How Do You Deal with Inerplanetary Aerocapturing in 1.0.4?

[Geschosskopf]

CAVEAT

This is an attempt to have a rational discussion. Do NOT attack other players' opinions because they differ from your own. Put all zealotry aside here.

The purpose of this thread is simply to amass data on how all members of the community deal with the issue of aerocapturing/braking at interplanetary transfer speeds. Being able to do this has long been a staple of KSP gameplay because it saves fuel when going to places with atmospheres. Now, some say this is totally "unrealistic" based on how things are in our own real universe, and they're entitled to that opinion. If they never do it themselves, that's fine. But there are many who do use aerocapturing because they think it's perfectly legit, and in single-player games, what other people do in their own games is their business. So let's not get into the rightness or wrongness of the concept as a whole, OK?

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THE CONTEXT

1.0.4 introduced a whole new heat system which, from what I can tell of its inner workings, is considerably more rational and "realistic" than what we had in 1.0.2. So far, so good. But a set of equations is just a machine, mechanically crunching inputs into outputs. Thus, the results are only as good as the inputs. So the heat system must answer 2 questions. First, is the heat system a valid model for KSP and, second, what are the best inputs for it? When you reply to this thread, please try to answer both questions.

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MY ANSWER

I believe that using interplanetary aerocapture is perfectly legit and adds a challenge now that it can kill you. I deal with it by reducing the reentry heat value to 10-20% (still experimenting). This results in a challenge that's worth facing. Higher heat levels result in no challenge becuase they force you either to avoid the atmosphere entirely or use a mod or hack to negate the heat.

1. Validity of the Model

As indicated above, I think the inner workings are reasonably valid as to how things work on Earth and, by extension, to other planets in our real solar system. However, KSP is in a radically different, toy-sized solar system so no Earth-derived system will ever be a good fit for all places in it. It can be made to approximate Earth-like results in 1 area, but that will produce strange/undesirable/wrong (whatever you want to call it) results everywhere else. So no matter what you do with it, you can't optimize it across the board. Thus, it all boils down to where you prefer to optimize it, which is a question of inputs. Therefore, I will accept the model as "valid" (considering it's the one we have to deal with) and move on to the inputs.

2. Validity of the Inputs

Because the model is incapable of producing what I consider desirable results at all planets simultaneously, I have to choose which planets I want desirable results at, and what I'm willing to accept as a result at other planets. If I make reentry from LKO very dangerous, I preclude being ab le to aerocapture at other planets or when returning from them to Kerbin. OTOH, if I make interplanetary aerocapture doable, then I make returning from LKO a doddle. HOWEVER, in 1.0.4 with 100% heat, I find returning from LKO a doddle anyway, and my interests all lie at other planets, not Kerbin. So, turning that down costs me nothing. Therefore, I choose to do that so I have an achievable challenge at other planets.

My testing indicates that 1.0.4 increased reentry heating by a factor in the neighborhood of 4-5x over what it was in 1.0.2. That is, setting 20% reentry heat in 1.0.4 produces about the same amount of heat as 100% reentry heat in 1.0.2. Because the reentry heat slider only moves in 10% increments, I have been loath to try entering 5% increments.

NOTE: For them as started a 1.0.4 game with 100% reentry heat and now regret that decision, it's easy to change. Open the save file. Up near the top is a block called PARAMETERS. Scroll down in this to a sub-block called DIFFICULTY. The last line in this is reentry heat. 1.0 = 100%, 0.1 = 10%, etc.

[Robotengineer]

CAVEAT

This is an attempt to have a rational discussion. Do NOT attack other players' opinions because they differ from your own. Put all zealotry aside here.

Now I know why this thread hasn't had any replies...

[Jouni]

I use aerobraking as one tool in my toolkit, along with engine burns and gravity assists. I find interplanetary travel more interesting, if I have to use different techniques for different missions.

The first step is always having good encounters. When you're arriving from Kerbin to Jool, you hit Laythe's atmosphere at around 3000 m/s. You only need to lose a few hundred m/s in the initial aerobraking pass to get captured in Laythe's SoI. Alternatively, you can play with gravity assists from Tylo and Laythe or burn engines before and after aerobraking to make the pass through the atmosphere even safer.

The second step is choosing the tool according to the ship. A probe can land on Eve directly after arriving from Kerbin, while a heavy ship has to use its engines to slow down first. A plane can lose a lot of speed in the upper atmosphere, while an interplanetary ship coming in engines first probably has too small cross section for any meaningful aerobraking. A ship with its fuel tanks empty can find aerobraking much more useful than the same ship fully fueled.

The third step is not being too ambitious. You only need to lose just enough speed to get captured on the first pass. if you're trying to land or to reach a low orbit, you have all the time in the world to lose speed on the subsequent passes.

[Mister Dilsby]

Now I know why this thread hasn't had any replies...

I'm really, really into this topic but I don't have any atmospheric entries on the mission board for about 177 game-days and 21 real-days. If there was a box for it, I'd check, "Hope 1.0.5 comes out and brings everything back to near 1.0.2 levels for heating at interplanetary velocities, and if not I get to use any means necessary to make all the ships I launched in 1.0.2 survive because I call shenanigans on the GM."

ETA: There being no "shenanigans on the GM" button, I picked "100% heat and toggle off when necessary"

[Streetwind]

I don't really feel qualified to comment for the moment since I'm still waiting for Kopernicus to fix a career mode crash bug before I start a new save. I want to use a solar system rescale, hence the need for Kopernicus.

What I'm interested in is - does replacing the aero model (i.e. installing FAR) dramatically change reentry heating? In particular, does it change anything about the perception that Kerbin reentry is effortless while aerocapture at other planets is an axe murderer hopped up on caffeine?

I'm not sure yet what aero model I'll use for my next save, and while I'm technically leaning towards FAR (it just feels more... you know, steady, reliable, while stock is still being overhauled with each patch) I'd like to know what side effects that may have.

[HoloYolo]

I just slow down seeing as I don't know the numbers and how to get enough delta-v with a quadrillion heat shields.

[hellion13]

I use 120% heat. And for me the air around Duna is no longer able to be used for aerobraking its too thin. Got down to 10km at 1500m/s and still had to use my engines to get an actual orbit when I shot back out having used only a whole 2 units of ablator.

Haven't been to Jool yet. Cant say anything about it.

Kerbins is alright. Thick enough that straight in entries arent possible anymore. Forgetting a heatshield is a death sentence for anything orbital. Fairings are needed (for me anyway) stuff rips off or overheats way to fast.

parachutes are fun(read: russian roulette whether they open in time or even at all). Useless on duna but fun.

Thats the extent of my experience so far with ksp 1.0.4.

[Geschosskopf]

I don't really feel qualified to comment for the moment since I'm still waiting for Kopernicus to fix a career mode crash bug before I start a new save. I want to use a solar system rescale, hence the need for Kopernicus.

D'OH! I should have put in a poll option about using rescaled KSP. That's an entirely different kettle of fish than using the stock size.

What I'm interested in is - does replacing the aero model (i.e. installing FAR) dramatically change reentry heating? In particular, does it change anything about the perception that Kerbin reentry is effortless while aerocapture at other planets is an axe murderer hopped up on caffeine?

An interesting question. I look forward to somebody answering it. But if nobody does, I suppose you could test it yourself. Just make a copy of your current install and put FAR in it.

From what I understand, FAR's voxelization of ship configurations for drag computations is a lot more "predictable" than stock aero. By that I mean that other game systems and mods can use values generated by FAR in their own calculations much easier. For instance, if you have FAR, then the wonderful Trajectories mod will work for you, but Trajectories can't handle stock aero under a variety of circumstances (such as using fairings). By this token, I would assume that (whatever it does to other aspects of the game) FAR would simplify designing ships for interplanetary aerocapture because the player would get an emperical feel for what works and what doesn't easier than with stock air.

[regex]

The only time I aerocapture in KSP is when doing something like the MSL and, since I find no need to do an MSL-type mission in KSP (because we're talking about a toy-sized solar system and I don't have to worry about fuel costs or carrying large amounts of hypergolics to slow down), I don't aerocapture. Performing an aerocapture with a large, fragile deep-space tug carrying often-exposed cargo should result in the loss of the mission, IMO, so I feel KSP has things right.

E: Oh, missed this.

is the heat system a valid model for KSP

Absolutely, given no other frame of reference and desiring a relatively realistic game.

what are the best inputs for it?

What they are now seems to be fine. Edited June 29, 2015 by regex

[Nigeth]

I don't like the changes to the heating very much. Not because of the heat system though. My problem is that KSP doesn't give you the tools and know how necessary to avoid aerocapture entirely. This change leads to a resulting game that is harder for most players for the sake of 'more realism'. Which in that particular case doesn't mean 'more fun'. Also doesn't make the game any more realistic.

Real world missions don't use aerocapture or aerobraking (those are technically two different techniques btw.) Except for two notable exceptions (the Magellan probe and the Mars global surveyor) interplanetary missions usually use other measures to adjust velocity. Either gravity assists, burning rocket fuel or a combination of both. Sometimes the delta V budget is so limited that a mission can only achieve a fly by. (New Horizons for example).

Cassini-Huygens had to do two gravity assist fly bys of Venus, a gravity assist fly by of Earth and one of Jupiter to be able to end up at Saturn (https://en.wikipedia.org/wiki/Cassini%E2%80%93Huygens_timeline#/media/File:Cassini_interplanet_trajectory.svg) and it took the probe 6 years to arrive there.

You can't plan such a trajectory with the limited simulation model KSP provides (it would be very hard at least). You'd need a 'true' n-body simulation. Even then you'd need the know-how and mathematical planning necessary to design such complex trajectories. Even if you'd have all that you'd still probably have to wait years or even decades of in game time for a launch window.

The game doesn't help you in any way either. There is no tutorial that explains gravity assists to you. There is no launch window planner if you don't install mods. The default patched conic approximation won't show you your trajectory through the Kerbol system (it stops after 3 conical patches) so that you couldn't even plan something like this in stock without mods even if the simulation model was magically accurate enough to make such an endeavor worthwile.

All it achieved is to make the game harder for most players without adding more realism to it, Just because some players are under the false impression that this is 'more realistic'. Even worse it isn't even half as good as deadly reentry, a perfectly fine mod anyone that craves added realism should have already installed anyway.

Right now you can't really do interplanetary missions via aerobraking. Worse you can't really do an interplanetary return to Kerbin via aerobraking. So you'll either have to haul huge rockets with insane delta v budgets through interplanetary space (space truckin') meaning that you'll spend more time assembling your mission in orbit over Kerbin than actually doing it. Usually using 'near future' type means of propulsion which doesn't really make the game more realistic (it only exchanges added realism in one game system by making another less realistic). Or you use ore extraction and refuel to generate the insane delta-v requirements in-flight which is not necessarily realistic either. Or you build ridiculous contraptions with a truckload of heatshields and/or abuse the added radiators.

Or do what you did and basically turn it off entirely (limiting it to 20% you might as well turn it off completely).

All done just because a few vocal players didn't find stock heating quite challenging enough yet were too lazy to install DRE. If this had been a planned feature that had gotten enough development time it may have been different. As it stands the new system is only half baked since the rest of the game hasn't been caught up to speed in order to give you the tools and means necessary to deal with that change.

- - - Updated - - -

I also don't really understand why Squad assigns its limited development time and budget to implement a feature only a vocal minority claims is needed. Especially when there is already a mod that does the same.

[PDCWolf]

"How do you deal with interplanetary aerocaptures"

I don't. I use gravity assists or burns. The biggest problems are moon-less bodies or very small bodies, which obviously require bigger efforts. I sent an Ion based satellite to the Sarnus (OPM) system and visited all moons with about 2000 m/s dV or less, contrary to the 17km/s dV that the calculator gave me for my braking burn alone.

[Nigeth]

(we're talking about a toy-sized solar system and I don't have to worry about fuel costs or carrying large amounts of hypergolics to slow down

Quoted, because you exemplify the point I'm trying to make. Suppose for a second that Squad would approach all in-game systems with the same attention to realism as it did with heating. Would you still be OK? What if the heating stays as it is but hauling an insane amount of delta v and mass became impossible for the sake of 'realism' and you also couldn't use nuclear engines or any other sort of 'near future' propulsion system? What if they added something like TAC life support and you'd also have to make sure your Kerbals survived for years in deep space? What if they implemented something like "Dang it!"? What if the implemented something like remote tech?

You can't just pick and choose and somehow be OK with all the systems you don't care about being less realistic just as long as the one you care about is. Well you can but the result is not added realism just a game that is differently not realistic. It also might not necessarily something that is still fun to play.

I also don't really get why all of this has to necessarily be a part of the stock game when there is already a great and vibrant modding community that provides mods like realism overhaul, real solar system, FAR, DRE, real fuels, TAC life support and many more that already do what you want.

[regex]

Quoted, because you exemplify the point I'm trying to make. Suppose for a second that Squad would approach all in-game systems with the same attention to realism as it did with heating. Would you still be OK? What if the heating stays as it is but hauling an insane amount of delta v and mass became impossible for the sake of 'realism' and you also couldn't use nuclear engines or any other sort of 'near future' propulsion system? What if they added something like TAC life support and you'd also have to make sure your Kerbals survived for years in deep space? What if they implemented something like "Dang it!"? What if the implemented something like remote tech?

I'd be totally fine with it because that's the game I want to see from KSP. As it stands I have to download a ton of mods to make it that way but I'm pretty happy with the stock game overall as of 1.0, even though it still needs a lot of work.

You can't just pick and choose and somehow be OK with all the systems you don't care about being less realistic just as long as the one you care about is.

You are absolutely right which is why I always argue that Squad should fix the root of the problem, which is the toy-sized solar system. Fixing that would require a host of other changes that would make the game far better.

I also don't really get why all of this has to necessarily be a part of the stock game when there is already a great and vibrant modding community that provides mods like realism overhaul, real solar system, FAR, DRE, real fuels, TAC life support and many more that already do what you want.

Because the stock game deserves so much better than the tiny joke of a solar system it has right now. KSP deserves to be a hardcore spaceflight sandbox where you can build and explore different concepts while respecting realism. Hopefully a competitor will come along that puts realism first; I'd pay AAA game prices for that sandbox.

[Technical Ben]

I'm planning and testing in sandbox as always before I attempt career. Why? I don't mess with Kerbals lives.

If it's going to fail, I need a quick retry, instead of "loosing" lots of funds and science for a change in mechanisms (as I'm use to lots of old stuff I have to "unlearn"). That and I don't mind doing it all career, but I've done it pre-heat, so it would be the same just with heatshields now.

So I plan on making things a bit more interesting. For example I'm using 3 stacked shields, as spares to test with. So I can figure out if 1 would be good enough, or if it's best to take spares.

[Mischief]

You can still aerocapture with stock settings. You just have to be gentle with it. For example returning to Kerbin at 4k m/s, you aim for 45k altitude and expect 2 or 3 orbits to safely burn that velocity off. I tend to leave the transfer stage on but empty and come in a bit sideways. Creates more drag but spreads the heat over more parts.

For jool or eve you build a capture stage. Ablation shield and radiators, go high and expect 2 or 3 orbits to burn velocity enough, then eject capture stage and use a tiny bit of your return burn to normalize orbit. You may get best efficiency burning radial/anti radial rather than prograde at apoapsis and again at peroapsis.

I have found aerocapture to be my new favorite aspect of mission planning. You need a ship designed for it and a lot more forethought but you can carve over 1k dv out of your weight for other things or significantly move your approach vector and show up early if you design well.

I play with scansat and being able to send my scansat cluster in 30 days ahead of the manned mission is significant - I play with life support to so time is important.

[Evanitis]

1.0.4 got me to learn gravity-assisting. I was kinda' always aware of this technique, but I never knew it's so effective and easy. That and careful, slow aerobraking lets me to expect more spare dV than I ever had in previous versions. I'm having great fun: SSTOs orbit easier, going interpalnetary needs a different kind of approach, but I wouldn't say it's harder.

[Speadge]

i used aerocapturing on eve with a beginning of 3500m/s.

sure, u cant go down to 20k on first approach... and use some engines as well... but its doable without heatshields!

background: started the mission way before 1.04 and they arrived after 1.04 came out. so i didnt plan heatshields-and survived even without.

=> spent ~1km/s dv for slow down AND landing

[Geschosskopf]

Or do what you did and basically turn it off entirely (limiting it to 20% you might as well turn it off completely).

I don't agree or I would have turned it off completely instead of just riening it in . Because I wanted a challenge, I took the time to do tests to figure out what is, IMHO, actually challenging and what is not. Let me explain.

I used to be an indy gamedev myself so I look at gameplay challenges from that perspective. Viewed this way, a challenge worthy of inclusion in a game has to satisfy 2 criteria. First, the challenge must be doable or it's not a challenge but an unavoidable constraint on player actions. Second, the reward has to be worth the effort when compared to the option of NOT doing the challenge or there's no incentive for players to attempt the challenge. Challenges that nobody takes up are a complete waste of game designer effort.

The reward for interplanetary aerocapturing is merely a reduction in the dV required for the trip. And that just means you can do the trip with a smaller, simpler, cheaper ship compared to not aerocapturing. This really isn't that huge of a reward, which means that any solution to interplanetary aerocapture that adds much to ship/mission size, complexity, and expense will significantly eat into or exceed the benefits, especially when compared to the baseline "MOAR fuel" option. IOW, from an effort/cost-to-reward POV, the options of building a monster heat shield or setting up the whole ore-mining infrastructure really aren't valid solutions.

This means that for interplanetary aerocapture to be a worthwhile gameplay challenge, it must fairly easy. IOW, something you can't ignore but which still doesn't require a huge effort to solve. The higher the effort required to achieve it, the more attractive the option of ignoring the challenge entirely becomes, either via "MOAR fuel", just turning heat off completely, or using some mod/hack/exploit that simply negates the heat.

It was this thinking that led me to use 20% reentry heat. Any higher and "MOAR fuel" wins, so there's no challenge. Any lower and there's not enough heat to be challenging at all.

I admit, 20% compared to 100% doesn't sound like much, but I submit that this is an artifact of trying to force a system designed for real life into the totally different KSP universe. Simply recalibrating the scale of the GUI reentry heat slider, so that today's 20% becomes the new 100%, would solve that problem.

Edited June 29, 2015 by Geschosskopf

[Jouni]

You can't plan such a trajectory with the limited simulation model KSP provides (it would be very hard at least). You'd need a 'true' n-body simulation. Even then you'd need the know-how and mathematical planning necessary to design such complex trajectories. Even if you'd have all that you'd still probably have to wait years or even decades of in game time for a launch window.

Complex gravity assist sequences are entirely possible in KSP. You don't have to be as precise as in the real world, because launches are cheap and the solar system is small. Some players have even mastered them while playing 100% stock.

The reason why we don't have proper mission planning software in the stock game is that the development team is too small for such a complex game. Unfortunately, it Squad hired more developers, it would just delay the development until the new guys are up to the speed. To be of any real use, those new developers should have been hired a couple of years ago at the latest, but there was probably not enough money for it.

Fortunately KSP is quite mod-friendly, and we have a huge pile of mods, with at least an order of magnitude more developer resources than the stock game. Most of the features one would want have already been implemented at least once.

Right now you can't really do interplanetary missions via aerobraking. Worse you can't really do an interplanetary return to Kerbin via aerobraking. So you'll either have to haul huge rockets with insane delta v budgets through interplanetary space (space truckin') meaning that you'll spend more time assembling your mission in orbit over Kerbin than actually doing it.

I've found that the delta-v budgets for interplanetary missions are quite similar in 1.0.4 as they used to be in 0.90. You need less delta-v to reach orbit and more delta-v after interplanetary transfers. While typical rockets used to have a 15% payload fraction, simple designs now lift over 20% of the launch mass, and interplanetary ships can be correspondingly bigger.

I also don't really understand why Squad assigns its limited development time and budget to implement a feature only a vocal minority claims is needed. Especially when there is already a mod that does the same.

It's not about a vocal minority or a vocal majority, but about the original concept. The idea has always been to make realistic spaceflight games more accessible than Orbiter. For every major feature Orbiter has, this involves trying to figure out whether something similar can be implemented in a way that adds interesting gameplay, but does not add unnecessary complexity to the game or drown the player in excessive details. For a long time, Squad was sceptical whether reentry heating could be implemented in such a way. The success of DRE ultimately convinced them, and they've been tweaking the amount of heating since then.

[1of6Billion]

Ah, that's why my Jool mission keeps exploding as soon as the craft hits the atmosphere........

Poor Bill c.s.

[clivman]

I use a mix of light aerocapture and burns

[ShadowZone]

1.0.4 got me to learn gravity-assisting. I was kinda' always aware of this technique, but I never knew it's so effective and easy. That and careful, slow aerobraking lets me to expect more spare dV than I ever had in previous versions. I'm having great fun: SSTOs orbit easier, going interpalnetary needs a different kind of approach, but I wouldn't say it's harder.

could you maybe expand on that? I find it difficult to get gravity assists. Usually they happen totally random to me.

[Dr Farnsworth]

Has anyone noticed the gigantor XL solar array's not withstanding aerobreaking/ aerocapture very well, or maybe I should say not withstanding aerobreaking/ aerocapture at all.

[Yakuzi]

"N/A: I never leave Kerbin so the question doesn't apply to me."*

*At least until the indecisosphere get's resolved.

[regex]

could you maybe expand on that? I find it difficult to get gravity assists. Usually they happen totally random to me.

The most common one I know of is using Tylo to get into a stable Jool orbit.