Estimated top velocity where a kerbal can survive aerocapture?

[Evanitis]

Umm... you know.. I'm just curious. Anyone has experience on that matter? Maybe enough math expertise to give a ballpark number?

By 'kerbal' I mean a kerbal in EVA suit. By aerocapture I mean a dip in Kerbin's atmo to get a elliptical orbit. I survived it coming back from the Mun and started to wonder about the limits of the technique.

[sardia]

How did he not pop from the heating? Did you only skim the atmosphere?

[Guest]

It's not velocity that matters but how much friction the Kerbal encounters.  If you're really gentle about it you could probably circularize from Minmus or even an interplanetary trajectory over many passes.  Mars Climate Orbiter (I think?) used the same sort of aerobraking technique with its solar panels (after retro-burn to bring it into an elliptical orbit).

[A35K]

You can't perform an aerocapture at Kerbin if you are coming from the Mun, as you would not be in an escape orbit anyway (unless you went for a particularly fast return...)

An aero brake from Mun altitude is probably survivable by a Kerbal, and you can do multiple passes at high altitude yo avoid too much friction.

Edited January 28, 2016 by A35K

[Evanitis]

37 minutes ago, A35K said:

You can't perform an aerocapture at Kerbin if you are coming from the Mun

Ahh, indeed aerobrake in this case. Aimed for ~64k pe, and yeah took two passes and a bit of eva fuel to park on LKO.

I really wonder if I could do this from interplanetary space. My guess is.. not likely. But kerbals keep surprizing me with their resilience and creativity to to save themeselves from certain deathtraps my sloppiness creates for them. Maybe I could try it with a Mun assist...

[FyunchClick]

This topic reminds me of the jetpack grand tour, but that was before reentry heating IIRC (or not it's posted 6-2015). Still awesome.

Edited January 28, 2016 by FyunchClick

[Snark]

31 minutes ago, FyunchClick said:

This topic reminds me of the jetpack grand tour, but that was before reentry heating IIRC (or not it's posted 6-2015). Still awesome.

EVA reentry heating used to be a lot more gentle pre-1.0.5.

For example, in 1.0.4 it was pretty straightforward to send a Kerbal home from Minmus.  I mean, all the way home, as in go from "standing on the surface of Minmus" to "standing on the surface of Kerbin", with nothing more than EVA propellant.  Could reenter at 3000+ m/s with no problem at all, with judicious choice of Pe.  Didn't even require multiple passes, just a straight reenter-and-go-down-to-the-surface.

That's no longer possible in 1.0.5, for which I'm duly thankful.  Seemed way OP to me.

Now if they'd just do something about those 600 m/s jetpacks...

[Jeanjvs]

7 hours ago, regex said:

 Mars Climate Orbiter (I think?) used the same sort of aerobraking technique with its solar panels (after retro-burn to bring it into an elliptical orbit).

Actually, Mars Global Surveyor was the one that used aerobraking to lower its apoapsis. Ironically, the Mars Climate Orbiter made an unintentional aerobreaking after using non-SI units during a course correction maneuver

Edited January 29, 2016 by Jeanjvs

[Guest]

2 minutes ago, Jeanjvs said:

Actually, Mars Global Surveyor was the one that used aerobraking to lower its apoapsis. Ironically, the Mars Climate Orbiter made an unintentional aerobreaking after using non-SI units during a course correction maneuver

Ah, thanks.  I knew it was one of the Mars probes but neglected to look it up in my haste this morning.

[katateochi]

Once the limits for safe EVA aerobraking have been found, I suggest that it is termed "the Flambé limit".

 

[bewing]

The problem goes like this:

(1) Reentry heating (watts per second) = drag * mass * velocity^3

So, issue 1 is that we don't know the drag of an EVA suit. I guess we have to assume the .09375 metric ton mass is correct.

(2) Basic elevation of temperature = ( (Eq. 1) * (seconds in atmosphere)) / (thermal mass * specific heat)

But the thermal mass is the mass of the suit without the kerbonaut, and we don't know that -- or the specific heat of the suit (but it's probably pretty low). And the number of seconds in atmosphere depends on your exact trajectory. We probably also have to assume that there is not enough time for radiative cooling to make any difference at all.

And then we need to know the temperature limit of an EVA suit, and we don't know that either. So, unfortunately, the only way to calculate all these unknowns is to aerobrake 100 kerbonauts in carefully controlled fashion and see which ones don't make it.

 

 

 

Edited January 29, 2016 by bewing