Author Topic: F9 Second Stage Reusability  (Read 205463 times)

Offline macpacheco

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Re: F9 Second Stage Reusability
« Reply #300 on: 04/11/2017 06:12 PM »
People make too much of the 4400 satellite number of CommX.
SpaceX can generate a large % of CommX revenue with less than 10% of the constellation in operation.
The goal of so many satellites is to provide services even for customers that have quite a restricted view of the sky (urban canyons), and ultra high bandwidth on the full system.
If they start without catering to such customers, they can make due with a few hundred satellites and generate billions USD/yr in revenue.
The balance of satellites can wait until ITS/mini ITS/Raptor F9 is operating.

The best customers for CommX are those that must choose between unreliable internet, slow internet or ultra high latency internet. CommX delivers reliable/fast/mobile/low latency, but can charge a substantial premium in return. Competing in urban canyon scenarios are the low profitability situation where you must go against the big fiber telcos.

GEO dedicated satellite links cost over 20x as much as land line links with huge latency. SpaceX can win over that entire market with moderately lower costs.

CommX has a lot more market potential outside mainland USA and Europe, several times more market. In places where there's no fiber or there's a single fiber cable that's fails nearly every month.

It makes zero sense to launch the entire constellation with Gen I satellites. It makes far more sense to operate a reduced Gen I constellation, roll out a fuller constellation with Gen IIs and only roll out the full thing with Gen III satellites. By the time Gen IIIs are ready to roll, ITS or mini ITS is flying.
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Offline JamesH65

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Re: F9 Second Stage Reusability
« Reply #301 on: 04/11/2017 06:56 PM »
People make too much of the 4400 satellite number of CommX.
SpaceX can generate a large % of CommX revenue with less than 10% of the constellation in operation.
The goal of so many satellites is to provide services even for customers that have quite a restricted view of the sky (urban canyons), and ultra high bandwidth on the full system.
If they start without catering to such customers, they can make due with a few hundred satellites and generate billions USD/yr in revenue.
The balance of satellites can wait until ITS/mini ITS/Raptor F9 is operating.

The best customers for CommX are those that must choose between unreliable internet, slow internet or ultra high latency internet. CommX delivers reliable/fast/mobile/low latency, but can charge a substantial premium in return. Competing in urban canyon scenarios are the low profitability situation where you must go against the big fiber telcos.

GEO dedicated satellite links cost over 20x as much as land line links with huge latency. SpaceX can win over that entire market with moderately lower costs.

CommX has a lot more market potential outside mainland USA and Europe, several times more market. In places where there's no fiber or there's a single fiber cable that's fails nearly every month.

It makes zero sense to launch the entire constellation with Gen I satellites. It makes far more sense to operate a reduced Gen I constellation, roll out a fuller constellation with Gen IIs and only roll out the full thing with Gen III satellites. By the time Gen IIIs are ready to roll, ITS or mini ITS is flying.

Space X themselves have said 800 to start the constellation up, that's 20% of the final number, not 10%. These satellite are travelling fast in LEO. That means you need more as they go out of line of sight more quickly.

I have no problems with the concept of the system, I think its a fantastic idea and will make Musk very very rich, but can only work with very cheap launches, and lots of them. Which is their plan! So rock on!

Offline RedLineTrain

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Re: F9 Second Stage Reusability
« Reply #302 on: 04/11/2017 09:57 PM »
Space X themselves have said 800 to start the constellation up, that's 20% of the final number, not 10%.

More like 7%.

http://spacenews.com/fcc-gets-five-new-applications-for-non-geostationary-satellite-constellations/

Offline sanman

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Re: F9 Second Stage Reusability
« Reply #303 on: 04/11/2017 10:26 PM »
And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

So does 2nd stage reusability include water landing? Or does a desire to avoid seawater corrosion firmly require landing on dry terra firma?

If landing on dry land is required, then can that be done with chutes, or would it require powered thrust?

Offline adrianwyard

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Re: F9 Second Stage Reusability
« Reply #304 on: 04/11/2017 10:51 PM »
It seems mid-air helicopter capture is an option for something the size of an empty Falcon second stage (but not much heavier).

This method won't earn SpaceX the style-points they usually get for powered vertical landings, but it adds up in terms of practicality, low-mass, and gentle loads on structure.

Online ZachS09

Re: F9 Second Stage Reusability
« Reply #305 on: 04/11/2017 11:15 PM »
"Liftoff of Falcon 9: the world's first reflight of an orbital-class rocket."

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #306 on: 04/12/2017 12:31 AM »
Musk wants to make Falcon rockets fully reusable

https://spaceflightnow.com/2017/04/11/musk-wants-to-make-falcon-9-rocket-fully-reusable/
Thanks for posting the link Zach. Like I kept saying, I don't know why folks were thinking otherwise...
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Offline CharlieWildman

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Re: F9 Second Stage Reusability
« Reply #307 on: 04/12/2017 02:37 AM »
One thought. This comes close after successful experiment with bringing back fairing. And fairing probably doesn't have any complicated solutions for reusability.

And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

I like the KISS approach for 2nd stage reusability.  Seems possible that a nose mounted heat shield and some nose weight could be ready to go for this flight.  Don't even really need a parachute.  Just good telemetry showing how things worked out.
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Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #308 on: 04/12/2017 08:46 AM »
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.
If you build something directly from the equations in a design handbook or ASME standards and delivers adequate, predicted performance it's engineering.

If the design equations in the open literature don't give you the performance you need.
If you're simulations don't match the recorded flight data or do so with so much uncertainty they are practically useless.
If you can't put a model in a wind tunnel because no wind tunnel exists that comes anywhere close to matching the conditions you need to model.
If you have to do curve fitting, dimensional analysis on the equations and restructure your CFD to get a model that matches the real world.


That's science.

I have great respect and admiration for what SX have accomplished. I'm quite sure they have raised the bar for any future competitor. 

The joker in the pack is of course the question of how much more science will they have to do before they get to full reuse and that answer is impossible to know.

This is "Unknown unknowns" territory.  :(
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Offline Radical_Ignorant

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Re: F9 Second Stage Reusability
« Reply #309 on: 04/12/2017 08:49 AM »
One thought. This comes close after successful experiment with bringing back fairing. And fairing probably doesn't have any complicated solutions for reusability.

And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

I like the KISS approach for 2nd stage reusability.  Seems possible that a nose mounted heat shield and some nose weight could be ready to go for this flight.  Don't even really need a parachute.  Just good telemetry showing how things worked out.

They could do that. It would fit their approach how they made booster reusable by experimenting with hardware as it is. But then they have parachutes for fairing - making bigger parachute doesn't seem complicated *if* nothing critical is relying on it. So why not?

And my guess is that their investigation which caused them to say "no reusability for F9 second stage" stands correct and there is nothing which invalidates it (given their initial powered landing idea). But after test of fairing recovery thing they came up with different idea "hi, this works so well, maybe we can even bring whole 2nd stage" and then run the numbers and they are convinced it can work.

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #310 on: 04/12/2017 08:50 AM »
Musk wants to make Falcon rockets fully reusable

https://spaceflightnow.com/2017/04/11/musk-wants-to-make-falcon-9-rocket-fully-reusable/
So for the first stage refurb was about 50% of new build and they expect future refurbs to be 5% of new build cost.

That's very useful information. Thank you.
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Offline Rei

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Re: F9 Second Stage Reusability
« Reply #311 on: 04/12/2017 09:14 AM »
So does 2nd stage reusability include water landing? Or does a desire to avoid seawater corrosion firmly require landing on dry terra firma?

Almost certainly on a landing pad (whether on an ASDS or on land). They'll never achieve economic reuse viability if they let their turbopumps flood with seawater.  I think SpaceX has made their feelings about splashdown landings pretty clear.

I actually posted a thread the other day thinking over the issues of some of the economic issues of returning a second stage back to the US for relaunch, because it would end so far downrange that the amortization and operations costs on the ASDS would start to become significant. Not problematic at first, but if they ever wanted to achieve the case where propellant becomes the majority of their launch costs, it would be problematic then. However, I deleted it after it occurred to me that S2 delivering to LEO doesn't have to do a reentry burn immediately after releasing the payload; it could stay in orbit as long as it needed to in order to get the alignment needed to return to the launch site or other convenient location.  For GTO, if I'm not mistaken (correct me if I'm wrong) the orbit they're generally on intersects the Earth, but they could raise it without huge dV requirements.
« Last Edit: 04/12/2017 09:16 AM by Rei »

Offline Radical_Ignorant

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Re: F9 Second Stage Reusability
« Reply #312 on: 04/12/2017 09:44 AM »
And add second thought: they barely can change anything in second stage. So this leaves idea of something similar to "reusability kit" - except no engines, no landing legs, just TPS, some weight to adjust CoG and parachutes. This "kit" can be heavy on this particular flight, as it's only test and there is no real payload. If it's mounted as payload, but never separated it doesn't invalidate this flight as qualification flight. And since it's adding some experimental stuff attached as payload it fits description of "hail mary". If result of this test is promising then later they can work on integrating this stuff into S2.

So does 2nd stage reusability include water landing? Or does a desire to avoid seawater corrosion firmly require landing on dry terra firma?

If landing on dry land is required, then can that be done with chutes, or would it require powered thrust?

As stated by Rei that's very impractical solution. But it doesn't mean first try (demo FH flight) won't target bringing S2 into water. And they stated that fairing won't end up in water as well, so the same technique maybe can be applied.

Offline ChrisWilson68

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Re: F9 Second Stage Reusability
« Reply #313 on: 04/12/2017 10:18 AM »
What SpaceX does could be better characterized as R&D.  I build astronomical instruments to do science.  The distinction is that tons of research goes into how to implement various 'features' of the instrument -- each of these research projects is jokingly called a 'science project' -- but really they are engineering or technical evaluations, thus R&D.  Once the instrument is built, tested, and integrated at an observatory, science begins.
If you build something directly from the equations in a design handbook or ASME standards and delivers adequate, predicted performance it's engineering.

If the design equations in the open literature don't give you the performance you need.
If you're simulations don't match the recorded flight data or do so with so much uncertainty they are practically useless.
If you can't put a model in a wind tunnel because no wind tunnel exists that comes anywhere close to matching the conditions you need to model.
If you have to do curve fitting, dimensional analysis on the equations and restructure your CFD to get a model that matches the real world.

That's science.

Nope.  That's R&D.

Offline guckyfan

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Re: F9 Second Stage Reusability
« Reply #314 on: 04/12/2017 10:24 AM »
I firmly believe it will be powered landing on land or ASDS. I have some doubt that deorbit with the main engine can provide the needed precision with startup and wind down instabilities. So they need smaller engines. The next step, making the engines strong enough for landing and providing the fuel, won't make it that much more complex. The harder part is getting it through reentry without breaking up, heatshield and aerosurfaces, protection for the engine, if not the engine bell extension.

The first attempt with the FH maiden flight may not have the landing engines and propellant. It may just be a water landing with the lowest speed attainable with the main engine. It would demonstrate the harder part, the reentry and with some luck (plus maybe a floating device) ability to recover the wreckage.

I see the second stage closer to the first stage than to the fairing.

Offline Kaputnik

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Re: F9 Second Stage Reusability
« Reply #315 on: 04/12/2017 12:19 PM »
I firmly believe it will be powered landing on land or ASDS. I have some doubt that deorbit with the main engine can provide the needed precision with startup and wind down instabilities. So they need smaller engines. The next step, making the engines strong enough for landing and providing the fuel, won't make it that much more complex. The harder part is getting it through reentry without breaking up, heatshield and aerosurfaces, protection for the engine, if not the engine bell extension.

The first attempt with the FH maiden flight may not have the landing engines and propellant. It may just be a water landing with the lowest speed attainable with the main engine. It would demonstrate the harder part, the reentry and with some luck (plus maybe a floating device) ability to recover the wreckage.

I see the second stage closer to the first stage than to the fairing.

A single Merlin is controllable enough to bring a vehicle to zero velocity at zero altitude- that's pretty impressive. Yes the US is a quarter of the mass so it is a tougher task, but it doesn't seem unreasonable to me that they have a good enough handle on the startup/shutdown transients that the MVac is up to the job. And if a small additional correction is needed, there are N2 thrusters and prop venting available too.


The big question (time for a poll??) is whether the US is going to enter engine first or not- and also whether the Hail Mary attempt on the FH demo will be representative of any future operational plans in this regard.
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Online FutureSpaceTourist

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Re: F9 Second Stage Reusability
« Reply #316 on: 04/12/2017 01:31 PM »
Recovering first and second stages, plus fairings too, make the logistics of recovery rather more interesting:

Quote
All at sea about reusability

SpaceX is talking about not only increasing their flight rates, but attempting to recover the Falcon 9 payload fairing and second stage as well. Dick Eagleson examines how efforts to prove out second stage and payload fairing recovery might proceed and looks at related logistic challenges for SpaceX as it moves to greatly increase its launch cadence.
Monday, April 10, 2017

http://www.thespacereview.com/article/3212/1

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #317 on: 04/12/2017 01:36 PM »
Would SpaceX's pad failure count as science? They (presumably) created novel states of matter outside a lab, after all.
Definitely given no other rockets blown up like that during a GHe load.

If it wasn't that would imply SX were pretty sure it would go bang on the pad or simply did not care one way or the other.

I don't think anyone believes SX are reckless.


Wrong takeaway and summary.  It isn't science, it is an engineering.  It was just a standard engineering trade within established ground rules.  Nothing new was discovered.  The control surfaces were required because Spacex uses low impulse GN2 thrusters (a ground rule).  Using higher performance thrusters (hyper or RP-1/GOX) would negate the need for control surfaces.   It was a complexity trade.
Plausible.
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Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #318 on: 04/12/2017 01:43 PM »
MVac's are static tested w/o the nozzle, so maybe. Probably not, rockets aren't LEGO elements.


Edit/Lar: fixed pet peeve.
Which implies you could jettison the Niobium extension and run the Merlin on its basic nozzle during landing. I'm assuming it's bolted on. Of course that puts explosive bolts into your refurb and testing costs. That brings a load of baggage.

That said Niobium is also quite expensive. It's about $40 000/tonne and is a "Strategic Metal" in the US. I think SX would prefer to keep the nozzle on the Merlin if at all reasonably possible. [EDIT I think they'd burn a lot of sim time to avoid it before they accepted there was no alternative. And assuming it worked they'd still keep working to eliminate it on general principles of added operational risk, materials cost and refurb time  ]
« Last Edit: 04/12/2017 01:52 PM by john smith 19 »
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Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #319 on: 04/12/2017 01:48 PM »
However, I deleted it after it occurred to me that S2 delivering to LEO doesn't have to do a reentry burn immediately after releasing the payload; it could stay in orbit as long as it needed to in order to get the alignment needed to return to the launch site or other convenient location.  For GTO, if I'm not mistaken (correct me if I'm wrong) the orbit they're generally on intersects the Earth, but they could raise it without huge dV requirements.
Or you can got the other way and have the US deliver slightly sub orbital so it comes down without a de-orbit burn on the "other" US coast.
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