Why Can't I get this in orbit on duna??

[dan2600]

I have 2000 DeltaV, and a spark engine. my TWR is >1...all the guides I see say duna needs 1300 delta v to get into orbit...but I can't get this into orbit...what am I doing wrong? thanks!

[MarkusF]

The second stage, the one with 1812m/s, is triggered by decoupling the upper fuel tank, right? Does the fuel tank fall down to Duna after decoupling, or is it pinned to the rocket due to the acceleration? If so, you would still have to accelerate its dry-mass and MechJeb wouldn't consider this in its calculations.

If it doesn't fall off: Throttle down to zero before triggering the second stage, trigger the stage and wait for the fuel tank to be out of the vessel's flightpath before throttleing up again.

[n0xiety]

I am having the same problem with 1.02 mate. Atmosphere feels alot thicker and higher now so don't think you can get away with a non aerodynamic lander. I just barely took of with my lander that had 3200 dv and barely met with my main ship at orbit. It was so barely that i had 100dv left when i finally docked. And atmosphere seems to go up to 55k now not 41k as it used to be. I had a non aerodynamic lander design just like yours and noticed it pulled me down really hard. Btw if your main craft doesn't pass 1ton try using monopropellent puff engines. They might suprise you about their thrust to weight ratio. Engines themselves are really lightweight and monopropellent is actually lighter then liquid fuel too. So it kind of gives the same amont of dv as a spark engine yet gives maybe 5 times more thrust since you can use more then 1 engine easily and don't loose any dv.

[dan2600]

Thanks for the replies.

I tired dumping the tank, and got the full 1812m/s without any overhead (which should get me into duna orbit)

It must be something with Duna's atmosphere in 1.02 needing a LOT more delta-v

The estimated delta-v is going down about twice to three times as fast as the delta-v I'm gaining. So your 3200 DV = orbit sounds about right...seems like you need 3 times as much delta v for duna atmosphere in 1.02...at least it's not just me!!

[Daveroski]

You seem to be going for a 100K orbit. Have you tried going for 65K?

[dan2600]

can only get to 30KM before running out of fuel.

[Anquietas314]

Well, I don't know if this helps you but I can at least confirm your ship should have enough deltaV. Here's (part of) my career mode Duna mission:

VAB (fully fueled - launches with just enough deltaV to land on Duna because launching and pushing the thing all the way to Duna full is stupid ):

In orbit of Duna after collecting all the science from Duna and Ike (18,000 or so. I didn't manage to find the Duna's Craters biome, but I completed the tech tree so screw it ):

As you can see my lander is hardly the pinnacle of aerodynamic engineering. I would have to guess the problem is your flight path during the ascent. I flew that lander in a fairly shallow ascent path; basically turn to 45 degrees immediately on launch and reduce to 20 or so after the first 10km, made it to orbit using about 1400m/s dV, plus some extra for rendezvous with the transfer stage I brought along. The lander was also capable of launching with both ore tanks full. If it helps, the atmosphere stops at 50km.

[g.koster]

may be on idee to get it on a mountain top on duan and refuel there again?

[n0xiety]

Oh believe me man your design is quite aerodynamic compared to mine. Myne was like those mun landers with wide fuel tank at the bottom and then lander can and some science equipment on top of it finishing with an unshilded clampotron. Atmosphere was pulling me down alot when i looked at it with f12 it showed red drag on duna. You know its bad when something shows red drag on duna.... Well i was still able to meet with my ship but took more than 3000dv. Oh another thing is lander wanted to flip so bad when i tried gravity turn in low atmosphere i couldn't do it untill i got up to like 20k.

[metaphor]

I just got a lander very similar to yours into 60 km orbit for about 1550 m/s from 2700m altitude. But you're right, the atmosphere of Duna is very thick now for small unaerodynamic craft, a lot thicker than in 0.90, even at 30 km altitude.

edit: with the 1.0 aerodynamics it took about 1380 m/s to get into 60 km orbit with the same lander.

Edited May 10, 2015 by metaphor