Duna Aerocapture in 1.0.2

[rcp27]

My career is approaching a key milestone as my first Duna transfer window is nearly here. Obviously I would prefer to avoid burning too much fuel for a Duna capture, but I've not yet tried such a manoeuvre since the demise of the old atmosphere.

If I don't have a heat shield, how deep in the atmosphere can I put my Pe on arrival from Kerbin without breaking my ship? Will this give enough braking to capture, or will I also have to burn the engines to at least get a high elliptical orbit? If I can't do that without burning up, what is the deepest into the atmosphere I can go without damage? I've used aerobraking in 1.0.2 to transfer from Minus to LKO at about 40 km, but obviously that's starting in a non-escape orbit, so going round for another pass or so is not the same sort of disaster it would be if I was relying on a single pass to capture from solar orbit. Any other advice?

Edited May 18, 2015 by rcp27

[HyperbolicKerbonaut]

Excuse me if I misunderstand, but you want to know about aerocapture at Duna? I aerocaptured at around 17,000m and there was no overheating, no heat shield required. You may or may not need to burn a little bit, but it's negligible. I had to try a few different altitudes and it seemed, based on only a few tries, that there is a pretty small margin of error between aerocapture and full reentry.

My reentry effect is set to 110%.

How or why would you aerocapture to get from Kerbin to Minimus?

[Murph]

How or why would you aerocapture to get from Kerbin to Minimus?

You don't, but you can from Minimus to Kerbin, which is what the OP said.

[rcp27]

I want to know what is a good altitude to set for the Duna Pe as I arrive so that I can get a captured (i.e. not escape) trajectory in Duna, so that I don't need to burn fuel to arrive (and whether burning up is a problem).

Regarding Minmus, not aerocapture as such, but using aerobraking to bring your Ap down from Minmus orbital height down to LKO. This saves a huge amount of fuel if you want to use a re-suable tug to shift things like space station or surface bases on Mun or Minmus, by using a non-landing tug.

The point about coming in from Minmus is if you set your Pe too high to get much braking, you are already in a captured orbit, so you can get the braking delta-V from multiple passes. If you are coming through on a hyperbolic orbit, as you will if arriving from interplanetary space, if your Pe is too high, you may just end up in a lower energy hyperbolic orbit rather than capturing into a returning elliptical orbit.

My objective for Duna is to get a first pass through Duna's atmosphere that will capture me from a hyperbolic orbit to a high-Ap elliptical orbit. I can then raise my Pe to a higher but still atmospheric altitude and circularise on Duna with several passes. The question I have, therefore, is what altitude should I aim to have my Duna Pe when arriving from Kerbin so that I get enough braking to capture my orbit but not deep enough to either bring my Ap down into the atmosphere on the first pass, or burn up due to heating.

Edited May 18, 2015 by rcp27

[1greywind]

~12 km PA works for me.

Edit: Remember, that aerobraking effectiveness highly depends on craft shape. This crafts stack (lander + tug) gets Duna aerocapture with 12 km PA: http://images.akamai.steamusercontent.com/ugc/35245682311255554/3B7ED0221E40C6957EA9F49B04F9B4FED8DCF231/

Edited May 18, 2015 by 1greywind

[SanderB]

airbrakes facing toward the engine can make retrograde (engine-first) aerobraking extremely effective and very precise, as long as they are on the far end of the center of mass of the ship compared to the oncoming airstream. You can easily pick a higher than normal (like 5-15km higher) periapsis with aerobrakes because they can increase your drag by 5 to a 100 times depending on how large the surface is that they cover versus the surface area of the craft that is facing into the airstream. I used airbrakes to a precision landing on the launchpad in a challenge earlier today.

Edited May 18, 2015 by SanderB

[-Velocity-]

I tried the usual 13 km aerocapture into polar orbit on Duna last night and everyone died horribly. Nothing blew up- I retracted the solar panels of course (MAKE SURE YOU USE THE SHIELDED ONES), but I simply lost all my velocity turned my ship into a long smear of debris and body parts on the surface. So I reloaded and eventually I aerocaptured successfully from like 19 km or 20 km. It seems the atmospheric drag has changed significantly- duh. Nothing burned up, either, and I didn't have a heat shield. You don't have to do all your aerocapturing and aerobraking in one pass either, it's fine to go into a highly elliptical orbit after the first dip... even if you're planning to go back to Kerbin, because of transfer windows you've got all the time in the world to kill at Duna before the next window.

[ArchGaden]

I retracted the solar panels of course (MAKE SURE YOU USE THE SHIELDED ONES)

Good advice there... early into my career, I lined up a batch of 6 interplanetary probes to send out (launched to 500km staging orbit with maneuvers planned and set in an alarm clock mod). As it was still quite early in career and with few related contracts, I had to keep the designs very minimal. Without thinking, I went with the cheaper solar panels. That became a big issue with my aerobraking maneuvers when the probes finally got to their destinations.

On that note, I managed a decent aerobraking maneuver through Duna at about 21km without burning off my panels. It didn't quite capture the probes in Duna orbit, but it still saved me a lot of fuel. With new aerodynamics and heating, aerobraking is much more difficult now. There isn't a one size fits all number now and if you want to make effective use of aerobraking, you'll have to account for it in the craft design (ie, use retractable solar panels, stow radial components in a utility bay... perhaps even add brakes or wings)

[rcp27]

I tried the usual 13 km aerocapture into polar orbit on Duna last night and everyone died horribly. Nothing blew up- I retracted the solar panels of course (MAKE SURE YOU USE THE SHIELDED ONES), but I simply lost all my velocity turned my ship into a long smear of debris and body parts on the surface.

Back in 0.25, on my first visit to Duna, I came very close to a similar fate. On that occasion I had just enough thrust and fuel to burn back to orbit, but it used most of my return trip fuel, and I had to wait a couple of years for a rescue tanker. I learned the lesson well (though thankfully without loss of life).

It seems the atmospheric drag has changed significantly- duh.

This is why I created this thread. I've seen well enough around Kerbin how radically the atmosphere has changed, hence I realise that the rules of thumb I used to use for Duna aerocapture are likely to be useless in 1.0.2.

You don't have to do all your aerocapturing and aerobraking in one pass either, it's fine to go into a highly elliptical orbit after the first dip.

I completely agree 100% with this. The only objective I have for my first pass is just to go from hyperbolic (non-return) to elliptical (captured) orbit. Bringing the Ap down and getting a nice circular orbit at a low enough altitude is something that can be done with a much higher Pe for less aerodynamic stress on multiple passes once I'm captured, it's just the initial capture I'm worried about because it's a one-shot afair.

I guess I'll go for a 20 km Pe first try and keep a quicksave ready from far enough away to allow for easy adjustment for when it goes horribly wrong.

[SDEngineer]

rcp27 - yes, the aerocapture to lithocapture window is very small these days, and varies a lot based on each individual craft. My first simple Duna satellite probe that I sent in aerocaptured anywhere between 19 and 21.5km - any higher and it failed to capture, any lower and it wound up suborbital. My second Duna satellite, larger, less aerodynamic, and carrying a lander (bound for Ike) aerocaptured between 20.5 and 23km. Clearly with the new aero, it is much more individual, and seems that it will be unlikely that there will be a single "good" trajectory to take inbound, likely to any atmospheric body.

[n0xiety]

It really all depends on your ship. I had a rocket with tower design which had rhino engines with huge tanks at bottom facing towards the fire and did a 6km pass and still survived on Duna. All the solar panels and other fragile stuff were protected at upper sides and nothing exploded.