Landing at Duna in the exact spot

[aluc24]

Hello,

I want to create a Duna base in career mode. Obviously, the parts will be landed separately on the surface, then moved closer and docked together. For that to happen, I need to land all of these parts (and later, other parts when expanding) very closely together, no more than several hundred meters apart.

How can I achieve that? MechJeb has landing autopilot with atmospheric reentry predictions, but somehow it often puts estimates wrong, as far as 30km from chosen landing spot. Also, it doesn't account for drogue chutes, which are kind of necessary before deploying the mains.

How do you do it? What's the proper way?

[arise257]

Practice makes perfect, but once you get your first piece down, targeting it and orbiting to a convenient point of descent with the rest is all there is to it. It's really just like trying to land precisely on Kerbin, with less gravity and thinner air -- maybe even a little easier since the parabolic path of descent is less affected by air and gravity.

If you want to make it easier, you can put wings on the base modules to give them a bit of maneuverability -- affix them to radial decouplers so that you can get rid of them you land. You can also put wheels on your modules so that you can drive them up to each other.

[davidy12]

Descent auto pilot is what I do and then I use Translatatron to land next to a landing area (Hab, Ascent vehicle, etc).

[KerBlammo]

Yes, practice makes perfect here. I put an entire base down in one go so I didn't have to assemble it on the surface, but I still had to put a lander down nearby, I was able to put it within 100m in the "simulator" (hyper edit), and landed it roughly 250m away when I did it "for real".

My basic approach was start from a low orbit just above the edge of Duna's atmosphere and burn so that the periapsis was 3-4km and about 90 degrees around Duna from the target. This causes you to come in at a shallow angle and get the maximum effect from areobraking. As your spacecraft slows you'll see your projected trajectory intersect the surface and move closer and closer to your target. Depending on the areodynamics of your base you may need to adjust your initial periapsis up or down from the ~4km I used with my lander.

The trick is to start your final landing burn at just the right moment so you kill your forward velocity and come down near the target, but you should be able to wait until you are within a few km of the target (both horizontally and vertically) at which point your trajectory should be still overshooting the target, but not by much. MechJeb's readout of true altitude and time to impact are useful information here.

There are no doubt other methods of doing this, but the above worked for me.

Good luck!

Edited November 5, 2015 by KerBlammo

[aluc24]

Okay, thank you all, but what are you talking about are powered descents. I would like to with parachute only descent. Meaning that I would only burn a little to bring down periapsis, and from there on, descent only using drogue and main chutes. Carrying engines and fuel for powered (or partially powered) descent adds a lot of complexity, weight and cost...

[KerBlammo]

You'll probably need at least a last second burn at landing anyway. My base came down under parachutes but was still just a little too fast when it reached the surface. IIRC it needed less than 100 m/s for the de-orbit and touchdown burns combined though. Without a powered descent its going to be much harder to achieve a precise landing, but I have never tried it myself.

[SlashTen]

Try the Trajectories mod. It is really useful for landing on atmospheric bodies as well as for aerobraking. Just be aware that your craft will have to be stable during re-entry (i.e. no tumbling) for the prediction to be accurate.

[KerikBalm]

I also have this problem... but I don't dock them on the surface (some limited clawing though)...

My solution is to add aerodynamic surfaces... but even then, I only get within a few hundred meters.

This is my base...

I landed the rover and airplane first... then tried to but the hab down close to them... I got within a few km of the rover, but the rover is quite stable, and it drove over to the hab. The plane flew over...

Then because the lowlands in my save have no ore, I landed the ISRU on the nearby highlands (the same mountains seen in the background of that picture), and filled up, then did a suborbital hop... it wasn't even a long hop, and I quickloaded many times to improve accuracy, but as you can see, it was still off by ~200 meters.

So to get to and from the surface, I have a 3 kerbal winged lander*... it does as well from orbit as the ISRU does from a 100-200 km suborbital hop:

I can fly it well enough to get it going pretty much straight over the top of the hab... but timing the drogue and then main chute deployment is quite hard if I want to be within 1 km... as I'm still travelling more than a few hundred m/s when gliding in the atmosphere.

So... the best I can manage is to put things down in a cluster so that its not soo bad to drive a rover between vessels.

*actually, the Hab itself carries enough fuel to get to orbit, and the ISRU vessel is mostly meant to supply an orbital fuel depot... so everything except the plane and rover can get to orbit... and the rover can actually get to space but not orbit with its overdesigned retrorocket system

Edited November 5, 2015 by KerikBalm

[aluc24]

Well, okay, I see, but I play KSP with Hard mode, meaning - no reloads. First shot must be the the right shot. That's why I'm investing a lot in planning... I'll try Trajectories mod. Any other advice?

[GeneralVeers]

How do you do it? What's the proper way?

Simple: don't use MechJeb. You've obviously proven through experience that MechJeb isn't up to the task of putting modules on target.

The best way to do it is old school. General rules:

-- Your approach should be via equatorial orbit if possible, otherwise the target will drift sideways relative to you as you approach it.

-- Line your orbit up so you pass directly over the target.

-- Decelerate as you approach it. Then, when you're directly overhead of the target, retro thrust sideways until you're dropping straight down. Preferably after the nav ball goes to Surface mode, that way "down" is actually straight down.

[fourfa]

Does a straight-down drop like that provide enough time for chutes to fully deploy on Duna?

[aluc24]

Simple: don't use MechJeb. You've obviously proven through experience that MechJeb isn't up to the task of putting modules on target.

The best way to do it is old school. General rules:

-- Your approach should be via equatorial orbit if possible, otherwise the target will drift sideways relative to you as you approach it.

-- Line your orbit up so you pass directly over the target.

-- Decelerate as you approach it. Then, when you're directly overhead of the target, retro thrust sideways until you're dropping straight down. Preferably after the nav ball goes to Surface mode, that way "down" is actually straight down.

But doing this requires to kill almost all of the orbital speed. That's quite a lot of fuel...

[Just Jim]

While you'll have to adjust for the thin Duna atmosphere, I use Scott Manley's method of precision landing. With practice I've learned to land pretty much anywhere I want using this.

[aluc24]

While you'll have to adjust for the thin Duna atmosphere, I use Scott Manley's method of precision landing. With practice I've learned to land pretty much anywhere I want using this.

This is great tutorial for non-atmospheric bodies, but as I said, what I want to make is a precision non-powered descent, using parachutes only... With engines, I can land within 100m of my target, it's no problem. But I want to do it without engines.

[Graveworks]

This is great tutorial for non-atmospheric bodies, but as I said, what I want to make is a precision non-powered descent, using parachutes only... With engines, I can land within 100m of my target, it's no problem. But I want to do it without engines.

How about using the techniques above combined with partially opening your chutes as you approach the target and then manipulating the full opening altitude to come to a stop just as you come over the target?

[ForScience6686]

I have the same concerns on my duna trip. I decided to go with multiple crafts and only one being manned. This way I can test landing with the unmanned craft to get a hang of it for the manned craft. If I mess it up I've sent a rover to ferry the crew. Anything that might need exact placement can then be moved on ground with small hops or wheels.