Having trouble getting off Laythe

[Mitchz95]

So today I managed to land Will Kerman safely on the surface of Laythe. Huzzah and all that. Now I'm facing an even greater challenge: getting him back into orbit so he can rendezvous with the transfer stage. According to KER, the lander has about 3,100m/s left (when physics load, 2,800). The wiki says that should be more than enough, but every time I take off I seem to run out of fuel before I can circularize. What is the optimal ascent path for a rocket-powered lander?

[Taki117]

My Advice, Treat Laythe like Kerbin, but you can start your gravity turn earlier. (About 5km if memory serves) Also, don't forget Laythe has an atmosphere! You need to account for atmospheric drag.

[Mitchz95]

My Advice, Treat Laythe like Kerbin, but you can start your gravity turn earlier. (About 5km if memory serves) Also, don't forget Laythe has an atmosphere! You need to account for atmospheric drag.

How sharply should I turn at 5km? On Kerbin I turn 45 degrees at 10km, then cut engines when my apoapsis hits 80km and set a maneuver node for the circularization.

[cantab]

Circularise with the jet pack.

[Mitchz95]

Circularise with the jet pack.

Unfortunately, there's no command pod on my transfer stage. So I'd have no way to get him back to Kerbin. I guess I could send a rescue mission to pick him, but he'd be pretty bored sitting in orbit by himself.

[EdFred]

What's your TWR on Laythe?

You can have eleven billionty dV, but if your TWR is 0.2 you aren't going anywhere.

[Mitchz95]

What's your TWR on Laythe?

You can have eleven billionty dV, but if your TWR is 0.2 you aren't going anywhere.

At 100% thrust, it reads as well over 2.0. I've tried reducing it to match terminal velocity, but it seems no matter what I do I'm 200m/s short.

I guess I could get out and push to finish circularizing, but that seems a bit … imprecise.

[Specialist290]

How sharply should I turn at 5km? On Kerbin I turn 45 degrees at 10km, then cut engines when my apoapsis hits 80km and set a maneuver node for the circularization.

A while back I put together a handly little atmospheric pressure table for all the bodies that have atmospheres. Without going into the math, Laythe's atmo starts out a little bit thinner and thins out a little more quickly than Kerbin's does. The ~8-11km bracket on Kerbin (where I typically start most of my gravity turns myself) is roughly within the same pressure range as the ~5-8km bracket on Laythe. Other than that, if your launch profile works for Kerbin, it'll probably work well for Laythe (barring piloting errors, of course).

[HafCoJoe]

I'm sorry I cannot give advice on a rocket powered descent other then plan by landing one that can take off of Kerbin :/. If you want my opinion for future missions read on!

My real suggestion is building a lander wit jet engines and detaching them when they burn out. I have a video of my Laythe descent in my most recent streams if you want an example lander. Try going sideways much more than I did. I practiced descent from Kerbin and tried taking off from Laythe the same general way on the assumption that it's atmosphere was only 8/10 of kerbin and not much different (though it is pretty different). I made it back to my return station fine but I raised out of atmo much faster than I planned and used a considerably smaller amount of jet fuel than I planned (I emptied the tanks to 30 of 150 units when launching and I only used like 7 units when leaving atmo. Just meant more rocket fuel needed). For a base I suggest a stable plane and base on wheels.

Edited May 8, 2014 by Avera9eJoe

[EdFred]

At 100% thrust, it reads as well over 2.0. I've tried reducing it to match terminal velocity, but it seems no matter what I do I'm 200m/s short.

I guess I could get out and push to finish circularizing, but that seems a bit … imprecise.

You're already right on the edge, since wiki says 2800dV is needed, and you are *right there* Your ascent is going to have to be near perfect. Your missing it by about 7% which is probably about what most people are at with perfection vs execution. Just keep tweaking your ascent profile.

[Mitchz95]

Well, I've given up. No matter what I do, I can't seem to bridge that 200m/s gap. Guess I'll have to send a rescue mission …

What's really frustrating is that the lander was overbuilt; it should have had well over 3,500m/s for the ascent and rendezvous. But when I entered the atmosphere, my trajectory put me over a tiny lake in the middle of the continent, so I had to burn the engines to get over it. If I'd just waited half a second before deorbiting, I'd be on my way home right now.

Ah, well. At least I'm not using any life support mods. Thanks for the help, everyone.

[LameLefty]

The biggest thing you need to do is not aim for that 80 km apoapsis on ascent. Laythe is smaller than Kerbin and has lower gravity. A stable orbit for Kerbin is anywhere over 70 km, so you can probably reach a stable ~60km-ish orbit with what you've got.

[cantab]

For Laythe, a 55.5 km orbit will suffice, in case you were trying for higher. Of course this assumes you have control of the transfer stage to rendezvous.

In fact, if you do have control of the transfer stage, you could put the lander on a suborbital trajectory and rendezvous with it from there. It won't be easy, you'll need your timing to be just so, but it's possible. If it then leaves you short of delta-V to get home, use gravity assists to help - Tylo or Laythe can boost you out of the Jool system, or else look for a Duna encounter or another Jool encounter to help drop your solar orbit periapsis for the Kerbin intersect.

[Mitchz95]

For Laythe, a 55.5 km orbit will suffice, in case you were trying for higher. Of course this assumes you have control of the transfer stage to rendezvous.

I've been going for 55km. Once I even tried going for 45km, in the hopes that I could push myself out of the atmosphere via EVA. I still wasn't able to circularize.

In fact, if you do have control of the transfer stage, you could put the lander on a suborbital trajectory and rendezvous with it from there. It won't be easy, you'll need your timing to be just so, but it's possible. If it then leaves you short of delta-V to get home, use gravity assists to help - Tylo or Laythe can boost you out of the Jool system, or else look for a Duna encounter or another Jool encounter to help drop your solar orbit periapsis for the Kerbin intersect.

Hmm … that might actually work. It's be pretty dangerous, but if I manage to pull it off it would go down as one of my most dramatic missions. Thanks for the suggestion!