Duna's Atmosphere in 1.x

[Geschosskopf]

Prior to 1.0, flying on Duna was a significant challenge. Back in those High And Far Off Days Of Gods And Heroes, Duna's atmosphere was very analogous to the cliché description of Mars' atmosphere: "too thin to ignore, too thin to be useful". Making anything fly at all was a challenge. Being able to control it was a bigger challenge. Being able to land safely was even worse. And then, having made something capable of all that, getting it from the ground on Kerbin to Duna was even harder. I had a challenge thread for making a flying machine for Duna, active for about 2 years, and only about 10 people ever managed to succeed at it.

But now we have 1.0.2 and it's a totally different story. Duna's atmosphere has become the opposite of the cliché. Now, it is most accurately described as being "thin enough to ignore completely yet thick enough to fly in effortlessly should you so desire". It is now exceedingly easy to fly on Duna and I expect, if things remain as they are, that everybody will be doing this as a matter of routine in preferrence to long-range rover trips. Ironic, isn't it? So many folks whining about how the new aero stuff makes flying difficult, when on Duna it makes it way too easy. So I've closed my challenge thread.

Anyway, whatever you think about the 1.0.2 aero stuff on Kerbin, when applied to Duna, it's not at all a good thing. Anybody else notice this?

[Tada]

Meh, duna atmosphere treats me same as it did in previous versions...

[Geschosskopf]

Meh, duna atmosphere treats me same as it did in previous versions...

You obviously never tried to fly an airplane there.

[Levelord]

You obviously never tried to fly an airplane there.

I have. It's still the same, except that landing is now significantly harder because of the terrain and the fact that brakes and airbrakes are worthless in the thin atmosphere to slow you down in time. Still need to pack heavy chutes like I did in 0.25.

[Brotoro]

I've tested planes on 1.0.2 Duna... And I found that I can cruise at about twice the altitude that I could in the old Duna atmosphere (because of the increased lift in the new atmosphere), and I found that it was much easier to land horizontally on the surface (which I was able to accomplish every time I tried it in 1.0.2, but hardly ever managed it safely in 0.90).

Whether or not it's a good or bad thing is a matter of preference, of course.

[Spatzimaus]

and I found that it was much easier to land horizontally on the surface (which I was able to accomplish every time I tried it in 1.0.2, but hardly ever managed it safely in 0.90).

I didn't really have a problem back in 0.90:

That was my long-range SSTO spaceplane, designed to go straight to Laythe from Kerbin without refueling. On a whim I tried it out on Duna, and it landed just fine. Granted, I'll bet that part of it was my use of the B9 landing gear (which has better shock absorption than the stock small gear) but it still wasn't bad at all for a complete dead-stick landing.

I'd bet that a big part of it is lift. That spaceplane design had plenty of lift for 0.90, so it could handle Duna's thin atmosphere just fine. In 1.02, everyone's using less wing on their Kerbin-ascending designs due to the new drag rules, and it's now just not nearly enough for Duna. A Duna-specific design in 1.02 might be just fine (although I think you'd really need something like the Firespitter electric propellers).

[luizopiloto]

Try fly safe at Eve...

[Geschosskopf]

I have. It's still the same, except that landing is now significantly harder because of the terrain and the fact that brakes and airbrakes are worthless in the thin atmosphere to slow you down in time. Still need to pack heavy chutes like I did in 0.25.

Actually, what you describe is the pre-1.x situation, especially if you really wanted to fly anywhere on Duna, not just landing in the smooth, low-altitude basins. If you wanted to land out in the main dune fields which cover 80% of Duna's surface, at altidues averaging 2000m or so, which used to be the equivalent of about 16km on Kerbin, you needed a real Gossamer Albatros sort of plane. Which is what you'd expect given the very thin air.

Nowadays, however, all control surfaces, including airbrakes, work nearly as well on Duna ss they do on Kerbin, and you get way more lift out of way less wing. The result is that you can fly what are, compared to pre-1.x, absolute bricks all over Duna no problem. You can fly much higher, go faster, land slower, and stop shorter at higher alitutude.

I didn't really have a problem back in 0.90:

http://i.imgur.com/pxadYKq.png

That was my long-range SSTO spaceplane, designed to go straight to Laythe from Kerbin without refueling. On a whim I tried it out on Duna, and it landed just fine. Granted, I'll bet that part of it was my use of the B9 landing gear (which has better shock absorption than the stock small gear) but it still wasn't bad at all for a complete dead-stick landing.

Where did you land? In a basin or out in the dunefields? It used to make a big difference. Not so much anymore.

I'd bet that a big part of it is lift. That spaceplane design had plenty of lift for 0.90, so it could handle Duna's thin atmosphere just fine. In 1.02, everyone's using less wing on their Kerbin-ascending designs due to the new drag rules, and it's now just not nearly enough for Duna. A Duna-specific design in 1.02 might be just fine (although I think you'd really need something like the Firespitter electric propellers).

Looking at your pic, that thing had nowhere near the lift needed to sustain true flight on pre-1.x Duna, as opposed to holding itself up with thrust. It would probably fly along just fine at idle speed these days, however.

Check out some of the entries in my old challenge thread and compare them to your thing. For example:

http://forum.kerbalspaceprogram.com/threads/50619-CLOSED-Flying-Duna-AGAIN-%28Thanks-for-Participating%29?p=1039168&viewfull=1#post1039168

http://forum.kerbalspaceprogram.com/threads/50619-CLOSED-Flying-Duna-AGAIN-%28Thanks-for-Participating%29?p=1073737&viewfull=1#post1073737

Now compare all that to this thing I made today. Just slapped it together, no thought involved, and it blew all the parameters of the old challenge completely out of the water in terms of performance and payload. In the old days, folks would do without cockpits just to save weight. Nowadays, that's not an issue at all due to all the lift we now have on Duna.

It could land at 30m/s at 3000m ground altitude, which was essentially impossible pre-1.x, Yet it could exceed 20km and reach nearly 400m/s on just 1 electric prop, whereas previously most planes struggled to reach 5km and barely topped 100m/s. And all while carrying 6 Kerbals all internally.

So, it's abundantly obvious that things are much different now, and that Duna's air in no way resembles the near-vacuum it's supposed to be.

[Captain Sierra]

Hold on, lemme do some quick testing (boots up hyperedit save).

EDIT: Still thin as crap when I fly in it. I chalk your success up to the use of the Big-S wings which have a HUGE lift rating (they're not meant for use on Mk2 fuselage planes and their use on such planes is arguably overpowered).

Edited May 25, 2015 by Captain Sierra

[Superfluous J]

Haven't tried to fly on Duna in 1.0 yet, but other than needing more wings and preferring the lowest altitudes for landing, I didn't find flying on Duna particularly hard. In fact, it sometimes felt more like flying on Earth than Kerbin due to the ability to actually low-speed glide without coming to a stop and dropping from the sky.

[selfish_meme]

Pre 1.0 couldn't land but got close enough to almost hit a rock

http://imgur.com/a/N2D6M

[Bill Phil]

I think the atmosphere of Duna essentially acts like the upper atmosphere of Kerbin...

Or maybe the game doesn't recognize the difference between Duna's atmo's material and Kerbin's Atmo's material.

[regex]

I think the atmosphere of Duna essentially acts like the upper atmosphere of Kerbin...

Well, it's probably based on a Unity FloatCurve just like Kerbin. I have no idea what the curve is modeled on, though, but a barometer should be telling barring vomiting variables.

Or maybe the game doesn't recognize the difference between Duna's atmo's material and Kerbin's Atmo's material.

The game never did that.

[Nansuchao]

Flying with FAR, landing on Duna with a plane it's a real challenge. Due to the thin atmosphere, every plane will stall at still high speed, so almost everytime you need parachute.

[timsfitz]

My 1 man ion plane flew very well on Duna in the past and could make orbit fairly easily. I hope it still works now.

[tater]

The landing gear should break off on anything but tarmac anyway.

[Spatzimaus]

Where did you land? In a basin or out in the dunefields? It used to make a big difference. Not so much anymore.

Dunes. There was a LOT of hopping on the terrain when I landed, and I'm amazed it didn't tumble during the LONG braking, but it somehow made it down in one piece.

Looking at your pic, that thing had nowhere near the lift needed to sustain true flight on pre-1.x Duna, as opposed to holding itself up with thrust.

It's not easy to see from the picture, but it's got metric buttloads of lift. First, the Mk2 parts used as its fuselage base provide a little lift. Then, I used wing segments above and below the main fuselage to smooth out the design. And finally, that wing, while it looks small, is actually a triple wing with two full "shell" sections above and below a swiss cheese'd middle wing, like so:

That's with the top wing shell removed. Here's a shot where you can better see the shapes of the shells:

Point is, it had a LOT of lift, primarily due to my using wing segments for aesthetic reasons. I had no problems at all taking off from Duna and returning to orbit, and I didn't need to stand on the tail to do it. In 1.02, that much wing would be horrible for drag on Kerbin, of course.

[katateochi]

I've not tried flying at Duna in 1.0.x so far. That's a pity, for two reasons a) Flying at Duna was an interesting challenge I never saw your Duna flying challenge thread, I would have posted my Duna glider if I had;

(more pics with ascent from Kerbin and transfer to Duna)

[KerikBalm]

#1) Duna just made the deficiencies of the old atmosphere extremely apparent. No V^2 relationship to lift, but its there fore drag?! = wing L/D drops the faster you go. Thinner air = must go faster.

#2) Your old challenge seems ot have nothing but entries using modded parts... this should be a sign

#3) I don't see how FAR (which you gave bonus points for!) is so different from the current aero. Its that wings properly produce lift according to the square of velocity that makes it viable now. FAR did that.

On my FAR installs, I never got around to flying on Duna, but I sure did with NEAR. Flying on duna was super easy with NEAR.

#4) Duna's atmosphere gets to about 0.18 atmospheres of pressure... that *should* be easy to fly in.

Its not analagous to a Martian atmosphere... it never has been (only in the loose sense, that it is thin).

A martian atmosphere analogue would be much thinner, and have a larger scale height than Kerbin's, not smaller.

Also, it seems like now Kerbin's atmosphere no longer follows the scale height equation.

See:

http://forum.kerbalspaceprogram.com/threads/122790-Everything-I-ve-been-told-about-atmospheric-pressure-in-KSP-is-wrong?p=1967024

Its actually about 4x thicker at ~60 km than it was previously. (It really starts to deviate a lot from the old equation between 30 and 60 km)

I wonder what goes on at Duna.

I know its absolute height has increased.

Has its thickness increased too?

[Majorjim!]

I can attest that teeny tiny aircraft still work in Duna's atmosphere. Much to the delight of Valentina.

[xtoro]

I had a great flying mission with my plane. Didn't notice a huge difference except that braking is almost useless now.

Took off from the Kerbin runway, flew to Duna, landed, planted flag, took off back into orbit, back to Kerbin, landed back on Kerbin.

Highlights:

My entire mission to Duna and back using 100% reusable parts can be found here

[OhioBob]

Duna's atmosphere has changed significantly from v0.90. Datum level pressure has not changed, but the rate of pressure drop with increasing altitude is much less. The game also now calculates density as a function of pressure, temperature, and molecular weight, unlike before when it was simply a function of pressure. At low altitudes the density of Duna air is less than pre-1.0; however, at high altitudes it is much greater. At the datum level, Duna air is about half as dense as before, at 3000 m it's about the same, and at 6000 m it's about twice as dense. By the time we get to 15000 m, the air is more the 10 times denser than v0.90.

Edited May 25, 2015 by OhioBob
spelling

[xtoro]

I for one welcome our new aero and atmo overlords.

[Geschosskopf]

Duna's atmosphere has changed significantly from v0.90. Datum level pressure has not changed, but the rate of pressure drop with increasing altitude is much less. The game also now calculates density as a function of pressure, temperature, and molecular weight, unlike before when it was simply a function of pressure. At low altitudes the density of Duna air is less than pre-1.0; however, at high altitudes it is much greater. At the datum level, Duna air is about half as dense as before, at 3000 m it's about the same, and at 6000 m it's about twice as dense. By the time we get to 15000 m, the air is more the 10 times denser than v0.90.

Well, that explains a lot. The average elevation of most of Duna's surface is about 2500m (between 1500-3500m in the vast dune seas). So now that and above is all totally flyable, whereas before it was hard to even get up that high, let alone fly above it and land there safely.

Really seems counterintuitive, given that Duna's not supposed to have much of an atmosphere. I'm thinking this is an unintended consequence of making the air Kerbin-specific (or rather, too impossibly much like Earth).

[KerikBalm]

Really seems counterintuitive, given that Duna's not supposed to have much of an atmosphere.

How so? as already mentioned, Mars has a larger scale height than Earth, not smaller.

Add on top of that that its atmosphere is composed of mostly gases heavier than Earth's, and that it is colder... the density drop is much lower than on Earth, proportionately.

You keep talking about what Duna is supposed to have...

If they wanted it to be like mars, they would have given it 0.01 atm of pressure at the datum level.

They didn't, they gave it 20%

That is a significant atmosphere.

What made it seem thin before was the really low scale height.

It doesn't make sense for it to have a much smaller scale height than Kerbin, if it has much lower gravity.

Its not counter intuitive - its what you should expect.