SpaceX Falcon 1/9 1st Stage Recovery: Engines Only?

[dwb0407]

What are the technical, practical, and economic challenges of designing the Falcon 1e/9 1st stage to recover only the engine assembly?

Reasons driving this line of thought:
1. Engines are valuable, the remainder of 1st stage is just tank metal.
2. If only the engine assembly is recovered, the recovery mass is much smaller.
3. The entry trajectory is suborbital, so the heat shield shouldn't need to weight to much, and would be taking the mass of the current purposed full 1st stage recovery system.
4. Tank sections are easy / cheap to manufacture (relatively), so why save them and spend the same $$ refurbing old/damaged ones.

Initial Concept (open for everyone to poke holes @)
1. Structure in put between tank and engine assembly consisting of pica heat shield, and small package of orientation thrusters, recovery hardware. To get the necessary diameter to protect the engine bells, either 1, the rocket gets a small skirt (costing margin, and aerodynamics), or mechanical extensions spread after stage1 separation(extremely complex).
2. Post Stage 1 separation, stage one separates between the engine assembly, and tank.
3. Tank is left fall and burn up.
4. Orientation thrusters fire on engine assembly to orient the heat shield forward.
5. Standard parachute recovery of engine assembly.

Thoughts?

Don

[Mike_1179]

4. Tank sections are easy / cheap to manufacture (relatively), so why save them and spend the same $$ refurbing old/damaged ones.

There might be a few guys at MAF who would beg to differ

[kevin-rf]

There might be a few guys at MAF who would beg to differ

But if Elon out sourced the tanks to MAF they would have jobs come 2011

[Jim]

The whole idea of separating the tanks complicates the stage and reduces reliability and adds weight.

There would need to be mechanical and fluid connections that will need to be separable.  The fluid ones would be problematic in terms of cost.

[Lee Jay]

5. Standard parachute recovery of engine assembly.

How do you get it to float without the empty tank?

[dwb0407]

Hadn't thought of the floating issue, over-come with the addition of a splash down raft, but that adds more weight.

Jim - How many fluid lines are we talking about? I'm thinking two.
LOX and RP-1. Can anything be easily engineered using the ET door and related hardware on the Shuttle as a concept model?

How much weight are we really talking about adding?
The TPS on stage 1 has to be of significant mass, parachutes already in the design.....

I guess the real question is: Is the mechanical complication worth the "savings" of recovery / reuse of the engines?

Edit: and, I guess, would it be easier to devise such a system, than it will be to recover the whole stage intact?

[lbiderman]

Hadn't thought of the floating issue, over-come with the addition of a splash down raft, but that adds more weight.

Jim - How many fluid lines are we talking about? I'm thinking two.
LOX and RP-1. Can anything be easily engineered using the ET door and related hardware on the Shuttle as a concept model?

How much weight are we really talking about adding?
The TPS on stage 1 has to be of significant mass, parachutes already in the design.....

I guess the real question is: Is the mechanical complication worth the "savings" of recovery / reuse of the engines?

Edit: and, I guess, would it be easier to devise such a system, than it will be to recover the whole stage intact?

Actually, no, is simpler this way: KISS in itīs very true form (ok, I know stage recovering is definetely not simple). Put TPS on the complete stage, no need for extra tubing (which means more failure modes), and the empty tanks provide flotation.
Of course, SpaceX has still to prove they can accomplish this. Most likely, they will test it and work from there.

[Antares]

"Easily engineered" Ugh, this is true for about 10^-5 of the times it is uttered. From now on, the metric for such a statement is "Can the proposed solution be purchased with a personal credit card?" Anything else is not easy, nor is this a sufficient condition.

[Mike_1179]

"Easily engineered" Ugh, this is true for about 10^-5 of the times it is uttered. From now on, the metric for such a statement is "Can the proposed solution be purchased with a personal credit card?" Anything else is not easy, nor is this a sufficient condition.

If it was easy, you wouldn't need an engineer to do it

[zaitcev]

ULA folks gave this option a serious thought as a way to extend the supply of RD-180 engines and reduce the cost of Atlas-V launch. IF I remember right, their conclusion was that the numbers would close (over a few years) if only someone came with the money to do the development. It may be an optimistic assement, of course (or I forgot something). Also, they had a much more expensive engine to save, and the strategic threat of supply interruption. Try to find their presentation and perhaps they explain how they planned to make the engine module to float, and how the connectors were supposed to penetrate the heat shield.
-- Pete

[Comga]

Jonathan Goff has discussed this in his Selenian Boodocks blog last September.  His particular concept was to snag the detachable engine compartment of an Atlas V in mid-air.

If as zaitcev saysULA found this to be feasible, and it "just" needs funding, SpaceX is both investing and getting investment for what they (Musk) feels is technology that will reduce the cost of spaceflight.

Jim is inevitably correct, as usual, but the increases complexity might turn out to be worthwhile.  (Just look at our newer cars. At least 10% of the increased complexity are things we actually need.)

And of course Anteres is correct: Nothing is simple, particularly with launch vehicles.

[MP99]

If you want to separate the engines from the rest of the stage, could this be done with a linear charge of explosives around the bottom of the barrel section of the tanking. (This would be similar to the charges which unzip SRB for an abort, but around the tank instead of down the SRB).

But I suspect SpaceX may want to recover the whole stage, even if it's just to recycle the tank material. And, of course, the tank provides flotation (if it survives intact).

cheers, Martin

[Damon Hill]

I recall a proposed scheme to recover the Saturn 1C stage by blowing off the forward LOX tank dome and having it parachute to a modest water impact that would burst open vents (sort of a dashpot effect).  The LOX tank would submerge and leave the rest of the stage above water.  Possibly flotation bags.

The inevitable salt spray might be hard on the combustion chamber, but it shouldn't be too hard to 'harden' the rest of the engine components.  I don't remember if the LOX or kerosene tankage was considered to be reusable/refurbishable.

Obviously there's going to be a payload penalty for the added recovery gear, and some additional costs in repair/refurbishment/replacement.

[pippin]

I think the KISS solution to this would be to not separate the engine assy but to design the recovery system in a way that it didn't care whether the tankage comes back intact or not but only focuses at the engines.

This is a booster stage, weight penalty doesn't count as much as with upper stages.

[William Barton]

The whole idea of separating the tanks complicates the stage and reduces reliability and adds weight.

There would need to be mechanical and fluid connections that will need to be separable.  The fluid ones would be problematic in terms of cost.

How many fluid connections are we talking about? Are the 9x Merlins individually plumbed to the tanks, or are their two mains going to a manifold? The latter would make sense, but I have zero info.

[ugordan]

How many fluid connections are we talking about? Are the 9x Merlins individually plumbed to the tanks, or are their two mains going to a manifold? The latter would make sense, but I have zero info.

Sort of like this...

[Nick L.]

That's gotta be the weirdest looking aerospace part I've ever seen...

[ugordan]

I call it the octopus.

[gospacex]

Why would you want to detach the tank?

Add some drag chutes to ensure that stage impacts "nose" first. The tanks are not planned to survive in flightworthy condition.

Forward (LOX IIRC?) tank is to be flooded with water (it may be damaged on impact; it may be even desirable to design it to do that or to have some puros to blow some holes in it).

RP-1 tank remains watertight and provides flotation.

Inflatable rafts near engines ensure that the stage floats engines up, so that they are not submerged in the salt water. I don't know how feasible is that though, engines may be too heavy.

[Antares]

If you want to separate the engines from the rest of the stage, could this be done with a linear charge of explosives around the bottom of the barrel section of the tanking. (This would be similar to the charges which unzip SRB for an abort, but around the tank instead of down the SRB).

Creates completely unnecessary cost, complexity and failure modes.