SpaceX Plans to Land Next Falcon 9 on Solid Ground | Hacker News Reader

SpaceX Plans to Land Next Falcon 9 on Solid Ground

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238 pointspaulsutter132 comments

I think now that they have proven they can 'hit the hole', almost spot on, they'll be able to get approval to go for a try on cleared land space. It sounds like to me, landing on land would be ideal; less expensive and less risk with stabilization and rough waters.

They need to be able to stabilize the rocket's landing in all sorts of conditions if they want to have any hope of landing it on another planet. It's not like interplanetary launches will be able to schedule launches to choose optimal weather conditions for the landing. Maybe, if they're lucky, they'll be able to orbit briefly to avoid bad weather at the landing site, but moderate winds and wind gusts are going to be a problem. If it's impossible to reliably land under those conditions, the whole idea is flawed for the purposes of interplanetary flight. You can't have rockets going to Mars, and only have 50% or 75% surviving for relaunch. That's not the kind of cost reduction that will make interplanetary travel and resupply feasible.

It would obviously help with LEO launch costs, though, or any return landings on Earth. Even if rocket stages are only recovered some of the time, and not reliably, that's a significant cost savings and well worth doing. It's just that Musk is so intent on interplanetary travel driving all this technology. If it's only for cost savings for Earth landings, a parachute system or a specially designed (more accommodating) landing complex/barge could work too, right?

> (paraphrasing multiple comments) "but this is to re-land rocket stages on Earth"

Here's an interview where he specifically talks about his long term goal of landing rocket stages on other planets. He says parachutes negatively affect reusability, I'm not sure how much of that is potential damage or off-site landing and how much is the necessity to reinstall a parachute for the next launch. The point here is that he is clearly not thinking only of Earth landings in developing this technology. I think some sort of assisted landing or more developed landing site could increase chance of recovery and reusability for Earth landings, decreasing total launch costs for Earth orbit missions, at the cost of not being applicable to landings on other planets.

[1] https://www.youtube.com/watch?v=SOpmaLY9XdI?t=11m30s

At the same time, getting to a point where SpaceX has a 10X pricing advantage over there competitors could have a nice effect on their R&D budget for solving problems that may not be immediately applicable on Earth.

> They need to be able to stabilize the rocket's landing in all sorts of conditions if they want to have any hope of landing it on another planet.

Well, not really. Dragons (and Red Dragons, for interplanetary travel) are way, way less sensitive to the whims of weather. The issue with the first stage is that you have a very large, very fragile, very bottom-heavy tin can that you're trying to balance on a moving platform.

This is entirely different than trying to land a pod, which is what we'll be doing on other planets. Dragon v2 will be landing on land (though doing parachute recovery from water for initial CCS missions, as per NASA spec), and we'll see how stable it is then.

On top of that, they are trying to do it with the main engines, combined with the light weight of the almost empty stage..the power can only be reduced so much. They can't hover and stabilize. They literally have to have a landing burn that makes the velocity at height 0... = 0. Which is incredibly hard enough on stable ground, even more on water. Maybe they'll figure out how to cut off engines as the stage slows down so that the acceleration change isn't so drastic and it could actually have a miniature 'abort' land. Where it would go back up slightly to re position itself in the event of weather, wind, rough waters, etc.

> Which is incredibly hard enough on stable ground, even more on water.

I dunno, my Kerbal Space Program experience is that water at least doesn't have mountains to crash into.

If Dragon lands on some other planet, how does it get back without a stage 1 also landing on said planet?

It's refueled in-situ and launched back up with a minimal payload weight. Getting off the surface of Mars back into an orbit with a low weight (basically crew + life support + minimal payload) is pretty straightforward, considering the low gravity and thin atmosphere. From there, you can dock to a much larger tug ship and go back to Earth orbit, refueling on orbit and landing propulsively again.

I didn't spend the time searching google to provide citations, but it is feasible to generate fuel autonomously on the Martian surface and store it for future use.

Can we launch a vehicle that will de-orbit, safely land, and then begin processing fuel using nuclear (edit: I removed solar here; solar would not provide enough power for such a facility) for power and the Martian atmosphere and soil as feedstock? Not quite yet, but we're getting there.

I don't think it is so much an issue of ability so much as desire. Most of the tech has been dreamed up for decades, but it needs funding and a green light (particularly the nuclear reactor, given that there were protests about even Curiosity's RTG).

Personally, I think there's a huge amount of talent just waiting for the right moment to strike, and then the whole Mars thing is going to burst right open.

I believe solar would work, but it would just take longer.

EDL for a substantial payload to Mars hasn't been done before, but there's no reason to think it's a show-stopper. A lot of the engineering challenges for that are the same as the engineering challenges for returning the first-stage to Earth, like supersonic retrorockets.

From what I read around the Internet, they're planning on using methane-powered engines since methane gas is apparently present on Mars.

There's not enough to harvest. The idea is to make the methane.

http://en.wikipedia.org/wiki/Sabatier_reaction

Side note, I'd recommend to you the book "The Martian", which just happens to involve a man stuck on Mars doing about just what you described. I had the audiobook, the narration is crazy awesome.

http://www.audible.com/pd/Sci-Fi-Fantasy/The-Martian-Audiobo...

I agree, but I think right now, even more important, is getting the model for private space flight/exploration right. Currently, the majority of SpaceX's revenue is through government contracts. Cost savings through reuse-ability should be the number one focus, not the technology on how to land on another planet through adverse and unpredictable conditions. The ASDS is really cool and all, and could definitely be something interesting down the road...like a spaceport sitting right off the coast of a major city, ready to take you to the moon hotel...or the other side of the world in under an hour.

But I think achieving major cost savings by landing the rocket in such a way that it could be launched the next day, that should be our first goal right now.

Which is why it makes sense to now attempt an over land landing. They had to make sure it wouldn't miss and accidental land in the middle of Miami or something.

I'm not sure...

Is Miami important to our overall goal of becoming a multiplanetary civilization? I don't see what Miami adds to the mission and I am quite sick of everyone being so precious about it. I have an ex girlfriend from Miami and honestly, I think we would all be better off if we stopped making excuses for her, defending her, covering for her and just let Elon give her what's coming to her!

wow. I guess I overstepped a line.

*I don't really have an ex from Miami. Never been there. No ill wishes for the city. ..just to be clear.

HN does not take well to joke comments. It's not specifically mentioned in the guidelines, but falls generally under "off-topic". Feeling is "this isn't Reddit."

Especially un-funny joke comments. Of course that line is vague and hard to spot, but I'm comfortable in saying that this particular attempt was way on the wrong side of it. I think it could have been rather amusing if it had stopped about a third of the way in.

Well if you're going interplanetary, you could just orbit until the weather conditions on the surface are conducive to landing. It's not like you have to predict the weather eight months ahead of time, you just need to know the rough climate conditions and then orbit until you have a day that lines up.

Yeah, weather is an interesting point. I wonder if having numerous back-up landing sites worldwide would give a robust enough system.

It's been less than 10 minutes from launch to land, so they know exactly where they are going to land when launching.

Uh, we've already had a few near landings in non-ideal Earth weather. Mars barely has weather. It has wind, sure, but the air on Mars is about 150 times less dense. I.e., it won't be blowing over any rockets. So basically, landing anywhere on Mars is easy compared to Earth if they just find a flat spot.

That also makes air-braking more challenging. The first stage isn't coming in at orbital velocities, but I'm assuming they are shedding a good amount of velocity using the air?

The Falcon first stage actually does less aerobraking than a returning capsule. Due to its lack of heat shielding, it's necessary for the first stage to slow its descent with the engines before it hits thicker atmosphere.

Landing is an awful lot harder than taking off, it seems to me; a single engine rocket with stabilizing jets is a bit like trying to land a pogo stick - possible, but inherently problematic. I know this must seem stupidly obvious, but I wonder if a better design for a reusable launch vehicle isn't 4 engines connected by a frame with the payload in the center, basically a chair.

Yeah, it sounds horribly unwieldy with a bunch of structural challenges, but the thing is it's self-stable in a way that a vertical column can never be. A few years ago the wisdom was that small (remote control) helicopters could only be flown stably with a coaxial main rotor. Quadcopters would work in theory, but everyone figured 4 motors on an frame was going to be even more complex to mange and that the stresses on the frame would likely weaken it too much, the power-to-weight ratios wouldn't work out and so on and so on. Now everyone is using quadcopter configurations because they are much easier to control and not actually that difficult to build.

My naive opinion is that output has never quite been consistent enough from rocket to rocket to make the idea of bolting multiple rockets together seem worthwhile unless they were all part of a single fuselage; one of the four would always be putting out too much or too little power and the whole contraption would fly off course in short order. but since the SpaceX rockets depend on liquid rather than solid propellant, and very precise pumping is not that big of an engineering challenge these days, it seems like it should be worth experimenting with on a small scale.

quadcopters I am not an aerodynamics person, but as far as i understand the 4-8 rotor configuration works because of how light the involved tech is/has become. In terms of payload, quads flat out suck. Yes, they are getting better, but currently they cannot haul. I realize we are talking about explosive thrust versus turbine generated thrust, but that alone makes me think this configuration [4 rocket chair] is unfeasible. Just my .02$.

AIUI rockets are tall and thin to reduce the aerodynamic stress on them while they're accelerating. It's not about being worried about them flying apart per se. The Falcon already has 9 engines at the bottom, but they're clustered closely together to fit under a narrow fuselage.

The SuperDraco offers deep throttling down to 20% so it's feasible with SpaceX's current technology (though I'm not quite so sure about throttling the Dracos currently on the F9), though I'm not sure about payload sizes.

A frame with four legs is not self-stable in flight at all. The thrust on all four legs must be identical to prevent rotations, and rotations are not self-cancelling.

Quadcopters must be computer controlled because the control loop must be very tight. Humans cannot fly them without electronic attitude control. It is certainly no easier than the gimbal control of a rocket, which is similar to balancing a stick on your hand. We give that control problem to undergrads as homework.

I thought quad copters were a special case because of their size and because of the simple and controllable electric power-train that doesn't work so well with gas motors. I would imagine rockets have even more lag, and maybe more narrow thrust-efficiency windows than something like gas motors.

I don't think the physics of balancing a rocket on the way down are any different from doing it on the way up.

I'm also not sure where you got the idea that using multiple boosters is a problem. Look up the Atlas 5, Delta IV Heavy, the Space Shuttle, Ariane 5, etc, etc. (And multiple engines on the same booster have been used since the start of the space program.)

Oh, when I said 'part of a single fuselage' boosters was what I had in mind. Sorry in that wasn't clear.

It's always tempting with difficult control problems to imagine why not just do what feels stable? Why not just hold it in place with something? Why not make it shorter and wider? For an example of why not - compare a turtle to a human. The human is inherintely unstable and its vital organs are exposed through weak flesh. If we lose control of our unstable balance, we die when our head hits the ground. The turtle is naturally stable and armor plated! But which one is really best at surviving?

Given that turtles can live for hundreds of years...you tell me ;-)

Tortoises, not turtles.

I don't think they can completely give up on the barge though. As I understand it they'll always need barge landings for the Falcon Heavy core?

Maybe they're just itching to get a success on their pelt.

Why will they always need the barge for the Falcon Heavy core? I think they would be more likely to need it for a second stage than the Heavy's core, because SSECO occurs very far down range, and at such a high speed that the rocket cannot make it back to the launch pad without a great deal of fuel.

Alternatively, they could be planning to launch from Texas, and recover some stage(s) in Florida.

*edit: in another comment on this discussion, kllrohg mentioned that SpaceX's stated intent has been to land all stages back at the launch site.

https://news.ycombinator.com/item?id=9388762

http://www.space.com/13140-spacex-private-reusable-rocket-el....

Falcon Heavy boosters will be able to boost back and land at the pad. Falcon Heavy cores will be too far down range, and will have to land on a barge pretty significantly out to sea.

I agree, as others have said the dynamics of a barge is a necessary challenge to prove the technology. But they need some more positive press, maybe a gif that doesn't end in an explosion hehe.

On a side note the colloquialism 'success on their pelt' is totally new to me, I've always heard it as 'success under their belt'.

I think he meant 'success under their belt'. If you google for both phrases, the belt wins has far more results and they're actually relevant.

I don't believe there is any such idiom. The idiom is "under one's belt", meaning to succeed at something. I have never heard, nor can I locate via Google, any similar idiom using the word "pelt".

Yeah I suspected it was a typo or something, but I kind of like it...

> next attempt to land

Not the next F9 launch. They won't have legs the payload needs all the fuel. Next launch after that is a Dragon test so it isn't that one either. Maybe June we'll see that.

Those ULA comments at the end are very odd and contradictory.

Hmm, I read it as intended - that the next time they will try to land will be on land.

This page is quite a useful (although not 100% accurate) summary of the near-future of SpaceX: http://spacexstats.com/upcoming.php

Certainly interesting that the FCA are willing to try a land-launch before getting a successful landing on the barge.

I think they've ruled out the barge landing at this point. Seems like even with the stabilization, there is still too much movement. I dont see any reason they couldn't bring it back over water onto a landing pad. It should be really easy to keep the landing pad clear.

It is my understanding that the eventual goal has always been to land where they takeoff/launch from.

I never read anything that pointed towards that objective. Note that the first stage gets a lot of horizontal velocity, so bringing it back to the launch pad is expensive (fuel-wise). It is better to just cancel out the horizontal vector, follow a parabolic trajectory and land east of the launch pad.

This is what lead me to believe that:

http://spacenews.com/spacex-leases-cape-canaveral-launch-pad...

https://www.youtube.com/watch?v=4Ca6x4QbpoM

http://www.space.com/13140-spacex-private-reusable-rocket-el...

"After separating in orbit, the two stages of the rocket would come back to Earth and land at the launch pad."

They've always intended both the boosters and the second stage to return to the launch site.

Recent statements indicate that they've given up on second stage recovery for the F9. Just too hard given current margins. That'll be in some future architecture.

It's just the least valuable thing to try to recover. Pick your battles and all that. While a recoverable payload yes its much harder but bringing something back which is valable on top of the spacecraft.

Getting S2 backs seems like 90% of the problems plus some others and not much of a payoff.

Return to Launch Site (RTLS) has been the goal from day one. Yes, it's expensive in terms of payload (about 30%), but SpaceX thinks it's worth it. The cost to fill all tanks is ~$200,000, which pales in comparison to everything else. They will land every rocket they can (determined by how much ΔV the payload requires). I'm quite sure that reusable Falcon Heavy launches will be cheaper than expendable Falcon 9 launches, which incentivizes customers with payloads on the margin to choose the Heavy, which allows SpaceX to return at least 2 cores to the launch site.

(Neat little aside: launches from Florida and Texas can also take slight advantage of the earth rotating beneath the rocket in the direction they want it to.)

I think they want to return to a launch site, just not neccessarily the site that launched the rocket in the first place. AFAIK that's why they want to have multiple sites.

Almost certainly not. They're still working on building a second drone ship on the west coast. Even after they accomplish landings on land, there will still be a need for barge landings in two scenarios: Falcon 9 launches with payloads large enough to prohibit a full boostback burn, and more importantly, Falcon Heavy launches. On the Heavy, the two strap-on boosters will be able to make it back to land but the core stage will be much further downrange and moving much faster, almost certainly necessitating an ocean landing.

According to their events page, 22 July will be the first attempted (to use their phrasing) ``land landing''.

http://spacexstats.com/upcoming.php

That is not an official SpaceX website.

This website is not in any way associated with SpaceX.

That's a fan-run site; not an official schedule.

> "Just purely the boat moving, even in a low sea state, it's hard to imagine that vehicle is going to stay vertical," Shotwell said. "That vehicle is big and tall, compared to the itty-bity-greater-than-a-football-field-size ship."

Is this a new development? This contradicts both a lot of things I read over the Internet (granted, those were not official SpaceX statements) and the apparently still ongoing plans to build a second barge.

IIRC they're anticipating that some missions from Florida will have a performance profile preventing a return to land.

If it's actually that serious a problem (and I'm not a rocket scientist, so I don't know), it suggests a solution: stabilize the landing bed on the ship relative to the sea. Perhaps have the bed float above the ship electromagnetically such that you can control the field strength applied to any part of the platform dynamically as the ship bucks underneath it.

There might be a reason that people don't let me design large mechanical systems...

> There might be a reason that people don't let me design large mechanical systems...

Naah, I can totally see this working in Kerbal Space Program...

Elon Musk actually joked/hinted (in a tweet) that they were making modifications to the barge similar to the flying SHIELD helicarrier.

Heh, for some reason I always felt there's a connection between (Marvel's Cinematic Universe) SHIELD and SpaceX.

Yeah. The entire article seems weird. It also has this:

> the natural instability that occurs when a landing pad floating in the ocean has a very heavy rocket land on top of it has led to a series of near-misses for the technology.

But the two landing failures were due to running out of hydraulic fluid, and to a flight control instability; the landing pad had nothing to do with it.

As has been pointed out almost endlessly over the past day, almost all the mass in the rocket is in the lower end by the time it hits the pad, so despite what anyone can imagine it isn't that hard to keep it vertical.

The hard part is landing it softly enough and vertically enough that it won't break or fall over due to residual velocity. Once it's down, in low seas, the few degrees wobble of the barge won't have an effect.

Or in other words: I can't imagine SpaceX engineers haven't worked all this out in detail, and I can't imagine SpaceX would be trying this if they didn't have good reason to think it would work, and I can't imagine that SpaceX engineers aren't professionally competent, so, based on the standard "what I can't imagine can't be true", Shotwell is spouting irrelevancies.

This is the problem with imaginary arguments: if anyone thinks that what they can or can't imagine is relevant to what is true, they have to yield the argument to me, who can't imagine there is anyone in this day and age who still beleives that.

Well, the point is, Shotwell is the COO of SpaceX, which makes this whole thing weird.

>granted, those were not official SpaceX statements

From the Elon Musk AMA:

Q: How will you secure the first stage of the Falcon 9 to the barge when it lands? Gravity or some mechanism?

A: Mostly gravity. The center of gravity is pretty low for the booster, as all the engines and residual propellant is at the bottom. We are going to weld steel shoes over the landing feet as a precautionary measure

http://www.reddit.com/r/IAmA/comments/2rgsan/i_am_elon_musk_...

Here's a much better quality video of the previous attempt: https://www.youtube.com/watch?v=rAzwuEmZcmE

That thrust vectoring!

Are there any articles or press out there that describe the stabilization tech used on the barge?

A lot of the things when looking through Google seem to focus on the challenges of guiding the rocket but not stabilizing the platform.

I guess it tends to be a non-issue since it seems their plan all along was landing it on land, but I'd be really interested to see the design story that went into the barge.

There is nothing special about the barge stabilization, it's off the shelf marine tech. A few azimuth thrusters controlled by a station keeping system.

The only unusual thing about it is that the azimuth thrusters are a lot more powerful than would normally be put on a barge that size to give it better positional control in rough seas.

I know this was a few days ago, but I forgot to check back. The reason I ask, is that this company http://seakeeper.com/ used to be a customer of mine. It seems like an extremely cool concept and I know it works for smaller vessels and the company is currently developing larger solutions for the government and oil industries.

This is what the SpaceX barge uses:

https://www.thrustmaster.net/out-drive-propulsion-unit/porta...

There are two kinds of stabilization required: Side-to-side, which would use azimuth thrusters, and up-down which can be implemented with SWATH: http://en.wikipedia.org/wiki/Small-waterplane-area_twin_hull

My question isn't really about stabilising the platform, as others have mentioned that should be off the shelf marine tech.

But this isn't exactly landing a helicopter on a ship/platform. I'm expecting a rocket to be a fair bit heavier... as that weight comes down, unless it's perfectly on centre, you now have a large force acting to unbalance the platform. Whilst X-Y may be stabilised, the pitch and the yaw is going to be affected by that weight.

I saw this on the planned launch schedule a few days ago. The date mentioned there is 22 July 2015. I was surprised they were getting clearance to try so soon since they haven't quite nailed sea landings yet. I guess it could be argued they have seem to have the navigation part down pretty well though, minimizing the odds they will drop this in a neighbourhood.

I guess the important part is that they've proven they can hit the target. Thats the risky part of testing over land. One assumes that it's a recognised risk that at the point of actually landing there is a risk of explosion, and a land-based site will account for that.

They haven't gotten clearance yet, but they hope to. Edit: SpaceX page indicates an attempt in July so they must have.

Since they're launching that one out of Vandenberg, maybe the Air Force is more accommodating to crazy schemes like this than NASA is, or maybe the facilities are just ready for it there first.

Does this mean they'll be launching from another facility? Right now, the trajectory goes over to the sea, and bringing the first stage back to dry land is expensive. They'd have to launch far away from the east coast.

Yes, this launch will take place from Vandenberg Air Force Base in California (according to http://spacexstats.com/upcoming.php)

Two factors:

1. Yes, they will eventually be launching elsewhere. SpaceX is currently building its own launch facility in Brownsville, TX, which would indeed permit landing at the cape.

2. Elon Musk seems to think that despite the expense, they can fly the rocket back to the launch pad for lighter payloads.

Florida's an awful long way from Brownsville. Take a look at the launch danger zones chart; first stage recovery is just off the coast. Maybe you could finagle a second stage recovery in Florida from Texas, but only from very specific inclinations. Doesn't seem likely to be useful.

My guess is that once they have their facility operational in TX, they will primarily launch from there, and keep Florida and California as backup options for their clients / use when necessary.

There's a Falcon 9 launch from Vandenberg scheduled for July 22. VAFB is a large coastal installation with lots of room for a return to land.

schedule: http://spaceflightnow.com/launch-schedule/

read near the end of this story for a statement that booster return to land is planned for the July 22 launch:

http://www.nasaspaceflight.com/2015/03/spaceport-america-spa...

Sounds like a July 22nd party in Cape Canaveral is in order?

Vandenberg is actually in California :)

I meant a landing party! :) (I may be wrong about where they intend to land, but see - https://en.wikipedia.org/wiki/File:New_Landing_Complex_1_sig...)

>Jason 3 is a scientific Earth observation satellite designed to monitor and precisely measure the world’s oceans. Falcon 9 will attempt to land back at SLC-4W, marking the first land landing.

http://spacexstats.com/upcoming.php

Instead of moving the rocket to meet the platform, would it be feasible to employ some stabilization mechanism so that the barge stays relatively level and the rocket doesn't have to correct as much?

If the goal is to recover a rocket from LEO, yes. If the goal is to use this as a training mission to land a rocket on another planet, then no.

Landing on another planet with the rocket's first stage?

It does that. The barge has four thrusters for stabilization. The problem is not the barge moving, but rather control problems. They would have happened on land too--unless by landing on a larger area you have a simpler control problem, which may be true.

Someone may have asked this already, but why not use some kind of system similar to "mobile" oil rigs? The kind that float into place, partially submerge, then tether to the sea floor? Seems like the best of both worlds to me...

[edit]...It could also serve as the launching platform. In this way the launch/recovery pad could be floated to the rocket, boarded and built, moved into position near the equator, then launch and recover.

That's what Sea Launch used[1].

Note that the drone ship doubles up as a recovery vehicle to ferry back the stage to land. Also a sea launch platform will be a permanent structure while the drone ship's purpose is to be a test platform for landing on land.

[1] http://en.wikipedia.org/wiki/Sea_Launch

I just love the term "flight termination system". It sounds so much better than "self destruction system" :)

Even cuter term is "range safety" :).

Anyone know how this flight termination system works? Obviously it self-destructs. But, under what parameters? Does Mission Control send the signal, or does the rocket determine this on its own?

The range safety officer has a button that they can press. I'm not sure if the rocket can do it on its own as well.

Somewhat amusingly, the Russians do not use these systems. They launch from the desert in Kazakhstan, so they just let their rockets crash and burn.

My understanding is that there's a bunch of automated triggers --- e.g. if the vehicle leaves its flight corridor, it's supposed to get terminated. That doesn't necessarily mean that it goes bang; for a vehicle like the F9, shutting down all the engines is fine in most circumstances.

However, there is also a Range Safety Officer with a hand on a big red switch (or at least, a metaphorical hand on a metaphorical switch). They're the final authority on whether the vehicle lives or dies.

The shuttle may or may not have had a self-destruct system in the orbiter itself; I'm finding conflicting references. The SRBs and tank certainly did; the RSO pushed the button after Challenger disintegrated on launch to stop the SRBs flying away.

Yes, pushing the button while the SRBs and tank were attached to the orbiter would have killed the crew. Being the RSO is a job for very sober, very thoughtful people.

Mojave Desert seems like a good candidate. I'd let them use my land http://www.ysoheil.com/2014/08/soheils-village.html

What was the % cost reduction in being able to land the boosters again? I read it somewhere a while back but can't find it. It was pretty significant if I recall. TIA.

According to Elon, reusable rockets will drive the spaceflight costs down 100x.

The booster is $60 million, the fuel charge for it is $200k. Other costs are involved in the final price per kg of payload, obviously.

Obviously the math checks out, but I wonder what fraction of the price involves carrying the booster's landing capability (bigger tanks, landing legs, thrusters, bigger booster, etc) to its apogee. I mean that, compared to a single use disposable booster that doesn't carry all that aloft.

30% is the cited figure for a complete return, and is factored into the 100x number.

The first stage accounts for about 75% of the total cost of the Falcon 9, so best case would be a 75% cost reduction. Any refurbishment needed before flying again would reduce that, as well as whatever fixed costs there are for a launch, like fuel, salaries for on-site workers, consumable launch pad equipment, or whatever. Refurbishment is the big wild card. If the rocket is ready to go again with no work then it could come close to that 75% reduction. If it requires extensive work before it can fly again then it could be a lot smaller.

Sweet, thx. That's a pretty big game-changer.

Indeed. SpaceX is already one of the cheaper launchers out there, and cutting their price by 1/2 or 3/4ths would be a huge deal. You can see why everyone is so interested in their crazy barge landing project.

Shouldn't be that surprising. Military has been blowing up missiles and detonating bombs on land at military testing sites for decades.

Let's hope that the next cause of a rapid unscheduled disassembly won't be the rocket landing on a landmine.

Yes but normally these missile and bombs are all isolated to these remote areas. Imagine the rocket is launched from Florida, it might need to fly over populated areas to reach its 'land' landing area, which is different.

How about an oil rig like structure at sea?

Those are expensive structures. Also there probably aren't spares lying around that can be tasked and moved into the range.

Right now there are plenty of spares that can be had for cheap. With oil at $50/bbl and offshore being more expensive than onshore, you can be sure that there are jack up rigs (the kind you want) available. Here is a listing: http://www.worldoils.com/searigs/

This is an old rig which you could probably get for less than scrap value since it's going to take a bunch of effort to break it down into things which you could actually re-melt. http://www.worldoils.com/searigs/jackuprig101.php

Looking here, depending on where you park it that gets you anywhere from a couple of miles offshore up to say 100 or more. It depends on the topography of the ocean's floor. http://maps.ngdc.noaa.gov/viewers/bathymetry/

Im pretty sure an oil rig with a completely flat deck would be an ideal platform, at least for sea landings. However they are extremely expensive.

Dumb question: why can't they land (drop) into a large pool filled with some inert liquid?

Once that inert liquid is into every single component on the engine how do you safely and cost efficiently remove it?

What inert liquid wouldn't vapourise at least partially under the force of a rocket engine?

Mostly though you can't find a nice friendly pool of inert liquid on Mars or anywhere else but the Earth in our solar system ;).

Probably because a rocket engine is pretty hot on landing, so the thermal shock upon contact with the liquid would deform it or cause cracks.

There's no pool of inert liquid on Mars.

When you look at any design out of SpaceX, you need to keep in mind the fact that Elon himself drives the requirement of 'this has to help humans get to Mars'. It extends through the Falcon, the Dragon and a whole heap of other aspects of what they do.

Land the rocket on some flame-proof air bags. It doesn't have to land vertically does it? Let it fall over gently if need be.

No flame-proof airbags are available on Mars.

AFAIK most of SpaceX's design decisions are based around this.

But can't the vehicle carry them to Mars? Kind of like the airbag system for one of the rovers, can't remember which one (Curiosity?)

Or even better, how about getting it to land sideways on purpose? I don't see how that would be more difficult than doing it upright.

Imagine the material that a coke can is made off.

Now imagine a cylinder made of that material 3-4 times wider than a barrel and 20-30ft high.

That's why you can't land them sideways they'd just crush themselves.

I guess you are right. It wouldn't make sense to make a rocket that can withstand vertical AND horizontal forces. That would be like launching a brick I guess.

Thanks for the pointer.

The dang thing is a couple mm thick and ten stories tall. There's no "gentle" option available for tipping over. The solution is to land it right. It'll happen.

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