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1
IIRC what made the ice that the shuttle so much worse, was that it was tank insulation foam combined with ice. IIRC, the foam and ice made a kind of composite structure that was much less brittle than just ice alone. Also meant larger pieces.
2
Im thinking Kwaj is a real option for BFR, from a floating platform.

Why would they launch in the middle of nowhere when they have a floating platform? Boca Chica comes to mind.

there is near zero SpaceX infrastructure left on Kwaj.  near none
There is range infrastructure by the US military. Which is why SpaceX was there in the first place. Pegasus sometimes flies out of Kwaj for exactly the same reason.

...but you're much smarter.

By range infrastructure you mean a radar?  There doesn't seem to be much else, and it seems busier with military stuff these days than it was during the Falcon 1 campaigns.
3
I wish someone would have asked this during the presentation, but is it possible for such a hinge to be exposed to the thermal conditions of atmospheric entry on Earth and Mars and not become structurally compromised?
I may be wrong and I have not seen it in any of the renderings, but I would imagine that the "bottom" side of the wing where it is attached to the body could have some sort of "extended edge" that overlaps the hinge. That edge would then prevent the plasma from directly hitting the hinge. The leeward side would still be exposed and might get hot, but I would assume it to be more manageable that way.
4
What internal insulation? The tank wall is ship's outer wall and "lowest mass solution is just to mount the heat shield plates directly to the tank wall" -EM. Only insulation is TPS itself. If you watch the Falcon Heavy launch, -which used fast load too, there were still nearly metre size ice-sheets falling down and evaporating in the rocket exhaust. The fins TPS need to be designed to withstand this.

What about carbon dioxide ice when leaving Mars? The BFR will be fueled over a 2 year period while the fuel is being made. Could large amounts of co2 ice build up?

Rappel-lines and ice picks?

"Tank wall" means structure. Internal insulation would not be structural.

But the TPS external insulation could also be designed to prevent water ice buildup on the pad and dry ice buildup on Mars.
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SpaceX BFR - Earth to Deep Space / Re: BFS Engineering Thread
« Last post by envy887 on Today at 10:37 PM »
Why does the fuselage have to be so cylindrical, as opposed to more of a lifting body shape?...
Because it's more efficient structurally (i.e. lower dry mass) and simpler to construct (i.e. lower cost).

I don't think the former is true, all things considered. But manufacturing non-cylindrical tanks is probably too much of a PITA.

The BFS is primarily a pressure vessel, and a domed cylinder is the 2nd most structurally efficient shape for a pressure vessel after a sphere.

Since getting a spherical vehicle to do a lifting reentry is pretty difficult, a domed cylinder is the next best choice for minimizing dry mass.
6
AFAIK Arianespace has currently 61 launches on it's launch manifest (and five launch commitments).
In this Arianespace press-release they state that they have 59 launches on their manifest. This brakes down into:
Vega         6x
Vega C      3x
Soyuz      28x
Ariane 5   17x
Ariane 6    5x

Later there were two press releases for:
- THEOS-2 (800kg Vega or VegaC with rideshare) lets assume a Vega =>7x
- KOMPSAT 7 (KARI 2000kg) Vega C => 4x

We also know that:
- Oneweb has ordered 21 Soyuz launches. (So seven other flights)
- Ariane 5 will launch BepiColumbo and JWST (So 15 dual GTO launches or ~30 GEO comsats)
- Vega C = 1) CSG2   2) Airbus VHR-2020 1&2  3) Airbus VHR-2020 3&4  4) KOMPSAT-7
- Vega has at least one SSMS (Small Satellites dedicated ride-share) flight.

I've not seen any further Sentinel launch order for Arianespace, but we know there are a lot on order.
Is it me or is there a long time gap between institutional satellite order and the announcement of the launch contract.?
7
SpaceX BFR - Earth to Deep Space / Re: BFS Engineering Thread
« Last post by envy887 on Today at 10:32 PM »
My attempt at back-of-the-enveloping upper limits:

A quick measurement on the rotating BFS from the spacex.com/mars page gives roughly 420 m^2 (projected) for the body and 40 m^2 for each rear brake (perpendicular), with the center of pressure 2.5 m from the hinge axis. Assuming a worst case of highly loaded maximum g belly flop reentry with rear brakes perpendicular to the airflow:

200 t @ 6 g gives ~12 MN total force.

Using the newton theory drag coefficients which are 2 for a plate and 4/3 for a cylinder (correct me if I remember incorrectly):

12 MN * 40 m^2 *2 / (420 m^2 *4/3 + 2*40 m^2 *2) = 1.3 MN per rear brake.

Corresponding torque is 1.3 MN *2.5 m = 3.3 MNm.

While landing it looks like the rear brakes actuate through the whole range of motion in about 4 s. Overestimating that as 120 degrees is 1/12 Hz = 5 rpm. Mechanical power at maximum torque, neglecting inertial loads, would be:

2 * pi /12 s  * 3.5 MNm = 1.7 MW per rear fin.

Again, these are very approximate estimates but I'm actually surprised that the force is close to Elons "1 MN" since I went for overestimation. I think BFS will max out at much less than 6 g even on direct entries but the rear brakes will never be perpendicular to high speed air flow in any case. They are held far back in the simulation and the higher the payload the further back they will be. Which is good because an example of 3.3 MNm electro-hydraulic actuators are steering gear for large ships and seem to be (...1 min google...) around 25 t (although with a slightly lower emphasis p weight optimization).

The vehicle isn't going to enter at 90 degree angle of attack with brakes extended straight out, ever. For one thing, that would be a ballistic entry, which is a Very Bad Idea at those velocities. Also, 6 g is too high, even for an upper bound. Entry heating goes with deceleration rate (and a 300 second entry at 6 g is almost 18 km/s) so there's no reason to decelerate that fast unless the vehicle can't generate enough lift to decelerate slower - and I see no reason to believe that is the case here. The simulation shows an average deceleration of about 1.7 g. I'd consider 3-4 g a better upper bound.

The torque estimation is very sensitive to the actual drag coefficient, which varies significantly with extension angle, vehicle angle of attack, and velocity. The projected area of the fin also varies with extension angle and vehicle angle of attack. The power estimation is very sensitive to the necessary angular rate of change of the brakes. If you change each of those values to other entirely reasonable guesses, the power requirement drops by more than 10 times - which suggests this really isn't a problem you can get a good handle on with a BOTE calculation.

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Rocket Lab / Re: RocketLab Electron Smallsat Launcher
« Last post by Comga on Today at 10:25 PM »
I don't know the exact travel times from LA to the cape via Panama. But I wouldn't be surprised if it is actually *quicker* to get to NZ from LA. There's no canal to slow you down.

But would a Mahia launch site provide any advantages over Cape Canaveral or Brownsville? Less sea and air traffic to worry about? Less bureaucracy?

This is not a SpaceX thread.  The Mahia launch site was built and is operated by Rocket Lab for their small launch vehicles.  If you think SpaceX needs to look for more launch sites please use one of the threads in the SpaceX section.

What gongora said...
I was SO hoping a post in this thread was a new launch date but it’s just chatter.
Frankly for an outfit that talks about hitting an operational pace one month after launch #2 this very long delay with no reason information doesn’t inspire confidence.
It’s downright concerning.
And hey, I know Rocketlabs has no interest in our being confident but it’s still odd.
If they have projected a date fit their customers why keep it confidential?
Surely the are as unconcerned with disappointing the public as they are unconcerned with informing us?
And if they still can’t set a date, whatever could  the issue be?
9
Im thinking Kwaj is a real option for BFR, from a floating platform.

Why would they launch in the middle of nowhere when they have a floating platform? Boca Chica comes to mind.

there is near zero SpaceX infrastructure left on Kwaj.  near none
There is range infrastructure by the US military. Which is why SpaceX was there in the first place. Pegasus sometimes flies out of Kwaj for exactly the same reason.

...but you're much smarter.
10
Per L2, liftoff is currently scheduled for 19:22 local time on October 6th. That's October 7th at 2:22 UTC.
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