Hypersonic airfoils for booster return.

[Exoscientist]

 SpaceX prefers vertical powered landing to horizontal winged landings for their booster to do RTLS since it requires little modification to the booster and because it would also work on airless bodies. However, using wings may offer an advantage. Based on the lengths of the burns for the return portion of the boosters flight on the Orbcomm-2 mission, I estimate the amount of propellant that must be reserved for the booster RTLS as ca. 46 metric tons (mT). This results in a large performance hit of a 30% loss of payload according to Musk. 

 However, estimates of wing weight are about 10% of the landed weight, which probably could be reduced to 5% with carbon composites. So for a F9 booster with an estimated dry mass of 20 mT to 25 mT, you would only need an additional 2 to 2.5 mT, and likely half that with composites. This would results in large reduction of the payload loss.

 But the question is could we use wings to allow a RTLS when the booster flies at hypersonic speeds, say, at ca. Mach 7? I think it might be possible, or with minimal propellant burn, if your airfoil has high hypersonic lift-drag ratio. To be sure this would be very different from the Space Shuttle's delta-wing shape. The shuttle has been described as akin to a flying brick with a hypersonic L/D ratio of only 1, though its subsonic L/D is better at about 4.5

 However, airfoils of high hypersonic L/D are known:

Waverider Design.
http://www.aerospaceweb.org/design/waverider/waverider.shtml

 

 So my challenge to Kerbal-mavens is if you have a Mach 7 L/D of about 7, could your first stage booster at a max speed of Mach 7 do a return to launch site?

 

   Bob Clark

[Temstar]

It will be hard, but it should be doable. I can think of three such designs proposed:


Flyback Zenit booster for Energia II. Energia II also has a winged core stage that returns from orbit.



Baikal


Ariane 5 liquid flyback booster

Notice something? They all have nose mounted jet engines to allow them to return to launch site. Clearly gliding alone is not going to cut it. And jet engine and it's associated jet fuel will unfortunately boost the dry weight.

I did try to make this concept work in KSP, but since KSP does not allow you to control lower stages while upper stages are burning I had to change the concept to a SSTO or stage and half design and recover the boosters from orbit. Since the boosters reach orbit in my design the jet engine is no longer required as coming back from orbit with a winged booster means huge cross range capability already.

[Nibb31]

You will be way beyond the 10% mass penalty. Wings are one thing, but you need control surfaces and landing gear, which need hydraulics, some way to maintain pressure in those hydraulics (an APU or a propulsion unit). At Mach 7, you're also going to need some sort of TPS, so your wings can't be made solely of composites. And of course, your structure is going to need to be much heavier because it has to handle all sorts of dynamic loads instead of just containing fuel in vertical position.

Edited January 20, 2016 by Nibb31

[magnemoe]

Note that Russia has an benefit of landing on ground downrange, no need for boost or flyback, just landing and transport back, 

[Temstar]

Curiously while researching flyback boosters I ran into this design:


http://buzzaldrin.com/space-vision/rocket_science/starbooster/

I guess Buzz Aldrin and I came upon the same idea

[fredinno]

1 minute ago, Temstar said:

Curiously while researching flyback boosters I ran into this design:


http://buzzaldrin.com/space-vision/rocket_science/starbooster/

I guess Buzz Aldrin and I came upon the same idea

How would the 3rd version even be stable?

[Temstar]

It looks like Athena II has a solid powered core stage. I'm guessing both the StarBooster 200 and Athena II have gimbaled nozzle with fairly wide gimbal range.

[SargeRho]

25 minutes ago, fredinno said:

How would the 3rd version even be stable?

The same way the STS stays stable: Taking gimbaling to absurd levels.

[fredinno]

24 minutes ago, Temstar said:

It looks like Athena II has a solid powered core stage. I'm guessing both the StarBooster 200 and Athena II have gimbaled nozzle with fairly wide gimbal range.

No, but shouldn't the assymetric thrust screw it over? Athena II's Castor motors were not deigned for Assymetric.

[Exoscientist]

4 hours ago, Nibb31 said:

You will be way beyond the 10% mass penalty. Wings are one thing, but you need control surfaces and landing gear, which need hydraulics, some way to maintain pressure in those hydraulics (an APU or a propulsion unit). At Mach 7, you're also going to need some sort of TPS, so your wings can't be made solely of composites. And of course, your structure is going to need to be much heavier because it has to handle all sorts of dynamic loads instead of just containing fuel in vertical position.

 Actually, it's the total of all those components that's commonly less than 10%. Also since the booster is not reaching orbit, but only Mach 7 the need for thermal protection is much less.

 

  Bob Clark

[Exoscientist]

2 hours ago, magnemoe said:

Note that Russia has an benefit of landing on ground downrange, no need for boost or flyback, just landing and transport back, 

 Yes. That is the key problem. To do RTLS, not just land downrange, you need to be able to turn around via aerodynamics alone, not burning engines, at hypersonic speed. That high speed means you need high aerodynamic force to turn around, hence the need for high L/D ratio.

 This modeling of the descent at hypersonic speed, as the altitude reduces and air density increases while the vehicle is banking, turning all the while is non-trivial.

  Bob Clark 

[Nibb31]

2 hours ago, Exoscientist said:

 Actually, it's the total of all those components that's commonly less than 10%. Also since the booster is not reaching orbit, but only Mach 7 the need for thermal protection is much less.

 

  Bob Clark

Citation needed.

An empty conventional booster is mostly aluminium tankage, designed for vertical loads, and a few tons for the engines. For example, the expendable F9 1.1 first stage weighs empty ~23 tons (including 9x470=4.2 tons of engines), for a size of 44m x 3.66m. That is much lighter, than an equivalent sized aircraft, like the Airbus A321, which weighs empty ~47 tons (including 2x2200 = 4.4 tons of engines) for pretty much the same dimensions.

That's a 100% difference, not 10%.

The mass of the engines is similar for both the airliner and the rocket, so the difference in weight is mainly due to the stuff that makes the A321 fly like an aircraft (wings, structure, hydraulics, flight controls, landing gear, power, etc...) and the stuff that makes it comfortable for people (pressurization, windows, seats, galleys, toilets, etc...)

Adding wings, structure, APUs, hydraulics, and everything required to turn a booster into an aircraft (even without the people carrier equipment) will make the total mass much closer to the mass of an aircraft than to a rocket. Maybe not 100%, but certainly not 10%. 10% mass penalty is what it takes to simply add landing legs and grid fins to the F9. 

You don't necessarily need a heavy TPS, but the X-15 flew to Mach 6.7 and needed a special ablative coating. Wings add surface, and more surface means more mass for the coating.

Edited January 20, 2016 by Nibb31

[magnemoe]

1 hour ago, Exoscientist said:

 Yes. That is the key problem. To do RTLS, not just land downrange, you need to be able to turn around via aerodynamics alone, not burning engines, at hypersonic speed. That high speed means you need high aerodynamic force to turn around, hence the need for high L/D ratio.

 This modeling of the descent at hypersonic speed, as the altitude reduces and air density increases while the vehicle is banking, turning all the while is non-trivial.

  Bob Clark 

Note that Falcon 9 first stage does not turn much, the gravity turn is not optimal as they prefer to add more vertical speed and less horizontal. speed at seperation was a bit over 3000 km/h but far less than 1000 was horizontal and had to be canceled. Stage climbs to 200 km before going down, this is an benefit as you reduce the speed needed to return.

With an winged first stage you will probably want an faster than optimal gravity turn so you don't end up too high to be able to turn after separation, this will increase speed requirements for the same upper stage+ payload. yes you will probably want to gain attitude after the turn to reduce air resistance. 

[fredinno]

5 hours ago, Exoscientist said:

 Actually, it's the total of all those components that's commonly less than 10%. Also since the booster is not reaching orbit, but only Mach 7 the need for thermal protection is much less.

 

  Bob Clark

Honestly, the fact that it would not be able to adapt to both expendable and reusable (if the performance is needed- we have yet to see an advantage over reuse.) and additional complexity makes the SpaceX version look more appealing.

[wumpus]

10 hours ago, Nibb31 said:

You will be way beyond the 10% mass penalty. Wings are one thing, but you need control surfaces and landing gear, which need hydraulics, some way to maintain pressure in those hydraulics (an APU or a propulsion unit). At Mach 7, you're also going to need some sort of TPS, so your wings can't be made solely of composites. And of course, your structure is going to need to be much heavier because it has to handle all sorts of dynamic loads instead of just containing fuel in vertical position.

There should be means around much of the hydraulics.  You would use freely swinging control levels connected to the controlled control lever (similar to how rudders can be made to work on large ships).  Presumably the smaller controls can be directly controlled at the source (some sort of strong servo).

The real issue is where all your R&D goes.  Space X is putting it all into the Merlin* engine and rocket controls.  This keeps their vision on tract and keeps any gained knowledge in house.  Going with wings and replacing hydraulics keeps piling problems on top of problems, none of which matter at all in the long view of space flight.

My understanding is that this was how the shuttle was originally planned (well there were plenty of proposals that look like this, I'm sure there were SSTO proposals as well, but this looks like it would have worked).  Presumably in the 1970s it would have required manned controls in the first stage (or not, Buran flew entirely unmanned), and flown down.  Considering that the Shuttle landed from orbit, this was presumably possible, but more expensive (for the first article) than a single shuttle.

* and of course other engines.  But keeping the focus on the existing parts keeps the same scientists and engineers focused on all their big problems.  But I'm sure they spent the first few years investigating all the different ways to come down (the original design used parachutes.  I'm pretty sure it took some severe convincing by repeated failure that retrorockets beat parachutes).