king of nowhere Posted July 5, 2021 Share Posted July 5, 2021 (edited) 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 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 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 July 5, 2021 by king of nowhere Quote Link to comment Share on other sites More sharing options...
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.