Easy LKO and SSTO rockets

[Warzouz]

The other day, I was wondering why SSTO rockets are so cheap to use, and why I didn't used them in beta 0.9. Sure I was in Science game mode, and quite a newbee, but there wasn't real SSTO rockets I remember of back then.

And then I remembered we used to go to LKO for 4500m/s, not 3200...

A very quick and dirty calculations using my Cygnus launchers (http://forum.kerbalspaceprogram.com/threads/123195)

A 15 tons payload to LKO

- Needs a 80 tons SSTO stage in 1.0.x (1 mainsail)

- Needed a 260 tons SSTO stage in beta 0.9 (3 mainsails)

In few words, the changes from beta to 1.0 made rockets 3 times smaller to go to LKO. This allows SSTO rockets to really be efficient, especially if recoverable.

Do you share this point of view ?

[Alshain]

Yes, I agree, but I will add this is better. They were too big in beta anyway. The 4000+ delta-V requirement made rockets unrealistically large, you almost had to use asparagus staging or a pancake rocket. With the current ~3400 requirement, our rockets can look like rockets. Sure you can still use asparagus rockets and if you really want to fight aerodynamics you can use pancake rockets, but the game should try to parallel (but not simulate!) real life.

I like being able to orbit a rocket that looks like something SpaceX or Boeing or Lockheed would build on the launchpad.

[ment18]

All rockets were nerfed heavily from 0.90 to 1.0. I think there was a blanket loss of about 50 ISP everywhere, except for nerv and dawn. In addition, rockets didn't lose thrust to air pressure in 0.90, only fuel efficiency. The SSTOs would have had more Dv back then. There was also mass less landing gear(cubic struts and landing wheels) and massless solar panels/batteries.

Delta-v is also heavily affected by aerodynamics to if you payload isn't a 2.5m fuel tank you are going to spend more than 3.2km/s to get to LKO. Wider fairings also cost aero and weight.

I don't like rocket SSTOs because they are hard to land on target. One can't really aim them well and aerodynamics are hard. One the way up you want the top to go forward, but on the way down you want the rear engine forward. With wings on the back this can be hard, especially with out air brakes. You also have to have serious skills/extra fuel, or heavy parachutes to land and heavy, draggy landing gear.

[Alshain]

I don't like rocket SSTOs because they are hard to land on target. One can't really aim them well and aerodynamics are hard. One the way up you want the top to go forward, but on the way down you want the rear engine forward. With wings on the back this can be hard, especially with out air brakes. You also have to have serious skills/extra fuel, or heavy parachutes to land and heavy, draggy landing gear.

Lol, I've never heard that one before. I mean, to each his own, but you get a 96% refund if you land it anywhere in the huge flat area around the KSC. You don't need a pinpoint landing

[ment18]

Lol, I've never heard that one before. I mean, to each his own, but you get a 96% refund if you land it anywhere in the huge flat area around the KSC. You don't need a pinpoint landing

I'm bad at aero landing I guess, I usually have to fly my planes dozens of kilometers back to KSC after reentry.

[Alshain]

I'm bad at aero landing I guess, I usually have to fly my planes dozens of kilometers back to KSC after reentry.

Ah, well that just takes practice. In time you start to learn just about how much your orbit will change as you pass through the atmosphere. It takes a little while, but it is indeed easier to learn on a plane first IMO. For a plane all you have to do to move your trajectory is pull up or nose down where as with a rocket you usually get to bring in the trajectory but if you come in too short there is no going back. Alternatively you could use the Trajectories mod but after a while you just start to recognize where your initial trajectory from orbit should be.

[LostOblivion]

Yes, I agree, but I will add this is better. They were too big in beta anyway. The 4000+ delta-V requirement made rockets unrealistically large, you almost had to use asparagus staging or a pancake rocket. With the current ~3400 requirement, our rockets can look like rockets. Sure you can still use asparagus rockets and if you really want to fight aerodynamics you can use pancake rockets, but the game should try to parallel (but not simulate!) real life.

I like being able to orbit a rocket that looks like something SpaceX or Boeing or Lockheed would build on the launchpad.

I agree with this. With the diameters and quantities of fuel they've chosen, the current requirement of delta-v to orbit makes much more sense.

I remember many of my old 1.5 m rockets were usually silly tall, whereas now they seem more realistic.

[Warzouz]

Delta-v is also heavily affected by aerodynamics to if you payload isn't a 2.5m fuel tank you are going to spend more than 3.2km/s to get to LKO. Wider fairings also cost aero and weight.

True, I forgot about that.

I don't like rocket SSTOs because they are hard to land on target. One can't really aim them well and aerodynamics are hard. One the way up you want the top to go forward, but on the way down you want the rear engine forward. With wings on the back this can be hard, especially with out air brakes. You also have to have serious skills/extra fuel, or heavy parachutes to land and heavy, draggy landing gear.

Landing on a ultra precise point is not required. Landing at KSC will grant you 98% of the dry value. Landing anywhere within 70km will grand you 97%. Don't bother about precision for only 1%. The only "skill" you need is to know where to deorbit.

Yes, I agree, but I will add this is better. They were too big in beta anyway. The 4000+ delta-V requirement made rockets unrealistically large, you almost had to use asparagus staging or a pancake rocket. With the current ~3400 requirement, our rockets can look like rockets. Sure you can still use asparagus rockets and if you really want to fight aerodynamics you can use pancake rockets, but the game should try to parallel (but not simulate!) real life.

Yes. But I would think the "pancake" shape was more due to the wobbliness of wet noodle joints. It was very hard to do a steady vertical 4 stage rocket such as Saturn V. Pancakes were easier because you could plug many (dragless & weightless) struts. The rocket were more rigid with such a flat design.

[Alshain]

Yes. But I would think the "pancake" shape was more due to the wobbliness of wet noodle joints. It was very hard to do a steady vertical 4 stage rocket such as Saturn V. Pancakes were easier because you could plug many (dragless & weightless) struts. The rocket were more rigid with such a flat design.

Not really very hard. I mean, sure it was up until the Unity update (I think it was 0.23?) but after that the "wet noodle joints" were gone and it was really skill that determined what was possible. People who made the mistake of attempting a 4 stage rocket with a single stack size were setting themselves up for failure, but the Saturn 5 Apollo wasn't a single stack size, it had 3 stack sizes in a pyramid-ish design. That was easy to do in early versions from the stance of construction and flight, but packing enough fuel in a rocket like that might have been difficult before 1.0.

[Acet]

I'm bad at aero landing I guess, I usually have to fly my planes dozens of kilometers back to KSC after reentry.

Aerobrakes!

As I recently found out when figuring how to bring back to Kerbin small but heavy containers from Minmus (mined commodities from MKS-Lite), aerobrakes not only make the impossible possible (in this specific case those things were like bullets and never got below safe chute speed before crashing, even at very shallow entry angles, if I didn't put aerobrakes in them) but because you can turn them on or off at will can also be used during re-entry to fine tune landing.

Before this discovery I was also having trouble with that, mostly because different ships now have different ballistic descent profiles, depending on their drag, weight and even which direction they are facing at different points when coming down (on start of descent sometimes it helps to present a high-drag aspect), so one had to figure out for each new ship design when and how steep to start one's atmospheric entry to end up close to the KSC. With the addition of aerobrakes I now have something which gives me quite a lot of control during descent (the difference in drag between ON and OFF can be huge) without the need for extra fuel or near impossible manoeuvres to change the side pointing at the wind.

(Edited for grammar fixing and clarification)

Edited October 19, 2015 by Acet

[Van Disaster]

I don't like rocket SSTOs because they are hard to land on target. One can't really aim them well and aerodynamics are hard. One the way up you want the top to go forward, but on the way down you want the rear engine forward. With wings on the back this can be hard, especially with out air brakes. You also have to have serious skills/extra fuel, or heavy parachutes to land and heavy, draggy landing gear.

Why land them? single-stage-to-orbit doesn't mean single-stage-to-orbit-and-back-again, there's nothing about reusability implied there. It's just the cheapness of having one set of engines, mostly.

[Warzouz]

Why land them? single-stage-to-orbit doesn't mean single-stage-to-orbit-and-back-again, there's nothing about reusability implied there. It's just the cheapness of having one set of engines, mostly.

Linguistically right, but operationally wrong. SSTO are heavily linked to reusability (space plane or rocket). The whole point of a SSTO is to keep everything packed so you'll be able to get all back easily. Without reusability SSTO are totally pointless, they cost more and are less efficient.

[Van Disaster]

Linguistically right, but operationally wrong. SSTO are heavily linked to reusability (space plane or rocket). The whole point of a SSTO is to keep everything packed so you'll be able to get all back easily. Without reusability SSTO are totally pointless, they cost more and are less efficient.

Well we could argue this a lot, but for now lets say there are a few ways of building SSTO launchers. They don't have to stay in one piece *in* orbit ( just like any other launcher ), and you can use varying numbers of engines at various points in the flight profile, including all of them at certain points. We can't do this IRL because there's considerably more problems with fuel crossfeed & restarting engines than in KSP as well as us having crazily strong materials and a low requirement to orbit ( and lack of IRL need to lift stupidly high masses ), so we can build multi-stack vehicles without too much hassle. Really small payloads don't need multiple stages either.

Whatever though, I deliver 90% of stuff to orbit in spaceplanes and have been for years, technically SSTO or not. I don't tend to approach rocket design in the usual way.

[Alshain]

Linguistically right, but operationally wrong. SSTO are heavily linked to reusability (space plane or rocket). The whole point of a SSTO is to keep everything packed so you'll be able to get all back easily. Without reusability SSTO are totally pointless, they cost more and are less efficient.

No, operationally what you describe is an RLS or RLV. References to SSTO often imply an RLS and a craft can be both but they aren't mutually inclusive. Really, people should stop using the acronym SSTO on the forum if their intent is to convey its re-usability and use RLS (Reusable Launch System) or RLV (Reusable Launch Vehicle) instead. None of the three exist in the real world, the Space Shuttle is the closest to a successful RLS but it still wasn't 100% reusable and the Falcon 9, if it ever works, will be a true RLS. There are no SSTOs, even in prototype, the Skylon is the only active project I know of.

Edited October 19, 2015 by Alshain

[DancesWithSquirrels]

I don't like rocket SSTOs because they are hard to land on target. One can't really aim them well and aerodynamics are hard. One the way up you want the top to go forward, but on the way down you want the rear engine forward. With wings on the back this can be hard, especially with out air brakes. You also have to have serious skills/extra fuel, or heavy parachutes to land and heavy, draggy landing gear.

I don't have many mods, but Kerbal Engineer and Trajectories are key for me. And with Trajectories, I can always put a rocket SSTO back on peninsula around KSC. I rarely hit the runway, but almost always end up within a few kilometers. Here's a horribly non-aerodynamic 0.90 example:

Note that the Mammoth has a 20 m/s tolerance, and makes for excellent landing gear!

Album at:

Javascript is disabled. View full album

Hint - in a retrograde rocket SSTO, disable pitch/roll/yaw on any tailfins, and it becomes far easier to control with reaction wheels or RCS (I put sets of vernors on them for reentry, even if they don't need it for releasing their cargo).

[Terwin]

I don't have many mods, but Kerbal Engineer and Trajectories are key for me. And with Trajectories, I can always put a rocket SSTO back on peninsula around KSC. I rarely hit the runway, but almost always end up within a few kilometers. Here's a horribly non-aerodynamic 0.90 example:

I seem to be having problems with trajectories, with my last landing I was aiming half way to the 'Oops too short' mountain range, and I still landed in the water.

I am slowly moving my target area further and further back, but I either splash down past the KSC or land before the Oops Too Short mountains.

No air brakes as of yet and I can't usually open any chutes higher than about 6km, so not quite sure what I am doing wrong.

(I will often try to point surface - radial as long as I can to help slow down in the thinner air, then try to minimize my pro/retrograde time, usually with some sort of spin)

On the plus side, I still get > 90% recovery, so there is that...

[Alshain]

I seem to be having problems with trajectories, with my last landing I was aiming half way to the 'Oops too short' mountain range, and I still landed in the water.

I am slowly moving my target area further and further back, but I either splash down past the KSC or land before the Oops Too Short mountains.

No air brakes as of yet and I can't usually open any chutes higher than about 6km, so not quite sure what I am doing wrong.

(I will often try to point surface - radial as long as I can to help slow down in the thinner air, then try to minimize my pro/retrograde time, usually with some sort of spin)

On the plus side, I still get > 90% recovery, so there is that...

Heading a bit into off topic territory but make sure you open the Trajectories window and select your descent method. By default it assumes you are entering prograde. Click the prograde or retrograde button to make sure it calculates drag correctly in its equation. (the AoA sliders should read 180 degrees)

Edited October 19, 2015 by Alshain

[jackal40]

I don't have many mods, but Kerbal Engineer and Trajectories are key for me. And with Trajectories, I can always put a rocket SSTO back on peninsula around KSC. I rarely hit the runway, but almost always end up within a few kilometers. Here's a horribly non-aerodynamic 0.90 example:

Hint - in a retrograde rocket SSTO, disable pitch/roll/yaw on any tailfins, and it becomes far easier to control with reaction wheels or RCS (I put sets of vernors on them for reentry, even if they don't need it for releasing their cargo).

Thanks for the info on trajectories, hopefully that will help me improve my landing (crashing) skills.

[magnemoe]

Ah, well that just takes practice. In time you start to learn just about how much your orbit will change as you pass through the atmosphere. It takes a little while, but it is indeed easier to learn on a plane first IMO. For a plane all you have to do to move your trajectory is pull up or nose down where as with a rocket you usually get to bring in the trajectory but if you come in too short there is no going back. Alternatively you could use the Trajectories mod but after a while you just start to recognize where your initial trajectory from orbit should be.

I have problems hitting the area between the mountains and the shores.

Add that landing legs on the rocket adds drag at bottom who make them unstable on reentry.

Have an crew shuttle who I'm able to do this with but for most payloads I don't bother, tend to be more effective to use the engines on the payload as second stage for the last 3-500 m/s.

- - - Updated - - -

No, operationally what you describe is an RLS or RLV. References to SSTO often imply an RLS and a craft can be both but they aren't mutually inclusive. Really, people should stop using the acronym SSTO on the forum if their intent is to convey its re-usability and use RLS (Reusable Launch System) or RLV (Reusable Launch Vehicle) instead. None of the three exist in the real world, the Space Shuttle is the closest to a successful RLS but it still wasn't 100% reusable and the Falcon 9, if it ever works, will be a true RLS. There are no SSTOs, even in prototype, the Skylon is the only active project I know of.

True however an non reusable SSTO is pretty pointless anyway with a few exceptions like where you fill it op and send it somewhere else.

An reusable two stage system like falcon 9 reusable is not practical in KSP.

An RLS with a core and SRB to help during launch can be more cost efficient than an pure SSTO rocket.