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louis

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From: UK

Registered: 2008-03-24

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Mini BFS

Interesting video from Curious Elephant on the Mini BFS

https://www.youtube.com/watch?v=4OJroTlq654

Last edited by louis (2018-11-15 13:32:26)

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SpaceNut

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Re: Mini BFS

reposting as this can be used to help in the abilities that a full scale ship will be testing in the scaled down version:

This is the payload recovery option which allows for it to land just as the first stage does.
The end of the second stage looks like a modified dragon capsule super draco engine design.

GW had worked out the engine design for moon and mars landing and it should be very simular but will need more fuel to make it possible.

First stage recovery needed 1/4 of the full fuel tank to make a landing possible.

This sure beats trying to catch them in a speed boat net....

SpaceNut

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Re: Mini BFS

The wings are the payload shroud opening to allow the satelite to be launched from with in the structure. Once its gone they close so that the shroud is return via propulsive landings on earth in the same way that the first stage does.

Notice that the stage has the same design as the red mars capsule in that its got the super draco engines canted at the base to provide the escape velocity if there is an issue and if they are not used they can then be used in the retro pulsive mode.

elderflower

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Registered: 2016-06-19

Posts: 1,262

Re: Mini BFS

I am reminded of the seeds of the great dipterocarp trees of SE Asia. I wonder if there is any mileage in reopening the shroud when we get out of hypersonic speeds on re-entry,  further reducing the speed of descent without using a parachute.

SpaceNut

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Re: Mini BFS

You are saying after the heat of entry has dropped before opening. The force of the air will increase with the fall to earth and while its strength is that in a closed position would the wing shape make it against that force let alone the piston used to make it open stay open against that force which will increase. Next would be the natural possibility that it would spin as it falls with them open.

kbd512

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Re: Mini BFS

The places between the retro-rocket engines could have very stiff and strong stub wings that swiftly slow the vehicle, just like the Snakeye bomb that we use for low altitude bombing.  The place in the picture where the caption points to "Compact size due to lower fuel tank position" is exactly where the stub wings would go.  The payload clamshell could stay closed during the entire reentry sequence.  The wings would open first, just like the clamshell, and then swivel into an attitude that permits the vehicle to fly somewhat like a heavy lifting body, kinda like the Space Shuttle, in a nose high angle of attack.

Edit: Almost forgot, but this new upper stage would land on the tips of the stub wings when it came time to land, like a miniature Falcon booster, but using the wings as landing gear instead of purpose built landing gear, since that adds weight that's only useful for the landing phase of the flight.

Last edited by kbd512 (2018-11-17 21:15:00)

Oldfart1939

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Registered: 2016-11-26

Posts: 2,379

Re: Mini BFS

Latest Tweet from Elon Musk: Falcon 9 second stage redesign abandoned, and efforts put toward BFR.

Last edited by Oldfart1939 (2018-11-17 22:15:55)

kbd512

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Re: Mini BFS

I think they're finally in over their heads, but we'll see what happens.

SpaceNut

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Re: Mini BFS

Copied posts from Journey to Mars:

In that regards the mini bfr sure seems to be a good design step in that its got propellant remaining once achieving orbit after doing its business of satellite launch. It also looks like that its going to be adapted for manned flight as well.

SpaceNut,

If you take Dragon (cargo capsule), Dragon 2 (crew capsule), Mini BFS (mini reusable cargo shuttle), Falcon 9 (medium lift), Falcon 9 Heavy (lift), Bigelow Aeropsace inflatables (radiation and debris protected habitats), on-orbit refill of LOX/LH2 upper stages with IVF, high power SEP, HIAD inflatable heat shields, and landers that use storable chemicals just like Apollo did, then you have a real lunar or Mars exploration program that doesn't require waiting a decade or more for gigantic rockets / spaceships and rocket fuel refineries.  I'm not saying Elon Musk shouldn't pursue BFR/BFS, but if he gets the reusable cargo shuttle right, then NASA has figured out the life support and everything else, so we have everything that's absolutely required to go to Mars and start exploring without an unacceptably high risk of failure.

RobertDyck

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From: Winnipeg, Canada

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Re: Mini BFS

Super-Draco engines are designed to use N2O4/MMF. That has slighly lower Isp than LOX/RP1. Although RP1 is more expensive than Jet-A, MMF is more expensive yet. And N2O4 is definitely more expensive than LOX. If there's a failure, N2O4 is toxic. A Dragon spacecraft doesn't carry much N2O4/MMF, but the upper stage would. BFS is supposed to use LOX/LCH4, so how applicable would this be?

SpaceNut

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Re: Mini BFS

The journey for mars would still suffer from Lox boil off unless we can actively cool it but for earth use any of the fuels will do. This would give test data as well for recovery and engine types for any of them.

kbd512

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Re: Mini BFS

Robert,

LOX could be substituted for N2O4 to improve specific impulse and impulse density beyond what's achievable with RP-1.  The first ISPP experiments on Mars are supposed to produce LOX.  It might be easier to start with a storable fuel / monopropellant for exploration missions to perfect oxidizer production first, then start making LCH4 after the initial exploration missions locate the best near-surface water sources to exploit.  It's a viable way to significantly reduce delivered tonnage for the initial missions, using Dragon as the MDV/MAV, until suitable landing sites are marked for BFS.  The various Hydrazines can be decomposed as monopropellants for EDL, too.  Aerojet-Rocketdyne makes a line of dual-mode thrusters for N2O4/MMH, but I can't think of any reason why LOX couldn't be used as the oxidizer following a redesign.  There's less risk associated with that plan and it doesn't detract from the plan to use LOX/LCH4 because it's proving the viable of producing three quarters of the total propellant tonnage associated with using LCH4.

The Isp for LOX/MMH, LOX/50-50, or LOX/UDMH are very near or above LOX/LCH4, with a nice density impulse increase over LOX/LCH4.

LOX/RP1: Isp(sl) 289; Id 294
LOX/LCH4: Isp(sl) 299; Id 235
LOX/Hydrazine: Isp(sl) 303; Id 321

NTO/MMH: Isp(sl) 280; Id 325
NTO/Hydrazine: Isp(sl) 286; Id 342

RobertDyck

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Re: Mini BFS

Falcon 9 upper stage uses LOX/RP1. The new proposed stage uses SuperDraco engines, which are designed for N2O4/MMH. BFS would use LOX/LCH4, but that's for TMI. What does it use for RCS? It would have to reserve some for Mars EDL, but yes it could use active cooling.

My point is the proposed upper stage uses Dragon EDL technology, not BFS.

RobertDyck

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Re: Mini BFS

What happened to designs from the video SpaceX released before Falcon 9 first launched? It was to have a heat shield on top, enter atmosphere upsidedown. Then flip for a propulsive landing. If BFS is to flip, why be afraid of it? The fully reusable second stage would still use one Merlin 1D vacuum engine, and use it for landing. Or is that engine not capable of deep throttling?

::Edit:: Found the video. From 29 Sep 2011. Second stage recovery from 1:09 to 1:57. Actually shows 4 small rocket exhausts from the sides of the main engine. That implies some sort of smaller engines for landing. Could they use SuperDracos for landing? Use of the Merlin 1D vacuum engine for de-orbit and boost-back would permit use of the same propellant tank. SuperDracos use different propellant. Separate tanks could use a bladder for pressure feed. The same SuperDracos could be used as ullage engines prior to de-orbit burn.

Last edited by RobertDyck (2018-11-18 21:24:45)

SpaceNut

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Posts: 28,825

Re: Mini BFS

Thanks for finding the image.

That sort of means that they have lost site on the original plan for the Falcon 9 stage recover-ability but is it the same second stage as the Falcon 9 Heavy?

The BFR is more like a lifting body...
SpaceX announces BFR lunar passenger, mission for Earth’s artists

flight path for the moon

of course the mars BFR is quite different as well

of course this is more like what we thought a mars lander would be like

but that was before the superdraco launch escape test and landing.

RobertDyck

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Re: Mini BFS

You can click the image for the YouTube video.

SpaceNut

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Re: Mini BFS

Not able to watch the video my computers current state and I am not sure that I will try to make it much better than it is at this point.

A larger diameter core would keep the rocket from getting taller as it would appear that after the second stage is adapted that we would need to cut into the payload to make up the mass shift to that stage to make it recoverable. Only the center core would need to be larger as the booster could be the same as it always were as they fall off first as we want it to be closer to a 10 m diameter any ways for mars use.

As for Mars from earth the fuels RP1, kerosene, methane engines switching for use should not be all that difficult on mars before reuse and I do think that the journey to mars for Lox is the only issue.

RobertDyck

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From: Winnipeg, Canada

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Re: Mini BFS

My computer is still running Windows XP 32-bit. I have an AMD Phenom 9600 quad-core @ 2.31 GHz, and 4 GB of RAM but only 3.25 GB usable. Runs XP very well. I watch the video with Firefox; latest version is Firefox ESR (End of Service Release) 52.9.0 (32-bit). To play internet video, you will need Adobe Flash player, and keep that up-to-date as well. However, there is a customization to make H.264 video work. With the latest version of Firefox, that video format was disabled. There are Firefox settings to re-enable them. If that's your problem, I could email a link to a web page describing how to fix it.

Last edited by RobertDyck (2018-11-19 19:30:18)

kbd512

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Re: Mini BFS

SpaceNut,

I would think that a shorter, fatter lander would be optimal for stability and minimizing the cargo transfer problem.  Using the 9m booster core diameter, the upper stage diameter can be a maximum of 1.5 times the booster diameter before aerodynamic problems begin to rear their ugly head during ascent.

SpaceNut

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From: New Hampshire

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Re: Mini BFS

This image does not have the bfr wings for feet to support a landing so I am wondering if the heat shield has the landing feet that pop through it as the red dragon did.

Something else that comes to mind with satellite repair and recovery is the payload shrouds ability to close back up and the docking bay adapter. Send up an empty payload rocket with a manned capsule rocket to do a space walk to capture and return an ailing satellite back home for repairs.

This plays into space x satellite deployment as well...

SpaceNut

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From: New Hampshire

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Re: Mini BFS

here are the discussed topics and there are probably more
China testing robotic satellite capture systems
Starlink - Space X's space internet project
Servicing Earth Satelites

SpaceNut

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Re: Mini BFS

This makes the 4th topic in what is the hopper stage testing now aka starship

The company has been working on a Starship test article for low-altitude flight tests at the company's South Texas launch site under development. That test article, dubbed a "hopper," would have the same nine-meter diameter as the full-scale vehicle of the vehicle, but would not be as tall.

SpaceX had shifted to a "fairly heavy metal" for use in the vehicle and not using carbon composite materials, which are lightweight but have high strength but have a much lower temperature of operation.

SpaceX had developed a "superalloy" for Raptor, called SX500, designed to handle hot oxygen-rich gas at pressures of up to 12,000 pounds per square inch. "Almost any metal turns into a flare in those conditions,"

SpaceNut

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Re: Mini BFS

Looking at the size and engine count this looks like it what would be used for lunar flyby and for possible lunar landing.for cargo or crews to begin working and to stay on the moon.