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We need better deltaV maps


king of nowhere

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I've never run an interplanetary mission to a single planet. I found that once you put in all the effort to get your payload in orbit and on escape trajectory from kerbin (4300 m/s total), then it becomes much cheaper to give your probe a little bit of extra fuel to send it to a second planet than to build a new probe from scratch and pay again the 4300 to escape from kerbin.

The deltaV maps are very good at calculating the cost to reach a target from Kerbin. but once I am not starting from kerbin, they turn out to be completely useless. The only useful bit of information there is how much it takes to land on a planet.

Look, for example, at jool. So i go in kerbin orbit, with 3400 m/s. Then I spend roughly 2000 m/s to get a jool intercept. So far, the map is accurate.

Then the map tells me I need 160 m/s to get captured by jool. Putting aside that it's always easy and preferrable to get a jool capture by gravity assis (as the map won't take that into account) I found that to hold if i enter with a low jool periapsis. Which is something I really don't want to do; it saves a bit on intercept speed, but it gives a much higher intercept speed on the moons. Much better to enter at the moon's altitude.

Let's say then i want to go to tylo. It says I have to spend another 400 m/s to get an intercept. Maybe. Maybe not. Actually, if I am in elliptic orbit around jool, chances are I will soon get a tylo encounter anyway. And then the map says I need to spend 1050 m/s to get a circular tylo orbit. Again, that's bogus. Finally, it says I need 2270 m/s to land/take off, and this is the only useful piece of information there. Afterwards, if from Tylo I want to go to Vall, the map gives me zero help. Nowadays, I'm not looking at the map anymore.

 

So, here is what I propose to improve the map.

1) for all moons, do split the intercept speed in "to get in elliptic orbit" and "to circularize". In tylo's case, it would take 250 to get captured in elliptic orbit, and 800 to circularize. This is supremely important for planning a multi-moon mission, because once you're out of a moon's SoI, you can start using gravity assists. Before that, you have to pay with rocket burn. So this addition would tell me that, if I wanted to go somewhere else after landing on Tylo, i have to pack 2270 to reach tylo's orbit, and then I'd have to pack at least 800 more to leave tylo's SoI. If I wanted to stop in an elliptic orbit around tylo, to then leave again for another target, i'd only have to pay 250. If I want to place a mothership in tylo's orbit and then separate a lander, the mothership would only need 250, but the lander would need 800 to circularize in addition to the 2270 to land. As shown in the tentative picture here (of course it doesn't look good, if I knew how to do this properly I'd consider doing it myself)

Spoiler

ccCdrHf.png

This information is the most useful, and it would also be very easy to add. If you do nothing else, please do this

2) do add costs for going from one planet/moon to its next neighboors. For Tylo, include an arrow to go to Vall, and another arrow to go to Bop. For Jool, include arrows to go to Dres and Eeloo. One can make a Jool-Eeloo transfer with as little as 400 m/s, but from the map there's no way to tell.

EDIT: this is a tentative example. Still very crude; a proper one should split the deltaV between extra to leave the starting moon, and intercept to get captured on the second. Plus the diagonal number for the plane change. Also, the values are filled by memory and unlikely to be accurate

Spoiler

VI29wGg.png

3) for gas giants, instead of calculating the costs assuming intercept with a periapsis 10 km above atmosphere, calculate them assuming periapsis equal to the orbit of the innermost moon. It's still not a perfect solution, but much more realistic than what's currently done.

4) just like there are symbols for "aerobraking possible", do add a symbol for "gravity assist possible", followed by how much you can realistically gain from a moon. Relevant only for gas giants. Every experienced player knows how to get captured around Jool with a flyby of tylo or laythe, but looking at the map there's no way to tell. In fact, in my first jool mission, looking at the map, I tried instead to aerobrake on jool. Of course, it ended poorly. And now I have installed OPM; is it possible to get captured around Neidon by gravity assist? its moons are Vall-sized, is that enough? can I plan my Neidon mission assuming I'll be able to skip injection deltaV, or not? I know I can use Mun to gain 50 m/s, doing a duna mission with 950-1000 m/s because mun pays the rest of the cost. I can use Mun to reduce intercept speed by a similar amount on returning. Adding to mun a "gravity assist: 50" symbol would give this information without needing to figure it out by trial and error.

 

Now, someone may argue that there's no need to add this information because people already know it. To which I'd reply that we veterans already know how much you have to spend for the various intercepts, so there's no need for a deltaV map at all. In general, the purpose of a deltaV map is to give informations useful for planning missions, and I believe my proposals would lose nothing, and make the map much more useful.

Edited by king of nowhere
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54 minutes ago, modus said:

Looking forward to the end result, since you already started

 

26 minutes ago, linuxgurugamer said:

Presenting the information in a usable manner is as always a problem, would be interested in seeing the solution.

 

i trapped myself neatly, didn't I?

In the next days I may give it a better try.

 

Quote

OTOH, this would appeal to a small niche of players.  Most players depart fro, and return to, Kerbin

Difficult to say. Generally speaking, everything everyone does in this forum only appeal to a small niche of players.

Most players quit the game before ever leaving Kerbin's sphere of influence. Most players don't visit the forum and never even learn about the deltaV map. Most players who visit the forum use alexmoon tool or mechjeb or other stuff and don't use the deltaV map. I am in none of those categories and still I don't use the deltaV map for reasons explained above. I could say that the map already appeal to a small niche of players. And those with OPM installed are an even smaller minority of that small minority, and yet somebody took the effort to expand the map for OPM.

On the other hand, the jool 5 challenge thread has dozens and dozens of submissions. Making the map useful for the Jool 5 experience is the main benchmark of my suggestion, so it would at least appeal to those players.

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You could always create a simple spreadsheet to run the vis-viva and hyperbolic velocity calculations, then write down the answers. That's how the original subway map was created, with rounding up to the nearest 10 m/sec.

I created my own calculator years ago for the same purpose; I often need to plan burns that don't appear on the subway map.

Best,

-Slashy

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9 hours ago, GoSlash27 said:

You could always create a simple spreadsheet to run the vis-viva and hyperbolic velocity calculations, then write down the answers. That's how the original subway map was created, with rounding up to the nearest 10 m/sec.

I created my own calculator years ago for the same purpose; I often need to plan burns that don't appear on the subway map.

Best,

-Slashy

would that actually work?

to the best of my knowledge, the vis-viva doesn't take into account inclination. nor does it have good ways to calculate oberth effect

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So far I tried building it for the Kerbin system. It conveys accurate information on how much you need for a Mun-Minmus transfer, and it still looks readable to me

8OI4Pfr.png

the graphic is very basic, I am not capable of giving this a fancy outlook so I'm not even trying. For now I'm trying to persuade people that the extra information is worth including.

The Mun-Minmus transfer in both ways has the same cost, but I checked with some Joolian moons and it's not always the case, so I'm leaving the moon-moon transfer with the two directions written separately. Same for interplanetary transfers, they can be asymmetric, especially when plane changes are taken into account.

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4 hours ago, king of nowhere said:

would that actually work?

to the best of my knowledge, the vis-viva doesn't take into account inclination. nor does it have good ways to calculate oberth effect

My spreadsheet doesn't take inclination into account, but neither does the subway map. It does, however, solve the Oberth problem and calculates the gateway orbit at both ends for any given transfer. It also calculates transfer windows, departure angles, and transit times.

Best,

-Slashy

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The map does show "maximum plane change dv". I don't see how this would be a problem to include. Just pick the worst case of inclination difference while still showing optimal Hohmann transfer requirements.

Not that it matters too much, just wait few orbits and the moons will align properly, it's not like you have to wait a year for a transfer window.

Edited by The Aziz
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  • 4 months later...
On 7/5/2021 at 7:00 PM, king of nowhere said:

I've never run an interplanetary mission to a single planet. I found that once you put in all the effort to get your payload in orbit and on escape trajectory from kerbin (4300 m/s total), then it becomes much cheaper to give your probe a little bit of extra fuel to send it to a second planet than to build a new probe from scratch and pay again the 4300 to escape from kerbin.

The deltaV maps are very good at calculating the cost to reach a target from Kerbin. but once I am not starting from kerbin, they turn out to be completely useless. The only useful bit of information there is how much it takes to land on a planet.

 

This might be the solution that you are looking for:

It does not have gravity assist features yet, and isn't printable on paper, but it does run on a tablet/phone while you play KSP on the main computer.

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On 7/5/2021 at 11:38 PM, king of nowhere said:

and it still looks readable to me

This is my biggest issue with the dV map -it is simply, to me, unreadable.  And it is hard to figure out how much dV I need if I'm like you and hitting multiple bodies in one launch.

Edited by Scarecrow71
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Specifically for Jool, this is the map I used to plan out my Jool-5 mission.

https://imgur.com/skAIz90

In stock, Jool is the only planet this is really important on; most other planets only have one moon, and Kerbin's two would be easy to map out as per those recommendations. But Jool is complicated, since you basically need a subway-style map from every body.

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