Author Topic: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)  (Read 382142 times)

Offline tea monster

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #120 on: 10/11/2017 11:10 AM »

I think that this is the mechanism for the flaps as seen in this slide from the IAC presentation.

Also of interest is the landing leg positions. I don't see any in this frame.

In this one though, there is what appears to be bits of angle iron welded onto the outside of the hull.

At first glance, it doesn't appear to be very mechanical for retraction.

Offline octavo

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #121 on: 10/11/2017 11:51 AM »


. They don't seem to have enough clearance against the Raptor nozzle to move significantly upwards, which will limit pitch adjustment.

This. It looks to me like those flaps can't pitch the nose down at all.

Offline hkultala

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #122 on: 10/11/2017 12:04 PM »


. They don't seem to have enough clearance against the Raptor nozzle to move significantly upwards, which will limit pitch adjustment.

This. It looks to me like those flaps can't pitch the nose down at all.

flaps down == nose down. can do this.
flaps up == nose up. cannot do this.

But maybe the skirt around the engines will be made differently shaped so that in the actual version the flaps can also turn upwards.

« Last Edit: 10/11/2017 12:06 PM by hkultala »

Offline octavo

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #123 on: 10/11/2017 12:21 PM »




. They don't seem to have enough clearance against the Raptor nozzle to move significantly upwards, which will limit pitch adjustment.

This. It looks to me like those flaps can't pitch the nose down at all.

flaps down == nose down. can do this.
flaps up == nose up. cannot do this.

But maybe the skirt around the engines will be made differently shaped so that in the actual version the flaps can also turn upwards.

Thanks! I even spent a minute thinking about which was which and still got it wrong!

Offline Semmel

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #124 on: 10/11/2017 12:47 PM »
In which flight regime do the flaps actually work? I cant think of them having much effect during the flaming part of the reentry. Is my intuition wrong here? I would expect to still have extensive steering thruster usage to get the nose onto the correct angle. Since the thrusters are hard to point downwards due to the heat shield at the bottom, how DO they pitch the nose up? With thrusters firing upwards at the top of the engine section, behind the center of mass?

Offline AncientU

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #125 on: 10/11/2017 01:26 PM »
In which flight regime do the flaps actually work? I cant think of them having much effect during the flaming part of the reentry. Is my intuition wrong here? I would expect to still have extensive steering thruster usage to get the nose onto the correct angle. Since the thrusters are hard to point downwards due to the heat shield at the bottom, how DO they pitch the nose up? With thrusters firing upwards at the top of the engine section, behind the center of mass?

Could be that the airframe design has a natural nose up moment. 
Flaps counter this with small extension, and pitch nose down with larger extension.
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Online envy887

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #126 on: 10/11/2017 01:35 PM »
In which flight regime do the flaps actually work? I cant think of them having much effect during the flaming part of the reentry. Is my intuition wrong here? I would expect to still have extensive steering thruster usage to get the nose onto the correct angle. Since the thrusters are hard to point downwards due to the heat shield at the bottom, how DO they pitch the nose up? With thrusters firing upwards at the top of the engine section, behind the center of mass?

Almost the entire entry is in this very high AOA orientation relative to the flow field, so they will probably try to make this as naturally stable as possible. This orientation has both a lot of drag, and a lot of lift, so it's optimal for entry. In this orientation, then can actually get some pitch-down torque by retracting the flaps above the plane of the lower wing surface.

To make this stable, both the CG and COP need to be roughly near the center of the vehicle fore/aft, which is exactly where the intersection of the blue and green axes is in the animation. The COP need to be towards the dorsal side of the vehicle, and the CG towards the ventral side.

I think they will only need RCS for 1) vacuum control before the aerosurfaces get enough flow for control; 2) for yaw control; and 3) for the final backflip before the Raptors start.

Offline SLC

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #127 on: 10/11/2017 01:40 PM »
As for the flight regime where the body flaps are effective, the experimental HL-20 study I cited a few posts back was done at Mach 10, and there the body flaps gave "effective roll control".

For pitch control, I'm guessing (like AncientU) that the fore-and-aft mass distribution of the BFS would be trimmed to give a default pitch up, and both flaps would normally be half-extended to counteract that.  They could then move around that default position to control both roll and pitch.

The first page of this paper on the IXV has an image of heat distribution during re-entry:

https://www.esa.int/esapub/bulletin/bulletin128/bul128h_tumino.pdf

If that's any guide, the body-flaps will get very hot.

Offline Lar

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #128 on: 10/11/2017 05:21 PM »

Could be that the airframe design has a natural nose up moment. 
Flaps counter this with small extension, and pitch nose down with larger extension.

I am of two minds about this, as I beleive a non neutral airframe will have increased drag since the flaps will have to be half extended. On the way down that seems like a good thing, drag is goodness. But on the way up, it puts an additional load, however slight, on the ascent engines, compared to a similar airframe that's neutral.... And worse, it might introduce some asymmetric forces on the coupling between the booster and the ship. That may or may not be significant, IANARS
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Offline SLC

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #129 on: 10/11/2017 05:35 PM »

Could be that the airframe design has a natural nose up moment. 
Flaps counter this with small extension, and pitch nose down with larger extension.

I am of two minds about this, as I beleive a non neutral airframe will have increased drag since the flaps will have to be half extended. On the way down that seems like a good thing, drag is goodness. But on the way up, it puts an additional load, however slight, on the ascent engines, compared to a similar airframe that's neutral.... And worse, it might introduce some asymmetric forces on the coupling between the booster and the ship. That may or may not be significant, IANARS
But on the way up, the flaps would be fully retracted, flush with the skin, wouldn't they?  No need for fore-and-aft trim if you're accelerating vertically upwards, no matter how the fore-and-aft mass distribution changes as the propellants are consumed.

Offline Kaputnik

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #130 on: 10/11/2017 07:08 PM »

Could be that the airframe design has a natural nose up moment. 
Flaps counter this with small extension, and pitch nose down with larger extension.

I am of two minds about this, as I beleive a non neutral airframe will have increased drag since the flaps will have to be half extended. On the way down that seems like a good thing, drag is goodness. But on the way up, it puts an additional load, however slight, on the ascent engines, compared to a similar airframe that's neutral.... And worse, it might introduce some asymmetric forces on the coupling between the booster and the ship. That may or may not be significant, IANARS
But on the way up, the flaps would be fully retracted, flush with the skin, wouldn't they?  No need for fore-and-aft trim if you're accelerating vertically upwards, no matter how the fore-and-aft mass distribution changes as the propellants are consumed.

There's still aero loads, though.
If the flaps need to be slightly extended to fly straight, that means the vehicle has asymmetrical aerodynamic properties. Like shuttle, you'd need vectored thrust to maintain straight flight.
Waiting for joy and raptor

Offline ncb1397

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #131 on: 10/11/2017 07:20 PM »
Another thing that doesn't seem to quite add up is power. Design appears to use maximum - 12 m radius PV fins, which yields something around 90 KW @ earth and 35 KW @ Mars aphelion. Doesn't seem like enough to heat the 853 cubic meters of pressurized volume. Going to need some of that natural gas for heat in a lot of scenarios.

That's impossible to judge unless you know how much insulation the cabin has, and how much insolation it receives (which depends on vehicle attitude).
In space the only way you lose heat is radiation. I didn't see any radiators, but they could have been hidden on the other side of the solar panels. Also, the heatshield on the bottom should be dark which will serve as a radiator. Waste heat from electronics, the life support system, chemical reactions powering human bodies, and whatever else needs energy on the ship should keep things plenty warm, they just have to keep the radiators sized and positioned correctly to balance the energy needs. If they need more heating, they just need to point the black side of the ship a bit more towards the sun.

The point is, you couldn't run 20 hair dryers on 35 KW. Shrinking the design, power, fuel and everything else but not shrinking the passenger count tends to lead to less technical credibility. As far as tilting the ship, I've never seen any indication that the solar fins pivot. They are always rendered in the same position. So, tilting the ship just exacerbates the power situation. For comparison, the Shuttle supported a crew of 8 and the 3 fuel cells could produce 21 KWs of continuous power.
« Last Edit: 10/11/2017 07:26 PM by ncb1397 »

Online envy887

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #132 on: 10/11/2017 07:45 PM »

Could be that the airframe design has a natural nose up moment. 
Flaps counter this with small extension, and pitch nose down with larger extension.

I am of two minds about this, as I beleive a non neutral airframe will have increased drag since the flaps will have to be half extended. On the way down that seems like a good thing, drag is goodness. But on the way up, it puts an additional load, however slight, on the ascent engines, compared to a similar airframe that's neutral.... And worse, it might introduce some asymmetric forces on the coupling between the booster and the ship. That may or may not be significant, IANARS

Total drag during first stage ascent will be on the order of 30 m/s, the slight addition from partially extended flaps would be on the order of single-digit m/s losses. Drag losses during 2nd stage ascent are entirely trivial on Earth and extremely small on Mars.

Offline john smith 19

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #133 on: 10/12/2017 03:17 PM »

To make this stable, both the CG and COP need to be roughly near the center of the vehicle fore/aft, which is exactly where the intersection of the blue and green axes is in the animation. The COP need to be towards the dorsal side of the vehicle, and the CG towards the ventral side.
And to remain there throughout the deceleration through about 20 Mach numbers?

Maybe all that mass above the propellant tanks will do the trick and the BFS will fly like Skylon, not like HOTOL.
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.

Online envy887

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #134 on: 10/12/2017 03:25 PM »

To make this stable, both the CG and COP need to be roughly near the center of the vehicle fore/aft, which is exactly where the intersection of the blue and green axes is in the animation. The COP need to be towards the dorsal side of the vehicle, and the CG towards the ventral side.
And to remain there throughout the deceleration through about 20 Mach numbers?

Maybe all that mass above the propellant tanks will do the trick and the BFS will fly like Skylon, not like HOTOL.

More like 30 Mach numbers, from interplanetary entry to subsonic on Earth. Will be interesting to see whether they can make it stable (or nearly so) through hypersonic, supersonic, transonic, and subsonic regimes. At least it's only hypersonic and high supersonic at Mars.

Not sure that they don't want it to fly like HOTOL; the only time lift is a significant factor is during entry and descent, where they want as much drag as possible and a very high AOA. They don't have to orient for lift during terminal landing or at all during ascent.

Offline spacenut

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #135 on: 10/12/2017 03:29 PM »
I have a couple of questions on the ITS vehicle.  From what I see, the center of gravity for the vehicle would need to be low enough not to topple over when landing vertical.  When landing most if not all fuel will be expended, thus lower mass on the bottom of the vehicle.  If it lands on earth with 50 tons downmass and on Mars with 150.  How will this weight be balanced on the bottom? 

Also when returning to earth through the thick atmosphere, are the wings or winglets used to keep the lower mass level with the upper mass to keep from coming in bottom first? 

I'm assuming the engines will weight about a ton so that is 31 tons on the bottom.  I'm assuming a titanium bottom around the engines adding more weight, I suppose this totals 50 tons to offset the 50 tons in the cargo bay if 50 tons is returned. 

Offline octavo

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #136 on: 10/12/2017 03:51 PM »
I have a couple of questions on the ITS vehicle.  From what I see, the center of gravity for the vehicle would need to be low enough not to topple over when landing vertical.  When landing most if not all fuel will be expended, thus lower mass on the bottom of the vehicle.  If it lands on earth with 50 tons downmass and on Mars with 150.  How will this weight be balanced on the bottom? 

Also when returning to earth through the thick atmosphere, are the wings or winglets used to keep the lower mass level with the upper mass to keep from coming in bottom first? 

I'm assuming the engines will weight about a ton so that is 31 tons on the bottom.  I'm assuming a titanium bottom around the engines adding more weight, I suppose this totals 50 tons to offset the 50 tons in the cargo bay if 50 tons is returned.
I think you're confusing the booster and spaceship. Only 6 engines on the the ship.

Online Oersted

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #137 on: 10/12/2017 07:50 PM »
The BFR will be built in the Los Angeles port area.

Gwynne Shotwell Q&A. The quote below is not verbatim but from notes by Reddit-user "Sticklefront": https://www.reddit.com/r/spacex/comments/75ufq9/interesting_items_from_gwynne_shotwells_talk_at/

"Where will the BFR be built?

We're looking at building a facility by the water in LA. We thought we'd build it in our factory in Hawthorne, but we priced transport to the harbor, and it came out to $2.5m per trip. It would require taking down stoplights, and just wouldn't be worth it. So we will build a new facility by the water. We will eventually also have a number of production sites by out launch sites."

Offline lamontagne

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #138 on: 10/12/2017 09:06 PM »
Here are possible arrangements for one of the room floors shown in the presentation.

The horizontal arrangement holds 30 people, the vertical one at least 24, with 4 rooms for couple.  The vertical arrangement is identical with the presentation, while the horizontal has 2 less rooms but 2 more bathrooms.  There would be no windows in the lower rooms (on the heat protected side), but this was easier to model  :-)

If the BFS is used as a surface habitat I guess the horizontal arrangement is more likely.  Was that clearly part of the plan?

« Last Edit: 10/12/2017 09:07 PM by lamontagne »

Online envy887

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Re: IAC 2017 -- BFR v0.2 - DISCUSSION THREAD 3 (Post Speech)
« Reply #139 on: 10/12/2017 09:07 PM »
Here are possible arrangements for one of the room floors shown in the presentation.

The horizontal arrangement holds 30 people, the vertical one at least 24, with 4 rooms for couple.  The vertical arrangement is identical with the presentation, while the horizontal has 2 less rooms but 2 more bathrooms.

If the BFS is used as a surface habitat I guess the horizontal arrangement is more likely.  Was that clearly part of the plan?

BFS was to be used as a an early surface hab per the 2016 presentation. That doesn't seem to have changed.

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