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Voting closed: 04/02/2020 08:43 pm


Author Topic: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion  (Read 435507 times)

Online Chris Bergin

New thread for discussion of the Starship prototype being built in Boca Chica, Texas.  Previous posts on this prototype can be found in these threads:

Discussion 1

Discussion 2

Discussion 3

Discussion 4

Discussion 5

Discussion 6

SpaceX BFS : Phase 2 - Starship Orbital Prototype(s) - Photos and Updates -1

SpaceX BFS : Phase 2 - Starship Orbital Prototype(s) - Photos and Updates -2 (Latest)

SpaceX Texas launch site Discussion and Updates - Thread 9

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Offline First Mate Rummey

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What about a poll about SN3 destiny, like on thread 6?  ;D

Offline zodiacchris

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Oh, very funny! 🤪

Offline capoman

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Static fire Apr 1 and 150 hop on Apr 6? It's optimistic, but could be doable. Will need legs installed by then of course. Likely after static fire. I doubt nosecone will be added for this short hop. Would be just duplicating Hopper 1's hop.

Offline RocketLover0119

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Static fire Apr 1 and 150 hop on Apr 6? It's optimistic, but could be doable. Will need legs installed by then of course. Likely after static fire. I doubt nosecone will be added for this short hop. Would be just duplicating Hopper 1's hop.

I personally think it will do more than a 150m hop, not many though maybe 3 or so hops IMO.
"The Starship has landed"

The 150m Hop plan is leftover from previous testing... 

I'd guess that they would start with some "tethered hops" before going for free flight hops.

Biggest hurdle to any hopping right now is Thrusters for attitude control.  Any evidence so far that these have been installed?

Offline zampone

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Cricket, grasshopper, Olympic athlete, F9 .. who jumps without strong legs .. crashes. So no legs .. no jump.
When I see the legs besides the Raptors then it will be time.
Go SN3! but first get three pairs of shoes.

Offline capoman

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The 150m Hop plan is leftover from previous testing... 

I'd guess that they would start with some "tethered hops" before going for free flight hops.

Biggest hurdle to any hopping right now is Thrusters for attitude control.  Any evidence so far that these have been installed?

I'm guessing that since they have had issues with tanks, that tanks, then Raptor fire will be done first before installing additional hardware such as legs and thrusters. It think SpaceX has learned to test components before getting too far into a build. The tanks and Raptor firing are still high risk tests.

Offline cdebuhr

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The 150m Hop plan is leftover from previous testing... 

I'd guess that they would start with some "tethered hops" before going for free flight hops.

Biggest hurdle to any hopping right now is Thrusters for attitude control.  Any evidence so far that these have been installed?

I'm guessing that since they have had issues with tanks, that tanks, then Raptor fire will be done first before installing additional hardware such as legs and thrusters. It think SpaceX has learned to test components before getting too far into a build. The tanks and Raptor firing are still high risk tests.
Do they strictly need RCS thrusters for a straight up-and-down hop?   For more drastic moves, sure.  But as long as its a nice, gentle up and down with the fiery bits pointed squarely at the ground, 3-engine TVC gives them at least some control authority on all 6 axes.  Might that be enough for initial testing?  My recollection from Hopper was that the RCS thruster packs were only needed for roll control, as you can't really get that from only one engine.

Offline wannamoonbase

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The 150m Hop plan is leftover from previous testing... 

I'd guess that they would start with some "tethered hops" before going for free flight hops.

Biggest hurdle to any hopping right now is Thrusters for attitude control.  Any evidence so far that these have been installed?

Given the vehicle size, I'm not sure a tethered hop works or provides much value.  Several hold down static fires at different durations and power levels have value.

Given the close proximity of the pad to the build area, each time they do one of these they have to suspend building vehicles.  So the timing and number of tests may want to be at a minimum or compressed.
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Offline capoman

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #10 on: 03/27/2020 02:55 pm »
The 150m Hop plan is leftover from previous testing... 

I'd guess that they would start with some "tethered hops" before going for free flight hops.

Biggest hurdle to any hopping right now is Thrusters for attitude control.  Any evidence so far that these have been installed?

I'm guessing that since they have had issues with tanks, that tanks, then Raptor fire will be done first before installing additional hardware such as legs and thrusters. It think SpaceX has learned to test components before getting too far into a build. The tanks and Raptor firing are still high risk tests.
Do they strictly need RCS thrusters for a straight up-and-down hop?   For more drastic moves, sure.  But as long as its a nice, gentle up and down with the fiery bits pointed squarely at the ground, 3-engine TVC gives them at least some control authority on all 6 axes.  Might that be enough for initial testing?  My recollection from Hopper was that the RCS thruster packs were only needed for roll control, as you can't really get that from only one engine.

Good question, although I think the Raptor's control would more coarse as compared to the fine control of thrusters. My guess would be since they are testing the last phase of landing, they would want to simulate the control that will be used for future landings. My bet would be to have thrusters, even if Raptors could do it. That also begs the question, would they use hot or cold thrusters at this point? Using hot thrusters and testing a full tank size with three Raptors, autogenous pressurization, and legs, is a lot on an early test.
« Last Edit: 03/27/2020 02:58 pm by capoman »

[...]
My recollection from Hopper was that the RCS thruster packs were only needed for roll control, as you can't really get that from only one engine.

Yeah -- and that was somewhat exaggerated compared to the needs of a normal rocket, because the hopper's funny legs acted as a sail/lever arm in the not-insignificant wind (which as any kiter can tell you increases tremendously with height).

Though Starship will of course have the same issue, and should have a lot less mass to turn compared to hopper due to Hopper's hefty construction

Offline ZChris13

The 150m Hop plan is leftover from previous testing... 

I'd guess that they would start with some "tethered hops" before going for free flight hops.

Biggest hurdle to any hopping right now is Thrusters for attitude control.  Any evidence so far that these have been installed?
They only needed thrusters for roll control, and they won't be needing them with three engines.

Offline Tuna-Fish

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #13 on: 03/27/2020 03:52 pm »
OK, I here submit for review SS SN04 main fluids piping diagram.
IMHO OFC

The big thing that's missing is that there needs to be high-pressure gox and gch4 tanks between the autogenous pressurization exhaust from the engine and the main tanks. Just pushing the gas directly from the engine to the tank would result in horrible control issues as there would be a lot of lag between "pressure too low/high" and changes at the rate of production at the engines. This would be easy to fix by just putting a small buffer with room in both directions (able to handle much higher pressures than the main tank, always pressed to ~10B or so) between them. With that, you can keep the pressure at the main tanks very controlled and stable.

And, those tanks would also be quite useful for the gox/ch4 control thrusters they are building.

Offline Eka

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #14 on: 03/27/2020 04:50 pm »
OK, I here submit for review SS SN04 main fluids piping diagram.
IMHO OFC

The big thing that's missing is that there needs to be high-pressure gox and gch4 tanks between the autogenous pressurization exhaust from the engine and the main tanks. Just pushing the gas directly from the engine to the tank would result in horrible control issues as there would be a lot of lag between "pressure too low/high" and changes at the rate of production at the engines. This would be easy to fix by just putting a small buffer with room in both directions (able to handle much higher pressures than the main tank, always pressed to ~10B or so) between them. With that, you can keep the pressure at the main tanks very controlled and stable.

And, those tanks would also be quite useful for the gox/ch4 control thrusters they are building.
A suitably large pipe for the flow volume at reduced pressure and a pressure reduction valve is all that should be needed. Remember the Raptors are producing up to 300 bar pressures. The tanks are at 6 bar. Put the pressure reduction valve at the Raptor, and have it output 50 bar. A relatively small pipe could then deliver that to the propellant tank where there is a valve for controlling the flow into the tank.
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Offline AS-503

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #15 on: 03/27/2020 04:53 pm »
OK, I here submit for review SS SN04 main fluids piping diagram.
IMHO OFC

The big thing that's missing is that there needs to be high-pressure gox and gch4 tanks between the autogenous pressurization exhaust from the engine and the main tanks. Just pushing the gas directly from the engine to the tank would result in horrible control issues as there would be a lot of lag between "pressure too low/high" and changes at the rate of production at the engines. This would be easy to fix by just putting a small buffer with room in both directions (able to handle much higher pressures than the main tank, always pressed to ~10B or so) between them. With that, you can keep the pressure at the main tanks very controlled and stable.

And, those tanks would also be quite useful for the gox/ch4 control thrusters they are building.

Shuttle was autogenous and did not have these tanks.
That said, i do not know how Shuttle regulated this pressure.

Offline volker2020

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #16 on: 03/27/2020 04:55 pm »
The 150m Hop plan is leftover from previous testing... 
That also begs the question, would they use hot or cold thrusters at this point?
After having read that they intend to use hot gas thrusters, which have a number of potential upsides, I fail to see any info, showing that they actually work on them. If it would be that easy, I guess we would see more them out in the field.

Offline aero

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #17 on: 03/27/2020 05:05 pm »
The thing that makes hot gas thrusters (CH4 +O2) easy is the availability of those two gasses on the Starship. I doubt anyone would use those two gasses for thrusters if the ship were fueled with a different propellant. I don't recall them having ever been used in the past 60 years.

However, just because SpaceX has a good handle on using those gasses in the Raptor engines, doesn't mean that the same is true for using them in hot gas thrusters. The requirements are different.
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Offline DusanC

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #18 on: 03/27/2020 05:10 pm »
OK, I here submit for review SS SN04 main fluids piping diagram.
IMHO OFC

The big thing that's missing is that there needs to be high-pressure gox and gch4 tanks between the autogenous pressurization exhaust from the engine and the main tanks. Just pushing the gas directly from the engine to the tank would result in horrible control issues as there would be a lot of lag between "pressure too low/high" and changes at the rate of production at the engines. This would be easy to fix by just putting a small buffer with room in both directions (able to handle much higher pressures than the main tank, always pressed to ~10B or so) between them. With that, you can keep the pressure at the main tanks very controlled and stable.

And, those tanks would also be quite useful for the gox/ch4 control thrusters they are building.
A suitably large pipe for the flow volume at reduced pressure and a pressure reduction valve is all that should be needed. Remember the Raptors are producing up to 300 bar pressures. The tanks are at 6 bar. Put the pressure reduction valve at the Raptor, and have it output 50 bar. A relatively small pipe could then deliver that to the propellant tank where there is a valve for controlling the flow into the tank.
Yeah I missed that.
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Offline DusanC

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Re: SpaceX Starship : Texas Prototype(s) Thread 7 : Discussion
« Reply #19 on: 03/27/2020 05:28 pm »
OK, I here submit for review SS SN04 main fluids piping diagram.
IMHO OFC

The big thing that's missing is that there needs to be high-pressure gox and gch4 tanks between the autogenous pressurization exhaust from the engine and the main tanks. Just pushing the gas directly from the engine to the tank would result in horrible control issues as there would be a lot of lag between "pressure too low/high" and changes at the rate of production at the engines. This would be easy to fix by just putting a small buffer with room in both directions (able to handle much higher pressures than the main tank, always pressed to ~10B or so) between them. With that, you can keep the pressure at the main tanks very controlled and stable.

And, those tanks would also be quite useful for the gox/ch4 control thrusters they are building.
A suitably large pipe for the flow volume at reduced pressure and a pressure reduction valve is all that should be needed. Remember the Raptors are producing up to 300 bar pressures. The tanks are at 6 bar. Put the pressure reduction valve at the Raptor, and have it output 50 bar. A relatively small pipe could then deliver that to the propellant tank where there is a valve for controlling the flow into the tank.
I like this as the high temperature gas is taken from preburners I was concerned that there would be a thermal shock on the pipeline to tank connection on the transient from high temp gas to low temp liquid fuel.
When you reduce the pressure the pressure this much (from 100s to 10s bar) there would also occur a nice temperature drop of the gas. Maybe even make a heat bridges between pipeline and tank wall to precool the gas.

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