Author Topic: F9 Block 5 Updates, Discussions, and Speculations  (Read 165199 times)

Online Lars-J

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #240 on: 04/01/2017 10:30 PM »
Any chance the new grid fins will pop open on ascent?

What would be the possible benefit of that? They add a lot of air resistance - great for descent, but there is zero benefit of doing that on the way up.

Perhaps they can maintain AoA without thrust vectoring, allowing the engine thrust to be used more effectively.  For example, the "free" lift generated by the high AoA would be used to gain altitude allowing the engine thrust to more directly contribute to delta v?

Thrust vectoring *is* the most efficient way to do anything at that altitude. The AoA flying observed in the latest launch was at the very edge of the atmosphere anyway. With aerodynamic surfaces, you *always* trade lift/control against air resistance. You do not get one without the other.

Offline AncientU

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #241 on: 04/01/2017 11:17 PM »
So that means 10% more payload for FH to LEO?  Then would FH get 60 tons to LEO in reusable mode?  What about expendable mode? 70-75 tons?  That could mean lots of heavy units for NASA's proposed moon orbiting station, without using the SLS. 

Several years ago when they were trying to figure out what to do after Shuttle, a lot of guys on this thread said 50 ton units to orbit would be optimal and cheaper with expendable rockets.  They were advocating Atlas V heavy, or Atlas V phase II, and Delta IV heavy with solids and cross feed to get to 50 tons.  Now SpaceX will soon do it with reusable boosters instead of expendable.
Nope that's not how it works. Extra thrust by itself only reduces gravity losses. For FH this helps a little more, cause the center booster can now throttle down sooner and save more fuel for after side booster separation. But that's not 10% more payload to LEO.
But the bottom line is only missions to the Moon/Mars and beyond actually need extra performance.
A risky enhancement would be to shutdown the 3 center booster engines equipped with restart capability, as the center booster could even shutdown all of its engine at some point if it had the ability to restart them right before side booster sep. Or equip even more center booster engine with restart capability and shut them down too. That would provide much of the cross feed benefits.
Perhaps, maybe, who knows, SX could do this for Red Dragon missions, as this would be solely SpaceX's risk.
Or after SX demonstrates thousands of M1D engines performing flawlessly.
In order to get more benefit from extra thrust, stages would have to be stretched, but the stages are already at the road transportability limit.

Don't look backward for the bottom line, look forward:
Propellant deliveries
Bigelow modules
Satellite constellations (NG will be carrying 80 sats)
Reusable second stages
Other stuff we haven't though of yet

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Offline Jim

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #242 on: 04/04/2017 02:56 PM »

Any chance the new grid fins will pop open on ascent?  Perhaps they can maintain AoA without thrust vectoring, allowing the engine thrust to be used more effectively.  For example, the "free" lift generated by the high AoA would be used to gain altitude allowing the engine thrust to more directly contribute to delta v?

Such a scheme would have to trade off against the extra drag generated by the deployed grid fins. I've no idea if it's worth it.  But something like this would match more directly with Elon's statements about increased payload, which don't seem to have the qualifications you'd expect if he were talking about only "increased payload for RTLS launches".

Bad idea on many levels. 

A.  long rockets don't fly at a AOA.  They try to avoid it.
b.  No reason to add more stress to the interstage
c.  Grids are behind the fairing.

Online OneSpeed

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #243 on: 04/05/2017 02:06 PM »
A.  long rockets don't fly at a AOA.  They try to avoid it.

Whilst I agree that the grid fins would not work on ascent, SES-10 flew at a non-trivial angle of attack from the 1:40 mark.

Offline guckyfan

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #244 on: 04/05/2017 02:58 PM »
I have a question on the new grid fins. They will have significant more control authority. I have translated that in my mind as they are bigger. Was I wrong? Will they be bigger or only a different more efficient form?

Offline meekGee

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #245 on: 04/05/2017 03:03 PM »
I have a question on the new grid fins. They will have significant more control authority. I have translated that in my mind as they are bigger. Was I wrong? Will they be bigger or only a different more efficient form?
IMO larger, and curved, since you can do that easily while forging, and it adds strength.
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Online Tuts36

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #246 on: 04/05/2017 03:45 PM »
Elon Musk (answering Chris G's question at the post- SES 10 launch presser):

Quote
... Block 5 is more like version 2.5 of Falcon 9, is probably the most accurate way to think about it. And the most important part of block 5 will be operating the engines at their full thrust capability, which is about 7 or 8, almost 10% more than what what they currently run at. Number of other improvements to have reusability - goes to the forged titanium grid fins, so that'll bring in a number of factors - block 5, version 2.5 will also incorporate a number of elements that are important to NASA for human spaceflight.
  (emphasis mine)

I've been trying to find more information on what these changes are.  My limited NSF search skills brought me to some discussion of the merlins' stress cracking, and NASA wants those addressed before they start launching people. 

Are there any other (non-paperworky) major modifications required on NASA's behalf?  And regarding the engine cracking, has anybody here heard anything about whether or not the redesigned version has reached the test firing stage, etc?  And what are the odds that the changes made to solve the stress cracking also permitted that extra performance boost he mentions?


Offline meekGee

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #247 on: 04/05/2017 04:07 PM »
Elon Musk (answering Chris G's question at the post- SES 10 launch presser):

Quote
... Block 5 is more like version 2.5 of Falcon 9, is probably the most accurate way to think about it. And the most important part of block 5 will be operating the engines at their full thrust capability, which is about 7 or 8, almost 10% more than what what they currently run at. Number of other improvements to have reusability - goes to the forged titanium grid fins, so that'll bring in a number of factors - block 5, version 2.5 will also incorporate a number of elements that are important to NASA for human spaceflight.
  (emphasis mine)

I've been trying to find more information on what these changes are.  My limited NSF search skills brought me to some discussion of the merlins' stress cracking, and NASA wants those addressed before they start launching people. 

Are there any other (non-paperworky) major modifications required on NASA's behalf?  And regarding the engine cracking, has anybody here heard anything about whether or not the redesigned version has reached the test firing stage, etc?  And what are the odds that the changes made to solve the stress cracking also permitted that extra performance boost he mentions?
I think Musk's versioning system is designed very specifically to troll detractors...

I mean, there's literally exactly one instance of each new numbering scheme  :)
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Online wannamoonbase

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #248 on: 04/05/2017 04:23 PM »
I think Musk's versioning system is designed very specifically to troll detractors...

I mean, there's literally exactly one instance of each new numbering scheme  :)

Seems possible, there is no consistency with each versions naming.  I'm a little surprised he didn't adopt something more software based.  Like F9 v2.2.1

SpaceX, just a few things planned for 2018: FH, Starlink Prototypes, Block 5, Dragon 2, Increased launch rate.

Offline cscott

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #249 on: 04/05/2017 04:48 PM »
Elon Musk (answering Chris G's question at the post- SES 10 launch presser):

Quote
... Block 5 is more like version 2.5 of Falcon 9, is probably the most accurate way to think about it. And the most important part of block 5 will be operating the engines at their full thrust capability, which is about 7 or 8, almost 10% more than what what they currently run at. Number of other improvements to have reusability - goes to the forged titanium grid fins, so that'll bring in a number of factors - block 5, version 2.5 will also incorporate a number of elements that are important to NASA for human spaceflight.
  (emphasis mine)

I've been trying to find more information on what these changes are.  My limited NSF search skills brought me to some discussion of the merlins' stress cracking, and NASA wants those addressed before they start launching people. 

Are there any other (non-paperworky) major modifications required on NASA's behalf?  And regarding the engine cracking, has anybody here heard anything about whether or not the redesigned version has reached the test firing stage, etc?  And what are the odds that the changes made to solve the stress cracking also permitted that extra performance boost he mentions?
I think Musk's versioning system is designed very specifically to troll detractors...

I mean, there's literally exactly one instance of each new numbering scheme  :)
I think it's more that the internal numbering schemes are not meant for public consumption, and Elon struggles to come up with good "public facing" version numbers. In this interview he was trying to convey that "Block 5" wasn't a huge deal and was a minor change compared to "Falcon v2" (whatever that was).  He had similar problems with "Tesla Model 3" which most folks think is "the latest and greatest", with the model S and X being versions 1 and 2.  He's been taking pains on twitter to try to convey that Model 3 is in fact the weakest and cheapest, and that the Model S is in fact still the flagship of the fleet.  Of course, the Model S doesn't have a real version number either, since it is subject to the same continual refinement in manufacturing that SpaceX uses.  In the car world however we are a little bit used to the idea of using "model year" as a proxy, so the "2017 Model S" is more advanced than the "2016 Model S"... even though the real hardware change didn't happen synchronized to a model year.

Anyway: habitual weakness of Elon, along with scheduling.  The engineers know what he's taking about.  The rest of us will manage to survive somehow.
« Last Edit: 04/05/2017 08:16 PM by cscott »

Online matthewkantar

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #250 on: 04/05/2017 09:27 PM »
I have a question on the new grid fins. They will have significant more control authority. I have translated that in my mind as they are bigger. Was I wrong? Will they be bigger or only a different more efficient form?
IMO larger, and curved, since you can do that easily while forging, and it adds strength.

There must be a reason for the oblong pentagon shape of the grid fins shown in the ITS video. Maybe they will look more like those.

Matthew
« Last Edit: 04/05/2017 09:35 PM by matthewkantar »

Offline JamesH65

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #251 on: 04/05/2017 09:33 PM »
I have a question on the new grid fins. They will have significant more control authority. I have translated that in my mind as they are bigger. Was I wrong? Will they be bigger or only a different more efficient form?
IMO larger, and curved, since you can do that easily while forging, and it adds strength.

There must be a reason for the oblong pentagon shape of the grid fins shown in the ITS video. Maybe they will look more like those.

Matthew

To get them out in to the main airflow, past any skin effect? No point in having fins where they don't have much effect.

Offline hrissan

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #252 on: 04/06/2017 07:31 AM »
IMHO titanium grid fins are big deal if they allow more shallow angle of attack during descent.

I've drawn the picture for myself to think about reentry. Shallower path makes the stage to fly longer path @ each atmospheric density, thus arriving to next density with reduced speed. The difference to stresses should be dramatic, as the drag is proportional to v^3.

Offline cambrianera

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #253 on: 04/06/2017 11:22 AM »
IMHO titanium grid fins are big deal if they allow more shallow angle of attack during descent.

I've drawn the picture for myself to think about reentry. Shallower path makes the stage to fly longer path @ each atmospheric density, thus arriving to next density with reduced speed. The difference to stresses should be dramatic, as the drag is proportional to v^3.
http://www.ukra.org.uk/docs/newsletter/1098volume7issue3.pdf

Look at the "Super Roc Rocket Gliders" article.
Obviously on a model rocket you can't have active means to keep a unstable, shallow angle of attack, but a full size rocket with grid fins...
And yes, dissipating more energy in higher atmo @ lower density means less propellant for braking.
Maybe SpaceX already did partially that with SES-10.
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Online Herb Schaltegger

Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #254 on: 04/06/2017 11:51 AM »
IMHO titanium grid fins are big deal if they allow more shallow angle of attack during descent.

I've drawn the picture for myself to think about reentry. Shallower path makes the stage to fly longer path @ each atmospheric density, thus arriving to next density with reduced speed. The difference to stresses should be dramatic, as the drag is proportional to v^3.
Drag is proportional to velocity squared, not cubed.
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Offline Lar

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #255 on: 04/06/2017 12:00 PM »
IMHO titanium grid fins are big deal if they allow more shallow angle of attack during descent.

I've drawn the picture for myself to think about reentry. Shallower path makes the stage to fly longer path @ each atmospheric density, thus arriving to next density with reduced speed. The difference to stresses should be dramatic, as the drag is proportional to v^3.
Drag is proportional to velocity squared, not cubed.

Still a significant savings if the stage can fly a shallower angle.... we've established that there is no reasonable way to turn around aerodynamically with just grid fins that doesn't generate a lot of heat so shallower angle means droneship has to be farther downrange (unless you spend something on a boostback or "slowdown" burn but that would increase the angle of reentry I would think unless you got turned all the way around)
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Offline envy887

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #256 on: 04/06/2017 01:43 PM »
IMHO titanium grid fins are big deal if they allow more shallow angle of attack during descent.

I've drawn the picture for myself to think about reentry. Shallower path makes the stage to fly longer path @ each atmospheric density, thus arriving to next density with reduced speed. The difference to stresses should be dramatic, as the drag is proportional to v^3.
The stresses of interest are heating rates, not drag - and heating rate does scale with velocity cubed.

Offline macpacheco

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #257 on: 04/06/2017 03:09 PM »
IMHO titanium grid fins are big deal if they allow more shallow angle of attack during descent.

I've drawn the picture for myself to think about reentry. Shallower path makes the stage to fly longer path @ each atmospheric density, thus arriving to next density with reduced speed. The difference to stresses should be dramatic, as the drag is proportional to v^3.
Drag is proportional to velocity squared, not cubed.
Drag force is ~v
Drag power is ~v
What matters is reducing drag power, which is why entry heating is ~v.
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Offline meekGee

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #258 on: 04/06/2017 03:43 PM »
IMHO titanium grid fins are big deal if they allow more shallow angle of attack during descent.

I've drawn the picture for myself to think about reentry. Shallower path makes the stage to fly longer path @ each atmospheric density, thus arriving to next density with reduced speed. The difference to stresses should be dramatic, as the drag is proportional to v^3.
Drag is proportional to velocity squared, not cubed.
The force of drag is.  But power dissipated goes by v cubed I believe.
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Online matthewkantar

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Re: F9 Block 5 Updates, Discussions, and Speculations
« Reply #259 on: 04/06/2017 04:39 PM »
I am not sure how the grid fins are currently fabricated, maybe egg crate style out of Al plate and then welded, maybe cut out of thick plate and then curved. In any case, I think forging will give them much more design freedom.  They will be able to taper the vanes to make the lighter and more aerodynamic. They will be able to thin the elements smoothly from the root where strength is needed to the tip where loads are much lighter.

The shape from the ITS video shows some of this. I am very interested to see what they come up with given the freedom forging will allow, though at great expense. Tooling costs make getting this right the first time very important. Any guesses on how much three+ square meter dies for a gigantic press are going to cost?

Matthew

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