Kowgan

[1.7.3] Community Delta-V Map 2.7

Recommended Posts

On 10/5/2019 at 9:12 AM, Armisael said:

I think most of the capture numbers are wrong. I've gone back and looked at Curious Metaphor's numbers (based on the dv map linked on the front page), and I can only replicate them when I assume that you're departing from an orbit at the 50x time warp altitude (not what's listed on this thread's map), and that you're attempting to escape to infinity (which you aren't in this game). It's really simple to verify - if you hyperedit yourself into an 80km Kerbin orbit, you'll see that it simply doesn't cost 950 m/s to escape the SoI. I've checked Kerbin, Eve, Mun, and Laythe, and they all line up with my numbers within 0.1 m/s.

Here are my numbers.

BgTYyvO.png

 

(If someone can tell me what I've done wrong I'd be happy to understand how I'm misreading the map, of course)

I only did a quick check for Kerbin Low Orbit (80km) to SoI in Stock KSP and agree, there seems to be some variation between the numbers on the dV map (last updated in 2017, I believe) and current KSP; to wit, it does indeed take 930 dV from LKO to SoI, not 950. 

According to the change log on the OP, the last update was in 2017, but the last time the dV numbers were touched at all was in July 2016. Not bad, considering that was KSP 1.1.3, and we had only been switched to Unity 5 a few months earlier. All in all, my hat's off to the original crunchers of numbers!

Share this post


Link to post
Share on other sites

@Armisael That's some interesting data you gathered there. On the second half of the chart, did you gather those numbers only while warping? If so, what are your results while not warping at the same altitude (minimum orbital alt)?

I revisited CuriousMetaphor's Delta-V Map from 2013 and took a look at the notes.
His chart is indeed set for minimum orbital altitude, and not the 10km above minimum as seen in this one. The 80km orbit standard was set by Jellycubes in the original chart, followed by Wac's, and, posteriorly, by the current one. The practical numbers were different back then, so maybe 950m/s was accurate from 80km orbit at the time. I'm not sure if Jellycubes grabbed the numbers from Curiousmetaphor and did not consider the 10km difference. Either way, mea culpa for not taking that into account for this chart.

I'm happy to review the vacuum numbers, update the chart and credit you, if you're interested.

Share this post


Link to post
Share on other sites

Everything on that chart to the right of the low orbit altitude is calculated, mostly using the vis-viva equation (with the exception of the 50x time warp altitude). I’ve done some testing (edit: using maneuver nodes, not burns) to confirm my results were right using hyperedit, but haven’t tested on all bodies. I can upload the file when I get home from work

It’d certainly be neat to have my name on something so important to the community, but the real driver for me was getting that 310 m/s number for Mun capture fixed.

(For what it’s worth I think the 10k above minimum is a very reasonable standard.)

 

EDIT: Link on google sheets

Edited by Armisael

Share this post


Link to post
Share on other sites

Awesome. I'm working on the update.

There's something else. Curiousmetaphor's low orbit altitudes are mostly different from the ones in this - Some are the same; some are higher and some are lower. Nevertheless, the dV numbers to achieve low orbit were kept the same. So, obviously there are some inaccuracies (mostly insignificant), but I reckon they work just fine right now; especially if you take into account that each player will have a different ascent profile, etc.
I thought about replacing the diminishing numbers from LO->SOI by increasing the ones in Surface->LO and keep the total dV usage the same, but given how different each celestial body altitude is between those two maps, I decided for keeping the same Surface->LO values and just alter the total dV value usage. Feedback on this will be appreciated, once the update is out.

Share this post


Link to post
Share on other sites

V2.7 released
- Updated to KSP 1.7.3

- Updated Low-Orbit-to-SOI-Edge values (Thanks @Armisael!)
- Updated credits


KSPedia version is pending update. Following the old tutorial by DMagic resulted in errors upon generating the .ksp file. As such, I've included the .png file for the KSPedia page in the GitHub source for anyone who's able and willing to generate and share said .ksp file. My regards in advance.

Share this post


Link to post
Share on other sites

The arithmetic all looks correct. I don't understand the intended routes between bodies well enough for out-of-Kerbin bodies well enough to meaningfully comment on those.

If you were interested in landing values:

DW2E5qR.png

Exact values are less important for these than the capture costs, I think, since it's so much harder to actually achieve these. I also might opt to disagree with the rounding on Minmus - rounding 174.93 to 170 is... technically correct, but perhaps unhelpful.

Edited by Armisael

Share this post


Link to post
Share on other sites

I agree that numbers shouldn't ever be below minimum required. and if needed, should be rounded up instead. But are the non-rounded numbers on your chart the absolute minimum in any scenario?
In any case, planning expects players to carry extra fuel, especially when manual control is used instead of autopilots. So although rounding down isn't the most appropriate, I woudln't call it totally useless or unhelpful. It's not that big of a deal, is it? ;)

In other words: Remind me to round it up to 180m/s on the next update. :)

Edited by Kowgan

Share this post


Link to post
Share on other sites

You already have Minmus's value at 180 m/s, so that's already handled. No need to change anything; the comment was on my numbers.

The numbers above are costs for Hohmann transfers to/from sea level with perfect point burns. I'm not aware of any superior technique. Bielliptic transfers and gravity assists are the usual culprits but I don't see how you'd use them for a simple landing.

You can beat them if you land at or ascend from taller geography; landing on Mun at 5.5km ASL saves you about 8 m/s. I'm not aware of any resource listing the tallest point as a function of latitude on each body, or even just on the equator. I also need to think over the precise math on how much dv it's worth expending to reach a non-equatorial high point. I suppose we could simply use 10km below the listed low orbit and assume that altitude is available equatorially.

Edited by Armisael

Share this post


Link to post
Share on other sites

IIRC, the low orbit values are "10km above the highest terrain point/peak" for non-atmospheric bodies. These are usually mountains or overall elevated points; not the zero mark ASL. But I'll leave you to these calcs. :)

Share this post


Link to post
Share on other sites

I think this is more a philosophical matter. Should ascents and landings describe that absolute best possible case, a more average case, or a worst-case (based on landing location, not technique)? I think expecting people to know that they'll need to land on the top of the tallest mountain is somewhat unreasonable, but I suppose that's up to you. Some more numbers (min/max/mean equatorial surface altitudes were measured using a kOS script that measured the surface elevation on the equator every 0.01°).

Bq9kobC.png

Edited by Armisael

Share this post


Link to post
Share on other sites

The 10km above tallest terrain wasn't designed to help people landing on these locations. Rather, it's a safety margin, so people don't crash while orbiting. Same goes for atmosphere.

These are some good numbers to know. It shows the orbital atitude on the chart is innacurate, if they're designed 10km above terrain. Maybe there's something to do with timewarp speed, then? Idk, gotta check that.

Share this post


Link to post
Share on other sites

I was really looking at how much dv it actually costs to reach orbit from the surface (or to land), which depends both on orbital altitude and surface elevation. I think the reasonable thing to do for the landing numbers is to assume that the craft is landing at either the mean or minimum equatorial altitudes; the altitude of the orbit is mostly a separate choice.

Share this post


Link to post
Share on other sites
On 10/9/2019 at 5:58 PM, Kowgan said:

IIRC, the low orbit values are "10km above the highest terrain point/peak" for non-atmospheric bodies. These are usually mountains or overall elevated points; not the zero mark ASL. But I'll leave you to these calcs. :)

the "10km above highest point" are not totally accurate too,  example with :

"The Mun's highest points reach a maximum altitude of more than 7061 m"
https://wiki.kerbalspaceprogram.com/wiki/Mun
Dv map: 14km (counting the 10km above i understand)

 "Tylo has a rocky surface. It has a varying elevation between 0 meters (Tylo baseline height) and peaks of more than 11290 meters."
https://wiki.kerbalspaceprogram.com/wiki/Tylo
Dv map: 10km

but all these Dv numbers are good enough for me, even on  no atmo bodies it will depend of the rocket.

Share this post


Link to post
Share on other sites

Yeah, I suspected that couldn't be right. Maybe there's something to do with warp speed at these altitudes? Idk. ¯\_(ツ)_/¯

Share this post


Link to post
Share on other sites

Would you ever consider putting this on displate? I'd love to have a metal version to hang over the desk for reference :)

Share this post


Link to post
Share on other sites

I was looking for a DV Map for the OPM Planets and seeing, that the current one is 3 years old, I read through the OPM Changelogs and found the following changes since OPM 1.8.1 that propably affected the DV map for it:

  • Different atmosphere height for Sarnus (possibly Urlum, Neidon and Tekto aswell) as reported by another user here in this thread
  • Karen missing around Plock
  • lowered gravity of Slate
  • maybe different safe orbit heights due to terrain reworks of the rocky bodies for OPM v2.0.0 (not sure how much it will affect the numbers since I'm not on my PC right now)
  • the new updated v2.7 SOI numbers for the stock part of the OPM dv map.

While these are quite a few changes I don't think it would be too hard to update the map. And then it should stay up to date for a while, since I dont think OPM will chance much anymore. At least as far as the dv requirements are concerned.

I already played a bit with the .svg files and managed to add Karen around Plock, but since I'm new to Inkscape and missing the dv numbers rn, don't expect to much from me. I have never done anything like this before :D

I guess the real work is more about figureing out the new dv requirements and not putting it in the map. But maybe if I'm bored on the weekend I will try. 

If someone wants to explain to me how the dv are measured in game, which mods I need (hyperedit?) etc I would be very grateful.

 

Share this post


Link to post
Share on other sites

They're (apart from atmospheric entry) not "determined in game" - they are calculated.

Share this post


Link to post
Share on other sites

If it's any help I recently found that constant vertical velocity launches tend to use almost the same as optimal gravity turn launches. The benefit is that dv of CVV launches can be calculated analytically. Assuming constant TWR and zero vertical velocity, and neglecting any sideral rotation, gives that if you are taking off from a body with a given mu and r with a certain twr, and going for a zero altitude circular orbit, it takes: 

(1/2)*Sqrt( mu/r ) * twr * ln( (1+twr)/(twr -1 ))

If that helps.

 

Share this post


Link to post
Share on other sites

Hi, I am somewhat new to KSP. I got to the Mun and Minmus relatively easy. Now I am slowly getting ready for a trip to Eve and Duna, and I think your map will be very useful for the prep. However, I am a little confused about the return Delta-V. Your map tells me exactly how much I'll need in the best and worse cases, but how much fuel will I need to return? Do I simply double it? Is it included in these outcomes?

I try to play the game with no mods, so any help and info is very welcome! Thanks in advance ;)

Share this post


Link to post
Share on other sites
6 hours ago, dshodaw said:

Hi, I am somewhat new to KSP. I got to the Mun and Minmus relatively easy. Now I am slowly getting ready for a trip to Eve and Duna, and I think your map will be very useful for the prep. However, I am a little confused about the return Delta-V. Your map tells me exactly how much I'll need in the best and worse cases, but how much fuel will I need to return? Do I simply double it? Is it included in these outcomes?

I try to play the game with no mods, so any help and info is very welcome! Thanks in advance ;)

To plan for the return trip then yes you generally read the DV map backwards but there's no need to include all the values all the way back to Kerbin since you can take advantage of Kerbin's thick atmosphere to aerobrake for capture and re-entry and ignore any legs with the little arrow symbol pointing towards Kerbin.

Launching from a planet's surface back to low orbit should take the non-aerobrake DV listed for landing (1450 m/s for Duna and over 8000 m/s for Eve). For a return from Duna orbit the DV is thus about 360 + 250 + 130 (+ up to 10 plane change). A return from Eve orbit would be 1300 + 80 + 90 (+ up to 430 for plane change)

Note for going to and returning from other planets timing is very important. You want to make sure the angle between Kerbin and your target planet is correct for both legs (see https://ksp.olex.biz/ for a helpful online guide for eyeballing the angles). If you don't make your transfer at the right time it can cost a LOT more DV than shown on the chart.

There are also some tutorials you might want to check out on the wiki section of this site: https://wiki.kerbalspaceprogram.com/wiki/Tutorials

Share this post


Link to post
Share on other sites
Posted (edited)

I'm in the process of updating New Horizons is being updated by @GregroxMun for KSP 1.7.3 and 1.8.1.  Is there anyone who would be interested and able to do it?  If so, please let me know 

Edited by linuxgurugamer

Share this post


Link to post
Share on other sites

This mod seems to have stopped working for me since 1.9
I recall the 1.9 release notes said something about how they load the KSPedia pages in-game?

Share this post


Link to post
Share on other sites
On 2/19/2020 at 9:46 PM, Mockery said:

This mod seems to have stopped working for me since 1.9
I recall the 1.9 release notes said something about how they load the KSPedia pages in-game?

Yeah, not working for me either.

Share this post


Link to post
Share on other sites

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.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.