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Delta-V map

Nuprin Feelgood

By Nuprin Feelgood
in KSP1 Discussion

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Kerolyov

Kerolyov

Posted
Posted
High eccentricity of your target (or departure) bodies orbit can have a similar effect. The body won't be where the chart expects or travelling at the expected speed. This tool http://alexmoon.github.io/ksp/ should give a much better estimate which takes eccentricity and inclination into account.

tomf I think you're right in my case I'd already done an inclination correction burn at the AN/DN (can't remember which!) the issue was the burn to get into Moho orbit took waaaay more (1000 or so) deltaV than the 2200 the chart on the first page suggested. Using the link you gave suggested optimal dV for trip to Moho from LKO was actually 5000 ms-1 rather than the 3800 the chart suggested. So looks like eccentricity might be the issue, so watch out for eccentric planets kids, you might find they demand more Dv than you assumed.....

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SkyRender

SkyRender

Posted
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So to get back from the Mun straight into a landing on Kerbin do you need 210, 860, or 1070 m/s of delta v?

That depends on what you're planning to do. If you plan to aerobrake, somewhere between 210 and 260m/s will be sufficient. If you plan to slow down first before you ever enter the atmosphere, you're going to need closer to that full 1070m/s. As I noted before, there are a ridiculous number of ways to go about things, so a lot of what is necessary depends on what you choose to do.

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bptrav

bptrav

Posted
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Still quite unrealistic. Why would anyone go to Jool low orbit if he want's to reach Pol?

As others mentioned there is no way a single chart can account for every possible transfer. You might find this chart more appropriate for that case:

NKZhU57.png

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RoboRay

RoboRay

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Posted (edited)
Although these maps never account for dV needed to get into orbit while coming in at crazy speeds ...

If you do your transfers by applying the listed amount of ÃŽâ€v (meaning you are at the proper phase angle for a minimum-energy transfer), you will not be "coming in at crazy speeds."

If you apply more ÃŽâ€v to accomplish the transfer, it should be apparent that the amount of ÃŽâ€v required for the capture is also going to change.

Edited by RoboRay
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KerbMav

KerbMav

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Crazy speeds defines at speeds I never had to deal with before - at least not at bodies without an atmosphere or a moon to sling into orbit of the planet.

Somehow I played a lot in Kerbins orbit the last three months, only landing on Mun once in a while, somewhat neglecting Minmus and shooting probes at Duna and Eve - only this week I tried orbiting Moho and did not have the 3-4000m/s dV to slow down, even though I launched at the time of a window.

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Kolenka

Kolenka

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Well, you said the map doesn't account for coming in at those speeds. Looking at the map, it does indicate you're going to need more than 3km/sec for the capture. :)

Moho is one of the more challenging destination to reach.

I'll second the comment about the challenge with Moho. I'm in the middle of redesigning my probe launch vehicle just so I can get more dV to make a landing. No issues getting anywhere else so far, but I haven't made a trip past Jool with it yet.

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gtrusler

gtrusler

Posted
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Instead of trying to brute-force your way out of Kerbin's gravitational pull, set up a maneuver node that will intercept the moon, and then send you on an escape trajectory, save you some 90 or so delta-v.

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weezl

weezl

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When you are coming back from a moon to its parent body, that is from the Mun to Kerbin, shouldn't it take less delta V as you are going back down into the "gravity well" instead of climbing out of it.

Really only if you aero-brake. If you burn and circularize at kerbin capture then your capture burn is about the same as your exit burn (in the mid-800s). You are still equalizing your velocity against the same amount of gravity, and at about the same distance from the orbital body.. Once exiting its orbit, once entering it. The *big* difference where Kerbin is concerned is that your de-orbit is not equivalent to your ascent burn at takeoff. You are letting the atmosphere do the same work for you coming down as you had to do on your own going UP.. so its a lot cheaper.

No matter what, I tend to over plan a bit on deltaV to make up for the monkey behind the wheel (me). So I add 10% or so to many of the numbers.. ESPECIALLY the take off numbers and the landing on planetary body number that doesn't have atmosphere. The exit burn from the Mun and the capture burn are essentially the same.. but I think the exit from Mun is a tad less because of the gravitational force exerted by Kerbin..

One thing I tend to do to reduce landing cost on the manned missions is run an unmanned probe to my landing location and scout good flat ground to land on.. this gives me landing altitude information, and location on the body.. allowing me to run narrower on the missions that have to lift more raw weight.

That said.. there is a BIG IF here.. all this depends on the pilot choosing an equivalent low energy maneuver for entry/exit to a planetary body's SOI. This isn't necessarily the most intuitive thing to do if you don't know orbital mechanics, although messing around with the maneuver nodes can be instructive in how you can plot intercepts that still work, but are more expensive.

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malkuth

malkuth

Posted
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Well, transfers haven't really changed....

The only things that need updating are ascents from kerbin, Duna, and Eve. (as far as I've heard eve is impossible now)

where you hear that from.. Yesterday they were saying spaceplanes were impossible.. I take that impossible stuff with a large grain of salt..

Eve should be easier like kerbin is.

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Endersmens

Endersmens

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where you hear that from.. Yesterday they were saying spaceplanes were impossible.. I take that impossible stuff with a large grain of salt..

Eve should be easier like kerbin is.

But I heard that the new ISP system meant that engines got a big fat zero thrust on Eve's surface. Maybe that's not true, but I haven't tested it yet.

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andruszkow

andruszkow

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But I heard that the new ISP system meant that engines got a big fat zero thrust on Eve's surface. Maybe that's not true, but I haven't tested it yet.

Airbreathing engines must be worth something now on Eve, at least? Landers might be built around Rapiers now instead.

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