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Is your rocket an accidental SSTO?


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I like to balance practicality and aesthetics with all of my designs... I also like to add a dash of reality, for example, if I'm using MJ for a launch, I alter various settings and vehicle parameters (TWR etc.) until I'm no longer getting reentry burn on the way out. 

But something that does annoy me slightly is that even my simplest regularly used rocket (1.25m fairing, 2xFL-T800, and a swivel) is nearly an SSTO - in reality the first stage of a rocket doesn't do the majority of work to reach orbit, the second does. For example the SpaceX launch of THAICOM 8 sees MECO and first stage separation at 8331km/h (2314m/s) @ 67km, the second stage then finishes its burn at 36,435km/h (10,093m/s).

I often find second stages in KSP are not overly important (if the payload has its own propulsion at least) though this is a very broad statement and is entirely mission dependant... though is true for a lot of in Kerbin SOI work.

This isn't really a criticism of the game and nor am I suggesting this is something that should be fixed... it's just simply how physics works given the size of Kerbin. I just find myself a little uncomfortable with it - does anyone else?

Edited by MR L A
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This is related to the way Kerbal Space Program is balanced. We have a solar system that needs roughly a third (0.1^0.5=0.316...) of the delta-v required to get anywhere, but instead of balancing the parts by limiting the Specific Impulse (which scales linearly with delta-v) the game is balanced to make the dry mass of the rocket compared to the wet mass of the rocket much higher. (which scales logarithmically with delta-v, so you can't do a 1:1 mapping of delta-v cost to rocket requirement).

If you want realistic performance out of your rockets, I'd recommend either playing in a rescaled solar system, or using the SMURFF mod to make the dry masses even worse. (I had an Isp scaling config somewhere but I can't find it, PM me if you want to try it and maybe I'll go look for it later)

Note that 1/3rd the Isp of KSP's rockets results in really bad specific impulses. We're talking gunpowder-like performance.

I've long felt uncomfortable with it, especially with the SLS parts from 0.23.5.

Edited by GregroxMun
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No as I use MJ for planning but as GregroxMun says its pretty easy to do, making something who can land reliable afterward is harder. 
Remember that 2.4 km/s orbital speed would make the X-15 plane pretty much orbit capable and an falcon 9 would be able to put second stage into orbit 

One tricks I have done is to taken first stage into orbit for later use, either for fuel stations or to refuel and use for interplanetary missions. 

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3 hours ago, MR L A said:

 For example the SpaceX launch of THAICOM 8 sees MECO and first stage separation at 8331km/h
(2314m/s) @ 67km

Kerbin low orbit speed is 2240m/s, at 70km. Everything checks out.

What you need is a heavier planet. RSS?

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Use Rescale 3.2x and the rockets start performing a lot more like real life designs. At 3.2x you'll require 1.8x the DV for any maneuver - or about 5900 DV for Kerbin Orbit. The game would be so boring for me without this.

@Galileo hasn't updated it for a while, but despite the big "this won't work in 1.4" warning, it works just fine for me in both 1.4.x and 1.5.x. I've used it for many many hours without probs

One note - I'd skip using Kronometer which is recommended by ReScale. Many mods like Kerbal Alarm Clock and Transfer Window Planner won't play well with it. Instead use the Stock 24 hour clock. The only thing that will be off if you use 24 hour clock without Kronometer is that a Kerbin "day" is actually two full rotations of the planet, but everything else in the game behaves just fine.

 

Edited by Tyko
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Your payload is too small :wink:

Yeah, I had some of these problems but most of them were on the edge between the 1.25m capabilities and 2.5m engines power. My payload was too heavy for single stack 1.25m rocket (and I don't use SRBs) but too light for any 2.5m engine with decent sea level isp. I had to add two clones of first stage on the sides to make it work.

Yet, some of my 2.5m rockets were SSTOs.

Edited by The Aziz
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In my OPM career, I’m sending probes everywhere because TAC LS! To launch them however, is use a Twin Boar to create  an SSTO launcher. It’s highly versatile, because I can add up to 1.5xJumbo-64 and still have a good twr on launch while having enough Dv to get to orbit.

Massive Boosters in LKO is a problem though... I end up playing with them by using hyperedit. I tried recovering them, but it’s too small a return.

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8 hours ago, Tyko said:

Use Rescale 3.2x and the rockets start performing a lot more like real life designs.

Very much this. 3.2x is for me the perfect balance between fun and challenging. I can still do anything but I have to actually work at it. And time to orbit isn't as bad as the full 10x "realistic" resizing.

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