Duna Aerobraking/capture/landing Observations in 1.02?

[Jonboy]

In old KSP, I could usually aerocapture at Duna coming in at interplanetary speeds with a periapsis of around 11km to 14km. You really needed to get that deep into Duna's atmosphere before you would start to see any appreciable braking. Even at 1500 m/s I rarely saw reentry heating effects at this altitude and with Deadly Reentry installed I never needed heat shields to survive aerocapture. Vessel size and shape also didn't really make a difference with the old aero.

I was at the point in my new 1.0 career today where I wanted to land a large science base on Duna's poles. Instead of a conventional insertion, I opted for aerocapture to reduce the size of my interplanetary stage. I encased the base and rover in a fairing as a heatshield, since I was unsure how much reentry heating would be present in Duna's new atmosphere.

Since Kerbin's new atmosphere is much less soupy, I assumed the same would be true on Duna, and decided to try a rather low 5km periapsis for my first attempt. This resulted in me smashing straight into the ice caps at about 800 m/s, with all my parachutes failing due to aerodynamic stress. I F9ed and tried again with a higher periapsis of 15km. This appeared to be just below what is needed for a Low Duna Orbit aerocapture. There were significant reentry effects and the front of my fairing just bairly started to overheat. My apoapsis was dragged all the way down to almost above the atmosphere, at about 49km (the Duna atmosphere starts at 50km now).

Falling from that altitude, the atmosphere quickly slowed me from 800 m/s to 250 m/s about 5km up. I deployed my chutes, and only 8 of the mk2 radials slowed my base down to about 10 m/s, and I landed barely using the retrorockets. The little rover dropped separately with 6 mk2 chutes and landed at 6 m/s with no retrorockets. Here's a few shots from the atmospheric insertion and landing:

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So somewhat counter-intuitively, it seems like Duna's atmosphere is soupier than ever before - for my next aerocapture attempt I try a periapsis around 18km. And it seems parachutes are definitely still a viable option for Duna landings. Does anyone else have observations on Duna aerobraking in 1.2? What periapsis did you use? Did you need heatshields? How much does vessel size and shape effect aerobraking? I'm eager to hear other people's results in the new atmosphere.

[Frozen_Heart]

Its due to ongoing kerbal efforts to terraform Duna. They've succeeded in making the atmo denser than before.

[Tada]

Complete aero-capture was always kinda hard on Duna. I used aerocapture + engines most of the times in previous versions also. The margin betweeen capture and crashing into surface was very thin even back then.

[Hotblack Desiato]

apparently dunas atmosphere is now more like the atmosphere of mars. on mars, the lower gravity causes the atmosphere to extend further up into space (the karman line on earth is at 100km height, on mars it's 71km, yet mars has less than 1% of earths surface pressure (for venus, it's 266km, for titan it's 152, even with just 1.6 bar on the surface, a weaker gravity-field than moon and the very low temperature).

did anyone try something similar with eve? with that surface gravity, I'd expect eves atmosphere height to be lower than on kerbin.

[Jonboy]

Haven't got to Eve yet in my 1.02 career, but I'm about to launch a Gilly satellite for a contract. I'll try saving some delta-v with a pass through Eve's atmosphere and see what happens.

[RocketBlam]

I can't seem to land on Duna now. I've set my chutes to open at 4500 altitude, and they still will not fully deploy before impacting the surface.

Now trying 5000...

- - - Updated - - -

Nope... setting them to 5000, they open, but do not slow the craft enough and I still crash.

Seriously, 1.0 + seems to have major issues.

[Sidereus]

I can't seem to land on Duna now. I've set my chutes to open at 4500 altitude, and they still will not fully deploy before impacting the surface.

Now trying 5000...

- - - Updated - - -

Nope... setting them to 5000, they open, but do not slow the craft enough and I still crash.

Seriously, 1.0 + seems to have major issues.

Just how fast are you coming in, and at what angle? Sounds like you're coming in waaay too steep and too fast.

I landed a simple probe today (an OKTO probe core, a FL-T400 fuel tank, the LV-909 engine , some legs, 8 OX-STATs, and science gear) without any problems. Didn't even use a heatshield. Took a somewhat shallow approach coming from Ike - periapsis was around 10km IIRC. Once I got down to about 15km I slowed down some using my engine , then as soon as I came in under 500m/s or so I killed my engine to conserve fuel and popped my Mk16 parachute at about 5000m, with it set to open at 2500m. That slowed me down to about 30m/s, then when I got down to about 80m I fired my engine to kill my velocity until I was going around 4m/s. Easy landing.

[RocketBlam]

I previously landed a probe here with chutes too and didn't have all these problems.

I'm coming in from about 120k, with a periapsis of 32k.

I did finally make it down, but only by burning until I was down to about 100 m/s so after the chutes opened, I was not going too fast and had time to do something.

Also, on Kerbin, the "altitude" that the chutes open is above the ground. If you set it for 500, they open 500 meters above the ground whether you land at sea or on a mountain. On Duna it seems to be above sea level, because they just don't open 5000 meters above the ground. They open when ASL altitude hits 5000.

Edited May 4, 2015 by RocketBlam

[Jonboy]

What atmospheric density did you have your parachutes set to open at? My usual strategy with Duna is to set all my parachutes for the lowest possible atmospheric density and 5000 meters. Then I stage them when I feel like I need them to open, I've never had a problem with them not opening and I have only ever used retrorockets to slow down a bit just before impact. It's usually not a problem to get down to 10 m/s if you use enough.

[RocketBlam]

They're set to the lowest they go, .01.

They pre-deploy just fine (although doing so about 600 m/s causes them to rip off).

[Geschosskopf]

I have been doing a fair number of Duna aerocaptures and landings lately and here are my observations.

Pre-1.0:

Aerocapture to LDO needed, as you say, 11-13km. Even that low, you usually didn't see any reentry flames at all. And parachutes didn't do a whole lot for you unless you A) had lots of them and started your descent from just above the top of the atmosphere aiming to land about 1/4 of the circumference ahead, popping the chutes at like 15km and streaming them the rest of the way while retroburning full power for like the last horizontal 100km of your approach. During the descent, you got zero flames.

Post 1.0:

The sweet spot for aerocapture is usually (depending on the angle at which you intercept Duna and thus your speed when you get there) between 17-22km. Any lower and you usually end up lithobraking. Any higher and you usually don't capture. And you always get some flaming even at these altitudes, although usually not enough to even need a heatshield for. On landing, you still don't get any flaming so need a heat shield even less than for aerocapture. Furthermore, you no longer need to make the long, flat descent profile or retroburn through it with streaming chutes. You slow down naturally a lot faster and chutes work more better. You can do a conventional, Kerbin-type landing profile, saving the chutes until the ground is starting to look threatening. You still need WAY more chutes than at Kerbin of course, but they work more like you're on Kerbin than on Duna as we used to know it. I managed to land a 15-ton base module on just chutes yesterday, hitting the ground at 2450m at 5m/s when I'd specified at max altitude of 1000m in the design.

Bottom Line:

So all in all, aerocapture at Duna is somewhat trickier than it used to be because the difference between lithobraking and not capturing is much tighter than before. Used to be, you had a lot more leeway there. Put your Pe at 12km and you'd be sure to capture, so the main point of F5-F9 repeats at Duna was tweaking the Pe up or down a few hundred meteres to get exactly the Ap you wanted afterwards. Nowadays, F5-F9 is a matter of life and death and you have rather less control of your resulting Ap. (can't WAIT for the Trajectories mod to get updated ). OTOH, landings are a lot easier now because the atmosphere is now thick enough actually to be of significant help in slowing you down, while still being thin enough not to burn you up.

[Temeter]

I previously landed a probe here with chutes too and didn't have all these problems.

I'm coming in from about 120k, with a periapsis of 32k.

I did finally make it down, but only by burning until I was down to about 100 m/s so after the chutes opened, I was not going too fast and had time to do something.

Also, on Kerbin, the "altitude" that the chutes open is above the ground. If you set it for 500, they open 500 meters above the ground whether you land at sea or on a mountain. On Duna it seems to be above sea level, because they just don't open 5000 meters above the ground. They open when ASL altitude hits 5000.

You need some engines for the final descent, just a short burn before takedown. I think duna was always like this, as long as you didn't spam chutes in 0.9? I like it, just landing by chutes is a bit simple and using a short burn remindes me of real Mars missions.

Also far superior to the older version since your chutes aren't just gone as soon as you hit 0.1 airspeed... That one did cost me some nerves.^^'

On the bad site, no point in ever using drogues.

Edited May 4, 2015 by Temeter

[adinfinitum]

did anyone try something similar with eve? with that surface gravity, I'd expect eves atmosphere height to be lower than on kerbin.

I'm not sure what the proper height for aerocapture at Eve was pre-1.0.x, but in 1.0.1 I sent a probe there, intending for aerocapture. Periapsis was either 70 or 75 km, velocity was roughly 4000m/s, and it slowed me down enough that I ended up going right down into a landing instead of an orbit

[Jonboy]

Great observations there, Geschosskopf. I had no problems coming in from orbital velocities, even with a rather steep descent. The atmosphere slowed me down to about 260 m/s and I popped the chutes.

And yes, I didn't realize how much I missed Trajectories until I didn't have it anymore! It's one hell of a mod and made everything involving atmospheres so much less tedious.

[Geschosskopf]

I'm not sure what the proper height for aerocapture at Eve was pre-1.0.x, but in 1.0.1 I sent a probe there, intending for aerocapture. Periapsis was either 70 or 75 km, velocity was roughly 4000m/s, and it slowed me down enough that I ended up going right down into a landing instead of an orbit

Wow, that's a big change. Pre-1.0, you needed 60-65km for aerocapture. Also, back then, nothing, no matter how big, needed a chute to land on Eve. Everything slowed down to about 20m/s by the time it reach ground level so you just needed a blip of the engine to land safely. I wonder if that's still the case.

[orven]

I lowered periapsis to about 13-14 km and after braking my apo was slightly below Ike's orbit, so I needed second round for landing. There were no heatshield or fairing or anything, just poodle engine, mk3 to 2.5 m adapters as a pair of fuel tanks and 2.5 service bay for probe and science stuff.

[ShortBusDriver]

Thanks for the information, I just did my first aerocapture with Duna @ 14.5 km. My ship was just a probe, but the insight was perfect. Thanks