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Matuchkin
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@winged What engine mods are you using? Those look great! Don't have such a great engine selection here. Also I have a question that would probably go better in the discussion thread but I don't care. I am trying to design a lander. The best lander and orbiter propellant I have found so far is either Aerozine/NTO or MMH/MON3. There are others if I remember correctly but I just can't think of them. Now for some reason, these propellants become unstable at random times and I cannot activate my engine until it randomly turns back to being stable. This happens while timewarping, after a burn or just at a completely random time when I'm not firing the engine or timewarping. Is this a glitch? I am playing in the 1.2 pre-release. Or is there a way to fix it? And also, I'm thinking of reverting to 1.1.3 in this installation. How do I do that? I made a copy from steam with this one.

Thanks!

Fire

Edited by Firemetal
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@Firemetal, hey, the unstable fuels are due ullage I think. You need to put some force on the fuel so it flows to the bottom of your fuel tank, this can be done by ullage rockets. (tiny retro rockets, only pointing forward). Or by accelerating with your rcs. The fuel becomes unstable after its Pe because the crafts slows down from there and it becomes stable by itself after its Ap.

Also, a reason for instability is because some fuels boil of, to be precise: all fuels with liquid in its name.

 

Hope this helped. :)

~drlicor 

 

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12 minutes ago, DrLicor said:

@Firemetal, hey, the unstable fuels are due ullage I think. You need to put some force on the fuel so it flows to the bottom of your fuel tank, this can be done by ullage rockets. (tiny retro rockets, only pointing forward). Or by accelerating with your rcs. The fuel becomes unstable after its Pe because the crafts slows down from there and it becomes stable by itself after its Ap.

Also, a reason for instability is because some fuels boil of, to be precise: all fuels with liquid in its name.

 

Hope this helped. :)

~drlicor 

 

Ahh. I did forget to mention it became stable when firing RCS... Thanks!

Fire

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@Firemetal, ah indeed, yes than it's just normal, like real life. 
When a rocket is on the launchpad you don't to worry about things like ullage, because gravity pushes the fuel down eventually. But in space, or when decelerating, the fuel in the tanks are free to move forward and the engines lose their pressure, and you get the message 'vapor in the fuellines'.
But indeed, this all can fixed by firing ullage rockets or the RCS for a few seconds so the fuel is pushed backwards to the engines. 
The Russians have a whole other technique, it's called hot staging. When the first stage burn out, and the second stage is about to start, the fuel can flow upward due the change of acceleration, Most rockets have those ullage rockets which help the engine to start and keep the fuelflow normall, But mother russia likes it the other way.
The second stage starts a good 30 seconds before the first stage flamed out. This way, you've never the problem of upwards flowing fuel, however, there's a bit more danger in it.

 

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21 hours ago, DrLicor said:

When a rocket is on the launchpad you don't to worry about things like ullage, because gravity pushes the fuel down eventually. But in space, or when decelerating, the fuel in the tanks are free to move forward and the engines lose their pressure, and you get the message 'vapor in the fuellines'.

I actually never understood why. I mean, sure, microgravity takes effect in such conditions, but isn't your rocket already accelerating? That should push the fuel backwards, which should fuel the engine, which should accelerate the rocket even more, which should push more fuel backwards, etc. How does that not happen?

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@Matuchkin, not during staging, compare it with shifting a racecar.
When you shift up, you get that little shock frontwards you know? That's the same with fuel. 
When the acceleration stops for a few seconds, it tends to go more to the front. It's not the movement of the rocket of the rocket that counts, it's the momentum. Not the speed, but the acceleration. The one you define with m/s2

The tank and the fuel are pushing the rocket forward, but the atmosphere is pushing it a tiny bit backwards that causes a de-acceleration. And because the fuel is heavier than the density of the atmosphere, it tends to flow forwards. 
A funny experiment you can do to test this, is a balloon with a certain gas, tied in a car. The car simulates the rocket/fueltank, the balloon the fuel. When you get your foot of the gas pedal, the balloon with a heavier gas, will slowly move forward in the car, the balloon with a lighter gas, helium for instance, will move backwards.

Here's a vid that explains it all :)

a7b108e8dca865d2972094197beaa7fedadf0c15f5298fd3f4aea36d2cbf1924.jpg


 

Edited by DrLicor
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28 minutes ago, Matuchkin said:

I actually never understood why. I mean, sure, microgravity takes effect in such conditions, but isn't your rocket already accelerating? That should push the fuel backwards, which should fuel the engine, which should accelerate the rocket even more, which should push more fuel backwards, etc. How does that not happen?

As much as I understand, you have to mind in which direction the fuel is accelerating relative to the engine. If the fuel is being accelerated by the same force as the engine is, then Delta a = ~0 (there may be some minimal difference, as the outter structure is being affected by aerodynamic resistance in the upper atmosphere). This means, that the fuel is not - minimally - changing its velocity to the engine.

Edited by Karol van Kermin
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@Karol van Kermin, Same as with refueling on earth, you need to have a higher pressure in the refuel-tank. This causes to flow the fuel to the lowest pressure tank. In many rockets/spacecrafts, helium is used to generate pressure and control the fuel flow. 
On ISS there's a special robot that managed the fuel flow. The RRM-module. But in the end, I understand it has to do with pressure. 

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23 hours ago, DrLicor said:

The second stage starts a good 30 seconds before the first stage flamed out.

Say what? In most vehicles that do this, the stage starts 2-3 seconds before flameout (for Chang Zheng, the verniers are ignited 6 seconds ahead, that's the most I could find).

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@Ravenchant, verniers of the second stage provide great stability and can be used as sort of ullage rockets.
I've read an article a while ago about some russian rocket that hotstaged 30 seconds before flame out. But I don't think it was on full throttle, at least, I assume not.  

Oh and something totally different. I'm currently working on some MM-configfiles to make the MK4 mod ready and realistic for RSS/RO. So maybe I post a new ship out here haha. 
It just I wanted a larger cargo-ship than the current space shuttle. And the MK4 mod looks neat good for that. 

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Well I have been designing and redesigning my LLM-1 mission for a while and have a design that looks as if it will work.

3ds7Gwj.png

I have begun to use KER again since calculating all this dV and TWR with a windows 7 calculator gets tedious. In my stock game, I can still do this but not in RO. I wanted to make a design that was close to either the Saturn V or Ares V for practicality purposes but that all depends on the weight of the payload, so with a nearly 70 ton payload to go to the moon, that just wouldn't work. It is a 3 stage rocket with about 1200 m/s spare to reach orbit. Since I'm using the Apollo CSM engine with 36 ignitions and approximately 3500 m/s of dV on it's own, I might be able to use a bit of that to get the optimal lunar transfer but only if the dV left in the burn is <500 m/s.

Flying the mission now. Will post a report later. (This depends on whether or not it is successful)

Fire

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Started a new RO + RP-0 save a couple of days ago. This time around, I decided to role play as an alternate Chinese National Space Administration, and started the game at 1956, the year that the China started its ballistic missile program (I think). It's right now 1961, and my newest mission is to become the first nation to send a man-made object to a planet other than the Earth. Named "Menkan 1," this probe will hopefully fly by Venus by the end of 1962, transmitting valuable information on Venus' temperature and its potential magnetic field. The Menkan 1 will be delivered atop the Jingshen 63B (don't get too excited, this never existed in real life). The Jingshen 63B has 6 boosters, each with RD-107s and a central 3 meter fuel tank powering yet another RD-107.

Menkan 1 in orbit around the Earth:

Ps0Iwja.png

 

The Jinghsen 63B launch vehicle, standing on the launchpad at the Jiuquan Space Center:7I3kVHH.png

Edited by AndrewDrawsPrettyPictures
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Well as you might guess, my previous rocket I posted here failed. I took a short hiatus from KSP after that to rethink my design. Then someone in the "What did you do in KSP today thread" inspired a new design. One Kerbal, minimalistic lander design, direct landing.

So, with all of this in place, I decided to yolo it. Rocket stats looked ok, got good enough power generation, nice DV and TWR, no need for lander testing. So I launched into orbit and encountered my first problem: not enough nitrogen to power the Falcon 9 RCS packs, it ran out very fast. Also had no forwards and backwards thrust so no ullage. Well, to solve this problem, I activated the RCS in a later stage and then when it came time for TLI burn, shut the RCS down. This worked very well and TLI burn was completed and the stage was jettisoned.

Now I knew that my propellant would decay, I just didn't know that all of it would be gone by the time I reached the Moon. Now I had two hydrogen fuelled stages, one of them decayed and the other was fine. Is this because on one, the engine was active and on the other it wasn't? I'd love to know so I can save some fuel next time.

So then I used the tiny bit of fuel left in the decayed stage to adjust my Periapsis  and then ditched it. I still had enough fuel to land and come back. and it was time to capture into lunar orbit. Since I was doing it on the dayside, I decided to just land. And now things got good. The music I was listening to, (Two steps from hell) was getting really epic and I was shooting across the lunar surface at over 2km per second under 50 kilometers from sea level. I charged through the last hydrogen fuelled stage and was about to fire up the lander and then... I discovered that the fuel in the lander wasn't pressurized. Aww c'mon! At least I was under a lot of pressure! But anyway this pressurized tank thing is becoming the new solar panels. I forget it every mission!

So then I reverted back to VAB. Anyway I'll fix this rocket and then attempt it again hopefully better next time.

But that's it for now.

Fire

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1 hour ago, Firemetal said:

But anyway this pressurized tank thing is becoming the new solar panels.

Yeah, This happens to me a lot, too. Usually on transfer or capture stages of my interplanetary ships, so I find out a few years after liftoff, that sucks.

 

Today I continued to build my first long-term stay lunar base. The thing that was the most difficult for me was to design the landers for various payloads, considering that only two deeply throttleable engines can be used, either the LEM descent stage engine, or a little one that was used on Surveyor. this was the design for the hab, the heaviest part, around 12 tonnes:

uAzsVdy.png

A huge rocket was needed to send it to the Moon, a 4,200 tonne beast:

OPnx10l.png

And this is how my base looks so far, a pressurised rover for long term exploration, an RTG power plant, and the newly delivered habitation module:

AkK1jTI.png

The goal of the next mission of the Grissom program will be to connect the hab to the power plant and test all the equipment.

I'm curious, how do you design your landers for airless bodies? Is there a trick I'm missing, or are silly designs like mine necessary due to lack of suitable landing engines?

Michal.don

 

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The Struve Lunar base is complete, and I had one of my proudest engineering moments followed by a facepalm of tremendous proportions.

TatePPA.png

The base itself looks and works just fine. The Grissom XV mission completed all the work in one EVA and verified all the hardware works as intended. With one exception. The LSTV, Lunar Surface Transfer Vehicle.

HuG8Y0h.png

I considered the LSTV one of my greatest engineering succeses. Weighing just over 4 tonnes, it should be capable of transporting the crews to and from orbit. It needs about 2,3 tonnes of fuel for each journey, so it would be refueled both on the surface and in orbit. This should make the lunar missions much cheaper, because each vehicle will carry just the fuel for the LSTV instead of a 16-tonne LEM.

The LSTV is powered by 9 engines, 5 running on CaveaB and four, throttleable on MMH/MON10. Three separate action groups are used for the engine management to provide varying levels of thrust during different parts of descent and landing. Despite not so great initial TWR, precision landings are possible with reasonable margins (proved by landing both of the a few metres apart right next to the base).

Now comes the facepalm part. I did not account for the weight of the crew....... :blush:

So, instead of having two reliable vehicles deployed, I have a possible deathtrap for the first crew to test those. The safety margins might be just enough, but it is far from certain. So I have a difficult choise - design a brand new vehicle, which I'm not certain will be able to utilise the same type of fuel, or sweat bullets each and every time tranferring crews to the base....

So, not a particulary good day for me.

Michal.don

 

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  • 4 weeks later...

I'm back! And so is this thread.

Last time, I had a rocket that could land on the moon and return... However the capsule couldn't survive re-entry so... Back to the drawing board!

I decided to start doing stuff in Earth's SOI like relay systems, space stations, etc. And to start, I decided to build a reusable booster. I mean I'm not playing career, so this is redundant but who cares. I like SpaceX if you could not already tell by my profile picture. So I begun building Orodruin 9. Second stage is Hydrogen fuelled, 1st stage is Kerosine fuelled. Lets go!

However the first landing test flight ended up like the real Orodruin. It blew up.

u7wAtiS.png

It blew up because I started the landing burn too early and ran out of fuel. But I still have confidence that it can work. So I downloaded FMRS this morning.

Uh, so yeah. To be continued.

Fire

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