I attended a conference from the head of the CNES (Centre National d'Etudes Spatiales, ~ French NASA) in Paris a week ago and he talked about that.
Ariane 6 is going to be built with a cost effective approach and trying to focus on market needs (3D printing of parts, reusability of the first stage, etc.)
At first, concerning SpaceX, his group of experts told him that the design of the rocket wasn't going to work and was going to explode at high altitude due to fluctuation. They also told him that the first stage would just go through the barge, sinking both the first stage and the barge. Now they are taking new entrants way more seriously.
I can't imagine how anyone with the slightest clue could conclude that the first stage would sink the barge. The scales are just too different; the barge outweighs the rocket by orders of magnitude.
I hope this is one of those "lost in translation" things, because otherwise I fear for that group of supposed experts.
> the barge outweighs the rocket by orders of magnitude
The energy amount the rocket impacts with is dominated by its speed, not its mass. A small, fast-travelling projectile can make a hole in just about any kind of armour. The terminal velocity is quite low, but that's in part because of the way it is engineered — an ICBM would probably be able to put a hole through a ship deck with ease.
There is a lot of reasoning by analogy vs. reasoning from first principles going on, and the latter seems to be winning. But the main driver of the space industry is governmental funding, not commercial. Much of those statements were probably political; SpaceX have prevailed, and indeed found some champions of their own (John McCain is rabidly behind them, and some of the statements he comes up with are ludicrous in their own right, for example), though not before enduring some setbacks.
The energy amount the rocket impacts with is dominated by its speed, not its mass. A small, fast-travelling projectile can make a hole in just about any kind of armour. The terminal velocity is quite low, but that's in part because of the way it is engineered — an ICBM would probably be able to put a hole through a ship deck with ease.
While what you've said is true, in practice it isn't a problem.
If the F9 first stage is out of control and going too fast, it will almost certainly miss the barge to begin with. The barge is small, the ocean is big, and the F9 has to maneuver very precisely to reach it.
If it does reach the barge, it will likely be moving relatively slow, and thus is less likely to sink the barge, even it things go crazy at the last moment.
That brings up an interesting question, can't the range safety officer just scuttle the first stage after separation? I can't imagine that they don't have that capability after separation.
mass != momentum. I'm sure the thinking was that they wouldn't be able to slow the rocket down enough and that the speed of impact would punch through the barge. The autonomous control needed to get the rocket to slow down and stop at just the right time, while accounting for the movement of the barge, the movement of the rocket (eg: unpredictable wind impact), and the difficulty of gathering telemetry through the rocket engine exhaust, is pretty amazing.
They initially aim the rocket to the side, then correct over to the barge after the engine lights, so a failure there doesn't cause a high-speed crash.
Either way, the relative masses matter. It takes a lot more effort to punch a hole through something much more massive than your projectile! It doesn't make much sense that a light, nearly spent rocket stage would punch all the way through a massive barge. And even if it did, the hole still wouldn't be big enough to sink it.
Also the fact that if the rocket has actually lost control its unlikely it would hit the barge anyway at least at any significant amount of speed. The only time that would be likely is if it loses control right at the end where is velocity is low.
> I'm sure the thinking was that they wouldn't be able to slow the rocket down enough and that the speed of impact would punch through the barge.
Would any "expert" really believe SpaceX didn't run the numbers millions of times, and do millions of simulations to confirm they could slow it down before actually spending the money to buy and outfit drone ships, build landing legs onto their rockets, etc. etc. ?
I mean, honestly, while the devil is in the details for an actual landing, they must have been pretty damn sure they could at least slow the thing down sufficiently.
Of course, but my point is that the barge is so much more massive that the idea of punching a hole all the way through doesn't really make sense, and even if that were possible, such a small hole wouldn't sink it anyway.
Ariane 6 looks like it will be a fine rocket. Should be quite competitive if they can get it to market before, say, 2010, and if SpaceX's reusability efforts come to naught.
Otherwise, I fear it'll be much too little, much t0o late.
Well, but SpaceX hasn't. They have not reused any rockets. They've landed a few rockets, they've test-fired one of the landed rockets. But that's far from a track record of reliably recovering their rockets, turning them around and sending them back up that could drive the massive cost benefits that they hope for.
I'm not really playing skeptic here -- SpaceX's progress has been incredible, and I'm inclined to believe them that they can do it -- but it hasn't happened yet.
Newton's approximation for impact depth [1] gives a way to calculate how thick the barge deck would have to be to survive a high speed impact from the rocket stage. The impactor punches through until it has displaced an equal mass. An empty F9 stage masses about 23,100kg and has a diameter of 3.66m. [2] Steel has a density around 7,700 kg/m^3. Doing the math, the deck would need to be about 29 cm thick to survive a high speed impact. Estimates are the actual barge deck is 25-35 mm thick [3], so 1/10th that thickness. If the F9 stage came down onto the barge completely uncontrolled, it probably would punch through!
Punch through the deck. Which we already know can happen, the SES-9 landing attempt punched a nice hole in the deck. But you'd need to punch all the way through the hull to even think about sinking the barge, and of course the barge is built with compartments so even that wouldn't do it.
I expect the hull is thinner than the deck: it isn't designed to hold up to a rocket blowtorching and landing. But good point about compartments: the barge may well be able to survive a rocket-sized hole punched through it!
I'm kind of fascinated -- and not necessarily in a good sense -- with how unbelievably conservative the aerospace industry became right after its greatest moment of glory. That would have been Apollo in 1969. Seems like after the Moon landings everyone just said "welp, that's it, nothing else will ever be done."
I agree, I can imagine NASA became complacent, stopped embracing risk, prioritised perfection over practicability and became similar to many public sector departments.
Ariane 6 is going to be built with a cost effective approach and trying to focus on market needs (3D printing of parts, reusability of the first stage, etc.)
At first, concerning SpaceX, his group of experts told him that the design of the rocket wasn't going to work and was going to explode at high altitude due to fluctuation. They also told him that the first stage would just go through the barge, sinking both the first stage and the barge. Now they are taking new entrants way more seriously.