Author Topic: BFR Private Passenger Moonflight - DISCUSSION THREAD  (Read 103263 times)

Offline Lampyridae

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #160 on: 09/14/2018 10:53 AM »
As for the actuation of the fins, is there a plausible explanation for making something that looks exactly like a hinge but is not a hinge?
A slot to extend rolled solar panels or thermal radiators.

Thermal radiators would reflect back onto the fin. Plus, they'd have to plumb their heat circuit it all the way past the propellant tanks. Also doesn't explain why the base of the fin has something just like a hinge base. Solar panels... why make a massive door like that?

The only other half-sane idea I can come up with is that the fins are detachable for some reason.
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Offline OneSpeed

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #161 on: 09/14/2018 11:39 AM »
I dont understand how the skirt around the engines could be a giant vacuum nozzle. To generate any kind of effect, it would need to be extended far enough out to make capture the radially expanding gases of the engines and direct them aft-wards. To do this, the skirt would have to be quite long. How long? I dont know, but much longer than what is shown in the picture. How would that work?

The skirt might not have to be that long. The effect would rely more on the interaction between multiple exhaust plumes causing supersonic flow between the nozzles, back towards the dance floor, and hence additional thrust. Here's a post from two years ago discussing the mechanism, and a link to a fascinating NASA study of base heating sensitivity.

https://forum.nasaspaceflight.com/index.php?topic=34197.msg1571267#msg1571267

The Reddit discussion followed soon after.

Offline jpo234

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #162 on: 09/14/2018 11:42 AM »
You want to be inspired by things. You want to wake up in the morning and think the future is going to be great. That's what being a spacefaring civilization is all about. It's about believing in the future and believing the future will be better than the past. And I can't think of anything more exciting than being out there among the stars.

Offline Star One

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #163 on: 09/14/2018 12:04 PM »
I wonder how much more the BFS design will change before they actually build one, or is this actually more or less it considering the ambitious timeline they’ve set themselves.

They don't have a factory yet, I doubt there's the need to fix the design until the factory is ready.

They do have a tent though.

Offline Cheapchips

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #164 on: 09/14/2018 12:08 PM »
They either need the factory or a bigger tent for the booster.

Edit: meant to add. The factory is for churning out 'final' BFS's in volume.  They've lots of options for prototypes and the moon mission, depending on timelines
« Last Edit: 09/14/2018 12:12 PM by Cheapchips »

Online envy887

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #165 on: 09/14/2018 12:18 PM »
Is it just me or is this thing's aspect ratio (height to width) significantly lower? Could just be perspective as one is angled away to show the engines. And trying to measure the relationship between cargo bay and fuel bay yields a ~45% greater length on the fuel bay on the new one vs. a ~65% greater length on BFS 2017 (just based on where the lower door line is).

It's just perspective. Here's a 9x48 ogive-tipped cylinder rotated to match the perspective in the rendering. They are the same length:

Online envy887

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #166 on: 09/14/2018 12:24 PM »
They might even just be regular sea level Raptors, since that would provide sufficient performance and allow landing back on Earth.

I can't be the only one to have noticed that the nozzles are glowing, i.e. radiatively cooling? If it's straight up sea level Raptors, that wouldn't be the case, but would be the case for an additional nozzle extension a-la MVac. Yet the size measurement suggests sea level nozzle size.

So, where does the engineering-based model end and artistic license enters?

Geometry is probably based on CAD. Lighting and textures are almost certainly artistic, since the Earth and Moon would never be lit from different directions.

Offline r4mir3zx

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #167 on: 09/14/2018 12:41 PM »
What if the fins will be completely folded up during reentry so that they won't need reentry thermal protection at all? Or are they necessary, do they have any role during reentry?

Offline seawolfe

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #168 on: 09/14/2018 12:49 PM »
From Diagram for the new BFS Concept

Now THIS is starting to look like a REAL spaceship....right from the 1950's movies!   ;D

Online matthewkantar

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #169 on: 09/14/2018 01:21 PM »
The hinges are freaking me out. The canard hinges too. Shuttle had some hinges, but they were perpendicular to travel and hidden behind the wing. The fins at the base of the new BFR rendering are parallel to travel and not behind anything.

Will they be counting on the shockwave keep lava hot air flows away?

Matthew

Offline ugordan

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #170 on: 09/14/2018 01:22 PM »
They might even just be regular sea level Raptors, since that would provide sufficient performance and allow landing back on Earth.

I can't be the only one to have noticed that the nozzles are glowing, i.e. radiatively cooling? If it's straight up sea level Raptors, that wouldn't be the case, but would be the case for an additional nozzle extension a-la MVac. Yet the size measurement suggests sea level nozzle size.

So, where does the engineering-based model end and artistic license enters?

Geometry is probably based on CAD. Lighting and textures are almost certainly artistic, since the Earth and Moon would never be lit from different directions.

That's all fine, but where are you seeing the Earth?

Online wannamoonbase

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #171 on: 09/14/2018 01:24 PM »
From Diagram for the new BFS Concept

Now THIS is starting to look like a REAL spaceship....right from the 1950's movies!   ;D

Yeah it is, need some more info but seems that is coming on Monday. 

The skirt on the rear looks like thermal control from radiating heat from the raptors.  The simple sketch from the previous BFS bothered me as there didn’t appear to be a way to reject or control the heat on the structure.  These appears better.
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Offline rpapo

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #172 on: 09/14/2018 01:24 PM »
They might even just be regular sea level Raptors, since that would provide sufficient performance and allow landing back on Earth.

I can't be the only one to have noticed that the nozzles are glowing, i.e. radiatively cooling? If it's straight up sea level Raptors, that wouldn't be the case, but would be the case for an additional nozzle extension a-la MVac. Yet the size measurement suggests sea level nozzle size.

So, where does the engineering-based model end and artistic license enters?

Geometry is probably based on CAD. Lighting and textures are almost certainly artistic, since the Earth and Moon would never be lit from different directions.

That's all fine, but where are you seeing the Earth?
That other little blob in the upper right looks like a lens-flare type artifact, not like Earth in the distance.
An Apollo fanboy . . . fifty years ago.

Offline JamesH65

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #173 on: 09/14/2018 01:33 PM »
The hinges are freaking me out. The canard hinges too. Shuttle had some hinges, but they were perpendicular to travel and hidden behind the wing. The fins at the base of the new BFR rendering are parallel to travel and not behind anything.

Will they be counting on the shockwave keep lava hot air flows away?

Matthew

Probably not worth getting freaked out. SpaceX seem to have some knowledge in this area with the current grid fins, and TBH, we are not even sure they are hinges.

I tend to assume that, being the experts, SpaceX are much better positioned to know about this sort of thing than I am. That way I don't get freaked out.
« Last Edit: 09/14/2018 01:33 PM by JamesH65 »

Offline Rocket Science

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #174 on: 09/14/2018 01:44 PM »
What happened to all the "wings are useless in space" talk... Just sayin'

Useless if you are going from one airless body to another. Neither Mars not Moon flights qualify..
I guess you plan on returning to Earth at some point and Mars entry is atmospheric but you will spend less time before rotating to vertical descent to touchdown...
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Offline Lampyridae

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #175 on: 09/14/2018 01:46 PM »
I had a forehead-slap moment when a friend pointed out that the Mig-105 did have variable dihedral wings.

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Offline Rocket Science

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #176 on: 09/14/2018 01:56 PM »
The hinges are freaking me out. The canard hinges too. Shuttle had some hinges, but they were perpendicular to travel and hidden behind the wing. The fins at the base of the new BFR rendering are parallel to travel and not behind anything.

Will they be counting on the shockwave keep lava hot air flows away?

Matthew
Hinged wings were tested on entry on the BOR-4 and the Spiral as well for subsonic flights...

« Last Edit: 09/14/2018 02:01 PM by Rocket Science »
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Offline JonathanD

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #177 on: 09/14/2018 02:08 PM »
So just quickly reading through the last 7 pages, a quick summary as I now understand it:
- 3 relative big tail wings
- 2 of them hinged, thus able to change angle, possibly to create more plane like config during aerobraking?
- all 3 fins with pistons as landing feet.
- likely extendible and I would guess starting of fully extended and only adjusting when rocket tilts. So if they can react quick enough, they could keep landed rocket as upright as possible, by simply retracting the leg that has most pressure until all legs have same pressure...?!
- 2 top fins acting as F9's gridfins
- normal sea-level engines, with extendible skirt for vacuum, to get from 6 independent raports 2 one big combined vacuum engine?
- that skirt likely has multiple functions once in space and not accelerating? Like heat radiation, radiation protection?

Did I miss anything?

Nothing missed per say but some additional details/questions it raises:

- Fins create more ground clearance for the raptors - could be part of the consideration for their larger size as there was prior talk about debris issues when launching from a foreign body.

- No indication of how PV power generation system works

- Not 100% sure that the lower fins are actually hinged, it looks like the "hinge" in the picture could be an aero stabilization feature.  Such a hinge mechanism would be pretty heavy, I would think they'd want to avoid that.

- Between the fins and the new front canards the vehicle has a lot more control surface area, will be very interesting to see how this affects their reentry flight profile for the Earth and Mars.

- Single center engine reintroduces the question of lack of redundancy in an engine-out scenario during landing burn.

- On-orbit rendezvous for refueling appears to just have gotten a lot more complicated!

Offline Nibb31

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #178 on: 09/14/2018 02:12 PM »
Cargo DreamChaser has hinged wings too. It's shouldn't be a huge problem.

The thing that freaks me out the most with BFS is the backflip manoeuver. Coming in belly first and flipping around in a transonic airflow to land on its tail is unprecedented and is going to be super scary.

I'm also worried about the surface area of the landing stilts. That's potentially something like 100 tons on each landing leg putting weight on a surface area of a few square centimeters.
« Last Edit: 09/14/2018 02:16 PM by Nibb31 »

Online meekGee

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Re: BFR Private Passenger Moonflight - DISCUSSION THREAD
« Reply #179 on: 09/14/2018 02:25 PM »
Cargo DreamChaser has hinged wings too. It's shouldn't be a huge problem.

The thing that freaks me out the most with BFS is the backflip manoeuver. Coming in belly first and flipping around in a transonic airflow to land on its tail is unprecedented and is going to be super scary.

I'm also worried about the surface area of the landing stilts. That's potentially something like 100 tons on each landing leg putting weight on a surface area of a few square centimeters.

I think the flip happens very early in the re-enetry, and the transonic transition happens well after it is flying vertically.

At least on Earth.  On Mars, with 1% atmosphere, it matters less.

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« Last Edit: 09/14/2018 02:27 PM by meekGee »
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