GoSlash27

Jouni, We know pretty accurately what DV will get a ship into LKO regardless of it's mass. While the T/W ratio does affect this, it's pretty negligible so long as it's within the window of 1.4-2, so not something to worry about IME. Just build the ship for 4,500 DV and make sure the T/W is correct. The rest will sort itself out. Best, -Slashy

Smith, The DV map is accurate for continuous burns taking advantage of the Oberth effect, and you've got the idea of how it works. It does not, however, take into account DV saving tactics such as aerobraking, slingshotting, etc. Your return trips to Kerbin will never use as much DV as the map suggests because you're using Kerbin's atmosphere to convert excess DV into heat. If Kerbin had no atmosphere, you'd have to fire engines to soak up the DV and the map would be correct. Beware using this map for interplanetary trips when you're not doing one continuous burn from launch, tho'. Simple flight plans (escaping Kerbin SoI and then burning for an intercept) will take much more DV, while slingshotting/aerobraking will take much less. Best, -Slashy

Back in the olden days, they used log tables for high- precision answers and slide rules for spitballing. I still use a slide rule for KSP; Pickett #120. It's not as precise as a calculator or spreadsheet, but it shows all possible solutions for a given ratio at the same time, which makes it faster. Best, -Slashy

K77, I would be greatly shocked if you were able to just pick up on rocket science and run with it without any headaches. It takes all of us some time to adapt, so don't feel stupid; we all went through this. Your rocket equation in standard form is DV= 9.81*Isp*ln(Mw/Md). Plugging in your example, DV= 9.81*(225)*ln(3.7475/.5)= 2,207*ln(7.5) = 2,207*2.014 = 4,445 m/sec. Just barely enough to make orbit without any payload whatsoever. With good piloting and absolutely no reserves, you need 4,300 m/sec DV to reach LKO. So re-working the equation for maximum payload... DV=9.81*Isp*ln(Mw/Md) DV/(9.81*Isp)=ln(Mw/Md) e^(Dv/(9.81*Isp))= Mw/Md <-- Your required wet-to-dry ratio, or "Rwd" plugging in the numbers... e^(4,300/(9.81* 225)=Rwd e^(1.948)=Rwd 7.017=Rwd Knowing that your Mw/Md must be at least 7.017 and that your payload is part of both wet and dry mass, we can continue reworking the equation. 7.017= (Mlw+Mp)/(Mld+Mp) ; The sum of the masses of your wet launcher and payload divided by the sum of the masses of your dry launcher and payload must equal 7.017. 7.017= (3.75+Mp)/(0.5+Mp) 7.017*(0.5+Mp)= 3.75+Mp 3.509+ 7.017Mp= 3.75+Mp 3.509-3.75=Mp-7.017Mp -.241=Mp(1-7.017) -.241=Mp(-6.017) -.241/-6.017=Mp .04=Mp. You can't orbit any more than .04t of payload with a single RT-10 booster. And even then, that's with good piloting and absolutely no reserve. Using the numbers from your link, 400*9.81*ln(3.72/1.72)= 3,924*ln(2.16) =3,924*.771= 3,027 m/sec DV, which agrees with their answer. Hths, -Slashy

Claw, Excellent work! This should be extremely useful for testing contracts. How did you determine drag losses vs. gravity losses? Thanks, -Slashy

Stock unrealistic go kart, and also a new world's record. 787 M/sec. (edit) 1,137 M/sec?? Or maybe not... rcscart.craft

The same limits would still apply. Regardless of what your ship's mass is, you still need a known DV to attain orbit. Unless they make a fuel tank massless or dramatically improve the wet/ dry ratio, Eve SSTO will remain impossible. OTOH, if they ever do make a "massless" fuel tank, then pretty much anything is possible. Best, -Slashy

A monopropellant SSTO would be easy using O-10 engines. The atmospheric DV limit is 4,615 M/sec. It's just a matter of how much mass you want to orbit. I don't know if a mono SSTO could out- perform a conventional rocket in terms of payload/ lifter mass, tho'. At least AFA small payloads. You can SSTO a Mk.1 can to LKO with a total vehicle mass of 10 tons using conventional propellant. Likewise, you could employ conventional tanks and Vernor RCS thrusters. Worse Isp, but better wet/ dry ratio. Best, -Slashy

Unfortunately, it doesn't quite work like that. Your engines have no mass, but your tanks do. Knowing that your most mass- efficient propellant tank has a hard limit for wet to dry ratio of 8.5 allows you to mathematically derive an absolute upper bound for DV. It works out to the numbers I posted above; 4,619 M/sec atmospheric and 6,090 M/sec vacuum. Adding engines and tanks will never exceed these limits no matter what you do. Regards, -Slashy

paramecium, infinite fuel would be cheating. Any setup can make SSTO with infinite fuel. Best, -Slashy

The easy way to do this IMO would to launch a test rocket and "map" the DV vs. altitude. AFAIK nobody's bothered doing this yet. You note the fuel mass and dry mass of the rocket and launch it. Every 5km altitude, you note the percentage of fuel used. The rocket equation will tell you how much DV it required to attain the altitude. If you keep the acceleration within reasonable bounds, these results will be repeatable for any future rocket you send up, regardless of mass. Best, -Slashy

ScareCake, In addition to the above, you could consider reducing your payload, splitting it among multiple transfer vehicles, and eliminating one of the LV-Ns. Especially the "reduce payload" part. Designing your surface payload and launch vehicle to be as mass- efficient as possible reduces your lander's mass. Reducing your lander's mass has a dramatic effect on your payload mass. Little changes at the far end of a mission have a dramatic effect on earlier stages. Although honestly... 12,000 m/sec DV is more than plenty enough. Rather than looking for ways to increase your DV, why not look for ways to use your existing DV more efficiently? Best, -Slashy

I'd say an easy location in the tech tree is buff enough. IRL you would never use a turbojet to try to get to orbit. Best, -Slashy

Macko, I have no idea, but I'm definitely intrigued! Which video was this in? -Slashy

Update: I got to wondering whether the new update changes things with the O-10 monopropellant engine. It doesn't... Maximum DV from the O-10 engine assuming no payload is 4,619 atm and 6,090 vac. Neither is enough for SSTO from Eve. The vernor thruster fares worse due to it's poor Isp. After playing around with ion gliders for half of forever, I'm willing to call this one busted. We still have yet to see one reach Kerbin orbit without control surfaces as wings, and Eve is a much taller order. (edit) Galane, I have designed a Kerbin all rocket SSTO that weighs 10 tons when configured to lift a Mk1 pod. I have another 5 ton model that doubles as a rover. It doesn't take much rocket to pull it off. But Eve requires a lot more DV; it can't be done at any size. Best, -Slashy

This would seem to be a useful rule of thumb, but as several people have pointed out (myself included), you don't actually have to launch anything in order to answer this question. The inverted rocket equation I gave you will spit out the answer immediately. I also don't use any mods for KSP, so it's just that much more important to understand and use the math in your design process. For certain, you'll never be able to design optimized vehicles without going through the math... and there are many things you simply can't accomplish without optimized vehicles. I'm going to try to put together a comprehensive tutorial on all the different forms of the rocket equation and how it can be used to answer all sorts of questions along these lines; how much payload a given rocket can accelerate to a given DV, or how much fuel a given rocket needs in order to accelerate a given payload to a required DV, etc. Best, -Slashy

It's just simple math, really. e^(DV/9.81Isp) gives you your required ratio of wet to dry mass in order to make orbit. Knowing how much your launcher weighs wet and dry, you can rearrange the rocket equation to read Mp=(RwdMld-Mlw)/(1-Rwd) where Mp is the mass of your payload Rwd is your required wet to dry ratio Mld is the mass of your launch stage dry and Mlw is the mass of your launch stage wet. This will tell you exactly how much payload you can lift with your launcher. Best, -Slashy

I have a single rover design I use for all my missions. The way I figure it, an ideal system theoretically requires no rovers. All of your habitation modules, kethane plants, return vehicles... everything is delivered precisely where it needs to be, fully fueled, fully assembled. Rovers exist because perfection doesn't, so a rover needs to be able to do everything on the surface I can't do from orbit. This gives me requirements for my rover. 1) It must be all-terrain capable. Preferably capable of swimming to shore. 2) It must be capable of transporting a load across the surface. 3) It must serve as a construction vehicle. These are all "hard" requirements. Anything else it does are bonuses, but if you can make it do more, it simplifies your logistical problem. You still have to get the rover itself to the surface. You still have to get your payload to the surface or orbit. A good design allows the rover to serve as an SSTO delivery vehicle as well. 4) It must be capable of deorbit and landing with a payload on every habitable body in the system. 5) It must be capable of SSTO operation to orbit with a payload from every habitable body in the system... with the exception of Eve, which is impossible. Fuel is, of course, the #1 logistical concern, so it needs to be able to serve all these functions while serving as a tanker. This design serves all those functions and also has a "flying car" capability that comes in handy from time to time. Feel free to use it or improve it for your needs. Best, -Slashy

I don't really know, but I suspect it's the insertion burn. Those would represent times when you arrive carrying excessive DV that has to be burned off in order to establish orbit. Just a guess. Best, -Slashy

Positive displacement blowers don't have blades, but rather lobes. Likewise, centrifugal blowers have vanes. How loosely are we defining "blades"? Curious, -Slashy

I won't repeat what everyone else here has already said, but I'll share how I do it. 1) Plan before you design. Figure out what it is you're trying to do and how you plan to accomplish it. Sort out your phases and DV budget. 2) Design before you build. Work out the math to make sure you've got a good design before you hit the VAB. You'll save a lot of frustration and expensive fireworks. 3) Check before you launch. Pretty much everybody has mentioned this already. Checking your staging, solar panels, etc. Come up with a checklist to keep from forgetting things. 4) Test before you put Jeb in the seat. Take a dry run or 2 to sort out the gremlins to avoid frustrating tragedies. It's more fun to explore without worrying whether you can trust the system. 5) ...and this is most important... Learn something, have fun, and share what you learn. KSP gives you the chance to learn new concepts and explore aerospace engineering. When you're learning, even failure can be fun! The key is in identifying the gaps in your understanding and filling them rather than getting frustrated. When you take that new understanding and succeed with it, it's very rewarding! It's also rewarding to pass on your knowledge to newcomers and help them along. Best, -Slashy

If there is only one unit of measurement in use, it's implicit. As of last update, meters per second was the only unit for velocity in KSP. Except in my installation, which is furlongs per fortnight. /steampunk -Slashy

Well... people will come to a conclusion, anyway. Perhaps not that one...

Alleged meters per ostensible second change in speed?

I think we all understand that "M/sec" is implied when people speak of DV. Point in fact, "delta vee" is actually shorthand for "change in velocity", which is also technically incorrect, as "velocity" requires a Cartesian vector. So if you *insist* on using correct terms, it's "X meters per second change in speed" so have at it. Otherwise, I understand what people mean when they say "fifteen hundred dV". And while we're on a grammar .... kick, you should use quotation marks within sentences that contain quotes. ex. It's like saying "I need this room to be a few temperatures higher". /Nobody's perfect Regards, -Slashy p.s. It's rude to call out other posters by name as you have done here.