Duna expedition need some advice

[mikey117]

So I will give you guys some background info. I have just made a 25ton lifter to the duna system. ,which with my 3kerbal lander gets me landed on Duna and back into orbit with a bit of fuel left. So my plan is to launch multiple lifters an send 3payloads to Duna ( 1x lander, 1x fuel tank to be left I orbit for the landers return to kerbin. And one 25ton satellite and mini lander cluster) and 2payloads to Ike( 1xlander and sat / mini lander cluster).

My question is how much time should I allow between launching each vessel?,so that they all enter the Duna system at roughly the same time but not too close together so I have time to get each one into a stable orbit before the next payload arrives

I was thinking to just launch them one day apart ,but unsure If this will make them enter Duna's SOI also 1day apart.

Any advice would be much appreciated.

[Streetwind]

It's not really about when you launch; it's about when you make your transfer burn. So feel free to launch all of your ships into parking orbits first.

Then, staggering your transfer burns by how much time you expect to need is your best bet. But it's not going to be done with that. Even if your transfer burns are all 100% identical, your ships' exact times of arrival will drift from your expectation because Duna's position changes relative to Kerbin while you wait. And your burns aren't going to be 100% identical either - you're going to have errors of imprecision in there.

So as an additional step, after all of your ships have completed their transfer burn, you need to check each ship's actual arrival time again to make sure it still has enough margin before and after for you to be comfortable. If you find a ship that needs tweaking, you should be able to use a combined prograde/retrograde and radial-in/radial-out maneuver to slightly delay or accelerate the flight, depending on your needs.

 

Edited May 24, 2017 by Streetwind

[Starman4308]

It's usually not a big deal, as different transfer burns tend to scatter arrival pretty well. If you're uncertain, you can do as @Streetwind suggested and adjust time to encounter at a correction burn,  which can be quite cheap.

EDIT: Though, one minor point, if you're playing with Real Fuels and using a cryogenic propellant, you probably don't want to wait long in your parking orbit, preferably leaving before you've even finished one complete orbit.

Edited May 24, 2017 by Starman4308

[Cpt Kerbalkrunch]

You can employ the same parking technique around Duna, if you need to. The tendency early on is to see each ship through to the end, but you can usually just jump back and forth to whatever's most necessary at that moment (Kerbal Alarm Clock being the only mod I can't live without).

However, if this is your first time at Duna and you leave a ship in orbit, beware of Ike. It's best to stay inside it's orbit (and well clear), or you'll jump to your ship and find it orbiting the sun or, even worse, get the dreaded "vessel ID no longer exists".

[Human Person]

If your vessels happen to arrive at the same time (wich is really unlikely, even if you make the transfer at about the same time), you can change the time of arrival with a mid-course maneuver. For that, make a maneuver and pull it a bit in Radial-Direction and compensate with prograde/retrograde tweaks. 

Edited May 24, 2017 by Physics Student

[DD_bwest]

the chances of them arriving at the exact same time are relatively low.  I am currently doing a duna mission and i did my transfer burn for each at roughly the same time.  I finished one, switched vessels and did the other, so they were at most 1 orbit apart (100km parking). with nodes that looked almost identical  and the first vessel arrived 11 hours after the second lol.  you shouldnt have to much trouble just going for it, writing down the encounter dates and making any corrections

[mikey117]

9 hours ago, Cpt Kerbalkrunch said:

The tendency early on is to see each ship through to the end

yeah ive landed a probe on Duna during last transfer window. Done the warp all the way out and landed , it wasnt until i came back to ksc i thought damn i should have sent more.lol. So this time im sending a fleet .

thanks for the quick replies folks. Should give a bit more peace of mind .

also I'm on console so sadly do not have access to mods. I would kill for mech Jeb / kerbal engineer. Whichever one has the DV readout. But for now I'm stuck with eyeballing my builds. Literally had to do a practice run to Duna in order to test my landers capability.

Its maddening

 

Edited May 24, 2017 by mikey117

[Spricigo]

22 minutes ago, mikey117 said:

also I'm on console so sadly do not have access to mods. I would kill for mech Jeb / kerbal engineer. Whichever one has the DV readout. But for now I'm stuck with eyeballing my builds. Literally had to do a practice run to Duna in order to test my landers capability.

 

You may always do the math yourself  with the rocket equation