AuoroP

I checked and 1km/s does not exceed terminal velocity as long as you're above 23.395 km. This is not true for 6.020 km whose terminal velocity is is 181.0 m/s. I don't have hard data on this but my intuition tells me that terminal velocity is a cruise limit for jet engines and the flight you're suggesting exceeds this limit by 552%. So I'll admit that drag loss would make this cruise only theoretical. I got a laugh out of imagining a Bob Kermin putting two jet engines (front and back) on a fuel tank and speeding ahead until they're exceed 1m/s and yelling OMG TOO FAST!!! STOP!!! I never liked Bob because what always seemed to freak him out was being in space. I've long suspected Kerbal nepotism: a Kerbal senator's wife's useless brother needing a job? Finally a test arises which is ideally suited to him! I can also imagine how much happier Jeb would be if he were cruising along at 1km/s in a jet and then decided to stop because Bob's screaming was ruining the experience. We would know that stopping would require a delta-v of 1000 m/s. Still if there is a maximum possible delta-v for a single stage, I still think there should be a value for jets; even with a star and a guffawing laugh beside it. What number would you pick? I'll be enjoying my first flight with Bob Kermin the jet sailor!

The Isp I used was already 2.5 times higher than the magical Ion drive so I just want to check that the game hasn't already accounted for what your adjustment. Otherwise, I would dismiss gravity and drag losses not being accounted for with any other theoretical limits and arrive at 473,657 m/s. I'm not seeing why this is true. Higher ratios means higher limits so ratios 15:1 or 11:1 beat the otherwise winners FL and Rockomax ratios of 9:1 but I don't see how that relates to efficacy. A single intake is a small fraction of the mass of a LF tank but provides unbounded oxidizer but if you insist on bringing your own oxidizer with you then 55%, 110/(90+110), of your LF tank is oxidizer a jet engine doesn't need.

Very clever insight! I did notice a couple of caveats. The OP is correct that FL and Rockomax tanks have a ratio of 9:1 but there are a couple tiny LF tanks with their own ratios: ROUND-8's is 5.44 (full 0.136t and emtpy 0.025t), Oscar-B's is 5.25 (full 0.078675t empty 0.015t). The OP also missed jet engines and jet fuel. A basic jet engine has an Isp of 2000 at sea level. The Mk1 fuelselage has a ratio of 3.14 and all the others have a ratio of 5 (exactly). Putting the best possible case together we have 31,577 m/s = 2000 s * 9.81 m/s^2 * ln(5/1) I also wanted to more verbosely explain the OP. The ratio the OP was talking about is the mass ratio used in the rocket equation: Mfull / Mempty. The Rockomax X200-16 (handily) has a full mass of 9 t and an empty mass of 1 t. The OP had the insight that all the FL and Rockomax fuel tanks have a ratio of 9 t / 1 t and further that as you keep adding more and more tanks the weight of the engine becomes more and more neglible unil we just throw away all other mass besides fuel tanks and we get an upper limit on an idealized stage delta-v that is, for the LV-909: 8,400 m/s = 390 s * 9.81 m/s^2 * ln(9/1)

In answering the question why do I care, you missed the biggest in my mind: it gives you the power to plan your rocket stages. I would have preffered if you'd used the Isp and constant version of the rocket equation because people will have seen that value in the game and and maybe even have an idea that it relates to rocket efficiency. Your example just seem to just randomly pick a exhaust velocity which doesn't help people plan better rockets. A good, but dated, example is the wiki's advanced rocket design. I recently showed that you need a delta-v of 1500 m/s to get out of the lower atmosphere and a delta-v of 3000 m/s to get into low Kerbin orbit. Surely, being able to plan rocket stages knowing when you'll hit these two marks is a huge reason to care about delta-v. Other people have made delta-v maps that then tell you how much delta-v it will take to get around the Kerbol system.

I noticed that you didn't mention terminal velocity - this is the speed you want to be aiming for during your launch. I can attest that I've checked the Wiki's page on Kerbin's of altitudes and velocities and I believe they are all correct. I would advise you try a launch and pay special attention them especially during primary ascent (straight up) or you can use MechJeb's option to limit you to terminal velocity. MechJeb also has a (sandbox) window called Ascent Guidence that will allow you to watch MechJeb launch your rocket. You can also watch three launches of Scott Manley in his YouTube video: You may be disappointed to find that he does not explain what gravity turns are or how they should be done; he just seemed to be bothered that they didn't start early enough because they were waiting until they were out of the lower atmosphere bar (12km).

The only craft which this won't work for are craft that don't have a high enough TWR to keep them limited to terminal velocity. But for these craft you get the great power of delta-v budgets and planning by breaking that one useless estimate up into two stages that you're going to know will get you out of the thick atmosphere and allow you to complete your gravity turn! So if your SSTO still goes straight up and then does a gravity turn you can now budget delta-v for both phases: 1000 m/s for straight up to 5km and then probably 3200 m/s for the gravity turning part. Thanks for pointing this out! I'm terrible at communicating because I assume people will see that I've used the atmosphere Isp for the LV-909 and it would have been really helpful to point out that I made the assumptions that I could simplify Isp to taking the atmosphere value under 12km and the vacuum above. Thanks for the correction. I obtained that value about a year ago via a single flight up while watching a barometer so I'm sure your value is more accurate. In the flight I mentioned, I started turning immediately after my second stage started at 8km. I kept my rocket pointing between the prograde circle and the outside of the cross. I didn't add any extra turning initially besides jumping right into that spot between the circle and cross

Cross posted to r/KerbalSpaceProgram. If you like to budget your designs on delta-v there are two outstanding questions about the delta-v you need to launch from Kerbin: how much deltaV for primary ascent and how much for a gravity turn. [RESIZE=720] For the TLDR folks, the answer is in the title: a stage delta-v of 1500 m/s gets you moving straight up at terminal velocity and your fuel runs out around 12 km. The accepted answer for a Kerbin launch requires 4500 m/s so the gravity turn will require 3000 m/s = 4500 m/s - 1500 m/s. So if you're still around you'll probably be interested in specifics about the methodology. Obviously, this is pretty easy. Design a single stage ship with just enough fuel to get it past the 12km lower atmospheres bar. [RESIZE=720][/RESIZE] Recipe: 6x OX-STAT solar panels (top and bottom) above a Stayputnik pod. Below that we add 3x Z-200 battery rings. Below that a TR-18A decoupler. Below that a FL-T100 fuel tank with Lv-909 engine. The atmosphere Isp for the LV-909 is 300 s. Then add another 6x Z-100 batteries. The total mass is 1.28 and the dry mass is 0.78. The stage delta-v is 1450 m/s. I happened to conduct this research before I saw Scott Manley's adjustment video for gravity turn tutorials and learned that my target of waiting for barometric pressure to drop to 10% at 11.7 km for starting a gravity turn is too late. I did more testing and discovered that 1200 m/s gets you up to 8 km and it is possible to complete a lazy (did not move prograde fast enough) gravity turn into a circular 75 km orbit with only 3100 m/s in the second stage. 3000 m/s is enough to put you mostly in orbit and yet keep your second stage from turning into space junk.

Refined Kerbin delta-v Launch 1500 m/s Up, 3000 m/s Gravity Turn Cross posted to r/KerbalSpaceProgram. If you like to budget your designs on delta-v there are two outstanding questions about the delta-v you need to launch from Kerbin: how much deltaV for primary ascent and how much for a gravity turn. [RESIZE=720] For the TLDR folks, the answer is in the title: a stage delta-v of 1500 m/s gets you moving straight up at terminal velocity and your fuel runs out around 12 km. The accepted answer for a Kerbin launch requires 4500 m/s so the gravity turn will require 3000 m/s = 4500 m/s - 1500 m/s. So if you're still around you'll probably be interested in specifics about the methodology. Obviously, this is pretty easy. Design a single stage ship with just enough fuel to get it past the 12km lower atmospheres bar. [RESIZE=720][/RESIZE] Recipe: 6x OX-STAT solar panels (top and bottom) above a Stayputnik pod. Below that we add 3x Z-200 battery rings. Below that a TR-18A decoupler. Below that a FL-T100 fuel tank with Lv-909 engine. The atmosphere Isp for the LV-909 is 300 s. Then add another 6x Z-100 batteries. The total mass is 1.28 and the dry mass is 0.78. The stage delta-v is 1450 m/s. I happened to conduct this research before I saw Scott Manley's adjustment video for gravity turn tutorials and learned that my target of waiting for barometric pressure to drop to 10% at 11.7 km for starting a gravity turn is too late. I did more testing and discovered that 1200 m/s gets you up to 8 km and it is possible to complete a lazy (did not move prograde fast enough) gravity turn into a circular 75 km orbit with only 3100 m/s in the second stage. 3000 m/s is enough to put you mostly in orbit and yet keep your second stage from turning into space junk.