Good Pe for Reentry from Minmus in 1.0.4?

[Srpadget]

So I have a couple early-tech ships which were launched back in V1.0.2 which are now on their way back from Minmus. (Yes, I juggle way too many missions simultaneously; it's actually pretty rare for me to warp more than maybe half an hour at a time. But that's not the point just now.)

My question: What's a good reentry profile in V1.0.4 for the standard early-game combo of Mk1 pod, Mk16 chute, 1.5m heat shield? Yes, I know I could pop up a temporary sandbox save and find out for myself, but I also know that'd take a bunch of time that I don't want to spend and I'm perfectly okay with cribbing those lessons from those of you who've already done it. I'm currently aiming at a Pe of 37km and have tweaked the chute to fully deploy at 1500m altitude. I'll manually stage the chute once velocity drops below 250m/s.

I figure the chute is okay as is, but that I'll want to lower the Pe a bit further if I want to avoid having to brake across multiple orbits given the new lower-drag physics in 1.0.4. OTOH, I don't want to lower it TOO much given the new more sensitive thermal models in 1.0.4.

So, Oh Wise And All-Knowing Forum: Where should I set my periapsis for a Minmus return with a basic pod/chute/shield reentry vessel?

Edited July 14, 2015 by Srpadget

[HoloYolo]

As long as you have a heatshield protecting all important stuff you can go for immediate lithobraking if you want.

[Reactordrone]

37km should be fine. You can go a little higher for a more gentle slowdown but you'll have to do more passes. Anything in the high 30s to low 40s range should bring your apoapsis inside the Mun's orbit on the first pass.

ETA- a heatshield won't save you on a very steep reentry. Too low too fast will exceed the temperature limits of the shield and it will explode taking your entire ship with it.

Edited July 14, 2015 by Reactordrone

[Snark]

I usually aim for about 30 km myself for such situations, and it seems to work fine. If the returning craft is like you describe, it comes down just fine, uses up maybe ~100 units of heat shield (perhaps a bit less), comes down with no problem.

[Srpadget]

The first of 2 is exactly as described (Val piloting, so no need for a probe core). The second has an Octo probe core between the pod and the chute (launched later, with a scientist on board so I could do more biome-science-farming).

I'd like to avoid having to take the time to do multiple passes (let's face it, the way I play? If I do an aerobrake followed by a pass out to "inside Mun's orbit" before a second pass which may or may not do the rest of the job? It'll probably be a week or more real-time before Val FINALLY lands. I think I launched her sometime in early June, but I'm not sure....) and do a single-pass reentry direct to ground.

So it sounds like I should probably retarget down to a Pe around 30 km or just slightly above. (Sorry, but there's just something that causes me a slight hesitation to take seemingly-suicidal advice from someone named "Kaboom!" Can't imagine what that might be... )

(Come to think of it, the second ship pretty much HAS to do it all in one go: once I jettison the return vehicle so that the heat shield is exposed, I'm also losing my solar panels and batteries on a ship controlled by a probe core. So...30 km it is, and see how Val does in a *slightly* lower-mass reentry vehicle.)

[Reactordrone]

(Come to think of it, the second ship pretty much HAS to do it all in one go: once I jettison the return vehicle so that the heat shield is exposed, I'm also losing my solar panels and batteries on a ship controlled by a probe core. So...30 km it is, and see how Val does in a *slightly* lower-mass reentry vehicle.)

As long as the crew isn't a tourist they will be able to deploy parachutes, they just won't have SAS piloting ability but since you won't have engines that won't be a huge concern.

[Snark]

So...30 km it is, and see how Val does in a *slightly* lower-mass reentry vehicle.

The good news is that it's not super finicky-- you have a pretty big margin of error, at least with small/light craft. My experience is that anything over 25 km is safe, and anything under 35 km will aerobrake to the surface in one pass. So if you aim for around 30, you should be just fine.

[Kryxal]

For that matter, on a high pass you don't have to toss the rest of the rocket ... a pass at 38-40 km might scrub off 2-300 m/s that way, so maybe 36 MIGHT get a single "skip" ... and if not, just toss the remainder when barely suborbital.

[Srpadget]

Set Pe to something in the near vicinity of 31.3km, and Val is now enjoying lording it over Jeb (who has not yet been further than Mun). Worked a treat--and yes, based on this one data point there's a pretty big margin for error: used up maybe 40-ish points of ablator, so plenty of room to come in lower, and came in with nary a 'skip' so there's clearly plenty of room to come in higher and still make it in a single pass.

Thanks, folks, you saved me a great deal of trial-and-error!

[Wemb]

Set Pe to something in the near vicinity of 31.3km, and Val is now enjoying lording it over Jeb (who has not yet been further than Mun). Worked a treat--and yes, based on this one data point there's a pretty big margin for error: used up maybe 40-ish points of ablator, so plenty of room to come in lower, and came in with nary a 'skip' so there's clearly plenty of room to come in higher and still make it in a single pass.

Thanks, folks, you saved me a great deal of trial-and-error!

If you had some dV left, you could also, probably come back higher, burn to slow down and make it without a heatshield.

Wemb

[Sharpy]

50km is a 100% safe without heatshields. It's an altitude where if you're coming in too fast, you'll get ejected through the other side; you'll begin the descent only when slowed down to a safe speed.

[Wemb]

50km is a 100% safe without heatshields. It's an altitude where if you're coming in too fast, you'll get ejected through the other side; you'll begin the descent only when slowed down to a safe speed.

Yup, but I meant if he didn't want to do multiple braking orbits. The only time I'd bother with a heatshield in the early missions is if I'm bringing back a science Jnr pod - which had a tendancy to make my capsules spin over and come in parachute first. Then the heatshield was more ballast than protection.

Wemb

[BlackHat]

Get the trajectories mod, and you will be able to see if the arriving craft will "skip" back out of the atmosphere, or land. with it you can lower your approach Pe and find the minimum needed to prevent skipping back out.

[ygarl]

The whole "skipping off the atmosphere" is one of the scariest two possible failures in RL with real manned craft.

In the real world of course, you'd skip off and just suffocate/starve.

[Kryxal]

The problem there isn't the skip trajectory, but that you're not planning on the skip trajectory. Doing one without the life support needed for the additional time is bad...