SpaceX Falcon 9R launch

RobertDyck · 2015-01-10 22:22:42

louis wrote:

How does the barge work? Virtually any sea conditions will involve some pitch and roll. I'm assuming they must have some sort of gyro system on board that attempts to compensate and create a stable surface? Or maybe it has very strong magnets to hold the legs as they touch down? But that seems unlikely.

Description says they don't anchor. Instead they have water thrusters that adjust for drift to keep the barge on-station. Automated control is able to keep the barge so close to station that variation is less than the size of the deck. But pitch and roll? No mention what so ever. And there doesn't appear to be anything to secure it. Just gravity.

Some decades ago, the Canadian military developed a technique to land a helicopter on a relatively small ship. The helicopter would drop a cable, a "bear trap" on the ship would grasp the end of the cable. Then helicopter would use its rotor to pull up, pulling the cable taught. Then a winch on the helicopter would reel in the cable, pulling the helicopter down. Since the helicopter's rotors are pulling up, if a wave heaves the ship up, the helicopter follows instead of crashing into the deck. This allows a helicopter to land on a frigate or destroyer. Even in heavy seas, with the ship heaving up and down, pitching and rolling. Once the helicopter lands, clamps grab the skids of the helicopter. But how would you do that with a rocket? You can't. Just wait for calm weather before launch.

Last edited by RobertDyck (2015-01-10 22:23:45)

RGClark · 2015-01-11 09:05:41

I really, really dislike the inability to hover for the Falcon 9R. With the
method used now, it has to make its engine firing be precisely timed so that
it reaches zero velocity with respect to the landing spot by the time it
lands. This method does not allow fine alterations in case of changes in
conditions by the time it reaches the landing point. These could be due to
unexpected changes in winds, but in the case of a barge landing it becomes
especially concerning with the rolling, pitching surface of a ship. From the
description of this failed landing attempt, the first stage reached the
barge but landed too roughly. A hovering capability would allow you to vary
how gently you wanted the landing to be even under changing conditions.

The reason why the F9R can't hover is that even when throttled down as far
as it can go, a single Merlin 1D still produces more thrust than the weight
of the first stage when the stage is close to empty upon landing. However,
there are some relatively low cost methods to give the F9R hovering
capability:

They could replace the single central Merlin 1D with the Merlin 1A, which
has lower thrust. They could use variable sized nozzles to alter the thrust.
They could use inserts into the thrust plume that diverts the thrust
horizontally. They could use the exhaust that comes only from the preburner,
i.e., from the turbine exhaust nozzle visible to the left of the engine
here:

Others?

Bob Clark

c.f.,

Merlin 1A engine for a hovering Falcon 9 v1.1 first stage.
http://exoscientist.blogspot.com/2014/0 … con-9.html

GW Johnson · 2015-01-11 11:29:57

Spacex already knows what happened. The news reporters are technically rather ignorant, generally speaking. That's why the truthsome tidbits get left out of their stories.

I found one buried in today's newspaper: they simply ran out of hydraulic fluid for the steering grid fins before it landed. Presumably, it lost attitude control, which also costs them their retro thrust vector. The news story said they already upped the hydraulic fluid quantity by 50% for the next shot.

The barge has steering thrusters. Marine engineers use these quite frequently in modern passenger ships. These not only help control position, they also help a great deal with reducing pitch and roll. But they can do nothing for straight up-and-down "heave" of the wave action .

Bob Clark is quite right about Falcon-9R needing to hover. That capability coupled with a small radar to perceive the relative motion of the "heave" would enable self-compensation for a more reliable ship landing. That kind of dynamics is elementary to a Navy carrier pilot, but not to an Air Force pilot.

If however, Spacex really plans to land on an island instead, then what they are doing will work on dry land which does not move. Unless they add hover capability and the small radar, it seems unlikely to me that barge landings will be reliably successful in anything but the very calmest seas.

GW

SpaceNut · 2015-01-11 13:03:25

The hovering time is the problem for the stage as that means more fuel storage is needed to continue to slow the stage to rest on the deck.

Are the landing legs, spring loaded or built with a landing obsorber compression system like a cars leaf spring or shock obsorber system? If not maybe its time to look at adding the dragon capsule Draco engines to the base of the stage to make the throttling to slow the vehicle that last 50 to just a few feet.

Impaler · 2015-01-11 13:08:12

I think this hovering issue may be addressed in the Raptor rocket family that SpaceX is now sketching out. It was recently announced that this engine is aiming at a half million ftlbs of thrust, considerably smaller then earlier speculation and hints, and less then the ~10x extrapolation from the current Merlin/Falcon family.

This implies MORE first stage engines, my guess is 20 in a honeycomb arrangement, 1 central engine, a second ring of 6 around that and a outer ring of 13. This gives one center line engine which if it can throttle down to 50% would be just 1/40th (2.5%) of the liftoff thrust. That may be enough to do a decent hover. This is admittedly a lot of engines in the first stage, it immediately reminds of the the N-1, once again SpaceX would be following in Russian footsteps if it went this route. On the other hand the Falcon Heavy will launch with 27 engines, if that becomes a normal routine launch then 20 dose not look very scary.

How the second stage would work I am not sure, it would seem to need more then one Raptor engine, anything from 2-4 seams reasonable. In any event a second stage is not going to be able to hover because it's engine count is to small and their is no center engine, and even if their was it would be producing too much thrust. Second stages will inevitably need smaller touch-down engines, presumably located on the landing legs.

GW Johnson · 2015-01-11 15:16:31

2nd stage recovery on a TSTO is quite different from 1st stage recovery. The difference is orders-of-magnitude worse aeroheating. Falcon-9 (or heavy) 1st stages (cores in the case of Heavy) already retro thrust rather significantly to reduce what would have been a Mach 10-ish entry to something nearer Mach 3 or 4.

The second stage (either vehicle) would hit air in the vicinity of Mach 25 without retro thrust, or else would need a "real" heat shield (and a lot more airload gee resistance structurally) to do most of the job by aero-deceleration. The retro-thrust requirement is so huge (Mach 25 down to 3 or 4?) your only practical choice is a real heat shield and gobs of structural "beef", which is very heavy. I don't see that activity going on anywhere.

So, I don't think I'd worry too much about 2nd stage recoveries just yet. Spacex doesn't seem to be looking at it. Not for Falcon-9 or Falcon-Heavy. It wouldn't be any different, no matter how big the rocket, as long as it was TSTO.

GW

RobertDyck · 2015-01-11 15:59:09

Here is a video of what SpaceX intended. The video is from September 2011. Details of the first stage legs are different. Is this how they intend to recover the second stage? It shows a heat shield at the top end, legs at the bottom.
https://www.youtube.com/watch?v=OX2-qEC7P_I

Impaler · 2015-01-11 19:05:04

Yea that video was really cool with some provocative music too. But it's defunct now in the sense that they are not going to even try 2nd stage recovery on Falcon family rockets. It remains to be seen if they try that same overall profile with the Raptor family rocket or if they go for something totally different.

A true heat-shield is a must have for that 2nd stage recovery, the question is do you go nose first as the video depicts which requires you to flip over (which the video dose not show), or try to cover the engine with some kind of clam-shell heat-shield and come in tail first.

Mark Friedenbach · 2015-01-12 00:10:48

2nd stage recovery simply doesn't make sense. You kill a lot of performance by adding that weight and extra fuel so high in the stack. Better economics to make the 2nd stage simple and cheap.

Doesn't mean it can't be reusable though. You could start collecting these things in Earth orbit and reuse them on in-orbit constructed crafts.

Tom Kalbfus · 2015-01-12 10:02:03

Mark Friedenbach wrote:

2nd stage recovery simply doesn't make sense. You kill a lot of performance by adding that weight and extra fuel so high in the stack. Better economics to make the 2nd stage simple and cheap.
Doesn't mean it can't be reusable though. You could start collecting these things in Earth orbit and reuse them on in-orbit constructed crafts.

The second stage could be a reusable orbiter like the Shuttle. So you kill performance, the question still remains does recovery of the vehicle make up for the lost performance? The shuttle recovered its side-mounted solid fuel rockets, the external tank burned up in the atmosphere, could we improve on that?. The second stage of the shuttle was simply a big orange fuel tank attached to the shuttle. If the fuel tank is part of the bottom stage and we recover that entirely, you only need fuel for the rest of the journey into orbit after the separation of the bottom stage. You don't have to build a new bottom stage and the fuel tank that goes with it, if you can recover it. I think the one thing the Shuttle program did for us is give us experience in maintaining bottom stage rocket engines and reusing them. The Shuttle Orbiter was simultaneously part of the bottom stage and also the top stage.

Impaler · 2015-01-12 15:23:19

Solid Rocket 'recovery' on Shuttle system was always a CROCK, the things are just giant steel tubes at that point, the value recovered is tiny. The propellent that needed to be put back into the tube is 80% of the cost of manufacture. Liquid fueled rockets are worth recovering because the liquids are <1% of the cost. Many false analogies have been made between solid and liquids in this regard, implying that recovery of a burned out metal tube is comparable to recovering of a complex liquid rocket engine based vehicle. From a monetary standpoint the Shuttle boosters were an expendable asset, and solids are not fit for human spaceflight in my opinion, they exist only to subsidize their use a military weapons and to give lift-off thrust to underpowered first stage HydroLox vehicles which have proven to be terrible in cost performance vs Hydrocarbons.

The Shuttle orbiter was extremely inefficient as a stage, 3/4th of the mass reaching orbit was the orbiter itself, it would be hard to do worse then that. Still it may ultimately end up being impractical, we have had to wait for decades to get 'almost' first-stage recovery. I would not be surprised if we have to wait another few decades for 2nd-stage to become viable. Maybe we will even see a return to 3 stage rockets with the second stage being sub-orbital and making a return much like the 1st stage (far down range) and the 3rd being more a capsule that can splash in the ocean. More stages are 'bad' but if we have reliable first-stage recovery, and reliable capsule recovery but a kind of black-zone in the middle then it's tempting to split the 2nd stage in half and use the two techniques that we already know work.

Last edited by Impaler (2015-01-12 15:27:14)

GW Johnson · 2015-01-12 18:57:15

There's a reason the vast majority of the missiles out there (from any source anywhere in the world) are solid propellant rockets. It's because they are both the cheapest option that there is, and the most carefree that there is, when looked at from a life cycle standpoint. The second closest is ramjet, with turbine a very, very distant third.

Yep; solids are cheap. And they are operationally carefree. Better than anything else we know how to do. The world's weapon arsenals are what they are, for a very bloody damned good reason.

The expectations and preconceived notions for SRM's that most people seem to have, are at variance with what actually obtained on the shuttle program. Those motors actually did rather well, in spite of all the expensive impediments and out-and-out mismanagements, that NASA managers contrived to heap upon them.

A fair fraction of these case segments really were reloaded and reflown. (The loss rate just goes to prove that parachute landing in the ocean is unsurvivable, even at 10% inert fraction.) They turned out to be about as reusable as the shuttle orbiter itself, or more so, by about any measure that is quantifiable.

That's why both Atlas-5 and Delta-4 (ULA products) both use SRM's when the core thrust is inadequate off the pad. Low down in the atmosphere, Isp isn't all that important, it's nothing but brute force thrust that matters. There's nothing on this Earth that beats solids for brute force thrust, with the sole exception of nuclear explosions.

That being said, what you have to consider for reusable stages is how hypersonic you are at atmospheric entry for your recovery. Most cores are 5-10% inert mass fraction stages. These are very structurally fragile, even if aeroheating were not an issue, and it is.

Spacex Falcon 1st stages generally burn out near 10,000 fps (3 km/s), as all TSTO 1st stages do. In the absence of any other influences, that's the entry speed upon hitting air again (energy is conserved, after all), and it is not very survivable (shuttle Columbia broke up at about Mach 12, or about 12,000 fps or 4000 m/s).

You have a choice: either put a heat shield (heavy!) on this thing, or carry some extra propellant (also heavy!) to slow it down to a more survivable entry interface speed. Speeds like that are nearer Mach 3 (3000 fps, 1 km/s). Spacex has done the latter, and seems near to succeeding, far sooner than any of us ever expected. I am surprised and pleased by that outcome. Spacex has "done good"!

For second stage of a TSTO, entry speed is very near LEO orbital speed: near Mach 25 (25,000 fps, or 8+ km/s) at entry interface. If you think Mach 10 protection is hard to achieve, try this! It's worse (by far) than speed squared dependence on speed. So that's an all-up heat shield. No chemically-powered machine could ever afford the propellant to slow from there to near Mach 3 by retro-thrust.

It would make more sense to recover this 2nd stage in LEO after the circularization burn, if there were a use for it up there in LEO. There isn't a use yet, that's why no one has done it. Sorry, fact of life. But, it could be done, if there were a use. That kind of on-orbit re-use would be the cheapest and most technologically-feasible thing we could do.

There just is not yet a use for such hardware, and the orbital debris problem weighs against it until there is a specific use. Sorry, that's just life.

I think the shuttle proved that large spaceplanes are not a very good idea, for the kinds of technologies we have at our disposal. That says nothing about small ones, I might add. But large payloads are probably most efficiently (and cost-effectively) placed in LEO with big vertical launch rockets, for the forseeable future. If you can lower the price by recovering stage 1, fine. If not, well, that answer still stands.

If you need solid strap-ons to get your launch rocket off the pad with big payloads, well, fine. Do it. There's nothing wrong with that. Design them correctly (NASA still does not), and you can even man-rate them.

GW

Mark Friedenbach · 2015-01-12 22:07:31

Well the annoying thing is that by international treaty you need to provide full lifecycle guarantees about any hardware you put up there. That's part of why we never kept shuttle external tanks up there, even though that would have been a tremendous resource. Without a plan for dumping them in the ocean if/when station-keeping fuel is used up, you'll never get regulatory approval. It's a hurdle that can be overcome, but "let's just keep it up there until we come up with a use" is not a good enough justification...

Impaler · 2015-01-12 22:36:03

I'm not aware of any such treaty stipulation, Russians have been leaving empty booster rockets in LEO for AGES with nary a whiff of life-cycle planning, that's the space-junk problem. Shuttle Tanks weren't left in orbit because. 1) It would reduce other payload that was actually needed/desired. 2) The thing is so incredibly light and low density it would have a rapidly decaying orbit meaning we can not effectively stockpile them 3) They would be completely unguided, uncontrollable tumbling and likely dangerous to approach again if just left them free floating 4) They have nasty residual propellents in them which are going to boil 5) ALL the crazy ideas about sticking external tanks together and living in them and such were completely bonkers, we have NO ability to cut into, modify, seal up any of this stuff in-space. The only propositions that had any chance of working were with a modified tank with a port in the bottom and that was never made cause we built a REAL space-station instead, just because the ISS is also made of aluminum cans dose not mean any aluminum can makes a good space-station.

RobertDyck · 2015-01-12 23:34:44

Oh. Are we talking about using tanks in orbit? Skylab was a modified S-4B stage. That's the 3rd stage of a Saturn V, or upper stage of a Saturn 1B. In fact, Skylab was made from the 3rd stage that was going to launch Apollo 20. Stages for Apollo 18 & 19 were to far completed, it was less expensive to modify a stage that wasn't fully assembled rather than tear a completed one apart. But the point is it had to be modified. A hatch in the upper tank. A small airlock through the bulkhead between LH2 and LOX tanks to dispose of kitchen waste. The anti-vortex baffles of the LH2 tank were replaced with a pair of open mesh grids that served as floor and ceiling for the living spaces. The mesh grids still acted as anti-slosh and anti-vortex baffles; and interior partition walls helped. Most importantly, the addition of a pop-out screen that acted as micrometeoroid shield and sun shade. Much of that pop-out screen ripped off during launch, had to be replaced by a tarp. The fairing for one of the main solar arrays ripped off during launch, losing that solar array. That's what tore off a section of the pop-out screen. Most importantly, the S-4B stage had a metal skin, so tank insulation was not exposed like the Shuttle ET. That was something Skylab didn't need modified, but a Shuttle ET would. Skylab demonstrated how to design a "launch wet" station. That required extensive modification, and all that adds significant weight. Doing the same with a Shuttle tank was possible, but it would have been so heavy that the orbiter wouldn't have been able to carry anything in its cargo hold.

Impaler · 2015-01-12 23:42:06

Skylab was not wet launched, wet means full of rocket fuel at the time of launch.

Ok back on top now, pictures of the Drone ship have been released (probably not by SpaceX itself but by 'space paparazzi'). Their is some burn damage and some charred/melted 20ft shipping containers, and some pancaked scrap metal on the deck. Hard landing seems a bit of an understatement, it was more of a crash, not an explosion just a crash.

This is an interesting speculative animation of what might have a happened.

I think this looks close, but some of the bottom/top of the rocket was in fact shorn off as it went over the side and this is what the scrap on the deck is as it is clearly not a whole rocket in that pile.

Last edited by Impaler (2015-01-12 23:52:22)

Mark Friedenbach · 2015-01-12 23:51:25

Impaler, the Outer Space Treaty stipulates that nation states are held liable for hardware left in space if someone in their jurisdiction owns the hardware. What naturally evolved out of that is a passing on of that liability to the private interests, which requires insurance by law to avoid the bankruptsy loophole. And no insurer would be willing to take on the risk from dead weight in a dangerous orbit with no station-keeping or avoidance fuel.

Impaler · 2015-01-12 23:59:28

NASA owned all the parts of the Shuttle system before they left the ground because they purchased the vehicle, not a service, the private contractors that built the shuttle would not have been liable in any way. If NASA had wanted to use them in space they would hardly have been stopped by the cost of liability insurance, as far as I know NASA self-insures all it's satellites and in-space assets. In the event of some damage NASA would just pay out of pocket for the damages. The law is not the reason it wasn't done, it was the total technological pointlessness and infeasibility of the idea.

Last edited by Impaler (2015-01-13 00:00:45)

Void · 2015-01-13 06:51:39

http://www.space.com/28236-spacex-rocke … fluid.html

He says "hydraulic-fluid". So looks like they are really getting close to their goals.

GW Johnson · 2015-01-13 19:05:50

See paragraph 2 of post 53 above.

It went out of control when the grid fin steering system ran out of hydraulic fluid. Whether part is on deck and part on the bottom of the Atlantic does not change that outcome.

If they can maintain control to touchdown, then they just might be able to pull this stunt off. It'll be a lot easier on an island with no up-and-down "heave" motions.

GW

RobertDyck · 2015-01-16 20:33:29

Video of the crash
https://vine.co/v/OjqeYWWpVWK

Elon's tweet said it ran out of hydraulic fluid. But how do open mesh metal grids provide steering when moving at slow speed just a second before landing? At that point, wouldn't the engine gimbal provide steering? I would expect any attempt to use the fins would result in, well, this.

SpaceNut · 2015-01-16 20:51:36

So where is the hydralic fluid going, sound like that needs to be fixed as that sort of system is a closed loop normally not open for loss to occur.

GW Johnson · 2015-01-17 01:03:33

The video they released shows it right over the deck coming down fairly slowly, but cocked over at a rather large angle, something like 40 degrees off vertical. The accompanying news story said one of the four grid fins had quit working, and that the gimballing rocket motors (motor?) couldn't compensate for it. The story said the fin failed for lack of hydraulic fluid. (It's my understanding that only one of the 9 engines is firing at touchdown, but that all are gimballed for steering when operating.)

That sort of sounds like a hydraulic leak, without enough reserve to make up for it. Common enough failure mode. Edit: the hydraulic press in my shop recently blew a rod seal. It loses lots of hydraulic fluid unless I park it in just the right position.

Grid fins work subsonically like an extremized form of biplane and triplane wings. The channels forcibly redirect the airflow to a new angle, which is lift. Supersonically it still does that, but at large drag due to the big normal shock standing out in front of the grid fin unit. These are operational on the Russian AAM that NATO designates AA-12. Supersonically-draggy fins are "perfect" for what Spacex is attempting.

GW

Edit: Looks to me like they very nearly pulled this landing off. Kudos to them! It's about the only imaginable way to recover a first stage with a modern stage inert weight fraction in the vicinity of 5%. In terms of landing loads, that's a very flimsy structure.

Last edited by GW Johnson (2015-01-17 08:50:25)

Decimator · 2015-01-17 14:29:37

GW Johnson wrote:

That sort of sounds like a hydraulic leak, without enough reserve to make up for it. Common enough failure mode. Edit: the hydraulic press in my shop recently blew a rod seal. It loses lots of hydraulic fluid unless I park it in just the right position.

The grid fin hydraulics are an open system. Pressurized RP-1 powers the grid fins, and drains into the main RP-1 tank after use. No compressor.

GW Johnson · 2015-01-18 10:14:51

Well, a pre-pressurized "one-shot" approach with a convenient liquid makes a lot of sense, weight-wise. They just underestimated how much the grid fin actuators might demand, I guess. Maybe a seal leaked a bit and increased the effective demand, too. Who knows?

GW

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#51 2015-01-10 22:22:42

Re: SpaceX Falcon 9R launch

#52 2015-01-11 09:05:41

Re: SpaceX Falcon 9R launch

#53 2015-01-11 11:29:57

Re: SpaceX Falcon 9R launch

#54 2015-01-11 13:03:25

Re: SpaceX Falcon 9R launch

#55 2015-01-11 13:08:12

Re: SpaceX Falcon 9R launch

#56 2015-01-11 15:16:31

Re: SpaceX Falcon 9R launch

#57 2015-01-11 15:59:09

Re: SpaceX Falcon 9R launch

#58 2015-01-11 19:05:04

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#59 2015-01-12 00:10:48

Re: SpaceX Falcon 9R launch

#60 2015-01-12 10:02:03

Re: SpaceX Falcon 9R launch

#61 2015-01-12 15:23:19

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#62 2015-01-12 18:57:15

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#63 2015-01-12 22:07:31

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#64 2015-01-12 22:36:03

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#65 2015-01-12 23:34:44

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#66 2015-01-12 23:42:06

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#67 2015-01-12 23:51:25

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#68 2015-01-12 23:59:28

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#69 2015-01-13 06:51:39

Re: SpaceX Falcon 9R launch

#70 2015-01-13 19:05:50

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#71 2015-01-16 20:33:29

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#72 2015-01-16 20:51:36

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#73 2015-01-17 01:03:33

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#74 2015-01-17 14:29:37

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#75 2015-01-18 10:14:51

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