Author Topic: Falcon Heavy center core - downrange barge landing or just expend it?  (Read 31329 times)

Offline spacenut

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Yep, space is hard, and with all of the above having to be checked out.  That will take TIME.  Time enough to ship back to the launch site either inspecting in route, or when it gets back.  The first few successful attempts will determine what has to be beefed up to continue landings.  It might cost more than they are willing to spend.  It might be cheaper just to build a new rocket and maybe just save the engines like ULA is going to do.  Building or beefing up the rocket to achieve reuse might cut half the payload weight.  It that going to be acceptable?  And if so, for how many reuses?  The first Falcon heavies will probably just expend the central cores. 

Offline Robotbeat

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Getting reflight to happen quickly is a prerequisite for what SpaceX is trying to ultimately do. SpaceX will have to solve all the problems Jim mentioned and more.
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Offline Coastal Ron

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Yep, space is hard, and with all of the above having to be checked out.

I know "space is hard" is a handy phrase to use to explain the likelihood of failure, but the Falcon 9 1st stage only spends a small amount of it's time in "space" (i.e. above 100km).  And the toughest part for the 1st stage is really not in "space", but down in our soupy atmosphere.  Just thought I'd point that out...

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The first few successful attempts will determine what has to be beefed up to continue landings.  It might cost more than they are willing to spend.

You do realize that what you stated IS the initial plan?  Safely recover a stage, and then ship it to a test area for extended testing to validate whether what they have been planning will work.  Flying the stage back from the ASDS on a regular basis would likely not happen until after their test program concludes.

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It might cost more than they are willing to spend.

The only way to know that is to actually TRY to do it.  There is a saying "if you don't swing the bat, you can't hit a home run".  If SpaceX succeeds in what they are trying to do, it's a paradigm shift in space flight.  They are willing to spend significant amounts of money to see if they can succeed.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline LouScheffer

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I have never seen a single valid reason given for the assumption that there will be expensive refurbishment. Simple, cheap straightforward servicing is much more likely.

Until they recover a stage and examine it, it's unclear how long it will take.  For a possible range, airplane checks run:
A check  - 20-50 person-hours - overnight
B check  - 120-150 person hours, 1-3 days
C check  - 6,000 person-hours, 1-2 weeks
D check - 50,000 person-hours, 1-2 months

Until we know where the required servicing falls on this spectrum, it's impossible to say how the economics will shake out.  And not even SpaceX knows this yet - they have a plan, of course, but experimental data often forces changes in plans.

Offline guckyfan

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I have never seen a single valid reason given for the assumption that there will be expensive refurbishment. Simple, cheap straightforward servicing is much more likely.

Until they recover a stage and examine it, it's unclear how long it will take.  For a possible range, airplane checks run:
A check  - 20-50 person-hours - overnight
B check  - 120-150 person hours, 1-3 days
C check  - 6,000 person-hours, 1-2 weeks
D check - 50,000 person-hours, 1-2 months

I emphasize I still have not seen any valid reason to assume very high refurbishment cost, only idle speculation, which is what usually only the SpaceX fans are accused of. I have argued that SpaceX has very good data on the engines and is very optimistic in that point, doubtless with very good reasons.

I have pointed out that the only point where data are not good enough is the airframe, mainly the tanks. There is good reason to assume that most of the inspections will fall in the A category. After all beside the engines (for which good data are available) a first stage is a lot less complex than an airplane. Complexity is what drives inspection cost for airplanes.

Offline JamesH

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I have never seen a single valid reason given for the assumption that there will be expensive refurbishment. Simple, cheap straightforward servicing is much more likely.

Until they recover a stage and examine it, it's unclear how long it will take.  For a possible range, airplane checks run:
A check  - 20-50 person-hours - overnight
B check  - 120-150 person hours, 1-3 days
C check  - 6,000 person-hours, 1-2 weeks
D check - 50,000 person-hours, 1-2 months

I emphasize I still have not seen any valid reason to assume very high refurbishment cost, only idle speculation, which is what usually only the SpaceX fans are accused of. I have argued that SpaceX has very good data on the engines and is very optimistic in that point, doubtless with very good reasons.

I have pointed out that the only point where data are not good enough is the airframe, mainly the tanks. There is good reason to assume that most of the inspections will fall in the A category. After all beside the engines (for which good data are available) a first stage is a lot less complex than an airplane. Complexity is what drives inspection cost for airplanes.

It doesn't have to be high refurb  cost, just costs greater than the cost of returning a stage by barge.

A fly back involves refueling on the barge, it requires a check out of the engines, possible strengthening of the legs,  and the extra use of the flyback engine. Compared with a crane barge to lift the stage to a return ship, or simply returning it on the landing barge.

Whichever of those is the cheapest, will be the one that is used.

There is a reason why shipping stuff from China is cheaper by boat.

Offline guckyfan

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It doesn't have to be high refurb  cost, just costs greater than the cost of returning a stage by barge.

A fly back involves refueling on the barge, it requires a check out of the engines, possible strengthening of the legs,  and the extra use of the flyback engine. Compared with a crane barge to lift the stage to a return ship, or simply returning it on the landing barge.

Whichever of those is the cheapest, will be the one that is used.

There is a reason why shipping stuff from China is cheaper by boat.

I agree. My argument was after the discussion shifted to general cost and feasibility of reuse. I am afraid that discourse was OT for this thread.

Offline meekGee

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I have never seen a single valid reason given for the assumption that there will be expensive refurbishment. Simple, cheap straightforward servicing is much more likely.

Until they recover a stage and examine it, it's unclear how long it will take.  For a possible range, airplane checks run:
A check  - 20-50 person-hours - overnight
B check  - 120-150 person hours, 1-3 days
C check  - 6,000 person-hours, 1-2 weeks
D check - 50,000 person-hours, 1-2 months

I emphasize I still have not seen any valid reason to assume very high refurbishment cost, only idle speculation, which is what usually only the SpaceX fans are accused of. I have argued that SpaceX has very good data on the engines and is very optimistic in that point, doubtless with very good reasons.

I have pointed out that the only point where data are not good enough is the airframe, mainly the tanks. There is good reason to assume that most of the inspections will fall in the A category. After all beside the engines (for which good data are available) a first stage is a lot less complex than an airplane. Complexity is what drives inspection cost for airplanes.

It doesn't have to be high refurb  cost, just costs greater than the cost of returning a stage by barge.

A fly back involves refueling on the barge, it requires a check out of the engines, possible strengthening of the legs,  and the extra use of the flyback engine. Compared with a crane barge to lift the stage to a return ship, or simply returning it on the landing barge.

Whichever of those is the cheapest, will be the one that is used.

There is a reason why shipping stuff from China is cheaper by boat.

You're missing the entire point...  The reason to fly back is NOT to save on barge costs.  It is to have the stage ready to re-fly the next day, just like a direct RTLS core.  That's where the savings are.

I am sure that it is cheaper to land the stage on a barge than it is to lose 20% (or whatever the fraction is) of the payload.  Yet SpaceX decided to take that hit, because they want RAPID reusability, not just reusability.

Why do they want rapid reusability?  Since they want to fly extremely often, and if it takes 20 days to get your stage back, (10 days each way to some 1200 km landing site) then you have to maintain a large fleet of cores and shops to manage that.

Fly-back is a lot less attractive when you're only flying once per month.
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Offline LouScheffer

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Whichever of those is the cheapest, will be the one that is used.

There is a reason why shipping stuff from China is cheaper by boat.
You're missing the entire point...  The reason to fly back is NOT to save on barge costs.  It is to have the stage ready to re-fly the next day, just like a direct RTLS core.  That's where the savings are.
I think you are confusing the goal and the means.  The goal is to have a rapid launch cadence and low costs.   One way to do this is rapid re-use, but it's not the only way.

You could have a small number of cores and re-cycle them quickly.  In the limit of only one core and daily launches, you would indeed need to fly them back.  But alternatively, for daily launches, you could have 4-5 cores and a fast boat carrying them back.  You could even have a fleet of barges, though that seems more expensive yet.

From an economics and accounting point of view, keeping a fleet of cores costs very little.  It is not the cost of the cores, since every core gets used to exhaustion anyway.  Instead, it's the interest on the money you (at least conceptually) borrow to build your stable of cores.  At current interest rates, that's only a very small fraction of the core costs.  This is the cost that flyback has to compete against.

A numerical thought experiment may make this more clear.  Suppose you want daily flights, and a core is good for 30 flights.  So each year you need 12 cores.  So with rapid re-use, you fly the core on Jan 1, fly it back, fly again Jan 2, etc.  By the end of January you have used it up.  You start with a new core in February, etc.  Alternatively, you buy 12 cores January 1st.  You launch #1 on Jan 1, #2 on Jan 2, etc.  By Jan 13 you need to have the first core is back so you can re-use it.  In this scheme you have 12 days to get each core back.   The cost is that you buy each core, on the average, 6 months earlier, plus somewhere to store the cores as you work.  Neither of these seems prohibitive compared to the cost, and wear and tear, of re-use.  Plus this scheme is a lot more resilient against weather, core loss, etc.

For weekly launches, you may have the option of flying them back, shipping them back, or barging them back, depending on the number that can RTLS or be expended, and how many cores each approach implies.  In the end, SpaceX will not do rapid reuse if it's not cost effective.  They are being careful to make sure the design allows this, but they would not insist on it, just from philosophical bull-headedness, if there's a cheaper way.  Musk has shown this type of pragmatism several times.

Offline spacenut

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Refurbishment of a core will cost more and take more time than people realize I believe.  There is also a reason all commercial airlines fly sub-sonic.  It cost Concorde a lot more to inspect, repair, replace, and refurbish than it does on a sub-sonic craft.  I believe these rocket cores will be the same.  They also quit flying the SR-71 due to costs.  I believe the turn-around time for the Concorde was several days.  They will not be able to fly a core on a rocket the next day.  It takes all of the rocket launching companies about 10 days to assemble a rocket, refuel, check out everything and launch and that is with all new rockets.  So I don't see a fast turn-around on any core, or any rocket engine saved.  It will take time.  And what better way to check out the core than where they assemble them.  Crews and equipment are already there, not on the barge. 

Sometimes Musk just talks.  Remember second stage recovery?  Not happening, not cost effective yet.  Short term, they will either expend it, or ship it back or ship it back for refurbishment.  Long term (10 years out from successful landings), they can make 40 cores a year, and if they can reuse them 10 times, that is 400 cores in 10 years, over one per day.  They will then start expending the older stages.  So, I just don't see the case of launching back. 

Offline JasonAW3

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Refurbishment of a core will cost more and take more time than people realize I believe.  There is also a reason all commercial airlines fly sub-sonic.  It cost Concorde a lot more to inspect, repair, replace, and refurbish than it does on a sub-sonic craft.  I believe these rocket cores will be the same.  They also quit flying the SR-71 due to costs.  I believe the turn-around time for the Concorde was several days.  They will not be able to fly a core on a rocket the next day.  It takes all of the rocket launching companies about 10 days to assemble a rocket, refuel, check out everything and launch and that is with all new rockets.  So I don't see a fast turn-around on any core, or any rocket engine saved.  It will take time.  And what better way to check out the core than where they assemble them.  Crews and equipment are already there, not on the barge. 

Sometimes Musk just talks.  Remember second stage recovery?  Not happening, not cost effective yet.  Short term, they will either expend it, or ship it back or ship it back for refurbishment.  Long term (10 years out from successful landings), they can make 40 cores a year, and if they can reuse them 10 times, that is 400 cores in 10 years, over one per day.  They will then start expending the older stages.  So, I just don't see the case of launching back.

Truth be told, as I understand it, they intend to address the return and refurbishment of each stage individually.  Right now, they are mostly concerned with capsule and first stage recovery.  Second stage recovery will be worked on after they have a good record of first stage recovery.

Right now, it appears like they're trying to imp;rove the performance margin enough so that second stage recovery is possible.  (Plus, improving the Mass to Orbit ratio a bit helps too).
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Offline JamesH

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Whichever of those is the cheapest, will be the one that is used.

There is a reason why shipping stuff from China is cheaper by boat.
You're missing the entire point...  The reason to fly back is NOT to save on barge costs.  It is to have the stage ready to re-fly the next day, just like a direct RTLS core.  That's where the savings are.
I think you are confusing the goal and the means.  The goal is to have a rapid launch cadence and low costs.   One way to do this is rapid re-use, but it's not the only way.

You could have a small number of cores and re-cycle them quickly.  In the limit of only one core and daily launches, you would indeed need to fly them back.  But alternatively, for daily launches, you could have 4-5 cores and a fast boat carrying them back.  You could even have a fleet of barges, though that seems more expensive yet.

From an economics and accounting point of view, keeping a fleet of cores costs very little.  It is not the cost of the cores, since every core gets used to exhaustion anyway.  Instead, it's the interest on the money you (at least conceptually) borrow to build your stable of cores.  At current interest rates, that's only a very small fraction of the core costs.  This is the cost that flyback has to compete against.

A numerical thought experiment may make this more clear.  Suppose you want daily flights, and a core is good for 30 flights.  So each year you need 12 cores.  So with rapid re-use, you fly the core on Jan 1, fly it back, fly again Jan 2, etc.  By the end of January you have used it up.  You start with a new core in February, etc.  Alternatively, you buy 12 cores January 1st.  You launch #1 on Jan 1, #2 on Jan 2, etc.  By Jan 13 you need to have the first core is back so you can re-use it.  In this scheme you have 12 days to get each core back.   The cost is that you buy each core, on the average, 6 months earlier, plus somewhere to store the cores as you work.  Neither of these seems prohibitive compared to the cost, and wear and tear, of re-use.  Plus this scheme is a lot more resilient against weather, core loss, etc.

For weekly launches, you may have the option of flying them back, shipping them back, or barging them back, depending on the number that can RTLS or be expended, and how many cores each approach implies.  In the end, SpaceX will not do rapid reuse if it's not cost effective.  They are being careful to make sure the design allows this, but they would not insist on it, just from philosophical bull-headedness, if there's a cheaper way.  Musk has shown this type of pragmatism several times.

Very much this, with the addition that next day flying of the F9h may never be necessary. It's going to be years before there is 'fly every day demand' and by that time there may be a better way of doing it (BFR for example).

Offline Coastal Ron

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Refurbishment of a core will cost more and take more time than people realize I believe.  There is also a reason all commercial airlines fly sub-sonic.  It cost Concorde a lot more to inspect, repair, replace, and refurbish than it does on a sub-sonic craft.

You are conflating many factors that aren't related to rocketry, such as the economics of the Concorde.  For instance, part of the reason why the Concorde was not as profitable was because it could not overfly land areas that were inhabited.

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They also quit flying the SR-71 due to costs.

Actually we don't know why, but the aircraft was over 30 years old.  If anything the success of the reusable Mach 3.3 SR-71 bodes well for the reusable Falcon 9 1st stage.

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They will not be able to fly a core on a rocket the next day.

Why?  Musk has stated that they designed it to do just that - gas-n-go.

And remember they won't be doing that until they have completed their test program for reusability, which is where maintenance issues will be uncovered and addressed.  So I'm not sure you are accounting for the learning process they have already planned to undertake.

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It takes all of the rocket launching companies about 10 days to assemble a rocket, refuel, check out everything and launch and that is with all new rockets.

See, this is where you don't understand what the new paradigm will be.  All those checks are done because the rockets are not proven.  They haven't have a chance to see what the infant mortality is of that particular rocket.

But once you're flown it, and once you've done a test program to understand how well your design holds up with multiple reuse, then you don't need to do that much checking.  Just like in-service airliners have far fewer checks that brand new ones that have never flown.

The other thing you miss is that the customers for reusable stages might be some of the same ones they have today (some are already bidding for the same rockets that will launch one of their payloads), but what Musk is really hoping to do is to create new markets for inexpensive rides to space.  That's where the advantages of reusability really show up.  But that won't happen until reusability is perfected and priced out, and the pricing will dependent on what they find in their reusability recertification process.
If we don't continuously lower the cost to access space, how are we ever going to afford to expand humanity out into space?

Offline spacenut

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Costal Ron, you are taking ONE thing Musk has said and running with it.  It isn't going to happen.  It is not economical, therefore it doesn't make sense.  Musk is pragmatic.  If something isn't going to work or costs too much he abandons that idea.  Everyone here has stated why it isn't going to happen, yet you keep trying to justify it.  Yes, the COSTS to maintain a SUPERSONIC Concorde is the reason why it was abandoned, not just because it couldn't fly over land.  You have planes going and coming across the Atlantic and Pacific DAILY.  If you paid $500 to fly from NY to London on a subsonic, but had to pay $1,500 for Concorde, MOST will pay $500.  The rocket IS SUPERSONIC and core has to slow down to land.  This puts stress going up with all the weight, and stress coming down for a rocket that is as light as possible.  Going supersonic causes a lot of expansion and contraction on the metals, thus leading to stress cracks, that must be inspected and possibly rewelded.  I've inspected pipeline welds before with xrays.  Stress cracks in the metal can be internal and not show up on the outside. 

Also, I'm not talking about UNPROVEN Atlas V, and Falcon 9.  They are proven, but still take about 10 days from the time of arrival to launch.  They have to be checked for shipping damage, lifted up, staged, connected, and fueled up, and they have to be launched at a certain time to make the proper orbit.  That can't be done physically today in 24 hours.  They are not going from point a to point b on a map like an airliner, but in any multitude of orbital positions, thus having to launch in a "window" of opportunity. 

The "short" hops by a partially fueled core back to the launch site is and never will be necessary.  More stress on the cores, engines, and legs, and a 50% greater chance of a crash landing destroying the core.   Putting 8-10 cores in a warehouse after inspection is possible.  I say flybacks will not happen as well as most everyone here.  Like I said, they were going to try to land the second stage but gave that up at least for now because it wasn't cost effective.  They will probably land 5-10 cores and thoroughly check them out before trying to relaunch one.  If it works a second time, they will have 5-10 still in stock to keep going.  No need for flybacks. 

Offline guckyfan

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Just as a side note.

People usually refer to "refurbishing" when talking about getting a stage flight ready again. I prefer "servicing". Elon Musk is aiming for gas and go, like a F1 racing pitstop, and that not necessarily for the speed but for cost. Refurbishing implies high cost, servicing or gas and go imply low cost.

He also may want to do fast turnover, days or a week not a month, because after  months more checks before reflight may be necessary. All these may make refly for reuse actually be operationally desirable.

Disclaimer: I still don't believe that is what actually will happen.

Offline spacenut

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I don't think the flyback will happen.  However, that is not to say there will not be a fast turn around in rocket terms, just not gas and go.  I think they will have 5-10 successful landings.  All of these will be checked out thoroughly.  Changes will have to be made, minor or major, don't know without successful landings in session.  Then with these 5-10 readied for reflight, will begin reuse.  And, because they will now have a supply on hand, turn-around time may seem fast, but it still might take 10 days for shipping back, checking out, and reflying.  In the meantime other flights will take place, using new, or one of the backlog of used ones that have been checked out.  Government flights will want new ones for a while.  Civilian flights will probably use a flown core.  So, with the mix, I just don't see a need for flying back from the barge.  At the cape, you will still have Atlas or Vulcan flights.  At Boca Chica, a core stage could land on the barge a couple of miles off Key West, or Tampa, or even the cape.  A few hours later the barge can off load to a truck to be brought back to either the Cape or Boca Chica,  In the meantime side cores that have landed, can be refueled, checked out, and launched as F9's while waiting for the cores.  F9 is not going away when FH comes on line, so they can be launched in the meantime while waiting for downrange cores to return.  If you have half F9 launches, and half FH launches, that is only 25% of cores waiting for return.  You still have 75% of your cores ready for launching something else.  Also, depending on the weight of the payload, some customers might require expendable launches or expendable cores.  I see cores of FH eventually becoming the expendables, thus no need for return. 

Offline mvpel

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The rocket IS SUPERSONIC and core has to slow down to land.  This puts stress going up with all the weight, and stress coming down for a rocket that is as light as possible.  Going supersonic causes a lot of expansion and contraction on the metals, thus leading to stress cracks, that must be inspected and possibly rewelded.

The thing is, Spacenut, the Facon 9 is not really as light as possible. It was designed from the start to be reusable, so they didn't shave everything down just far enough to make it through a single launch as is customary in the launch-vehicle industry. Instead, they got everything down far enough to make the vehicle robust enough for repeated re-use. And then they added  two tonnes worth of reuse-related hardware when moving From 1.1 to F9R configuration in the form of grid fins and actuators, landing legs, and so on.

And judging by their presentation at the GPU Technology Conference 2015 where they described their computational fluid dynamics simulation of the entire Raptor engine combustion cycle, they have a level of modeling and simulation efficiency that is probably unprecedented in the history of humanity, so it's highly unlikely that they have not run tens of thousands of simulations (at a minimum) of booster re-entry profiles to examine every last detail of the flight.

They undoubtedly know exactly where and when the maximum airframe temperature and stress occurs with a simulation resolution that depicts every last eddy and swirl of the boundary layer at the skin of the vehicle, and they could probably reproduce the entirely in simulation to the point where you couldn't tell the difference. And if they found something gettnig too hot, they can just slap a bit more SPAM on it.

So I don't see any reason to suspect that they don't know exactly how much stress, expansion and contraction, and heating occurs during flight, down to the fraction of a millimeter or degree, and exactly what impact that has on the airframe.

The minutia of fatigue crack propogation in lithium-aluminum alloys - which "display superior (long crack) fatigue crack growth properties, resulting from a prominent role of crack tip shielding, principally due to deflected and tortuous crack path morphologies, induced by the shearable nature of coherent b' precipitates, crystallographic texture, and anisotropic grain structures" - is a subject of meticulous worldwide study in which SpaceX is undoubtedly intensively participating.

And in any case, a comparison between the complex multifaceted fastener-riddled aluminum fuselage of the Concorde, spending hours and hours in a harsh supersonic environment, to the friction-stir-welded monolithic lithium-aluminum alloy tanks of the Falcon 9 spending a few minutes in a harsh hypersonic environment under a layer of SPAM is not really valid, as I see it.

And when they roll out the Falcon Heavy - the most powerful rocket since Saturn V - if it turns out they need to add a few hundred kilograms here or there to make something more robust in order to reach the desired number of flight hours for the airframe, so what? If that robustness bumps a payload from the upper limit of a Falcon 9 to the lower limit of a Falcon Heavy, it's just a matter of buying more fuel.

You can bet, however, that they won't do flyback from the ASDS until it's more cost-effective than an ocean voyage for their launch cadence goals. Will that be a few years, or many years from now? They probably have an idea, but I guess the rest of us will have to just wait and see.
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Offline llanitedave

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Keep in mind the ASDS will need regular maintenance as well.  It can't stay out at sea indefinitely, and even with the shields, the rocket plume on landing will have effects that need to be mitigated between uses.
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Offline oiorionsbelt

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What's the longest firing time any single Merlin 1D has had? It was mentioned somewhere by EM that they were aiming for 40 times reuse. In all likelyhood, if that's true, then they may well have fired a single 1D for ~7,500 secs that would certainly give them a lot of data about wear.
« Last Edit: 11/17/2015 05:52 PM by oiorionsbelt »

Offline guckyfan

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What's the longest firing time any single Merlin 1D has had? It was mentioned somewhere by EM that they were aiming for 40 times reuse. In all likelyhood, if that's true, then they may well have fired a single 1D for ~7,500 secs that would certainly give them a lot of data about wear.

He said 40 cycles which most likely means 40 firings, some engines are fired multiple times for one flight. Plus we don't know if they will do static fire for every reflight.

However he also said a Merlin engine has no meaningful limit to its lifetime. After those 40 cycles some highly stressed components need to be replaced. Which of course some interpret as most parts of the engine costing nearly as much as a new engine and some as some parts of the turbo pumps at relatively low cost.

Given that Elon Musk clearly has no major concerns spending cycles I am in the camp of a not so expensive overhaul after 40 cycles.

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