How fast is TOO FAST to get an aerocapture?

[MerlinsMaster]

Hey Guys,

So I had a ship going to Duna, and upon entering its SOI I made my corrective maneuver to aerobrake, setting to periapsis to 7km. It burned up in the atmosphere. I went back to my quicksave, set the periapsis to 16km. The ship didn't slow down enough and is now forever in deep space.

I noticed my velocity was approx 5000km, and that seemed a little fast. So my question is, was it too fast? What is the maximum velocity you can enter Duna's atmosphere and expect to get an aerocapture?

[capi3101]

I'ma gonna point you to the aerobraking calculator - http://alterbaron.github.io/ksp_aerocalc/

It should get you to where you need to be. As a rule for Duna, 12.5 km is the general periapsis you need to shoot for if you're wanting to stay orbital. Much below that and you're going in; much above it and you won't slow down enough for orbit.

[KerikBalm]

5km/s is awrfully fast for a duna trajectory... you shouldn't be doing much more than 1,000 m/s over orbital velocity, which IIRC was about 900 m/s.

I guess you are using DRE?

Or do you mean that your ship aerobraked into a suborbital trajectory?

From what I've seen in stock, for any craft within reason, its easy enough to aerocapture.

With NEAR installed, and a streamlined craft, and using some modded parts (basically other nuclear thermal engines, but better TWR), and laucnhing outside a transfer window, I was still able to aerobrake... although just barely... I was nearly scraping my ship on the mountaintops...

11.5-12.5 is basically what you want to do in most cases, assuming a hohman transfer near a launch window, and something like a .2 drag co-efficient

[xtoro]

I've never had an issue going down to 11km with no heat shield using DRE, just make sure you're pointing retrograde so the engine takes the heat. Engines can handle more heat than other parts.

[Pecan]

Aerobraking is a part of the solution but need not be all of it. If you're coming in too fast in the first place burn retrograde as well, possibly starting well before you even get into the atmosphere.

[cantab]

This may help provided you're in stock aero

http://alterbaron.github.io/ksp_aerocalc/

You'd have to be going insanely fast for an aerocapture to be impossible, as in dozens of km per second.

[MerlinsMaster]

I'ma gonna point you to the aerobraking calculator - http://alterbaron.github.io/ksp_aerocalc/

It should get you to where you need to be. As a rule for Duna, 12.5 km is the general periapsis you need to shoot for if you're wanting to stay orbital. Much below that and you're going in; much above it and you won't slow down enough for orbit.

This may help provided you're in stock aero

http://alterbaron.github.io/ksp_aerocalc/

You'd have to be going insanely fast for an aerocapture to be impossible, as in dozens of km per second.

That's exactly what I was using, and it told me to go for a 7km periapsis. The result is usually an eccentric but complete orbit. This time, the result was sizzle, sizzle, SIZZLE, BOOOM!!

I guess you are using DRE?

Yes, I am.

[MerlinsMaster]

Aerobraking is a part of the solution but need not be all of it. If you're coming in too fast in the first place burn retrograde as well, possibly starting well before you even get into the atmosphere.

That was my conclusion as well. What I am aiming to find out, though, is what velocity do I need to decelerate down to? What's the maximum speed I should dare come in at?

And I'm assuming it's a different figure for each of the bodies with atmospheres. So if you happen to know what they are, please, do tell.

[Wanderfound]

That was my conclusion as well. What I am aiming to find out, though, is what velocity do I need to decelerate down to? What's the maximum speed I should dare come in at?

And I'm assuming it's a different figure for each of the bodies with atmospheres. So if you happen to know what they are, please, do tell.

On Kerbin, the general rule is to stay above 20,000m while hypersonic, and above 2,000m while supersonic. The rest should scale from that.

[MerlinsMaster]

I've never had an issue going down to 11km with no heat shield using DRE,

I'll try that number next time I'm there.

just make sure you're pointing retrograde so the engine takes the heat. Engines can handle more heat than other parts.

Yeah, that's my move. Unfortunately, it wasn't enough this time.

[MerlinsMaster]

On Kerbin, the general rule is to stay above 20,000m while hypersonic, and above 2,000m while supersonic. The rest should scale from that.

Sweet. But where is the line between hypersonic and supersonic?

[Wanderfound]

Supersonic = Mach 1, about 350m/s. Hypersonic = Mach 5+, about 1,750m/s. Exact Mach varies with atmospheric pressure, but I think the m/s speeds should do for DRE if you scale altitudes for different top-of-atmosphere heights. Keep an eye on the temp meter regardless.

Edited October 22, 2014 by Wanderfound

[MerlinsMaster]

Supersonic = Mach 1, about 350m/s. Hypersonic = Mach 5+, about 1,750m/s. Exact Mach varies with atmospheric pressure, but I think the m/s speeds should do for DRE if you scale altitudes for different top-of-atmosphere heights. Keep an eye on the temp meter regardless.

Good to know. Thanks.

[metaphor]

If you're going less than about 1300 m/s by the time you get out of the atmosphere, you'll be captured into an orbit around Duna.