Simple Merlin-derived SSTO

[todofwar]

9 minutes ago, John JACK said:

Accelerating extra dead weight of tankage, ducts and redundant engines with payload 7000 m/v to orbit needs much more fuel than decelerating near empty first stage (without payload) less than 1000 m/s. SSTOs may be wicked cool, but they are ineffective.

Wouldn't it be Liquid Flyback Booster?

I was saying use this as a liquid flyback booster instead of an SSTO, I seem to have communicated that poorly. 

[sevenperforce]

On 5/2/2016 at 9:52 AM, todofwar said:

I was saying use this as a liquid flyback booster instead of an SSTO, I seem to have communicated that poorly. 

Oh, I see. Booster for what, though? A separate reusable stage?

Did some more calculations with the new uprated Merlin 1D, and it looks like we could make orbit on a single engine, using VTVL with a horizontal-attitude landing on lift fans; the lift fans serve double duty to supercharge the inlet duct during liftoff. Here's a mockup:

 

 

 

GLOW is 99.5 tonnes, total fuel is 90 tonnes. 3,790 kg of payload. Assuming 50% increase to engine mass to account for the fixed ducting. Assuming a tankage/structure/avionics mass of 3.7 tonnes with 1,280 kg reserved for TPS, landing legs actuators, landing fuel reserve (for the gas generator, not for the actual engine), structural modifications, and the lift fans.

Not quite sure where to put the crew cabin. I suppose I could have done it with the AAR ducts on the sides rather than the top and bottom, allowing me to put the crew cabin right in front of the engine.

Edited May 3, 2016 by sevenperforce

[MatterBeam]

32 minutes ago, sevenperforce said:

Oh, I see. Booster for what, though? A separate reusable stage?

Did some more calculations with the new uprated Merlin 1D, and it looks like we could make orbit on a single engine, using VTVL with a horizontal-attitude landing on lift fans; the lift fans serve double duty to supercharge the inlet duct during liftoff. Here's a mockup:

 

 

 

GLOW is 99.5 tonnes, total fuel is 90 tonnes. 3,790 kg of payload. Assuming 50% increase to engine mass to account for the fixed ducting. Assuming a tankage/structure/avionics mass of 3.7 tonnes with 1,280 kg reserved for TPS, landing legs actuators, landing fuel reserve (for the gas generator, not for the actual engine), structural modifications, and the lift fans.

Not quite sure where to put the crew cabin. I suppose I could have done it with the AAR ducts on the sides rather than the top and bottom, allowing me to put the crew cabin right in front of the engine.

What's the payload to orbit? How scalable is the design?

[sevenperforce]

9 minutes ago, MatterBeam said:

What's the payload to orbit? How scalable is the design?

3,790 kg to orbit. You can scale it up for a bit pretty easily -- double with two Merlin 1Ds, triple with three, and so forth -- and gain a little bit in payload fraction due to the square-cube law making the dry mass lower, but your AAR gains will start to suffer as you pack more engines in. You'll also run into more structural issues; this is a low-drag design but the aerodynamic stresses are still pretty high, so a larger version will have to deal with higher moments of torque in flight.

My goal was really to design the smallest possible SSTO rather than a large one. Obviously a larger SSTO will have a better mass fraction, but a larger SSTO will also have greater turnaround time and higher reuse costs. 

Toying with the idea of SuperDraco-assisted takeoff and landing to replace the lift fan...depends on whether I can get the duct geometry to work.

[todofwar]

50 minutes ago, sevenperforce said:

Oh, I see. Booster for what, though? A separate reusable stage?

Did some more calculations with the new uprated Merlin 1D, and it looks like we could make orbit on a single engine, using VTVL with a horizontal-attitude landing on lift fans; the lift fans serve double duty to supercharge the inlet duct during liftoff. Here's a mockup:

 

 

 

GLOW is 99.5 tonnes, total fuel is 90 tonnes. 3,790 kg of payload. Assuming 50% increase to engine mass to account for the fixed ducting. Assuming a tankage/structure/avionics mass of 3.7 tonnes with 1,280 kg reserved for TPS, landing legs actuators, landing fuel reserve (for the gas generator, not for the actual engine), structural modifications, and the lift fans.

Not quite sure where to put the crew cabin. I suppose I could have done it with the AAR ducts on the sides rather than the top and bottom, allowing me to put the crew cabin right in front of the engine.

Yeah, my thinking is basically have three of these, except the one in the middle would have a nice big cargo bay. All three are reusable lifting bodies.

[sevenperforce]

4 minutes ago, todofwar said:

Yeah, my thinking is basically have three of these, except the one in the middle would have a nice big cargo bay. All three are reusable lifting bodies.

Why not just two?

[cantab]

The pointy one is a cool render, but I doubt it's doable with current materials. You're expecting an entire SSTO to weigh not much more than the Dragon capsule alone.

[todofwar]

1 hour ago, sevenperforce said:

Why not just two?

For symmetry mostly. I don't think you'd want to strap something to the front of a ship like that. You could have two and do a shuttle like launch I suppose. 

[sevenperforce]

47 minutes ago, cantab said:

The pointy one is a cool render, but I doubt it's doable with current materials. You're expecting an entire SSTO to weigh not much more than the Dragon capsule alone.

Well, it's not actually a lot bigger than a Dragon capsule. Smaller cross-section, actually. This design was essentially a thought experiment to see how small an SSTO could be. 

The Falcon 9 upper stage is about the same size but is significantly lower in dry mass.

30 minutes ago, todofwar said:

For symmetry mostly. I don't think you'd want to strap something to the front of a ship like that. You could have two and do a shuttle like launch I suppose. 

Symmetry would demand a biamese launch. The ship is smaller on the belly than on the back so it can act as a lifting body; mating belly-to-belly is really the only way to go. 

Edited May 3, 2016 by sevenperforce
typo

[todofwar]

1 hour ago, sevenperforce said:

Well, it's not actually a lot bigger than a Dragon capsule. Smaller cross-section, actually. This design was essentially a thought experiment to see how small an SSTO could be. 

The Falcon 9 upper stage is about the same size but is significantly lower in dry mass.

Symmetry would demand a biamese launch. The ship is smaller on the belly than on the back so it can act as a lifting body; mating belly-to-belly is really the only way to go. 

Wouldn't belly to belly be a biamese launch? Again, I'm talking about using this as a fly back booster. I guess you couldn't make the center craft symmetric in my idea anyway, so a biamese tsto or have an angle of attack such that your thrust vector is through your center of mass despite having only engines on one side a la shuttle would be the best way. 

More generally, what about landing this as a sea plane? Would the savings in wheels be negated by the increased structural requirements? 

[sevenperforce]

11 minutes ago, todofwar said:

Wouldn't belly to belly be a biamese launch? Again, I'm talking about using this as a fly back booster. I guess you couldn't make the center craft symmetric in my idea anyway, so a biamese tsto or have an angle of attack such that your thrust vector is through your center of mass despite having only engines on one side a la shuttle would be the best way. 

More generally, what about landing this as a sea plane? Would the savings in wheels be negated by the increased structural requirements? 

Yeah, belly-to-belly is biamese. I guess I'm not sure what you're trying to get at with a flyback booster.

No wheels in the single-engine second render; it lands on the lift fans.

[todofwar]

https://en.wikipedia.org/wiki/Liquid_fly-back_booster

So, instead of having the center craft be a rocket like they had in that system, you make the center craft another spaceplane that will serve as your reusable orbiter. I do it all the time in KSP, so it must work . IRL it failed because you ended up needing so much mass in wings, wheels, and engines, all of which had to survive launch. But your system would allow these boosters to be simple lifting bodies and glide back.

As for landing on the fins, wouldn't that necessitate a powered descent? 

[sevenperforce]

2 minutes ago, todofwar said:

https://en.wikipedia.org/wiki/Liquid_fly-back_booster

So, instead of having the center craft be a rocket like they had in that system, you make the center craft another spaceplane that will serve as your reusable orbiter. I do it all the time in KSP, so it must work . IRL it failed because you ended up needing so much mass in wings, wheels, and engines, all of which had to survive launch. But your system would allow these boosters to be simple lifting bodies and glide back.

As for landing on the fins, wouldn't that necessitate a powered descent? 

Right, I know about the LFBB design; I'm just trying to figure out your implementation.

Yeah, powered descent, but powered by the lift fan.

[wumpus]

You're sure enough about the dry weight to calculate the cargo to 10kg?  In a rocket with 90 tons of fuel?  How many struts did you use?

[sevenperforce]

8 minutes ago, wumpus said:

You're sure enough about the dry weight to calculate the cargo to 10kg?  In a rocket with 90 tons of fuel?  How many struts did you use?

Too many sig figs, I know.

[sevenperforce]

Here's another version, with the ducts on the side and SuperDracos inside the augmentation duct for launch augmentation and supersonic flow control. They fold down with the landing "legs" during landing for biaxial propulsion. Haven't done the math yet though. Crew variant shown.

[Elukka]

I really like how they look, visually speaking.

My main reservation is dry mass, for the ducts, fuselage and heat shield. I don't know how to try and estimate those myself however.

[sevenperforce]

5 hours ago, Elukka said:

I really like how they look, visually speaking.

My main reservation is dry mass, for the ducts, fuselage and heat shield. I don't know how to try and estimate those myself however.

Thanks! I wanted them to look badass (a small part of why I am so set on a vertical landing in horizontal attitude) but still be functional.

The dry mass for the fuselage is higher than for a comparable "simple" liquid rocket (e.g. the Falcon 9 second stage) but I'm not sure if the margin is high enough. I'd need to look at the mass/volume characteristics of wet wings w/o control surfaces in order to get a better general estimate.

I really wish there was a way to have biaxial takeoff as well as biaxial landing, for sheer rule of cool as well as enhanced ease of operations, but that's a struggle. Kind of need a supercharger there, unless we can come up with a way to entrain air more aggressively with dynamic compression.

[todofwar]

On 5/3/2016 at 4:15 PM, sevenperforce said:

Right, I know about the LFBB design; I'm just trying to figure out your implementation.

Yeah, powered descent, but powered by the lift fan.

If only there was some kind of software or game an amateur like me could use to demonstrate what I mean. Oh wait!

Last photo ended up first for some reason, but basically the idea is you fire the outer two boosters, then disengage (I have to disengage with them still running to avoid collisions with the tail fins on the main craft) and use the center ship to reach orbit and deliver payload. Then you fly your boosters and main ship back. 

My thought was your overall design could work with this concept rather nicely, especially if they could land like sea planes and avoid the need for an extra jet engine and enough fuel to fly back to base. 

[Thor Wotansen]

What are you doing for aerodynamic control on those?  There's not much space for control surfaces so you might need some pretty hefty reaction wheels in there, and with that very pointy shape, slowing down on reentry might be a challenge.

[sevenperforce]

On 5/14/2016 at 1:51 PM, Thor Wotansen said:

What are you doing for aerodynamic control on those?  There's not much space for control surfaces so you might need some pretty hefty reaction wheels in there, and with that very pointy shape, slowing down on reentry might be a challenge.

My thought was to do a blended lifting body/ballistic surface so that as long as you come into the atmosphere pitched up, the craft will auto-orient to the maximum-drag blunt-front orientation. Active stabilization on launch.

[Nibb31]

In other words, magic.

Without control surfaces, it would either go nose-first (like a nuclear warhead) or bottom first (bye bye engine). You would need it to look something like ESA's IXV:

[sevenperforce]

58 minutes ago, Nibb31 said:

You would need it to look something like ESA's IXV:

...yes, that would be the plan.

Edited May 17, 2016 by sevenperforce

[Nibb31]

...which has control surfaces and a blunt reentry shape. If only it could actually produce enough lift to glide back to landing...

The problem is that you want to design a vehicle that with too many different (and contradictory) flight envelopes:

• Vertical launch
• Orbit
• Reentry
• Hypersonic glide
• Subsonic glide
• Horizontal landing

It's nearly impossible to design an airframe shape that can operate gracefully in all those different environments. Plus, you want it to be SSTO and have a positive payload fraction. 

Edited May 17, 2016 by Nibb31

[MatterBeam]

4 hours ago, Nibb31 said:

...which has control surfaces and a blunt reentry shape. If only it could actually produce enough lift to glide back to landing...

The problem is that you want to design a vehicle that with too many different (and contradictory) flight envelopes:

• Vertical launch
• Orbit
• Reentry
• Hypersonic glide
• Subsonic glide
• Horizontal landing

It's nearly impossible to design an airframe shape that can operate gracefully in all those different environments. Plus, you want it to be SSTO and have a positive payload fraction. 

Not far off from what the Space Shuttle did...