Delta-V Discussion

[Endersmens]

I thought about putting this in general discussion, but since its about gameplay discussion, i put it here instead.

So i've decided to open this thread to talk about delta-v. More importantly, transfer delta-v requirements. I know there are delta-v maps, but i want to know how much delta-v it takes YOU to make a tranfer. If you use a calculator for phase angles, please specify your phase angle also. If you just eyeball it, im jealous. I will update this post with the different delta-v/phase angles you guys post here.

NOTE: This is NOT a competition. However, i will be sorting them from lowest delta-v to highest, especially if phase angles are given, to give newies options. Also, screenshots of the manuevers are welcome and appreciated, but not neccesary.

So, i will offer the first delta-v needed. I sent a three part mission to Jool, and exactly 1960 m/s got me an encouter with each one, with a ~500 m/s correction burn halfway though. I am unaware of the phase angle at this moment, i will update this later with that. (if i can get "edit" to work)

So here is the chart that will be updated. I will try to order them from average lowest to average highest. (my best guess)

Mun:

Minmus:

Duna:

Eve:

Dres:

Jool:

Endersmens: 1960m/s Transfer burn with ~500m/s correction burn half way. Total: 2460 Delta-v needed.

Eeloo:

Moho:

Again, this is NOT a competition, so don't go bragging about how you got the least delta-v for a transfer. This is to be used as a resource. (yes i'm aware that there are calculators for this, but i was uneasy about using one, i wanted someone elses opinion, thus, the reason i made this thread)

[Pecan]

I tend to go with what the deltaV maps say +10% contingency, which I almost invariably end-up using. So far so good (or at least, adequate).

[Superfluous J]

I use this delta-V map right here and find it to be pretty accurate. I add about 10% to everything for a margin for error and tend to come home successfully but with near-empty tanks.

To actually do the transfers I "eyeball it" with maneuver nodes. Once I'm going I never ever pay attention to dV (unless I'm getting worried that it's getting low) so can't really say what everything actually costs, but I can say that I'm easily within 5-10% (plus or minus) what's on that chart, every time.

I used to use the various transfer window helpers out there but these days I do this (Note I'm saying "Kerbin" and "Duna" but this literally works for any Hohmann Transfer):

1. Plan a node to JUST escape Kerbin, preferably in front of or behind depending on where you're going. For Duna, you should escape just in front. I use PreciseNode and leave Kerbin usually with about 900-950 m/s. If I went 1 m/s less I'd stay captured in Kerbin's SOI.
   
2. Plan a second node on your ship's orbit around Sun. Give it enough prograde thrust to reach Duna's orbit, and set Duna as a target. You should get connection markers and unless you're very lucky they won't be near each other.
   
3. Drag that 2nd node around (you'll have to also modify it's prograde amount due to the two orbits not being perfect circles) until you actually have an encounter. Hopefully it'll be a real SOI change encounter but if you just get the markers really close that's enough.
   
4. Delete the first node. KSP will remember the 2nd node's location but its directon and amount will be totally wrong. If you have PreciseNode, see below instead of performing the next steps.
   
5. Warp to that Maneuver node (Kerbal Alarm Clock is very nice here) and when you get there, delete it and create a NEW maneuver node about where you'd have to burn. To get to Duna, this is a little after your ship will go into Kerbin's shadow.
   
6. This node should easily get you a Duna encounter. You may need to burn normal on ejection. Do it. Drag the node around to get it as good as possible. So long as you connect with Duna, you're fine. Correction burns once you have an SOI encounter are miniscule.
   
7. Do the burn, and follow the maneuver node as precisely as you can.
   
8. Feel like a baws
   

If you use PreciseNode, you can do one better:

1. Instead of leaving that maneuver node that's at the right time but the wrong place as a simple marker, let's make it an actual correct node!
   
2. Using PreciseNode (never EVER touch the maneuver node itself. It'll snap back to the current orbit and you'll have to start over), move your burn forward and back in time until it's at the correct place in orbit around Kerbin to burn out to Reach Duna.
   
3. Also modify the dV needed, and note that it's less. There's Hohmann at work. Actually, it may be a LITTLE more but it'll assuredly be less than this plus the 900-950dV you had on the first maneuver node at the beginning.
   
4. Keep adjusting this node until you have a maneuver to Duna planned, possibly hundreds of days in the future.
   
5. Warp to and execute that node. Like above, follow the node as closely as you can. You're throwing a dart across the Solar System and trying for a bullseye.
   
6. Lean back and bask in the awesomeness that is you.
   

[Endersmens]

I tend to go with what the deltaV maps say +10% contingency, which I almost invariably end-up using. So far so good (or at least, adequate).

That's precisely the point of this thread. The maps give you the delta-v if you do it perfectly. I would like to see actualy requirements from actualy transfers. This will help others design their ships without using too much excess Delta-v (like me. 9,800 delta-v to minmus and back.....droped over 3 km/s in non-empty stages)

[Endersmens]

Sorry for double posting, i am unable to edit posts, that meant to say "Acutal" instead of "actualy" both times

[Pecan]

LOL, yes, I do understand that, it's a good and worthy thread, well done. I'm just saying, as 5thHorseman has too now, that +10% on those figures seems pretty accurate for me.

[Superfluous J]

LOL, yes, I do understand that, it's a good and worthy thread, well done. I'm just saying, as 5thHorseman has too now, that +10% on those figures seems pretty accurate for me.

Yes. If I wasn't clear you could take the numbers on the chart I posted, add 10% to all of them, and that's about what I get. I've done it enough to be confident in that without having to do it, though if i have the time I may do it later tonight.

[breakthrough]

Delta-v maps are generally pretty accurate in my experience with the notable exception that capturing around Moho will take an additional 1,000m/s above what is on the map for all but a flawless transfer.

[cantab]

I don't have exact figures to hand, but I do recall that I find 860 m/s not quite enough for a Mun transfer, I often end up using more like 900.

[Taki117]

To get to the mun is about 900m/s (Assuming you start from LKO) Much more than that and you are doing something horribly wrong.

[allmhuran]

I'm not sure whether this falls outside the scope of what you want to achieve, but it may be worth mentioning in a footnote (or whatever) that the cost of getting to anywhere in the solar system is just a couple of meters per second more than the cost of getting to Eve, since Eve is the cheapest to get to, and you can slingshot your way around after that.

Eg, to Jool:

1) Burn from Kerbin to Eve (1050 m/s)

2) Slingshot off Eve to put your apoapsis above Kerbin

3) Radial intercept and slingshot off Kerbin to put your apoapsis near Dres

4) Second slingshot off Kerbin to put your apoapsis at Jool

5) (If necessary) polar slingshot off Duna to correct your orbital plane

Total cost is generally about 1100 - 1150 m/s.

[GoSlash27]

I have found that transfer DVs are pretty much right out of the window for anything that's not in the same orbital plane. It ends up taking whatever it takes *shrug*...

Kerbin surface to LKO takes about 4300 to 4500 and Mun is right on the money at 870. Anything else... It varies so widely that a DV map is almost useless. Generally it takes way less because I can "cheat" by using the other bodies to accelerate or decelerate me, but sometimes it ends up taking way more than the map suggests.

Perhaps it will firm up as I gain experience?

Best,

-Slashy

[allmhuran]

I have found that transfer DVs are pretty much right out of the window for anything that's not in the same orbital plane. It ends up taking whatever it takes *shrug*

If you are looking at the delta V map that 5thHorseman linked, then the numbers in green represent plane change delta V, but I believe work on the assumption that you:

- start on the origin's orbital plane

- end on the destination's orbital plane

- perform the inclination change at the ascending or descending node

While this is usually all true, it's not always all true.

[Endersmens]

I'm not sure whether this falls outside the scope of what you want to achieve, but it may be worth mentioning in a footnote (or whatever) that the cost of getting to anywhere in the solar system is just a couple of meters per second more than the cost of getting to Eve, since Eve is the cheapest to get to, and you can slingshot your way around after that.

Eg, to Jool:

1) Burn from Kerbin to Eve (1050 m/s)

2) Slingshot off Eve to put your apoapsis above Kerbin

3) Radial intercept and slingshot off Kerbin to put your apoapsis near Dres

4) Second slingshot off Kerbin to put your apoapsis at Jool

5) (If necessary) polar slingshot off Duna to correct your orbital plane

Total cost is generally about 1100 - 1150 m/s.

well, since i made this for newer players, and also for myself, i would say that is too much. plus that would be what, 3-4 years of transfer time? Im more looking for straight up hohmman tranfers, most likely with a plane change/correction burn.

I have found that transfer DVs are pretty much right out of the window for anything that's not in the same orbital plane. It ends up taking whatever it takes *shrug*...

Kerbin surface to LKO takes about 4300 to 4500 and Mun is right on the money at 870. Anything else... It varies so widely that a DV map is almost useless. Generally it takes way less because I can "cheat" by using the other bodies to accelerate or decelerate me, but sometimes it ends up taking way more than the map suggests.

Perhaps it will firm up as I gain experience?

Best,

-Slashy

Yes, i once sent a moho flyby, and had a near 2000 m/s plane change burn. I do believe it gets better with experience yes, i believe my only other jool mission took around 2,200 m/s with a correction right at the edge of the SOI. Now i'm sitting on 1960 every time with 400-500 m/s correction burn, which i feel are necesary, thanks to SAS completely destroying the encounter on the escape from kerbin.

[Pecan]

...Yes, i once sent a moho flyby, and had a near 2000 m/s plane change burn.

The plane-change for Moho listed on the deltaV map (I use the same as 5thHorseman linked) is 2,520m/s so I'd say you did well - why the sad face?

[allmhuran]

, thanks to SAS completely destroying the encounter on the escape from kerbin.

This probably isn't SAS.

If you are at a high warp value when you cross a sphere of influence boundary, then you will usually travel several thousand kilometers past the boundary by the time the game recalculates your trajectory. The solution is to drop your warp value to, say, 50x or less as you approach SOI boundaries.

[RenevB]

The plane-change for Moho listed on the deltaV map (I use the same as 5thHorseman linked) is 2,520m/s so I'd say you did well - why the sad face?

Those green numbers are worst case scenarios, so I'd say that needing 2k out of a maximum 2.5k is worth a sad face.

Back to the OP: in my experience, the numbers from the delta-v maps are pretty spot-on. It's always advised to overdesign and take a little more, mainly because maneuver nodes assume an instantaneous change in velocity while actual burns take time. Also landing on airless bodies will probably take more, if you do it slowly and safely instead of using suicide burns.

[Red Iron Crown]

I've had generally good results with metaphor's delta-V map and adding a 10-15% margin for user error. I tend to stick to efficient launch windows so the estimates are pretty close.

Lately I've been tooling around the Jool system's moons a fair bit and I've found the map to be less accurate there, probably because I don't drop down to a low orbit around every body.

[Endersmens]

Hmmmph. Everyone is saying the exact same thing. This is kinda a bust. What should I do now ? Copy the map into my chart and add say 10 percent?

[Pecan]

Hmmmph. Everyone is saying the exact same thing. This is kinda a bust. What should I do now ? Copy the map into my chart and add say 10 percent?

Bit early to call it, I think - so far you've mostly got those of us that have an easy answer 'the chart works for me (+10%)'. The threads only been open since yesterday and what you're trying to do is useful, so leave it a few more days first.

[Dkmdlb]

For Mun I usually do about 840 from 100km, for Minmus it's usually 100 m/s more.

[EdFred]

When I first started out I needed a margin of about 50%. Then it dropped to 20%. Then to 10%. Missions to Mun and Minmus, I can get under 5% above ideal. Generally my first trip to a new body is in the 15% over range, return trips are in the 5-10% over range.

[Endersmens]

I'm slowly starting the stage of delta-v planning. Up until now, it's been "make sure i have enough" not "make sure i dont have too much" now i am starting legit staging designs that wont waste delta-v. I'm used to dropping more than half full stages before landing a lander. Now i'm gonna change that into dropping a half full stage into orbit and going back for it.

[metaphor]

I've had generally good results with metaphor's delta-V map and adding a 10-15% margin for user error. I tend to stick to efficient launch windows so the estimates are pretty close.

Lately I've been tooling around the Jool system's moons a fair bit and I've found the map to be less accurate there, probably because I don't drop down to a low orbit around every body.

The way I calculated the delta-v's needed for the moons of Jool (and all other moons) is to assume that, when coming from an interplanetary trajectory, you burn retrograde at Jool periapsis right above the atmosphere (or aerobrake) and get into an elliptical transfer orbit with apoapsis right at the target moon's orbit. So for example when coming from a Kerbin-Jool transfer orbit you have to burn retrograde 320 m/s at Jool periapsis in order to get into an orbit that has its apoapsis at Pol's orbit (380 m/s for Bop, etc). And from that orbit it takes 770 m/s at Pol to get captured into Pol orbit. Those delta-v's should be pretty accurate, but that's not always the best way to do it. For the big moons it's more efficient to just capture straight into orbit around them without going low near Jool. Gravity assists can significantly change the delta-v as well, and they're pretty easy to get in the Jool system. Also, this chart doesn't include the delta-v to go from one moon to another, which is really different (since you wouldn't go down to a low Jool periapsis before transferring to the other moon).

If you want delta-v to go from any one place to any other, this post is a good resource.

[Red Iron Crown]

Thanks for that insight, metaphor, and the link to the other maps, very useful.