Regarding Jool's atmosphere...

[ShadowZone]

So, has anyone of you have managed to successfully use Jool's atmosphere to capture your interplanetary ship in an orbit around the big green giant?

I have tried many times yesterday with my current design for a deep space exploration vehicle (250 tons). Suffice to say, I failed... hard...

I was NOT using heat shields and the probably would not have helped, since one of the parts that exploded first was smack in the middle of the spacecraft - a Mk3>2.5m adapter, facing the direction of flight with the Mk3 edge first (apparently that caught a lot of Jool's atmosphere - I had 2.5m parts connected directly to the Mk3 side of it - I thought it looked cool...

Maybe it was the velocity or angle? Maybe the Periapsis height?

I had an orbit of 900.000.000 Ap and 190.000 Pe - entered the Atmosphere at 8000m/s

After many many fails I hyperedited myself into Jool's orbit and set the orbit to an extreme eccentricity to have the maximum possible stress on the vehicle... that was the reason for this weird orbit.

So, what are your experiences with Jool's atmosphere? Have you managed to use it to shave dV off your capture burn?

Suffice to say after my plight of yesterday, I do not think the current aero model is too forgiving for reentry

[Geschosskopf]

Hmm, I'm wondering where you got the 8000m/s velocity if you were already in a closed orbit around Jool (as in, an Ap existed). That's considerably higher than escape velocity. I've done several Jool transfers in 1.0.2 and have never come close to going that fast even on the initial pass into the system prior to capturing.

Prior to 1.0.2, Jool aerocaptures were rather exciting due to their duration. You had to come in somewhere around 150-170km and spend a long time enveloped in harmless flames. In 1.0.2, however, I find Jool aerobraking rather boring. About 185-190km is all you need, you're barely scratching the surface, and you're not in the air long enough to get hot enough to worry about even without a heat shield.

Of course, a lot depends on the cleanliness of your transfer out to Jool. If you intercept Jool at a large angle to its orbital path, then you'll have a higher velocity relative to Jool so will need to dig deeper, burning longer and hotter. OTOH, if you arrive at Jool nearly parallel to it's path, then you have low relative velocity and an inconsequential aerocapture.

[Deadpangod3]

odd, i had someone tell me you dont even need a heatshield in jools atmosphere, since youd be going fast enough that youd be losing heat as fast as you gain it.

[magnemoe]

Hmm, I'm wondering where you got the 8000m/s velocity if you were already in a closed orbit around Jool (as in, an Ap existed). That's considerably higher than escape velocity. I've done several Jool transfers in 1.0.2 and have never come close to going that fast even on the initial pass into the system prior to capturing.

Prior to 1.0.2, Jool aerocaptures were rather exciting due to their duration. You had to come in somewhere around 150-170km and spend a long time enveloped in harmless flames. In 1.0.2, however, I find Jool aerobraking rather boring. About 185-190km is all you need, you're barely scratching the surface, and you're not in the air long enough to get hot enough to worry about even without a heat shield.

Of course, a lot depends on the cleanliness of your transfer out to Jool. If you intercept Jool at a large angle to its orbital path, then you'll have a higher velocity relative to Jool so will need to dig deeper, burning longer and hotter. OTOH, if you arrive at Jool nearly parallel to it's path, then you have low relative velocity and an inconsequential aerocapture.

Makes sense, the only issue would be that you build up plenty of speed dropping down Jool gravity well.

Also if you come inn fast, say you burn 4 km/s to get to Jool you might come in very fast, I came in on Eve at 3.8 km/s, used 1/3 of my heatshield, worse was that the probe landing legs on the back burned up and this caused the probe to flip, luckily I was almost done with the aerobrake so then I told it to fly engine first it went well.

[Jonboy]

For my ships I found I have to come in a bit higher that 190 km. In the old aero, it seemed you had a fairly large margin of error when it came to aerobraking. With the testing I've done in 1.0.2, it seems that the margin is much smaller, especially when dealing with Jool. I try to just barely dip into the atmosphere, somewhere between 195km and 197km seemed to be the sweet spot.

Edit: This is coming in from an interplanetary transfer with a speed of ~8000 m/s.

[Gargamel]

I "successfully" aerobroke (braked? hmmm...) in Jools atmo using a very heavy probe. Came in over 8500 m/s and entered at 195k alt. I did use mechjeb to help estimate the resulting orbit.

But the reason I put "successfully" in quotes is that it caused an acceleration bug. Maybe it's some element of gameplay I'm not aware of, such as a heating issue (ie the Voyager (Pioneer?) anomaly where the generator's heat output was causing a very very tiny, but noticeable acceleration). After I entered the atmosphere, it wouldn't let me timewarp, saying I was under acceleration. Even after leaving atmo, the acceleration continued. I had a 'stable' orbit, minus the kraken, but since I couldn't timewarp, I didn't feel like waiting 80 days to see if it would go away, and with the accel, it probably would have knocked me out of orbit.

So I just reverted, many times, to a quicksave, and after the slingshot around jool, it's now on a 300 year looping orbit. It's still got 4500 dv left after a mun, minmus, Duna, Jool tour(13 ion engines with 16 generators and a few solar panels), so I may do something with it eventually.

[Wiseman]

I've had pretty much the same experience as the other posters in the thread so far. I'm currently working on a large Jool operation with many ships and resupply vessels coming in every few years, and the first step is usually to either swing by Tylo for some free gravity-assisted slowdown, or a 190-195km aerobrake pass around Jool to get an apoapsis near Jool's moons. It looks harrowing, but checking the thermal colors after I left the atmosphere, my ship was cool as a cucumber. No heatshield, just used a Rhino to face the airstream, and it didn't change colors at all in the thermal overlay.

Edit:

But the reason I put "successfully" in quotes is that it caused an acceleration bug... snip

I've had the same issue. It only seems to happen around Jool, too - I had to quicksave, load, and then dive to the space center and time-warp a few hundred kilometers away to get it to stop doing that.

Edited May 29, 2015 by Wiseman

[NecroBones]

I "successfully" aerobroke (braked? hmmm...) in Jools atmo using a very heavy probe. Came in over 8500 m/s and entered at 195k alt. I did use mechjeb to help estimate the resulting orbit.

But the reason I put "successfully" in quotes is that it caused an acceleration bug. Maybe it's some element of gameplay I'm not aware of, such as a heating issue (ie the Voyager (Pioneer?) anomaly where the generator's heat output was causing a very very tiny, but noticeable acceleration). After I entered the atmosphere, it wouldn't let me timewarp, saying I was under acceleration. Even after leaving atmo, the acceleration continued. I had a 'stable' orbit, minus the kraken, but since I couldn't timewarp, I didn't feel like waiting 80 days to see if it would go away, and with the accel, it probably would have knocked me out of orbit.

So I just reverted, many times, to a quicksave, and after the slingshot around jool, it's now on a 300 year looping orbit. It's still got 4500 dv left after a mun, minmus, Duna, Jool tour(13 ion engines with 16 generators and a few solar panels), so I may do something with it eventually.

Anomalous acceleration is an old bug. It usually is applied to the command pod (root part, maybe?), and until you exit the game and come back in, it'll keep happening. If it's a hard enough acceleration, it may rip your vehicle apart. It usually hits when you use timewarp after exiting an atmosphere, in my experience.

[yorshee]

I've had the same issue. It only seems to happen around Jool, too - I had to quicksave, load, and then dive to the space center and time-warp a few hundred kilometers away to get it to stop doing that.

That happens to me sometimes. It lets me timewarp again once I get to an altitude of 1000km.

...Back to the actual topic of this thread: 195km is the best Jool aerocapture altitude for me, though I haven't tried it without a heatshield or fairings. I'm too paranoid of stuff exploding. D:

[moogoob]

No heatshield, just used a Rhino to face the airstream, and it didn't change colors at all in the thermal overlay.

No idea if Squad has any intentions to change this, but using engines as impromptu heat shields is easily my saviour of early career mode. They're heavy so bring the centre of mass in their direction (IE you fall engine-first), they're heat-resistant because they use, you know, FIRE, and they have high drag facing backwards which is great to reduce the amount of time you spend in the heat zone.

[martinborgen]

No idea if Squad has any intentions to change this, but using engines as impromptu heat shields is easily my saviour of early career mode. They're heavy so bring the centre of mass in their direction (IE you fall engine-first), they're heat-resistant because they use, you know, FIRE, and they have high drag facing backwards which is great to reduce the amount of time you spend in the heat zone.

Bern there, done that. I think the reason this wouldn't work IRL is because the engines are cooled by the cryogenic rocket fuel. A running engine however!

[OhioBob]

Bern there, done that. I think the reason this wouldn't work IRL is because the engines are cooled by the cryogenic rocket fuel. A running engine however!

It is usually only the big pump-fed engines used in launch vehicles that use regenerative cooling. Many spacecraft engines use ablative cooling. This is a very common practice with pressure-fed hypergolic systems. Some very small engines even use radiation cooling.

[kellen]

I think,the solution found by the calculator is in the form of an orbital maneuver. Point your craft at the angle given by the calculator and thrust until the orbit periphrasis matches that given by the solution. Your orbital velocity should not significantly change.

Thanks,

http://en.wikipedia.org/wiki/Essay