GoSlash27

I concur with the others here. If you transfer the fuel to the high tanks, retract the low landing gear, and screw around with it, you *might* be able to get it vertical again. Sending Jeb EVA to push is a little risky, but you'd be amazed what kerbals can do. Just be ready to transfer control back to the ship quick! Good luck, -Slashy

Jouni, I'm sure the upload links are long-dead by now, but I'll take a look and see. *edit* sorry, they're gone now I haven't used those since back in .23. I don't even have the original craft file anymore. You could probably recreate it, tho'. It had a standard asparagus arrangement using aerospikes and x-200-8 for the boost. Layer-caked above that was a standard asparagus arrangement of 48-7S with FL-T200 tanks for the transstage and injection. It was very minimalist, like all of my stuff. Sorry, -Slashy

Actually, I really *don't* use staging on Eve. Not anymore. My colonization plan requires SSTO everywhere to simplify logistics, so I cheated like Hell. Infiniglide coupled with Kraken drive gets me from Eve surface to orbit and back to base without a drop of fuel. Ain't 'shamed, -Slashy

Jouni, My asparagus lander does the same job (1 tonne to Eve orbit) with a total mass on the surface of 52 tonnes, so it's more than just a little more mass-efficient. And my design traded off mass ratio for aspect ratio, structural rigidity, and ability to be refueled on the surface, so it *could've* been lighter. Asparagus staging can make a huge impact on mass ratio. Best, -Slashy

Rocketeer, I think by the OP's wording, he's referring to the same concept the rest of us are. Asparagus staging refers to parallel tank/ engine assemblies where all engines are firing and the outer stages crossfeed fuel and oxidizer to the inner stages and are discarded when empty. Simply radially attaching boosters is not "asparagus staging"... at least not by anyone's definition except yours. I think Red Iron said it best: Best, -Slashy

Agreed. Best, -Slashy

I disagree with this part. Asparagus staging is using the fuel in the early stages to feed all the active engines. It doesn't work if you can't transfer fuel between stages, and of course you can't transfer solid propellant. Best, -Slashy

KerbMav, Oberth effect is actually a way of explaining the disparity in kinetic energy that results from doing the same burn at different speeds. Other than that, yeah... that's pretty much it. K^2, The hohmann transfer is actually not the most efficient way to change orbits, that honor goes to the bi-elliptic transfer. The reason that it works is, indeed, the Oberth effect. IRT the original question, yes, depending on the circumstances you can save some DV by dropping first, but it's easy to overdo it and wind up costing yourself more at the end. Generally not worth it for small changes, as the investment is more than the return. Besides making transfer burns cheaper it also works in reverse, making captures cheaper. You should do capture/ circularization burns at periapsis to get the most delta Ek reduction for your delta v. Best, -Slashy

Tw1, I'm definitely not on board with adding complexity to KSP simply to make it more realistic. *I* personally am fine with playing it that way, but the folks at Squad aren't trying to make a simulator. They just want to make a game that's engaging, but not so complicated that the uneducated get overwhelmed and give up. Best, -Slashy

Grazi. Kerbin is, IMO, the most unique environment in the system AFA mission priorities. It's the only place where you can build the rocket, wheel it out fully-fueled, and launch it. Everywhere else requires placing your launch vehicle on the surface from orbit intact after having (ultimately) launched it from Kerbin's surface and transported it there across deep space. Prior to the last couple of updates, nobody cared about cost, so it wasn't a factor. Big mass ratios means big payloads so it was the way to go. But now price is a huge deal. The buy- in is low for SRBs on a single- shot mission, while SSTOs are clearly the cheapest operating cost for sustained missions. But out at the other end of the mission, the priority hasn't changed. The better your mass ratio, the lower your payload off of Kerbin and thus the cheaper and easier the mission overall. So in that sense, asparagus staging isn't overrated at all. It's excellent for the jobs that suit it. But lifting payloads from LKO isn't a job that suits it very well. Best, -Slashy

Sorry for spamming, but I just thought of another way of explaining it that may be more intuitive. You know how when you do a transfer from LKO to mun or minmus the apoapsis climbs very slowly at first, but towards the end of the burn it's rocketing upwards at a much faster rate? It's not due to you being close to Kerbin or anything like that. You could do the same thing on an interplanetary transfer and see the same effect; the apoapsis climbs slowly at first, but climbs much more rapidly towards the end. So what causes that? You'd expect it to be linear. Halfway through the burn, you'd expect your apoapsis to be halfway to the target, but that's not how it works out. This is the Oberth effect at work. As you accelerated, your kinetic energy (and thus your apoapsis) increased at an exponential rate. The first 100 m/sec didn't buy you much, but the last 100 m/sec made a radical change. Harnessing the Oberth effect is making the same change in apoapsis for less DV by doing your burn while travelling at a higher speed. Hope that makes sense, -Slashy

I would also like to see this. I'd feel a lot better if I knew they had successfully anchored in. Best, -Slashy

Always the okto-2 for me. Lighter is better. If I need more reaction wheel torque, I'll add reaction wheels further down the stack where they hurt my mass ratio less. Best, -Slashy

Whether or not it's overrated depends on how you rate launch vehicles. If you're looking for high mass ratios at the expense of everything else, it's awfully hard to beat. If you're looking to factor in cost, then it's not very good. Suppose you want to design a mission to Eve. SSTO is impossible there without cheating or glitch exploits and jets don't work. You want the lightest possible return vehicle because you have to move it out there and place it on the surface. You're gonna use an asparagus booster for that job because the mission dictates best mass ratio. Kerbin surface to LKO, OTOH, is a different job and different priorities apply. Best, -Slashy

andrewas, Actually, it's cumulative for all the frames you're referencing. They don't have to affect you to count. You get a free 175 m/sec for launching East, plus 2,300 m/sec for LKO, plus 9,300 m/sec for Kerbin's orbit around Kerbol. All of this applies to a transfer to another planet. If you were transferring to another star system, you would also pick up the velocity of Kerbol around the galaxy. Best, -Slashy

GregA, We're talking about different concepts. Pushing off of an asteroid is force (newtons). Changing your velocity is delta v (m/sec). Kinetic energy is energy (Joules). Pushing off of an asteriod at high speed vs. low speed won't increase the force with which you pushed, nor will it increase the speed you add by doing so. But it *will* add more kinetic energy than it would have done at low speed, and thus will more greatly affect your apoapsis. Best, -Slashy

Speed <> kinetic energy, but we often short-hand them as the same thing. For a fixed mass, they're comparable... but misleading since the relationship between them is not linear. Delta- vee is delta- vee. That never changes based on your starting velocity. Likewise, thrust, burn times and fuel flow don't change depending on your starting velocity. But delta- kinetic energy *does* change based on your starting velocity. Adding 1KM/sec to your velocity won't do as much to change your apoapsis at low speed as it will do at high speed. Please bear with me if I'm rehashing something you're already familiar with, but I need to present this to illustrate how it works. Kinetic energy is 1/2M*V^2. The kinetic energy after you do a burn is 1/2M*(v+D)^2. <-- "D" is your delta-vee. We don't care about the mass or an exact value, so let's eliminate the stuff that doesn't change. Kinetic energy is proportional to (v+d)^2. Let's foil this out to look at what effect our burn is causing. Ek is proportional to v^2+2vd+d^2 Our burn did not cause the initial change in velocity, we arbitrarily chose that. So we'll eliminate that. 2vd+d^2 ^ This is the effect that your burn has on your total kinetic energy. That "v" sitting in there is giving you a boost in your gain simply because you were going faster when you did it. Why it matters is because doing your transfer burn at as high a velocity as possible can save you a huge amount of delta-vee (and hence fuel) over doing it at a low velocity. So much so, that the gain will even offset the loss in kinetic energy associated with climbing out of a gravity well. It would seem that the most effective way to do a transfer is to climb out of the gravity well (about 1Km/sec) and refuel, then proceed on your way. But in reality, that robs you of 2,300 m/sec you could've had during your burn had you refueled in LKO and burned from there. You still have 9,300 m/sec from your orbit around Kerbol, but you *had* 11,600 m/sec at the bottom of the gravity well. Doing your burn from down there would've saved you 1,800 m/sec to get to the exact same kinetic energy, so even losing the 1,000 climbing out, you still come out ahead. Even better, you could climb out and refuel, then dive back in and do your burn. That would add another 1KM/sec to your velocity at burn, which saves you even more. It's counter-intuitive, but that's how it works. All because DV isn't linear to kinetic energy. Best, -Slashy

Boots::mud:talkie::toast.

IMO the best altitude is LKO, 70KM. Least amount of DV required to get supplies to it, excellent harnessing of the Oberth effect, and no guess-work for finding transfer windows for the next mission. Best, -Slashy

Or conversely, a tic mark in each planet's orbit to show when it will be in alignment for the transfer window on Kerbin's current orbit. Either of these would work fine as a "give it to them" solution. As an in-game solution, you could have a team of Kerbals tasked with finding transfer windows. Asking them questions would cost funding. Best, -Slashy

arkie, I'm ambivalent about it either way. It's a game, so I totally understand if the developers don't want to make it too realistic (difficult). Otherwise, people will look outside to web references/ mods/ etc to find their transfer windows. But something should be done, since people can't make the trip without transfer windows. They don't want the players giving up in frustration, either. So give them the windows or make them earn them... whichever they decide. But the solution should be in-game. Best, -Slashy

This is correct. All the stuff about escaping gravity wells/ etc is a distraction from this, and you worded it very well. Getting a desired apoapsis (or periapsis) is not a matter of change in velocity, but rather a change in kinetic energy. Since velocity is not linear with respect to kinetic energy, it stands to reason that a fixed quantity of velocity will add more kinetic energy when you're moving quickly than it does when you're moving slow. This is the Oberth effect. Sounds like you've got it pegged. Best, -Slashy

It will save you some DV in the long run, but it makes your transfer windows awfully tricky. Minmus needs to be in the correct phase relative Kerbin (it usually isn't) and you have to account for the time it takes to fall to Kerbin. Plus you have to correct for the inclination change at Kerbin periapsis Kind of a big hassle for the little gain in kinetic energy, so I don't bother. Best, -Slashy

LethalDose, I'm fine with moving the transfer efficiency discussion to another thread. What were we originally discussing? Oh, right... finding transfer windows Really something the team needs to address in-game, but there are many different work-arounds. I'm going to try out the idea I had back on page 2; place a simple satellite in Kerbol orbit just ahead of Kerbin for planning purposes. Using that, you can set a maneuver node and drag it around, which will tell you how many days you have until the transfer window opens up. Best, -Slashy

LethalDose, It is actually more efficient to begin your mission from Minmus, setting aside the cost of hauling fuel up there, it's just harder to make the timing work. Assuming a fueled ship were to spring into existence orbiting Minmus, it would take very little kinetic energy to fall to a 70KM periapsis over Kerbin, and you'll be doing about 3100M/sec when you arrive for your transfer burn. This saves you a big chunk of DV for the Jool transfer due to the Oberth effect. This would be worth trying in-game for an exact savings in DV, but I'd expect roughly 700M/sec under an LKO departure. According to my back-of-the-envelope calculation it's 160M/sec to set up the 70KM periapsis and a 1,055m/sec burn to get to Jool. I'm interest to see what it actually works out to. As for returning, it's more efficient to refuel in LKO, as you can aerobrake your excess kinetic energy. Best, -Slashy