The Aerogravity Assist Challenge

[Lockheed X-17]

I did some skimming on Wikipedia one time and found this page about the Aerogravity assist. According to the Wikipedia entry;

"An aerogravity assist, or AGA, is a theoretical spacecraft maneuver designed to change velocity when arriving at a body with an atmosphere. A pure gravity assist uses only the gravity of a body to change the direction of the spacecraft trajectory. The change in direction is limited by the mass of the body, and how closely it can be approached. An aerogravity assist uses a closer approach to the planet, dipping into the atmosphere, so the spacecraft can also use aerodynamic lift with upside-down wings to augment gravity and further curve the trajectory. This enables the spacecraft to deflect through a larger angle, resulting in a higher delta-v (change in velocity). This in turn allows a shorter travel time, a larger payload fraction of the spacecraft, or a smaller spacecraft for a given payload.The related techniques of aerocapture, aerobraking, and atmospheric entry also attempt to use the body's atmosphere to help reduce propulsion requirements. In an aerogravity assist, however, the goal is not to use the atmosphere to slow the spacecraft down, but instead use it to achieve a larger change in direction.

Aerogravity assists, though proposed in theory, have not yet been used in practice." -https://en.wikipedia.org/wiki/Aerogravity_assist

So would there be a be a possible aerogravity assist, yay or nay?

(P.S. Post here what you did regarding about the techinque, if possible, bring photos)

[Wanderfound]

It's standard interplanetary spaceplane aerocapture technique. It's less "aerodynamically curve into orbit" and more "hold yourself down in the thick air until you've bled off enough speed", although that's ultimately much the same thing.

[More Boosters]

http://i1378.photobucket.com/albums/ah120/craigmotbey/Kerbal/Kerbodyne%2025/Kerbodyne%20Kosciuszko/screenshot164_zpse5493404.jpg

It's standard interplanetary spaceplane aerocapture technique. It's less "aerodynamically curve into orbit" and more "hold yourself down in the thick air until you've bled off enough speed", although that's ultimately much the same thing.

I think he means abusing lift so you don't lose as much vertical speed, and benefitting further from the Oberth Effect as you have a higher orbital velocity. So I believe he means the opposite of aerocapturing, he means to use the atmosphere to get an even better gravity assist.

As for the topic itself I'm not sure you can generate enough lift at don't-vaporize-instantly altitudes to offset the friction and benefit from the whole ordeal. Can you please provide proof that this is possible as to abide by the challenge creation rules?

Edited September 11, 2015 by More Boosters

[eurybaric]

I think the issue here is that atmospheres in KSP are rather small and cut off too fast. it's either you're in deep enough , losing speed and such, or too high with barely any aerodynamic effect.

I've been wrong before though.

Cheers!

[eddiew]

In an aerogravity assist, however, the goal is not to use the atmosphere to slow the spacecraft down, but instead use it to achieve a larger change in direction.

If you don't overheat, you can hang around in the atmosphere as long as you like... which will produce a bigger change in direction - but it may also capture you into orbit (the ultimate change of direction).

I can't see any way in KSP that you could use the atmosphere to change direction without slowing down however. The atmosphere does not shunt you sideways; it just slows you down. You can't get hundreds of metres per second from 'lift' at the high altitudes required to not be captured.

[PLAD]

I used the atmosphere in a flyby of Jool to set up an encounter with Eeloo in my Lowest Delta-V to Eeloo challenge a while ago, but that was before the current atmosphere models. The problem was that the energy the ship had when arriving from Kerbin was higher than what was needed to get to Eeloo, so to reduce the Eeloo arrival speed I had to bleed off energy at Jool. Because the ship was going slower after the aerobrake it also ended up in a more favorable departure direction. Jool's atmosphere had to kill only 142m/s so I think that high pass could be repeated in version 1.04 but I'm not sure.

This does not seem to be strictly what you are describing. If you look earlier in the mission I linked to you will see I fly by Kerbin twice because it cannot turn my ship enough with just one flyby. In theory one could use the atmosphere to turn the ship into the proper departure direction in just one pass, but you are going to lose a lot of energy to drag. In this example the ship needed to turn an extra 20 degrees or so while traveling at 4350m/s, let's see, that's about 200km (20 degrees of arc along the atmosphere) of traveling low enough in the atmosphere for it to turn your ship while it's going that fast, I picture astronomical drag losses even if the ship doesn't explode. I just don't see it as possible, the drag losses should exceed the benefit of the direction change by a huge amount.

It's not theoretically impossible though...

[MaverickSawyer]

I've seen it done in Orbiter, so I'm sure that you can do it at Kerbin or Duna if you're careful. Jool and Eve are not possible due to the sharp rise in pressures, and I don't know enough about Laythe to hazard a guess.

[The_Rocketeer]

In theory I guess it's possible anywhere, but the likelihood of it going pearshaped is pretty broad. Essentially what you're talking about is using an atmospheric altitude to trade off part of the gravity turn speed-velocity for lift induced directional-velocity. It's not really any different to aerobraking, it's just aerobraking under power... I guess.