Laythe in 1.0.4

[Anglave]

I'm an old timer. I play stock except for KER. I played many older versions of the game, and then I played 1.0.2 enough to get used to the new aero. I'm not having a problem with rocket flipping or new ascent profiles.

I downloaded 1.0.4 and decided to start a sandbox game because I played through Career in 1.0.2 and I don't see much reason to do so again. Decided to design a Laythe land-and-return mission. My first Laythe land-and-return was in about 0.19, so I've done this before.

No problems with Kerbin ascent or interplanetary transfer. Planning to aerobrake at Jool, but I know they've fiddled with the aero and the heating, so I brought nearly 2k ÃŽâ€v extra, just in case.

Good thing I've got the extra budget, because I found that even looking at Jool's atmo at interplanetary transfer speeds is instant death. I know the atmosphere runs out to 200k. I'm aiming at 195k periapsis, and burning up about a second after touching the atmosphere, at about 199,800m.

Tried burning to slow down before atmospheric contact, and found that it didn't make enough difference. Wound up plotting a Flyby of Jool (no atmospheric contact), leading to a Laythe encounter, burning all but the last few drops of fuel to slow down enough, and managing aerocapture at Laythe.

Aside -- this current heating / drag model makes interplanetary application of aerobraking all but completely useless. The game says Jool has no atmosphere (none, nada, zilch) above 200km. But at 199.8km, so much that I'm fried to a crisp in under a second. Yet friction with atmosphere at that altitude wouldn't even begin to slow me down below escape velocity. Is aerobraking just not a thing we do anymore?

Anyway, was able to land on Laythe, with the lander being entirely undamaged and on-budget for the mission. It's packing ~2800ÃŽâ€v and ~1.3 TWR on Laythe (atmospheric asl) according to KER.

I plant my flag, get back in, and blast off. Only to find that I'm way WAY short of making orbit. My next stage (intended for Hohmann transfer back to Kerbin) doesn't have much TWR, but does have a bit of extra ÃŽâ€v in the budget, but I'm nowhere near close enough to orbit for the pitiful engine to make it.

I tried the launch multiple times, with multiple ascent profiles. I tried a full-speed straight up and turn. I tried a 5° auto-gravity-turn slant. I tried keeping my speed lower for longer. Nothing I could do got anywhere close to orbit. My from-the-hip estimate is that I'm at least 1k ÃŽâ€v short, probably more like 1,500 or 2k short. I get up to a 50km parabola and run out of fuel just as I'm turning to circularize.

I went back and checked, both in flight mode and in the VAB, and KER says I have just over 2800ÃŽâ€v (atmospheric) on Laythe.

Now, my lander craft isn't particularly aerodynamic. It's not a brick, but it's short and wide (as a lander should be). It's got landing legs and fuel lines and about a dozen struts.

I guess my question is, is this a problem with KER, or am I really 1,000 or more ÃŽâ€v short because of aerodynamic drag? Did they change Laythe's atmosphere in a recent update that's not reflected on the Wiki? It seems to be really thick for a really long time, on ascent. Did the new aero values in 1.0.4 make Laythe require significantly more ÃŽâ€v for surface-to-orbit, or throw off KER's calculations somehow?

Here's my craft. That's the whole mission, not just the lander in question, but it should be easy enough to pull out. It's the four stages with ~1.3 TWR on Laythe, at sea level.

Is it just me, or does Laythe now take more like 4k ÃŽâ€v surface-to-orbit?

Edited June 30, 2015 by Anglave

[Captain Sierra]

-snip-

I don't immediately have access to KSP right now so downloading your craft isnt gonna help much. You can either wait for someone else, wait about an hour at which point I can load and see your craft, or throw up some screenies real quick if you have them.

As for aerocapture, Jool is particularly brutal. The atmo gets thick fast and you're coming in a a very high velocity. Honestly a direct Laythe capture might be safer. Since i cannot see your ship, do you have a heat shield, how big, and you are entering retrograde, correct?

[Guest]

Is it just me, or does Laythe now take more like 4k ÃŽâ€v surface-to-orbit?

Older delta-V maps show Laythe requiring 3.2km/s to orbit. At a minimum it should require more than Tylo orbit. Considering Kerbin ascent takes me roughly 3.5km/s, I would say you should need at least 3km/s for Laythe.

[Anglave]

I don't immediately have access to KSP right now so downloading your craft isnt gonna help much. You can either wait for someone else, wait about an hour at which point I can load and see your craft, or throw up some screenies real quick if you have them.

Since i cannot see your ship, do you have a heat shield, how big, and you are entering retrograde, correct?

I'm entering retrograde, correct, though it doesn't seem to make much difference as I get total annihilation of everything in under a second.

No, I didn't bring a heat shield. Which I concede may make a difference.

However, 1) it doesn't fit into my design well, especially as there's no aerodynamic occlusion of physically overlapped (but not stack-connected) parts.

2) my issue with aerobraking under the current model is that in reality I could just aim higher at the atmosphere. If it's thick enough that I'm burning up, then there's a place higher that it'll still slow me down but I won't burn. However, in the game I can't brake at 210km, because the atmosphere STOPS at 200km. A heat shield might make my 190km maneuver more survivable (though I have my doubts), but it's not going to resolve this fundamental flaw, which the 1.0.4 changes make considerably more severe.

- - - Updated - - -

Older delta-V maps show Laythe requiring 3.2km/s to orbit. At a minimum it should require more than Tylo orbit. Considering Kerbin ascent takes me roughly 3.5km/s, I would say you should need at least 3km/s for Laythe.

Just how old is your "older" delta-V map? I've been using this one since 0.18, and it shows the same 2800ÃŽâ€v the Wiki lists. I realize values will have changed as of the new aero, but it was my understanding that generally speaking values have gone down. For example, Kerbin used to require 4500ÃŽâ€v, but now requires somewhat less, as you note.

- - - Updated - - -

Interestingly, this map (from the same era) does list the ÃŽâ€v requirement as 3400, which "feels" more like what I'm experiencing in-game. Why, then, do my normally trusty old map and the Wiki agree on the wrong number?

Edited June 30, 2015 by Anglave

[Guest]

Just how old is your "older" delta-V map?

Looks like the one I referenced had the values for Laythe and Tylo all messed up for some reason, whooops.

[mikegarrison]

Aside -- this current heating / drag model makes interplanetary application of aerobraking all but completely useless. The game says Jool has no atmosphere (none, nada, zilch) above 200km. But at 199.8km, so much that I'm fried to a crisp in under a second. Yet friction with atmosphere at that altitude wouldn't even begin to slow me down below escape velocity. Is aerobraking just not a thing we do anymore?

I agree that there is a mismatch in 1.04 between aerobraking and heat tolerance.

However, I want to point out that "friction" is not the cause of the heat (or much of the braking drag). The heat (and a lot of the drag) is caused by compression of the air (including the massive bow and aft shocks) rather than from friction.

- - - Updated - - -

my issue with aerobraking under the current model is that in reality I could just aim higher at the atmosphere. If it's thick enough that I'm burning up, then there's a place higher that it'll still slow me down but I won't burn.

Yes, Jool's atmosphere has always been something of a brick wall. The game doesn't really model the fact that real atmospheres extend out a loooong way, and this is especially true on Jool and Eve. I think they make the pressure at the cutoff height a fixed percentage of the pressure at sea level, and the pressure at "sea level" of Jool is very high.

[Geschosskopf]

Yes, Jool's atmosphere has always been something of a brick wall. The game doesn't really model the fact that real atmospheres extend out a loooong way, and this is especially true on Jool and Eve. I think they make the pressure at the cutoff height a fixed percentage of the pressure at sea level, and the pressure at "sea level" of Jool is very high.

Yeah, at least Jool's atmosphere (and prorbably Eve's, too) is lopped off at the shoulders by the arbitrarily imposed cap on atmosphere height. It would be nice if their atmosphere tops were raised to their pressure asymptotes. which seems to be the case at Kerbin. Either that or adjust their sea level pressures so the asymptotes are at the arbitrary caps. Without doing either of these, there's no thin, wispy, upper layers to aerocapture in. You to from vacuum to instant death, even at the shallowest of penetrations, which is rather silly.

[herbal space program]

Oy. I guess I'm going to have to consider this for my supposed Laythe-and-back SSTO mission....

[LittleBlueGaming]

I hadn't been to Jool yet, so just flew a mission there seeing what all the hubbub was about... sure enough, instant destruction. Kerbal physics

[NovaSilisko]

As I recall, the atmospheric falloff on Jool has been flawed for a long time. It doesn't fade out smoothly - there's a cutoff, for some reason. It's mostly manifesting itself as a more serious problem now due to reentry heat.

[kiwi1960]

What you are facing is real enough, its one reason why man has not been to Mars yet. If anything, given the time warp, KSP is too easy.

What you may have to do is what NASA might have to do, break the mission down into stages. Get a refueller there in orbit first, maybe even a drill to get fuel. NASA proposed sending a ship to Mars first with equipment that can extract fuel from the atmosphere, or soil, I forget which now.

Sending one ship there and back probably won't cut it. One refueller may not be enough. Either way, rather than just build and go, you are going to need to plan ahead. Each stage will need its own plan... stage 1, get there, stage 2, slow down, stage 3, land... etc etc... Getting there is easy... slowing down, harder. Crack that and you will OK.

Remember, if its too easy, its not worth doing, and you will probably get tired of KSP in no time flat.

You have a challenge... failure is not an option, nor is giving up... Tally ho!

[mikegarrison]

The difficulty of making sure you have enough delta-v for the return trip is part of the Mars problem, for sure. We've never even returned an unmanned probe from Mars, much less a manned expedition.

But the Jool aerobraking problem is just a KSP issue. (Real aerobraking at Jupiter would be a problem, but probably more due to radiation hazard and maybe Jupiter's rings rather than anything modeled in KSP.)

What you are facing is real enough, its one reason why man has not been to Mars yet. If anything, given the time warp, KSP is too easy.

What you may have to do is what NASA might have to do, break the mission down into stages. Get a refueller there in orbit first, maybe even a drill to get fuel. NASA proposed sending a ship to Mars first with equipment that can extract fuel from the atmosphere, or soil, I forget which now.

Sending one ship there and back probably won't cut it. One refueller may not be enough. Either way, rather than just build and go, you are going to need to plan ahead. Each stage will need its own plan... stage 1, get there, stage 2, slow down, stage 3, land... etc etc... Getting there is easy... slowing down, harder. Crack that and you will OK.

Remember, if its too easy, its not worth doing, and you will probably get tired of KSP in no time flat.

You have a challenge... failure is not an option, nor is giving up... Tally ho!

Edited July 1, 2015 by mikegarrison

[Mesklin]

Aerobreaking about Jupiter is not fantastic. It was happened at 1995 by Galileo probe, 47 km/s was arrival speed with strong g-force in 230G.

[mikegarrison]

Aerobreaking about Jupiter is not fantastic. It was happened at 1995 by Galileo probe, 47 km/s was arrival speed with strong g-force in 230G.

Right, but the Galileo probe is a lot less concerned about taking in a massive dose of deadly ionizing radiation than a human crew would be. 230G is also a bit much for humans. Fortunately for Kerbals, they seem to be completely immune to both radiation and acceleration.

[MalfunctionM1Ke]

This is my old Laythe Lander... I wonder how it would behave on it now

[KerikBalm]

I think you're better off aerobraking at laythe now.

When you drop your PE down to Jools atmosphere, you are going at least 8km/second... and heating follows a V^3 law IIRC.

If on the other hand, you time it so that you come in from behind laythe (not encountering it head on), your relative velocity will be much lower, and you should be able to get much more aerobraking in (not to mention, its atmosphere starts at a much much thinner value)

Other than that... I've heard people try to use tylo gravity assists to capture.

- - - Updated - - -

Also note that your lander is a pancake, and will have lots of aerodynamic losses (although this should be good for aerobraking it).

You should really include air breathing engines for laythe, and you should also note that the 48-7s is no longer such an awesome engine... consider skippers or T-1 aerospikes.

equal or better TWR, and better Isp.

[herbal space program]

I think you're better off aerobraking at laythe now.

When you drop your PE down to Jools atmosphere, you are going at least 8km/second... and heating follows a V^3 law IIRC.

If on the other hand, you time it so that you come in from behind laythe (not encountering it head on), your relative velocity will be much lower, and you should be able to get much more aerobraking in (not to mention, its atmosphere starts at a much much thinner value)

Other than that... I've heard people try to use tylo gravity assists to capture.

- - - Updated - - -

That's what I was thinking of doing, or rather I was thinking of trying to use Laythe as a pre-braking step to lower the speed at which I'm coming into Jool's atmosphere. I thought maybe that if I could drop my speed to the point where I'm close to getting captured by Jool, I would just barely need to touch Jool's atmosphere to finish the job, and wouldn't have to come in nearly as fast.

[Rosco P. Coltrane]

Also, don't overlook the idea of using Jool's moons to capture you without any kind of aero involved.

I avoided this for a long time thinking it would be too cumbersome, but now I'm doing it every time I go to Jool. With a little patience you can play with nodes before arriving or at Jool SOI and get your self a multi-moon assisted capture really easy. PreciseNode helps here, because, among many things, it allows you to increase the number of predicted orbits (+1 is what you need usually). Then, the only aero-capture you'll do is around Laythe and at a lot lower speed.

[Geschosskopf]

Also, don't overlook the idea of using Jool's moons to capture you without any kind of aero involved.

I avoided this for a long time thinking it would be too cumbersome, but now I'm doing it every time I go to Jool.....

This is the conclusion I've been unwillingly coming to myself. At any substantial level of reentry heat setting, Jool is often instantly fatal except for small things all wrapped up in fairings and heat shields. But at any heat setting low enough to survive Jool, everything else (except maybe Eve---ain't tried that yet in 1.0.4) might as well not have heat at all.

In my several recent test runs of banking off Tylo, it appears that if you can set it up prior to reaching Jool's SOI, you'll be a lot better off. That way, you can tweak your arrival time at Jool so Tylo's in the best place. If you wait until you enter Jool's SOI, then Tylo's position is pure luck of the draw. While it seems fairly certain that you'll always be able to hit it even then (maybe having to bank off another moon first), if Tylo's not in a good place, you'll have to do some bothersome burns to get back to where you want to be after you brake off it. I think the worst-case scenario for this would be in the neighborhood of 600-800m/s based on some observations of highly non-optimal arrangements, on top of what you normally bring with you. That includes flipping from a 120^ (as in retrograde and inclined) inclination to Jool after passing Tylo, which cost a bit less than 500m/s to finally get settled down at Laythe.

Expect to hit Laythe at anything from 3500-4500m/s whether you go straight into it from Kerbin or bank off Tylo. IOW, a speed in the range of coming home to Kerbin from Duna. But Laythe's atmosphere lacks a thin, wispy upper layer so the flames start pretty much instantly when you get into it.

[juanml82]

As I recall, the atmospheric falloff on Jool has been flawed for a long time. It doesn't fade out smoothly - there's a cutoff, for some reason. It's mostly manifesting itself as a more serious problem now due to reentry heat.

Is there a mod to fix it?

[NathanKell]

NovaSilisko: that's true as of 0.90, no longer true in 1.0 (for any atmosphere). Cutoff is gradual and there's no wall, it's just the slope is a bit too sharp on Jool (and perhaps elsewhere, but Jool is what I'm familiar with).

[Geschosskopf]

NovaSilisko: that's true as of 0.90, no longer true in 1.0 (for any atmosphere). Cutoff is gradual and there's no wall, it's just the slope is a bit too sharp on Jool (and perhaps elsewhere, but Jool is what I'm familiar with).

If there is no wall at other planets, then why do massive flames start the instant you touch them whereas at Kerbin you have to get halfway into in the atmosphere before there are any flames, and they build up gradually when they do appear? Even at Laythe you get instant flames, evne though its air is supposedly less dense than Kerbin's atmosphere, and you hit them both at similar speeds?

[NathanKell]

As I mentioned, the _slopes_ are too sharp, or rather, they start at too high a slope rather than starting flatter and curving upwards more as they should. That is, pressure increases too rapidly on Jool, and a bit too rapidly on Laythe. But unlike .90 where the atmosphere went from a pressure of zero to a pressure of 0.0001 kPa in no meters, 1.0 atmospheres don't have walls. They may have a fairly linear slope between 0 kPa at the atmosphere edge and 0.51kPa at 38km (Laythe), but it's still a slope, not a wall.

As for why you get flame effects: I suggest using mechjeb or KER or AeroGUI or something to measure density, and compare where you get a given density on Jool, on Kerbin, and on Laythe. A similar test would be to ensure you have exactly the same surface velocity in all cases, since that will eliminate the effect of velocity on the strength of the flames (the flames are proportional to the 0.75 power of density and the cube of velocity).

[Anglave]

Update since OP

I redesigned my craft, bringing more ÃŽâ€v and slightly higher TWR in the lander stage, and switching to LV-N on the interplanetary stage, so I could bring enough ÃŽâ€v to push the heavier lander, while retaining the same Kerbin lifter design. The interplanetary stage uses an LV-N / Poodle hybrid compromise between ÃŽâ€v and thrust. I realize a lower thrust (carrying less engine mass, just one pair of LV-N ideally) would be more efficient, but 20+ minute burns to get out of LKO are not acceptable. Even doing multiple periapsis kicks, you end up on escape trajectory with entirely too much burn time remaining, leading to much less efficient transfers.

After landing at Laythe, I did on-site tweak the aerospikes to 60% thrust limit, in order to provide more relative vectored thrust at lower throttle settings during ascent.

My mission was a success, completely ignoring aerocapture at Jool, and instead burning the engines to slow down and establish a survivable aerocapture encounter with Laythe.

The return portion of the mission (from Laythe surface back to Kerbin) worked flawlessly, and I confirm that it does take about 3400 ÃŽâ€v to get from Laythe surface to orbit. Shall we edit the Wiki? The ~2800 ÃŽâ€v number stated there will absolutely strand you.

Also, regarding aerobraking in 1.0.x, from a related thread:

Well, it seems to be as I predicted it would be. Tweaking [the game] to make reentry from LKO somewhat dangerous makes just barely touching a significant atmosphere at interplanetary speeds pretty much instant death. I blame density, which is significantly greater at higher altitudes than pre-1.0, and which the arbitrary caps placed on atmosphere heights exacerbates by lopping off the upper, thinner layers you'd normally be aerobraking in.

I'm thinking the only way to fix this is to run the atmospheric density curves out to their asymptotes and let that determine the heights of atmospheres, which I suspect will be GREATLY higher than they are now.

This is a clear and concise statement of my observations in 1.0.4 as well. Until this is addressed by fixing the heating math, or fixing the atmospheric density slopes, or raising the arbitrary atmospheric height caps, I plan to play with my heat setting at a much lower value. Reentry from Mun and LKO is already easy. Making it even easier doesn't concern me, but making aerobraking from interplanetary speeds even possible is of much greater interest to me.

Screenshots added:

Note that the lander stage looks much the same, but the (mostly cosmetic) adapter cones have been replaced by fuel containing cones.

Edited July 7, 2015 by Anglave
Screenshots Added

[Red Iron Crown]

I'm currently running a Laythe mission with an interplanetary spaceplane, and had planned a direct aerobrake at Laythe. Unfortunately, I could only choose between burning up and not capturing. So I used a Tylo slingshot to capture and set up an encounter with Laythe, then used that encounter as another slingshot to further reduce encounter speed before aerobraking for capture at Laythe on the next go round. Even then, it took multiple passes to lower to a near circular orbit.

I'm having the same problem on return to Kerbin, a direct aerobraking capture either burns up or fails to shed enough speed. I'm going to have to use the multiple slingshot technique again, I suspect.

Edit: A pic of slingshot shenanigans to capture at Jool and get the orbit down near Laythe's:

Edited July 8, 2015 by Red Iron Crown