Is it possible to do a skip reentry with KSP's new stock aero?

[lincourtl]

This is something I miss from Orbiter -- being able to realistically manage reentry heating by skipping off the upper atmosphere. I tried yesterday bringing Valentina back from the Mün, but didn't seem to be able to pull it off. In fact, I just seemed to prolong the most dangerous part of her ride by coming in too shallow. I really thought I was going to lose her, but those new shields have amazing amounts of ablative material slathered on them. The thermometers radially attached to the upper part of the capsule weren't so lucky.

Overall though, despite some of the expected buggy-ness, I am seriously impressed with Squad's new stock aero and heating system. They add to up to making for a great thrill ride. I'll probably still use nuFar, and Deadly Reentry, when they're ready because I like that level of realism, but I really think Squad did a bang up job on 1.0. So far it's shaping up to be my favorite update since we got bac9's lovely space center.

Edited April 29, 2015 by lincourtl
Marking as Answered because it is, but it's still a great conversation. Feel free to carry it on.

[SyberSmoke]

Technically, yes you can skip off the atmo. There is a BUT there though, a pod will more then likely not be able to because it does not have any control surfaces. Something with wings though could catch enough lift to change direction and skip.

[lincourtl]

Technically, yes you can skip off the atmo. There is a BUT there though, a pod will more then likely not be able to because it does not have any control surfaces. Something with wings though could catch enough lift to change direction and skip.

Hmm. It seems like with the new aero we should be able to make it work with pods too.

[Motokid600]

I'm not sure it's possible to perform an actual skip. You need to have an off set CoM on the pod that can provide lift. To what extent angling your heatshield off prograde with a symmetrical CoM does anything like that.. I don't know.

Squad should do it like in RSS/RO. The pods get a "descent mode" which shifts the CoM. And it's ALOT of fun being able to fly your pod with roll.

The stock planets are really too small to perform a skipping reentry, but you can emulate it. If you set your periapsis to the right height you'll fly past it during reentry and will start to gain altitude again. And if you did it right the drag will pull you in for a second reentry.

Kinda Iike a skip, but not really.

[lincourtl]

I'm not sure it's possible to perform an actual skip. You need to have an off set CoM on the pod that can provide lift.

Ah! That's what I was forgetting. You're right there.

Squad should do it like in RSS/RO. The pods get a "descent mode" which shifts the CoM. And it's ALOT of fun being able to fly your pod with roll.

I did not know RSS/RO did that. Cool idea!

The stock planets are really too small to perform a skipping reentry, but you can emulate it. If you set your periapsis to the right height you'll fly past it during reentry and will start to gain altitude again. And if you did it right the drag will pull you in for a second reentry.

Yeah, that's what I was aiming for -- sort of a simulated skip. Oh well. Maybe next time.

[Shpaget]

On my first 1.0 return from a Mun flyby mission I set up my Pe to 40 km. It was enough to reduce my Ap to about a 10 000 km. I did one more pass and got the Ap to IIRC 3 000 km, I then reduced the Pe to 30km and burned retrograde in atmo. The craft had a Terrier at the bottom which survived the whole thing. I only lost two radially attached batteries.

Not quite what you describe, but apparently, on some missions, you can aerobrake small crafts in multiple stages.

[lincourtl]

On my first 1.0 return from a Mun flyby mission I set up my Pe to 40 km. It was enough to reduce my Ap to about a 10 000 km...

Yep. That's the other way of doing it -- trading off shock-layer heating for time -- and it's a good one, especially when you're coming in from an interplanetary transfer. If I recall correctly, the Mars Reconnaissance Orbiter did successive aerobraking passes for almost five whole months! Obviously this probably would not be ideal in the real world with real humans.

[Claw]

The game tries to emulate this to some extent by providing blunt body lift. There is a slider to play with the lift value in the debug options. I don't know how well it's balanced, but lift surfaces aren't strictly required.

Cheers,

-Claw

[NathanKell]

Pod torque is strong enough you don't even need to offset your CoM, you can fly a lifting descent from torque alone. That said, if you put a radial chute on the side, it'll offset the CoM.

And yep, body lift (and thus lifting reentries) are modeled.

[lincourtl]

And yep, body lift (and thus lifting reentries) are modeled.

I must not have gotten my reentry profile right then. It may be the bug in the heatshield configs too.

[NathanKell]

With a pod, you want to point something like 10-15 degrees above the retrograde marker. Grab AeroGUI (from the releases forum), it'll show you your lift/drag ratio.

[lincourtl]

With a pod, you want to point something like 10-15 degrees above the retrograde marker. Grab AeroGUI (from the releases forum), it'll show you your lift/drag ratio.

Superb! I hadn't seen that yet. You are a modding machine, NathanKell!

I'll have to try that out

[SRV Ron]

I was testing moon orbiters. The three Kerbal pod did a skip while returning from Mun. Reentry window was about 26,000 meters. The pod was flying SAS off with a fixed heat shield. It came down to the 26,000 meters, then skipped back up to 45,000 meters and finally settled back to a landing.

[mic_e]

Doesn't the 1.25m heat shield greatly shift the CoM?

[DaMichel]

I found the lift/drag ratio at altitude, high mach, and high AoA to be really low compared to the lift/drag that oldFAR provided.

Failed to do lifting reentry from Mun transfer orbit. Held the capsule at 10 - 20 deg AoA. No apparent lifting.

Try this with a spaceplane: Do reentry, where at ca. 40 km altitude you suddenly increase your pitch to 45 deg or even more. See what happens. I managed to grind to a complete stop this way. I.e. after this braking maneuver my velocity vector pointed straight down but i lost only a few km of altitude. So from 20 km altitude i went down vertically. I'm sure FAR would have sent me back to space again.

Likewise during ascent, whenever i try to pitch up to pull out of a shallow dive, i loose a big chunk of my speed while still descending.

Edited April 30, 2015 by DaMichel

[SRV Ron]

Doesn't the 1.25m heat shield greatly shift the CoM?

I had applied the hot fix to the shield so that the pod flies stable heat shield first with SAS off.

[monstah]

Doesn't the 1.25m heat shield greatly shift the CoM?

It shifts the center of drag, but not mass. Even if it did, it would pull the CoM down (from the VAB perspective), so it would still be symmetric. Offset CoM means you need to pull it away from the rocket axis.

Why is it needed, anyway? Is it to point the pod away from perfectly retrograde? As Nathan said, the torque from the pod is enough for that.

[tsotha]

With a pod, you want to point something like 10-15 degrees above the retrograde marker. Grab AeroGUI (from the releases forum), it'll show you your lift/drag ratio.

I was playing with this yesterday and the AoA of my pod during reentry didn't seem to affect anything at all.

[RuBisCO]

I did skiping with FAR and 10X Kerbin, just set the Pod CoM off center 0.1 to 0.15, then let aerodynamic forces stabilize it. Using the 1.0 Stock phyics the pods don't even seem controllable unless SAS is on, aerodynamically unstable.

[lincourtl]

I did skiping with FAR and 10X Kerbin, just set the Pod CoM off center 0.1 to 0.15, then let aerodynamic forces stabilize it. Using the 1.0 Stock phyics the pods don't even seem controllable unless SAS is on, aerodynamically unstable.

Were you using the fixed heat shields configs, or the ones that shipped with 1.0? As soon as I applied the "fix", everything worked pretty normally.

I still haven't managed a skipping reentry in 1.0, but I've got some travelers coming back from Duna so I'll try again. All my previous attempts were with the single crew pod.