Tylo descent profile

[Lunar Sea]

I want to nail it on the first try. 

[Plusck]

Tylo descent profile?

1) bring Pe down to a couple of kilometres above the surface. Pick a spot which is nice and flat for a long, long way.

2) burn retrograde just before you get to Pe. Watch your vertical climb/descent rate on the meter (or in KER/Mechjeb). As you reach Pe it will start to rise for a short while. When you slow enough for Pe to move around the planet, it'll start to fall.

3) as soon as the vertical speed exceeds a certain "reasonable" amount (depending on your TWR), start burning slightly radial-out until it stabilises at a constant rate. Knowing how long until you plan to reduce velocity to zero (you should have placed a node to find this out, before starting), divide this time by your altitude, and keep vertical descent at exactly that number.

4) if you get 3) right, you will attain zero horizontal velocity just as you arrive at the ground. Very gently alter your thrust so that you come down at a constant rate. Setting SAS to retrograde hold might help here.

[JedTech]

Tylo will nail you on your first try. This is working as designed.

But here's a suggestion: Keep a very high thrust to weight ratio. Like 1.5 to 3.0

Edited September 7, 2016 by JedTech

[Pecan]

Yeah, as @plusck and @jedtech have said, there's nothing special about Tylo as a vacuum body, except that it will kill you.  My only tips are; Twice as much fuel as you expect and F5 before starting.

[Aegolius13]

Your profile will depend hugely on how much TWR you're packing.  On the lander for my recent Jool 5, I started with a TWR only a bit over 1.  I had to begin my descent from a 40km-ish orbit, and burn retrograde basically all the way down.  

Also, while Tylo is not hugely mountainous, topography can make the difference between "perfect suicide burn" and plain old suicide + burning.  

Thus, it's likely you'll have to use a little trial and error to get it just right.  If you think you have a little spare delta-v, obviously better to err on the side of starting higher. 

 

[Snark]

Also, given how high the dV requirements are, I'd advise not trying to build a SSFO unless you're a glutton for punishment.  Use staging. Drop tanks during descent, asparagus during ascent.

[Lunar Sea]

I just checked my ship, still halfway to Jool and noticed the auxiliary fuel lines from the drop tanks aren't connected to the main tank correctly, they attached to the landing gear! Argh! The subassembly was fine! I hate the VAB sometimes. It's a pretty simple design, basically the X200-8 'tuna can' with a lander can on top and 1 Aerospike on the bottom, with six stacks of Oscar-Bs asparagus staged. I guess I'll just have to manually transfer the fuel from the 36 Oscar tanks during the descent. What could go wrong? 

[fourfa]

Fuel lines in assemblies are risky, they often seem to reattach all wonky. Regardless - you could temporarily install a fuel pump mod to force it to observe the intended stock behavior. Then uninstall- or keep it for the enormous creative possibilities it opens up

Edited September 8, 2016 by fourfa

[Mikki]

consider a three staged lander... and much TWR

[juanml82]

19 hours ago, Plusck said:

Tylo descent profile?

1) bring Pe down to a couple of kilometres above the surface. Pick a spot which is nice and flat for a long, long way.

2) burn retrograde just before you get to Pe. Watch your vertical climb/descent rate on the meter (or in KER/Mechjeb). As you reach Pe it will start to rise for a short while. When you slow enough for Pe to move around the planet, it'll start to fall.

3) as soon as the vertical speed exceeds a certain "reasonable" amount (depending on your TWR), start burning slightly radial-out until it stabilises at a constant rate. Knowing how long until you plan to reduce velocity to zero (you should have placed a node to find this out, before starting), divide this time by your altitude, and keep vertical descent at exactly that number.

4) if you get 3) right, you will attain zero horizontal velocity just as you arrive at the ground. Very gently alter your thrust so that you come down at a constant rate. Setting SAS to retrograde hold might help here.

The problem with "a couple of km above the surface" is that it takes a lot of time to kill horizontal velocity and you'll fall quickly. So, usually, you'll need to bring Pe to several dozen km above the surface.

Depending on the lander' size, I'd build the descend stage around a Rhino engine. Huge, but it combines plenty of thrust with very good isp. The aerospikes are a good option for smaller vehicles. I wouldn't trust that part of the descend to more efficient, but less powerful vacuum engines (Terrier, Poodle, Nerv) because of the time required to kill horizontal velocity without, at the same time, crashing into the ground

[Plusck]

15 minutes ago, juanml82 said:

The problem with "a couple of km above the surface" is that it takes a lot of time to kill horizontal velocity and you'll fall quickly. So, usually, you'll need to bring Pe to several dozen km above the surface.

That's the whole point about adding a radial-out vector to kill vertical acceleration. If you have a low-TWR craft (and on Tylo, it's expensive to have anything else), you are likely not to have sufficient thrust to do a suicide burn in any meaningful sense: you simply cannot negate vertical speed in time before hitting the surface. And the higher you have to fall, the more the total vertical acceleration you will need to kill.

So rather than risking everything on the off-chance you can slow in time, you just need to pack extra fuel and prevent vertical acceleration from happening in the first place.

[Lunar Sea]

Damn, that ride was a hoot. Took me 4 or 5 tries. You guys' advice really helped. Having to manage fuel transfer from the outer tanks definitely increased the workload! I coulda done it on the first if the damn fuel lines had attached! 

Also found out high thrust can really exacerbate any weight imbalances. God I love this game. 

Now I want to go again! With a better lander!

 

 

Edited October 29, 2016 by Lunar Sea