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.
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.
Quote from: Req on 03/31/2017 02:56 amMusk 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?
Quote from: deruch on 03/31/2017 03:22 amAlso 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...
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.
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"
Quote from: Req on 03/31/2017 02:56 amDuring 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?
Quote from: cppetrie on 03/31/2017 03:08 amQuote from: Req on 03/31/2017 02:56 amDuring 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?
Quote from: guckyfan on 04/01/2017 03:02 pmQuote from: cppetrie on 03/31/2017 03:08 amQuote from: Req on 03/31/2017 02:56 amDuring 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?
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.
Quote from: Lars-J on 04/01/2017 10:17 pmNew 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.
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! :-)
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?
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)
- 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.
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?
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.
Quote from: guckyfan on 04/02/2017 10:08 amSo 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.