Author Topic: F9 Second Stage Reusability  (Read 189475 times)

Offline Negan

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Re: F9 Second Stage Reusability
« Reply #580 on: 03/05/2018 06:53 PM »
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield why?
Greater fuel margins allow for more retropropulsion?

Just because TSTO can launch more payload for the same number of burnt heatshields.

Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.
« Last Edit: 03/05/2018 06:58 PM by Negan »

Offline uhuznaa

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Re: F9 Second Stage Reusability
« Reply #581 on: 03/05/2018 07:40 PM »
I find this discussion fascinating. Consider the significant iterative payload upgrades we've seen with F9 while enabling reusability, no less. Even if BFS can repeat only a fraction of those gains? The option for SSTO Starlink deployments seems just too good for SpaceX to pass up.

A stretched chomper-style BFS with extra SL Raptors? Yes, please.

It would probably be wise to see the projected dry mass and payload capabilities of BFR/BFS (including the theoretical SSTO capability) as the end result AFTER several iterations, with the first "block" having considerably less payload than that. Just as SpaceX didn't build the reusable F9 FT Block 5 right after the Falcon 1 they probably will be happy if the first BFR/BFS will make it to orbit and back undamaged with a very small payload and allows them to look over it to improve the next one they will build.

If there will be a BFS that can do SSTO it might be the third, fourth or fifth iteration but certainly not the first.


Offline envy887

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Re: F9 Second Stage Reusability
« Reply #582 on: 03/05/2018 07:54 PM »
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield why?
Greater fuel margins allow for more retropropulsion?

Just because TSTO can launch more payload for the same number of burnt heatshields.

Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.

Same thing. What's cheaper if you have to launch 12,000 satellites: $3M for 10 tonnes or $5M for 150 tonnes?

Offline Elmar Moelzer

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Re: F9 Second Stage Reusability
« Reply #583 on: 03/05/2018 10:39 PM »
It would probably be wise to see the projected dry mass and payload capabilities of BFR/BFS (including the theoretical SSTO capability) as the end result AFTER several iterations, with the first "block" having considerably less payload than that. Just as SpaceX didn't build the reusable F9 FT Block 5 right after the Falcon 1 they probably will be happy if the first BFR/BFS will make it to orbit and back undamaged with a very small payload and allows them to look over it to improve the next one they will build.

If there will be a BFS that can do SSTO it might be the third, fourth or fifth iteration but certainly not the first.
I see it the other way round. The currently projected dry mass and payload capabilities are the beginning and future iterations (like was the case with F9) will be much more capable.
IIRC SpaceX never projected as huge payload capabilities for F9 and engine performance for Merlin as we are seeing today.
Also, what speaks against your conjecture is that Musk mentioned that they would take BFS all the way to orbit (without BFR) for their test flights. Unless my memory is failing me here.

Offline Negan

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Re: F9 Second Stage Reusability
« Reply #584 on: 03/06/2018 12:52 AM »
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield why?
Greater fuel margins allow for more retropropulsion?

Just because TSTO can launch more payload for the same number of burnt heatshields.

Actually the "wear and tear" metric is pretty useless. We are talking about depreciation which is a component of launch cost which is the only thing that matters. Considering the whole launch cost is supposed to be less than an F1 launch, BFS depreciation could very well be less than the fuel cost of the BFR.

Same thing. What's cheaper if you have to launch 12,000 satellites: $3M for 10 tonnes or $5M for 150 tonnes?

Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?
« Last Edit: 03/06/2018 12:57 AM by Negan »

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #585 on: 03/06/2018 01:19 AM »
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Any sort of commodity bulk carrier on a predictable set of routes?

Online Lar

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Re: F9 Second Stage Reusability
« Reply #586 on: 03/06/2018 02:40 AM »
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Any sort of commodity bulk carrier on a predictable set of routes?

I.e. Late Stage BFS operations on certain routes....
"I think it would be great to be born on Earth and to die on Mars. Just hopefully not at the point of impact." -Elon Musk
"We're a little bit like the dog who caught the bus" - Musk after CRS-8 S1 successfully landed on ASDS OCISLY

Offline AC in NC

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Re: F9 Second Stage Reusability
« Reply #587 on: 03/06/2018 03:09 AM »
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Can someone unring this bell?  Perhaps reframe what is being discussed?  I think you two are talking past each other.

Offline Negan

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Re: F9 Second Stage Reusability
« Reply #588 on: 03/06/2018 03:11 AM »
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Any sort of commodity bulk carrier on a predictable set of routes?

Based on the following I would use number of estimated trips to determine useful life in this case:

The useful life of identical assets varies by user, and they depend upon the asset's age, the frequency of its use, the condition of the business's environment and the asset's repair policy.
« Last Edit: 03/06/2018 03:23 AM by Negan »

Offline Negan

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Re: F9 Second Stage Reusability
« Reply #589 on: 03/06/2018 03:19 AM »
Highly doubtful they will measure the useful life of BFS based on tonnage to orbit. Can you name another transportation system that would use this measurement?

Can someone unring this bell?  Perhaps reframe what is being discussed?  I think you two are talking past each other.

Only if all <10 ton payloads cease to exist. BFS's useful life will be determined by frequency of use not tonnage to orbit. Depreciation equals cost divided by estimated useful life.
« Last Edit: 03/06/2018 03:40 AM by Negan »

Offline AC in NC

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Re: F9 Second Stage Reusability
« Reply #590 on: 03/06/2018 03:48 AM »
Only if all <10 ton payloads cease to exist. BFS's useful life will be determined by frequency of use not tonnage to orbit. Depreciation equals cost divided by estimated useful life.
No one (well speedevil kind of did but tangentially and not seriously) said it does.  As I said, you two are talking past each other arguing unrelated details.
« Last Edit: 03/06/2018 03:49 AM by AC in NC »

Online wannamoonbase

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Re: F9 Second Stage Reusability
« Reply #591 on: 03/09/2018 03:00 PM »
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield why?
Greater fuel margins allow for more retropropulsion?
Also because you're not taking very large tanks to very high velocities.

Staging hides in the"dry mass" portion of the rocket equation, once you taken into account a finite payload ratio.

ABCD: Always Be Counting Down



And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.
SpaceX, just a few things planned for 2018: FH, Starlink Prototypes, Block 5, Dragon 2, Increased launch rate.

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #592 on: 03/09/2018 03:49 PM »
And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.

If you've solved stackability, and orbital recovery, three stage is an interesting option.
It allows large payloads to very, very high energies.

But, that is a pretty large 'if'.
Any non-trivial 'zeroth'' stage for almost all useful purposes means a much higher velocity at the next stage burnout, and for it to be far downrange.
About the only exception would be if it was a slow ballistic stage to lift the stage off the pad at low speed, to clear weather, and to allow for use of vacuum engines on the main stage.

But, even if you wanted to do this, you can't, unless your engines are on a considerably wider part of the stage, because you don't have the area.
A 'low' speed at staging, as implied by a two stage vehicle with an energetic second stage means recovery is so much simpler.

F9 - no way would it make sense in the context of reusability.

Online wannamoonbase

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Re: F9 Second Stage Reusability
« Reply #593 on: 03/09/2018 05:54 PM »
And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.

If you've solved stackability, and orbital recovery, three stage is an interesting option.
It allows large payloads to very, very high energies.

But, that is a pretty large 'if'.
Any non-trivial 'zeroth'' stage for almost all useful purposes means a much higher velocity at the next stage burnout, and for it to be far downrange.
About the only exception would be if it was a slow ballistic stage to lift the stage off the pad at low speed, to clear weather, and to allow for use of vacuum engines on the main stage.

But, even if you wanted to do this, you can't, unless your engines are on a considerably wider part of the stage, because you don't have the area.
A 'low' speed at staging, as implied by a two stage vehicle with an energetic second stage means recovery is so much simpler.

F9 - no way would it make sense in the context of reusability.

I agree completely.  Especially with the current market.  Just having a reuseable first stage is enough apparently to crush everyone else in the industry.

However, 3 stages could be hugely beneficial. 

A large diameter vehicle, say 12 meters, would provide lots of space for vacuum nozzles.  I like wider and shorter vehicles to minimize tank surface area for subcooled propellants.  The optimum stage zero would be cross-feed, leaving stage 1 fully fueled.  But we know that's not likely to happen.

3 stages just seems like a good way to optimize taking less mass all the way to orbit then having to bring it back.  Taking something to 5+ miles per second just to bring it back to zero is a lot of work.

Edit: None of this is going to happen on F9 or FH, so I'll let it go.  Would be pretty cool though, but they know what they are doing and they can get to a high launch rate and make money with the Block 5 vehicles.
« Last Edit: 03/09/2018 05:58 PM by wannamoonbase »
SpaceX, just a few things planned for 2018: FH, Starlink Prototypes, Block 5, Dragon 2, Increased launch rate.

Offline hkultala

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Re: F9 Second Stage Reusability
« Reply #594 on: 03/10/2018 07:43 AM »
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield.

Less wear on the heatshield why?
Greater fuel margins allow for more retropropulsion?
Also because you're not taking very large tanks to very high velocities.

Staging hides in the"dry mass" portion of the rocket equation, once you taken into account a finite payload ratio.

ABCD: Always Be Counting Down


And here I am thinking about 3 stage vehicles.  It would make the orbital stage easier.


Always when thinking about stages, there has to be a plan WHAT the stages are. Not just how many there are.

Reusability for 2-stage LEO is straighforward:

First stage gives some 2km/s staging velocity and can return to the launch site.
Second stage can easily reach LEO with good payload fraction from the staging point, and can then stay in the orbit long enough so that it can return to the launch after the trajectory passes over the launch site later.

Reusability for any other configuration gets more complex:

SSTO to LEO with all the heat shielding etc gets very hard, the stage is very hard to make.

And TSTO to GTO means that
1) Considerable more delta-v needed than for LEO.
1a) First staging has to occur at higher velocity making RTLS vry difficult
1b) Second stage still has to give more delta-v to the payload. doing that while having heat shield etc is getting difficult
2) If the launch site is not at equator, the second stage no longer passes over the launch site. Even if it could land, it could not land to the launch site, unless it spents some propellant for inclination change.

so, three stages might be preferred for reusable GTO/high energy missions.


So, what would the three stages be?

3STO would not be very practical for reusable craft. Where would a suborbital second stage return?

What would seem to make most sense is to have a TSTO + a space tug for high energy orbits.
That would minimize the mass going to the final orbit, and minimize the mass that has to do the inclination change to come back to the launch site.
first stage could easily do RTLS, second stage could return from LEO that passes over the launch site.
And because the delta-v from LEO to GTO is not very much, third stage could even have heat shield and be able to do the inclination change to come back to over launch site.

However, this might not fit to F9 very well. But, for BFR.. would increase the single launch(no refueling)  payload to high energy orbits considerably. Sending a ~5-tonne upper stage to GTO instead of 85-tonne spaceship while the 85-tonne spaceship stays on LEO.

And Blue origin plan looks like this, they have an optional third stage. So normal LEO configuration is TSTO, later high energy configuration adds a third stage. (though they will initially do 2-stage to high energy orbits also before their 3rd stage is ready and before their second stage is reusable)
« Last Edit: 03/10/2018 07:45 AM by hkultala »

Online Robotbeat

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Re: F9 Second Stage Reusability
« Reply #595 on: 04/15/2018 11:14 PM »
Posted on the TESS thread, but:

Elon: “This is gonna sound crazy, but ...
SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon“
https://twitter.com/elonmusk/status/985654333860601856?s=21
« Last Edit: 04/15/2018 11:16 PM by Robotbeat »
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Online cppetrie

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Re: F9 Second Stage Reusability
« Reply #596 on: 04/15/2018 11:15 PM »
Posted on the TESS thread, but:

Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21
Too much Teslaquila again. April fools was 2 weeks ago.

Online IanThePineapple

Re: F9 Second Stage Reusability
« Reply #597 on: 04/15/2018 11:17 PM »
I hope we find out when they'll start doing this, but maybe it's just a design in R&D at this point.

Online Robotbeat

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Re: F9 Second Stage Reusability
« Reply #598 on: 04/15/2018 11:18 PM »
Posted on the TESS thread, but:

Elon: https://twitter.com/elonmusk/status/985654333860601856?s=21
Too much Teslaquila again. April fools was 2 weeks ago.
I actually kinda believe it. Not literally a party balloon, but maybe some other large balloon or ball Ute.

TESS is absolutely tiny, so maybe the upper stage has enough performance to spare here.

Just need more COPVs in the upper stage for the greater helium load.
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Offline yokem55

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Re: F9 Second Stage Reusability
« Reply #599 on: 04/15/2018 11:19 PM »
Well, they have the helium for it. So, assuming this isn't a crazy joke, they use the giant balloon to generate more drag in the high upper atmosphere to slow the stage more before coming in too hot?

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