Author Topic: Refurbishment of Used Stages/Vehicles  (Read 208390 times)

Online cppetrie

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Re: Refurbishment of Used Stages/Vehicles
« Reply #640 on: 03/31/2017 03:08 AM »
During the presser, Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.
If I understand that correctly they want to increase the amount of aerobraking done by the grid fins in order to decrease fuel margin required for landing. Yes?

Online deruch

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Re: Refurbishment of Used Stages/Vehicles
« Reply #641 on: 03/31/2017 03:22 AM »
During the presser, Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.
Also could be used to decrease peak heating by flying through the upper atmosphere a bit longer.  Reducing TPS needs or re-entry burn length, etc.  Lots of ways to optimize for best results.
Shouldn't reality posts be in "Advanced concepts"?  --Nomadd

Offline manoweb

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Re: Refurbishment of Used Stages/Vehicles
« Reply #642 on: 03/31/2017 04:12 AM »
Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.

This sounds quite an interesting concept but I have no idea what is a L/D of 1. Would you explain a little more in detail this concept?


Also could be used to decrease peak heating by flying through the upper atmosphere a bit longer.  Reducing TPS needs or re-entry burn length, etc.  Lots of ways to optimize for best results.

What is TPS in this case? This means it will arrive further downrange? Not sure having to go much further with the barge contributes to "rapid" reusability...

Online cppetrie

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Refurbishment of Used Stages/Vehicles
« Reply #643 on: 03/31/2017 04:25 AM »
Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.

This sounds quite an interesting concept but I have no idea what is a L/D of 1. Would you explain a little more in detail this concept?

I had to look it up as well. Lift-to-drag ratio. Typically a plane/glider is trying to maximize this number and most commercial airliners have ratios exceeding 15. Some have values as high as 37. In this case a value approaching 1 would seem to indicate an objective of making an aerobrake that can also act as a control surface.
https://en.wikipedia.org/wiki/Lift-to-drag_ratio

Quote
Also could be used to decrease peak heating by flying through the upper atmosphere a bit longer.  Reducing TPS needs or re-entry burn length, etc.  Lots of ways to optimize for best results.

What is TPS in this case? This means it will arrive further downrange? Not sure having to go much further with the barge contributes to "rapid" reusability...
TPS = thermal protection system??
I agree landing further down range is probably not ideal although if another day to port reduces refurb time by a couple days it's a net gain. Might even save enough fuel margin to permit RTLS for more payloads, even some GTO missions.

Edit: added link to wiki article; fixed to not point to mobile version
« Last Edit: 03/31/2017 05:06 AM by cppetrie »

Offline manoweb

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Re: Refurbishment of Used Stages/Vehicles
« Reply #644 on: 03/31/2017 04:59 AM »
I suggest the link to be https://en.wikipedia.org/wiki/Lift-to-drag_ratio so it will not force people that use a computer to read a "mobile" version of wikipedia. If you access from a cellular phone, it will still render correctly.

I have read such page and now I am somewhat familiar, on a qualitative basis, with the L/D ratio. Now, when Mr. E. Musk said "the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1", this means that the L/D ratio is going to be increased or decreased compared to the "current" aluminum ones?

In other words, the current grid fins have a L/D of less than 1 and they want to increase it, or viceversa?
« Last Edit: 03/31/2017 05:09 AM by manoweb »

Offline Kaputnik

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Re: Refurbishment of Used Stages/Vehicles
« Reply #645 on: 03/31/2017 06:26 AM »
The grid fins don't themselves have a L/D, it is the vehicle as a whole which does.
A L/D of 1 would be an increase/improvement over the current design. It means that the stage can travel as far horizontally as it does vertically.

Landing further downrange is perfectly acceptable if it opens up reusability of heavier and hotter flights. An extra day or two of barge steaming time is insignificant. They will have lots of cores and can always build more barges.
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Offline mme

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Re: Refurbishment of Used Stages/Vehicles
« Reply #646 on: 03/31/2017 06:41 AM »
The grid fins don't themselves have a L/D, it is the vehicle as a whole which does.
A L/D of 1 would be an increase/improvement over the current design. It means that the stage can travel as far horizontally as it does vertically.

Landing further downrange is perfectly acceptable if it opens up reusability of heavier and hotter flights. An extra day or two of barge steaming time is insignificant. They will have lots of cores and can always build more barges.
A greater L/D might also allow a few more missions to RTLS.
Space is not Highlander.  There can, and will, be more than one.

Online Lee Jay

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Re: Refurbishment of Used Stages/Vehicles
« Reply #647 on: 03/31/2017 08:43 PM »
Looks like Wayne Hale agrees with Jim (and so do I).

https://twitter.com/waynehale/status/847774460933439488
"Congratulations SpaceX. It's been nearly six years since we've seen the launch of a reused rocket. #spaceshuttle"

Offline Aussie_Space_Nut

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Re: Refurbishment of Used Stages/Vehicles
« Reply #648 on: 04/01/2017 03:11 AM »
My favourite quote from the SES 10 press conference was when Elon mentioned "building up the space fleet" when answering a question on what they were doing with the flown rockets at the cape I think. It made me smile! :-)

Offline guckyfan

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Re: Refurbishment of Used Stages/Vehicles
« Reply #649 on: 04/01/2017 03:02 PM »
During the presser, Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.
If I understand that correctly they want to increase the amount of aerobraking done by the grid fins in order to decrease fuel margin required for landing. Yes?

Provide lift so it stays longer in high altitude thin air. It seemed New Glenn intends to reenter without reentry burn. At least the animation did not show one. Maybe block 5 can do that too. It would be a large saving of propellant. If New Glenn can indeed do that with its higher reentry speed then why not Falcon?

Online cppetrie

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Re: Refurbishment of Used Stages/Vehicles
« Reply #650 on: 04/01/2017 03:37 PM »
During the presser, Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.
If I understand that correctly they want to increase the amount of aerobraking done by the grid fins in order to decrease fuel margin required for landing. Yes?

Provide lift so it stays longer in high altitude thin air. It seemed New Glenn intends to reenter without reentry burn. At least the animation did not show one. Maybe block 5 can do that too. It would be a large saving of propellant. If New Glenn can indeed do that with its higher reentry speed then why not Falcon?
Ok so is the idea to make the re-entry profile flatter so more aerobraking can be accomplished on the way down rather than having it fall more vertically where it would have less time to bleed off speed via aerobraking? Essentially more glider like and less meteor like?

Offline Kaputnik

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Re: Refurbishment of Used Stages/Vehicles
« Reply #651 on: 04/01/2017 04:37 PM »
During the presser, Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.
If I understand that correctly they want to increase the amount of aerobraking done by the grid fins in order to decrease fuel margin required for landing. Yes?

Provide lift so it stays longer in high altitude thin air. It seemed New Glenn intends to reenter without reentry burn. At least the animation did not show one. Maybe block 5 can do that too. It would be a large saving of propellant. If New Glenn can indeed do that with its higher reentry speed then why not Falcon?
Ok so is the idea to make the re-entry profile flatter so more aerobraking can be accomplished on the way down rather than having it fall more vertically where it would have less time to bleed off speed via aerobraking? Essentially more glider like and less meteor like?

Pretty much. It sounds like the new grid fins will themselves create more drag, and the ability to fly a shallower entry also spreads out the heating loading. Incidentally, lifting entry is also key to getting Red Dragon down on Mars safely- such a heavy object would othwise crater into the surface long before it had slowed down enough for the retros to take over.
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Offline Lars-J

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Re: Refurbishment of Used Stages/Vehicles
« Reply #652 on: 04/01/2017 10:17 PM »
During the presser, Musk said that the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1, which will actually have the net effect of increasing payload to orbit by reducing the fuel needs for landing.
If I understand that correctly they want to increase the amount of aerobraking done by the grid fins in order to decrease fuel margin required for landing. Yes?

Provide lift so it stays longer in high altitude thin air. It seemed New Glenn intends to reenter without reentry burn. At least the animation did not show one. Maybe block 5 can do that too. It would be a large saving of propellant. If New Glenn can indeed do that with its higher reentry speed then why not Falcon?

New Glenn will stage faster, and enter the atmosphere at shallower angle. F9 comes in at a much steeper angle, and when doing RTLS it almost drops vertically straight down. So they may not be able to do the same.

Offline guckyfan

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Re: Refurbishment of Used Stages/Vehicles
« Reply #653 on: 04/02/2017 02:11 AM »
New Glenn will stage faster, and enter the atmosphere at shallower angle. F9 comes in at a much steeper angle, and when doing RTLS it almost drops vertically straight down. So they may not be able to do the same.

They are flying the trajectory that makes most sense with the present method of reentry. They can change the trajectory for new needs.

Offline Lars-J

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Re: Refurbishment of Used Stages/Vehicles
« Reply #654 on: 04/02/2017 06:19 AM »
New Glenn will stage faster, and enter the atmosphere at shallower angle. F9 comes in at a much steeper angle, and when doing RTLS it almost drops vertically straight down. So they may not be able to do the same.

They are flying the trajectory that makes most sense with the present method of reentry. They can change the trajectory for new needs.

Not for RTLS - Unless they want to burn a lot more propellant. But then what was the point of eliminating the braking burn?  :)

This may in fact be the reason why NG does not do RTLS, it could be designed for a shallow reentry angle.
« Last Edit: 04/02/2017 06:20 AM by Lars-J »

Offline guckyfan

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Re: Refurbishment of Used Stages/Vehicles
« Reply #655 on: 04/02/2017 10:08 AM »
So if you have the fuel for RTLS, do that and maybe only reduce the reentry burn to 1 engine. But on marginal missions for downrange landing do a lower  trajectory, that is where saving is most needed.

Online AncientU

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Re: Refurbishment of Used Stages/Vehicles
« Reply #656 on: 04/02/2017 11:07 AM »
My favourite quote from the SES 10 press conference was when Elon mentioned "building up the space fleet" when answering a question on what they were doing with the flown rockets at the cape I think. It made me smile! :-)

The interesting feature of this reuse capability is that SpaceX now has roughly the launch vehicle availability (new production plus 2-3 reuses per core) to launch the entire world's orbital payloads* -- 80-90 launches per year. 

When Block 5 begins production, each core will have that capability.

Pad operations, fairing availability, and second stage production become the new limits.


*  Of course there are a couple payloads that have unique mass/trajectory needs that will require FH capability which is yet to be proven.
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Offline john smith 19

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Re: Refurbishment of Used Stages/Vehicles
« Reply #657 on: 04/02/2017 04:55 PM »
Today Mr. E. Musk suggested they might replace the aluminum grid find with titanium ones. Follow up metallurgical questions:

- why titanium and not inconel or tungsten, if the issue is resisting to the heat. (Yeah I know tungsten is crazy). However, and I am no titanium metallurgist, is it really good at high temperatures?
When looking at materials for aerospace the density matters.
Roughly the specific gravities relative to a unit volume of water (water is 1) are
Aluminum 2.8
Beryllium 1.85
Lead 11.37
Tungsten 19.25
Inconel 8.44
Titanium 4.51

On this scale Lead is not all that dense and Tungsten is more on the same order as Uranium.

Titanium buys you a melting point close to 3x that of Aluminum, and Aluminum (like most metals) looses a lot of its strength well below its melting point. 

In an ideal world Berylium would rule as it's even lighter than Alumium and twice the melting point.

Except
a)It and it's oxide are highly toxic, needing sealed machining cells.
b)It's brittle near room temperature (but gets better as it gets hotter) and
c) It's about 200x more expensive than Aluminum. That's head and shoulders more than either Inconel, Titanium and IIRC Tungsten. 

Quote from: manoweb
I will do some research but while I am pretty sure it can easily beat aluminum, I did not know titanium was considered in high temperature applications. Now that I think about the Blackbird was made out of titanium, so my concerns here are bogus
- Mr. E. Musk apparently mentioned a forging process for such structure, and the biggest in the world for titanium. Why not machine it? (And I probably show my complete ignorance with this question)
Actually a fair question given you need a very big press to forge it.  Machining loses a lot of material and forging does give a better "grain" to metal (yes metal grain is a thing in high performance applications).

Titanium does offer another option. You could assemble plates of it and diffusion bond it in a vacuum furnace. The down side is you make up a "pack" of Ti plates with steel spacers. You then have to remove the spacers and that may involve a lot of machining anyway.
Quote from: manoweb
- Titanium is much denser than Alu, and it may be that in this application, they just need large area to have enough control authority, so they won't be able to make the structure thinner - they might have to take a mass penalty for the sake of reuse. And it's totally fine, just worth noting.
There is also reliability. Up till now the grid fins have been Aluminum or Aluminum coated with a Thermal Protection System, probably the SX version of the PICA ablative NASA developed.

That means the upper use temperature is set by how long the TPS can save the underlying Aluminum before fully burning away, leaving the Aluminum a melting puddle. But for multiple uses you want to limit any given flight to a fraction of that, as you wouldn't want to be re-covering that waffle pattern with little bits of PICAX every flight.

Making the fin out of Titanium means no TPS layer to worry about burning through (or being put on wrongly and falling off in flight, which is possible). That also means greatly reduced inspection, so faster turnaround.

The greater control authority of the new fins should also more accurate positioning of the stage before you have to fire the engines for the hoverslam. If this can be shown to happen consistently then you can reduce the propellant load for this to happen.

This stuff is all about trading off different factors to get the best overall outcome in terms of payload to orbit, landing propellant and ease of refurbishment and manufacture.
« Last Edit: 04/02/2017 05:08 PM by john smith 19 »
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Offline john smith 19

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Re: Refurbishment of Used Stages/Vehicles
« Reply #658 on: 04/02/2017 05:31 PM »

I have read such page and now I am somewhat familiar, on a qualitative basis, with the L/D ratio. Now, when Mr. E. Musk said "the new titanium alloy grid fins will be a larger design which provides enough control authority to give the stage an L/D of approximately 1", this means that the L/D ratio is going to be increased or decreased compared to the "current" aluminum ones?
Increased.

L/D varies over a speed range. A L/D of 1 for subsonic aircraft is very bad (IIRC most big passenger jets are in the 15-30 range) but for supersonic 7 (concorde at M2) is quite good. Shuttle was somewhere in 1-1.5 range at M5. The Apollo capsule was around 0.3-0.5 (and rocket stages are much more like the Apollo capsule than the Shuttle). Giving a stage a L/D of 1 would be a major achievement.

At very high speed even quite low L/D can give remarkable results. IIRC something with a hypersonic L/D of 2.5-3 can have a cross range of basically a whole hemisphere
BFS. The worlds first Methane fueled FFORSC engined CFRP structured A380 sized aerospaceplane tail sitter capable of flying in Earth and Mars atmospheres. BFR. The worlds biggest Methane fueled FFORSC engined CFRP structured booster for BFS. First flight to Mars by end of 2022. Forward looking statements. T&C apply. Believe no one. Run your own numbers. So, you are going to Mars to start a better life? Picture it in your mind. Now say what it is out loud.

Offline Lars-J

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Re: Refurbishment of Used Stages/Vehicles
« Reply #659 on: 04/02/2017 10:02 PM »
So if you have the fuel for RTLS, do that and maybe only reduce the reentry burn to 1 engine. But on marginal missions for downrange landing do a lower  trajectory, that is where saving is most needed.

No, you don't seem to understand. The higher trajectory *IS* the optimal one. The stage isn't thrusting upwards... It merely cancels and reverses its horizontal vector. The same apogee would have been reached with or without a boost-back burn. Doing a shallower boost-back profile does in fact consume MORE propellant.

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