Author Topic: F9 Second Stage Reusability  (Read 193558 times)

Online Robotbeat

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Re: F9 Second Stage Reusability
« Reply #560 on: 02/01/2018 01:01 AM »
I wouldn't put it past SpaceX to throw some TPS and a parachute on a 2nd stage for a Falcon 9 launch with a particularly light LEO payload.

SpaceX is king of "we're probably not going to do this thing" then "well, we changed our minds."
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Online meekGee

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Re: F9 Second Stage Reusability
« Reply #561 on: 02/01/2018 11:46 AM »
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.
Dragon is a good analogy actually..  same diameter, similar mass, a little shorter...  S2 has avionics...

Will require moving the cg and center of drag, adding heat shield, maybe dropping the large nozzle.

None of these are against the laws of physics or even of common sense engineering.

It's just that there are finite engineering resources, and BFS is front burner now.
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Offline hplan

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Re: F9 Second Stage Reusability
« Reply #562 on: 02/24/2018 06:22 PM »
I wouldn't put it past SpaceX to throw some TPS and a parachute on a 2nd stage for a Falcon 9 launch with a particularly light LEO payload.

SpaceX is king of "we're probably not going to do this thing" then "well, we changed our minds."

Elon seems to be talking about contingency plans in case the BFR takes longer to develop than planned--for example, a bigger fairing.

Let's say it takes 5 more years before BFR is flying commercial payloads. With 50 StarLink launches per year that could be 200 launches before BFR is flying.

That's 200 upper stages -- possibly $2 billion worth.

I know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?

Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #563 on: 02/24/2018 06:58 PM »
I know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?

Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.

They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.

How much you believe that is another question.
It can also recover F? second stages from LEO.

This could bring forward reusability by a year or two over a 'pure' BFR+BFS mature system.

There is also the interesting question of how much you believe now the second stage cost derived from the old statement of 'x% of the cost of the stage is saved with reuse'.

Especially in the case where manufacture of the first stage, sharing at least some of the equipment is at least reducing in cadence due to wholesale reuse, it's a mature technology largely.

Has there been any concrete recent statement about second stage costs?
Is it possible they've dropped from 40%  to 20 or lower?

That would drastically change the economics of actually bothering at all.

« Last Edit: 02/24/2018 06:59 PM by speedevil »

Offline Elmar Moelzer

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Re: F9 Second Stage Reusability
« Reply #564 on: 02/26/2018 05:12 AM »
Has there been any concrete recent statement about second stage costs?
Is it possible they've dropped from 40%  to 20 or lower?

That would drastically change the economics of actually bothering at all.
This is something I have been wondering about. If S2 and Merlin Vac were originally designed for reuse with all the margins and bells and whistles that come with that. How much could the cost of the second stage be reduced if they decide to completely drop (or shelf) the reuse idea for S2?
Might be able to shave off a little bit of dry weight too...
« Last Edit: 02/26/2018 05:15 AM by Elmar Moelzer »

Offline hkultala

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Re: F9 Second Stage Reusability
« Reply #565 on: 02/26/2018 10:11 AM »
I know SpaceX wants to put all its resources into BFR, but is it really not worthwhile for SpaceX to invest a couple hundred million in adding TPS and fins to the upper stage, with the chance to save $1-2 billion in upper stage costs?

Even if performance is poorer and a FH is required instead of an F9, this could be worthwhile if the hope of a block 5 cost of a couple million to refly a booster works out.

They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.


Which LEO and which payloads?

Practically no payload wants to go to such orbit that BFS could launch them as SSTO.

There are practically about six classes of payload destination:

1) GTO/GEO
2) GPS (12h orbit)
3) Polar Orbits/SSO
4) ISS
5) BEO (interplanetary probes etc)
6) Just anything to be able to say that "we are in space" and stay there for two weeks.

of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.
« Last Edit: 02/26/2018 10:13 AM by hkultala »

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #566 on: 02/26/2018 02:56 PM »
They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.


Which LEO and which payloads?

Practically no payload wants to go to such orbit that BFS could launch them as SSTO.
<snip>

of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.

At least several hundred do.

Starlink, specifically.
"Both of these satellites will be deployed in one mission aboard a SpaceX Falcon-9 v1.2 launch vehicle into an orbital plane of 514 km circular at 97.44 degrees inclination. After insertion, the satellite orbits will be raised to the desired mission altitude of 1125 km circular. ".

They have at least some manoeuvring capability. Having the capability to fit somewhat larger tanks to raise from 200km seems wholly plausible, or for very small inclination trims.

SSTO capacity depends on the details of course, BFR/S can sort of manage if large parts of the architecture wholly fail. BFS, everything has to work.

 
Quote
Next step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload
(Elon - Reddit).

If you take various assumptions that seem plausible, you get answers from 10-40 tons or so to SSTO.
The latter is almost certainly wrong - but note for example that the mass for BFS given at IAC was 85 tons, with massive passenger windows, and in principle removing those and leaving an empty shell may be lighter, so who knows.


The raw numbers for payload are uncertain, but the most basic calculations indicate it can get several Starlink to orbit, and allow them to do interesting things they need to practice for BFS anyway - orbital fuel transfer, ...

Paying for your launch vehicles testing with actual operational uses seems a very Elon thing to do.

As to 28 degrees - well, there is 25 degrees as well - for Texas, or 9 if they go back to Omelek.

It can't do large inclination changes, direct launch to circular (even 1100km) orbit, ...
But can it launch a large subset of Starlink sats, perhaps most if you make different assumptions (that a couple of refuellings are OK, doubling the prop on the sats  ...) - perhaps.

Offline envy887

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Re: F9 Second Stage Reusability
« Reply #567 on: 02/26/2018 04:10 PM »
They have said that they are planning on doing BFS first, then BFR.
BFS in principle, if it works to specs, can in principle launch F9 class payloads SSTO to LEO at least.


Which LEO and which payloads?

Practically no payload wants to go to such orbit that BFS could launch them as SSTO.
<snip>

of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.

At least several hundred do.

Starlink, specifically.
"Both of these satellites will be deployed in one mission aboard a SpaceX Falcon-9 v1.2 launch vehicle into an orbital plane of 514 km circular at 97.44 degrees inclination. After insertion, the satellite orbits will be raised to the desired mission altitude of 1125 km circular. ".

They have at least some manoeuvring capability. Having the capability to fit somewhat larger tanks to raise from 200km seems wholly plausible, or for very small inclination trims.

SSTO capacity depends on the details of course, BFR/S can sort of manage if large parts of the architecture wholly fail. BFS, everything has to work.

 
Quote
Next step will be doing orbital velocity Ship flights, which will need all of the above. Worth noting that BFS is capable of reaching orbit by itself with low payload
(Elon - Reddit).

If you take various assumptions that seem plausible, you get answers from 10-40 tons or so to SSTO.
The latter is almost certainly wrong - but note for example that the mass for BFS given at IAC was 85 tons, with massive passenger windows, and in principle removing those and leaving an empty shell may be lighter, so who knows.


The raw numbers for payload are uncertain, but the most basic calculations indicate it can get several Starlink to orbit, and allow them to do interesting things they need to practice for BFS anyway - orbital fuel transfer, ...

Paying for your launch vehicles testing with actual operational uses seems a very Elon thing to do.

As to 28 degrees - well, there is 25 degrees as well - for Texas, or 9 if they go back to Omelek.

It can't do large inclination changes, direct launch to circular (even 1100km) orbit, ...
But can it launch a large subset of Starlink sats, perhaps most if you make different assumptions (that a couple of refuellings are OK, doubling the prop on the sats  ...) - perhaps.

Starlink plans 7500 sats in 300 km VLEO, which is likely reachable with BFR as SSTO. Some of the inclinations would require launching out of VAFB, which shouldn't really be an issue.

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #568 on: 02/26/2018 04:34 PM »
Starlink plans 7500 sats in 300 km VLEO, which is likely reachable with BFR as SSTO. Some of the inclinations would require launching out of VAFB, which shouldn't really be an issue.

Quite.
The 'several hundred' was based on the assumption of one launch site, no capacity to launch to much more than a couple of planes and no large additional fuel on the satellites - basically the absolute worst case. (if it actually can do SSTO with several Starlink sats).
If you've got a spare 10 tons to your optimal launch inclination, you can pretty much launch to any inclination.

Offline dglow

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Re: F9 Second Stage Reusability
« Reply #569 on: 03/03/2018 03:41 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.

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #570 on: 03/03/2018 04:04 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.

Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.

Starlink satellites can be launched just fine out of the 3.6*3.6m door, and even once BFR is up and running, a very simple turtable will launch a plane a time or so in a very low stress mission with plenty of margin - ideal for development.

BFS+BFRs payload is just too big, and the flight rate is just too high to make a new vehicle make sense, even for Starlink.

(more than about half full - 70 tons - 140 satellites - and you start running into plane change issues on the satellites).

Things may differ if there are many large payloads that won't go out the 3.6*3.6m door.

Offline dglow

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Re: F9 Second Stage Reusability
« Reply #571 on: 03/03/2018 05:15 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.

Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.

Operationally, yes, but financially? BFR's bread is buttered by Starlink's revenues.

Quote
BFS+BFRs payload is just too big, and the flight rate is just too high to make a new vehicle make sense, even for Starlink.

New vehicle? No, but definitely a variation. SpaceX has shown a willingness to experiment and iterate, to opportunistically defer significant projects (FH) in order to obtain more immediate advantages (F9 booster return).

I'm betting that behavior won't change, especially as SpaceX attempts to juggle operational optimization of its existing LVs, construction and deployment of its cash cow, and development of a highly experimental new LV. In the execution of these three we will certainly witness several pivots of varying size and degree (e.g. ITS -> BFR).

I thought you made a strong case for SSTO operation above. If it offers a more economical means to Starlink deployment and with deployment/replenishment an ongoing need there's little doubt SpaceX would customize the vehicle for said operation. The chomper variant already demonstrates this willingness.
« Last Edit: 03/03/2018 05:25 PM by dglow »

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #572 on: 03/03/2018 05:43 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.

Modifying BFS much makes absolutely no sense for this, if it works at all, and if you are deviating from getting BFR up and running.

Operationally, yes, but financially? BFR's bread is buttered by Starlink's revenues.

By 'new vehicle' - I don't mean a new design of vehicle, I mean that in many cases, a specific BFS may be able to launch the complete Starlink fleet without any additional vehicles being built at all, as especially with BFR, once you've got a plane up at a time, there is little incentive to try for two planes, if in fact you can do rapid reusability.

Making a plane a week of satellites is quite taxing enough.

The savings from making a new BFS-SSTO specifically designed for satellite launching are small, as pretty much any case where this makes sense is diluted if it slows you at all from getting BFR up and running.

Also if it slows you from getting rapid reuse operationally working well for BFS.

Working out cadence on a 'small' launcher like BFS which doesn't have to be stacked, and does not require great infrastructure to launch it could be really valuable insights into designing the launch infrastructure for BFR.

Offline Lar

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Re: F9 Second Stage Reusability
« Reply #573 on: 03/03/2018 11:09 PM »
(fan) I could see some equipment in the cargo bay (a turntable dispenser with racks that ratchet each satellite to where it needs to be to be pushed out the cargo door, one after the other, as Speedevil alludes to) but not a new mold line. Not at first. I've said this before and will again, once the basic BFS system is up and running, THEN there may  be variants, but first, no.

(mod) what does this have to do with F9 Second Stage Reusability ?
« Last Edit: 03/03/2018 11:10 PM by Lar »
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Online Robotbeat

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Re: F9 Second Stage Reusability
« Reply #574 on: 03/04/2018 04:28 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.
Two stages is more efficient and puts much less wear and tear (relatively to payload) on the heatshield. Two stage to orbit, if you have capability for extremely rapid integration, is too good to pass up.
« Last Edit: 03/04/2018 04:29 PM by Robotbeat »
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Offline dglow

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Re: F9 Second Stage Reusability
« Reply #575 on: 03/05/2018 07:29 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?

Offline envy887

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Re: F9 Second Stage Reusability
« Reply #576 on: 03/05/2018 03:50 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.

Offline hkultala

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Re: F9 Second Stage Reusability
« Reply #577 on: 03/05/2018 04:11 PM »
[offtopic]


Quote from: speedevil
Quote from: hkultala
of these, only group 6 can be satisfied by SSTO-BFS. And the group 6 is very small, practically no satellite wants to be in ~200km orbit at ~28 degrees inclination.

At least several hundred do.

Starlink, specifically.

Starlink plans 7500 sats in 300 km VLEO, which is likely reachable with BFR as SSTO. Some of the inclinations would require launching out of VAFB, which shouldn't really be an issue.

Starlink has a polar/very high inclination orbit. Polar orbit needs about 400 m/s more than low inclination due not getting the starting velocity from earth rotation.

Definetely not reachable with BFS as SSTO, at least with landing fuel.

Even a low inclination LEO should probably not be reachable with any reasonable payload and landing fuel, reachable only without landing fuel with very small payload.

[/offtopic]
« Last Edit: 03/05/2018 04:41 PM by hkultala »

Online meekGee

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Re: F9 Second Stage Reusability
« Reply #578 on: 03/05/2018 05:20 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.

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Offline Kansan52

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Re: F9 Second Stage Reusability
« Reply #579 on: 03/05/2018 05:43 PM »
A recoverable 2nd stage would eat up payload mass. But would Starlink close the business plan? A reusable 2nd stage that put up only 1/2 the number of Starlink sats but could be reused over and over again. It would also have the advantage of easing pressure on the manufacturing line.

Of course if BFR/BFS is not ready in time.

I know they have said no a number of times but they do pivot when the situation presents an opportunity.

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