Author Topic: Kerbal Space Program or "Rocket science is harder than it looks"  (Read 278787 times)

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
Freakin' rockets...  How do they work?

That's my latest monstrocity, Tripod VI, which hits about 7.3 km/s on a vertical launch.  That doesn't hold a candle to Shade's work, but then again, Shade seems to know what he's doing.  ;)  I want to try to get this particular design into a stable orbit at some point.  That seems like a task that becomes more and more challenging as the size of the rocket increases, but that's why it's fun!

 

Offline crizza

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
Heck, I don't get anything into a stable orbit...
And the engines of the c7 pack are useless crap...
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Offline Commander Zane

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
Give a C7 craft anything more powerful than what the pack gives you and you'll be very likely to send it doing loops into the ground.
Even the SR-Mockingbird-esque craft I built normally uses three of those engines. Give it one of CaptainSlug's aerospike engines (Just slightly more powerful than the stock game's liquid thruster), you'll do alright. Give it two, you're pushing it. Three? Good luck trying to fly it level for five seconds.

 

Offline crizza

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
The only problem I realy have is that they don't have enouggh power...three stock liquid engines bring it up pretty well...three of the c7 engines and it starts two spin circles...
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Offline Retsof

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
Orbital insertions are confusing... Getting into an orbit is easy, adjusting it, not so much.  Example, I am at the highest point, and want to make it lower, so I thrust straight down.  This leaves the highest point exactly where it is but drops my lowest point lower.  I are cornfused.  :wtf:
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Offline Nuke

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
burn retrograde and it makes the opposite side of the orbit lower, prograde makes it go higher. if you want to lower your apogee, you need to wait till your at perigee and then burn retrograde. pointing your nose at the planet and burning your engine oddly doesnt have much effect other than wasting fuel. the way space ships approach planets in scifi movies is completely bogus, you never fly straight to the planet.
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Offline Herra Tohtori

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
Orbital insertions are confusing... Getting into an orbit is easy, adjusting it, not so much.  Example, I am at the highest point, and want to make it lower, so I thrust straight down.  This leaves the highest point exactly where it is but drops my lowest point lower.  I are cornfused.  :wtf:

It's not that confusing.

If you want to adjust the highest point of orbit, you perform a prograde or retrograde burn at the lowest point of your orbit.

If you want to adjust the lowest point of your orbit, you perform a prograde or retrograde burn at the highest point of orbit.

Zenith and anti-zenith burns should only be used for very small velocity changes, such as close range rendezvous and velocity synchronizing, or fine tuning the eccentricity of your orbit by minimizing the vertical speed component while keeping your orbital velocity as close as possible to the nominal orbital velocity at that specific altitude.

An elliptical orbit is a pretty nice element of how harmonics work in nature, actually. There's a periodic oscillation between potential- and kinetic energy levels. At periapsis, the kinetic energy is highest and potential energy lowest. The amount of kinetic energy will define how high the orbiting body will end up at apoapsis, where the kinetic energy is at its lowest and potential energy (altitude) highest.


Reducing kinetic energy at low point will mean the spaceship won't raise as high up on the "uphill" leg of its orbit. That'll mean the highest point of your orbit will be reduced, which is what you wanted to do in your example.

It can feel a bit unintuitive how orbits work, but if you keep at it you'll eventually gain a more natural understanding of how orbital mechanics works.


A good example would be a situation where you and a rendezvous target are on a similar, circular orbit, but the target is orbiting 100 km ahead of you.

The layman's best idea of meeting up with the target would likely be to point the nose at it and hit the burners, but in actual orbital mechanics, this would actually make you fall behind of your target.

The reason for this? Well, by increasing your orbital velocity, you push yourself to higher orbit, above the target orbit; and a simple geometric exercise will reveal that the higher orbit is a longer path to travel, and subsequently takes longer time to complete - ergo, by trying to go faster, you go slower.

The proper way to rendezvous with a target ahead of you would be to reduce your own orbital velocity so that you drop your own orbit's periapsis below the target orbit. That'll give you a shorter distance to travel, and you'll end up catching the target. Once you are close enough at apoapsis, you then accelerate to same orbital velocity as the target, and perform short range direct rendezvous maneuvers as required.
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Offline Nuke

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
if you really want to learn how to perform simple or complex orbital maneuvers you really got to play with orbiter. you really got to read manual though, and im not sure where i got it but theres a pretty good tutorial on how to fly to the moon and back in the delta glider. ksp keeps things simple though, play with the orbit map and see what kind of effects burns in different directions do, and you can get the hang of it pretty quickly.
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Offline crizza

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
Ha, I did it...Orbit...not a stable one, but as of now good ol' Jeb manages to go around kerbin several time...guess he will land somewhere around the southpole...or this strange island...
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Offline Nuke

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
once you got half of the orbit kill your engines and wait for apogee and do a prograde burn to raise perigee high enough to form a stable orbit. i like to reserve at least half a tank for orbital manuvers and some of the mod packs contain small tanks/engines for this purpose.
« Last Edit: October 10, 2011, 09:27:49 am by Nuke »
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Offline Bob-san

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
once you got half of the orbit kill your engines and wait for apogee and do a prograde burn to raise perigee high enough to form a stable orbit. i like to reserve at least half a tank for orbital manuvers and some of the mod packs contain small tanks/engines for this purpose.
I find that flipping the craft horizontal and burning towards the horizon also works. You need to get horizontal velocity to achieve a stable orbit. Otherwise, if you wait till the top of the orbit (and depending on your mass and engine) you may not have enough fuel or enough time. Then again my method isn't perfect--you can get into a far less eccentric orbit if you start getting horizontal momentum while still in the atmosphere (though that has the disadvantage of wind resistance).
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Offline Nuke

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
i was referring to maneuvers performed after orbit is achieved. to achieve orbit i usually progress between vertical at 20km to flat at about 50km. but once your trajectory covers a fairly large portion of the planet, then its time to kill your engines and wait for apogee to trim. what you dont want to end up with is a really high apogee and no horizontal velocity which i find to be a waste of fuel. its more fuel efficient to aim for a low orbit and use a hohmann transfer to raise it to the desired level.
« Last Edit: October 10, 2011, 11:23:37 am by Nuke »
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Offline Retsof

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
 :bump:  Experimental version out, we now have the Mun.
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Offline Nuke

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
downloading
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Offline Commander Zane

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Re: Kerbal Space Program or "Rocket science is harder than it looks"



Take that, Logic.

Unfortunately they died.

 

Offline Nuke

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
so after building a modest rocket capable of placing a ship into orbit with enough delta-v to **** around with, i proceed to launch to orbit:

i managed to plot a trans-lunar injection burn. this being only my second attempt (the first failing by me accidentally jettisoning a booster that i was still using). i figured out that you wanted to lead the moon of kerbin by about 1/4 an orbit. it was a retrograde orbit caused by a slight navigational error (jeb went the wrong way during the roll manuver). i thought i wouldnt make capture range as i crossed the moons orbit rather early, but managed to get capture on the rebound. i provided retrograde thrust to slow me down enough to get capture.

due to a glitch with the sas system, which i could not turn off and having it lock me out of the controls, i missed a second burn at periapsis to make my elliptical orbit more round. for some reason during the course of my orbit i lost some velocity and was in danger of hitting the moon on my next pass, but i was still locked out of my manuvering controls. after hitting keys at random i managed to turn the thing off and was close enough to apoapsis (though slightly past it) to fire a correcting burn. unfortunately i ran out of fuel before compleeting the maneuver. but fortunately for me i had a full tank of rcs fuel!. i had just enough time to pick that orbital trajectory off of the far side of the moon. coming bact arouhnd over the next several orbits i was able to make the orbit circular. a landing was out of the question but i wanted to see if the moon had any atmo. so i used the last of my rcs fuel and my the kick from my decoupler to dip into the ground:

jeb and crew, accepting their fate, bid farewell to their homeworld for the last time, as they decend into the realm of death, at around 570m/s:

« Last Edit: November 04, 2011, 03:57:21 pm by Nuke »
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Offline Kszyhu

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
About the SAS locking - I don't know if it's the intended behaviour or a bug, but you can't turn off SAS when there's time warp enabled.

 

Offline Commander Zane

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
All input functions lock above 2x compression.

 

Offline Nuke

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
i wasnt under any compression. i had dropped it to 1x before attempting to kill the sas and perform the maneuver. i think it had something to do with changing the to the orbital view changing changing and switching back. i tried everything, messed with compression, changed views, toggled the rcs (which it let me do), eventually the sas key responded. il try to see if it is repeatable, and report it to the ksp people if it is.

anyway i think the nav sphere now needs normal and anti-normal direction indicators so you can do plane alignment manuvers more easily. also need icons on the ascending and decending nodes in the orbital display to determine when to do a plane alignment manuver. you kinda have to do it by eyeball right now. look at the lunar orbit edge on and find the low/high part of your the orbit around kerbin, an do your normal/antinormal burn there, finding normal and antinormal is really difficult though, especially if you have a high inclination. its workable but not the way im used to deal with celestial navigation.

i am working on trying to land and return to kerbin now. i need a beefy stack to lift everything i need for the complete trip. i tried the saturn stack but it falls apart in this version. ive got the re-entry capsule, a decoupler, an rcs tank and quads, a lf tank and an engine to return home from lunar orbit with, i got small srbs to get off the moon and some smallish descent engines, and on top of that i need propulsion to get to the moon (ion engine!). and i still need to launch it. too bad you cant do a rendezvous maneuver yet.
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Offline Herra Tohtori

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Re: Kerbal Space Program or "Rocket science is harder than it looks"
Juturn V with the Munlander Mk.II Spacecraft




Juturn V is a three-staged launch vehicle.



First stage contains five kerosene and liquid oxygen burning, powerful engines. Aerodynamic control is provided with four moving fins. Future variants are expected to use gimbal engines on all stages. This first stage is used to lift the massive vehicle from the launch pad and through the lower atmosphere.



Second stage contains five hydrogen-oxygen burning rockets that have gimbal mounts to provide control during ascent. This stage burn lasts significantly longer than Stage #1 burn. Here, the second stage is just being separated.




The third stage is the actual Mun rocket. It is powered by a single, gimballed liquid fuel rocket engine and provides the necessary delta-v for final orbital insertion burn, transmunar injection burn, and munar orbit entry burn. Its power is in relatively long, sustained burns.





On top of the third stage is the Munlander Mk.II Spacecraft. The Munlander was originally developed as a Flophopper Mk.I craft used on Kerbin for various types of practice missions and even orbital re-entries, which is why its engine is rather overpowered for Munar landings, but Jebediah likes it the way it is and it was cheaper and easier to just bolt it on top of Juturn V rocket, than design a more suitable lander craft.

Munlander Mk.II contains technically two stages. The lower stage contains a powerful (and heavy) fission engine with excellent fuel efficiency, yet sufficient thrust to fly the spacecraft safely even on Kerbin's gravity field. In Mun landings, it has very wide safety margins - it has more than enough fuel for powered descent, landing, and even take-off, so it would be amiss to simply call it a descent stage. The lander uses Captain Slug's lander legs - three for optimal stability on uneven terrains. Due to heavy fission engine on the bottom, the lander is surprisingly capable at landing on tilted surfaces without toppling over - indeed, pilots have experienced a tendency to slide down slopes instead of toppling over. This gives the pilots additional safety margin in landings - if first landing zone is not suitable, the craft will not be as likely to fall over as its appearance would suggest.

The top stage was originally designed as an emergency escape pod for the Flophopper Mk.I design. In that incarnation, it had a habit of detonating the lower stage as the engine ignited. The Munlander Mk.II is, however, equipped with retrothrusters that should (in theory) push the lower stage away from the upper stage before engine ignition - and in case they malfunction, the RCS thrusters can also be used for forward thrust. Upper stage is powered by a small liquid fuel rocket engine and the craft has plenty of fuel to return to Kerbin from Mun mission.

The lower stage of Munlander Mk.II contains one RCS fuel tank and a single SAS module, and the upper stage contains a single RCS fuel tank.



For extravehicular activity on the Mun, the craft is fitted with rope ladders. It is hoped that in the future, additional cargo (such as Munar Rover, or scientific equipment) can be fitted in the space between fairings and the core of the lower stage.


On the very top of the stack is a Command Module that acts as the habitat for the crew during the duration of the mission.



Getting to Moon is not a very straightforward process, much less so than simply entering stable orbit.

After stabilizing an orbit around Kerbin, a transmunar injection burn needs to be plotted. Transmunar injection puts the spacecraft on a transfer orbit to rendezvous with the Mun.





After moving to the gravitational influence of the Mun, you will find your spacecraft most likely on a hyperbolic trajectory around or behind the Mun:




Near the periapsis, the third stage of Juturn V performs its last required task: Insertion on Munar orbit by slowing down the spacecraft with its remaining fuel.




Orbit successfully stabilized! The third stage had enough fuel in this mission that it actually moved the periapsis to the other side of the orbit, and the entry point became the new apoapsis for the orbit.

After orbit was stabilized, it was time to jettison the third stage. Munlander was now on its own, far from home.





Next step was planning the de-orbit, descent and landing zone. I decided I would be landing next to the large Mare on the lit side of the Mun, preferably near the rim mountains around it. That meant I would be starting my de-orbit and descent near the periapsis of the orbit. As the ship emerged from the shadow of the Mun, the vista was truly magnificent.



The de-orbit burn put the spacecraft on a shallow descent that would take it above the desired landing zone. During this high speed, unpowered descent, some final adjustments could be made for the general landing zone.



Powered descent started as the craft passed south of the dark Mare on the Mun. This maneuver put the craft on a steeper descent path but also slowed down the total velocity significantly. The angle of descent would gradially deepen until the craft would descend vertically before touchdown. Final descent began at altitude of about 6000 metres above Munar surface.





This first touchdown was in too steep territory, and as the ship tilted dangerously, commander Kerman increased thrust to take the ship back up, then located a more suitable landing area and finally put the ship down for good.




The final touchdown occurred at flight time 7 hours, 17 minutes and probably about 10-20 seconds (no one was watching the clock at the exact moment, so it'll never be known exactly). Landing area was a few dozen kilometres southeast of the aforementioned Mare, on the foothills of the ridge mountains.



After spending some jolly good time on the surface of the Mun, the Kerbalkind's brave ambassadors left this foreign world and headed home.




Full speed ahead! The remaining fuel on the lower stage of Munlander was sufficient to boost the spacecraft to a ballistic trajectory about ye high:



At the top of the arc, it was time to lay the lower stage to rest and separate the command/service module on top of it for the remainder of the mission, and then boost the ship first on stable orbit around the Mun:





Setting homebound orbit was trickier than I expected. Initially the trajectory looked all fine and good... with stunning visuals on the way home:

http://img513.imageshack.us/img513/1948/screenshot92d.png
http://img189.imageshack.us/img189/9049/screenshot93.png

...but, at the gravitational switch point between Mun and Kerbin, something strange happened:



Basically, I got stuck between two orbits and the game didn't know which one I was supposed to follow. What was even worse, the game thought I was experiencing acceleration, and limited time compression to 2x, so I spent ages in this point. Worse still, as the game was switching between the two trajectories, it also switched the orbit-relative camera angle all the time, making the normal view completely epileptic and unplayable. After a while, I got fed up, did a burn of couple dozen seconds at full power to get out of the conflict area, and eventually the flickering tuned down and eventually stopped. I didn't truly hit Lagrange point, but it was close.

However, now I had a problem, as the ship initially settled on this kind of trajectory:




...and I had to do some rather fuel consuming trickery to change my trajectory to this:



As I got close to perikerb, I did a long ass retrograde burn, trying to align my trajectory with Kerbal Space Center location - but, as it turns out, the trajectory fell a bit short.



After deciding I had finalized my trajectory, I jettisoned the service module:



Space center in sight... so close, yet so far. Already too deep in atmosphere. Well, nothing to it... will just perform normal parachute landing somewhere in the deepest Kerfrica.







This successful mission was a huge surprise to mission control who honestly expected them to run out of fuel or crash at some point during the mission. Reports from Kerbal Space Center indicate heavy casualties of the upper management team, suffering afflictions ranging from mild nervous twitching and epileptic seizures to full on heart attacks and cerebral hemorrhaging. Crisis team has been assembled to help the affected.
« Last Edit: November 05, 2011, 04:43:53 am by Herra Tohtori »
There are three things that last forever: Abort, Retry, Fail - and the greatest of these is Fail.