Arrival at Duna : A few months ago, we made a mistake...

[Ikare]

Hello!

A long time ago, I've sent a ship to Duna. And now, many months later, it has reached its destination! But...

Circularization is way more expensive than expected! I planned my deltaV budget based on the map here :

http://i.imgur.com/q0gC9H7.png

So, with a first stop around Ike, I calulated (250+2*(30+180)+360) = 1030m/s

And my ship has 1502m/s in its tank, so I thought it would be easyyy. But, really, it is not.

The first step, achieving extreme elliptical orbit around Duna, is alredy 950 m/s.

So what went wrong? Are the map values realist? Do I need to have a travel time of a full Duna year for them to be accurate?

Edited September 11, 2015 by Ikare

[Gaarst]

The values indicated in the delta-V maps such as the one you linked are mostly idealised values: you can need exactly the dV indicated, hardly less, or much more depending on your transfer.

I think that most of the delta-V lost in the process was in the initial insertion burn: when you went from hyperbolic orbit around Duna (escaping trajectory) to stable orbit around Duna. Depending on your ejection burn at Kerbin, this one can greatly vary.

How did you plan your transfer to Duna ? Did you use a window planner ? If no, then you probably launched at a bad window and therefore it is normal that you've needed much more dV that you first thought.

Also, if your Duna periapsis for the encounter was higher than indicated (60km on this map) then, you'd need more dV again to circularise.

Delta-V could also have been lost while messing around with Ike: again, non-optimal transfer window and high encounter periapsis can greatly increase the dV requirements.

Edit: remember that Duna has an atmosphere that is thin enough to aerobrake safely with most craft designs, and that Ike's large SOI can provide strong gravity assists. These two can greatly reduce the dV needed for your mission.

[Ikare]

Thanks! I was not able to catch Ike for help, but I used the atmosphere of Duna! With non-rectratable solar panels, it was... hot, but 2 of them survived!