How fast would I need to be going to aerocapture at Kerbin with my trajectory going 1 kilometer over the ocean?

[JacobJHC]

If I were to set my periapsis at 1000 meters and aerocapture into orbit how fast would I need to go? I am just curious how fast it would be and if anybody knows how to calculate such a question? (also this is using only a landercan and an inflatable heat shield 10 meters wide).

Seriously a piece of cake to anyone who can figure this out.

[munlander1]

On kerbin? I think you would burn up before you got close to 1,000 meters.  You trying something similar to what Scott  Manley did?

[0111narwhalz]

I think the correct answer is "many fasts." 

More seriously, the answer depends on the angle of attack. Obviously, pointing the nose directly into the airstream exposes the largest cross-section to air, which should slow it down severely. Conversely, if you orient edge-on, the vessel is thin and slightly more sharp-edged. To further complicate things, intermediate values will give you lifting-body effects, which would potentially prevent the vessel from ever reaching 1km, and instead "skipping" off the atmosphere.

It would seem that the proper way to do this is via experiment, since aerodynamics make my head go boom.

[JacobJHC]

1 hour ago, munlander1 said:

On kerbin? I think you would burn up before you got close to 1,000 meters.  You trying something similar to what Scott  Manley did?

Assuming that this wasn't an issue

[munlander1]

I might run something like this is ksp tomorrow. (Too late to do much) But the thing is, the faster you go the more you slow down. 

[kerbiloid]

At 1 km above the ocean you are already aerocaptured. In one piece or not.

Edited February 5, 2017 by kerbiloid

[natsirt721]

It probably isn't possible.  Drag increases with the square of the velocity, so it is likely that at the sorts of drags experienced on an escaping body at 1km no (sub-relativistic) speed is sufficient to clear the atmosphere.  There is an old aerobrake calculator here that can probably be reverse-engineered to acquire a solution, although it might use valid equations - it was accurate before the atmospheric revamp.  @alterbaron do you think that is doable?

Edited February 5, 2017 by natsirt721

[mikegarrison]

You can never aerocapture into a stable orbit. No matter how fast or slow you are going, no matter how deep into the atmosphere you go, you can never end up with a periapsis that is out of the atmosphere.

[0111narwhalz]

Just now, mikegarrison said:

You can never aerocapture into a stable orbit. No matter how fast or slow you are going, no matter how deep into the atmosphere you go, you can never end up with a periapsis that is out of the atmosphere.

I don't think that's part of the question here.

[tomf]

The trajectories mod can do the calculations you want. I would use that, hyperedit and a sandbox to get the answer. Put the craft into a hyperbolic orbit with the required PE then plan a maneuver that gives you enough velocity to leave the atmosphere while preserving your PE.

[munlander1]

46 minutes ago, tomf said:

The trajectories mod can do the calculations you want. I would use that, hyperedit and a sandbox to get the answer. Put the craft into a hyperbolic orbit with the required PE then plan a maneuver that gives you enough velocity to leave the atmosphere while preserving your PE.

I would also turn off air resistance heating with the mod+f12 cheat.  

Edited February 7, 2017 by munlander1

[YNM]

Lets be honest : I have no idea on the question.

- Before the aerobrake/capture, are you already in stable (ie. not changing SOIs and is either elliptical or circular) orbit around the body you'll execute it on ?

- If you happen to really mean aerocapture here (say, returning from soo far away, tens of times Jool distance), what Ap are you expecting ? At the farthest reach of the SOI ?

I'm not sure, but the planned Pe will differ from the lowest point where you'll go during the capture (risk of lithobraking). As the trajectory starts out as hyperbolic this would be a nuts question - there can be infinitely many combination which works. Also, is it aerodynamic ?

Edited February 7, 2017 by YNM

[magnemoe]

An problem here who YNM points out is that actual lowest point will be lower than 1 km. 
On the other hand, you will still be going at kerbin escape speed at Pe since you will brake afterwards too so that effect will be pretty low. 

Two factors for ship it need to keep drag low and it has to be heavy as an large mass is harder to slow down:
Use an arrow of large ore tanks, some fins to keep it pointed the correct way, make back streamlined too. 
You will need to move at high solar escape speed unless ship is unrealistic heavy. 

[munlander1]

I would also use the orbit cheat and download mechjeb to execute the burn to put you where you want to go.

[0111narwhalz]

On 2/4/2017 at 6:54 PM, JacobJHC said:

(also this is using only a landercan and an inflatable heat shield 10 meters wide).

We have a ship.

With less mass, you just need more velocity. I think you could get away with slightly less velocity if you oriented the heatshield to maximize lifting body effects.

What's the length of a chord through a 670km circle that is tangent to a concentric 601km circle? We can place an upper bound on the velocity by fifty times that per second-- if you come at it that fast, you will phase straight through the atmosphere, spending at most one frame in it. We can all agree that one from will not remove enough excess to capture, so this is the fastest possible.

Edit: I got 296km, for a maximum bound of 14807m/s. Check my math?

Edited February 8, 2017 by 0111narwhalz
MATH