SpaceX Starship/Super Heavy Engineering General Thread 4

[tbellman]

Quick thought for Manned Starship/HLS

In space the Ship LOX tank should still have a large quantity of gaseous oxygen.

Since you're carrying this along, could this be tapped off for use in Space Suits?

Kathy Lueders' source selection statement for HLS Option A does mention "Additionally, SpaceX's design allows for the sourcing of excess propellant, which will provide crew with a large reserve supply of life support consumables in the event of a contingency event".  So it appears someone already thought of that very idea. 

Second part, Could the residual GOX in that tank be repurposed for Life Support Use? Swap back in C02 that's scrubbed/cooled to maintain pressure. Or just use the boiloff.

Backfilling with carbon dioxide doesn't sound like a good idea.  There's a good chance that it will just freeze out and form ice (freezing point approximately 100°C higher than oxygen's boiling point) in the tank.  And the amount of pressure lost by using up oxygen for life support will be quite small, as Dan already mentioned.

[livingjw]

Here's a great picture of where hoops are used to reinforce, note the change in spacing.

I wonder how much of this is to also manage the water hammer effect during shutdown?

Picture from Boca Chica Gal.

- Hoops are there to stabilize the down-comer when the surrounding LOx pressure is higher than the LCH4 pressure in the tube. I believe SpaceX had one crushed.

- LOx pressure at the bottom of the tank is higher than near the top, so more stabilizing hoops are needed to guard against buckling.

- No effect on hammer wave inside the tube. The hoops are on the outside.

John

I'm pretty sure that squished downcommer was caused by pulling a vacuum inside it, not over pressure of the LOx tank.

When would the pressure inside the downcommer be lower than the LOx tank? I would expect that except for special testing cases that downcommer should always be filled higher than the LOx level.

Regarding water hammer, I'm not taking about interfering with a pressure wave, I'm talking about dealing with the pressure spike created by the momentum of the fuel suddenly being restricted due to a rapid change of the volume of flow.

Ever seen a burst copper pipe caused by water hammer? It happens (usually) closest to the valve that caused it and I bet a series of small reinforcing rings near the valve would stop the burst.

I've built a number of booster pump stations for municipal water systems and they use large surge tanks basically identical to what is being shipped to Boca Chica right now. Just shutting down one pump in the pump house and reducing flow by 20 percent creates a huge surge. Shutting down 33 engines at once will be a pretty significant change in momentum!

- To collapse the downcomer, all that is needed is a sufficiently large pressure difference. Doesn't matter how it came about.

- In this situation, the pressure difference is caused by the combined effects of ullage pressure and head pressure. Don't need a vacuum. Don't know why you think that.

- The LCH4 column height can be higher than the LOx height and still have a lower total pressure, due to lower ullage and lower density.

- If they filled the LOx tank and reduced the ullage pressure of the LCH4 tank and or emptied the LCH4 tank, this would set up the conditions for collapse of the downcomer.

- A snafu during the test could have caused the downcomer collapse, or they might have been testing the limiting case for collapse of the downcomer. They added more external reinforcement rings to the downcomer after the collapse, which implies that they expect this condition to occur occasionally during operation.

- How does reinforcement frames/rings outside of the downcomer effect the flow of LCH4 inside? I don't understand the connection you are trying to get at.

John

[Nomadd]

- A snafu during the test could have caused the downcomer collapse, or they might have been testing the limiting case for collapse of the downcomer.
John

The word "miscommunication" was used.

[Tangilinear Interjar]

- To collapse the downcomer, all that is needed is a sufficiently large pressure difference. Doesn't matter how it came about.

- In this situation, the pressure difference is caused by the combined effects of ullage pressure and head pressure. Don't need a vacuum. Don't know why you think that.


Poor wording on my part, pressure differential is what I was referring to, allowing the downcomer to fully drain without adding ullage pressure would cause the conditions.  I used the word vacuum because I am more familiar with the basic oil canning condition.  There's a really freaky example lost in the hills near LA of a 30 foot tall and diameter water tank that looks like the hand of God came down and squished it, just because the vent pipe got blocked and the tank drained.

- The LCH4 column height can be higher than the LOx height and still have a lower total pressure, due to lower ullage and lower density.

- If they filled the LOx tank and reduced the ullage pressure of the LCH4 tank and or emptied the LCH4 tank, this would set up the conditions for collapse of the downcomer.

I was assuming normal operating conditions but then again I was making assumptions.  Assumption one is that the level of liquid in the LCH4 downcomer will always be above the common dome (until after landing).  Assumption two is that ullage of LCH4 tank will be at least 2 atmospheres for structural integrity.  Due to the height of the downcomer and the need for more ullage pressure in the LOX tank to give adequate pressure to the engine turbines I guess there might be 4 or 5 atmospheres of pressure in the LOX tank and that would give 2 to 3 atmospheres delta at the top of the downcomer but not at the bottom, where there's more reinforcing.

- A snafu during the test could have caused the downcomer collapse, or they might have been testing the limiting case for collapse of the downcomer. They added more external reinforcement rings to the downcomer after the collapse, which implies that they expect this condition to occur occasionally during operation.

I'm confident that a snafu occurred and reinforcement has happened but I'm not sure the two are related (yes the timing does seem right).  I can not see any norminal operating situations where you would want a significant pressure differential throughout the entire downcomer, I can see more differential existing towards the top but they did not significantly reinforce that area so I am still leaning towards the additional reinforcement being to protect against the downcomer bursting, not oil canning.

- How does reinforcement frames/rings outside of the downcomer effect the flow of LCH4 inside? I don't understand the connection you are trying to get at.

I never was talking about affecting the flow inside, I seem to be doing a poor job explaining my thought on this.  The rings are there (in my opinion) to reinforce the downcomer from bursting when there is a large flow transient created when the engines are shut down.  The rings keep the downcomer from splitting, like my copper water pipes have at the end of a very long run terminating with a full flow valve shutting down quickly.

Bradney

[livingjw]

Bradney comments in blue:

...pressure differential is what is important.
- Agree

...allowing the downcomer to fully drain without adding ullage pressure would cause the {collapse} conditions.
- Agree

...ullage of LCH4 tank will be at least 2 atmospheres for structural integrity...
- My analysis estimates at least 2.5 bar gauge ullage at launch to meet pump head needs ~6bar. Ramping ullage pressure from ~3.6 bar gauge at launch to 5 bar gauge at max q seems reasonable.

... the need for more ullage pressure in the LOX tank to give adequate pressure to the engine turbines pumps I guess there might be 4 or 5 atmospheres of pressure in the LOX tank and that would give 2 to 3 atmospheres delta at the top of the downcomer but not at the bottom...
- LOx tank head alone yield ~6.5 bar of pressure. LOx is ~3 times denser than LCH4. Ullage pressure at launch will be ~0 bar gauge and ramp to ~3.6 bar gauge at max q.

- If the pressures at the bottom of the LOx tank and the bottom of the downcomer are the same at launch, then the pressure differential at the top of the LOx tank will be 1.5g*423kg/m^3x 36m=~2.2bar higher in the downcomer assuming an initial acceleration of 1.5 g.

...I'm confident that a snafu occurred...  As noted by Nomadd.
- Agree

...I can not see any nominal operating situations where you would want a significant pressure differential throughout the entire downcomer...
- Agree, assuming that both engine propellant pumps need similar minimum pressures which I do.

...I can see more differential existing towards the top but they did not significantly reinforce that area so I am still leaning towards the additional reinforcement being to protect against the downcomer bursting, not oil canning...
- The highest pressure differential is at the top of the downcomer. It is ~2.2 bar higher than the pressure at the top of the LOx tank assuming that the pressures at the bottom of the LOx tank and downcomer are equal.

... The rings are there (in my opinion) to reinforce the downcomer from bursting when there is a large flow transient created when the engines are shut down.  The rings keep the downcomer from splitting...
- As stated in my other posts concerning rings/frames of pressure vessels, they are a horrible way to strengthen a pressure pipe. Much lighter and easier to just thicken the walls.  No reason for rings/frames on the downcomer unless they are guarding against collapse.

- Under normal operating conditions there should be little pressure differential between the bottom of the downcomer and bottom of the LOx tank. At launch the top of the downcomer there will be ~2.2 bar outward pressure difference.  The question then is, what sets the downcomer burst and collapse pressure limits?

-  I think SpaceX probably designed the downcomer to ~4 bar tension. The rings are added to provide stability to handle compression loading of the downcomer from higher pressure LOx. Probably not as high as 4 bar, but some reasonable difference without a large weight penalty in rings/frames/complexity.

- I think SpaceX is designing the downcomer for abnormal conditions which can reasonably be expected to occur during the life of the vehicle. Miscommunications, valve failures and operational snafus happen (it already has). Makes sense to guard against a downcomer collapse if the weight penalty is not too severe, which I think is the situation here. Such a requirement makes sense.

- Another example of an ops requirement is for the StarShip-SuperHeavy stack to be self supporting with payload and without pressurization. This requirement is not uncommon for liquid rockets (post Atlas). This eliminates the requirement for continual pressurization during ops which makes servicing and operations easier. Performance hit, but ops win.

John

[Dmitry_V_home]

I never was talking about affecting the flow inside, I seem to be doing a poor job explaining my thought on this.  The rings are there (in my opinion) to reinforce the downcomer from bursting when there is a large flow transient created when the engines are shut down.  The rings keep the downcomer from splitting, like my copper water pipes have at the end of a very long run terminating with a full flow valve shutting down quickly.

Bradney

The use of rings is a typical solution for ensuring the stability of thin-walled shells working for compression under the influence of excessive external pressure.

[livingjw]

Dimitry,

   What rocket is that?

John

[joncz]

Dimitry,

   What rocket is that?

John

https://www.arms-expo.ru/articles/armed-forces/rvsn-ur-100-8k84-mezhkontinentalnaya-ballisticheskaya-raketa-shakhtnogo-bazirovaniya/

[ThatOldJanxSpirit]

Dimitry,

   What rocket is that?

John

https://www.arms-expo.ru/articles/armed-forces/rvsn-ur-100-8k84-mezhkontinentalnaya-ballisticheskaya-raketa-shakhtnogo-bazirovaniya/

Looks like SS-11 Sego in NATI language

[Dmitry_V_home]

Dimitry,

   What rocket is that?

John

UR-200 (8K81)
https://users.livejournal.com/---lin---/322156.html

[Dmitry_V_home]

Dimitry,

   What rocket is that?

John

UR-200 (8K81)
https://users.livejournal.com/---lin---/322156.html

Oops! This is UR-100 (8K84). UR-200 has a similar design.

[su27k]

DLR Paper: Critical Analysis of SpaceX’s Next Generation Space Transportation System: Starship and Super Heavy

For the first time in the history of spaceflight a fully reusable launch system appears possible within the
near future. Since its presentation in 2016 SpaceX’s next generation space transport system has gone
through multiple names and design iterations but some key design features remained constant: Full
reusability, Full-Flow Staged Combustion engines and deeply subcooled LOX/LCH4 as propellants.

The current design iteration is of special interest because hardware is being integrated and the first
test flights, including landings, of the upper stage have been completed. A key feature of this iteration
is the novel approach to use a “skydiving” maneuver to dissipate as much energy as possible through
aerodynamic forces before initiating a landing burn and landing vertically.

The implications of a fully reusable system of this size on the orbital launch market are significant even
if the ambitious plans for quick turnaround of stages are not fulfilled right from the beginning.

Within this paper, the two-staged system is analyzed from a technical perspective based on publicly
available information. The principal goal is to form an understanding of the high-level system properties.
Of special interest are the return methods, which exhibit some novel properties. Overall a reasonable
agreement between the generated models and the publicly available information is found. The design
and its driving factors are discussed and a fundamental understanding of the high-level properties of
the system is attained.

[FutureSpaceTourist]

Starship's Flight Termination System is a crucial safety feature, allowing the vehicle to be remotely detonated if it deviates off course, or has a chance of putting people in danger. Let's take a look at our understanding of this system. (1/10)
@CosmicalChief

https://twitter.com/ringwatchers/status/1634937773583892483

There are 4 remote charges on the Full Stack. 2 on the Booster and 2 on the Ship. This creates a redundant system so if 1 charge fails on one of the stages, there is a 2nd to do the job. (2/10)
@RGVaerialphotos

They are located over the common dome of both vehicles. When the detonation occurs, the common dome will be partially destroyed, allowing the Methane and Oxygen in the tanks to mix. They are ignited, and you can imagine what happens from here. (3/10)
@ChameleonCir

https://twitter.com/ringwatchers/status/1634937977830006784

Starship, like Falcon 9, uses what's called an Autonomous Flight Termination System (AFTS). This essentially means that the flight computer has control to terminate the vehicle itself. Below is a portion of text from the Falcon 9 User Guide. (4/10)

Our launch vehicles are equipped with an autonomous flight termination system (AFTS) to limit the potential damage caused by a launch vehicle malfunction. The system terminates the flight of the vehicle automatically if mission rules are violated. The use of an AFTS requires fewer range assets to support launch operations, resulting in fewer range constraints and increased launch opportunities.

We know Starship has an AFTS system because of this port on the Quick Disconnect panel, labeled as the "AFTS Inductive Inhibit". This likely sends a signal to the autonomous FTS system, telling the computer if it is armed or not. (5/10)
@CosmicalChief @NicAnsuini

https://twitter.com/ringwatchers/status/1634938154972004353

In addition to this safety system, the charges themselves are likely added much closer to the flight, to keep the explosives off of the vehicle. There are likely also "Remove Before Flight" safety pins on these charges. (6/10)
@thejackbeyer

Because the Full Stack is so tall, SpaceX's Aerial Work Platforms are unable to reach the FTS area on the Ship. This means that FTS installation and pin pulling may occur on the ground, before stacking for launch. (7/10)
@BocaChicaGal

https://twitter.com/ringwatchers/status/1634938361097097216

To date, the FTS enclosures have gone through multiple revisions to ensure that workers can easily access the charges. To date, we do not believe that the FTS has ever been activated on a Starship. (8/10)
@thejackbeyer @RGVaerialphotos @CosmicalChief

The first flight of Firefly's Alpha rocket is an excellent example of a Flight Termination System being used. However, it was commanded on the ground, not by the vehicle’s computer itself. (9/10)
@thejackbeyer

https://twitter.com/ringwatchers/status/1634938512410648583

Overall, the Flight Termination System is crucial to ensure the safety of people on the ground during Starship's flights. Ideally, this will never be used, but you’d want to have it and not need it, rather than need it and not have it. (10/10)

[Lee Jay]

Because the Full Stack is so tall, SpaceX's Aerial Work Platforms are unable to reach the FTS area on the Ship. This means that FTS installation and pin pulling may occur on the ground, before stacking for launch. (7/10)
@BocaChicaGal

That isn't necessarily true. If there is the need, they could put a personnel basket on the crane hook.  I don't know what they will do but they could do that if it was required.  It's a common practice in industry.  It does require some special procedures such as pre-lifting the basket to full height with weights instead of people and control over basket rotation with tag lines, but it's doable and I've done it.

[robot_enthusiast]

Because the Full Stack is so tall, SpaceX's Aerial Work Platforms are unable to reach the FTS area on the Ship. This means that FTS installation and pin pulling may occur on the ground, before stacking for launch. (7/10)
@BocaChicaGal

That isn't necessarily true. If there is the need, they could put a personnel basket on the crane hook.  I don't know what they will do but they could do that if it was required.  It's a common practice in industry.  It does require some special procedures such as pre-lifting the basket to full height with weights instead of people and control over basket rotation with tag lines, but it's doable and I've done it.

They do not have a crane capable of lifting anything to that height.

[RamsesBic]

Because the Full Stack is so tall, SpaceX's Aerial Work Platforms are unable to reach the FTS area on the Ship. This means that FTS installation and pin pulling may occur on the ground, before stacking for launch. (7/10)
@BocaChicaGal

That isn't necessarily true. If there is the need, they could put a personnel basket on the crane hook.  I don't know what they will do but they could do that if it was required.  It's a common practice in industry.  It does require some special procedures such as pre-lifting the basket to full height with weights instead of people and control over basket rotation with tag lines, but it's doable and I've done it.

They do not have a crane capable of lifting anything to that height.

IIRC, the LR11000 can be configured just as the LR11350. But they will need to have some more sections delivered (unless they already have them somewhere).
Or, I guess, they can use some jig added to the chopsticks that help reach the hight needed.
Compared to those methods I would think doing the job before stacking would be preferable. Both are risky.

[DanClemmensen]

Because the Full Stack is so tall, SpaceX's Aerial Work Platforms are unable to reach the FTS area on the Ship. This means that FTS installation and pin pulling may occur on the ground, before stacking for launch. (7/10)
@BocaChicaGal

That isn't necessarily true. If there is the need, they could put a personnel basket on the crane hook.  I don't know what they will do but they could do that if it was required.  It's a common practice in industry.  It does require some special procedures such as pre-lifting the basket to full height with weights instead of people and control over basket rotation with tag lines, but it's doable and I've done it.

They do not have a crane capable of lifting anything to that height.

The chopsticks work as a crane and are a lot more stable. Use them to lift a basket. Alternatively, the worker can go up the tower, across on the chopstick arm, and down to the FTS access on a bosun's chair or equivalent. May require a line to the opposite chopstick if the FTS access is dorsal instead of lateral.

[chopsticks]

But do workers walk out on to the chopsticks while they are up? Have they done this already?

[DanClemmensen]

But do workers walk out on to the chopsticks while they are up? Have they done this already?

This is a one-off. Free climbers, sailors on tall ships, high steel workers, and window washers do this sort of stuff all the time. Presumably they will come up with something much simpler for normal operation.

[chopsticks]

Don't care about sailors and what not. I was wondering if workers have already been seen walking on the chopstick arms while they have been up. I can't recall seeing this, but maybe someone else has?