"Archangel" Interplanetary SSTO Spaceplane [Updated 18.01.2015]

[Chronosheep]

Hello, Kerbonauts!

After following this forum for some weeks, I've decided I'd post one of my own crafts here.

Presenting my most successful craft of any kind so far: The Archangel.

This is an interplanetary SSTO spaceplane built without any cheaty air intake stacking (where is the challenge in building a SSTO when you have infinite air?), and using only minor amounts of part clipping.

I have taken earlier iterations of the plane to Laythe and Duna with plenty of fuel to spare upon return. In the right hands it would probably be capable of an Eeloo return trip.

This is a pure pleasure/exploration craft, and doesn't have any cargo capacity (but feel free to build your own cargo version).

For Laythe trips, I recommend dumping some of the oxidizer before launching. I also recommend this if you intend to use the jet engines upon returning to Kerbin.

The plane is meant to be flown with SAS on at all times. Large amounts of control surfaces keep it fairly stable even when the center of mass and center of lift are far separated (due to fuel consumption).

Update 18.01.2015

New version built using the intake placement order trick. This greatly reduces problems with asymmetric thrust and asymmetric flameouts.

The plane now needs far fewer air intakes than before, so I have removed a some of them.

It still has more air intakes than necessary, but I left them for aesthetic reasons.

The ascent instructions have been updated for this version.

Features

- Roughly 7,000 m/s of delta-v (rocket powered) to play with after reaching LKO.

- Belly thrusters for take-off and landing assist. VTOL capable on low-gravity bodies.

- Shielded Clamp-O-Tron and docking light.

- Probe core allowing for unmanned flights and SAS assist when flown by particularly incompetent kerbals.

- Full (somewhat overdimensioned) RCS suite.

- All the landing lights you'll ever need.

- Part count: 119

Action Groups

1: Switch between Jets to Atomic engine, toggle basic air intakes.

2: Toggle main air intakes.

3: Toggle belly thrusters.

4: Toggle Atomic engine.

5: Toggle Clamp-O-Tron shield and docking light.

6: Extend/Retract ladders.

Ascent Instructions

- Keep the nose pointed at 60 degrees till you reach 20,000m.

Open main air intakes (action group 2) at 15,000m.

- Point nose at 30 degrees till you reach 26,000m.

- Point nose at 20 degrees until your surface speed reaches 2,050 m/s.

Note: At around 30,000m, you will get some asymmetric thrust. Fight it, and do not throttle down. It will go away at around 32,000m.

- Once you reach a surface speed of 2,050 m/s, lock the heading to prograde, and throttle down to get a vertical speed of 40 m/s.

- Keep adjusting the throttle to maintain a vertical speed of 40 m/s until your liquid fuel level drops down to 1429.

If you reach a point where the vertical speed increases even without engine power, leave the engines running at the lowest throttle marker until the liquid fuel level reaches 1429.

- Once the liquid fuel level reaches 1429, kill the engines. Switch to nuclear engine (action group 1), close air intakes (action group 2).

- Your orbit should now typically be 36-42,000m periapsis, 85-105,000m apoapsis.

- Circularize at apoapsis. If everything went according to plan, it should still be above 70,000m when you reach it.

Download

Fist version was more prone to asymmetric flameouts, and needed more air intakes to compensate.

Ascent Instructions

- Keep the nose pointed at 60 degrees till you reach 20,000m.

Open main air intakes (action group 2) when engines start running low on air (typically around 17,000m).

- Point nose at 30 degrees till you reach 26,000m.

- Flatten trajectory sufficiently to reach 1,700 m/s surface speed before reaching 30,000m.

Throttle down when one of the engines begins to struggle (this also applies to subsequent steps).

- Climb slowly, aiming for a surface speed above 2,050 m/s at 34,000m.

- Keep 30-40 m/s vertical speed until you reach 40,000m.

- When your periapsis is above 30,000m, lock the heading to prograde. Keep throttling down when necessary until the engines are completely shut down.

- Your orbit should now typically be 40-45,000m periapsis, 100-130,000m apoapsis.

Switch to nuclear engine (action group 1), close air intakes (action group 2).

- Circularize at apoapsis.

Download

Edited January 18, 2015 by Chronosheep

[Hobbes Novakoff]

Looks nice! How many parts? (I have a potato for a computer)

[Majorjim!]

Looks good Chronosheep, nice and sleek.

Using 10.5 intakes per jet is air-hogging though. But don't let people tell you it's wrong!

[Captain Sierra]

Looks good Chronosheep, nice and sleek.

Using 10.5 intakes per jet is air-hogging though. But don't let people tell you it's wrong!

True, but when most people think of air hogging, the immediate assumption is the insane cubic strut intake clipping stacks people make, the kind that dominated the SSTO showcase thread before we got the improved shock cone intakes.

[Chronosheep]

Looks nice! How many parts? (I have a potato for a computer)

Thanks. The part count is 128. A bit high for a craft this small, but it does have quite many air intakes. Added it to the original post.

Looks good Chronosheep, nice and sleek.

Using 10.5 intakes per jet is air-hogging though. But don't let people tell you it's wrong!

True, but when most people think of air hogging, the immediate assumption is the insane cubic strut intake clipping stacks people make, the kind that dominated the SSTO showcase thread before we got the improved shock cone intakes.

My definition of air hogging (and what I had the impression was what most people think of as air hogging) is stacking or clipping air intakes in such a way that many of the intakes could not conceivably receive any air.

I built the plane in such a way that every intake would realistically be functional, and receive a large fraction of its maximal airflow.

Anyway, I removed the [Non-Airhogging] tag from the title to make it less misleading to people who don't agree with my definition.

[Yukon0009]

128 is a good part count for IP SSTOs. Good work Chronosheep!

[Rune]

Looks good Chronosheep, nice and sleek.

Using 10.5 intakes per jet is air-hogging though. But don't let people tell you it's wrong!

I actually count 13 for each, which would put this plane firmly in the diminishing returns part of the airhogging spectrum. He probably means part clipping when he says "airhog". Anyhow, totally excessive, and just as unrealistic as stacking a line of Ram intakes in cubic struts: we can roleplay they are the precoolers, because in RL air is compressible, and planes actually need less intake area the higher (and faster) they fly. That's what shock cones do in RL, BTW, they diminish the intake area at high speed (among other supersonic-related things).

Of course, nobody take this comment as criticism of anything except bringing up how other designs are "cheaty": we should banish that word, since it means so little in this game. This looks good, and it probably has more intakes than it needs if they were of other kind... and that's my real comment (I myself use 4-1 intake ratios with the ram intakes or the shock cones, works like a charm).

Rune. In RL the speed limitation has more to do with thermal limits and compression effects, than engines running out of air.

[Chronosheep]

I actually count 13 for each, which would put this plane firmly in the diminishing returns part of the airhogging spectrum. He probably means part clipping when he says "airhog". Anyhow, totally excessive, and just as unrealistic as stacking a line of Ram intakes in cubic struts: we can roleplay they are the precoolers, because in RL air is compressible, and planes actually need less intake area the higher (and faster) they fly. That's what shock cones do in RL, BTW, they diminish the intake area at high speed (among other supersonic-related things).

Of course, nobody take this comment as criticism of anything except bringing up how other designs are "cheaty": we should banish that word, since it means so little in this game. This looks good, and it probably has more intakes than it needs if they were of other kind... and that's my real comment (I myself use 4-1 intake ratios with the ram intakes or the shock cones, works like a charm).

Rune. In RL the speed limitation has more to do with thermal limits and compression effects, than engines running out of air.

The definitions of air hogging and what is cheating is clearly a subjective matter in this game.

I personally draw the line at clipping engines/fuel tanks/air intakes into each other in a way that could not conceivably work (unless you roleplay about what the parts actually are).

I would, however, much rather admit that this design is cheaty than claim that other designs are not.

Realistically, I'd say any amount of intakes that can get you above 30,000m is cheaty to some degree.

The reason why I consider intake stacking more cheaty is that you no longer have to take air intakes into account in your design at all - one might as well just multiply the intake area of the intakes by a factor 10.

Regarding the number of intakes, I found that this amount is required if you want to do all but the circularization on jet power.

It seems to me that the necessary number of air intakes does not only depend on the number of engines, but also on the weight of the craft.

Edited January 17, 2015 by Chronosheep

[Rune]

Regarding the number of intakes, I found that this amount is required if you want to do all but the circularization on jet power.

It seems to me that the necessary number of air intakes does not only depend on the number of engines, but also on the weight of the craft.

No, actually the intake/engine ratio sets the maximum speed and altitude of a design. You just happen to be using a very inefficient kind of intakes. TWR (thrust to weight ratio) does have something to do with it also, of course (if you don't have enough you won't get to altitude, for example, and an extremely high TWR can give you slightly higher cutoff speeds), but really, 90% of it is the intake-engine ratio. Because most KSP designs have TWR between 0.5 and 1.5, mainly. For more info, I've just been pointed to here, you seem to need it more than I do:

Javascript is disabled. View full album

Rune. Have you worked out the weight in intakes and how it hurts your in-space delta-v? Compare that with the weight of the empty rocket fuel tanks required to do the climb to orbit 200m/s earlier.

[Chronosheep]

No, actually the intake/engine ratio sets the maximum speed and altitude of a design. You just happen to be using a very inefficient kind of intakes. TWR (thrust to weight ratio) does have something to do with it also, of course (if you don't have enough you won't get to altitude, for example, and an extremely high TWR can give you slightly higher cutoff speeds), but really, 90% of it is the intake-engine ratio. Because most KSP designs have TWR between 0.5 and 1.5, mainly. For more info, I've just been pointed to here, you seem to need it more than I do:

http://imgur.com/a/3jrUJ

Rune. Have you worked out the weight in intakes and how it hurts your in-space delta-v? Compare that with the weight of the empty rocket fuel tanks required to do the climb to orbit 200m/s earlier.

Thanks, that link was actually quite enlightening.

I was not aware that the airflow to the different engines was affected by the order in which the intakes are placed.

One of the main reasons why I need so many intakes is that I have to throttle down to avoid asymmetric flameouts.

I might try reducing the number of intakes using this trick (though I'm quite happy with the looks of the current design).

As for the weight in intakes, it steals about 125 m/s compated to 8 RAM intakes, assuming that the same amount of fuel is used.

[Teefy]

im pretty gutted. i cant break the 40km height. it just wont go any higher.

im at 2200 m/s and 10 degrees ascending. eventually it just starts descending again. flame-outs are not the problem.

its me. i dont know how to fly an ssto and its frustrating me to no end.

could someone explain how it works in idiot language because apparently i missed something vital and above description might be enough for everybody but me.

much appreciated to anyone who obliges.

[Captain Sierra]

im pretty gutted. i cant break the 40km height. it just wont go any higher.

im at 2200 m/s and 10 degrees ascending. eventually it just starts descending again. flame-outs are not the problem.

its me. i dont know how to fly an ssto and its frustrating me to no end.

could someone explain how it works in idiot language because apparently i missed something vital and above description might be enough for everybody but me.

much appreciated to anyone who obliges.

This happens to me on some of my designs. What is happening is 1) you are losing pitch authority at higher altitudes. This can be helped by adding forward canards (it also helps if they have yaw/roll tweaked off). RCS and reaction wheels (as control surfaces lose most of their effectiveness up that high) are also good alternatives. You might also be experiencing 2) a loss in thrust vs terminal velocity. As you shut down engines, the resistance air applies begins to be stronger than the thrust you are still outputting and you start slowing down. At high speed and altitude, this results in a loss of lift slowing increasing your bird's tendency to nose-dive, which is creating the struggle to hold a positive AoA you're experiencing. Make sense?

[Teefy]

This happens to me on some of my designs. What is happening is 1) you are losing pitch authority at higher altitudes. This can be helped by adding forward canards (it also helps if they have yaw/roll tweaked off). RCS and reaction wheels (as control surfaces lose most of their effectiveness up that high) are also good alternatives. You might also be experiencing 2) a loss in thrust vs terminal velocity. As you shut down engines, the resistance air applies begins to be stronger than the thrust you are still outputting and you start slowing down. At high speed and altitude, this results in a loss of lift slowing increasing your bird's tendency to nose-dive, which is creating the struggle to hold a positive AoA you're experiencing. Make sense?

yes, but apparently this design can in fact fly above 40km. so its the pilot, e.g. me

you have to lower thrust or else the egines flames out. But then you gain too much air resistance vs thrust. how do you solve this paradox?

[Captain Sierra]

yes, but apparently this design can in fact fly above 40km. so its the pilot, e.g. me

you have to lower thrust or else the egines flames out. But then you gain too much air resistance vs thrust. how do you solve this paradox?

More intakes, or punch rockets sooner. Rockets don't need air and won't flame out on you, and adding more intakes increases the level of thrust you can output at a given altitude and speed. Generally my SSTOs don't make it to 2400m/s @ 40km, so I'm used to a much earlier rocket punch.

[Chronosheep]

im pretty gutted. i cant break the 40km height. it just wont go any higher.

im at 2200 m/s and 10 degrees ascending. eventually it just starts descending again. flame-outs are not the problem.

its me. i dont know how to fly an ssto and its frustrating me to no end.

could someone explain how it works in idiot language because apparently i missed something vital and above description might be enough for everybody but me.

much appreciated to anyone who obliges.

10 degrees sounds a little low to me.

You have to adjust the pitch to keep the vertical speed positive at all times (the vertical speed is the dial next to the altitude counter. The 2 dots between 10 and 100 indicate 20 m/s and 50 m/s).

It could also be that you ascended too quickly from 30,000m. You have to make sure to reach a surface (not orbital) speed of at least 2,050 m/s before reaching 34,000m with that version of the plane.

Anyway, I have now uploaded a new version of the plane, which is much less prone to asymmetric thrust and asymmetric flameouts.

It has a rather different ascent profile than the first version (see new ascent instructions), and is is (in my opinion) much easier to get to orbit.

It now has approx. 7,000 m/s delta-v available after reaching LKO.

Edited January 18, 2015 by Chronosheep

[Teefy]

made it on my first attempt with the new model!!

well done and congrats for making something that can orbit in the hands of a newbie like me! and with a boat-load of fuel left.

im honestly speachless.