[1.0] XT Landertron - Smart Retrorockets for Landers and Spaceplanes v0.08 Oct 10

[Zephram Kerman]

IIRC, the Shuttle SRBs were designed to gradually reduce thrust toward the end of their burn. This was done by shaping the exposed surfaces of the fuel during construction. So if your LanderTron motors change thrust over time, it would make sense to me.

But I think I like Aquilux' vent idea better. The visual cues help people understand what's going on. With any new mod, it's easy to think some problem is due to the mod not working. So simple and obvious might be preferable. (Also, that small automatic 'holddown' thrust would be very convenient!)

[DerekL1963]

I think that the reusable version, if you make it, should look kind of like the B9 aerospace separatrons but with a "vent nozzle" on the top angled 45° out, and a section along the side that is actually the fuel plug. The thought is that the rocket fires normally until touchdown, and then the vent nozzle pops open. With a much larger opening and no nozzle to speak of, the rest of the fuel burns off at a downright horrible ISP with the downward thrust dropped to almost nothing. (In fact, I think this behavior is preferable even for the one-shot version)

FWIW - this is a bog standard real world engineering technique for "shutting down" solid fuel rocket motors. (Usually there's no need to actually shut them down, you just need them to produce zero net thrust.) It wasn't used on the Shuttle for reasons that are off-topic here.

[XanderTek]

Version 0.04 is up! Landertrons now jettison unused fuel instead of exploding. Currently that doesn't result in any force, but perhaps it will in the future. A refuel option is available while in EVA, and a hexcan with spare solidfuel is included. The refuel command will cause the Landertron to grab solid fuel from the first source it sees on the vessel that isn't a Landertron. The hexcan can be grabbed and attached if you have KAS installed, allowing for easier refueling maneuvers.

Landertrons should now work fine when mounted on a sloped surface like the Mk1 pod, though angling them does waste a lot of fuel. You can even set them up so that they spin your craft while landing! Also, calculations should take into account when other mods change engine specs during flight (like KIDS).

Any thoughts on parameters you'd like to have the ability to adjust with the new tweakables feature in KSP 0.23?

I'm thinking about taking axuilux's idea and making it into a separate part: a smaller srb that's mounted upside down on your lander and triggers as soon as you touchdown. It would fire for a few seconds at very low thrust in an attempt to prevent you from bouncing or sliding. The original idea of adding this functionality to the Landertron is neat, but it would sometimes result in the engines pushing you downwards while you're still a meter or 2 up. Also, I'm not yet familiar with a method for reassigning the thrust vector like that.

Edited December 17, 2013 by XanderTek

[Desrtfox]

Version 0.04 is up! Landertrons now jettison unused fuel instead of exploding. Currently that doesn't result in any force, but perhaps it will in the future. A refuel option is available while in EVA, and a hexcan with spare solidfuel is included. The refuel command will cause the Landertron to grab solid fuel from the first source it sees on the vessel that isn't a Landertron. The hexcan can be grabbed and attached if you have KAS installed, allowing for easier refueling maneuvers.

Landertrons should now work fine when mounted on a sloped surface like the Mk1 pod, though angling them does waste a lot of fuel. You can even set them up so that they spin your craft while landing! Also, calculations should take into account when other mods change engine specs during flight (like KIDS).

Any thoughts on parameters you'd like to have the ability to adjust with the new tweakables feature in KSP 0.23?

I'm thinking about taking axuilux's idea and making it into a separate part: a smaller srb that's mounted upside down on your lander and triggers as soon as you touchdown. It would fire for a few seconds at very low thrust in an attempt to prevent you from bouncing or sliding.

They seem to be working well. Perfect for the one man capsule, and a little bounce with the 3 man capsule. The hexcan seems to not be enabled for career mode.

I really like the idea of the refueling needing the EVA. Good idea.

[mvronsky]

My Soyuz replica is now complete...

This mod is fantastic

Thanks

[mvronsky]

My Soyuz replica is now complete...

This mod is fantastic

Thanks

[Anister]

Am I the only one who thinks "DROP PODS"?

Yeah probarly not

EDIT: works great, but water landings are impossible sadly.

[aquilux]

I'm thinking about taking axuilux's idea and making it into a separate part: a smaller srb that's mounted upside down on your lander and triggers as soon as you touchdown. It would fire for a few seconds at very low thrust in an attempt to prevent you from bouncing or sliding. The original idea of adding this functionality to the Landertron is neat, but it would sometimes result in the engines pushing you downwards while you're still a meter or 2 up. Also, I'm not yet familiar with a method for reassigning the thrust vector like that.

To go into more detail, my thought was to have two engine modules as part of the one model, one pointed down with something like... thrust: 45 isp: 300, and the other with something like... thrust: 5 isp: 20, both of which would be fed by the solid fuel in the part.

The plugin would fire the primary engine like normal, but upon touchdown, it would simultaneously throttle down the primaries to a minimal level and activate the "vent" engines, giving the impression of venting the majority of the gasses out the top.

[XanderTek]

Version 0.05 is up! I added 2 new modes (selectable via tweakables) to the Landertrons. VSL is used to brake a landing space plane, and StayPut stops a lander from bouncing once it touches down. See the updated instructions in the first post. The hexcan has been added to the tech tree (sorry about that!). Also, in classic mode, activation height calculations will take into account the angle of your lander. Assuming you don't change that angle after they fire, you'll always reach the ground with roughly zero vertical speed. Your horizontal speed can decrease or increase in the process... so aim carefully!

To go into more detail, my thought was to have two engine modules as part of the one model, one pointed down with something like... thrust: 45 isp: 300, and the other with something like... thrust: 5 isp: 20, both of which would be fed by the solid fuel in the part.

The plugin would fire the primary engine like normal, but upon touchdown, it would simultaneously throttle down the primaries to a minimal level and activate the "vent" engines, giving the impression of venting the majority of the gasses out the top.

I understand, and its a good idea. My main concern is that the Landertrons often need to stop firing before touchdown. If this venting produced enough force to actually stop you from bouncing, that would mean significant downwards force before landing, which is bad for your craft. You really want the landing legs to absorb the shock of landing and begin to rise before adding any additional downwards force. It would work better if there were a delay between the main landertron firing and the venting, but that sort of strays from the idea of a semi-realistic solid fuel system. I'll continue to consider it.

Edited December 18, 2013 by XanderTek

[Desrtfox]

It seems the classic mode landertrons in 0.05 are detonating at end of fuel, rather than just consuming/jettisoning the extra fuel.

Also, regarding models, perhaps your could collaborate with PDCWolf:

http://forum.kerbalspaceprogram.com/threads/37138-Wolf-Aerospace-Perfectrons-L-E-S-Pack

Edited December 18, 2013 by Desrtfox

[XanderTek]

Odd... Did you update the part.cfg? There's an option in there that determines whether they explode. It should be boom=false

[Desrtfox]

Odd... Did you update the part.cfg? There's an option in there that determines whether they explode. It should be boom=false

I have not updated the .cfg. boom=false is what I have in my config. I'm running a lot of mods though, and given that .23 support is sketchy at best on some of them, I'll do some better testing for you. It may be a problem on my end.

[XanderTek]

It's working fine for me in 0.23. I repackaged it as v0.05a with a few minor fixes. I'm not sure it'll help, but try deleting the whole Landertron folder and using this new one instead. Also, if you're testing on a saved ship that loads with the Landertrons already in place, try removing them and putting new ones in their place. I've run into a few issues with the parts not properly updating when loading a ship that was last modified a few versions back.

Are you seeing the exact same functionality as the early versions: a fairly soft landing followed by an explosion? Are the tweakables options there when you right click?

Edited December 18, 2013 by XanderTek

[david8029]

How does this fair with FAR and Deadly Reentry?

[XanderTek]

How does this fair with FAR and Deadly Reentry?

Good question! I don't typically play with those so I haven't checked. My activation height calculations are based on the current acceleration the pod is experiencing, so that should automatically adjust to different air resistance. Landertrons only handle the last 100m or so of a flight. If you can get to that point without burning up, and with a velocity that doesn't exceed the delta-v in your landertrons, you should land just fine. With the stock game, you can just fall from orbit and you'll be within those parameters at 100m. It's up to you to get there with FAR and DR. Adding a drogue (or regular) chute would probably improve your chances, even if it wouldn't produce enough drag for a safe landing by itself.

If you get a chance to try it, let me know. I'd be interested to hear how it goes.

[Desrtfox]

Good question! I don't typically play with those so I haven't checked. My activation height calculations are based on the current acceleration the pod is experiencing, so that should automatically adjust to different air resistance. Landertrons only handle the last 100m or so of a flight. If you can get to that point without burning up, and with a velocity that doesn't exceed the delta-v in your landertrons, you should land just fine. With the stock game, you can just fall from orbit and you'll be within those parameters at 100m. It's up to you to get there with FAR and DR. Adding a drogue (or regular) chute would probably improve your chances, even if it wouldn't produce enough drag for a safe landing by itself.

If you get a chance to try it, let me know. I'd be interested to hear how it goes.

So, it seems the issue I am seeing is an issue with Deadly ReEntry. It seems like DR still has some .23 issues. At least one of those issues appears to be related to it's destruction of rocket parts based on G-force, which was ultimately what was causing the landertrons to explode.

[aquilux]

I understand, and its a good idea. My main concern is that the Landertrons often need to stop firing before touchdown. If this venting produced enough force to actually stop you from bouncing, that would mean significant downwards force before landing, which is bad for your craft. You really want the landing legs to absorb the shock of landing and begin to rise before adding any additional downwards force. It would work better if there were a delay between the main landertron firing and the venting, but that sort of strays from the idea of a semi-realistic solid fuel system. I'll continue to consider it.

Huh, I would've thought that the margin of error fell to the side of landing too hard, not stopping too soon. Personally I would prefer the risk of landing too hard instead of stopping too soon. If adjusted to cut out upon contact at the earliest, what would the margin of error look like? What's the highest speed impact that we'd be dealing with given there's enough delta V? What would it take to bring that number down to a reasonable level?

IMO, if I were to use this on something I would only care that my major parts would be okay. I really wouldn't mind if the gear broke because they can be fixed, and I wouldn't be mad if bigger things broke because to me the nature of this part makes it a serious gamble in the first place. To me it seems more fitting if there was a serious chance of lithobraking to kill the last dozen m/s upon contact, that way you could just fire these at/just barely past the last moment and let them run until your vertical speed goes positive, then pop the vents.

TLDR: I feel like people really wouldn't be using these if they wanted a gentle landing.

[Desrtfox]

Would it be possible to get the heightmultiplier and offset added as tweakables?

[DerekL1963]

TLDR: I feel like people really wouldn't be using these if they wanted a gentle landing.

At least in the case of the RL ones these are modeled on, a gentle(er) landing was the whole point of their existence. Why should the in-game ones be any different?

[XanderTek]

@aquilux

I'd like fairly gentle landings to be possible. As Derek points out the inspiration for this was the Soyuz, which lands at just 5 ft/s. Because you're often coming in so fast with landertrons, a fraction of a second difference in firing time can result in hitting the ground at 20+ m/s. I try to keep the average height of zero velocity at exactly ground level, but there seems to be some variance in how different ships perform. Stopping a little early is often safer than stopping a little late. Solid rockets alone will never be the softest landing, but I'm not going to go out of my way to make the landings rougher. If you want a harder landing, the heightmultiplier and offset variables are there in the part.cfg file to allow you to tweak the performance to your liking. Setting them to 1 and 0 respectively should result in few if any early stops.

As I said before, having something that exerts a downward force to stop you from bouncing on low grav bodies was a good idea. StayPut mode was added to do just that. The engines will wait until the lander absorbs the initial shock of touchdown, and then fire to keep it there.

@Desrtfox

I'll look into it. Currently, I'm only aware of modders having the ability to add tweakable buttons (like the ones I use to change modes), not sliders. Plus and minus buttons could work, but they'd be a bit awkward. Scratch that. Found some good slider examples. It'll be in the next version! Any other tweakables you'd like?

Speaking of those values, if anyone comes up with better default ones I'd love to hear it.

Edited December 21, 2013 by XanderTek

[aquilux]

As Derek points out the inspiration for this was the Soyuz, which lands at just 5 ft/s. Because you're often coming in so fast with landertrons, a fraction of a second difference in firing time can result in hitting the ground at 20+ m/s. I try to keep the average height of zero velocity at exactly ground level, but there seems to be some variance in how different ships perform. Stopping a little early is often safer than stopping a little late. Solid rockets alone will never be the softest landing, but I'm not going to go out of my way to make the landings rougher. If you want a harder landing, the heightmultiplier and offset variables are there in the part.cfg file to allow you to tweak the performance to your liking. Setting them to 1 and 0 respectively should result in few if any early stops.

Ah well, sorry about the misunderstanding. Would it be possible to get the option to turn on the combined vent and hold down force in the .cfg?

[XanderTek]

Ah well, sorry about the misunderstanding. Would it be possible to get the option to turn on the combined vent and hold down force in the .cfg?

No problem, I welcome the input. If I can find an easy way to do it, I'll try adding the vent+stayput as an option. However from what I've been able to figure out so far, it looks like pretty complex functionality to code. I'm not convinced it would improve landings, and it doesn't seem any more realistic than a multi-directional venting that results in no net forces. In addition, the basic functionality is already there with the StayPut mode. So long as I can't see any added value from this proposed mode, it's not going to be a high priority.

I am looking for more modes to add. I started playing around with a launch escape mode that fires automatically when it detects a part of the ship breaking/exploding. However so far, I think it might be a bit too hard to accurately determine which circumstances actually warrant an abort. Many minor mishaps can be recovered from. Without this automated functionality, the Landertrons would just be firing on command which is no different than sepratrons.

Small progress update: Tweakables for heightmultiplier and offset are working, and Landertrons will draw electric charge while armed. I'm in the process of testing both.

[XanderTek]

Version 0.06 is up! There are new tweakable options, electric charge is consumed, and there are color coded staging icons. Also, a larger radial model and a new inline one. Unfortunately, still using stock models. So far, my attempts at using blender haven't resulted in any models worth adding...

Oh, there does seem to be some conflict between this mod and MechJeb's "Prevent Overheat" option. Having that active while using landertrons results in your throttle getting stuck at zero. I'm working on figuring it out.

Your feedback is appreciated!

[Desrtfox]

Thanks for the update. I'll test it out over the next few days.

[XanderTek]

I uploaded v0.06a. Fixed the conflict with MechJeb by reworking how the engines are turned on and off. As a result, you'll only see a fuel bar next to the staging icon when they're actually firing. Use the icon color to determine if they're armed. The new method should cause fewer conflicts with other mods too. Also, after refueling a blank stage will be added to your staging, which means you don't need to move the Landertrons around manually before activating them again, just hit space once or twice. Lastly, the Landertrons now default to space plane mode when you grab a new one in the SPH.