Author Topic: F9 Second Stage Reusability  (Read 140271 times)

Offline meekGee

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Re: F9 Second Stage Reusability
« Reply #540 on: 01/29/2018 10:12 AM »
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.
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Offline JamesH65

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Re: F9 Second Stage Reusability
« Reply #541 on: 01/29/2018 10:36 AM »
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!

Offline meekGee

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Re: F9 Second Stage Reusability
« Reply #542 on: 01/29/2018 12:01 PM »
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
That's not true.

Which law of physics?

US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5

You could double the mass of the US for reusability hardware and still be good.

This is a business decision about schedule of development.
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Offline TrevorMonty

Re: F9 Second Stage Reusability
« Reply #543 on: 01/29/2018 01:45 PM »
I should of said recoverable not reuseable, as Shotwell stated they don't plan to refly recovered US. Most missions will use current expendable US, only fly recoverable US where mission performance margins can support it.

 While knowledge from capsules and shuttle can be applied to BFS US design, they are still totally different aeroshapes.
The only way to get BFS US design close to right first time is to fly subscale version.

Offline AncientU

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Re: F9 Second Stage Reusability
« Reply #544 on: 01/29/2018 01:52 PM »
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.
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Online hkultala

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Re: F9 Second Stage Reusability
« Reply #545 on: 01/29/2018 02:22 PM »
While knowledge from capsules and shuttle can be applied to BFS US design, they are still totally different aeroshapes.
The only way to get BFS US design close to right first time is to fly subscale version.

F9 upper stage is ALSO totally different aeroshape than BFS.

« Last Edit: 01/29/2018 02:23 PM by hkultala »

Offline ChrisWilson68

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Re: F9 Second Stage Reusability
« Reply #546 on: 01/29/2018 02:40 PM »
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.

Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs.  That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.

Offline AncientU

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Re: F9 Second Stage Reusability
« Reply #547 on: 01/29/2018 04:39 PM »
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.

Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs.  That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.

You are assuming that developing second stage reusability for Falcon will reduce their costs -- enough to justify the development effort.  They are developing recoverable fairings because this reduces their costs (<$5M/launch) and/or streamlines operations.  They are also working toward 24hr turn-around of flown cores.  At this level of granularity, it is easy to see that these activities are more cost-effective lines of development than reusable second stages.

They are soon going to be their own largest customer with Starlink launches... launch costs must already have their full attention, and they seem to be passing on second stage reuse for Falcon.
« Last Edit: 01/29/2018 04:40 PM by AncientU »
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Online aero

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Re: F9 Second Stage Reusability
« Reply #548 on: 01/29/2018 04:54 PM »
Has anyone here on NSF calculated how many tons of propellant would be needed to do the burns for recovery/landing of stage 2 if it were done similarly to the stage 1 recovery?

Of course, the propellant isn't the only extra mass that would be needed, maybe not even the most significant mass because the stage would most likely need to be strengthened, legs and grid fins attached, a landing engine, etc.

My point is that the extra mass would eat up the second stage payload. Could it even be done that way using all of the mass available now for payload? Add heat shield mass, too.
« Last Edit: 01/29/2018 04:57 PM by aero »
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Offline ChrisWilson68

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Re: F9 Second Stage Reusability
« Reply #549 on: 01/29/2018 05:22 PM »
They have zero competition for the Block 5 with booster-only reusability.
Doesn't make competitive sense* to beat that dead horse.


* But it will be interesting to see what they learn by practice returns -- entry, descent, un-soft landing -- of the second stage.

Even if they had zero competition, it still makes economic sense for them to do things that will reduce their costs.  That allows them to increase their profits per flight and/or increase the number of launches by increasing the market by lowering costs for their customers.

You are assuming that developing second stage reusability for Falcon will reduce their costs -- enough to justify the development effort.  They are developing recoverable fairings because this reduces their costs (<$5M/launch) and/or streamlines operations.  They are also working toward 24hr turn-around of flown cores.  At this level of granularity, it is easy to see that these activities are more cost-effective lines of development than reusable second stages.

They are soon going to be their own largest customer with Starlink launches... launch costs must already have their full attention, and they seem to be passing on second stage reuse for Falcon.

No, I'm not assuming that or anything else.  I'm not arguing SpaceX will or won't do second-stage re-use, or that it would or wouldn't be financially beneficial for them to do so.

You gave lack of competition as a reason for SpaceX not to work on second-stage reuse.  I merely pointed out that lack of competition doesn't mean there can't be economic reasons for them to work on second-stage reuse.

Maybe the economics of it doesn't favor second-stage reuse.  Maybe there are 100 other reasons not to do second-stage reuse.  All of that is irrelevant to my point, which is just that saying there isn't competition isn't really a good argument against them doing second-stage reuse.

Offline AncientU

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Re: F9 Second Stage Reusability
« Reply #550 on: 01/29/2018 08:08 PM »
I get what you are saying.  Just think that if they thought there would be significant cost reduction -- for instance, better than recovering fairings for a few million savings per flight -- then they'd be doing it because of their need for lots of flights (and profits, too).

The lack of competition just indicates that they won't grow their launch manifest, and the minimal potential cost reduction -- again bounded by the fairing recovery $$$ -- will be insufficient to stretch the market elasticity.

They are at point of diminishing returns on Falcon and are doing just what you are proposing by building BFR/BFS.
« Last Edit: 01/29/2018 08:08 PM by AncientU »
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Offline JamesH65

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Re: F9 Second Stage Reusability
« Reply #551 on: 01/30/2018 12:06 PM »
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
That's not true.

Which law of physics?

US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5

You could double the mass of the US for reusability hardware and still be good.

This is a business decision about schedule of development.

Mass, speed, and air drag. US has a limited up mass, it's travelling very fast, often in the wrong direction, it needs to slow down before it hits atmosphere or it will burn up, it need fairly heavy landing gear. All these combined mean it's very difficult to get everything you need in the US to do a return, and still have enough left over mass to actually launch anything. It's not really big enough.

Those ones.

I'm not saying it's impossible, just very difficult to make it worth doing.

Offline meekGee

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Re: F9 Second Stage Reusability
« Reply #552 on: 01/30/2018 01:35 PM »
Reuseable US is important as it can be used to prove BFR US reentry systems. F9 US doesn't need to do soft land, just reenter and set its self up for soft land. May well use Mid Air Recovery to capture it. Once they've demostrated all that they need, terminate program.
Absolutely.  A "mini BFS" F9US would have made perfect sense if the BFS development schedule wasn't as aggressive as it is.

But if you take the latter as a given, then at that point the former becomes a distraction.

It's a hell of a decision for Musk to have made, but he clearly made it.

 He who dares wins and all that.

Not that difficult a decision - laws of physics means bring back a F9 US used for a decent payload mass is only borderline possible. Making it cost effective would be incredibly difficult. They have quite enough difficult stuff to do with BFR!
That's not true.

Which law of physics?

US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5

You could double the mass of the US for reusability hardware and still be good.

This is a business decision about schedule of development.

Mass, speed, and air drag. US has a limited up mass, it's travelling very fast, often in the wrong direction, it needs to slow down before it hits atmosphere or it will burn up, it need fairly heavy landing gear. All these combined mean it's very difficult to get everything you need in the US to do a return, and still have enough left over mass to actually launch anything. It's not really big enough.

Those ones.

I'm not saying it's impossible, just very difficult to make it worth doing.
I know a law of physics when I see one, and those weren't.

Also, some of your statements of difficulty were plain wrong.

The stage is not "traveling in the wrong direction".  It is orbital.  You wait a couple of orbits and aim the reentry for near the coast.

You don't "need to slow down to avoid burning".  You need to "slightly slow down just like any reentering orbital vehicle"

You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements.  I allowed for doubling the stage dry mass because of that.

Also remember that many LEO missions are volume limited anyway.

So no, no physical laws.  Just a business decision.  If BFS wasn't front burner, they'd be working on it already.
« Last Edit: 01/30/2018 01:35 PM by meekGee »
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Offline Lar

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Re: F9 Second Stage Reusability
« Reply #553 on: 01/30/2018 03:39 PM »
The only way to get BFS US design close to right first time is to fly subscale version.

{{Citation needed}}
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Offline GWH

Re: F9 Second Stage Reusability
« Reply #554 on: 01/30/2018 04:10 PM »
Space shuttles and IXV have already proved what would be provable by reusable F9 upper stage. Wasting lots of resources to develop a new dead-end upper stage to F9 would have very little value.

What shuttle proved that reuse of a re-entry vehicle is possible. Shuttle did not prove out the economics of said reuse, in fact it proved out the dis-economies of reuse.

The value in that wouldn't be finding out if its possible, but if it can be done cheaply an routinely. Because just like reuse of the lower stage if you can't do the latter than the former is worthless.  Again, see the space shuttle.


Offline freddo411

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Re: F9 Second Stage Reusability
« Reply #555 on: 01/30/2018 04:42 PM »
Space shuttles and IXV have already proved what would be provable by reusable F9 upper stage. Wasting lots of resources to develop a new dead-end upper stage to F9 would have very little value.

What shuttle proved that reuse of a re-entry vehicle is possible. Shuttle did not prove out the economics of said reuse, in fact it proved out the dis-economies of reuse.


If you are going to claim that the Shuttle orbiter "proved out the dis-economies of reuse" -- FOR ANOTHER DESIGN --, you are going to have to provide a more detailed argument showing the staffing going into the refurb between flights, and what exactly they were spending their time on.   

Note that anytime spent on the SSME isn't a relevant example any longer, because SpaceX (and others) have demonstrated that flight-proven engines can refly with economical levels of refurbishment.

I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.

Offline GWH

Re: F9 Second Stage Reusability
« Reply #556 on: 01/30/2018 05:25 PM »
I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.

Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights.

In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts?

There are certainly ways to this through R&D, actually trying it being one of them. Dragon, while a source of data, does have the benefit of keeping its relatively small primary heat shield being protected for most of it's flight.


Offline deruch

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Re: F9 Second Stage Reusability
« Reply #557 on: 01/30/2018 09:27 PM »
US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5
I know a law of physics when I see one, and those weren't.

Also, some of your statements of difficulty were plain wrong.

The stage is not "traveling in the wrong direction".  It is orbital.  You wait a couple of orbits and aim the reentry for near the coast.

You don't "need to slow down to avoid burning".  You need to "slightly slow down just like any reentering orbital vehicle"

You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements.  I allowed for doubling the stage dry mass because of that.

Also remember that many LEO missions are volume limited anyway.

So no, no physical laws.  Just a business decision.  If BFS wasn't front burner, they'd be working on it already.

I'm curious what the 1:5 ratio you mentioned is based on?  I thought it was pretty clear that for adding recovery mass to the upper stage, it went 1:1 with payload.  Actually, it may be even a tiny bit worse than that because there is also a minor effect on first stage performance as well.
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Offline meekGee

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Re: F9 Second Stage Reusability
« Reply #558 on: 01/30/2018 09:48 PM »
US/payload ratio for LEO missions (the only type worth discussing in this context) is 1:5
I know a law of physics when I see one, and those weren't.

Also, some of your statements of difficulty were plain wrong.

The stage is not "traveling in the wrong direction".  It is orbital.  You wait a couple of orbits and aim the reentry for near the coast.

You don't "need to slow down to avoid burning".  You need to "slightly slow down just like any reentering orbital vehicle"

You need to carry a heat shield and a parachute, shift the c.g., and have structural reinforcements.  I allowed for doubling the stage dry mass because of that.

Also remember that many LEO missions are volume limited anyway.

So no, no physical laws.  Just a business decision.  If BFS wasn't front burner, they'd be working on it already.

I'm curious what the 1:5 ratio you mentioned is based on?  I thought it was pretty clear that for adding recovery mass to the upper stage, it went 1:1 with payload.  Actually, it may be even a tiny bit worse than that because there is also a minor effect on first stage performance as well.
No, not that ratio.  The penalty is 1:1 of course.

But an US that masses 4 tons will put a 20 ton payload in LEO.

So if the US mass goes 2x to 8 tons, payload goes down to 16 tons.

Which is a perfectly fine capability.

And if you really need 20, use an expendable US. (Which you need for GTO anyway)

.. and 2x is a very conservative assumption for heat shield and parachutes.



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Offline freddo411

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Re: F9 Second Stage Reusability
« Reply #559 on: 01/31/2018 04:20 PM »
I'm willing to believe that structures and TPS and other parts of the vehicle can be designed and built to require only minimal, economic amounts of refurb between flights.

Turning your point around please prove out how you've reached the conclusion that TPS and structures can be designed and built to require only minimal, economic amounts of refurb between flights.

In particular, how does one asses and ensure the life of these components? How does one optimize their processing to deal with something such as micrometeorite and orbital debris impacts?



It is an unproven assertion so far.   

SpaceX has quite a track record at this point of taking previously difficult, expensive and time consuming tasks (rocket engine refurb, capsule heat shield construction) and re-engineering them into reliable, inexpensive solutions.   I suspect that this is the case because they actually set out to make things into reliable, inexpensive solutions.

We'll just have to wait and see how difficult this ends up being for the TPS on BFS. 

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