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SpaceX To Attempt Falcon 9 Landing On Autonomous Spaceport Drone Ship
An anonymous reader writes: SpaceX has announced that at the conclusion of its next rocket flight, it will attempt a precision landing of its Falcon 9 first stage onto an autonomous ocean platform. They say the odds of success aren't great, but it's the beginning of their work to make this a reality. Quoting: "At 14 stories tall and traveling upwards of 1300 m/s (nearly 1 mi/s), stabilizing the Falcon 9 first stage for reentry is like trying to balance a rubber broomstick on your hand in the middle of a wind storm. To help stabilize the stage and to reduce its speed, SpaceX relights the engines for a series of three burns.
The first burn—the boostback burn—adjusts the impact point of the vehicle and is followed by the supersonic retro propulsion burn that, along with the drag of the atmosphere, slows the vehicle's speed from 1300 m/s to about 250 m/s. The final burn is the landing burn, during which the legs deploy and the vehicle's speed is further reduced to around 2 m/s. ... To complicate matters further, the landing site is limited in size and not entirely stationary. The autonomous spaceport drone ship is 300 by 100 feet, with wings that extend its width to 170 feet. While that may sound huge at first, to a Falcon 9 first stage coming from space, it seems very small. The legspan of the Falcon 9 first stage is about 70 feet and while the ship is equipped with powerful thrusters to help it stay in place, it is not actually anchored, so finding the bullseye becomes particularly tricky."
The first burn—the boostback burn—adjusts the impact point of the vehicle and is followed by the supersonic retro propulsion burn that, along with the drag of the atmosphere, slows the vehicle's speed from 1300 m/s to about 250 m/s. The final burn is the landing burn, during which the legs deploy and the vehicle's speed is further reduced to around 2 m/s. ... To complicate matters further, the landing site is limited in size and not entirely stationary. The autonomous spaceport drone ship is 300 by 100 feet, with wings that extend its width to 170 feet. While that may sound huge at first, to a Falcon 9 first stage coming from space, it seems very small. The legspan of the Falcon 9 first stage is about 70 feet and while the ship is equipped with powerful thrusters to help it stay in place, it is not actually anchored, so finding the bullseye becomes particularly tricky."
Why don't more billionaires do stuff like this?
I'm not saying do it "for the benefit of humanity", or even "for a profit". Just simply.... if you have billions of dollars, and you want to spend it on something, what can you possibly spend it on that wins in a sheer awesomeness category as "shooting a gigantic rocket up into orbit and then landing it on a robot boat in the middle of the ocean"? That's like a freaking video game, played with 1500 tonnes of aluminum and highly combustible fuel.
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from a safe distance.
The goal isn't to land on a barge, but back at the launch site (or at least near it). If they can show over a couple attempts that they get close to the target then they can move to doing this over land. They have already proven they can do this in Texas many times. It doesn't really matter if they tip over over land too hard at sea. What you don't want is that it missed by a mile or cartwheels out of control.
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I thought the main limiting factor of lifting mass to space was also having to carry the fuel with you? SpaceX hauls its fuel to get to space and even extra fuel to land. How are they able to afford to lift the extra mass? Are their engines that much more efficient? I'll stop with the questions marks ;)
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Should be much easier and cheaper. Any non-technical reasons? Tax?
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I don't know all the details, but you are correct.
They lose something like 30% payload capacity (maybe more?) for the reusable option. While this is significant, it means that they can recover the first stage and save enough to make the launch of smaller payloads so much cheaper that it is worth doing. Note that even the Dragon with 1.6 tons of payload seems to count as a 'smaller' payload.
So if they can refly the first stage without spending much time and money on preparing it for the next flight, this will reduce launch costs significantly.
Then for larger payloads, they don't recover the first stage in order to get more payload capacity.
The big question is whether they can refly the first stage without rebuilding the whole thing!
And I don't mean the speed of light kind.
EXACTLY the same as takeoff. NO difference.
Same amount of fuel? No, so not the same moments of inertia. During launch the engine is pushing in the direction of travel, during re-entry no. During launch, the aerodynamics include that nice fairing on the nose, which should be a bit less chaotic than coming engine first down. The period of 1300 m/s travel that you quote and compare to launch is not during launch (0 m/s) - it is probably closer to the period of maximum dynamic load and clearly during super sonic travel. The reverse part of that travel, the period of maximal dynamic load during re-entry in a non-aerodynamic configuration is rather more difficult than getting off the pad.
Except there's no tower to help stabilize if winds kick up, or if you tilt slightly, there's no upward force to keep you going.. CoM is a bigger problem on descent than on launch (though still a problem in either case!!)
Also, when you touch down, if you have any angular momentum... Bowling pins, anyone?
Every time I read a story about the Space-X reusable rocket I can't help but wonder if they have one eye on their stated goal of going to Mars. Landing a whole rocket vertically on the surface of Mars would probably go a long way towards making a return journey feasible.
Long term, this may be really neat.
The long term won't work out unless the short term missions continue to work flawlessly.
Hopefully this experiment will not take any of the focus needed to run the original mission in the ho-hum, just another safe mission mode.
(It's really impressive to run missions in this boring mode BTW!)
The tower drops away BEFORE liftoff.
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The mass is less, and presumably easier to control, but yes, that is a difference.
The relative speeds are the same. Launch starts at 0 and increases to 1300. Landing starts at 1300 and ends at 0.
Actually, that is a small difference. Launch starts at 0, but landing ends at 2 m/s, leaving shock absorbers to reduce it to the final 0.
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But our methods of getting there and back are downright comical...
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The money saved by not having to produce a new vehicle is offset by the money spent on fixed infrastructure and on recovering and refurbishing the vehicle for the next flight. Airline travel is as a cheap as it is because they've gotten between-flights maintenance down to essentially zero (basically only emergent work) - the expensive refurbishment and refitting occurs at intervals of months to years. (And the amortized costs of the facilities for doing so are spread over a large number of aircraft and a very large number of flights.) The Shuttle was expensive as it was because between-flights maintenance costs were very high. (And the amortized costs of the infrastructure were spread over a very small number of vehicles and small number of flights.)
So, if a first stage (new-in-box) costs $x million and refurbishment costs $.9x million (including the amortized portion of the fixed costs), then it'll have to fly ten times just to break even. The break even point calculation is very sensitive to flight rate, flight interval, and the number of vehicles in the fleet. The hope is, over a long time frame, to reach civil aviation levels... but there's a long way to go between here and there. (Particularly in light of the low flight rate of F9 launches that have sufficient spare payload capacity to allow them to be recovered.)
How many times do they expect to be able to use a rocket stage before the increased risk of failure (over a brand new one) causes them to scrap it?
Right, but the sentence you are make fun of is talking about stabilizing the rocket as it is coming back into the atmosphere, ass first in a no longer particularly aerodynamic configuration as it is missing the whole second stage and payload section. Flight stability in the nose going first direction is much better than in the engine going first direction. They are not complaining how hard it is to go that last 10m to the landing; I agree with you that stability control at that point is pretty easy. You know the first attempt they made for power re-entry failed because the axial rotation of the booster caused fuel starvation to the engine due to centrifigal force. Full tanks and no rotation at launch save you from that worry.
And as for less mass being easier to stabilize - can you balance a pencil on your finger? How 'bout a broomstick?
Even if they can only reuse it three times they'll bring down their (already very low for the industry) launch prices by quite a bit. I imagine in the short run they'll give each one a thorough check before they put it back on the pad probably with low level payloads (cube sats, cheap station supplies, etc) at a significant discount. Long term human flights and defense department launches (assuming they get either) will probably get to use brand new booster, more expensive satellites will get to use a second hand booster, and low level payloads will get to use a booster on its third (or more) launch. But as long as they can land them relatively softly there isn't really a reason why the booster structure itself shouldn't be able to handle a dozen or more launches. The engines may need a few parts swapped out every few flights but the bulk of it shouldn't really wear. The biggest thing that I can think of would be fatigue on the fuel transfer lines and tanks from freezing/thawing, I'm sure the tanks are fully integrated so if those start to fail the whole structure would need to be trashed, if the lines start to fail it depends on if they can remove/reinstall them without tearing the structure apart.
One important point that others above have alluded to but haven't outright stated:
While the exponential scaling of rocket equation is an important limiting issue when building larger and larger rockets, for any given rocket (or rocket configuration) the payload capacity is fixed. If you have a payload that is too large for a Falcon 1Pegasus, but doesn't need the full capacity of a Falcon 9, all that extra capacity goes to waste. It costs essentially the same amount to launch a Falcon 9 at 60% capacity as it does to launch it at 90% capacity. You can share payload with multiple customers, but that limits which orbits they can use.
Space X can calculate how much weight the recovery system and fuel requires and how much money they can save by reusing the first stage, and give a discount to customers who give up that additional payload capacity. If there is a market for those lower cost launches, then great. If not, then keep treating the 1st stage as disposable.
I don't know why they just don't land the thing in the water. It seems like waterproofing and preventing corrosion is a lot easier to solve than the controll problem of landing on a barge. Unlike landing on the moon, landing on a barge you have to deal with wind gusts, currents, and waves. A splashdown would leave a larger margin of error and neglect the need for landing gear.
Doesn't work, even with the the shuttles SRB's the difficulties of dredging them out of the water, cleaning all of the salt water out of them and fixing any damage from the impact quickly negates the savings (though part of the problem was halving to ship them between the Atlantic, the Cape & Rail). The problem is compounded when you have a complicated liquid fueled engine and all of its plumbing, electronics, insulation, etc. I even recall several concepts for getting rid of the SRB's and replacing them with liquid fueled boosters that would fly back to Cape Canaveral.
Yes the tower backs away and the holding clamps release. However this happens literally as the rocket blasts away. Have you never watched a a video of a Saturn V launch? Try this one a high speed 500fps 16mm footage from the base of the Apollo 11 rocket. Notice how the holding clamps release to let the rocket move away, which they only do when they get the signal from the onboard systems that all five F1 engines are working properly.
https://www.youtube.com/watch?...
At the point of landing it has become far less top heavy (most of the fuel is gone) and far more bottom heavy (remaining fuel, rocket motors, etc). Remaining upright in all but heavy seas/winds shouldn't be a problem. If they can prove an ability to land at least on the pad with decent frequency they may even be able to add some robotic equipment to quickly secure the rocket or eventually if I were them I'd purchase an old oil platform and outfit it with a full landing & transfer setup.
The recovery infrastructure may cost them a bit up front but I highly doubt the refurb costs be a major factor. All indications point to them designing the Falcon 9 from the ground up for reuse. The failing of the shuttle program was that it became a national symbol, not a transportation system. So they pulled it apart after every flight out of fear that something might fail while ignoring warnings from engineers about possible points of failure (flying in cold weather despite warnings and failure to fix foam issues). Becoming a national symbol also made it an easy place to hang pork, by some estimates I think shuttle refurb, refueling, launch complex maintenance, etc was only in the $200-300M range, the rest of the $1.5B per flight price tag was maintaining of a national network of barely related NASA facilities, massive tracts of land, wildlife programs, R&D & basic scientific research.
The balancing act is almost exactly the same at the last moment of forward flight as it is at the first moment of retro burn, just in a different direction.
Aerodynamics matter very little at high altitude. They matter some at lower altitude, but I doubt they make much difference when the engine is burning.
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White Sands Missile Range is right next to the Spaceport America and has 4,000 square miles of uninhabited desert. The Army tests rockets there all the time, and sometimes closes highway 70 (which passes through the range) when they do. Since the goal of cheaper launch costs is something the miltary would find useful, I am pretty sure Spacex could come to an agreement to do some testing using the range. Before talking to the Army, Spacex would probably want to run several real tests at sea, where they would expect the landings to fail until wthe worked out all of the bugs with the aerodynmics, winds, etc. Not so much to ensure you can land on a ship, but to ensure you can land within a few miles of where you want to. If you can do that, there are lots of places you can land.
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