demanding an hour of my time to retrieve a screenshot of what is basically true.

[Kasuha]

I have absolutely no idea what that means.

This whole thread is about travelling to and from Moho. You might notice, it's in the thread title. Maybe it would help if you spent some time reading what the discussion was about.

I am all open discussing questions of using gravity slingshots for travelling locally, I had a lot of fun with it in Jool system just recently. But it's not quite relevant to the topic here.

[The_Rocketeer]

I dismiss your remarks about reading the topic, obviously I hadn't bothered when I weighed in with suggestions for conserving fuel. For someone who posts such a lot you sure don't check your facts do you?

I am entirely on topic in suggesting that utilising the gravity of other bodies can assist in changing speed and/or direction to intercept another planet, of lower OR higher orbit than your current position. I never said that gravity of a tiny body will exclusively provide enough force to arrange your intercept for you, but it will conserve some fuel, and if you can arrange enough of these savings you will be able to travel significantly further with significantly less fuel.

Any planet or any moon will exert a force, and over a large distance travelled even the tiny change of Gilly's gravity could be magnified to millions of meters of difference in where you actually end up.

Please stop trying to score points.

[MajorThomas]

Can someone explain why one would want to first leave the SOI of the starting point (say, Kerbin) then perform a separate burn to get to the target (Duna, Moho, whatever)? I never thought anyone did this, but in this very thread I see that

1. Some people think it's common and/or recommended to do the two-step process. I don't yet see why.

2. Some say it's better to do just one burn. My intuition also says to do just one burn. (I also learned about the "Oberth Effect" from this thread (thanks!) which may have been the source of this intuition. That said, I took a class in orbital mechanics 20 years ago. It's probably buried in here somewhere.)

Thanks-

[The_Rocketeer]

Can someone explain why one would want to first leave the SOI of the starting point (say, Kerbin) then perform a separate burn to get to the target (Duna, Moho, whatever)? I never thought anyone did this, but in this very thread I see that

1. Some people think it's common and/or recommended to do the two-step process. I don't yet see why.

2. Some say it's better to do just one burn. My intuition also says to do just one burn. (I also learned about the "Oberth Effect" from this thread (thanks!) which may have been the source of this intuition. That said, I took a class in orbital mechanics 20 years ago. It's probably buried in here somewhere.)

Thanks-

Suggest this one's moved to a new thread.