The K Prize - 100% reusable spaceplane to orbit and back

[boolybooly]

Welcome back to the guest list sploden with a minimalist record for 0.23 and Advanced Pilot Precision Award. Thanks for your report and congratulations.

Redshift OTF, thanks for your mission report, congratulations on completing the K-Prize mission successfully with your lightweight craft Cormorant XI and earning an Advanced Pilot Precision Award for landing on the runway. Mechjeb is perfectly OK to use, I don't myself but that just personal taste. btw [imgUR] tags on this BB work best with just the code without #0 and no preceding url fyi. Welcome to the party guest list aka roll of honour.

Edited December 30, 2013 by boolybooly

[NikkyD]

I need to finish my program to simulate different possibilities regarding grav vs drag.

Im not so worried about the lower atmosphere. I go straight up like a rocket, im more worried about final speed n altitude, because thats what really saves me delta-V for creating a stable orbit. I admit, that here there is a benefit of having less weight (small caps) but ill have to see how much v-max it costs me.

The wings, tbh i just took the best normal wings and accepted it. I realized later that i dont really need them... i just want it to look like a plane, at least a bit. A can with 2 winglets just reminds me of comic book rockets

[British_Rover]

Why would u suggest that ? have u done the math ? its worse with the landing can because of its drag coeff

600 kg * 0.2 = 120

1000 kg * 0.08 = 80

edit:

didnt mean to be rude, but what u are suggesting is worse than what i have

Mass matters more then drag. It looked to me like you are trying to build the lightest manned vanilla SSTO possible and that means using the Mk1 can not the MK2 cockpit. Atmo drag falls of at an exponential rate with altitude so if you climb very quickly past 5,000 meters then you won't have much extra drag to deal with. The 400 extra KG of the MK2 cockpit matters a lot more at higher altitude then the drag. The higher drag will probably help with landing as well.

[NikkyD]

Mass matters more then drag. It looked to me like you are trying to build the lightest manned vanilla SSTO possible and that means using the Mk1 can not the MK2 cockpit. Atmo drag falls of at an exponential rate with altitude so if you climb very quickly past 5,000 meters then you won't have much extra drag to deal with. The 400 extra KG of the MK2 cockpit matters a lot more at higher altitude then the drag. The higher drag will probably help with landing as well.

The atmosphere may fall off at an exponential rate, but the drag increases at v^2*m*d [...].

I did calculate some drag at 30k with 2000 m/s and it was somewhere 32 kN with a coeff of 0.17. So if i have less weight, then i can use an even smaller ascent angle to battle less gravity, but mechjeb doesnt allow floats so im somewhere in the 1 digit degrees area here at the altitude.

Edit:

http://imgur.com/WchCzD1

simplified model, assumes perfect conditions etc. Not sure if all the calculations are in order, but there pretty close.

It only calculates up to 45 km, because of my phones resolution

horizontal is speed in 100 m/s steps

Edited December 28, 2013 by NikkyD

[Redshift OTF]

Using Mechjeb you can set the final orbit to say 100km, and change the turn shape to about 10%. When using the jet engine get the apoapsis as high as you can, around 75km if you can and coast above 50km before switching to rockets. The rocket engines will get your apoapsis to 100km, (if you're good enough you can get an apoapsis of 100km with jet engines alone).

The final burn you make at the 100km apoapsis is entirely dependant on how high the periapsis is. If you flew well enough to get the periapsis as high as 35km then the final burn will only be in the region of 50 deltaV but it takes a lot of horizontal flying and speed to achieve that, (with small planes you may even run out of jet fuel). Getting your periapsis to -50km is quicker and more achievable, (that's what I use), and you will still only need 150 deltaV to get that final orbit.

Another way to look at it, particularly if you are not using mechjeb, is to climb quickly to 10km and then set the glide angle of your plane so that the yellow pro-grade marker is at 10 degrees. You may need to angle the plane 20 degrees to get the prograde marker at 10 degrees but it depends on how much thrust your jet engine has.

Finally, light weight is not always better. I like the challenge of building light planes but sometimes they are so light the plane ends up with a very large thrust to weight ratio and you end up flying out of the atmosphere before you have had a chance to go more horizontal to raise your periapsis which means you will have to spend more deltaV using the rocket engines to achieve a circular orbit.

Hope that helps!

[sploden]

Those tiny crafts are unmanned! And as i wrote, i dont want to use glitches or part-placements what can only be achieved by using tricks.

The Chair is a manned craft. What is your definition of "trick?"

Edited December 28, 2013 by sploden

[NikkyD]

I cant build a craft with a manned chair with vanilla game. I can place a chair on the craft but i cant assign a kerbal to it. Using a 2nd craft to switch crew is imho against the rules, because you use a 2nd craft.

@ redshift

With jets alone i can reach AP of about 130 to 150, my best "almost" orbit was 70 AP / 45 PE. Its not stable but that would be jets alone. Im pretty sure you could achieve a stable 70/70 orbit with pure jets, LOTS of time and lots of fiddling.

I did try this:

http://imgur.com/9A7P3Wz

its ugly as hell, qualifies for a plane only with both eyes shut but... does the job (poorly).

I do need 100 kg more fuel with it. Ok, i implemented several things, but the start alone takes 5 units of fuel because of the higher drag at sealevel. So can vs cockpit may have saved 200 kg, but i definitely need more fuel. So the variant with plane cockpit is more fuelefficient.

Edited December 28, 2013 by NikkyD

[numerobis]

You can achieve a stable orbit with jets, but it requires tricks -- closing an intake and using it as a tank full of IntakeAir.

If you limit yourself to thrusting within the atmosphere (as one would normally do with a jet), it is impossible to raise periapsis out of the atmosphere.

[NikkyD]

Good to know.

Btw, Are wings actually useful at all ? Im thinking about building a bigger plane for my personal projects... is there a variant where forward thrust + wings results in better uplift than just rocket-style flying straight up ?

[numerobis]

Wings allow you to take off with TWR below unity. That means you don't need to haul as many jet engines along with you, which is a good way to save a lot of mass.

[Redshift OTF]

You could always attach a command pod to your plane with a decoupler, move the kerbal to the seat and then decouple the pod. But it depends on what personal rules you want to follow.

As numerobis said, I think it is impossible to raise your periapsis above 30-35km with jets alone. I think this is due to an in-built speed limit in the game with jets and without any more speed the periapsis won't go up. A 70-30 orbit is still a very good orbit and you'll probably only need a small amount of deltaV to make it circular. It sounds like you are almost there so don't give up.

Without wings you will need to angle your craft more to keep it level as the jet engines are party fighting gravity which means you aren't going to go as fast. This will mean you use more fuel to get anywhere so wings, if balanced properly are a big help.

[NikkyD]

a 70 / 45 orbit i already managed. Would have been 70 / 50 with more fuel. With crazy amounts of intakes something close to 70 / 70 is probably possible but to reach a stable orbit, in principle, you need to burn at the AP that has to be in space.

Storing air inside a closed intake sounds kinda shady. Why would the air have the necessary airspeed ??? Whats the point of airintakes storing air anyway ?

[numerobis]

As numerobis said, I think it is impossible to raise your periapsis above 30-35km with jets alone.

That's not what I said! You can get your Pe up to the edge of space with sufficient patience; I routinely bump it up to 50 km and sometimes 60 km. You just can't get it higher than the atmosphere: you can never get periapsis up higher than where you are when you're thrusting, and with jets, you can only really thrust within the atmosphere.

NikkyD: why do intakes store air is because it simplifies the implementation. IntakeAir just behaves like a fuel that is stored and moved to the engines that need it using the same code that's used for monopropellant and electricity. That means less work for the devs. Personally I think it would be better if engines had the intake built in, and there were no such thing as tacking on dozens of intakes.

[NikkyD]

Personally I think it would be better if engines had the intake built in, and there were no such thing as tacking on dozens of intakes.

Yes, i'd prefer that as well. Intake + housing + engine, thats it. Would be less to argue then.

[British_Rover]

I cant build a craft with a manned chair with vanilla game. I can place a chair on the craft but i cant assign a kerbal to it. Using a 2nd craft to switch crew is imho against the rules, because you use a 2nd craft.

@ redshift

With jets alone i can reach AP of about 130 to 150, my best "almost" orbit was 70 AP / 45 PE. Its not stable but that would be jets alone. Im pretty sure you could achieve a stable 70/70 orbit with pure jets, LOTS of time and lots of fiddling.

I did try this:

http://imgur.com/9A7P3Wz

its ugly as hell, qualifies for a plane only with both eyes shut but... does the job (poorly).

I do need 100 kg more fuel with it. Ok, i implemented several things, but the start alone takes 5 units of fuel because of the higher drag at sealevel. So can vs cockpit may have saved 200 kg, but i definitely need more fuel. So the variant with plane cockpit is more fuelefficient.

Eh I built a similar craft but with more fuel and I got it into the air with a lot less then five units of fuel. I used the rectangular wings though so I had more lift at the start. Those delta delux wings kind of suck.

[NikkyD]

It was just a first prototype. I kind of despise those cubic struct things, the rocket/plane should look like one object and not like bad-LEGO.

Also the LV1 with 1,5 thrust... gnaaa

[British_Rover]

It was just a first prototype. I kind of despise those cubic struct things, the rocket/plane should look like one object and not like bad-LEGO.

Also the LV1 with 1,5 thrust... gnaaa

Here is the one I built earlier. It is 3.96 tons on the pad and can be much lighter. Only need about half as much oxidizer.

http://forum.kerbalspaceprogram.com/threads/58968-SSTO-Without-Rockets-Challenge?p=809383#post809383

That craft had the minimist record for no rocket SSTO for a while.

What exactly are you trying to do make the lightest manned SSTO?

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Refining it now.

Edited December 29, 2013 by British_Rover

[numerobis]

I'm working on a reusable plane that gets to Laythe. I can design it in theory, and I can take it to orbit, but the margins are very tight -- I'll need a bit more calculating in order to actually hit my transfer window properly. In other words, the official flight hasn't occurred yet. Still, I think it's a pretty bird:

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It features all of the science equipment (but only one antenna), the lab, a hab module for each of the three crew, and manages to go up with just two turbojets. I gave it about 2050 m/s for the transfer to Jool, and 1100 m/s for the return, along with plenty of jet fuel.

I'll have to clean up the script I used to design this craft, and share it. I give it a payload, and the list of burns I need to perform; it tells me how much fuel I need, how many wings (small control surfaces, of course), and how many intakes. Makes it easy to vary the payload!

Edited December 29, 2013 by numerobis

[kepicness]

I was wondering if using the new saber engines in conjonction with a nuke would be more efficient than the jet/nuke combo (for interplanetary missions). One thing I know for sure is that getting really close to flameout isn't a danger since the engines just automatically switch from airbreathing to rocket. The plane would also be more versatile.

Any feedback on them would be apreciated.

[NikkyD]

Just some hints

Turbojets have a maximum speed of 2400 m/s, rapier has only 2200 m/s (both lose a lot of thrust above 2000 m/s but rapier faster n harder)

Turbojets 225 kN vs rapier 190 kN.

Weight 1.2t vs 1.75t

You will not get as fast and high with a rapier as u will get with a turbojet.

Space ISP of the rapier is 360, that is "ok" at best. There is the aerospike with almost 400 and the lvl 909 with 390.

For noobies the rapier has a lot of advantages. But once you want "more" you are not getting anywhere with it. In space it has bad ISP for longer trips (may be ok for a mun trip) and in the atmosphere its just not as powerful as a turbojet.

Keep in mind that in space, you have lots of time, so thrust doesnt really matter (to a point) but ISP does.

1 turbojet and 1 lv909 weigh 1.7t and give you the best performance in atmosphere and 390 ISP in space. (as a sidenote, you will have trouble building a stable ship with only one of each as you cant really center the thrust)

[kepicness]

Ok thanks, I'll just use them for ssto's designed to only get in orbit (since it's simpler). I'll stick to my 4 turbojet 2 nuke configuration

[boolybooly]

Good luck with Laythe numerobis, its a long way! It can be done but there are only an elite few K-Prize winners who have. Just Ctrl-F "Laythe" on the first page to see them.

British_Rover, am I right that you have completed a K_Prize mission with MINI_CANER? (Screenies not in order fyi.) Assuming so then congratulations and welcome back to the roll of honour though it looks like your Kerbal just missed the runway.

Edited December 31, 2013 by boolybooly

[barrenwaste]

You can easily balance a nuke and a turbojet if you use a couple of small struts inside a single long tank. First, connect the tank to the cockpit. Then zoom in until you are seeing inside the tank. Connect a small strut to the center back of the cockpit. Continue connecting small struts towards the rear of the tank without allowing them to snap together, manually place them all. Now connect your turbojet to the back of the tank. Next you want to connect your nuke to the small strut that allows the tail of the engine to stick out a bit through the turbojet. You may have to experiment a bit as if you get it wrong it will either be to tail heavy or explode on ignition. Finally, after balancing the nuke, you should use the rest of the struts to attach ramair intakes. You now have a ssto with two engines and the air intakes all included in the fuel tank and without cheats or mod.

[immelman]

Hi boolybooly,

After finally coming out of my turkey overdose may I present my Duna and back in 0.23 with the "Big Silly Bird 2"?

Really going to have to break this habit of getting back to the KSC with no fuel. Also landing conventionally on Duna is tough, even with a drogue and a lot of lift, it is hard to stop before crashing into another dune. If I ever do this again more landing wheels to stop the craft flipping on landing is a must, or just use parachutes for the actual landing. Apart from that a great little SSTO, very stable fully loaded or empty.

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Edited December 31, 2013 by immelman

[boolybooly]

Welcome back to the K-Prize immelman, congratulations on earning the coveted Expeditionary Astrokerbal Distinction for your Duna landing and highly regarded Advanced Pilot Precision Award for the safe return to KSC runway with Big Silly Bird 2, which has clearly had much thought put into its development with three pairs of delta wings for lift on Duna, a high air intake to turbojet ratio, twin Rockomax 48-7S and lightweight Mk1 Lander Can to improve the thrust to mass ratio. I can see why the undercarriage placement could make landings unstable on rough terrain since the rear pair are quite close together, a pair on the lower wings might be more stable but only if you can get them aligned and reinforced to prevent flexing, which with the current state of the SPH is trickier in practice than you might suppose, gl hf !