Author Topic: F9 - S2 reusable modification as evolution steps to BFS(ITS)  (Read 27761 times)

Offline DreamyPickle

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #120 on: 09/11/2017 08:40 AM »
Quote
Both stages are alike in that they will be bottom heavy so they will tend to flip heavy end on to the flow.

Yes, this is a real problem. Significant effort went in properly designing the center-of-mass for the shuttle, X-33 and similar vehicles. The BFS will also have the same problem as F9 S2: It will be extremely bottom heavy.

However if you look at http://BFS drawings you see two spherical tanks at the top of each propellant tank. If the landing propellant is moved in there then the center of mass will move forward quite a bit. It also has the advantage that by having a smaller surface area it heats up slower.



I don't know how to adapt this for F9.
« Last Edit: 09/11/2017 08:41 AM by DreamyPickle »

Offline john smith 19

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #121 on: 09/11/2017 11:23 AM »
I don't know how to adapt this for F9.
That's really the core of the problem with this thread. :(  Even if you can do all this to an F9 US how does that feed into ITS, or vice versa.

Small factoid.

The concept of "sump tanks" was used in the Kistler RLV design but AFAIK dates back to bowl shaped depressions in the tank ends of the Agena stage to encourage enough propellant to be retained by surface tension forces to smooth engine restart. NASA has also done work to improve fluid capture in tank feed lines by (effectively) tapering them, but historically this has been expensive to do. IIRC sounding rocket tests showed a 50% improvement in collecting fluid, not vapor.

Agena was a very impressive design. Part stage, part satellite bus and probably the only US hypergolic stage design with common bulkhead tanks, yet AFAIK then never failed.   :o
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Online rsdavis9

1)Roughly speaking a US had to lose 4x the energy per unit mass that a booster has to lose to land.


isn't the energy per unit mass 22 times?
(7/1.5)^2
bob

Offline wannamoonbase

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #123 on: 09/11/2017 01:18 PM »
1)Roughly speaking a US had to lose 4x the energy per unit mass that a booster has to lose to land.


isn't the energy per unit mass 22 times?
(7/1.5)^2


Kinetic Energy =  (4/1.5)^2 = 21.8 times

Heat Energy Power= (7/1.5)^3 = 101.6 times
« Last Edit: 09/11/2017 02:09 PM by wannamoonbase »
Excited to be finally into the first Falcon Heavy flow, we are getting so close!

Offline Robotbeat

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #124 on: 09/11/2017 02:03 PM »
Heat power, not energy.
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Online rsdavis9

Quote
Kinetic Energy =  (4/1.5)^2 = 21.8 times

Heat Energy = (7/1.5)^3 = 101.6 times
Sorry if I am being a dummy here but energy = heat energy.
Where did the 4 come from in the 4/1.5 shouldn't it be 7/1.5
Kinetic energy will turn into heat one for one.

EDIT:
Sorry I missed the correction of heat energy to heat power.
So why is Heat Power a cubed relation? Couldn't find any reference...
Probably something to do with hypersonic compression of a gas?
« Last Edit: 09/11/2017 03:03 PM by rsdavis9 »
bob

Online meekGee

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #126 on: 09/11/2017 03:03 PM »
Quote
Both stages are alike in that they will be bottom heavy so they will tend to flip heavy end on to the flow.

Yes, this is a real problem. Significant effort went in properly designing the center-of-mass for the shuttle, X-33 and similar vehicles. The BFS will also have the same problem as F9 S2: It will be extremely bottom heavy.

However if you look at http://BFS drawings you see two spherical tanks at the top of each propellant tank. If the landing propellant is moved in there then the center of mass will move forward quite a bit. It also has the advantage that by having a smaller surface area it heats up slower.



I don't know how to adapt this for F9.
Of course it is, but yes, it is solvable.

Very little fuel is left over after the reentry burn - only enough for the landing burn which in our case is non existent, so any contribution of fuel to the problems is non existent as well.

Heat shield and parachute  both  near the front end, will help with the c.g.  So will dropping the nozzle.

Drag device will help with the c.d.

Maybe the active control device is a sled, located near the heat shield.

Point is, if we're allowing up to 100% mass penalty, c.g. location can't be a show stopper.
ABCD - Always Be Counting Down

Offline Robotbeat

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #127 on: 09/11/2017 04:31 PM »
Quote
Kinetic Energy =  (4/1.5)^2 = 21.8 times

Heat Energy = (7/1.5)^3 = 101.6 times
Sorry if I am being a dummy here but energy = heat energy.
Where did the 4 come from in the 4/1.5 shouldn't it be 7/1.5
Kinetic energy will turn into heat one for one.

EDIT:
Sorry I missed the correction of heat energy to heat power.
So why is Heat Power a cubed relation? Couldn't find any reference...
Probably something to do with hypersonic compression of a gas?
Think of the mass of air that the cross section displaces. That displaced mass flow per unit time is proportional to velocity, and the energy dumped per unit mass is proportional to velocity squared (i.e. kinetic energy). Multiply those together and you get cubed.

Nothing at all complicated about this.
« Last Edit: 09/11/2017 04:34 PM by Robotbeat »
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Online rsdavis9

Quote
Kinetic Energy =  (4/1.5)^2 = 21.8 times

Heat Energy = (7/1.5)^3 = 101.6 times
Sorry if I am being a dummy here but energy = heat energy.
Where did the 4 come from in the 4/1.5 shouldn't it be 7/1.5
Kinetic energy will turn into heat one for one.

EDIT:
Sorry I missed the correction of heat energy to heat power.
So why is Heat Power a cubed relation? Couldn't find any reference...
Probably something to do with hypersonic compression of a gas?
Think of the mass of air that the cross section displaces. That displaced mass flow per unit time is proportional to velocity, and the energy dumped per unit mass is proportional to velocity squared (i.e. kinetic energy). Multiply those together and you get cubed.

Nothing at all complicated about this.

As einstein said if you can't explain it to your grandmother than you really don't understand it.
Thats why I like the simple first order "feel" explanations.

Thank you
bob

Offline envy887

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #129 on: 09/11/2017 08:14 PM »
Also agree that it's a sensible approach. Essentially the stage only needs to stay alive 24 hours or so. Batteries should handle that. LOX boil off shouldn't be a problem for a stage in LEO. De-orbit can be handled by a set of Dracos if necessary. Also useful for control during entry. It might not even be necessary to eject the engine nozzle. After the helicopter has caught the stage it could be lowered horizontally into a cradle on the ground so that the nozzle isn't impacted.

Doesn't even need to stay alive for 24 hours. For a typical GTO or ISS launch, it will pass over the Pacific within 1000 miles of California in 2 to 10 hours. Almost everything out of Vandy can once around 1200 to 1800 miles out in the Pacific within 2 hours. Just need a ship out of LA that can support a largish helicopter. Grab the stage under chutes, drop it in a large airbag on the deck, and bring everything home.

Offline john smith 19

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #130 on: 09/11/2017 10:29 PM »
1)Roughly speaking a US had to lose 4x the energy per unit mass that a booster has to lose to land.


isn't the energy per unit mass 22 times?
(7/1.5)^2
Note that word "roughly."  :(

To keep the maths really simple on the differences between S2 and S1 I took stage separation at 1/2 orbital velocity and altitude at 1/4 altitude. Hence "roughly" 4x difference. it kept the numbers simple enough to not need a calculator once you included both KE and PE.

But in fact the real story is even worse.  :( At 200Km it's nearer 7794m/s roughly 27:1 on KE.

I used the crude 4x because Shoywell said the current generation of F9 boosters were good for about 3 launches, so if the environment was 4x worse then doing what you did on the booster in terms of TPS thickness would not survive 1 use, and historically TSTO ELV's have split the delta V roughly in 2 equal pieces.

In fact (as you've noted ) the orbital situation is so much worse than the boost stage because booster MECO is well below 1/2 orbital speed.

IOW SX will need a TPS that's 27x better than the stuff on the booster per unit mass.
Most people don't expect that big a hit. Any area that's got say 1lb of TPS on the booster (and is equally exposed on the US) will need 27lb of TPS to protect it.

I'm pretty sure the science doesn't have that much stretch left in it.

[EDIT. TPS "design" is a bit of a misnomer. The composition, working and heat treatment of the materials involved can have such a huge effect on the final properties that it's more like baking. Just as flour, fat, salt and water can give you bread, pizza, flaky pastry or pie casing. Same ingredients, very different outcomes.]
« Last Edit: 09/12/2017 06:40 PM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline john smith 19

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #131 on: 09/11/2017 10:45 PM »
See, I never "abandoned" the idea that US recovery would work like booster recovery, since I've never had it in the first place.  You're the only one who had it.
And you don't know much about how engineers actually do their job either.

Generally if they find something that works, especially after a long hard search with dead ends, they will try to apply it as widely as possible to situations, unless it is very inefficient. I'd be very surprised if SX didn't run some simulations to double check if the S1 recovery plan could work for US use.
Quote from: meekGee
Instead, I look at the closer analog I can find, for a stubby orbital object with a mass of approximately 5 tons, and I see Dragon, or capsules in general.  I don't even consider the booster, since that's an entirely different problem, from any angle I look at it.
Which is short, very dense and can put all its structure in the shadow of the heat shield, which is impossible for a stage.
Quote from: meekGee
You say that "You're right that works for booster recovery won't work for US recovery, which I'd say SX have known since at least 2014."

Actually, I think they've known that since forever, since the thought of doing S1-like recovery for S2 never crossed their minds. 
You're entitled to your opinion. Perhaps you should take another look at the video SX released in 2011?
Quote from: meekGee
The reusability video showed ballistic re-entry, but used a landing engine/legs instead of parachutes.  THAT may have changed, but that's nowhere near doing boost-back and re-entry burns.
If you're already in orbit you don't have to do "boost back" as you're "coming round again" on the launch site. What you do need to do is decelerate enough to start the reentry process. Shuttle did it exactly the way the S1 does it, retro burn (using OMS) but then flipped back over for nose first entry as it would have been difficult to land rear end first.
Quote from: meekGee
As for an "actual plan" - what exactly are you expecting?  My engineering staff is currently pre-occupied with several other projects.
Something more than a wish list?

Wishing is for wizards who can cast spells.  :( I haven't found magic to work in this universe, so I tend to rely on engineering. 
« Last Edit: 09/12/2017 07:52 AM by john smith 19 »
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #132 on: 09/14/2017 12:53 PM »
https://twitter.com/elonmusk/status/908254079092002816
Quote

Long road to reusabity of Falcon 9 primary boost stage…When upper stage & fairing also reusable, costs will drop by a factor >100.

If F9 is going to be reusable with very high cycle counts, it implies that ITSy might be somewhat delayed?
Or could this in fact act to advance things, if revenue from the constellation comes online sooner than expected.



« Last Edit: 09/14/2017 01:00 PM by speedevil »

Online AncientU

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #133 on: 09/14/2017 02:57 PM »
https://twitter.com/elonmusk/status/908254079092002816
Quote

Long road to reusabity of Falcon 9 primary boost stage…When upper stage & fairing also reusable, costs will drop by a factor >100.

If F9 is going to be reusable with very high cycle counts, it implies that ITSy might be somewhat delayed?
Or could this in fact act to advance things, if revenue from the constellation comes online sooner than expected.

F9 fairing and second stage reuse are already in flight test (or late development); means that ITSy may be somewhat advanced.  Think of all this kaboomy goodness as prototyping for ITSy.
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Offline su27k

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #134 on: 09/15/2017 03:59 AM »
https://twitter.com/elonmusk/status/908254079092002816
Quote

Long road to reusabity of Falcon 9 primary boost stage…When upper stage & fairing also reusable, costs will drop by a factor >100.

If F9 is going to be reusable with very high cycle counts, it implies that ITSy might be somewhat delayed?
Or could this in fact act to advance things, if revenue from the constellation comes online sooner than expected.

If they want to start deploying constellation in 2019, they'll have to rely on F9, so a reusable S2 is a good investment, I don't think ITSy is part of the equation.

Offline Robotbeat

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #135 on: 09/15/2017 04:33 AM »
They want Falcon 9 highly reusable so they can shut down the Falcon production line and switch it over to BFR.
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Offline woods170

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #136 on: 09/15/2017 05:54 AM »
They want Falcon 9 highly reusable so they can shut down the Falcon production line and switch it over to BFR.
No. the Falcon production line will stay open, albeit down-sized. BFR and Falcon 9 will co-exist for quite some time with Falcon 9 being the working horse (needing fresh stages once in a while to replace warn-out reused ones) whilst SpaceX is working the bugs out of BFR.

Offline Lars-J

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #137 on: 09/15/2017 06:39 AM »
They want Falcon 9 highly reusable so they can shut down the Falcon production line and switch it over to BFR.
No. the Falcon production line will stay open, albeit down-sized. BFR and Falcon 9 will co-exist for quite some time with Falcon 9 being the working horse (needing fresh stages once in a while to replace warn-out reused ones) whilst SpaceX is working the bugs out of BFR.

Don't forget about the Falcon upper stages. They are build on the same production line as the first stages, so they will stay busy. (And reuse of falcon upper stages is far off, even if they will experiment)

Offline john smith 19

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #138 on: 09/15/2017 07:03 AM »
No. the Falcon production line will stay open, albeit down-sized. BFR and Falcon 9 will co-exist for quite some time with Falcon 9 being the working horse (needing fresh stages once in a while to replace warn-out reused ones) whilst SpaceX is working the bugs out of BFR.
Agreed. Lots of people have noted that SX does not retain production of anything that's served its purpose but IRL F9 is the design that's launching payloads right now.  FH is 2/3s more or less stock F9s and that's not even flown yet.  I doubt it will reach RL10/Centaur levels of longevity (is there any other US design from that era still flying?) but it seems safe to say it will be around for at least a decade.
"Solids are a branch of fireworks, not rocketry. :-) :-) ", Henry Spencer 1/28/11  Averse to bold? You must be in marketing."It's all in the sequencing" K. Mattingly.  STS-Keeping most of the stakeholders happy most of the time.

Offline livingjw

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Re: F9 - S2 reusable modification as evolution steps to BFS(ITS)
« Reply #139 on: 09/15/2017 11:39 AM »
I suspect that a reusable upper stage for F9 would have an internal layout where the cargo is placed between the propellant tanks. This would place the payload near the cg. Something like the X-37B but with a wingless lifting body similar to ITS.

John

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