John Doe

OK. Got it, and successfully pulled it off. I was just ending up with the moon right in the line of my initial escape trajectory towards it, so that my Pe to the moon was zero, with either the option of travelling the other direction, OR the option of smashing into the moon at a relatively high velocity.

But for the fact that the STS payload (the orbiter ) was ALOT heavier than the Apollo CSM / lM payload. YET the STS stack was quite a bit smaller than the Saturn V stack. If the Saturn V had to be big due to the Payload, one would think the STS stack would have had to have been more around the size of the current SLS / Orion, given the fact that the orbiter itself was much larger. (the Apollo craft weighed at around 37,000 lbs, where as the STS orbiter (without the two SRBs and External Fuel Tank) weighed in at around 151,419. IF more weight should necessarily mean a bigger stack, then it stands by reason that the STS stack should have been somewhere around twice as big as the Saturn V. ( This also accounts for the fact that the STS External tank, was roughly the same diameter, though considerably shorter than the Sat V stack,) However, the external tank, when the stack was pad-ready, was the largest and heaviest component of the stack, (66,000 Lbs Empty and 1,667,667 Lbs in launch-ready state) with most of the space / weight being nothing but fuel, as opposed to the Saturn V's weight being influenced a bit more hardware-dependent. This would tend to suggest that the size of a stack is dictated by the ratio of how much mass within the stack is actual fuel Vs. payload and hardware, which may not necessarily require an increase the size of the stack itself.

So then from what I'm reading here, is that upon reaching the Pa node of the tranfer orbit, near the moon, the moon should then, by operation of it's field of gravity, start causing a descent in line with it, since the moon's gravitational field should have more influence than kerbin's ? and what I'm seeing on the lunar insertion burn is that I end up changing directions after about 30 into the burn..

Ok to clarify things a bit, when I said prograde, I meant the retrograde marker, which is a prograde burn in orientation to the the moon. (i.e. firing in the opposite direction of velocity, in order to resist and slow the velocity.) Second, by parabolic orbit, i mean an quite elliptical orbit with around a LEO Pe to Kerbin (around 228,000 m or so ) and a really high Ap (around 3K m or so) which extends slightly beyond the moon, while keeping the moon inside the orbital path at the time I'm at or arround Ap, to where essentially I'm on the backside of the moon. (this seems to be, from what I've read in the NASA archives, what Apollo 11 did, when they did most of the dirty work of insertion into lunar orbit and the LM decent on the back side of the moon.) What I was also finding was that, within the training tutorial, that the retrograde burn was causing me to essentially change directions and end up on what the map calls an escape path back toward Kerbin.

The thing is that I'm trying to learn as much of the basic theory as I can, as to prepare myself for the lunar mission. I've figured out how to establish a nice, fairly ciruclar orbit. The thing is that my instinct is to then establish a parabolic orbit that places the moon on the inside of the orbit, as the transfer orbit, and then to do a burn from there to do a decent stage toward the moon, and finally to to counter my decent at a certain point by firing on the prograde, in order to establish a lunar orbit. Problem is that when trying to do this, my initial burn is a good 13 second burn, and I establish the parbolic orbit as planned. The second one usually ends up on a kerbin escape path, and I end up at an astronomical altitude (like 3K to 4K) orbiting the sun, by which point my rocket says no more, and I have to drop it, leaving poor Mr. Kerman in orbit around the sun forever.

Great so that explains WHY accelerating to a velocity of around 800 m/sec. or better (which my intuition told me was a good idea, in the sense of faster as early as possible would seem to afford one the best chance of orbit.) was just NOT working... lol. I was getting a velocity of around 900 m/sec. by 1 minute to 1:30 minutes into the mission. The question then becomes, just so I'm getting the concept right, why then, NASA's Saturn V rocket was so BIG. ( at around a little less than a 100m stack), If the idea that faster- sooner is a bad thing for establishing orbit. I mean, even with throttle control, the bottom of the Saturn V was a MONSTER as compared to the Redstone or Atlas rockets. and I would therefore at least think, that the velocity between the two (even given the differences between the weight of the payload) would be as such that the velocity encountered with the saturn V, but for the roll and turn which was standard in the Apollo launch sequence, would result in an escape path.

Got it- so the elipical shape of the orbit is really only elpitical by such small fractions that its not observable by looking at the geometric shape....(i.e. the shape is so marginally eliptical that it still appears to be circular. I was making the assumption that hyperbolic was synonymous with elliptic. I was also understanding the orbit to be an complete escape of gravity combined with the effect of inertia.

So, then basically what your saying is that it's pretty much impossible to raise Ap And Pe at the same rate? ( you actually have me confused. trying to really get the hang of orbits as there was this point in the basic demo about establishing a lunar orbit, wherein I am at the stage of being on a collision course with the moon, in which the only hint was "remember what you learned about orbits in the previous tutorial" which was basically nothing more than how to raise /lower Ap / Pe. So My instinct was to fire Prograde to slow down my velocity to avoid impact, and perhaps establish a Pe. (not a good idea) So basically Yeah, I'm trying to learn all the crap that the tutorial isn't saying. Also bear in mind that I'm used to flying STS missions in orbiter, which always involve the pretty much SAME type of orbit, and the orbiter is doing practically ALL of the hard parts- the burns are automatic once you program the computer to tell it what you want to accomplish. So really, outside of really basic concepts, I have no idea of how newtonian physics might somehow apply differently than what would be plainly obvious.

I'm using the old 0 series demo. So all I have are the three stock liquid engines, two sizes of fuel tanks, and the small SRB to work with. and none of the basic tutorials mentioned the concept of TWR. Basically what I'm after is a twist on the Saturn V design.( i.e. a massive tri-coupled lower stage with a moderate middle stage, and a smaller final stage, to where what we get is more or less something like a Saturn II-B sitting on top of a massive bottom stage, which is is quite large because of all the weight sitting on top of it.

Which makes the shape of the orbit an offset CIRCLE, NOT an Ellipse, by defintion. An perfect ellipse is twice as long as it is wide, with Ap and Pe at, or near, the length of the ellipse. Think about it like this. Take a coffee cup and turn it upside down. the perimeter of the cup represents a perfect circular orbit. Now, place a bottle cap in the middle. This represents the object orbited, such as Kerbin. Now, if we move the bottle cap, we see that we modify the Ap and Pe nodes, WITHOUT modifying the shape. (i.e The coffee cup DIDN'T change it's shape and turn into an ellipse just because we moved the bottle cap.) So long as we keep the Pe node high enough, (i.e. we don't place the bottle cap closer than x to the perimiter of the coffee cup, where x is the maximum Pe allowed that will allow a re-entry ) the laws of physics do not allow re-entry, and because we haven't accelerated towards an escape node, (which changes the shape and path of the orbit) we will not rise higher than Ap. Thus, we cannot travel outside the path of the orbit, and we cannot re-enter unless we drop the Pe enough. There's nothing I've been able to locate within newton's laws on gravity that state this theory to be incorrect, assuming that our velocity never changes. (which can be accomplished with a burn in the right direction at the right time.) I've seen nothing in newtonian physics that states that this cannot happen, though it is extremely difficult to make it happen.

What seemed to do the job was throttling down to about 75 percent or so after reaching a velocity of around 150 m/sec or so, before 10,000 m, executing the 45 turn , and Then opening up the throttle and burning all out, which in turn, caused my suborbital path to broaden out quite a bit. I have two possible schools of thought on this- The first one, the obvious one, is by keeping my velocity relatively low before the 10,000 m mark slowed down the overall max velocity proportionately. The second is that it saved the fuel until a point in the flight with significantly lower gravity / drag effects, and thus burning the engines at the same rate does more work, thus increasing velocity that you might not get otherwise.

only seems to hold true to a certain extent- What then, do you suppose happens if we offset a circular orbit, but not enough to lower the Pe below the threshold for re-entry? We haven't changed the shape, we have just lowered Pe and raised Ap.

Not necessarily- If I take a perfect circle and off-set it- its geometrical shape doesn't change, but relative to the object in the center, the Ap and Pe WILL change, Ap=Pe ONLY if we have a perfect circle AND zero off-set in relation to the object being orbited. The same can hold true for a perfect ellipse- Ap = Pe IF the shape is geometrically perfect AND there is zero offset of the body being orbited. (i.e. the object is perfectly centered within the geometric structure of the orbit.)

If your trying to be funny, don't quit your day job :-P

I figured out what happened. I was accelerating with about 8 times too much velocity during the initial phases of the launch, causing me to accelerate to Ap so fast that I ended up doing my burn too late, and thus have to fight both my fall toward the suborbital Pe AND at the same time fight to Raise the Ap, so in, effect I was doing two manuevers at once, in a single really LONG burn.

The following orbit is what I tend to get , and this is when I'm lucky, leaving little fuel left for re-entry or anything else. Ap is 7,198, 200 m and Pe is 104,820. I raised suborbital Ap to my figure of 100,000 m as the intended Orbital Pe. The initial suborbital path had a nice circular curve, but when I did the prograde burn at ap, my Ap rose like wildfire, while taking quite a bit to raise Pe.

Ok, so then basically we want to be working with a relatively LOW suborbital Ap, say at around 60,000 m? if i'm understanding that right? And I would also understand that when firing prograde, we are essentially pointing the rocket directly at the ground, with the nose cone pointed into space, and thus increasing velocity in what would be a vertical position from the ground. I would think that increasing velocity horizontally is just going to increase delta-v and thus cause you to reach Ap faster, if I understand things right....

If that were the case, I'd have seen the problems in the Stock Kerbal 5 from which I derived it from. I did not substantially modify the bottom stage. The major modification was adding the middle stage. The top and bottom stages are stock, and have been pretty much left alone. Yep. this is the 0.18.3 demo. Given the velocity figures I'm seeing, I don't think that drag is a problem. I'm seeing at least several hundred m/sec velocity inside the space of the first minute. The major problem is that If I execute the turn at the same point as with the stock version, I get a marginal and barely acceptable Ap, but my velocity is so fast that I don't have enough time raise the Ap enough to get an acceptable Pe for orbit. My Ap will raise up to a certain point, and then actually Lower right in the middle of the prograde burn, which is during the back half or so of the fuel capacity of the second stage. I also find that the second stage will burn out and have to be decoupled right in the middle of the insertion burn, assuming that initial Ap is high enough. If I try to correct this by keeping vertical and doing the turn on starting up the middle stage, I get an extremely elliptical suborbital path, which results in a really high orbital Ap, ending up at around 3,060,000 m, buit with a relatively LOW Pe by comparison, at maybe 200,000 m at the most, though the Pe here tends to be just over 100,000 m, and mind you this burns alot of fuel, leaving me just enough fuel to do an antegrade burn exactly timed with Ap in order to start re-entry. (i.e. lowering the Pe to around 40,000 or so at engine burnout. )

I would say thanks to everyone for taking the time to help me out. The other space simulator I play doesn't really involve building a custom stack so much as flying NASA's STS stack. This has been a radically different thing all together. The STS stack practically flies itself on its own, with autopilot doing most of the work of navigating to the propper vectors and controlling velocity. Most of the work then becomes taking the steps to decouple the stack at the right times, though the most challenging aspect of that has been landing the thing. I've yet to NOT belly flop the orbiter on the ground due to the velocity- around 1,000 m/sec on average at around 5,000 ft that you have to bring to practically zero within 5 seconds.

The only thing its really doing that's all that odd or eccentric is wobbling in the sense that would give you the impression its gonna break in two between the tri-coupler and the decoupler attaching the first stage to the rest of the stack. (though this isn't too bad- was just a little disconcerting the first couple test runs, not knowing what to expect, and it actually appears to be pogo oscillations, to boot! ) but other than that it now seems to be pretty much behaving itself. I've found that I'm having to wait until around 35,000 m or so (about the time the first stage decouples from the stack in flight) to execute any turns, because if I turn before this, my acceleration is too great to have enough time to correct vector to burn prograde to raise the Ap/Pe. If I turn at the 10,000 m mark, I'll end up raising Pe to around 50,000 to 60,000 max, and because the velocity is so great, I usually end up having to throttle up the engines and decouple them from the stack to avoid ending up planting it nose-cone first in Kerbin- impact crater and all. But I find that it works fine to delay the turn by about 1.75 to 2 times the the standard turn altitude. Reason being is because by the time I'm getting ready to burn prograde to raise the AP, invariably my velocity will already be close to orbiting velocity, at somewhere in the neighbourhood of 1,000 m/sec. what appeared to be causing the nasty handling was that extra set of wings that I pulled off the middle stage. Now that I've got this craft in basic workable condition. I also have tested with/without SRBs- and the SRB's are giving me enough thrust that they're probably what's getting my velocity as high as what it is, as the velocity drops by about 700 m/sec without the SRBs.

I should have to consider this. And HOW then would that 909 be heating ANYTHING up, when it wasn't burning, in the first place? (and mind you those run reports were from after I had addressed the SRB problem, which was caused by firing up the the bottom stage's 30s while I was still held down to the pad by the three Launch Stability enhancers, which I got rid of entirely, as I couldn't figure out how to get them to release After firing the SRBs but BEFORE firing the 30s.

And yes, I did address removing one of the pairs of winglets from the middle stage, moving a pair down to the bottom of the stage. The orbital view from near Ap is amazing, yet a bit uncomfortable considering its an orbital flight.

OK, I've found that with this slightly bigger rocket, I have to wait roughly until 25,000 m before executing the 45 degree yaw. This gives me a nice comfortable 3 minutes to Ap., though a very odd orbital path, with Ap at 3,063,772 m, and a Pe of only 104,458 m. The grey debris orbit was higher than any of the orbits I've managed to muster from the stock Kerbal 5, from which I developed from.

Well, going all 30's seems to work well, but for the fact that raising the Ap is still not happening fast enough, and my velocity at Ap is still much too fast, sending me into descent much too quickly before the Ap manages to raise enough to establish a high enough Pe. The stack, btw is 89m high.

The engines are 30s on the bottom stage. The middle stage's engine is a 909 , with another 30 on the top stage. I'm thinking of switching to all 30's the whole way through. The thing is that I'm reaching around 40,000m around 2:30 or so. The bottom stage seems to be working well enough right up until its time for the first decoupling, by which point the velocity is around 500 to 600 m/sec. The velocity continues to climb as i fire up the 909 in the second stage, but for some reason will not stay on prograde, initially being off by left yaw. However, at least based on the indication of the nav ball, it will start to roll as i correct my prograde vector, and thus will accelerate me to a 201,000 m suborbital Ap with less than 30 seconds to drop the middle stage (which still has most of its fuel left by this point) aim on the prograde vector, and fire up the remaining 30 to attempt to accomplish orbital insertion. Problem is that by the time I manage to actually do all this I've passed the initial suborbital Ap and am about halfway back down and by this time have no chance of raising the Pe above the required 60,000 m or so required for orbital insertion. I'm also considering maybe switching the top most 30 with the 909 to try to solve this. I've also found that letting the SRB's carry for about the first 400 to 800m before firing up the three 30's in the bottom stage at full throttle tends to prevents the problem with the explosions that I was seeing. The problem seemed to be that the exhaust from the 30s in the bottom stage were blowing up the SRB's on the pad. I figured this out by pointing the camera view straight down on top of the nose cone prior to launch, watching the SRBs go BOOM in disbelief the second I fired up the 30s just seconds after the starting up the SRBs for liftoff.