Author Topic: Falcon Heavy Demo Mission Payload Discussion  (Read 136385 times)

Online niwax

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #640 on: 03/09/2018 06:06 AM »
If anyone still wonders why they would send a car into space and televise it: https://arstechnica.com/science/2018/03/president-trump-amazed-by-the-falcon-heavy-landing-and-its-low-cost/

Offline AncientU

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #641 on: 03/09/2018 01:15 PM »
BTW, did we ever hear definitively if they removed the roadster's battery pack? I have a hard time believing they'd launch with it unless they both needed the mass and electrical capacity and were certain it would pose no danger to the mission (such as via rupturing or exploding in vacuum).

We haven't heard anything, but as the front brakes were removed (as seen from the footage), presumably to reduce mass, I think its a good bet that the batteries and other heavy internal parts were also removed.

Where Starman is going, he don't need brakes...
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Offline Nomadd

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #642 on: 03/09/2018 03:11 PM »


We haven't heard anything, but as the front brakes were removed (as seen from the footage), presumably to reduce mass, I think its a good bet that the batteries and other heavy internal parts were also removed.

Where Starman is going, he don't need brakes...

 That's because he doesn't need to go into Mars orbit.

Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #643 on: 03/09/2018 03:57 PM »
Elon on twitter:

"Will be at SXSW Sat/Sun with Jonah & Lisa, who created Westworld. Jonah made an incredible short reel of Falcon Heavy & Starman. Releases tmrw aft."

https://twitter.com/elonmusk/status/972149891848798208?s=19
« Last Edit: 03/09/2018 04:44 PM by Nehkara »

Offline cscott

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #644 on: 03/10/2018 08:01 PM »
BTW, did we ever hear definitively if they removed the roadster's battery pack? I have a hard time believing they'd launch with it unless they both needed the mass and electrical capacity and were certain it would pose no danger to the mission (such as via rupturing or exploding in vacuum).

We haven't heard anything, but as the front brakes were removed (as seen from the footage), presumably to reduce mass, I think its a good bet that the batteries and other heavy internal parts were also removed.
I don't think that picture is definitive proof.  See for example these photos of a Tesla Model X.  You can clearly see through the wheels, and the brakes are definitely still in place.

Offline Comga

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #645 on: 03/10/2018 11:21 PM »
We haven't heard anything, but as the front brakes were removed (as seen from the footage), presumably to reduce mass, I think its a good bet that the batteries and other heavy internal parts were also removed.
"presumably"  (my emphasis)
We can take it from the photo that the brake was removed, but we don't know why.
Reducing the mass seems unlikely to me.
Even the battery is probably small compared the total mass of the second stage and payload mount.
SpaceX could have just bolted the front camera to the hood and the side one to the passenger door, but they built those large projecting mounts.  This doesn't seem very sensitive to minimizing mass.
There are other guesses, like using the brake mounting points as anchors to lock out the suspension so the wheels didn't bounce wildly on launch. 
However, in the absence of inside knowledge, this is just another guess.

edit:typo
« Last Edit: 03/10/2018 11:21 PM by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Offline Comga

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #646 on: 03/11/2018 03:36 AM »
machdiamond beat me to it.

There are images of the suspension in the video linked in this post

Perhaps someone with a sharp eye for auto mechanics can spot a theme to what has been removed and what has been added to make the Roadster "flyable".

edit:  There's just not quite enough resolution to tell if the Matchbook Roadster with the miniature Starman on the dash has a microsopic Roadster with a nano-Starman on it's dash.
« Last Edit: 03/11/2018 03:38 AM by Comga »
What kind of wastrels would dump a perfectly good booster in the ocean after just one use?

Online Freddedonna

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #647 on: 03/11/2018 04:03 AM »
The Roadster has much bigger brakes (at least in relation to the wheel size)
 compared to the Model X though :

It's hard to tell from the pictures because of the angles and shadows, but from the Starman video (at this timestamp : https://www.youtube.com/watch?v=aBr2kKAHN6M?t=10923), it's pretty clear that we can see through pretty much the entire wheel (the car's body and some tubes seem to block the rest).

This doesn't seem very sensitive to minimizing mass.
There are other guesses, like using the brake mounting points as anchors to lock out the suspension so the wheels didn't bounce wildly on launch.

I don't know the weight of these specific discs, but they can be around 15 to 20 pounds each, and taking into account the rest of braking system (calipers, pads, fluids, etc), I can see this removing ~100 pounds from the total mass. Still a pretty small saving, I'd be more inclined to say they removed them to weld the wheels in place to reduce vibrations/variables.

Offline ddeflyer

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #648 on: 03/11/2018 04:05 AM »
Just a guess, but I would expect they removed the brakes because they'd want to remove the wheel hubs (and the rotors are attached between the wheels and hubs); why make the FEM simulations more complex with potentially spinning wheels when you could just bolt them in with some spacers/adapters. Once you've done that you'd need to remove the calipers since they would blow out the pistons and make a mess if you didn't. At that point they'd just be removing the whole brake system.

Frankly I suspect alot of the suspension wasn't in there; you don't want droplets of axles grease floating around or the dampers blowing oil out their seals, etc.

Offline CuddlyRocket

Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #649 on: 03/11/2018 06:28 AM »
Once you've done that you'd need to remove the calipers since they would blow out the pistons and make a mess if you didn't.

Pistons? It's an electric car. :)

Offline ddeflyer

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #650 on: 03/11/2018 07:20 AM »
I think you know what I mean, but just in case...

Brake calipers have hydraulic pistons that push the brake pads against the brake rotors. If you don't have the rotors in place then any pressure in the brake system will push the pistons out of the caliper leaving big holes for the slippery, messy, and corrosive brake fluid to come dumping out all over the place.

Offline cscott

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #651 on: 03/11/2018 02:36 PM »
Teslas use electric brakes:

https://teslamotorsclub.com/tmc/threads/p85d-electric-mechanical-braking-system.36882/

Solenoid, not hydraulic.  (Granted, not 100% sure this is was the case for 1st Gen roadster, but likely.)

Offline cscott

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #652 on: 03/11/2018 02:37 PM »
This doesn't seem very sensitive to minimizing mass.
There are other guesses, like using the brake mounting points as anchors to lock out the suspension so the wheels didn't bounce wildly on launch.

I don't know the weight of these specific discs, but they can be around 15 to 20 pounds each, and taking into account the rest of braking system (calipers, pads, fluids, etc), I can see this removing ~100 pounds from the total mass. Still a pretty small saving, I'd be more inclined to say they removed them to weld the wheels in place to reduce vibrations/variables.
There seems to be some work being done to the wheel hubs in the new starman video.  Goes by quickly so I can't be certain what I'm seeing there.

EDIT screenshots here: http://forum.nasaspaceflight.com/index.php?topic=44376.msg1797897.msg#1797897
« Last Edit: 03/11/2018 02:48 PM by cscott »

Offline envy887

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #653 on: 03/12/2018 01:30 AM »
Teslas use electric brakes:

https://teslamotorsclub.com/tmc/threads/p85d-electric-mechanical-braking-system.36882/

Solenoid, not hydraulic.  (Granted, not 100% sure this is was the case for 1st Gen roadster, but likely.)
Those still have a hydraulic piston. The "electric" part is a pump and a solenoid valve that pressurize and control the hydraulic circuit.

However, brake hydraulics are built to take hundred of atmospheres of pressure. They wouldn't even notice a little vacuum, nevermind explode or leak brake fluid.

Offline ddeflyer

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #654 on: 03/12/2018 03:16 AM »
Teslas use electric brakes:

https://teslamotorsclub.com/tmc/threads/p85d-electric-mechanical-braking-system.36882/

Solenoid, not hydraulic.  (Granted, not 100% sure this is was the case for 1st Gen roadster, but likely.)
Those still have a hydraulic piston. The "electric" part is a pump and a solenoid valve that pressurize and control the hydraulic circuit.

However, brake hydraulics are built to take hundred of atmospheres of pressure. They wouldn't even notice a little vacuum, nevermind explode or leak brake fluid.

As long as you have the rotors in there to limit the piston travel and block the lines before the master cylinder :-D (the reservoir isn't totally sealed)

Offline Nomadd

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #655 on: 03/12/2018 03:39 AM »
Teslas use electric brakes:

https://teslamotorsclub.com/tmc/threads/p85d-electric-mechanical-braking-system.36882/

Solenoid, not hydraulic.  (Granted, not 100% sure this is was the case for 1st Gen roadster, but likely.)
Those still have a hydraulic piston. The "electric" part is a pump and a solenoid valve that pressurize and control the hydraulic circuit.

However, brake hydraulics are built to take hundred of atmospheres of pressure. They wouldn't even notice a little vacuum, nevermind explode or leak brake fluid.
Not sure I get you. The problem I'd expect would be vacuum causing brake fluid to boil, forcing the pistons out if the rotors were missing. That would take almost no pressure.

Online FutureSpaceTourist

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #656 on: 03/12/2018 09:58 AM »
Interesting follow-up to debris debate:

Quote
French CNES launcher chief: Worries about SpaceX Falcon Heavy debris are overwrought
by Peter B. de Selding | Mar 12, 2018

WASHINGTON — The director of launchers of the French space agency, CNES, on March 11 entered the European debate about the inaugural flight of SpaceX’s Falcon Heavy rocket, apparently in an effort to dispel public misconceptions.

https://www.spaceintelreport.com/french-cnes-launcher-chief-worries-about-spacex-falcon-heavy-debris-are-overwrought/

Offline cscott

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #657 on: 03/12/2018 01:55 PM »
Teslas use electric brakes:

https://teslamotorsclub.com/tmc/threads/p85d-electric-mechanical-braking-system.36882/

Solenoid, not hydraulic.  (Granted, not 100% sure this is was the case for 1st Gen roadster, but likely.)
Those still have a hydraulic piston. The "electric" part is a pump and a solenoid valve that pressurize and control the hydraulic circuit.

However, brake hydraulics are built to take hundred of atmospheres of pressure. They wouldn't even notice a little vacuum, nevermind explode or leak brake fluid.
Following up: Electronic Wedge Brakes (EWB) don't have any hydraulics at all.  Siemens has been developing them for over a decade.  But in my cursory Google, I couldn't find any evidence they've yet been used in a passenger car.  The roadster appears to have had quite conventional brakes.

Offline Lar

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #658 on: 03/12/2018 06:03 PM »
Following up: Electronic Wedge Brakes (EWB) don't have any hydraulics at all.  Siemens has been developing them for over a decade.  But in my cursory Google, I couldn't find any evidence they've yet been used in a passenger car.  The roadster appears to have had quite conventional brakes.
It was a rolling chassis/body from Lotus so it would be surprising if it didn't.. much more engineering to fit non conventional brakes. That's not where Tesla was at that time.
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Offline Hog

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Re: Falcon Heavy Demo Mission Payload Discussion
« Reply #659 on: 03/12/2018 08:37 PM »
Teslas use electric brakes:

https://teslamotorsclub.com/tmc/threads/p85d-electric-mechanical-braking-system.36882/

Solenoid, not hydraulic.  (Granted, not 100% sure this is was the case for 1st Gen roadster, but likely.)
Those still have a hydraulic piston. The "electric" part is a pump and a solenoid valve that pressurize and control the hydraulic circuit.

However, brake hydraulics are built to take hundred of atmospheres of pressure. They wouldn't even notice a little vacuum, nevermind explode or leak brake fluid.
Not sure I get you. The problem I'd expect would be vacuum causing brake fluid to boil, forcing the pistons out if the rotors were missing. That would take almost no pressure.
I don't see hydraulic brake fluid boiling just because of vacuum.  Its not like blood or any similar fluid.
Paul

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