Design a SSTO that uses propellers or rotors instead of jets during atmospheric ascent

[It'snorocketscience]

Design a SSTO that uses propellers or rotors instead of jets during atmospheric ascent

I like useful challenges, and I hope this one may be considered as such. The goal, besides challenging oneself, is to create a new type of SSTO that can explore atmospheres with props or rotors, thereby saving fuel and enabling the exploration of oxygen-free bodies, like Duna. This would enable a craft to biome-hop for science or transport resources much more effectively than slow rovers and fuel-guzzling rocket planes/landers can in said atmospheres. While these kinds of biome-hopping and transport crafts do exist, they don't seem to exist in reusable SSTO form, it seems.

Props and rotors, unlike jets and intakes, also have the benefit of not being dead weight on Duna. So while props may offer worse performance on Kerbin, they'll pay you back during Duna ascent. Or at least, that's the theory.

Requirements:

• No airbreathing engines. The craft must be capable of flight using rotor/prop power alone in the destination planet’s atmosphere, but you can obviously use rockets to get to and fly in space.

• Self-sufficient SSTOs only. So, ISRU mining is allowed, but no assistance from external ships (asteroids are OK). You may not jettison any parts other than payloads that don’t help the main vessel in any way.

• Normal difficulty or harder, but for convenience, you may ignore commnet—pretend a network is already in place.

• The SSTO must be useful in career mode. There’s no point in a spacecraft if you can’t bring any Science, Kerbals, or payloads along. Carry at least one kerbal (chairs allowed), OR if you wish not to carry kerbals, carry at least 0.2 tons of parts from the “science” category, OR deliver a payload weighing at least 0.5 tons.

  • You may drop payloads once you are landed at your destination. If your destination is Jool, you may drop it low Jool orbit or into the depths of Jool.

  • Payloads must be attached/detached using docking ports, not decouplers.

• No mods or part tweaks other than official DLCs, FAR, aesthetic mods, and piloting or planning assists.

 

Challenge Tiers:

Tier 0: "Proof of Concept" (Normal): Build a prop/rotor SSTO that makes it to Kerbin orbit. Must be capable of takeoff/landing in Kerbin’s atmosphere on rotor/prop power alone.
Example: Reddit user u/chargan’s Orbital Chopper

Tier 1: "Practical Problems, Sober Solutions" (Hard): Fly your prop/rotor SSTO to Duna's surface and back. Must be capable of takeoff/landing in Duna’s atmosphere on rotor/prop power alone.

The challenge is simple in concept, but hard in practice. But, if you manage to accomplish Duna, there are other destinations to try, where almost no SSTO crafts have ever gone before...

Spoiler

Tier 2: "Insane Issues, Impractical Improvements" (Harder than hard):  Fly your prop/rotor SSTO to Eve's surface and back. DISCLAIMER: While YouTube user Brad Whistance has flown a prop SSTO to Eve and back, it was huge and laggy. To be fair, he didn’t use Breaking Ground props nor ISRUs, but consider yourself forewarned. The SSTO must be capable of takeoff/landing in Eve’s atmosphere on rotor/prop power alone.

Tier 3: "Impress Jebediah" (Hardest-est): Fly your prop/rotor SSTO to the “flying low” boundary on Jool (120,000m) and live to tell the tale. WARNING: Impressing Jeb and/or escaping Jool with a single stage might be impossible, even with props and rotors to get out of the atmosphere, so beware. ISRUs are allowed, but even if you can escape the atmosphere, the nearest moon will be a long burn from the depths of Jool’s gravity well. You could tow an asteroid to low Jool orbit for refueling, but first, you have to get it there…

 

Bonus Badges:
Within each tier, entries can receive the following awards. Ordered roughly by importance in career mode.
(ISRU comes last as you are strongly encouraged to use it.)

V: Heaviest payload delivered

IV: Greatest tourist capacity
(No chairs - tourists can’t go on EVA)

III: Cheapest craft

II: Lightest craft
(Wet mass, excluding payload mass)

I: No ISRU
(Multiple entries can earn this.)

 

Leaderboard:

Spoiler

Entries are ranked by tier, then by number of badges. If there is a tie in the number of badges, the badge types will determine ranking (An entry with the “Heaviest payload” award outranks an entry with the “No ISRU” award, BUT if the "No ISRU" entry happens to have the "lightest craft" award, it will have 2 badges and therefore outrank the "Heaviest payload" entry).

Tier 3: Prop/rotor SSTO to Jool's lower atmosphere and back:
(No entries yet.)

Tier 2: Prop/rotor SSTO to Eve and back:
(No entries yet.)

Tier 1: Prop/rotor SSTO to Duna and back:
Itsnorocketscience's "Duna Phantom"
No payload/tourist capacity. Cost: 40k. 15.6t wet mass. ISRU.
III: Cheapest craft + II: Lightest craft

xendelaar's "Honey bee"
No payload/tourist capacity. Cost: 176k. 127t wet mass. ISRU.

Tier 0: Prop/rotor SSTO to LKO and back:
(No entries yet.)

Good luck! If you have any trouble completing the challenge, browse this thread or just ask for help—there are many posts here with tips and links and instructions.

Edited June 23, 2020 by It'snorocketscience
Fixed spoiler, formatting and words. Increased clarity.

[Pds314]

Jool should be possible on NERVs if you can get above most of the atmosphere. Granted, possible does not mean easy, and I would assume there's probably gonna be tons of clipping involved.

[sevenperforce]

I've been wanting to try my hand at a true SSTA now that we can have easy props on Eve.

[It'snorocketscience]

20 hours ago, Pds314 said:

Jool should be possible on NERVs if you can get above most of the atmosphere. Granted, possible does not mean easy, and I would assume there's probably gonna be tons of clipping involved.

Jool actually has less gravity on the "surface" than Kerbin does, and the atmosphere thickness at 120k is about the same as 7.5k on Kerbin, but Jool has a mad orbital velocity of 6745 m/s, if I recall correctly. That's going to be a long burn, especially with NERVs, and the drag from the upper atmosphere and gravity losses are really going to add up.

So even though I really don't like part clipping, I decided to keep the rules as minimal as possible since the Eve/Jool levels of the challenge are already hard enough as it is. I think the transfer from low Jool orbit to Laythe is around another 3000 m/s of dV, too (I think?).

[Vanamonde]

The game's been out for 8 years so it's hard to come up with new challenges, but I don't believe this one has been done before. Interesting idea. 

[mystifeid]

On 4/17/2020 at 1:03 PM, Pds314 said:

Jool should be possible on NERVs if you can get above most of the atmosphere. Granted, possible does not mean easy, and I would assume there's probably gonna be tons of clipping involved.

Jool SSTA - out and return -  has been done. Look further down the page for a thread called "How close can you get to Jool."

Watching that video may spoil this challenge for you.

[Space Nerd]

How about adding Laythe to this challenge?

[It'snorocketscience]

7 hours ago, Space Nerd said:

How about adding Laythe to this challenge?

I didn't add Laythe to this challenge because I didn't think it would be practical... why be forced to use props or rotors if jets work on Laythe? With Duna/Eve/Jool there's no other option but to use props and rotors in the atmosphere, and jets would be dead weight.

[sturmhauke]

In general, an SSTO that can make Kerbin orbit can also make Laythe orbit.

[xendelaar]

On 4/18/2020 at 1:27 AM, It'snorocketscience said:

Jool actually has less gravity on the "surface" than Kerbin does, and the atmosphere thickness at 120k is about the same as 7.5k on Kerbin, but Jool has a mad orbital velocity of 6745 m/s, if I recall correctly. That's going to be a long burn, especially with NERVs, and the drag from the upper atmosphere and gravity losses are really going to add up.

Sorry for being off topic, but I got into an Joolian orbit with approximately ~5500-6000 m/s delta v after visiting my holiday home near the surface of Jool.   I noticed that the drag in the upper Joolian atmosphere is much lower compared to the drag on Eve's upper atmosphere.  because of Jool's low gravitational force, I think it's easier to reach orbit from Jool than from Eve. But you do need more delta v to get there... hmm.. I'll stop rambling now...

On topic: This challenge looks awesome and I will give it a go when I've got the time. 

[Klapaucius]

On 4/20/2020 at 8:36 PM, xendelaar said:

Sorry for being off topic, but I got into an Joolian orbit with approximately ~5500-6000 m/s delta v after visiting my holiday home near the surface of Jool.   I noticed that the drag in the upper Joolian atmosphere is much lower compared to the drag on Eve's upper atmosphere.  because of Jool's low gravitational force, I think it's easier to reach orbit from Jool than from Eve. But you do need more delta v to get there... hmm.. I'll stop rambling now...

On topic: This challenge looks awesome and I will give it a go when I've got the time. 

That video is amazing. Love the vacation house!

[Klapaucius]

@Brikoleur?  Your Eve craft?

[jinnantonix]

The functionality of exploring a non-oxygen atmosphere with electric props could be handled by an ISRU LOX rocket, plus a lightweight prop powered drone that can dock with the main craft.  Building a single prop powered craft that can lift the whole ISRU/rocket is certainly and interesting challenge but somewhat impractical.  Or am I misunderstanding something?

[xendelaar]

3 hours ago, jinnantonix said:

The functionality of exploring a non-oxygen atmosphere with electric props could be handled by an ISRU LOX rocket, plus a lightweight prop powered drone that can dock with the main craft.  Building a single prop powered craft that can lift the whole ISRU/rocket is certainly and interesting challenge but somewhat impractical.  Or am I misunderstanding something?

yeah, i've been toying around with helicopter SSTO vessels for several evenings now and man what do those things tend to get bulky fast! My first design was meant for a trip from Kerbin to Duna, but getting a heavy craft off the ground on Duna is nearly impossible with the thin atmosphere. Jool is probably a bit more easy, but it needs quite a lot of delta v and there's hardly anything useful reasons for going there.

9 hours ago, Klapaucius said:

That video is amazing. Love the vacation house!

Thanks mister! it took me quite some time to design a ship that could transport everything over there. It was a great challenge!

[Rejected Spawn]

6 hours ago, jinnantonix said:

The functionality of exploring a non-oxygen atmosphere with electric props could be handled by an ISRU LOX rocket, plus a lightweight prop powered drone that can dock with the main craft.  Building a single prop powered craft that can lift the whole ISRU/rocket is certainly and interesting challenge but somewhat impractical.  Or am I misunderstanding something?

Wouldn't that completely miss the point because it reverts the entire challenge to "build an SSTO that can bring a payload to Duna and back" just that the payload is slightly different from what's been done a thousand times?

 

Anyway wow this challenge is... is it even possible? Love the idea but after a number of attempts I've lost almost all hope of coming up with anything that even gets close to LKO while still being able to get around on EC in the atmosphere... That chopper thing obviously works but my sense of aesthetics would never allow me to build something like that, if I can't fly in style I'd rather walk so to speak.  

[It'snorocketscience]

13 hours ago, jinnantonix said:

The functionality of exploring a non-oxygen atmosphere with electric props could be handled by an ISRU LOX rocket, plus a lightweight prop powered drone that can dock with the main craft.  Building a single prop powered craft that can lift the whole ISRU/rocket is certainly and interesting challenge but somewhat impractical.  Or am I misunderstanding something?

Assuming "LFO rocket" means using stages, then that design is not an SSTO. SSTOs look cool, but practically speaking, they're cheaper to use multiple times because you can recover most of the craft's value upon returning at Kerbin.

If you were asking "why build an all-in-one prop SSTO when you can build a normal SSTO with a detachable drone", I imagined that a prop SSTO could return to orbit more efficiently than a normal SSTO (jets are deadweight whereas props/rotors are not). Okay, maybe a prop SSTO would be less efficient on Duna because the props would be useless in a thin atmosphere, but on Eve or Jool, the props would be the only way to escape the thick atmosphere.

Another practical goal of this challenge was to encourage innovation and find the limits of props and rotors. Just how fast and high can a prop craft travel? I've seen stock props by Brad Whistance travel up to 1000 m/s, although those crafts did employ a few (legitimate) tricks...

6 hours ago, Rejected Spawn said:

Anyway wow this challenge is... is it even possible? Love the idea but after a number of attempts I've lost almost all hope of coming up with anything that even gets close to LKO while still being able to get around on EC in the atmosphere...

Fuel cells tucked inside a payload bay are pretty handy for saving battery weight while maintaining sleek, low-drag looks and decent EC production... have you tried that? RTGs and extra batteries get heavy fast, and solar panels add extra drag at high speeds, not to mention that the deployable ones break at high speed obviously

9 hours ago, xendelaar said:

I've been toying around with helicopter SSTO vessels for several evenings now and man what do those things tend to get bulky fast! My first design was meant for a trip from Kerbin to Duna, but getting a heavy craft off the ground on Duna is nearly impossible with the thin atmosphere. Jool is probably a bit more easy, but it needs quite a lot of delta v and there's hardly anything useful reasons for going there.

Are you using a helicopter or plane design? I've found that helicopters are just too inefficient and heavy - they need rotors with a TWR above 1 while a plane can take off with something well below that.

Helicopters also produce more drag and struggle during rocket-powered ascent—pointing the nose up towards space (to use rockets) will cause the rotor blades to pull your craft backward (and upward) unless you shut them off, at which point they become inefficient wings. Meanwhile, a prop plane during atmospheric ascent into orbit can run its props and rockets at the same time, increasing ascent TWR without much issue.

Edited April 22, 2020 by It'snorocketscience
Fixed typos and increased clarity

[jinnantonix]

7 hours ago, It'snorocketscience said:

Assuming "LFO rocket" means using stages, then that design is not an SSTO. SSTOs look cool, but practically speaking, they're cheaper to use multiple times because you can recover most of the craft's value upon returning at Kerbin.

I wasn't assuming a staged rocket.  I was drawing attention to the fact that an ISRU +  LOX fueled single stage to orbit vehicle can be a very large craft.  Using props to get to altitude and speed could reduce the size, however only marginally - an altitude of 20km and a speed of 1000m/s on Kerbin is perhaps possible, but still well shy of the capability of jets.  Considering this, I was assuming that the design was more of the VTOL or helicopter type where the props were only for moving about on the surface at relatively low speeds.

I think you are perhaps overestimating the capability of props as a means for reaching orbit.  Or perhaps I am being too negative?   

Edited April 22, 2020 by jinnantonix

[xendelaar]

8 hours ago, jinnantonix said:

I wasn't assuming a staged rocket.  I was drawing attention to the fact that an ISRU +  LOX fueled single stage to orbit vehicle can be a very large craft.  Using props to get to altitude and speed could reduce the size, however only marginally - an altitude of 20km and a speed of 1000m/s on Kerbin is perhaps possible, but still well shy of the capability of jets.  Considering this, I was assuming that the design was more of the VTOL or helicopter type where the props were only for moving about on the surface at relatively low speeds.

I think you are perhaps overestimating the capability of props as a means for reaching orbit.  Or perhaps I am being too negative?   

I don't think you'll save that much delta v. did you actually get to an altitude of 20km in a prop vessel? I'm not getting anything higher than 14 km. 2 days ago I launched a ship from a floating platform at 10km and found that i almost had to use 3100 m/s to get into orbit. I do have to confess that the ascend profile wasn't very optimal though.

[It'snorocketscience]

9 hours ago, xendelaar said:

I don't think you'll save that much delta v. did you actually get to an altitude of 20km in a prop vessel? I'm not getting anything higher than 14 km. 2 days ago I launched a ship from a floating platform at 10km and found that i almost had to use 3100 m/s to get into orbit. I do have to confess that the ascend profile wasn't very optimal though.

You are right in that props have limited performance, but I've been toying around with low-tech jets in SSTOs. If the prop plane can get above 10k, nuclear and vacuum rockets will work at nearly full efficiency. If your craft is drag-optimized, one nuclear engine (or 60KN of thrust) for every 14 tons of weight will be just enough to push it into orbit, at least when starting from 14k at 750 m/s. (That speed wasn't obtained on my challenge craft, I discovered that my prop craft was flawed...)

I realized that my Duna verification attempt was flawed (I used stock parts but some mod in that savegame altered the stock parts ), so I'm going to try again in a fresh install to make sure Duna is possible. But I'm fairly sure it is possible—I've built many low-tech SSTOs before that use the "wheesly" jets, and those are only slightly better than props. While we can't use wheesly jets, it should be safe to say that props will get you above the worst of Kerbin's atmosphere (10km). The hard part seems to be being able to take off on Duna on prop/rotor power alone.

Edited April 23, 2020 by It'snorocketscience
Increased clarity

[sevenperforce]

I have not built any prop planes with the new parts -- do they need the KAL-3000? How do you start them?

[xendelaar]

4 hours ago, It'snorocketscience said:

You are right in that props have limited performance, but I've been toying around with low-tech jets in SSTOs. If the prop plane can get above 10k, nuclear and vacuum rockets will work at nearly full efficiency. If your craft is drag-optimized, one nuclear engine (or 60KN of thrust) for every 14 tons of weight will be just enough to push it into orbit, at least when starting from 14k at 750 m/s. (That speed wasn't obtained on my challenge craft, I discovered that my prop craft was flawed...)

I realized that my Duna verification attempt was flawed (I used stock parts but some mod in that savegame altered the stock parts ), so I'm going to try again in a fresh install to make sure Duna is possible. But I'm fairly sure it is possible—I've built many low-tech SSTOs before that use the "wheesly" jets, and those are only slightly better than props. While we can't use wheesly jets, it should be safe to say that props will get you above the worst of Kerbin's atmosphere (10km). The hard part seems to be being able to take off on Duna on prop/rotor power alone.

Very interesting idea. I haven't succeeded in making a prop plane fly on duna though. There is so little atmospheric pressure to play with that wings just make things heavy without providing enough lift/speed. I did make a helicopter once but that thing was stripped to its core haha. Adding fuel to that would make the craft too heavy to lift.. I think...

I'm hoping other people are having better luck at finishing this challenge. I'm constantly reminded why I dont like to build ssto's: they rapidly get so damn bulky and difficult to handle.  XD

I wont stop trying though

 

5 minutes ago, sevenperforce said:

I have not built any prop planes with the new parts -- do they need the KAL-3000? How do you start them?

My first planes didn't use the kal1000 units either. The rotors had fixed angles and the motor was either on or off... this works perfectly for planes. Helicopters are a whole different subject though

[mystifeid]

2 hours ago, sevenperforce said:

I have not built any prop planes with the new parts -- do they need the KAL-3000? How do you start them?

You don't need the KAL-1000. Lots of possibilities. Here is one:

1. Make sure you have assigned keybindings for the custom axis groups in the settings. Not sure about now, but they used to be unassigned by default. Look under Input -> Vessel -> Axis Actions. For each custom axis group you assign two keys - one to increment and another to decrement. Custom axis groups can come in handy for other things besides prop aircraft. I tend to use numberpad keys:
Custom axis group 1 - "/" and "*"
Custom axis group 2 - "8" and "9"
Custom axis group 3 - "5" and "6"
Custom axis group 4 - "2" and "3"

Custom axis keys also respond to the use of fine control (caps-lock) whereas, for example, the throttle keys do not - or at least they didn't in the past.

2. It used to be possible to disengage the engines in the SPH/VAB but at the moment it appears they are engaged when launched no matter what but you may still want to assign an action group to engage/disengage. Looking at a prop aircraft, these are the assignments -

Custom action group 1 - Toggle motor engaged
Custom action group 2 - Toggle motor power (full/zero torque)
Custom action group 3 - Toggle deploy (of prop blades)
Custom action group 5 - Toggle motor direction

Custom axis group 1 - Deploy angle (of prop blades)
Custom axis group 2 - RPM limit
Custom axis group 3 - Torque limit

Takeoff procedure is simply (engage SAS), toggle motor power (key 2), toggle deploy (key 3).

By default the deploy angle of prop blades now seems to be 60° but you may often want to pre-set a higher angle in the SPH/VAB - especially for a heavy VTOL craft.

As the craft gains speed through the air you will need to decrease the deploy angle of the blades to continue increasing speed. It will often be necessary to do this to get a rolling aircraft to lift off. You will need to continue matching deploy angle with speed to prevent the aircraft from falling out of the sky and your speed is affected by things other than the engines/props, such as AoA and air density. The corollary is that increasing the deploy angle works nicely to slow an aircraft on landing approach.

There are a lot of possibilities when it comes to choosing prop types, numbers of blades and engine type/size. You will need to perform some experimentation for each craft you build to find the optimum design.

Note that for each engine type, it is possible to change the motor size in the SPH/VAB. This affects the cost, power, mass and ec/fuel consumption.

A forward facing engine with clockwise rotation (default) requires blades with inverted deploy direction (not default) to move forward.

Using pairs of counter rotating engines tends to lead to easier control and increased power/speed.

The biggest irritation I find is the necessity of keeping at least one PAW open - to see the blade deploy angle and sometimes another PAW to see engine rpm/torque.

There is probably a lot more that can be said and others will doubtless have their own take on the use of the robotic engines.

Edited April 24, 2020 by mystifeid

[sevenperforce]

Thanks @mystifeid. I like the fine control provided by Squad -- I am doing some amazing things with abort modes right now on my increasingly granular Apollo 17 mission -- but if they set up a little lower barrier of entry it would be nice.

Edited April 24, 2020 by sevenperforce

[It'snorocketscience]

 

17 hours ago, xendelaar said:

[...] I haven't succeeded in making a prop plane fly on duna though. There is so little atmospheric pressure to play with that wings just make things heavy without providing enough lift/speed. I did make a helicopter once but that thing was stripped to its core haha. Adding fuel to that would make the craft too heavy to lift.. I think...

I'm hoping other people are having better luck at finishing this challenge. I'm constantly reminded why I dont like to build ssto's: they rapidly get so damn bulky and difficult to handle.  XD

[...]

The same guy (Reddit user u/Chagaran) I linked in my post who built an orbital chopper SSTO actually built a Duna helicopter, but unfortunately it required orbital refueling. Now, he didn't use ISRUs, nor nukes or ion engines, and his design did have some aerodynamic flaws (mk2 fuselages used as a cool-looking cargo bay at the expense of creating negative lift), but I bet he came close. Link: https://www.reddit.com/r/KerbalSpaceProgram/comments/fi03d8/upgraded_orbital_helicopter_now_duna_capable/?utm_source=share&utm_medium=web2x

I just realized something about Duna props—Normally, on Kerbin, large props and rotors require large motors to turn at full power against the drag created by the blades. But in Duna's thin atmosphere, drag is very low, so you can get away with strapping 8 medium or large props on smaller motors, and then add duplicate the setup to create the necessary thrust. If your props and rotors can reach the maximum 460 RPM easily, you need to make them work harder (attach more/larger props) or downsize the motors to save weight. Of course, these overworked props and rotors will struggle on Kerbin, but if you add more of them (you'll need several for Duna, anyway) I think it might just work.

I'm getting close to succeeding with my sleek 23 ton MK1 design. It uses an ISRU and is very drag-optimized—the 2 Jr. drills, solar panels, radiators, and science parts are crammed inside 3 small service bays, thereby eliminating much drag. Plus, I've crammed one small converter, radial ore tanks, and fuel cells inside a fairing, eliminating even more drag. Finally, I've got the wings angled up at 5 degrees so the plane can stay level without having to pitch up (which would expose the plane's body to the airstream and cause drag). So it's a really slippery plane—you guys should definitely try to minimize drag in your own builds as well.

But all the optimizations in the world can't replace the fact that I need more props. Two props barely even register in Duna's atmosphere. Forget "optimizations", It's time for MOAR BOOSTERS!

Edited April 24, 2020 by It'snorocketscience

[jinnantonix]

I am new to chopper design.  I have a bacis design that I think meets the criteria, although I am yet to get to orbit.  Any hints on how to stop the blades from stretching out under centrifugal force?