How to plan interplanetary arrival so it doesn't take 3K dV to orbit?

[Oddible]

My Eve arrival went badly. It seemed to be lined up fine, the arc of my arrival lined up with Eve's orbit just fine. Got an encounter while en route. But when I arrived it took nearly 3K to get an orbit (which I didn't have available so collected science all the way down to a crash instead).

How can I plan my insertion better? How can I tell if things are so wrong that they'll require that much dV to slow down?

Edited October 20, 2013 by Oddible

[Psycix]

Aerobrake!

Not much more to say.

[pat8996]

It all depends on how much fuel and how many engines you have, if you have allot of engines and fuel you'll be perfectly fine. How many engines did you have on the craft anyways?

[Oddible]

Aerobrake!

Not much more to say.

No atmosphere on Eve.

[Rampage9112]

No atmosphere on Eve.

First of all, there IS an atmosphere on Eve. It's actually thicker than that of Kerbin.

In order to do interplanetary transfers with more efficiency, it's very important that you take advantage that the Oberth Effect and do your entire interplanetary burn while within kerbin's gravity. (100km circular orbit is usually where I start). In order to know when to do your burn, use the calculator at ksp.olex.biz

If you're still having trouble getting an encounter, make sure you're on the same orbital plane. Eve's orbit has some inclination, so somewhere along the trip you'll have to adjust for that.

Edited October 20, 2013 by Rampage9112

[Oddible]

First of all, there IS an atmosphere on Eve. It's actually thicker than that of Kerbin.

In order to do interplanetary transfers with more efficiency, it's very important that you take advantage that the Oberth Effect and do your entire interplanetary burn while within kerbin's gravity. (100km circular orbit is usually where I start). In order to know when to do your burn, use the calculator at ksp.olex.biz

If you're still having trouble getting an encounter, make sure you're on the same orbital plane. Eve's orbit has some inclination, so somewhere along the trip you'll have to adjust for that.

Thanks, this is exactly what I'm doing. I have zero problems getting an encounter. This thread is asking how to ensure that the encounter isn't a screaming high speed fly by. I get the encounter just fine, but I am struggling with how to know whether I'll be able to slow down into an insertion orbit when I get there.

[AndreyATGB]

There isn't really a reliable way of reducing your relative velocity. Best you can do is aerobrake, for Eve around 70km will get you a nice 300-500km apoapsis. I'll guess that if you get the encounter at the second "pass" through Eve's orbit it should be lower. Best way of doing it is to get the encounter right on the ascending/descending node because you won't need any inclination adjustments.

Edited October 20, 2013 by AndreyATGB

[numerobis]

You shouldn't need 3 km/s off a Hohmann transfer from Kerbin -- what are you actually doing?

Coming in from a Hohmann transfer orbit you can aerocapture by setting your periapsis to about 70km on Eve. Probably 75 km would even be enough; at 70 km you're getting apoapsis well below Gilly's orbit.

[Kasuha]

There is atmosphere on Eve, so you could aerobrake and stop for free. If you for some reason don't want to aerobrake, bring your periapsis as close as possible to Eve (but above atmosphere, i.e. above 97 km) - the sooner the better, small corrections in interplanetary space are very effective and cheap; should also correct your trajectory as you enter Eve SOI - and burn retrograde at that periapsis. That's the most effective way to stop.

You don't need calculators for that, it can be done completely using game tools.

Edited October 20, 2013 by Kasuha

[LtHeckard]

Try Aerobraking. You can use the atmospheric entry to slow you down. since Eve's gravitational pull is stronger than Kerbins, you may need to Aerobrake more than you would do for Kerbin. You will need far less Delta V and Aerobraking is a very efficient way of getting into orbit with Eve. Aerobraking will not work on non atmospheric moons/planets due to lack of atmosphere.

[Oddible]

Nice, so I tried aerobraking - using the wiki's guidance and this thread and 70K didn't get my circular, and 20K was splashdown. Thanks for the tips - this will work, now to find out if I can find the sweet spot and circularize with my scant remaining fuel.

[Psycix]

No atmosphere on Eve.

What is this supposed to mean? Eve has the second thickest atmosphere in the game, only superseded by our friendly neighborhood gas-giant Jool.

Nice, so I tried aerobraking - using the wiki's guidance and this thread and 70K didn't get my circular, and 20K was splashdown. Thanks for the tips - this will work, now to find out if I can find the sweet spot and circularize with my scant remaining fuel.

Here, use this calculator to precisely calculate the required height of your periapsis.

http://alterbaron.github.io/ksp_aerocalc/

The most efficient thing is to do the course correction as soon as possible. Try to already get a low periapsis when doing the interplanetary transfer, and do the final steering as soon as you enter Eve's SOI.

[Oddible]

Here, use this calculator to precisely calculate the required height of your periapsis.

http://alterbaron.github.io/ksp_aerocalc/

Awesome, thanks guys, nailed it and salvaged this Eve trip. I brought 2 probes, one with parachutes one without. Kept the one without in orbit and dropped the one with chutes onto the surface!

[TheReaper]

get an encounter where you appearr behind the target relative to its prograde

aerobrake if posible,

test nodes so you will get lowest periaps posible on encouter,

[Dunbaratu]

If its a planet where there's no atmosphere to help, is it better to aim for a pass very close to the planet, and make your retrograde please-capture-me burn close to the body? I've been doing that under the assumption that because its normal for an orbit that swoops in low to a planet to have a high speed at its periopsis, that this means the lower you are, the less speed needs to be bled off in order to get captured. But it's entirely possible that this is 100% offset by the fact that the gravity will add to your speed as you fall in close. I haven't done the math to work it out to know if it really is better or not. Is it?

[allmhuran]

If its a planet where there's no atmosphere to help, is it better to aim for a pass very close to the planet, and make your retrograde please-capture-me burn close to the body?

Yes, for a couple of reasons.

1) The closer your approach, the longer you are in the planet's SOI, and the more severely your trajectory will be curved. This means you have more time to complete your deceleration.

2) The closer your approach, the more you take advantage of the Oberth Effect. This effect, in brief and simple terms, says that "spending energy while moving fast is better than spending it when moving slow". Since burning fuel = spending energy, it's more efficient to burn when your kinetic energy is high (moving fast) and your gravitational potential energy is low (nearer to the surface).

[Dunbaratu]

Yes, for a couple of reasons.

1) The closer your approach, the longer you are in the planet's SOI, and the more severely your trajectory will be curved. This means you have more time to complete your deceleration.

2) The closer your approach, the more you take advantage of the Oberth Effect. This effect, in brief and simple terms, says that "spending energy while moving fast is better than spending it when moving slow". Since burning fuel = spending energy, it's more efficient to burn when your kinetic energy is high (moving fast) and your gravitational potential energy is low (nearer to the surface).

I assume that effect only applies to when your desired delta V is in the same direction as your velocity. When burning normal or anti-normal to change inclination angle, it seems to be a lot more efficient when you're at apoapsis going slowly.

[Spyritdragon]

Highly suboptimal totally-not-Hohmann transfer orbit of my first Eve probe . Eve can aerobrake you into anything with the right periapsis set.

[allmhuran]

I assume that effect only applies to when your desired delta V is in the same direction as your velocity.

If you can handle some very simple maths, here's the explanation.

Imagine you are in a rocket that weighs 1 kilo (just to make things easy) sitting on the launchpad. Velocity = 0 m/s. Kinetic energy = 0. (Kinetic energy = 1/2mv^2, 1/2 of your mass times the square of your velocity.)

Now you spend 10 m/s worth of delta-V (fuel) to go up. New velocity = 10 m/s. New kinetic energy = 1/2 * 1 * 100 = 50. So your kinetic energy change is 50.

Now you spend the same amount of fuel again to gain another 10 m/s. New velocity = 20 m/s. New kinetic energy = 1/2 * 1 * 400 = 200. So your kinetic energy change this time is 150, for the same amount of fuel spent!

The same holds true for decelerations. Just reverse the figures.

[Psycix]

At the same time, however, the lower your velocity, the less delta-V it takes to do a course change.

Radial and normal burns should be done when traveling slow and far away. Prograde-retrograde when traveling fast.

[Dunbaratu]

If you can handle some very simple maths, here's the explanation.

Imagine you are in a rocket that weighs 1 kilo (just to make things easy) sitting on the launchpad. Velocity = 0 m/s. Kinetic energy = 0. (Kinetic energy = 1/2mv^2, 1/2 of your mass times the square of your velocity.)

Now you spend 10 m/s worth of delta-V (fuel) to go up. New velocity = 10 m/s. New kinetic energy = 1/2 * 1 * 100 = 50. So your kinetic energy change is 50.

Now you spend the same amount of fuel again to gain another 10 m/s. New velocity = 20 m/s. New kinetic energy = 1/2 * 1 * 400 = 200. So your kinetic energy change this time is 150, for the same amount of fuel spent!

The same holds true for decelerations. Just reverse the figures.

Right. So to ask the same question again. Is it true that it only works on the component of your delta-V that is in the same direction as your velocity vector?

In other words, if you are thrusting off at 45 degrees from your current direction, Is it true that only that cos(45) of your delta-V that is in the same direction as your current velocity gets the benefit of the v^2 effect?

Or if you are aimed normal to your direction, then it doesn't help at all, because none of your delta-V is in the same direction as your current velocity?

Is that correct? I don't feel as if this question was addressed. I ask because I'm pretty sure that it takes a heck of a lot less fuel to change inclination at apoapsis than periapsis, which seems to run contrary to the Oberth effect unless you also add that caveat about the direction of the delta V in question.

[Psycix]

Yes, it only goes for prograde and retrograde burns. (You seem to have missed my previous post by 5 minutes)

However, doing a inclination burn ALSO raises your apoapsis, and the oberth effect DOES apply for this. It's just not what you usually want to do when doing a normal/antinormal burn.

[Dunbaratu]

Yes, it only goes for prograde and retrograde burns. (You seem to have missed my previous post by 5 minutes)

However, doing a inclination burn ALSO raises your apoapsis

Only if you do the sloppy approximation to an inclination burn that you get from the maneuver nodes. When you request a normal or antinormal burn from a maneuver node, you don't *really" get one. What you get is a burn in a single direction, when to stay normal or antinormal through the duration of the burn requires rotating while you burn - something the maneuver node system doesn't have the capacity to do. If you want to change your inclination by 10 degrees, for example. the normal vector will turn 10 degrees while you're doing the burn. So you have to slowly rotate through 10 degrees while burning to keep following the normal vector. It's the fact that a straight-line maneuver doesn't do this that causes your apoapsis to change.

[Rage097]

Eve has a very thick atmosphere, Aerobraking is a highly preferred methood. When in interplanetary space, after getting an encounter, try fooling with manuver nodes until you get one that has a periapsis within Eve's atmosphere. This will slow you down a considerable amount, depending on how deep you are in the atmosphere. Use your saved fuel to bring the periapsis out of the atmosphere after you've acheived orbit.

[Psycix]

Only if you do the sloppy approximation to an inclination burn that you get from the maneuver nodes. When you request a normal or antinormal burn from a maneuver node, you don't *really" get one. What you get is a burn in a single direction, when to stay normal or antinormal through the duration of the burn requires rotating while you burn - something the maneuver node system doesn't have the capacity to do. If you want to change your inclination by 10 degrees, for example. the normal vector will turn 10 degrees while you're doing the burn. So you have to slowly rotate through 10 degrees while burning to keep following the normal vector. It's the fact that a straight-line maneuver doesn't do this that causes your apoapsis to change.

I never thought about that!

Thanks for the info, it all makes sense.