Author Topic: F9 Second Stage Reusability  (Read 226592 times)

Offline TrevorMonty

Re: F9 Second Stage Reusability
« Reply #940 on: 11/18/2018 09:16 am »
Well that was 933 posts for nothing.
What did you expect? This is Elon Musk we are talking about.

It's also NSF. This forum could spend 933 posts discussing if the next BFR will be chicken-powered.

Chicken power confirmed!
How manys chickens per booster and what  breed. These questions should keep us going till Elon's next tweet.

Online aero

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Re: F9 Second Stage Reusability
« Reply #941 on: 11/18/2018 03:20 pm »
Well that was 933 posts for nothing.
What did you expect? This is Elon Musk we are talking about.

It's also NSF. This forum could spend 933 posts discussing if the next BFR will be chicken-powered.

Chicken power confirmed!
How manys chickens per booster and what  breed. These questions should keep us going till Elon's next tweet.

Not actually chickens, they are falcons. Don't know what breed.
Retired, working interesting problems

Online matthewkantar

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Re: F9 Second Stage Reusability
« Reply #942 on: 11/18/2018 04:04 pm »
If they were chickens wouldn't Musk be clucking about it, not tweeting?

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #943 on: 11/18/2018 07:35 pm »
https://twitter.com/elonmusk/status/1063865779156729857
Funny, I thought this had been dead since 2014.

When you factored in the massive increase in KE and PE for orbital velocity, multiplied by the fact you trade 1 for 1 on a US rather than the 6 to 1 to 13 to 1 for the booster stage

Although I respect that the SX design team must have moved heaven and Earth to make it work without losing an unfeasible amount of payload.
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 Rocket Science

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Re: F9 Second Stage Reusability
« Reply #944 on: 11/18/2018 08:03 pm »
https://twitter.com/elonmusk/status/1063865779156729857
Funny, I thought this had been dead since 2014.

When you factored in the massive increase in KE and PE for orbital velocity, multiplied by the fact you trade 1 for 1 on a US rather than the 6 to 1 to 13 to 1 for the booster stage

Although I respect that the SX design team must have moved heaven and Earth to make it work without losing an unfeasible amount of payload.
;)
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #945 on: 11/18/2018 08:09 pm »
https://twitter.com/elonmusk/status/1063865779156729857
Funny, I thought this had been dead since 2014.

When you factored in the massive increase in KE and PE for orbital velocity, multiplied by the fact you trade 1 for 1 on a US rather than the 6 to 1 to 13 to 1 for the booster stage

Although I respect that the SX design team must have moved heaven and Earth to make it work without losing an unfeasible amount of payload.

Trailing ballute seems like one plausible solution that makes it seemingly work to greatly reduce heat flux.
It could also be applicable to S1 - and reduce or eliminate the need for an entry burn.
This may buy back some of the penalty, especially for FH high energy launches.
It could also be applicable to aerocapture for Mars for non-BFS.


They backed off on public statements about how much they were going to reuse shortly after first launch - since then there have been various statements going from 'testing' to learning to 'complete reuse in 2-3 years for $6M'.
It's been very far from clear it was dead, though it seems so now, who knows what the next tweet will say?
« Last Edit: 11/18/2018 08:13 pm by speedevil »

Offline Rocket Science

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Re: F9 Second Stage Reusability
« Reply #946 on: 11/18/2018 08:22 pm »
https://twitter.com/elonmusk/status/1063865779156729857
Funny, I thought this had been dead since 2014.

When you factored in the massive increase in KE and PE for orbital velocity, multiplied by the fact you trade 1 for 1 on a US rather than the 6 to 1 to 13 to 1 for the booster stage

Although I respect that the SX design team must have moved heaven and Earth to make it work without losing an unfeasible amount of payload.

Trailing ballute seems like one plausible solution that makes it seemingly work to greatly reduce heat flux.
It could also be applicable to S1 - and reduce or eliminate the need for an entry burn.
This may buy back some of the penalty, especially for FH high energy launches.
It could also be applicable to aerocapture for Mars for non-BFS.


They backed off on public statements about how much they were going to reuse shortly after first launch - since then there have been various statements going from 'testing' to learning to 'complete reuse in 2-3 years for $6M'.
It's been very far from clear it was dead, though it seems so now, who knows what the next tweet will say?
;)
"The laws of physics are unforgiving"
~Rob: Physics instructor, Aviator, Vintage auto racer

Offline Zed_Noir

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Re: F9 Second Stage Reusability
« Reply #947 on: 11/19/2018 03:06 pm »
Think Musk have nixed further development of a reusable F9 upper stage.

But that is not the end of attempting to recover the F9 upper stage. It could be the mini BFS test article Musk have earlier tweeted. Maybe even with paying customer(s) who will take the risk discount for the flight.

Just recovering an intact upper stage will give insights for the SpaceX hardware developers.

Online Tulse

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Re: F9 Second Stage Reusability
« Reply #948 on: 11/19/2018 06:01 pm »
If there is no intention to make the second stage reusable, how much benefit would there be to recovering it?  What information could be gleaned to make it perform more effectively?  The stage is already functioning fine, isn't it?

Offline Kansan52

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Re: F9 Second Stage Reusability
« Reply #949 on: 11/19/2018 06:07 pm »
If there is no intention to make the second stage reusable, how much benefit would there be to recovering it?  What information could be gleaned to make it perform more effectively?  The stage is already functioning fine, isn't it?

Recovering the miniBFR give them reentry data they want.

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #950 on: 11/19/2018 09:05 pm »
If there is no intention to make the second stage reusable, how much benefit would there be to recovering it?  What information could be gleaned to make it perform more effectively?  The stage is already functioning fine, isn't it?
The truth is no one really knows

Maybe all parts are indeed well within their design and operation limits many of them could be lightened and still be within them.

OTOH some of them could be surprisingly close to their limits and if a particular copy of that part is at the bottom of its acceptable QC parameter range and the environment is a bit more extreme than usual then it will fail.

No one really knows, so yes getting a returned intact US (even if never flew again) would be very useful in anchoring simulations in reality.
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 Wudizzle

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Re: F9 Second Stage Reusability
« Reply #951 on: 11/19/2018 09:48 pm »
Well that was 933 posts for nothing.
What did you expect? This is Elon Musk we are talking about.

It's also NSF. This forum could spend 933 posts discussing if the next BFR will be chicken-powered.

Chicken power confirmed!
I've suspected this for some time.

"The chicken manure therefore was able to support the methane yield at 270 L/kg of VS, a value comparably higher than other kinds of livestock wastes."
https://onlinelibrary.wiley.com/doi/pdf/10.1002/bit.260231013


Offline Nomadd

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Re: F9 Second Stage Reusability
« Reply #952 on: 11/20/2018 05:26 am »
Well that was 933 posts for nothing.
What did you expect? This is Elon Musk we are talking about.

It's also NSF. This forum could spend 933 posts discussing if the next BFR will be chicken-powered.

Chicken power confirmed!
How manys chickens per booster and what  breed. These questions should keep us going till Elon's next tweet.

Not actually chickens, they are falcons. Don't know what breed.
Merlins
Those who danced were thought to be quite insane by those who couldn't hear the music.

Offline docmordrid

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Re: F9 Second Stage Reusability
« Reply #953 on: 11/20/2018 08:15 am »
Falco columbarius. Small, but aggressive.
« Last Edit: 11/20/2018 08:19 am by docmordrid »
DM

Offline Wolfram66

Re: F9 Second Stage Reusability
« Reply #954 on: 11/21/2018 04:31 pm »
Well it could be ChickenHawk aka Cooper's Hawk... puts it in the raptor family
whilst not an official name, this designation has been applied to the following

Cooper's hawk (Accipiter cooperii)  Most commonly
Sharp-shinned hawk (Accipiter striatus)
Red Tail Hawk (Buteo jamaicensis)

Online LouScheffer

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Re: F9 Second Stage Reusability
« Reply #955 on: 11/21/2018 07:47 pm »
Well that was 933 posts for nothing.
It's not clear to me this is a contradiction.  It agrees with the line of thought that they will modify the S2 to test re-entry aerodynamics and thermal protection, but will not try to make S2 re-usable.

Offline speedevil

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Re: F9 Second Stage Reusability
« Reply #956 on: 11/21/2018 07:52 pm »
To avoid the problems with parachuting and capture, once the testing of entry is finished at 20km and ~mach 1, do a short burn to bring the velocity to around zero, and then latch S2 to a ballistic S1 that was launched some minutes earlier, which then goes on to land as normal.
Dynamic pressure at ~0 velocity and 20km is small enough that the cold gas thrusters can handle terminal rendevous.

Also works for Dragon - fairings would be harder.
« Last Edit: 11/21/2018 07:57 pm by speedevil »

Offline john smith 19

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Re: F9 Second Stage Reusability
« Reply #957 on: 11/21/2018 08:46 pm »
Trailing ballute seems like one plausible solution that makes it seemingly work to greatly reduce heat flux.
It could also be applicable to S1 - and reduce or eliminate the need for an entry burn.
This may buy back some of the penalty, especially for FH high energy launches.
It could also be applicable to aerocapture for Mars for non-BFS.
Depends.

On the upside they are one of the few SoA concepts that leverages the longitudinal strength of the stage, rather than needing it to be horizontally strong as well.

Downside. Deployment is going to be tricky. Putting it under the payload attach fitting is fairly easy, but puts the engines nose forward. OTOH the ideal location at the engine end (the center) is occupied by an engine.

Then we have materials. Parachute material is normally 70g/m^2 Nylon, but that starts to burn pretty easily. 

Higher temperature resistant materials start to get heavier.

The key issue is can you deliver more deceleration at higher altitude (and hence ideally at lowish temperatures) than an equivalent mass of ablatives.

Of course the real question about US recovery is can any approach dump enough of the combined KE & PE from orbit (at a low enough) mass penalty to preserve enough payload to make it worthwhile?

I've still not seen any actual trials of any approach so far by SX.
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 Hop_David

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Re: F9 Second Stage Reusability
« Reply #958 on: 11/24/2018 06:57 pm »
From my back of the envelope calculations, for a 150 x 35622 km GTO, I get an apogee speed of 1598 m/s.  Lowering perigee to 75 km requires an apogee speed of 1590 m/s, a deltaV of only 8 m/s.  That of course is a Hohmann transfer and current S2 design may make surviving that long difficult. Did you assume your delta V happens soon after satellite deploy when both it and S2 are going fast ?  That will definitely cost much more fuel there.

My numbers are pretty close to yours.

But what about circularization at apogee? That'd take another 1.4 km/s. And if orbit is circularized it'd then take another 1.4 km/s to drop perigee back into the atmosphere.

Or perhaps circularization is accomplished by something other than S2. In any case S2 would re-enter at around 10.2 km/s. It'd have about 1.73 times the kinetic energy to shed as something re-entering from LEO.

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