Author Topic: F9 Second Stage Reusability  (Read 137553 times)

Offline docmordrid

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Re: F9 Second Stage Reusability
« Reply #660 on: 04/16/2018 07:13 PM »
Once they have Crew Dragon's conformal Trunk solar arrays mastered ISTM using them to extend S2  battery life and prevent RP-1 gelling is low hanging fruit.
« Last Edit: 04/16/2018 07:15 PM by docmordrid »
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Offline Nilof

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Re: F9 Second Stage Reusability
« Reply #661 on: 04/17/2018 07:08 AM »
Another way to see the S2 reuse is that it paradoxically makes it easier to phase out the F9 in favor of BFR.

If SX is forced to maintain F9 capability for a time after commercializing BFR, they can keep a Falcon 9 stockpile going for a lot longer if the stockpiled rockets are fully reusable.

By the time the full BFR reaches the point where it has been launched a few times, Falcon 9 will likely have a launch record of a couple hundred launches and it'll probably stay a coveted launch option for any conservative customer, especially if we don't see any more major mishaps.
For a variable Isp spacecraft running at constant power and constant acceleration, the mass ratio is linear in delta-v.   Δv = ve0(MR-1). Or equivalently: Δv = vef PMF. Also, this is energy-optimal for a fixed delta-v and mass ratio.

Online speedevil

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Re: F9 Second Stage Reusability
« Reply #662 on: 04/17/2018 08:51 AM »
Another way to see the S2 reuse is that it paradoxically makes it easier to phase out the F9 in favor of BFR.
If BFR is flying, you can also plausibly delete S2 recovery hardware, and recover with BFS.
This lets you get the full nominal performance of the rocket, while being able to recover it, for customers that want to fly on F9.

I question if this market segment exists though, as anyone really insisting on F9 is likely to want a new one.

Online niwax

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Re: F9 Second Stage Reusability
« Reply #663 on: 04/17/2018 10:33 AM »
Another way to see the S2 reuse is that it paradoxically makes it easier to phase out the F9 in favor of BFR.
If BFR is flying, you can also plausibly delete S2 recovery hardware, and recover with BFS.
This lets you get the full nominal performance of the rocket, while being able to recover it, for customers that want to fly on F9.

I question if this market segment exists though, as anyone really insisting on F9 is likely to want a new one.

Do you mean sending up a BFS to pick up the stranded S2 in LEO and return it to the surface? That's absolutely insane. I love it.

Online speedevil

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Re: F9 Second Stage Reusability
« Reply #664 on: 04/17/2018 12:09 PM »
Do you mean sending up a BFS to pick up the stranded S2 in LEO and return it to the surface? That's absolutely insane. I love it.

Indeed.

To raise another point on S2 reuse - though this would not always technically be reusing the stage, put one on BFS, full, and you can throw about 12 tons very hard at Jupiter or Saturn, with no in-orbit refuelling, or some 30 tons at Mars.

Online rst

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Re: F9 Second Stage Reusability
« Reply #665 on: 04/17/2018 01:02 PM »
So, ummm... anyone have a mass estimate for the ballute-onto-bouncy-house recovery system?

One possibly relevant citation: a study of ballute systems for a somewhat more demanding application -- braking a 7500 kg capsule on a lunar return trajectory:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060018288.pdf

had "total system mass (not including inflation system) with 20% mass contingency" at 550 kg. On the flip side, there's a paper here on a somewhat more worked-out proposal for Cygnus recovery that has a baseline estimate of 482 kg for inflation, inflatable structure, and TPS -- but an additional 830 kg for avionics, instruments and "structure", for a total of about 1.3 mT.

https://websites.isae-supaero.fr/IMG/pdf/137-heart-ippw-9_v04-tpsas.pdf

Either way, this is on the low end for estimates of S2 recovery hardware, but a few hundred kg more or less could make a real difference as to whether you could contemplate using this scheme for missions beyond LEO.

Offline Space Ghost 1962

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Re: F9 Second Stage Reusability
« Reply #666 on: 04/17/2018 09:18 PM »
You don't know the scope of the system yet, so mass estimates could be way off. Also, these systems can have "compressible" systems, so his 100x greater ballistic coefficient needs to be referenced to an altitude and speed. Very different between say deployment, EI, and critical deceleration points.

Also, materials have changed, especially for the shroud lines one might use for this.

And you'd also like to know when/what the low altitude recovery posture is as well, as that's a significant part of the mass budget.

If this approach decelerates high enough, it might not require any heat shields/TPS at all.

Online Comga

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Re: F9 Second Stage Reusability
« Reply #667 on: 04/17/2018 09:28 PM »
Bingo
Remember how this discussion started two days, and three pages, ago:

Elon: “This is gonna sound crazy, but ...
SpaceX will try to bring rocket upper stage back from orbital velocity using a giant party balloon“
https://twitter.com/elonmusk/status/985654333860601856?s=21

"bring rocket stage back from orbital velocity" doesn't say anything about surviving or recovering.
"party balloon" does suggest something very light and thin.
It seems to be another low cost SpaceX experiment, and probably light weight.
They will learn from it, whatever happens.
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Online rst

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Re: F9 Second Stage Reusability
« Reply #668 on: 04/17/2018 10:06 PM »
"bring rocket stage back from orbital velocity" doesn't say anything about surviving or recovering.

"... and then land on a bouncy house", however, does.  They probably won't expect recovery on the first try (that's not what happened with fairings, and the blooper reel for booster landing attempts is spectacular), but it's clearly the end goal.

https://twitter.com/elonmusk/status/985684755877265408
« Last Edit: 04/18/2018 12:25 AM by rst »

Offline su27k

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Re: F9 Second Stage Reusability
« Reply #669 on: 04/18/2018 02:36 AM »
Additional information:

https://twitter.com/QuinnKupec/status/985736260827471872

Quote from: Quinn Kupec
@elonmusk If you're proposing what I think you are, an ultra low ballistic entry coefficient decelerator, then you and @SpaceX should come see what we have at the @UofMaryland . We've been working on this for awhile and just finished some testing

https://twitter.com/elonmusk/status/986070683426766848

Quote from: Elon Musk
@QuinnKupec @SpaceX @UofMaryland Yeah, exactly! Would be great to hear your thoughts. We’re going to try a few approaches. Can def be done, just about minimizing mass.

https://twitter.com/QuinnKupec/status/986075981004886016

Quote from: Quinn Kupec
Absolutely! That's what we are working on right now! I would love to share with you, or anyone from @SpaceX what we are doing. Please let me know a good way to get you my contact information.

Edit: Some googling results in a paper about this from UMD: Applications of Ultra-Low Ballistic Coefficient Entry Vehicles to Existing and Future Space Missions

Also a reddit post explaining the image: https://www.reddit.com/r/UMD/comments/8ctmv4/elon_musk_responds_to_a_umd_students_tweet/dxiarto/

Quote
Shout-out to the UMD Nearspace team and the Balloon Payload Program! The orange payload in the image is called TARDIS, and it essentially works like an upside-down umbrella, opening up wide when falling back to earth to decelerate. Quinn's been working on this for over a year, by now
« Last Edit: 04/18/2018 03:36 AM by su27k »

Offline Rocket Surgeon

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Re: F9 Second Stage Reusability
« Reply #670 on: 04/18/2018 03:40 AM »
Does any one have any good sources for the mass of steerable parafoils and/or the mass of the second stage? From the sounds of it, this system will use either a huge ballute to reduce peak heating to below 500oC (well below the melting temperature of Aluminium and removing the need for a heat shield) or a smaller deployable heat shield like HIAD*.

Regardless, I would be willing to put money down on them using a steerable parafoil and landing on Mr Steven like the the fairings for the last 5-10km, though if they go for the ballute they would probably have to cut if free.

I don't think they'd be able to steer accurately enough with out a parafoil to catch the second stage, so that would limit how big the rest of the system can be.

*My guess would be the former one as that more matches Elon's description, would weigh less, and would interfere less with the current design. If heating could be limited to below 400oC, the design could be rather simple and lightweight, using off-the-shelf materials like Kevlar and Mylar.

PS: I remember there being a thread discussing this sort of system for second stage recovery a few years ago, is that just me?
« Last Edit: 04/18/2018 03:42 AM by Rocket Surgeon »

Offline Swedish chef

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Re: F9 Second Stage Reusability
« Reply #671 on: 04/18/2018 07:03 AM »
PS: I remember there being a thread discussing this sort of system for second stage recovery a few years ago, is that just me?

Perhaps you are thinking of the fairing reuse thread? Lots of information on steerable parachutes in that thread.
https://forum.nasaspaceflight.com/index.php?topic=37727.1520

Offline OxCartMark

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Re: F9 Second Stage Reusability
« Reply #672 on: 04/18/2018 01:39 PM »
All lovely but one bit of concern in my mind - an extremely low ballistic coefficient is going to make this approach susceptible to wide variances in how far down range the touchdown point is relative to the point you retro fire to begin re-entry.  Hundreds of miles of variation(??).  Unless you have a way to adjust the drag (size, geometry) of the party balloon on the fly (preferably both increases and decreases) and a very current atmospheric model to adjust the initiation point of the re-entry.  A variable balloon and a late well informed decision on when to fire the engines.

And, let's not forget to what degree a simple balloon (if that's what it is) will shrink in size due to atmospheric pressure increase in going from "space" to some more airy portion of the atmosphere, so there may need to be some intermediate step between balloon and parafoil to get through the mid altitudes.

Seems that a framed solution such as an umbrella or a sheet with structure made of inflated tube ribs would meet the need better than a strict balloon.

Online speedevil

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Re: F9 Second Stage Reusability
« Reply #673 on: 04/18/2018 01:41 PM »
All lovely but one bit of concern in my mind - an extremely low ballistic coefficient
I'm 99.9999% sure that what's meant is the ballute increases the drag lots, by presenting a larger area.

This causes the heat per square meter of balloon to drop, as the kilos per square meter goes from about 100kg/m^2 to about 1.
It also causes it to reenter much faster after it hits the top of the atmosphere, reducing dispersion.

Offline OxCartMark

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Re: F9 Second Stage Reusability
« Reply #674 on: 04/18/2018 02:18 PM »
All lovely but one bit of concern in my mind - an extremely low ballistic coefficient
I'm 99.9999% sure that what's meant is the ballute increases the drag lots, by presenting a larger area.

This causes the heat per square meter of balloon to drop, as the kilos per square meter goes from about 100kg/m^2 to about 1.
Your statement matches my thinking 100% up to that point.

It also causes it to reenter much faster after it hits the top of the atmosphere, reducing dispersion.
No doubt once it hits the top of the atmosphere (which is a squishy border but high up in this case because of the very low loading) that'll be the case but the large variability occurs before that time in the re-entry, when the speed is very high and the atmospheric density is just a slight bit more than negligible.

Offline nicp

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Re: F9 Second Stage Reusability
« Reply #675 on: 04/18/2018 02:55 PM »
Surely if it's possible to get the second stage down to sea level in one piece without using much retro-propulsion (party balloons, ballute, whatever you wanna call it) the same must be true of the first stage. Just keep enough fuel to land it, no need for any burn except to get it into the right place.
Or am I being dense?
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Offline meekGee

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Re: F9 Second Stage Reusability
« Reply #676 on: 04/18/2018 03:01 PM »
Surely if it's possible to get the second stage down to sea level in one piece without using much retro-propulsion (party balloons, ballute, whatever you wanna call it) the same must be true of the first stage. Just keep enough fuel to land it, no need for any burn except to get it into the right place.
Or am I being dense?
For downrange recovery, and very large balloon, maybe, but it will be a bit more difficult because the stage is longer.

But you can't do RTLS with balloons, and the boostback burn is the main  consumer of propellant.

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Online speedevil

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Re: F9 Second Stage Reusability
« Reply #677 on: 04/18/2018 03:28 PM »
It also causes it to reenter much faster after it hits the top of the atmosphere, reducing dispersion.
No doubt once it hits the top of the atmosphere (which is a squishy border but high up in this case because of the very low loading) that'll be the case but the large variability occurs before that time in the re-entry, when the speed is very high and the atmospheric density is just a slight bit more than negligible.

Assuming reasonable knowledge of the atmosphere, and that a little fuel can be retained - for say a 1 second burn - 300kg or so, this gets you 250m/s or so delta-v, and firms up the entry position considerably.
If you can choose the inflation position of the ballute, this also helps.

Online Bananas_on_Mars

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Re: F9 Second Stage Reusability
« Reply #678 on: 04/18/2018 03:45 PM »
I remember that with the fairings there has been speculation about a bouncy castle on the fairing itself, instead of the fairing landing inside a bouncy castle that's waiting on the ocean, that you have to hit...

I've been thinking about a Zorbing Ball around the stage, providing the drag on reentry(maybe through partial filling?, partial lift (helium filled, party balloon)+ drag on descent, fully inflate to serve as an airbag to cushion the landing on the ocean(bouncy castle). How big would such a Ball be to limit terminal velocity to maybe 60km/h? What i'm proposing here might a all-in-one solution for EDL.

Online rst

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Re: F9 Second Stage Reusability
« Reply #679 on: 04/18/2018 03:59 PM »
Does any one have any good sources for the mass of steerable parafoils and/or the mass of the second stage? From the sounds of it, this system will use either a huge ballute to reduce peak heating to below 500oC (well below the melting temperature of Aluminium and removing the need for a heat shield) or a smaller deployable heat shield like HIAD*.

Second stage dry mass is widely estimated at between 4 and 5 mT (to which you'd have to add a bit to account for residual propellant, etc.).  As to masses of ballute systems, well... some dude posted pointers to a couple of relevant design studies (HIAD for Cygnus return and a more speculative study about lunar capsule return) a bit upthread at post 665, which came in at between 500 and 1500 kg depending on what you count (one had a fairly elaborate structural mount for the furled HIAD) to which you'd have to add mass of a separate parafoil system for terminal descent, if you add one.  Pointers to those papers again:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20060018288.pdf
https://websites.isae-supaero.fr/IMG/pdf/137-heart-ippw-9_v04-tpsas.pdf

ETA: also see subsequent comments from Space Ghost about how differences between these proposals and whatever SpaceX deploys (details so far unknown) could make these estimates off.
« Last Edit: 04/18/2018 07:09 PM by rst »

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