Stuck on designing my Interplanetary-capable Carrier SSTO, please help?

[TalonX273]

As the title says, I'm stuck with the design phase. More specifically, I want to figure out how much "stuff" I actually need on this SSTO, before I build it. I've been trying to figure out the calculations myself. But, I'm likely doing it wrong or I'm missing something. Because of that, I've been bashing my head against a wall for about a month now. So here, I concede defeat, and ask the community for help.

My primary goals for this Interplanetary-capable Carrier SSTO are:

• In a true Single Stage space-plane (no drop tanks or refueling!), visit Jool and each of it's moons, then return at KSC
  
• Deliver a satellite around Jool and each of it's moons in GSO (or Semi-GSO or any other high and stable orbits)
  
• Optional Ultra-Hardcore Goal: Drop a rover/science package at each moon
  
• Design it so it's modular, and can be used as a workhorse carrier to LKO
  

Here are the design specs I'm trying to achieve to meet the goals above:

• Must be 100% stock parts!
  
• The Carrier SSTO should have enough resources to reach LKO with it's Payload and/or fuel for Interplanetary Flight
  
• Payload and Interplanetary-only resources should stay isolated to the Payload Bay (this way, I can keep it modular)
  
• By my calculations, it needs to have 8000-9000m/s dV after it reaches LKO in order to visit and return from the Joolian System
  
• It should be able to carry about 6,000kg to Jool (each satellite is about 1,000kg)
  
• Assume standard SSTO ascent profile is in use and should be able to accelerate to 1800-2000m/s before using rockets
  
• Should include 3-4 Ram Air Intakes per TurboJet
  
• TWR for Jets and Rockets should be 2 in both modes. For interplanetary engines, have at least 0.1
  

If possible, I'd like to figure out how much of the following I actually need (in % of Total Mass; on average): Fuel %, Engines %, Dead Weight %, and Payload %. I have that partially calculated. Basically, it needs to be 64-70% Fuel Mass by the time it reaches LKO. Theoretically, that should give it the 8000-9000m/s dV I need. That's also assuming I'm using LV-N engines for the interplanetary portion of the flight. So that leaves me with about 30-36% of Total Mass for anything that isn't Fuel Mass.

Problem is, I don't know how to divide up that 30-36%. Plus, these percentages are only relevant after I reach LKO! This means, I don't know how much I actually need on the Carrier SSTO itself. If anyone can help me figure this out, I would appreciate it very much!

Miscellaneous Points:

• Current design scheme I'm using involves having CoM/CoL in the center of the payload bay.
  
• This whole thing is for the "Green Scout Challenge" on reddit. I'm essentially doing the Hard Mode version, but six times in one flight! That's why this has to be 100% stock. I might also have to avoid some parts/features from after version 0.20 to keep it "legal."
  
• The Hardcore Goal is likely impossible since I'll hit the Max Theoretical dV with that much weight. That's unless I make the packages MUCH lighter, or I make the SSTO unreasonably large.
  
• I was trying to create a sort of "template formula" for Carrier SSTOs. Essentially, I wanted a formula that can give me a good estimate of how much I need for an SSTO. It should be based on how much payload I want to carry and/or fuel for interplanetary flight. If anyone can figure that out, it would be extremely helpful for future designs!
  

Sorry this became rather lengthy. I hope someone can help me finish this design, because I sure as heck couldn't.

Thanks in advance,

- Talon

Edited March 5, 2014 by TalonX273
Formatting Corrections

[Sirine]

http://forum.kerbalspaceprogram.com/threads/37352-Exo-s-Rubberband-and-Duct-Tape-Emporium-SSTOS-Weird-Space-Ships-and-more!

This is the best you can get for a 100% STOCK craft.

[Kasuha]

SSTOs are limited in their total dv because they can never go above certain proportion of wet to dry mass. For pure fuel tank, assuming it has Isp of 800, it is 17226 m/s but your spaceplane also needs to carry a lot of other stuff and then this dv goes down steeply. So I'd say you'll either need to use Xenon or lower your dv requirements and rely heavily on gravity slingshots.

[Gauss H2K]

If you're intent on modularizing it, I would recommend not sending it up all together, and just build the SSTO stage that can be swapped out for an IP Stage, then re swapped for atmospheric return. It would reduce part counts, complexity, and dead weight (assuming you're using turbojets for atmo).

[John Crichton]

8-9k deltav isn't enough to visit all moons and Jool in one go...especially if you want to come back. At least I think it isn't enough.

Kethane would make it a lot easier and your craft lighter by the way.

Consider making an "interplanetary ring" for a smaller SSTO...that way you can use the SSTO to visit Jool's moons once there. Launch that ring with a normal rocket.

I'm currently preparing my grand tour, but I use a Kethane SSTO with c. 8k deltaV (can refuel at the destination!!) and an interplanetary ring. However, I also had to use that fuel mod allowing you to change the oxidizer/LF ratio to make it work.

Don't use turbojets, they're dead weight on all those moons. Personally I went with Rapiers to get something out of both, worlds with an atmosphere and worlds without one. Don't like nukes on my SSTO because the thrust is too ****ty to deal with some planets/moons.

PS: I actually tried what you want to accomplish...gave up after launching a 5 orange tank Kethane SSTO. It's just too damn large and unpractical.

Edited March 5, 2014 by John Crichton

[MarvinKitFox]

What exactly is your definition of SSTO?

As you are launching Probes, landers, etc.. you are already not bound to the "pure" rule of "everything must stay attached at all times, except fuel use"

Is the rule simply that everything launched must be returned, except fuel? That is much easier. Just make sure each "stage" dropped has the ability to return home.

Or Launch your ship, Undock the "launch module" in LKO. The go do your mission, return back to LKO, redock and land in one piece. No need to lug the launch stage with its heavy, likely air-breating-thus-obsolete-everywhere-else engines along on the whole trip to Jool!

*I* interpret a SSTO vehicle under the rule of "Bring back all the hardware that you launched, minus probes and landers". This means Launcher stays in orbit. Fuel tank for return flight is left to loiter in very high eccentric Jool orbit. *only* probes and landers slow down to lower orbits, and they do this 99% by Jool and Laythe aerobrakes. Do the rules require your landers to also be ssto? If not, consider an ultralight kerbal-return craft.

[Silverchain]

What exactly is your definition of SSTO?

As you are launching Probes, landers, etc.. you are already not bound to the "pure" rule of "everything must stay attached at all times, except fuel use"

It's only single stage to orbit, there isn't a requirement to keep everything attached once you're up there. All a craft needs to do to qualify as an SSTO is to make an ascent to orbit in a single stage, and what happens before or after that doesn't matter...

For instance the Apollo lunar module's ascent stages were SSTO, despite being launched only after multiple earlier staging and not being reusable.

[Claw]

I also highly disagree with that definition of SSTO. Single stage to orbit is wholly different than reusability. Many people build SSTO space planes that are capable of delivering cargo. Just because the cargo is decoupled doesn't mean it didn't get there in one stage.

I believe the OP states a space plane single stage to Jool and back. I suppose looking only at this would imply you are bringing everything home, but this is a different question than SSTO. To me, making it to every Joolian body, delivering probes, and returning without refueling is more difficult than just SSTO. SSTO here is one aspect of the overall plan.

Edited March 5, 2014 by Claw

[Red Iron Crown]

I not sure it's possible to cram enough delta-V into a single stage to do what the OP wants without resorting to ion drives. It gets much easier if refueling in LKO is permitted.

[Kasuha]

I'm pretty certain the challenge is meant "single stage to wherever you plan to release your probe". The baselevel challenge is bringing the probe to stationary orbit, so SSTO is fitting there.

I think it should be possible if probes can be released while the mothership transits the SOI and can circularize using their own fuel.

[TalonX273]

SSTOs are limited in their total dv because they can never go above certain proportion of wet to dry mass. For pure fuel tank, assuming it has Isp of 800, it is 17226 m/s but your spaceplane also needs to carry a lot of other stuff and then this dv goes down steeply. So I'd say you'll either need to use Xenon or lower your dv requirements and rely heavily on gravity slingshots.

I'm pretty certain the challenge is meant "single stage to wherever you plan to release your probe". The baselevel challenge is bringing the probe to stationary orbit, so SSTO is fitting there.

I think it should be possible if probes can be released while the mothership transits the SOI and can circularize using their own fuel.

Agreed. I did the math, and came to the same conclusion. I still think it might be possible though. I do have a flight plan calculated using an online calculator. (I forget which one) Of course, this flight plan might be optimized further since it doesn't include Gravity Assists or the Oberth Effect. If there's a better flight plan (that satisfies the challenge requirements), please share it!

Approx. Delta-V Requirements; "inside-out" approach, using online calculator:

• Note: Calculations start from 1y/1d; From/To orbits are chosen by the lowest calculable transfers using the online calculator.
  
• To Low Kerbin Orbit - ~4500m/s
  
• Kerbin Orbit to Jool Intercept - 1,990m/s (From 100km orbit, 1y/171d > To 15,000km orbit, 2y/208d | For 15,000km orbit via aerocapture, ~1000m/s dV required to circularize)
  
• Jool to Laythe - ~500-1000m/s
  
• Laythe to Vall - 110m/s (From 3000km orbit, 2y/215d > To 1900km orbit, 2y/215d)
  
• Vall to Tylo - 110m/s (From 1900km orbit, 2y/218d > To 5700km orbit, 2y/219d)
  
• Tylo to Bop - 670m/s (From 5700km orbit, 2y/223d > To 1000km orbit, 2y/227d)
  
• Bop to Pol - 340m/s (From 1000km orbit, 2y/238d > To 900km orbit, 2y/244d)
  
• Pol to Jool Orbit - ~500m/s (From 900km orbit, 2y/248d > To 190,000km orbit, 2y/250d)
  
• Jool Orbit to Kerbin - 1670m/s (From 190,000km orbit, 2y/264d > To 100km orbit, 3y/193d | For 100km orbit via aerocapture, ~500m/s dV required to circularize)
  
• >> Total: 11,890m/s dV! (or 12,500m/s, with added margin for error)
  

You are also correct with my definition of "SSTO." It must stay as single stage when delivering each payload to count. This means I can't drop all six satellites in Jool orbit and have them insert themselves into their orbits alone. It would only count as "one" satellite being dropped by the SSTO. As for inserting the satellites into their orbits on their own, during an intercept, I don't think that counts. I messaged the mods and they said they have to be in their "parking orbit" when dropped.

[TalonX273]

Update 3/6/14:

I've done some practical testing. I used a bare-minimum SSTO test platform with the following stats:

• Dry/Wet Mass: 16,474kg/51,474kg
  
• TurboJets: x4; TWR ~1.8 in Jet Mode; 4 Ram Intakes per Jet
  
• Rockets: x1 LV-N; TWR ~0.13 in Rocket Mode, after Jet Fuel is expended
  

According to this test, with this platform, the maximum Delta-V I was able to carry into orbit was about ~7500m/s. Now, this platform was essentially a poorly built flying orange tank, with 4 Mk1 tanks attached. Not to mention, I botched Cruise and Circularization Phases too. So it might be possible to cram a little more dV out of this. I'm not entirely sure what numbers to use for the Delta-V calculation, hence why I did a practical test.

Can anyone please confirm what's the maximum dV an SSTO can carry into orbit? Or is this test already the best case scenario? Once I have that number, the next step is finding the most Delta-V effecient flight path to execute the mission. If those two numbers don't match... Well, this mission is impossible then.

Thanks in advance,

- Talon

Edited March 7, 2014 by TalonX273