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SpaceX Landing Attempt Video Released
An anonymous reader writes: Last week, SpaceX attempted to land a Falcon 9 rocket on an autonomous ocean platform after successfully launching supplies to the ISS. It didn't work, but Elon Musk said they were close. Now, an amazing video has been recovered from an onboard camera, and it shows just how close it was. You can see the rocket hitting the platform while descending at an angle, then breaking up. Musk said a few days ago that not only do they know what the problem was, but they've already solved it. The rocket's guiding fins require hydraulic fluid to operate. They had enough fluid to operate for 4 minutes, but ran out just prior to landing. Their next launch already carries 50% more hydraulic fluid, so it shouldn't be an issue next time.
Maybe they save weight by not providing a return line?
09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
@alankerlin Hydraulics are usually closed, but that adds mass vs short acting open systems. F9 fins only work for 4 mins. We were ~10% off.
And pumps and motors.
All they need is a pressure tank.
This was the first time SpaceX had flown the new grid fin control system on a real first stage under real conditions. They did not know exactly how well the grid fins would behave. As it turned out, the grid fins had to move more than they expected during the descent (or the forces were larger than they expected), so they ran out of hydraulic fluid 30 seconds before landing. This is similar to an airplane losing control of its elevator just before landing. The fact that the rocket reached the barge and that its vertical speed was reasonably slow (certainly not 100m/s) indicates the resiliency of their systems. They are putting 50% more fluid into the system, so this shouldn't happen next time.
I think this video is epically cool. I can watch it again and again. Simply awesome.
This and no other is the root from which a tyrant springs; when first he appears as a protector - Plato (423 to 327 BC)
It is lighter and more simple to use up (to expel it when it has done its work) any hydraulic fluid than it is to have a scavenger system. While this would be a problem on your car if each time you pushed the break cylinders it squirt out the fluid after it had actuated the break on a rocket it saves on over all weight and complexity just to have "enough" fluid to do the job
Seems to me that I would save that for emergencies. Use the high speed descent to pressurize air for controlling.
While IANARE, The problem with pressurized air as a control mechanism is that it is elastic/compressible (while hydraulic fluid is basically non-elastic/non-compressible). Which means that if you use air your control is basically going to suck big donkey's balls as your control vanes will bounce around in the airstream as the air in the control system acts like a big spring. Thus degrading the landing accuracy of your rocket.
On the other hand hydraulic fluid being stiff means that when you send the control vane to a position it stays there, and the only thing that moves it is a leak or destruction of the vane. Note that they will be some bounce in a hydraulic system, but nowhere near as much as in an air based system.
Now as to the hydraulic fluid in this case being used up, I am guessing that they considered the mass imposed by a collection system and decided, "fuck it, it's too much mass to recycle it, we're just going to dump that shit overboard".
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WTF is going on with the left margin. God damn it, it is broken in every single browser. Are they crapping on classic slashdot to punish us for beta not working?
In a normal hydraulic system there is a pump that re-pressurizes and returns the hydraulic fluid to a reservoir. To save weight and complexity here since the hydraulics are only used for a few minutes they instead use an "open" hydraulic system in which the pressure comes from a tank of compressed gas and the hydraulic fluid is expelled or burned up as it is used. (The fluid goes one way - out - as it is used).
After the pressurized gas or fluid was used up they no longer had control over the fins.
he tweeted
Next rocket landing on drone ship in 2 to 3 weeks w way more hydraulic fluid. At least it shd explode for a diff reason.
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To borrow from the KSP forum, that's "Rapid Unscheduled Disassembly". Or, "explosions", to the uninitiated.
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To be fair, the pictures I've seen of the barge indicate it came through mostly unscathed. So they only blew up the rocket. :)
Hydraulic systems are in a loop, with the "spent" fluid recirculating back to the reservoir. How did they "run out"?
Where did the fluid go?
The system is an open hydraulic system. Closed systems require tanks and pumps which carry a mass penalty. They only need the system to function for about 4 minutes. Why bother with a closed system when the functioning period is so short. They will increase the amount of fluid by 50% so this shouldn't happen again. All in all a nearly successful experiment.
This and no other is the root from which a tyrant springs; when first he appears as a protector - Plato (423 to 327 BC)
The main hydraulic system on the F9 (for gimbaling the engine nozzles) uses RP-1 (i.e. rocket fuel) as its hydraulic fluid. Spent fluid from that system goes into the fuel tank.
The fins are driven by a separate system at the top of the stage, if they pumped the spent RP-1 overboard you'd have flammable liquids running down the stage, I'm pretty sure they don't want to do that. Returning the RP-1 to the fuel tank is unlikely (needs an insulated pipe around the outside, next to the cold LOX tank). So probably a separate waste tank near the fins.
Because parachute recovery is a method of salvage, while "crazy rocket landing" is a method of full reuse without refurbishment.
Keep in mind that refurbishing the waterlogged shuttle boosters ended up being 3X more costly than original estimates, much of the nozzle apparatus was completely trashed each time, and the whole process took months to turn around a single booster.
SpaceX is working toward an airplane/airport-style refuel-and-refly-immediately model. That autonomous landing platform is actually a fuel depot, with the eventual intention to refuel first stages and relaunch them immediately for short hops back to a proper launch facility where they can be fitted with a new payload within a day. Crazy? Maybe. Wrong? I don't think so.
I think not...(*poof*)
Remind me again, why doing this crazy rocket landing is better than using a parachute recovery like the shuttle boosters did?
SpaceX tried parachute recovery with the F9 v1 (the rocket flying now is the v1.1, though really is more like a version 2). After multiple attempts, they could not get the rocket to survive reentry. There are many reasons for this. First of all, the shuttle boasters were big heavy steal tubes. That's fine for a strap on booster, but not so good for the first stage. Rocket stages are very light weight, since the lighter the rocket the more payload it can carry (this is true for boosters too, but it's a different trade off when coupled to a "first stage".) Second the shuttle boosters separated at lower speed and a lower altitude than the first stage of an F9. So you have a much lighter, complex F9 reentering at much higher velocities. Third, the shuttle boosters were more "refurbished" than reused. The goal of SpaceX is to (ultimately) land the first stage and be able to refuel and relaunch it with a minimum of work. Shuttle boosters had to be fished out of the water, disassembled, cleaned, inspected, etc... SpaceX was hoping to use parachutes as a first step, but they always hoped to eventually land the boosters. Their timeline just got accelerated when uncontrolled reentries kept breaking up.
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It seems SpaceX is relying on a trial-and-error strategy during the development of the soft landing capability of their booster much more than they (or others in the industry) do for other components or capabilities of space launch or other aeronautical systems. I don't see (unmanned) rockets or drones being developed in this fashion. Even large rockets that can achieve orbit will normally be modeled, simulated and tested component-wise to the point that they will usually work at the first or second attempt when the entire system is integrated and tested for the first time. So why is this so different here? Is it just cheaper? Or is it actually that much harder to make the rocket land softly on its own exhaust jet than to make it go into orbit?
It's important to remember that the primary mission was a complete success. The Dragon delivered the cargo to the ISS and is awaiting trash and cargo to return to Earth. This was a post mission experiment meant to collect data. It's very common to completely loose a rocket in the early flights, but that's not what happened here.
SpaceX does what's called LEAN development, which is basically like agile software development. Really all development is incremental, the difference with lean/agile is you admit that instead of pretending that you can design the perfect solution from the start. SpaceX has a huge computer cluster and they model the hell out of everything they do. Then they try it to see how it works in the real world, measure the results and make improvements. The experiments are always done after stage separation in a way that collects important data without putting the mission as risk. You can call that trial and error, but that does the process a disservice.
There have been experimental rockets and landers that land vertically, most notably the DCX. But no one has reentered a first stage of an actual in service rocket, the previous vehicles have always been test platforms and never accelerating to launch vehicle velocities nor going to launch vehicle altitudes. NASA has flown aircraft to collect data from earlier SpaceX missions because no one else has EVER controlled a first stage's return to earth. (Shuttle SRBs were not controlled, just big steel tubes falling from lower and slower than the F9.) The first stage is a long cylinder with blunt ends and it reenters the atmosphere at hypersonic velocities. On top of that, it's a super light weight and fragile airframe. Just getting the thing down to terminal velocity in one piece is a big deal.
The LEAN development model is less expensive than the classic approach. It's also faster and yields really good results. You learn about problems sooner and don't bake them too deeply into your design. Look at it this way, the closest competitor to SpaceX in developing a reusable VTVL rocket is Blue Origin, started by Jeff Bezos. Blue Origin started with more money than SpaceX and before SpaceX. SpaceX is delivering cargo to the ISS, and about to test the Dragon V2 abort system in preparation of flying astronauts in 2017. They are also self funding the development of a much bigger reusable rocket (slightly bigger than the Saturn V). They are doing all of this while providing the least expensive launch prices in the world. Less expensive than Russia. Meanwhile Blue Origin hasn't even reached orbit. They aren't even trying to reach orbit, they are still developing a suborbital rocket, even though they have a number of experienced engineers that worked on the DCX. Oh, to be fair, Blue Origin is developing an engine for use by ULA (and Blue Origin) and doing some work on a man rated capsule. But nothing is anywhere close to flying.
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The first stage of a rocket is never going to Mars, or even to orbit. They may need something different on a third stage of a Mars rocket, but that's no reason not to keep the first stage simple.
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