Jool atmospheric craft

[steuben]

I'm trying to design a craft that can dip down into Jool's atmosphere, do Science!, and fly back up again.  Am I on the right track with this bird? And how low should I aim for?

 

Edited September 29, 2020 by steuben

[bewing]

I'm gonna be a complete downer here.

The problem is atmospheric density and heating. I've tried flying down into Jool's atmosphere once (as a one-way trip), and I was firmly convinced that it's completely impossible to come back up again if you go more than a few km down, or to take much in the way of science readings. The reason you can't climb back out is that the Isp of your engines goes to hell. The reason you can't take much in the way of readings is that all your science instruments will burn up if you expose them to the atmosphere at reentry speeds.

We all know that Eve is deadly, because of the high reentry speed, and the dense atmosphere. Jool's atmosphere starts out thin, but quickly gets more dense than Eve, and the reentry speed is even higher.

There's only one biome on Jool. And "in flight low" requires an altitude that's completely impossible to climb back from, because of Isp and drag -- and getting down there is what you would need to do to get a second set of science measurements.

So I'd basically say: the best you can do is go 1km into the atmosphere, maybe open a science bay, take all the readings you can, and then raise your Pe back above the atmosphere. And to do that you don't need wings. And you do need some actual heatshields.

 

[Guest]

I agree a lot with @bewing here...

But I think it's possible from surface if you where to have a staging aircraft. might take a while to find a good design but staging boosters or your propellers at a certain altitude could help a lot. Again, really the only way from surface to back without cheats or clipping is via staging. Although you might be able to prove many wrong if you every wanna try brad whistance/stratzenblitz level

[antipro]

how did you make that blueprint?

[Spricigo]

1 minute ago, antipro said:

how did you make that blueprint?

  Probably

[antipro]

2 hours ago, Spricigo said:

Probably

Thanks, searching on ckan I found 2 versions, I suppose is the KVV Continued , the other one isn't installable:
is it correct?

[Spricigo]

13 hours ago, steuben said:

And how low should I aim for?

Just bellow 120km. That is where the low atmosphere begin (or end ). 

 

 

10 hours ago, bewing said:

I'm gonna be a complete downer here.

The problem is atmospheric density and heating. I've tried flying down into Jool's atmosphere once (as a one-way trip), and I was firmly convinced that it's completely impossible to come back up again if you go more than a few km down, or to take much in the way of science readings.

 

10 hours ago, The Doodling Astronaut said:

I agree a lot with @bewing here...

Excuse me, but it really seemed a lot easier than that:

https://imgur.com/a/sSclDia#9y6uVYD 

 

13 hours ago, steuben said:

Am I on the right track with this bird?

Maybe you can figure out some way a 'bird' can work, but, after the experiment above, a streamlined  craft with lots of momentum and thermal capacity seems the way to go for me. (

 

[steuben]

My current blueprint kit is Kronal Vessel Viewer, Paint Shop Pro, Blogger Sans (for the font), a blueprint PNG i picked up somewheres on dem der intertubes thing.

As for the bird herself. right she's going to be tricky. As for the wings I'm going for style and cool. 

[jimmymcgoochie]

I’ve seen videos of some truly staggeringly complex vessels which were able to fly right down to mere centimetres above Jool’s death line at -250m, which used electric propellers, NERVs and ions to get back into orbit.
I just can’t see your design getting back into space, especially not with swivels/reliants for propulsion, if you go ‘low’ in Jool’s atmosphere; the delta-V requirements are too high and there’s a risk that it will burn up depending on your re-entry heat settings.
Your best bet is probably that diving rocket with a fairing to take the heat and a very elliptical flight path to avoid being dragged down by the, er drag. Ditch the wings as they just add unnecessary mass and unwanted drag.

 

[Fierce Wolf]

I once made a flying heat resistant blackbox with a minirocket to deliver the science, it kinda went sideways because of my sloppy solar panel placement (or lack thereof) in the minirocket. Still got some science and it didn't burn down!

[steuben]

I've tried a couple of drops down from 1500km to 180km. But every time I enter a flak-storm and "land" at about 183km. I climb back up to 250km  still landed and in a flak-storm. It's like I irritated some isolationist Joolian civilization. 

[Lt_Duckweed]

As long as you build a well optimized craft, just barely dipping bellow 120km and then going back to orbit isn't all that difficult.  Speed of sound is very high on Jool so heating isn't nearly as bad as you would expect, and 120km on Jool is the equivalent of about 8km on Kerbin so even Nervs will work reasonably well (and you should use nervs for the high delta v).

Basically you want minimal wing area so you can preserve as much speed as possible, use fairings as nosecones, and try to get town to 120km while still at 2000m/s or so, then ignite the nervs and burn back to orbit.

As a note, I say "not too difficult" but that presupposes already having a good grasp on aerodynamic flight.  I would recommend watching this tutorial:

 

I would say that once you understand the importance of wing incidence (explained in the video) and can get liquid fuel only sstos into kerbin orbit with several km/s left over you will be ready to tackle a Jool diver.

[king of nowhere]

22 hours ago, bewing said:

 

So I'd basically say: the best you can do is go 1km into the atmosphere, maybe open a science bay, take all the readings you can, and then raise your Pe back above the atmosphere. And to do that you don't need wings. And you do need some actual heatshields.

 

I have experimented this directly, and i can say for sure that you can indeed dip 2 km (but absolutely not 3) and do science in the high atmosphere with an orbiter. You can even get an EVA report, if you are fast enough to get it and put the astronaut back before he gets incinerated.

 

as for reaching low atmosphere, your best bet, when dealing with a thick atmosphere, is to use propellers. this way, the atmosphere becomes your friend. so you need thermal shielding to survive aerobraking, propellers to fly in the atmosphere, and rockets to get back into orbit. and given how much speed you need for jool orbit, you'll need nerv and/or ion propulsion. if you feel confident, you can try making a big project of it

[Spricigo]

19 minutes ago, king of nowhere said:

I have experimented this directly, and i can say for sure that you can indeed dip 2 km (but absolutely not 3) and do science in the high atmosphere with an orbiter.

C'mon! Why you still doubt if just a few post above I said i did it?* 

I already posted the album, but in case you missed, that is 80km deeper into Jools atmosphere:

No propellers, no engine firing, that is pure ballistic flight. Just breezing as if Jool atmosphere was nothing.

*For the record, that is with brute force (and not that much) to just get that specific task done. Kudos to @Lt_Duckweed for tackling the real challenge: 

Spoiler

 

 

 

 

 

 

 

[king of nowhere]

14 minutes ago, Spricigo said:

 

Quote

I have experimented this directly, and i can say for sure that you can indeed dip 2 km (but absolutely not 3) and do science in the high atmosphere with an orbiter.

C'mon! Why you still doubt if just a few post above I said i did it?* 

I already posted the album, but in case you missed, that is 80km deeper into Jools atmosphere:

 

ok, i should have been more specific:

you can dip 2 km, but not 3, with an orbiter that is not specifically designed for it.

i had an orbiter that was just designed for space operation, and i could dip it a couple km in the atmosphere without burning - barely. enough to get high atmosphere science and i could get achievement for atmospheric flight.

anything more requires a dedicated craft with dedicated solutions.

[bewing]

58 minutes ago, Spricigo said:

I already posted the album, but in case you missed, that is 80km deeper into Jools atmosphere:

Your album is missing an altimeter.

[FleshJeb]

I've gone to 85km and back out on a single stage with no heatshields or fairings. Heatshields and fairings have a high absolute temperature tolerance but they transfer heat extremely slowly, so once they're hot, you die.

The trick is radiating heat at a rate that allows you to survive.

Parts such as most nosecones, structural wings, control surfaces, and precoolers radiate heat at 95% perfect emissivity (default 60% for most parts), and they transfer it extremely quickly. (Big-S parts transfer heat at 1/2 the rate of structural wings, so if you use them, you usually die.) Some parts have extremely high insulative properties, such as service bays. In the example below, I have two service bays in a row. The front one is white hot.

Step 1: Transfer heat by chaining together parts with high heat transfer rate, and high radiative rate (see the individual part cfg files, and physics.cfg for defaults). The NCS adapter and small nose cone on my example below have multiple Type E structural wings attached and offset back. (There appears to be some heat occlusion going on when surface attaching, because some of the parts that are at the same level of the craft tree experience different heating depending on position.)

Step 2: Picking your flight path. Heat is radiated as a function of efficiency * (part temperature - ambient temperature) ^4.  (Stefan–Boltzmann law) Ambient temp makes a big difference (See the spoilered graph). We'll pick two cases, and ignore efficiency because it's the same in both cases: At 180 km, the ambient temperature is about 210K. A part at/near 2400K (most nosecones' max) is radiating heat proportional to (2400K - 200K)^4 = 2.3x10^13. At 120km, the ambient temp is about 140K. (2400K - 140K)^4 = 2.6x10^13. That's only 11% better, but heating is a process over time. Ambient space is 4K, so all your parts started at that temp. When they've heated up to 1200K, Being at 140K means you're radiating 31% more heat. Integrated over time, you can dump a lot more total energy the faster you get into the cold layer, rather than trying to bleed orbital speed in the hot layer. Cold is life.

 Jool atmo graph:

Spoiler

https://wiki.kerbalspaceprogram.com/wiki/File:Jool_Atmosphere_T%26P.png

In the example craft below, the main wings have angle of incidence. 1-3 degrees was good, 5 degrees resulted in them heating up too much and exploding. From low Jool orbit, I burnt 100m/s retrograde, flipped to prograde hold and upside down. The trajectory started flat, and rapidly transitioned to almost straight down. When I'd had enough of that, I flipped it right-side up, waited until past the periapsis, lit the Sparks and NERV, and powered out. In the process, it retained most of its orbital energy, and just redirected the direction of that energy (and the shape of the orbit) with the wings. It's very slippery, and presents a minimal cross-section to the atmosphere Aerodynamics is fuel AND life.

This run went to 110km and came back out:

This is the 85km run, and with a more robust design, I could definitely go lower:

https://imgur.com/R3pg9sz

There are certainly other ways to do this, but I had an enormous amount of fun, learned an amazing amount, and consider it the highlight of my KSP career.

[Spricigo]

10 minutes ago, bewing said:

Your album is missing an altimeter.

Fair point. I also noticed only now that the reports only says "flying at Jool" so, not that obvious that are reports from lower atmosphere (would be "flying high over" otherwise)

I'd argue that it looks much better without the many windows (PAWs, KER, KAC*)  I had open at the time.  Also, I don't want to  ruin the fun for people trying to figure the details by themselves.

 

Anyway: lower altitude 115.9km, higher atmospheric speed 8 334m/s, ~5min of atmospheric flight. The important bits of te craft are the fairings and what is inside, the tanks are mostly empty by the time of the dive and the engines not used util after reaching space again.

 

* @  past me:  Why KAC?!!