LV-909 - Luna 9 mission

[technion]

Hey guys,

I'm fairly new to the game and working through the historic missions.

I spent a lot of time struggling with the Luna 9 (first probe to the moon) mission. I never seemed to be able to get an appropriate Kerbin orbit with more than a few seconds left of fuel in the third stage. This seemed to be OK based on the wiki's guide.

The problem was that once I moved to stage four, the LV-909 just didn't seem to propel. I mean it looked like it was firing, you could see the trail coming out the back of the rocket, etc. But after numerous failed attempts at a Mun trajectory, I dropped an entire tank burning prograde at the apoapsis and the proapsis moved about 10m.

I can use the manoeuvre tool with stage three intact, and it will suggest a 26 second burn. If I drop that stage, the tool suggests the LV-909 rocket will take a three DAY burn to make the same trajectory. It just feels broken. Using the RCS thrusters gives way more thrust.

I was sure this was something in the way I built the rocket, but after nearly a day of being unable to fix it, I tried replacing the LV-909 on stage four with another LV-T30, nothing else about the build changed. Several guides assure me that, due to fuel efficiency reasons, this isn't the most appropriate - well it sure was for me because I've just landed this probe on the Mun (yay.. I can't believe how much time this took.. looking forward to getting a crew there!)

Anyway, I don't know if I should feel like I cheated this mission using the "wrong" engine, or whether I should feel I've done a "harder" mission or what, but I guess the pertinent question is, why did the LV-909 behave so uselessly to me?

[Johnno]

Anyway, I don't know if I should feel like I cheated this mission using the "wrong" engine, or whether I should feel I've done a "harder" mission or what, but I guess the pertinent question is, why did the LV-909 behave so uselessly to me?

No you shouldn't feel like you cheated the mission, it's a tutorial and not a 100% accurate recreation of the historical flight anyway. However, having flown that particular mission myself I can say that the craft works fine, the LV-909 itself couldn't have been the issue. Off the top of my head it sounds like you either clipped the engine into something, that there was something obscuring the engine or that something was clipped into the engine inside it.

As for a troubleshooting approach, I'd advice you to redo it and design it from the top down as you normally would, but try it between each stage. Design your payload, test it (even if it won't get off the ground). Then add the stage before it, and test. The continue so for each stage.

With the Luna 9 payload and a FL-T400 tank below it a LV-909 can lift it even on Kerbin, so put that on the pad and test it.

Could your decoupler have been on the wrong way so it dropped the tank and was still attached to the engine? That'd cause it to not exert any thrust. The arrow needs to point at what you want to detatch (so the engine).

[SRV Ron]

Hey guys,

I'm fairly new to the game and working through the historic missions.

I spent a lot of time struggling with the Luna 9 (first probe to the moon) mission. I never seemed to be able to get an appropriate Kerbin orbit with more than a few seconds left of fuel in the third stage. This seemed to be OK based on the wiki's guide.

The problem was that once I moved to stage four, the LV-909 just didn't seem to propel. I mean it looked like it was firing, you could see the trail coming out the back of the rocket, etc. But after numerous failed attempts at a Mun trajectory, I dropped an entire tank burning prograde at the apoapsis and the proapsis moved about 10m.

I can use the manoeuvre tool with stage three intact, and it will suggest a 26 second burn. If I drop that stage, the tool suggests the LV-909 rocket will take a three DAY burn to make the same trajectory. It just feels broken. Using the RCS thrusters gives way more thrust.

I was sure this was something in the way I built the rocket, but after nearly a day of being unable to fix it, I tried replacing the LV-909 on stage four with another LV-T30, nothing else about the build changed. Several guides assure me that, due to fuel efficiency reasons, this isn't the most appropriate - well it sure was for me because I've just landed this probe on the Mun (yay.. I can't believe how much time this took.. looking forward to getting a crew there!)

Anyway, I don't know if I should feel like I cheated this mission using the "wrong" engine, or whether I should feel I've done a "harder" mission or what, but I guess the pertinent question is, why did the LV-909 behave so uselessly to me?

The Add maneuver Mode can give erroneous readings when staging occurs during a burn. Just continue the burn until the counter reached zero or better yet, view the burn in map mode and cut power as soon as the intercept takes place. Be sure to throttle down near the end so you don't overshot the intercept.

The upper stage LV-909 is more then enough. Replacing with the LV-30 upsets the balance due to the heavier weight.

This two stage example using NovaPunch, the launch engine is the equivalent of one and a half LV-909, the first stage fuel tank similar to the FL-T400 in size, not only made orbit but has more then enough fuel left to orbit Mun or Minmus.

[Person012345]

I've never had that problem with the 909. As said above, could the engine have been clipped or obstructed?

[SRV Ron]

I've never had that problem with the 909. As said above, could the engine have been clipped or obstructed?

That is always a possibility. A posted pic may show what could be the problem.

I have tested the above example with an LV-909 but had to remove the SAS module to cut the weight so it would get off the launch pad. In that test it did reach orbit but fuel was wasted fighting gravity due to slow acceleration. (The 50 % more powerful NovaPunch engine with a 75 unit thrust is not vectored so the SAS is needed on that stage.) (An LV-30 or LV-45 is less efficient on that design due to the extra weight and too much thrust.)

[Epthelyn]

I've never had that problem with the 909. As said above, could the engine have been clipped or obstructed?

That sounds like the problem. 3 days for the dV required to get to the Mun is about 2mm/s per acceleration. Even circularizing after an encounter with Tylo using a single ion engine only takes 1-2 hours.

Some pictures of the rocket would be useful.