Jool-To-Orbit Spacecraft - is it possible?

[Der Anfang]

Obviously, you can't really "land" on Jool per se, but I am more asking whether it is possible to descend below 2 km with a rocket of sorts, then fire up those engines and get back into orbit? I have a feeling it would be quite similar to Eve, but not as much gravity. Yet, Jool is pretty much similar to our Earth in terms of physics and size, so you would need one hell of a rocket to achieve at least 7km/s(?), which means it would likely be much harder than Eve in terms of ultimate speed. If not 2 km, because I am still not entirely sure how TWR would be affection on engines that deep into Jool's atmosphere, so I think the better question would be: How low can you go before you lose your opportunity to get back into orbit with a properly designed rocket? What would you need?

Edited February 28, 2016 by Der Anfang

[Guest]

10km/s IIRC

Edited February 28, 2016 by Guest

[Borsek]

possible, but you would probably have an easier time getting out of system than into orbit

[robopilot99]

Found a link to a guy that says he made One. He doesn't say so in the post but he does state so if you scroll down a bit. I also recall hearing the Wackjob created one as well.

Edited February 28, 2016 by robopilot99

[Piper]

It's definitely possible, you just need a really big rocket, but the real trick is getting that rocket to Jool, entering the atmosphere, and doing it in one piece.

It's something I've always wanted to accomplish, or at least enter Jool's atmosphere and descend to an altitude that I can fly around a bit, and then return to orbit and dock with a return vessel.  But while I've built a space plane that should in theory be able to return to Jool orbit from its upper atmosphere, I've never been able to solve the reentry problem with such a massive spaceplane.  The heatshields would ablate and explode before even a fraction of the ship's orbital velocity had decreased, and that was from a very low circular orbit.  Now, the last time I tried, it was in 1.0.  From what I understand, the settings for Jool's atmosphere has since changed, making it somewhat easier to enter the atmosphere, so I should try again.  But even if and when I solve that problem, I still will have to get the whole thing to Jool, but I'm less worried about that, as it wouldn't be the first time I've had to get something massive into orbit.

 

[Snark]

Not a direct answer to your question... but if you do end up taking the trouble to build something that can go down to Jool, fly around, and get back up, might be nice if there were some places to fly around to.

Just sayin'. 

[Deadpangod3]

Someone did such a thing once, went down to like 0 meters and returned to orbit with a giant rocket, dont remember where i saw it though.

[Geschosskopf]

19 hours ago, Der Anfang said:

Obviously, you can't really "land" on Jool per se, but I am more asking whether it is possible to descend below 2 km with a rocket of sorts, then fire up those engines and get back into orbit? I have a feeling it would be quite similar to Eve, but not as much gravity. Yet, Jool is pretty much similar to our Earth in terms of physics and size, so you would need one hell of a rocket to achieve at least 7km/s(?), which means it would likely be much harder than Eve in terms of ultimate speed. If not 2 km, because I am still not entirely sure how TWR would be affection on engines that deep into Jool's atmosphere, so I think the better question would be: How low can you go before you lose your opportunity to get back into orbit with a properly designed rocket? What would you need?

I have dropped a probe into Jool in 1.0.5.  It's towards the end of this post.  So I can provide some intel.

First off, probably to wall of the horrible Kraken effects that used to happen on the actual surface, the surface collider is now at 240m altitude.  That's as low  as you can go these days.  If you freefall all the way there starting from a 1Mm Ap orbit set for a 100km Pe, you will be moving 125m/s when you hit this invisible wall.  However, conventional heatshields are all you need to protect fuel tanks---protruding parts and engines survive just fine.  It doesn't get nearly as hot as when landing on Eve.  The flames stop at about 125km.

As to getting back up again....  I would use a nuclear thermal jet engine and wings as much as possible, the advantage being you don't need any fuel at all for this part of the ascent.  Then drop all that when it hits its ceiling and go the rest of the way on aerospikes.

[KerbonautInTraining]

Not my video

This was made in pre-1.0. To do it now you'd need an even bigger, actually aerodynamic rocket that can aerobrake without exploding.

 

[Brainlord Mesomorph]

I was thinking of this in 0.25

You can experiment with designs on Kerbin by simply lofting the craft to LKO, reentering down to 2 km and seeing if you can make orbit again.

One of the biggest problems is that you have so much downward velocity that you have to cancel out before you even budge upwards. And without O2, you're going to need a lot of LFO. Wings helps with the first problem, multi-staging with th second,

So you end up with something like a Saturn V with wings,

(but you can get all the science on a fly-by or could in 0.25)

Edited February 29, 2016 by Brainlord Mesomorph

[Mastikator]

The atmosphere at 0 height in Jool is 15 times that of Kerbin sea level. Also 3 times as much as Eve sea level.

So even with only 0.8g surface gravity I'm doubtful that any thruster can even achieve > 1 TWR.

 

Edit- Just did a test. The Aerospike ISP at 1000m Jool is 98s, thrust of 50kN. Only by using empty fuel tanks and infinite fuel cheat am I able to get 2 sTWR.

So to answer your question, what you need is cheats. It's impossible in stock without cheats, there's no engine that has TWR > 1 WITH enough fuel.

Second edit- Correction, the Aerospike has enough thrust to get 1.4 TWR on the 4.6 ton rocket. The main problem is that you won't be going any faster than 400m/s until you get very very far up. So you need to sustain 400m/s for about 90km using super high TWR atmospheric thrusters and THEN once you're out of the atmosphere THEN you can finally begin to actually build up speed.

Edited February 29, 2016 by Mastikator

[Der Anfang]

2 hours ago, Mastikator said:

2 hours ago, Mastikator said:

The atmosphere at 0 height in Jool is 15 times that of Kerbin sea level. Also 3 times as much as Eve sea level.

So even with only 0.8g surface gravity I'm doubtful that any thruster can even achieve > 1 TWR.

 

Edit- Just did a test. The Aerospike ISP at 1000m Jool is 98s, thrust of 50kN. Only by using empty fuel tanks and infinite fuel cheat am I able to get 2 sTWR.

So to answer your question, what you need is cheats. It's impossible in stock without cheats, there's no engine that has TWR > 1 WITH enough fuel.

Second edit- Correction, the Aerospike has enough thrust to get 1.4 TWR on the 4.6 ton rocket. The main problem is that you won't be going any faster than 400m/s until you get very very far up. So you need to sustain 400m/s for about 90km using super high TWR atmospheric thrusters and THEN once you're out of the atmosphere THEN you can finally begin to actually build up speed.

So, basically my assumptions were correct. Have tested out how low you could go for any meaningful TWR? I certainly wasn't thinking that 0 metres (or "sea" level) would at all be viable.

3 hours ago, KerbonautInTraining said:

Not my video

This was made in pre-1.0. To do it now you'd need an even bigger, actually aerodynamic rocket that can aerobrake without exploding.

 

Yes, I remember seeing that video actually. The whole reason why I asked this question is mainly now due to the atmospheric ISP involved with 1.0.X.

 

[Mastikator]

The Aerospike had about 200 ISP at the 10km mark. With the tiny FT400 fuel tank and a command pod that was a little over 2 TWR. I only tested that part of the atmosphere with full fuel and infinite fuel cheat. You get to Kerbin Sea level atmospheric pressure at the 90km mark, so you're gonna have to use thrusters like the Mammoth pretty much all the way and they'll get 200-250 ISP.

Can you get TWR greater than 1? Sure

Can you get a rocket that sustains 400m/s -> 800m/s for 80km of soupy atmosphere with 200ISP rockets and then once you're outside then reach 6000m/s. It would take about 3-4 minutes just to leave the atmosphere, by then you will have lost 1500m/s d-v to gravity and probably 2000m/s d-v to drag.

You basically need 14000m/s d-v on a rocket that has 200 ISP and has about half thrust compared to Kerbin. That rocket in the video would not be able to get into orbit, it could probably escape the atmosphere though.

[magnemoe]

I went down to Jool ground level and out in stock back before 1.0. 
In 1.0x the killer is that pressure kills trust and that this scales past one bar. Back before 1.0 it did not scaled below one bar as I remember.

This rocket was able to return to orbit in .91 with kerbal on seat.

Rocket at launch, notice the mainsails on radial mounts 

Because of the aerospikes the accent stage is launced upside down with LV-N transfer stage pointing down. 

Has just looked at Jool accent in 1.0x, at sea level only the aerospike has any dV at all according to mechjeb. 
Its theoretical possible, you would need an giant pancake to have any chance at all, say its as plausible as building an blackpowder rocket able to reach orbit. 

[KerikBalm]

On 2/29/2016 at 3:07 AM, Piper said:

It's definitely possible, you just need a really big rocket, but the real trick is getting that rocket to Jool, entering the atmosphere, and doing it in one piece.

Well, I wasn't willing to say its definitely possible due to the TWR issues.

I ran into a similar issue here:

 

Using the mod that moves the KSC to Duna... it causes some atmosphere issues. The Atmosphere of duna gets treated as 1 atm for Isp calculations for some reason (even though pressure readings and drag and lift act as if it is 1/15th of 1 atmosphere).

Kerbin's atmosphere acted like it was at 15 atmospheres, and Eves as if it was at 60 atmospheres. It was impossible to get anything (stock) with a TWR greater than 1 at the surface of Eve, even on the tallest mountains, with empty tanks and the infinite fuel cheat.

It wasn't even *close* to 1:1 TWR.... I'm talking aerospikes and mammoths producing less than 1 kN of thrust...

So Jool's 15 atmospheres? ok... people here tell me you can get better than 1:1... but with an Isp of under 100s, an abysmal TWR, the rocket equation means that the rocket needed would be so big, and so flat, that I doubt its possible on any computer on Earth. The game would crash before you've got a rocket that could ascend from that low... and then the prospect of getting that rocket to kerbin orbit, and then to Jool? nope, I say its definitely impossible wouthout cheats or non-stock parts (such as an air augmented rocket, or a nuclear thermal turbojet)