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  #51  
Old 12-23-2015, 07:11 AM
Gorsnak Gorsnak is offline
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Originally Posted by Alessan View Post
I posit that one reason rocket parts have historically been so fragile is that up until now, no-one has ever had any reason to design them otherwise. Now they do.
Well, that's certainly one reason, but the other reason given by Stranger is sufficient all on its own. Lower mass is so far up the list of design parameters for orbital rockets that the others are barely on the same page. Every gram spent on something other than fuel is a gram of payload capacity you've lost.
  #52  
Old 12-23-2015, 03:13 PM
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Every gram spent on something other than fuel is a gram of payload capacity you've lost.
That's only true on the final stage. The ratio is much less on the boost stage(s).

SpaceX has said that second-stage resusability is a ways off for just this reason. The heat shields and stuff you need to deorbit are also heavy.

The first stage has much more comfortable margins. They can afford to have landing legs, aerodynamic controls, and reserve fuel. A gram spent here is only 0.2 grams lost on the payload.
  #53  
Old 12-23-2015, 03:40 PM
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Originally Posted by Dr. Strangelove View Post
That's only true on the final stage. The ratio is much less on the boost stage(s).

SpaceX has said that second-stage resusability is a ways off for just this reason. The heat shields and stuff you need to deorbit are also heavy.

The first stage has much more comfortable margins. They can afford to have landing legs, aerodynamic controls, and reserve fuel. A gram spent here is only 0.2 grams lost on the payload.
Interesting.

Is it the same engine on the second stage (but fewer of them) as on the first stage. Maybe the plan is to put new engines on the first stage, reuse them, and as they get near the end of their design life put them on the second stage.
  #54  
Old 12-23-2015, 04:19 PM
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Is it the same engine on the second stage (but fewer of them) as on the first stage. Maybe the plan is to put new engines on the first stage, reuse them, and as they get near the end of their design life put them on the second stage.
It's a very similar engine. The first stage uses nine Merlin 1D (M1D) engines, while the second uses a single Merlin 1D Vacuum (M1DVac) engine. The most obvious difference between the two is that the M1DVac has a very large nozzle bell to take advantage of the vacuum environment. Larger bell => more exhaust expansion => higher thrust => higher efficiency.

I would be surprised if the M1D could be converted to a M1DVac, however. I'm sure the differences are more significant than bolting on a new bell. Also, reliability is more important on the second stage--whereas the first stage can afford to lose an engine for a significant part of the flight envelope, if the second stage loses the engine it's all over.
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Old 12-23-2015, 05:29 PM
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Originally Posted by Dr. Strangelove View Post
It's a very similar engine. The first stage uses nine Merlin 1D (M1D) engines, while the second uses a single Merlin 1D Vacuum (M1DVac) engine. The most obvious difference between the two is that the M1DVac has a very large nozzle bell to take advantage of the vacuum environment. Larger bell => more exhaust expansion => higher thrust => higher efficiency.

I would be surprised if the M1D could be converted to a M1DVac, however. I'm sure the differences are more significant than bolting on a new bell. Also, reliability is more important on the second stage--whereas the first stage can afford to lose an engine for a significant part of the flight envelope, if the second stage loses the engine it's all over.
It can't be converted. The shape of the nozzle and combustion chamber is different, it's not just a matter of bolting a larger bell on, and you can't really replace the combustion chamber without essentially rebuilding the entire engine anyway. Maybe they could re-use some of the parts, valves and electronics and other small bits, but I expect they probably won't.
  #56  
Old 12-23-2015, 06:01 PM
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It can't be converted. The shape of the nozzle and combustion chamber is different, it's not just a matter of bolting a larger bell on, and you can't really replace the combustion chamber without essentially rebuilding the entire engine anyway. Maybe they could re-use some of the parts, valves and electronics and other small bits, but I expect they probably won't.
Yeah, this doesn't surprise me. In principle, they could have designed the M1Vac to be something very close to "bolt on a new bell", with some attendant loss of efficiency, but there's really not much point to it. Most of the complexity is in the turbopumps and such, which are common, but at the same time you're right that swapping out the combustion chamber would entail a full rebuild.

SpaceX has a quite detailed guide to their rocket here. I've actually yet to do more than skim it, but it has an impressive amount of information.
  #57  
Old 12-23-2015, 06:42 PM
Stranger On A Train Stranger On A Train is offline
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There aren't enough public details to say how much SpaceX has been able to simplify their ground operations. The few public bits are promising, however. For instance, SpaceX avoids the use of pyrotechnic fasteners. Although straightforward to use, they are one shot deals and can't be reused. They're also unsuitable for non-destructive ground testing. Similarly, SpaceX uses pneumatic actuators for the stage separators and nitrogen cold gas thrusters for the ullage motors, as compared to the more usual solid motors.
Pneumatic actuators are used for payload deployment or regulated delta-V in many vehicles, as are cold gas (typically N2) thrusters; this is in no way an innovation of SpaceX. The notion that a reusable delatching or actuating device must be more reliable than a one-shot pyrotechnic or or combustion device seems intuitive at the layperson level from the standpoint of being able to verify function, but in fact the opposite is true. I can address this topic in some depth insofar as I began my aerospace career designing mechanical delatching/latchup mechanisms and later worked with a wide range of pyrotechnic initiators, actuators, and separation/cutting/penetrating mechanisms.

Purely mechanical (non-pyrotechnic or non-mechatronic) mechanisms for latching and delatching have two ostensible states; open and closed (or latched and released, or whatever nomenclature the program uses). However, a mechanism with loose enough tolerances to function without binding may often have a range of various states in which it may settle, and these can have different stored and initiation energy states which are different enough to require separate characterization. In addition, the action of a latching mechanism in releasing stored energy is highly dynamic, to the point that normal mechanism analysis (which generally assumes quasi-rigid or linear elastic response) fails. Mechanisms released or actuated under load often see high stress and exhibit highly nonlinear mechanical behavior; linkages twist or flex, surfaces may experience such extreme friction that they reach melting temperatures, et cetera. Mechanisms are often very sensitive to random vibration, high shock, and coefficient of thermal expansion (CTE) environments. Under repeated actuation, mechanisms often exhibit significant wear which may change the degree of stored energy or the required initiation energy. Any change to the design or variation in manufacture or materials can also have a significant change to the behavior of the mechanism. Do you like the subdued but meaty "clunk" your car door makes when you close it? That's the result of several tens of thousands of person-hours to get that particular effect, and that is a mechanism that operates under just a few foot-pounds of received or stored energy. A device to restrain and release a separation ring or large payload fairing will operate with hundreds or thousands of foot-pounds of stored energy. In addition, most commanded actuation systems require a power source, which is frequently hydraulic or pneumatic in nature. This requires a pressurized system and pressure lines to each mechanism, which adds mass and complexity with the attendant reliability concerns. (Loss of pressurization or pressure anomalies probably make up at least a third of actual mechanical flight anomalies that I've seen; pressurized systems are some of the least reliable and most failure prone systems on a launch vehicle.) In the case of simultaneous or time sequenced release, multiple mechanisms such as fairing delatch are extremely difficult to develop.

Pyrotechnic systems, while not capable of pre-use functional verification, are relatively simple. The typical initiation requirements are just electrical leads to an initiator or interface to an ordnance transfer line. Pyrotechnics, as one shot devices, can be designed to operate with high energy margins since you don't have to worry about over-stroking or buckling a reusable mechanism (although the desire to limit the shock response or contain debris may limit the energy input). It is also almost trivial to design a pyrotechnic system with redundancy. Although you can't functionally test a pyrotechnic without expending it, good quality control and lot acceptance testing (LAT) has resulted in modern pyrotechnic devices that are exceedingly reliable. As an example, the NASA Standard Initiator (NSI), an initiator that NASA uses in virtually all pyrotechnic applications consisting of a threaded housing, hermetically sealed charge, hot bridgewire-initiatied charge, and four pin electrical interface, has been build and functioned in quantity exceeding hundreds of thousands of units, and it may be the single most produced aerospace ordnance device in existence. As far as I'm aware, there have only been two instances of a failure attributed to defect or inadequate function of the NSI, and both of these in testing under extreme cold (-290 °F) conditions. (There have been other failures associated with the use of the NSI but those are all attributable to incorrect application and or requirements mismatch.) A R=0.99998 realized reliability in a purely mechanical mechanism operating under such extreme conditions and stored energy would be ambitious to say the least.

There are legitimate reasons to eschew pyrotechnics; specifically, the personnel hazards (both real and presumed), the ESD concerns with pyrotechnic systems, the cost associated with lot acceptance testing; the cost to reject and destroy an entire production lot that fails testing; the high shock response conditions resulting from an ordnance device, et cetera, but the presumption of reliability isn't among them.

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Originally Posted by Dr. Strangelove View Post
The ideal is a rocket where you can press a button, it does a bunch of self-tests, and when it says OK you have high confidence that it will succeed. I'm sure SpaceX is still a ways off from this, but it's been a goal of theirs from the very beginning.
As it happens, there is well-known launch vehicle contractor that aimed to do just this with a specific, now quasi-retired launch system. They built an elaborate set of self-testing and self-diagnostic systems which attempted to identify problems as all stages of integration. The system actually more-or-less worked as advertised insofar as reducing diagnostic efforts. The problem, however, was that the focus of effort then shifted to getting the diagnostic systems to work correctly and debugging the issues it came up with, and the contractor did not end up saving any money or reducing the time to launch cycle. The ultimate lack of success of the system (both in terms of not reducing cost, and actual mission failures not related to problems with the vehicle integration) rendered their efforts moot, but even if they had continued it wasn't clear that there would be a significant savings. The fundamental flaw is that in trying to implement this automation they added to the complexity rather than removed it. Any real approach to reducing cost and effort needs to focus first and foremost on simplicity; reducing the number of operations and functions in order to reduce potential for failure. Adding more systems to increase reliability is like fucking for virginity; it just doesn't give you the result you are aiming for even if it is fun doing it.

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I posit that one reason rocket parts have historically been so fragile is that up until now, no-one has ever had any reason to design them otherwise. Now they do.
"Rocket parts" are not "fragile"; most components on a rocket (save for the delicate avionics that are unavoidably sensitive to dynamic and thermal environments) have higher margins than many parts on your automobile or household tools. However, they experience very high environments that are vastly beyond the normal experience of any ground based equipment. For instance, the MIL-STD-810G most aggressive transportation vibration test profile has an overall room mean acceleration level of 4.43 gRMS up to 500 Hz. (The root mean acceleration is the square root of the sum of the acceleration power spectral density; basically, a measure of how much overall acceleration per unit octave fraction of spectral bandwidth in the vibration profile.) The NASA General Environmental Verification Standard (GEVS) requires a bare minimum vibration test profile of 6.8 gRMS (Table 2.4-4) and recommends qualification at a level of 14.1 gRMS and acceptance at 10.0 gRMS. In practice, we often see levels on primary structure-mounted components exceeding 24 gRMS and I've seen measured levels up in the 60 gRMS range. In other words, the kind of vibration conditions experienced by launch vehicles are 2 to 15 times as much as that experienced by anything in a ground vehicle driving on the worst washboard road conditions. Shock response can be even worse; the highest shocks in any non-ordnance terrestrial application tend to be around 700 g at 1000 Hz. I've seen MPE shock environments on flight vehicles (due to the aforementioned pyrotechnic separation systems) that exceed 50,000 g at 900 Hz and climbing thereafter at the environment source (usually attenuated by distance and traverse through sprung joints).

Components on launch vehicles are not designed for "infinite life" per se, but they are designed to be as robust as feasible given the mass and volumetric envelope constraints. The problem with reuse isn't that component design is weak; it is that rocket launch vehicles operate at the basic limits of the materials being used, and making them more robust entails adding significantly more mass, which is detrimental to the essential function of a rocket, e.g. carry payload to orbit. The focus on reusability as some kind of game changer is based on the presumption that rockets can be designed for long (if not infinite) life the way airliners are. But even in extreme operations airliners are not exposed to the kinds of conditions and loads that that are experienced by a rocket during any flight. Complaining that we should make rocket launch vehicles capable of surviving repeated flights without refurbishment is like suggesting that we should genetically modify chickens to lay eggs that can withstand being dropped from six feet onto concrete; you might be able to do it, but the result isn't going to have much utility as an egg insofar as you are going to need a bandsaw to open the thing.

The actual cost of building the physical hardware, while not insignificant, is not the driving cost of a launch vehicle. Actual fabrication costs on systems that I've reviewed are somewhere about 10% of the total launch cost. The cost of propellant is typically less than 1% for RP-1/LOx. The real costs is all of the effort that goes into mission analysis and verification, and the integration and testing of building up the vehicle and assuring that it functions correctly. Vehicle reuse, by itself, doesn't save much if any of this cost. The savings to be had is in simplifying and automatic (as much as reasonably possible without adding complexity) the processing and integration process, and spreading the amortized costs of manufacturing and launch facilities across as many launches as possible.

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Originally Posted by Robot Arm View Post
Is it the same engine on the second stage (but fewer of them) as on the first stage. Maybe the plan is to put new engines on the first stage, reuse them, and as they get near the end of their design life put them on the second stage.
While the Merlin Vac-D (second stage engine) is of the same essential construction and heritage as the Merlin 1-D (first stage engines), they are different engines with different functional requirements. The MVac-D is optimized for vacuum operations, so it has a number of physical differences. Nor would it make sense to put a previously used engine with potential damage into a critical upper stage application where any engine failure or even reduced function may result in a complete mission failure. Rocket components are not Tinkertoys, and unlike Kerbal Space Program, you can't just swap out components or put in a bunch of struts to make things work and not break.

Stranger
  #58  
Old 12-23-2015, 07:33 PM
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To be clear, I did not intend to imply that pneumatic actuators, cold gas thrusters, etc. were SpaceX innovations. My point was that when given the choice, SpaceX has always chosen resettable systems. If we want to call something an innovation, it is their design philosophy, as opposed to the design of any particular subsystem.

I also did not mean to imply that resettable systems were somehow fundamentally more reliable than one-shot devices. The difference is in how you verify that a particular part will work. As you note, there are high costs involved with lot acceptance testing and the other mechanisms you need to ensure reliability for one-shot devices. Resettable systems are more forgiving.

As you've noted before, the same difference exists between solid vs. liquid fueled rockets. Solid boosters are more reliable than liquid in actual practice. But this reliability comes at great cost as compared to liquid fueled engines, which can (usually) be tested via static firing (the Lunar Module Ascent Engine notwithstanding).

At any rate, I do appreciate the detailed response.

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Originally Posted by Stranger On A Train View Post
As it happens, there is well-known launch vehicle contractor that aimed to do just this with a specific, now quasi-retired launch system. They built an elaborate set of self-testing and self-diagnostic systems which attempted to identify problems as all stages of integration. The system actually more-or-less worked as advertised insofar as reducing diagnostic efforts. ... The fundamental flaw is that in trying to implement this automation they added to the complexity rather than removed it. Any real approach to reducing cost and effort needs to focus first and foremost on simplicity; reducing the number of operations and functions in order to reduce potential for failure.
Interesting. Now I'm curious who you're talking about...

I certainly agree with the simplicity aspect, with a caveat. One shouldn't just look at a parts count to conclude that one system is simpler than another. It is just as important to look at commonality. Which is simpler: a rocket with a single staged-combustion engine, or one with nine gas generator engines? The latter certainly has more parts, but the former has more unique parts, and those parts are subject to harsher conditions.

On the F9, the pneumatic pushers are certainly more complicated than pyrotechnics. But perhaps not as much as one would think, since it uses the existing high-pressure helium system. Helium is complicated and tricky, but in the F9 is used for at least four subsystems: pushers, latch release, tank pressurization, and grid fin hydraulic pressurization. They amortize the cost of the system over several applications, and when they test it, it increases their confidence in the function of all dependent subsystems.

I do know that the DC-X project had a high focus on automated ground operations, and supposedly required only three support personnel. It's too bad the project was cancelled, but I think that at least some of the lessons carried over to other parties.
  #59  
Old 12-23-2015, 07:38 PM
race_to_the_bottom race_to_the_bottom is offline
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OK, it's cool that the landing was technically possible and that it was successful. But how much does it save? I recall NASA overselling the hell out of the savings of the reusable shuttle and its reusable boosters, so let's say you use the first stage 100 times. Between the extra cost to build in the capability to land and the cost of refurbishing after every use, what percent of the launch cost can be saved by using this?
The shuttle was a bad idea. There was no escape tower for the crew if the launch went bad. That meant there could be almost no margin for error. It carries heavy wings and landing gear all the way to orbit. It was said that the three main engines running liquid hydrogen and LOX were really screaming and on the high end of what was safe. Then they dumped the solid boosters in the ocean, which could not have been good.
  #60  
Old 12-23-2015, 08:47 PM
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Stranger, that was all fascinating. Tomorrow morning, when I hear/feel the "subdued but meaty clunk" of my car door closing, I'll pay a momentary silent homage to the many whose man-hours created that; and I'll enjoy presuming to make too much of the tenuous (but real) link between this and the engineering of great rocket systems.
  #61  
Old 12-23-2015, 10:36 PM
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A bit of math for anyone wondering what makes SpaceX's achievement so much more significant than Blue Origin's.

The Blue Origin New Shepard delivered a capsule to 100.5 km with no significant lateral velocity. Although they have not given the mass of the capsule, we can guess that it's around 5000 kg (based on similar capsules). This corresponds to a delivered payload energy of 4.9 GJ.

The SpaceX booster delivered the second stage of the rocket as its payload. At separation the payload was moving at about 1.67 km/s and 75 km altitude. It weighed ~105,000 kg. The sum of potential and kinetic energy delivered to the payload is thus about 224 GJ.

That's a factor of over 45x. Although Blue Origin's efforts are respectable, there's just no comparison in scale.
  #62  
Old 12-24-2015, 10:09 AM
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Originally Posted by Dr. Strangelove View Post
A bit of math for anyone wondering what makes SpaceX's achievement so much more significant than Blue Origin's.

The Blue Origin New Shepard delivered a capsule to 100.5 km with no significant lateral velocity. Although they have not given the mass of the capsule, we can guess that it's around 5000 kg (based on similar capsules). This corresponds to a delivered payload energy of 4.9 GJ.

The SpaceX booster delivered the second stage of the rocket as its payload. At separation the payload was moving at about 1.67 km/s and 75 km altitude. It weighed ~105,000 kg. The sum of potential and kinetic energy delivered to the payload is thus about 224 GJ.

That's a factor of over 45x. Although Blue Origin's efforts are respectable, there's just no comparison in scale.
A good diagram here to accompany your math.

Note too that the New Shepard has about 100K pounds of thrust, whereas the Falcon 9 has about 1.5M pounds of thrust.
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Old 12-24-2015, 10:39 AM
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Quite an accomplishment for both companies, to land the booster.
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Old 12-24-2015, 04:58 PM
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Maybe the difference between the two companies is:

Blue Origin views the Kármán line as the destination;
Space-X views it as a starting point
  #65  
Old 12-25-2015, 06:38 PM
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Changed the title as you asked.
Thanks!

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I don't know about cost effectiveness and yada yada blah blah, but that was incredibly cool! Is it overstating this to compare it with first stepping on the moon?
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It's not often you know the import of what you're seeing.

That's Kitty Hawk. That's one giant leap. That's a damned 21st-century Wonder of the World.
It's hard to say where this stacks up in terms of historical achievements. Maybe it's like breaking the sound barrier: a tremendous technical and scientific breakthrough, with a lot of military applications, but so far not very useful for commercial transportation. Or maybe it's like the Ekranoplans: impressive beasts that were a technological dead end.

In any case, it'll be fascinating to watch SpaceX and all the other new and reinvigorated aerospace development in the coming decades.

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Maybe the difference between the two companies is:

Blue Origin views the Kármán line as the destination;
Space-X views it as a starting point
I think that's not at all fair. Yes, the landing of the Falcon 9 booster is far more impressive than landing the New Shepherd suborbital launch vehicle. However, Blue Origin is playing a longer game, and certainly won't stop with the world's greatest amusement park ride.

For instance, for the New Shepherd they designed a state-of-the-art cryogenic engine fueled by liquid hydrogen. It is needlessly complicated and hard to develop for just a few suborbital hops. But it is exactly the sort of high-performance engine that will be useful for upper stages, and it may end up in the second stage of ULA's Vulcan next-generation heavy lift vehicle. Similarly, Blue Origin is also developing a much larger methane-powered engine suitable for heavy lift vehicles, and it has been selected for the Vulcan first stage. In the long term, Blue Origin also plans to develop their own reusable heavy lift launchers, in direct competition with the Falcon 9 (and oddly enough the Vulcan).

Suborbital hops for tourists will just be a side business for Blue Origin to help fund further development. Blue Origin and SpaceX are both advancing the state of the art at least as much as any other aerospace company in the last few decades.

Last edited by lazybratsche; 12-25-2015 at 06:39 PM.
  #66  
Old 12-25-2015, 09:56 PM
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Reading the Wiki on the "Vulcan"*, it seems like vaporware.

Once SpaceX raised the bar, they came up with their own "reusable" scheme (can't make this up):

"A later feature is planned to make the first stage partly reusable. ULA plans to develop the technology to allow the engines to detach from the vehicle after cutoff, descend through the atmosphere with a heat shield and parachute, and finally be captured by a helicopter in mid-air..."

"and then a giant eagle will grab us and we'll fly away!"

It seems ULA can't get Congressional funding for more than a year or so at a time, but it is now going to "co-develop" the methane engine with Blue Origin.

They think they might fly in 2019.

This is not a "long" game - it is a SLOW game (IMHO).




* - Can't make this up - "Vulcan" was chosen by "an on-line poll"; an organization called, oddly enough, Vulcan Inc., objected. How the Hell do you announce a name without even googling it first?

Last edited by usedtobe; 12-25-2015 at 09:57 PM.
  #67  
Old 12-26-2015, 12:05 AM
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"A later feature is planned to make the first stage partly reusable. ULA plans to develop the technology to allow the engines to detach from the vehicle after cutoff, descend through the atmosphere with a heat shield and parachute, and finally be captured by a helicopter in mid-air..."

"and then a giant eagle will grab us and we'll fly away!"
Not as far fetched as it sounds. The Corona spy satellites of the 1960s ejected a film canister that was meant to be snagged in mid-air. It's been tried a few other times as well.
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Old 12-26-2015, 12:56 AM
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Snagging a film canister is a bit different than snagging rocket engines.

And the only reason they added the "We can recover (some of) the first stage, too!" is SpaceX.
  #69  
Old 12-26-2015, 01:07 AM
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ULA is comprised of Boeing and Lockheed Martin - the guys who made the NASA rigs back when NASA had unlimited budget.

Why did they pair up, and why are they dependent on Congressional Budgets?
I take it neither wants to fund the "Next Generation" rocket out of their own pockets (they just bought another 20 engines FROM Russia) and it is simply budget constraints that make them pair up with Blue Origin and hope the methane engine is ready before Congress prohibits buying more engines from Russia.

Meanwhile, their launches are slated to use Atlas V rockets.

Maybe 2019 will see something new...
  #70  
Old 12-27-2015, 05:46 PM
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Why did they pair up, and why are they dependent on Congressional Budgets?
I think their argument was that they were splitting a small market: neither Boeing nor Lockmart was competitive for commercial markets, and government launches were limited to the US. They couldn't both survive on this, so they merged.

Of course they ended up with a temporary monopoly, which they seem to have taken advantage of. No one was particularly happy about it, but the DoD also didn't want to see either company collapse, so they saw a merger as the least worst option.

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I take it neither wants to fund the "Next Generation" rocket out of their own pockets (they just bought another 20 engines FROM Russia) and it is simply budget constraints that make them pair up with Blue Origin and hope the methane engine is ready before Congress prohibits buying more engines from Russia.
They also simply don't have the in-house expertise to develop their own engine. Of course, this is their own doing--they could have anticipated the possibility that business with the Russians might come to an end, and formed a propulsion group, but they didn't. SpaceX went from zero to a working orbital engine in 6 years; Blue Origin took perhaps a decade, depending on how you count it (which is still respectable, since the BE engine is more advanced than SpaceX's). Regardless, had ULA set this as a goal when formed, they could have had an alternative by now.

So yeah, it's the usual. Don't do anything until you absolutely have to, and certainly not unless someone else is picking up the tab. Great strategy in the pre-SpaceX days. At least they still have the heavy launch market, though that won't likely keep until 2019, even if Falcon Heavy is delayed a bit more.
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Old 12-28-2015, 01:45 AM
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So ULA is going to keep making clones of 'Glory Days' rockets and let SpaceX have the bulk of commercial launches.

They are following in the footsteps of the Big 3 US automakers - just ignore the good-and-getting-better imports until you are bankrupt, then run to Congress for protection.

But, for about 3 launches/decade, they have the market all to themselves. For now.

Just as Detroit has the USPS as a captive market.

Sad. Really sad.
  #72  
Old 12-28-2015, 02:33 AM
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To be fair to ULA, do you get something for the money: incredible reliability. Conservative engineering does have certain advantages. It just happens to be a dying business model.

It's also not guaranteed that Congress will come in and save the day. The Russians are the bad guys again. It doesn't look good to the constituency when you have to go hat-in-hand to them to buy your engines.

I dunno. Maybe Tory Bruno will pull something out of his sleeve. Maybe they'll genuinely reinvent themselves into a more nimble company. I'm not optimistic, but they certainly have plenty of talent left, so it's not utterly impossible.
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Old 01-15-2016, 08:00 PM
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Bumped for the next launch and assorted news:

SpaceX released a slick recap video of the launch and landing, including some previously unreleased footage of the final moments before landing.

The next Falcon 9 launch is scheduled for 10:42 AM PST from Vandenberg Air Force Base, carrying the Jason3 NOAA ocean monitoring satellite. For this launch the first stage will attempt another barge landing (I've heard that SpaceX doesn't yet have approval to land at Vandenberg). The launch should be streamed by both NASA and SpaceX, though with a barge in the middle of the ocean there probably won't be any live streaming of the landing.

During the Jason3 press conference, someone mentioned that the landed first stage from the previous launch completed a successful static fire. It seems to have had minimal refurbishment, as it's been photographed by space paparazzi reporters being towed and erected on the launch pad in all its scorched glory.

In related news, NASA has awarded the contracts for the next round of commercial resupply missions, supplying the ISS between 2019 and 2024. SpaceX and Orbital ATK, which are currently flying resupply missions, were selected. More surprisingly, Sierra Nevada was also selected, and it will use a cargo variant of the Dreamchaser spaceplane launched on Atlas 5. This means there will be three very different spacecraft launched on three different rockets. Each supplier was awarded a guaranteed 6 missions, but after that it seems that NASA will have the flexibility to select whichever can give them the capability they need at the best price.
  #74  
Old 01-15-2016, 08:09 PM
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If I can motivate myself to wake up at 5:30 in the goddamned morning (4 hr drive to make 10:42 AM launch + margin), I'm going to try to visit Vandenberg for the launch. Despite several attempts, I have yet to view an actual rocket launch. Too bad it won't be a return to launch site, but should be cool nevertheless.

Pretty cool that the static fire was successful, though not hugely surprising. The center engine already restarted itself successfully three times in flight after the main burn. Still, it's good to know that there was no additional damage after the final burn.

I really like this shot of the landed stage. Sooty, flecked paint, and obviously through a rough ride--and yet ready to go again.
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Old 01-17-2016, 02:56 PM
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Apparently, some combination of the rocket coming in too fast and the choppiness of the water affecting the landing platform resulted in one of the lander legs breaking. Not sure if this resulted in the rocket itself tipping over or not (there isn't any video of the landing itself yet for whatever reason, even though they have a camera right on the landing platform), but they're making it sound like the landing was not a success.
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Old 01-17-2016, 03:04 PM
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Anyone know why they try to land on a barge?

Do they not have permission to land on ground? It is my understanding that the ground landing created a sonic boom. One more sonic boom in the middle of a desert isn't going to be a big deal, so why the increased risk?

Is there some long-range plan to make their rockets able to launch from anywhere in the world, and the go-anywhere-there's-water barge would provide flexibility?
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Old 01-17-2016, 04:54 PM
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SpaceX tweets indicate that there was a soft, on-target landing, but the lock mechanism on one of the landing leg failed and the rocket tipped over. Looks like most of the business end is still on the barge! No official indication that the rough seas caused the failure. Future versions of the Falcon 9 are supposed to have upgraded legs.

But the most important thing, if not the most exciting, is that the payload made it to orbit. Even if SpaceX achieves economical reusability, they're reducing costs of expendable rockets and shaking up the entire launch industry.

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Anyone know why they try to land on a barge?

Do they not have permission to land on ground? It is my understanding that the ground landing created a sonic boom. One more sonic boom in the middle of a desert isn't going to be a big deal, so why the increased risk?

Is there some long-range plan to make their rockets able to launch from anywhere in the world, and the go-anywhere-there's-water barge would provide flexibility?

This launch almost certainly had the ability to land back at the launch site, given that the payload was only 550 kg. The latest version of the Falcon 9 should be able to return to the landing site with more than a 10,000 kg payload to low earth orbit. However, SpaceX didn't yet have approval to land at Vandenburg Air Force Base, and it appears that approval has to be granted by the FAA and the Air Force or NASA for each site. After all, each landing attempt can have a different trajectory with different property risks.

In the future, SpaceX is still planning to do barge landing whenever the payload is too heavy to allow return to launch site. This will be the case for the upcoming launch of the SES-9 geosynchronous communications satellite. It's a fairly heavy satellite, at 5,330 kg, and is going to a much higher orbit than Jason3. While there aren't any up-to-date official payload figures, some people have estimated that the Falcon 9 should be able to return to landing site with geosynchronous satellites less than 4,500 kg. Also, with the Falcon Heavy the central core will almost always be to far down range and traveling too fast to return to the landing site.

Last edited by lazybratsche; 01-17-2016 at 04:56 PM.
  #78  
Old 01-17-2016, 11:21 PM
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Just got back from Vandenberg. Sadly, I am now zero for three in getting to see launches. We heard the launch just fine--which was still very impressive--but we were fogged out and didn't even see an engine glow. Oh well.

There's a video of the landing out now. Pretty clearly a soft touchdown, but the one leg collapsed and it tipped over.

Elon is speculating that the heavy fog resulted in ice buildup around a steel collet that locks the leg into place. Seems... plausible.
  #79  
Old 01-18-2016, 05:15 PM
Hooleehootoo Hooleehootoo is offline
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Why doesn't the autonomous spaceport drone ship have a safety net?

The latest attempt did not succeed because a landing leg failed, causing the rocket to fall over. Why not keep it from hitting the deck of the ASDS with a net? I have in mind something in the shape of an inverted conical frustum. Off the top of my head, I guess it is because they would worry that the danger of it entangling the rocket is worse than having it salvage abnormal landings.

However, it seems like you could have the net be flat, or even at a downward angle from the deck of the ASDS. Then the Falcon would only tangle with the net when it completely misses the barge, so nothing is lost in the bargain (assuming the F9 is not able to increase its height and maneuver back to a height above the deck in case it reached this position). You would only erect the saftey net when the Falcon 9 is over the deck. It would be like the reverse of a flower opening.

The height of an F9 is such that it can fit lengthwise on the ASDS, so the idea can't work simply with rectangular pieces folding up from the sides, but ...? Maybe there could be several nets embedded in the deck and you hoist up the right one based on where the F9 is landing.

Elon, will you co-list me on the patent application ?
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Old 01-18-2016, 05:19 PM
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I think it would be much easier to simply re-design the legs...
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Old 01-18-2016, 08:08 PM
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The latest attempt did not succeed because a landing leg failed, causing the rocket to fall over. Why not keep it from hitting the deck of the ASDS with a net?
I suspect that the momentum involved would be more than a net could handle to not damage the rocket.
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Old 01-18-2016, 09:47 PM
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Anyone know why they try to land on a barge?

Is there some long-range plan to make their rockets able to launch from anywhere in the world, and the go-anywhere-there's-water barge would provide flexibility?
I'm guessing equatorial launches for geostationary satellites .

Last edited by Magiver; 01-18-2016 at 09:50 PM.
  #83  
Old 01-18-2016, 10:01 PM
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I'm guessing equatorial launches for geostationary satellites .
I believe that someone up thread posted that they may take off from Vandenburg, but are not allowed to land there.
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Old 01-18-2016, 10:27 PM
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The barge is for landing, not launching. They have no plans to launch from a barge.

lazybratsche has the correct answer above. They will use the barge:
- when they don't have permission to land back at the launch site (as with the most recent landing)
- for Falcon 9 missions that are too heavy, and there is not enough fuel for a boostback to the launch site
- for landing the center core of Falcon Heavy missions, since it stages much later than the boosters
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Old 01-18-2016, 10:44 PM
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The barge is for landing, not launching. They have no plans to launch from a barge.

lazybratsche has the correct answer above. They will use the barge:
- when they don't have permission to land back at the launch site (as with the most recent landing)
- for Falcon 9 missions that are too heavy, and there is not enough fuel for a boostback to the launch site
- for landing the center core of Falcon Heavy missions, since it stages much later than the boosters
I was thinking of Sea Launch. Which does serve as an equatorial platform for geostationary satellites.
  #86  
Old 01-18-2016, 10:56 PM
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I was thinking of Sea Launch. Which does serve as an equatorial platform for geostationary satellites.
Sea Launch seems like a better idea than it is. Unfortunately, the operational overhead of doing things in the middle of the ocean overwhelms the marginal performance benefit you get from being at the equator.

Maybe it would be a different story if they were able to automate more. But for some reason they need a command ship the size of a mid-sized cruise liner.
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Old 01-19-2016, 03:57 AM
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Shame that it failed, I do find it enthralling to see them getting closer and closer to a repeatable and reliable system.

One thing that occurred to me. As the rocket enters the final few metres to settle on the legs, could not three or four retaining arms "flip up" from the deck and provide some element of lateral support and stabilisation in case of a slightly uneven landing or leg failure?
  #88  
Old 01-19-2016, 06:56 AM
lazybratsche lazybratsche is offline
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I love how so many people watch the landing and really want a way to just grab the rocket to keep it from tipping over!

The problem is that rockets have to be as light as possible, so they are built to be just strong enough to handle forces along a nice straight line from the engines to the payload. The outer walls of the rocket are also the outer walls of the tanks and are just a few mm thick. Structurally they're a lot like a soda can*: hard to crush from top to bottom, but extremely easy to crush from the side. The tanks are also pressurized, so a small dent will quickly become a larger torn hole spewing kerosene or oxygen. I can't imagine that any of the proposed schemes to grab the top of the rocket will ever work. There are a some very strong mounting lugs on the bottom near the engines, but trying to grab those on a rocket that could land anywhere within a few meters of center seems like a ridiculous engineering challenge.

Edited to add: here's a picture that shows the segments that will become the entirety of the tank and rocket structure. They're reinforced with stringers on the inside, but it shows how thin the outer skin is.

*I've heard that the walls of the Falcon 9 are a lot thinner than a soda can scaled up to the same diameter, though I can't find a good cite this morning...

Last edited by lazybratsche; 01-19-2016 at 07:00 AM.
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Old 01-19-2016, 07:39 AM
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Edited to add: here's a picture that shows the segments that will become the entirety of the tank and rocket structure. They're reinforced with stringers on the inside, but it shows how thin the outer skin is.
I see what you are saying. Any support system coming in from the side is going to place a large amount of force on that thin skin if the rocket is substantially off-vertical. And if it isn't off-vertical then the support isn't needed (assuming that the legs can be modified to reduce the risk of failure.)

The other thing that I hadn't quite appreciated is the speed of the landing and variability in touch-down position. That presents a substantial challenge in getting an accurate, non-damaging support structure into place quick enough. Overall, improvements to the legs is likely to be the easier engineering challenge.

It is all still way cool though.

Last edited by Novelty Bobble; 01-19-2016 at 07:39 AM.
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Old 01-19-2016, 12:54 PM
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For a restraining system to be worthwhile, it is not necessary that if used it leave the rocket undamaged. It would be worth it if the money it saved by preventing explosions was greater than the cost of the system and the cost of damage done by the restraint.
  #91  
Old 01-19-2016, 04:34 PM
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*I've heard that the walls of the Falcon 9 are a lot thinner than a soda can scaled up to the same diameter, though I can't find a good cite this morning...
It's close. A soda can is 66 mm in diameter and uses 0.1 mm thick aluminum, for a 660x ratio. A Falcon 9 is 3660 mm across and has skin in the ballpark of 6 mm (this is my estimate from visiting the factory), for a 610x ratio.

A Falcon 9 first stage stores 389,000 liters of propellant with a dry mass of 23,100 kg, while a soda can stores 0.355 liters in 0.149 kg. That's 0.059 kg/l for the F9 and 0.042 kg/l for the can. So even with all the engines and other components included, it's barely more.

The second stage does even better, with 0.043 kg/l, which almost matches the can.
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Old 01-19-2016, 04:49 PM
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I love how so many people watch the landing and really want a way to just grab the rocket to keep it from tipping over!
I thought this animation from Reddit was a funny one. But the guy didn't really think through the physics. The sliders moving along the length travel 45 meters in about 0.5 s. Since they have to accelerate and decelerate, that means they need to go from 0 to 22.5 m in 0.25 seconds, which is 720 m/s2 of acceleration, which is 73 gees. Kind of a lot.

I think most of the ideas for grabbing the stage suffer from the same kind of problem. The scale here is huge--the stage is the height of a 10 story building. Legs are really just the best way. They'll fix the problems eventually. Aircraft landing gear also fails occasionally, but we don't invent crazy schemes for grabbing aircraft from the ground (well, mostly). It generally just works.
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Old 01-19-2016, 05:45 PM
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Shame that it failed, I do find it enthralling to see them getting closer and closer to a repeatable and reliable system.

One thing that occurred to me. As the rocket enters the final few metres to settle on the legs, could not three or four retaining arms "flip up" from the deck and provide some element of lateral support and stabilisation in case of a slightly uneven landing or leg failure?
I think the fail is not letting them land on solid ground in the first place. I mean WTH? What possible reason can they have for using such a setup?

We have a ridiculous amount of desert land out west that could be utilized for this.
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Old 01-19-2016, 06:23 PM
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We have a ridiculous amount of desert land out west that could be utilized for this.
The Russians and Chinese are all too happy to allow rocket overflights of populated areas. The US is not. Eastern-bound flights go from Cape Canaveral and polar flights from Vandenberg. In both cases, the rocket is over the ocean after launch. SpaceX's new launch facility in Boca Chica, Texas will also launch over the ocean (threading the needle between Florida and various islands along the way).

They will have a landing pad at Vandenberg eventually, but they just haven't gotten permission yet. I don't know why, but this stuff takes time.

At any rate, they will need the barge in the future, so they may as well keep practicing. They have done very well in targeting the barge with high precision; they just haven't quite stuck the landing yet. It seems there aren't many variables remaining.
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Old 01-19-2016, 07:47 PM
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I think the fail is not letting them land on solid ground in the first place. I mean WTH? What possible reason can they have for using such a setup?
They may launch from Vandenberg, but are not allowed to land there.
I believe that you have to use fuel to return, and a barge landing is less costly. Things at sea do tend to behave in such a way as to make a fellow seasick, it must be much more difficult to land on a barge that solid, level, unmoving land.
And the mentioned above overflying populated areas. A hot air balloon landed in Mama Plant's neighborhood, but a booster would have been a different matter.
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Old 01-19-2016, 09:18 PM
Magiver Magiver is offline
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They may launch from Vandenberg, but are not allowed to land there.
I believe that you have to use fuel to return, and a barge landing is less costly. Things at sea do tend to behave in such a way as to make a fellow seasick, it must be much more difficult to land on a barge that solid, level, unmoving land.
And the mentioned above overflying populated areas. A hot air balloon landed in Mama Plant's neighborhood, but a booster would have been a different matter.
Well I was thinking in terms of the deserts out West for both launch and recovery. Yes, no? I have no idea how far the rocket arcs over before it returns. I just hate to see a perfectly good rocket destroyed for no good reason. unless the ocean barge is super stable then this is an event destined to repeat itself.

Last edited by Magiver; 01-19-2016 at 09:23 PM.
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Old 01-19-2016, 09:34 PM
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Well I was thinking in terms of the deserts out West for both launch and recovery. Yes, no? I have no idea how far the rocket arcs over before it returns. I just hate to see a perfectly good rocket destroyed for no good reason. unless the ocean barge is super stable then this is an event destined to repeat itself.
I don't know how much fuel they would need to land in the desert, or how much it would cost to retrieve a booster from there. Where they put the satellite in orbit determines how they return, and I am completely ignorant of orbital mechanics.
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Old 01-19-2016, 10:21 PM
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Aircraft landing gear also fails occasionally, but we don't invent crazy schemes for grabbing aircraft from the ground (well, mostly). It generally just works.
Meh, it's been done.
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Old 01-20-2016, 09:33 AM
lazybratsche lazybratsche is offline
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Well I was thinking in terms of the deserts out West for both launch and recovery. Yes, no? I have no idea how far the rocket arcs over before it returns. I just hate to see a perfectly good rocket destroyed for no good reason. unless the ocean barge is super stable then this is an event destined to repeat itself.
For one thing, The US as a whole is pretty averse to sending rockets over even slightly populated areas. With disposable rockets all the lower stages and payload fairings would come crashing back to earth somewhere tens or hundreds of miles downrange. Even if SpaceX can reliably land their first stage, there's still a substantial risk of the rocket exploding and raining debris across a wide area downrange. And some of the debris can be pretty nasty: propellants that are mildly toxic (wash it off your skin before you get a nasty rash), other propellants that are very toxic (if you can smell it you might survive with hospitalization), and the occasional radioactive power supply.

In contrast, the Chinese government doesn't give much a fuck where their rocket debris lands. Usually that's just "haha an engine fell through the roof of a shack!" but it's also lead to the deadliest ever rocket accident. I doubt that would go over well with the US NIMBY crowd.

Secondly, rocket launches have to head in many directions depending on the orbit the payload needs to reach. Many go east-ish and are best launched from the lowest possible latitude, others go north-ish or south-ish or just about any direction. The optimal downrange landing spot would also vary based on the payload. All this means that you couldn't just use one or two pads for all landings.

Neither of those objections are absolute. Maybe decades from now, if rockets can launch and land as reliably as airplanes, there could be a launch pad somewhere like West Texas and a few dozen landing pads covering the optimal landing areas for most launches.

Getting back to crazy ideas to make barge landings more reliable, a semi-submersible platform could be converted into a much larger and more stable landing pad. (Not unlike Sea Launch's platform, except much simpler and cheaper since all that's needed is a flat surface, and maybe a crane and storage hangar.)

Last edited by lazybratsche; 01-20-2016 at 09:34 AM.
  #100  
Old 01-20-2016, 10:51 PM
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Nice links to the Chinese launch sites.

I thoroughly get the point about launching over civilian areas even if they're remote. But I'm talking about land out west where NOBODY lives. They'll be finding crashed planes out there until the end of time.

As for sea landings I think it would be much cheaper to focus on locking down the rocket than stabilizing the platform. In an era of robotic systems I would think it easier to seek out and latch on to the rocket then to try to control the pitch of the sea.
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