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21
As a European, it hurts to see this happening. I agree with your assessment. Which hurts even more. They fear, that if they built a launch vehicle that is supposed to land like F9 it would crash a few times before it works, like F9. That is a absolute no no for them. It has to work the first time or they would not try it. I am unsure why that is though.

Working or not, the stage is lost. Why don't give a try and do some tests?
22
Spinning the wheel a bit further (pun intended), how does the Raptor actually start? I mean, spark ignition or not, it needs to spin up its turbines. Following the ongoing discussion on the Merlin:

[...]
The LOX and RP-1 tanks are pre pressurized with helium. 
High pressure helium spins up the turbo pump.  LOX and RP-1 are ignited by TEA-TEB in the gas generator and  takes over from the helium.  The propellants meet in the combustion chamber and are also ignited by TEA-TEB.
[...]

But the Raptor doesnt have high pressure helium available. Its tanks are autogenous pressurization. So how do the turbine wheels of Raptor start? I do have ideas how it could be done but I dont want to wildly speculate. Does anyone has info on that?

They said it was spark ignited. The sparks probably ignite ignition torches which in turn ignites the pre-burners and the main chamber.  You can see the ignition leads on their CAD model.

This ignition approach would make all Raptors restartable assuming their propellants had enough head pressure.
Head pressure and an electrical power source is all that is required to start.

The start sequence is something like the following:
- crack valves and dribble in propellants to pre-chill the engine.
- open valves and propellants flow into their respective pre-burners.
- spark ignites stoichiometric mixture in torches.
- torches ignite pre-burners
- pre-burner exhaust spins turbines attached to propellant pumps. (one for methane, one for LOX)
- main chamber torch ignites gaseous propellants entering chamber.
- pumps start increasing pressure above head pressure and quickly climb to design pressure.

This requires detailed understanding of the combustion processes and the dynamics of the pumps, turbines and valves. It is a tightly choreographed dance.

John

23
So what gravity is generated at the poles of the object given its length and spin rate?

Using SpinCalc with 200 meter radius and one rotation every 7.3 hours yields about 0.0000012 g.

Need to spin it up to about 2 rpm to get 1 g.

http://www.artificial-gravity.com/sw/SpinCalc/SpinCalc.htm
24
Will Zuma require another static test since it was removed from TEL?


Sent from my iPhone using Tapatalk

Not by default. No clue what criteria would be used to decide if it needed one.

If they move it to SLC-40, that might be a factor.
25
Thank you Jim. This is exactly how I understood it but didn't feel confident enough to say much without a lot of qualification.

The propellant tank pressurization is primarily to provide rigidity to the airframe and provide adequate inlet conditions at the turbopump so there is no cavitation.
27
Machine-to-machine (thing-to-thing) connections to the internet are predicted to reach five times the world population in mid-2020s.  Still growing exponentially, while population is leveling off (predicted to peak around 10B by 2050).  Not sure if that includes autonomous personal vehicles.
28
>
This goes well beyond imaging/photography.  Coverage of the planet is potentially continuous, everywhere.  12,000 sats spread over 4*Pi* steradians (~40,000 square degrees) is more than a satellite per each 2x2degree square of the sky (simplifying, of course, since there will be overlap areas around 50-55degrees latitude, geometrical considerations, etc.).  If each imager/sensor has at least a 4 sq. degree footprint, coverage will be continuous.  And the bulk of the sats are (planned to be) only a few hundred km above the ground.

I can see DoD buying a 'subscription' or two, maybe NOAO, Nat'l Weather Service, etc. -- and DoD might be a bit more than interested in anywhere broadband comms, too.

Could negate the need for many expensive USG payloads methinks.

Which brings up STRATCOM General Hyten's recent statements

SpaceNews...

Quote
"And, as a combatant commander, I won’t support the development any further of large, big, fat, juicy targets. I won’t support that,” he insisted. “We are going to go down a different path. And we have to go down that path quickly."
29
Take a cylinder of half-height h, radius R, constant density p, and set up a cylindrical coordinate system with the z-axis parallel the axis of symmetry and 0 at the center. The on-axis gravitational potential is then as below where G is the gravitational constant.

PS google found this for me. I'll let you plug in the numbers
30
The last service mentioned is a surprise: Satellite Photography Services. Don't recall mention of putting an image sensor and telescope on board, but if Planet can do it with a few hundred 3x cube sats, why not add it to 12000 small sats ( full constellation ).

There's more:
Quote
scientific and technological services, namely, research, analysis, and monitoring of data captured via remote sensors and satellites; remote sensing services, namely, aerial surveying through the use of satellites

This goes well beyond imaging/photography.  Coverage of the planet is potentially continuous, everywhere.  12,000 sats spread over 4*Pi* steradians (~40,000 square degrees) is more than a satellite per each 2x2degree square of the sky (simplifying, of course, since there will be overlap areas around 50-55degrees latitude, geometrical considerations, etc.).  If each imager/sensor has at least a 4 sq. degree footprint, coverage will be continuous.  And the bulk of the sats are (planned to be) only a few hundred km above the ground.

I can see DoD buying a 'subscription' or two, maybe NOAO, Nat'l Weather Service, etc. -- and DoD might be a bit more than interested in anywhere broadband comms, too.

Could negate the need for many expensive USG payloads methinks.
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