My personal breakthrough Eureka moment I did by mistake.

[LadyAthena]

Soo I was just throwing some parts together, and had a whacky Idea to put 6-8 small rocket boosters at my mid stage around my main engine. I've never really had this idea before or tried it, always used rockets to get that initial boost out of the atmosphere.

The results was this... http://steamcommunity.com/sharedfiles/filedetails/?id=238089442

An Orbit around kerbal at over 4 million M, resulting in virtually no mid stage fuel being used since all I had to do was speed up an extra 300 m/s to achieve the orbit.

This seemed like a break through too me, I figured out a good way to save mid stage fuel for longer flights.

But onto the Mun I thought, and this happened...

http://steamcommunity.com/sharedfiles/filedetails/?id=238089447

I only had to speed up another 150-200 m/s to get a Mun Encounter, since I was already so high too begin with, which resulted in my speed being slow enough that the Mun actually pulled me into an orbit without using any more fuel, further resulting in virtually no mid stage fuel being burned.. Yet another Eureka moment <3

This is the ship: http://steamcommunity.com/sharedfiles/filedetails/?id=238247339

How the rocket works.

(Only launched twice so the #'s aren't specific)

During launch I ignite the first stage, and keep the throttle at 100%. When nearing the point of ascent where you normally tip the ship over to angle it at 10k m I turn off the throttle, allowing the rest of the boosters to take it the rest of the way saving fuel, since at this point it'll still gain speed. (Tipping it isn't recommended until the 3 solid boosters have been jettisoned or the ship will go all haywire on you).

Once the Solid boosters are jettisoned, turn the throttle back up too 100% and tip it too the proper angle ( 90 degree's I believe), and let it continue too burn the rest of the fuel.

Once you jettison the first stage completely, turn throttle back down too 0% and ignite the second stage, allowing the small boosters to do their job, since you are now out of the atmosphere of kerbal your speed will go from 300-500m/s and be boosted too around 1.5-2.5k m/s depending. Once the boosters are depleted jettison them, and allow yourself too travel at 0 throttle too the AP. At this point you should only need a few hundred extra m/s to achieve orbit.

The initial launch is a little wonky in my opinion since there are points where you turn the throttle off, but essentially I found putting solid rockets at the mid stage is a great fuel saver.

Edited March 14, 2014 by LadyAthena

[Force21]

Have any pictures of the rocket you built for this?

[Accelerando]

Mathematically speaking, it's impossible for your ship to be captured into Mun orbit with no fuel. If it works, that is extraordinary!

Congratulations! * 3 *

[LadyAthena]

Mathematically speaking, it's impossible for your ship to be captured into Mun orbit with no fuel. If it works, that is extraordinary!

Congratulations! * 3 *

Is it really? logically if you believe in the "big bang" theory then the reason the planets revolve around the suns is the same exact reason why I was captured in the Mun orbit without the use of fuel. It's just the speed I was moving was at just the right speed when hitting the Mun gravitational pull that it pulled me into an orbit. It's essentially the same exact reason of why planets were captured in the suns gravity well without the use of fuel.

[LadyAthena]

Have any pictures of the rocket you built for this?

Yes I've added a picture of it

[Streetwind]

Not really that unusual, honestly... it's just another variant of "throwing more fuel at the problem". You could, for example, have enlarged your mid stage fuel tank and tacked on some radial liquid engines, and gotten exactly the same effect. Or you could have added another stage below your bottom-most one and also gotten the same effect.

It all comes down to "payload fraction". That is, what percentage of your vehicle's mass on the launchpad is payload. Adding extra solid boosters means adding mass that is not payload - and thus, if your payload fraction stays the same, then your payload mass also increases and you end up getting something into orbit that you thought would still be a launch stage. (Of course, the payload fraction also changes a little bit, because it is dependant things like the rocket's drag and Isp and thrust-weight ratio, which are changed by the addition of the boosters that mix their own values into the average.)

How you define payload also plays a role - in most cases, it's "what is left after achieving a stable Kerbin orbit", but if you're trying to send a large mothership to Jool, then your payload is probably what remains after stabilizing a Jool orbit.

[Thiel]

Where are those small SRBs from?

[Streetwind]

KW Rocketry.

[wasmic]

Is it really? logically if you believe in the "big bang" theory then the reason the planets revolve around the suns is the same exact reason why I was captured in the Mun orbit without the use of fuel. It's just the speed I was moving was at just the right speed when hitting the Mun gravitational pull that it pulled me into an orbit. It's essentially the same exact reason of why planets were captured in the suns gravity well without the use of fuel.

Nope, wrong. The theories on the formation of the solar system (which are not part of the big bang theory) states that the solar system was, initially, a cloud of gas, which - after being hit by a shockwave from a supernova - began to contract, beginning to spin faster and faster over time, flattening into a disc. The vast majority of the matter in this cloud fell in close to the center and became the sun, while the disc began clumping together into the planets, and asteroids and stuff. No planet capture at all.

Mathematically, you'd have to enter an SOI at negative speed to be captured like that, and as everybody knows, negative speed is impossible.

[Madrias]

That's a cool idea! Might be just what I needed to make rockets actually work. I struggle with Career mode because my rockets barely go up, yet my keen understanding of airplanes allows me to hit space dragging wings. I'll have to give this a try and start strapping spare engines to the ships...

[LethalDose]

Is it really? logically if you believe in the "big bang" theory then the reason the planets revolve around the suns is the same exact reason why I was captured in the Mun orbit without the use of fuel. It's just the speed I was moving was at just the right speed when hitting the Mun gravitational pull that it pulled me into an orbit. It's essentially the same exact reason of why planets were captured in the suns gravity well without the use of fuel.

This doesn't really have anything to how the universe or solar system or was created IRL, or any other factual physics. Instead the statement "it's impossible to get into an orbit without thrust" is about KSP's patched conics physics system.

More specifically, you can't get into a closed orbit (that is, an orbit without an escape) around a satellite in KSP without thrust. To reach a body's sphere of influence in a patched conics system, you have to exceed it's escape velocity in relation to the body. So when you first enter a satellite's SoI from it's primary's SoI, it will always be a hyperbolic orbit with an escape. Basically, if you do nothing, you'll exit the SoI at the same speedyou entered the SoI, just in a different direction. You will ALWAYS have to change your velocity/orbital energy to get captured by a satellite. This is usually done by burning retrograde or aerobraking if you have a convenient atmosphere.

I guess there could be corner cases where if you just barely got into an SoI, and mucked around with time warp (which causes some ... twitchy... changes in orbits and positions due to floating point errors), you could get a closed orbit without thrust... but thats closer to a software bug than space flight.

In reality, asteroids can get capture and become orbiting satellites due to gravity interactions with other satellites. For example, the Galilean moons of Jupiter stabilize each other's orbits in due to orbital resonance. However, since we have 1 body patched conic physics in KSP, this isn't possible. Also, the asteroid capture/birth of the universe/big bang orbits you're talking about don't occur in time frames measurable in kerbal, or even human, life-spans so they're not really useful for spaceflight.

EDIT: Also, everything that wasmic said.

Also, Congrats on the breakthru! Here's to many many more!

Edited March 14, 2014 by LethalDose

[mellojoe]

I built a replica of the Delta-II rocket which was basically two orange tanks as a central stalk with 9 solid-rocket boosters surrounding it (yes, nine). The real life Delta-II and my replica both used the same launch procedure: Fire the main central engine plus six of the SRBs. Once the six ran out and were dropped off, the remaining 3 SRBs were fired up.

Once you get out of the thick atmosphere, terminal velocity is no longer a detrimental barrier to push through. Adding tons of acceleration after that point is very effecient.

[LadyAthena]

Not really that unusual, honestly... it's just another variant of "throwing more fuel at the problem". You could, for example, have enlarged your mid stage fuel tank and tacked on some radial liquid engines, and gotten exactly the same effect. Or you could have added another stage below your bottom-most one and also gotten the same effect.

It all comes down to "payload fraction". That is, what percentage of your vehicle's mass on the launchpad is payload. Adding extra solid boosters means adding mass that is not payload - and thus, if your payload fraction stays the same, then your payload mass also increases and you end up getting something into orbit that you thought would still be a launch stage. (Of course, the payload fraction also changes a little bit, because it is dependant things like the rocket's drag and Isp and thrust-weight ratio, which are changed by the addition of the boosters that mix their own values into the average.)

How you define payload also plays a role - in most cases, it's "what is left after achieving a stable Kerbin orbit", but if you're trying to send a large mothership to Jool, then your payload is probably what remains after stabilizing a Jool orbit.

The thing is, during mid stage, my "true" mid stage is more or less just the rockets, since I use virtually no fuel from the tanks, or nearly none.

I consider boosters not part of the ship, since they are a 1 shot all use, and can't turn them off. Instead of using fuel which I can use for other things and fine tune maneuvers, etc. isn't being used.

[LadyAthena]

That's a cool idea! Might be just what I needed to make rockets actually work. I struggle with Career mode because my rockets barely go up, yet my keen understanding of airplanes allows me to hit space dragging wings. I'll have to give this a try and start strapping spare engines to the ships...

I put an explanation of how my rocket works, as it is a bit wonky. You should check it out, might give you idea's.

[wilt57]

The thing is, during mid stage, my "true" mid stage is more or less just the rockets, since I use virtually no fuel from the tanks, or nearly none.

I consider boosters not part of the ship, since they are a 1 shot all use, and can't turn them off. Instead of using fuel which I can use for other things and fine tune maneuvers, etc. isn't being used.

They are still thrust generating devices that spend reaction mass to add or subtract velocity from your ship. Even if you decide to not use them until you are already in orbit, they took the expenditure of reaction mass to lift them to that point. They are ever so much part of the ship.

As for your Mun encounter, I don't see a PE tag on your orbit. Looks like a surface impact incoming.

Glad you are reaching new milestones in your space program. Keep it up!

[LadyAthena]

They are still thrust generating devices that spend reaction mass to add or subtract velocity from your ship. Even if you decide to not use them until you are already in orbit, they took the expenditure of reaction mass to lift them to that point. They are ever so much part of the ship.

As for your Mun encounter, I don't see a PE tag on your orbit. Looks like a surface impact incoming.

Glad you are reaching new milestones in your space program. Keep it up!

That's very true, but Boosters are 1 shot go, you can't use them to fine tune, land modules on planets, or any other very important, and fine tuning maneuvers. That's why too me it was a Eureka moment because I have saved precious fuel which otherwise would of been spent on orbital burns, etc.

take off the boosters... you have less fuel when you get too the Mun, potentially making the ship not capable of landing and returning... Add the mid stage boosters, you now have plenty of fuel. That's the point. It saved fuel more than just "adding more engines", even though yes the boosters are an engine per say, they are different, you can't shut them off and their useability is much lower...

Do you kinda get where I'm going with that? Not sure if I explained that well.

[TMS]

Low ISP devices should burn and be discarded first.

[cantab]

Yeah being captured by a planet or moon without a burn, aerobrake, or gravity assist from a moon if it's a planet would I think be related to the bug that orbits shift when timewarping across SOIs.

[Accelerando]

That's very true, but Boosters are 1 shot go, you can't use them to fine tune, land modules on planets, or any other very important, and fine tuning maneuvers. That's why too me it was a Eureka moment because I have saved precious fuel which otherwise would of been spent on orbital burns, etc.

take off the boosters... you have less fuel when you get too the Mun, potentially making the ship not capable of landing and returning... Add the mid stage boosters, you now have plenty of fuel. That's the point. It saved fuel more than just "adding more engines", even though yes the boosters are an engine per say, they are different, you can't shut them off and their useability is much lower...

Do you kinda get where I'm going with that? Not sure if I explained that well.

You've saved fuel in the parts of your ship that you can actively control, and that go into orbit, by adding these side boosters as a new stage, yes!

[merendel]

That's very true, but Boosters are 1 shot go, you can't use them to fine tune, land modules on planets, or any other very important, and fine tuning maneuvers. That's why too me it was a Eureka moment because I have saved precious fuel which otherwise would of been spent on orbital burns, etc.

take off the boosters... you have less fuel when you get too the Mun, potentially making the ship not capable of landing and returning... Add the mid stage boosters, you now have plenty of fuel. That's the point. It saved fuel more than just "adding more engines", even though yes the boosters are an engine per say, they are different, you can't shut them off and their useability is much lower...

Do you kinda get where I'm going with that? Not sure if I explained that well.

On the other hand you could have instead just added more liquid fuel to that middle stage for a much better ISP than solid rockets get. Either way you spent X amount of fuel to launch that much weight into orbit. However you could have gone much further on that same weight had you used more efficient engines/fuel. I suspect if you used mechjeb or flight engineer to calculate dV you'd find that if you replaced those mid stage SRB's with even a pair of liquid boosters (that could be droped when empty) of the same weight you'd have significantly more dV than your SRB solution.

I do like SRB's for initial launch, particularly to get a heavy rocket moving while its still full of fuel. Normaly by the time the SRB's run out the fuel has run down enough that the TWR is up to reasonable levels. However the ISP is just not worth bringing SRB's into orbit. Its just better to burn them off early and be done with it. From a standpoint of maximizing dV the rule of thumb is always burn off the lowest ISP thrust sorce first asumeing the manuver does not require more thrust than it can provide.

[LadyAthena]

On the other hand you could have instead just added more liquid fuel to that middle stage for a much better ISP than solid rockets get. Either way you spent X amount of fuel to launch that much weight into orbit. However you could have gone much further on that same weight had you used more efficient engines/fuel. I suspect if you used mechjeb or flight engineer to calculate dV you'd find that if you replaced those mid stage SRB's with even a pair of liquid boosters (that could be droped when empty) of the same weight you'd have significantly more dV than your SRB solution.

I do like SRB's for initial launch, particularly to get a heavy rocket moving while its still full of fuel. Normaly by the time the SRB's run out the fuel has run down enough that the TWR is up to reasonable levels. However the ISP is just not worth bringing SRB's into orbit. Its just better to burn them off early and be done with it. From a standpoint of maximizing dV the rule of thumb is always burn off the lowest ISP thrust sorce first asumeing the manuver does not require more thrust than it can provide.

Not sure with Ferram that is essentially a golden rule with the friction and drag aspect, the small SRBs are light, aerodynamic, and give a very sweet punch in speed. Nothing gets me from 400m/s to 2k m/s with so little weight, in so short a time, and so efficiently. You gotta also remember the cost, it's actually less than what I'd need otherwise.

Edited March 15, 2014 by LadyAthena

[wilt57]

Cost is important, and SRBs are cheap, but it isn't important yet.

I did some delta-v calculations. First, let's assume I have a 10 ton ship powered by an LV-T45. I do not have enough delta-v to complete my mission, so I add reaction mass to my orbital stage. For this specific scenario, I have two options:

A) Add two Rockomax BACC Solid Fuel Boosters on TT-38K radial decouplers or,

Add two liquid fuel and oxidizer boosters consisting of an FL-T800, an FL-T400, and an FL-T200 on TT-38Ks. They are cross fed to the base ship with fuel ducts.

This is a nice comparison because both the BACC and the stack of FL-T tanks add up to 7.875 tons full. Using this delta-v equation:

delta-v = ln(start mass / end mass) x Isp x 9.81,

For option A I have a starting mass of 25.8 tons, an ending mass of 10.05 tons, and a vacuum Isp of 250. I add 1,671.6 m/s of delta-v to my base 10 ton ship using option A.

For option B I have a starting mass of 25.9 tons, an ending mass of 11.9 tons, and a vacuum Isp of 370. I add 2,822.8 m/s of delta-v to my base 10 ton ship using option B.

If I indeed did these calculations correct, I add more delta-v per ton of mass lifted to orbit by adding liquid fuel and oxidizer than I do solid rocket boosters. I don't have the numbers for the SRBs you used form KW, but the point I'm trying to make is adding more reaction mass for an efficient liquid fuel rocket will gain you more delta-v than adding that same reaction mass for inefficient solid rocket boosters.

I hope I did the maths right! LOL

[MalfunctionM1Ke]

Clean seperation Trick

Since 0.23 you can also tweak the sepatrons just to give the Booster a tiny push.

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[Sirrobert]

Meh, you THINK it's a good idea because your rocket had more than enough fuel.

If you replace those central solid boosters with liquid boosters that weigh the same, you'll get way more deltaV. Because liquid rockets have higher ISP

[cantab]

You're almost certainly not going to use solid boosters in orbit anyway, because you can't control them. Meanwhile when you're still reaching orbit, and thus just want power without fine control, you've got to consider TWR and thus the thrust your engines give. In your example above you've compared an arrangement offering 200 kN with one offering 830.

I think the following are more of an apples-to-apples comparison:

Solid boosters:

Liquid boosters (LV-T30s), no asparagus:

The liquid boosters do still come out ahead, but by a smaller margin. The weight of the engines is offsetting the superior Isp somewhat.

The real advantage of liquid boosters is being able to asparagus them. I forgot to screenshot, but the asparagus one had two booster stacks, each with more fuel tanks to make the same launch weight, and brought the delta-v to around 2100 as reported by KER. Not having the main engine be dead weight while the boosters are firing meant only two not three LV-T30s were needed, in turn meaning more fuel could be carried.