SpaceX Tuesday...

[CraigyMc]

Beati Dogu said:

rxe said:

Is there anything on why they think the Raptors didn’t start properly on the way down? They need to fix that bit before flying again! Or do a static fire while flipping the rocket about....

I'm sure it's their top priority. I know they are working on being able to throttle the engines down more, so they can land on 3 engines. They're too powerful for that currently and it would start to go back up again. LOL

SN8's restart failure was because of lack of header fuel tank pressure. That caused one of the engines to run oxygen rich and start to consume itself.

SN9's landing failure was also related to a raptor not relighting as expected, although they didn't go into details on why it didn't relight.

SN10 they will attempt to relight all three for landing, then immediately shut down one of them, giving the two running engines needed for landing.
They can't just land with all three running because they can't throttle the raptor design low enough, reliably enough to support that.

[annodomini2]

CraigyMc said:

Beati Dogu said:

rxe said:

Is there anything on why they think the Raptors didn’t start properly on the way down? They need to fix that bit before flying again! Or do a static fire while flipping the rocket about....

I'm sure it's their top priority. I know they are working on being able to throttle the engines down more, so they can land on 3 engines. They're too powerful for that currently and it would start to go back up again. LOL

SN8's restart failure was because of lack of header fuel tank pressure. That caused one of the engines to run oxygen rich and start to consume itself.

SN9's landing failure was also related to a raptor not relighting as expected, although they didn't go into details on why it didn't relight.

SN10 they will attempt to relight all three for landing, then immediately shut down one of them, giving the two running engines needed for landing.
They can't just land with all three running because they can't throttle the raptor design low enough, reliably enough to support that.

They only need 2 to control the flip manoeuvre and 1 to land

[CraigyMc]

annodomini2 said:

CraigyMc said:

Beati Dogu said:

rxe said:

Is there anything on why they think the Raptors didn’t start properly on the way down? They need to fix that bit before flying again! Or do a static fire while flipping the rocket about....

I'm sure it's their top priority. I know they are working on being able to throttle the engines down more, so they can land on 3 engines. They're too powerful for that currently and it would start to go back up again. LOL

SN8's restart failure was because of lack of header fuel tank pressure. That caused one of the engines to run oxygen rich and start to consume itself.

SN9's landing failure was also related to a raptor not relighting as expected, although they didn't go into details on why it didn't relight.

SN10 they will attempt to relight all three for landing, then immediately shut down one of them, giving the two running engines needed for landing.
They can't just land with all three running because they can't throttle the raptor design low enough, reliably enough to support that.

They only need 2 to control the flip manoeuvre and 1 to land

Elon says different.

[GTO-3R]

annodomini2 said:

They only need 2 to control the flip manoeuvre and 1 to land

They do, but Elon admitted that they never considered lighting all three in case one of them didn't re-ignite. SN10 will light all three and if they all fire back up then the upper most raptor will be cut off

[MiniMan64]

GTO-3R said:

annodomini2 said:

They only need 2 to control the flip manoeuvre and 1 to land

They do, but Elon admitted that they never considered lighting all three in case one of them didn't re-ignite. SN10 will light all three and if they all fire back up then the upper most raptor will be cut off

Fingers crossed! SN10 for next week?

[Beati Dogu]

Eventually they'll have hot gas (methane) reaction control system (RCS) thrusters for the flip maneuver and attitude control. They won't need to use the engines for this any more.

[anonymous-user]

Beati Dogu said:

Eventually they'll have hot gas (methane) reaction control system (RCS) thrusters for the flip maneuver and attitude control. They won't need to use the engines for this any more.

I'll go and Google that because I have no idea what you are talking about and I'm feeling the need for some self development. Sounds very interesting though!

[AW111]

Beati Dogu said:

Eventually they'll have hot gas (methane) reaction control system (RCS) thrusters for the flip maneuver and attitude control. They won't need to use the engines for this any more.

While that is true, they still need to get a reliable engine restart while doing mid-air gymnastics.
I'm sure they'll nail it soon.

[anonymous-user]

garyhun said:

Beati Dogu said:

Eventually they'll have hot gas (methane) reaction control system (RCS) thrusters for the flip maneuver and attitude control. They won't need to use the engines for this any more.

I'll go and Google that because I have no idea what you are talking about and I'm feeling the need for some self development. Sounds very interesting though!

Ahh, the thrusters.

Is there a supply of hot methane from previous engine (raptor) burns for this (captured for later use) or is this a completely self contained system?

[CraigyMc]

garyhun said:

garyhun said:

Beati Dogu said:

Eventually they'll have hot gas (methane) reaction control system (RCS) thrusters for the flip maneuver and attitude control. They won't need to use the engines for this any more.

I'll go and Google that because I have no idea what you are talking about and I'm feeling the need for some self development. Sounds very interesting though!

Ahh, the thrusters.

Is there a supply of hot methane from previous engine (raptor) burns for this (captured for later use) or is this a completely self contained system?

The whole raptoe engine setup is self-contained. You can pump the results out anywhere you like, as long as the pipework can take the heat and pressure. Usually it goes out of the nozzle, but it doesn't need to.

[anonymous-user]

CraigyMc said:

garyhun said:

garyhun said:

Beati Dogu said:

Eventually they'll have hot gas (methane) reaction control system (RCS) thrusters for the flip maneuver and attitude control. They won't need to use the engines for this any more.

I'll go and Google that because I have no idea what you are talking about and I'm feeling the need for some self development. Sounds very interesting though!

Ahh, the thrusters.

Is there a supply of hot methane from previous engine (raptor) burns for this (captured for later use) or is this a completely self contained system?

The whole raptoe engine setup is self-contained. You can pump the results out anywhere you like, as long as the pipework can take the heat and pressure. Usually it goes out of the nozzle, but it doesn't need to.

Cheers!

[frisbee]

garyhun said:

Ahh, the thrusters.

Is there a supply of hot methane from previous engine (raptor) burns for this (captured for later use) or is this a completely self contained system?

They already have autogenous pressurization, pipe hot gas back into the fuel and oxygen tanks, to keep the tanks pressurized. Saves having to carry another gas.

[Flooble]

frisbee said:

garyhun said:

Ahh, the thrusters.

Is there a supply of hot methane from previous engine (raptor) burns for this (captured for later use) or is this a completely self contained system?

They already have autogenous pressurization, pipe hot gas back into the fuel and oxygen tanks, to keep the tanks pressurized. Saves having to carry another gas.

That's one of the things I find really confusing (and amazing). You have this super-chilled fuel, but you then pump hot gas into it to maintain the pressure (higher pressure normally leading to higher temperature). My naïve mind imagines the temperature in the tank getting too hot, I'm amazed they are able to make it all work.

[annodomini2]

Flooble said:

frisbee said:

garyhun said:

Ahh, the thrusters.

Is there a supply of hot methane from previous engine (raptor) burns for this (captured for later use) or is this a completely self contained system?

They already have autogenous pressurization, pipe hot gas back into the fuel and oxygen tanks, to keep the tanks pressurized. Saves having to carry another gas.

That's one of the things I find really confusing (and amazing). You have this super-chilled fuel, but you then pump hot gas into it to maintain the pressure (higher pressure normally leading to higher temperature). My naïve mind imagines the temperature in the tank getting too hot, I'm amazed they are able to make it all work.

The Space Shuttle used a similar system, the fuel is chilled to get more in the tank.

Once some of it is used, space begins to appear and so they fill it with fuel that has been used to cool the combustion chamber and nozzle. A valve will direct some to the engines and some to the tank.

This maintains the pressure in the tank and stabilises the flow to the turbo pumps, the trick is regulating the flow into each tank to maintain the correct pressure.

[frisbee]

Flooble said:

frisbee said:

garyhun said:

Ahh, the thrusters.

Is there a supply of hot methane from previous engine (raptor) burns for this (captured for later use) or is this a completely self contained system?

They already have autogenous pressurization, pipe hot gas back into the fuel and oxygen tanks, to keep the tanks pressurized. Saves having to carry another gas.

That's one of the things I find really confusing (and amazing). You have this super-chilled fuel, but you then pump hot gas into it to maintain the pressure (higher pressure normally leading to higher temperature). My naïve mind imagines the temperature in the tank getting too hot, I'm amazed they are able to make it all work.

Well they haven't quite been able to get it to work, they've gone back to helium. They'll eventually have to go back to it though.

[RizzoTheRat]

annodomini2 said:

The Space Shuttle used a similar system, the fuel is chilled to get more in the tank.

Once some of it is used, space begins to appear and so they fill it with fuel that has been used to cool the combustion chamber and nozzle. A valve will direct some to the engines and some to the tank.

This maintains the pressure in the tank and stabilises the flow to the turbo pumps, the trick is regulating the flow into each tank to maintain the correct pressure.

Presumably the bigger trick is getting the fuel in to the fuel lines. The shuttle never restarted it's engines did it? Meaning there was always acceleration to push the fuel to the back of the vehicle. Starship switches to different tanks for the restart but I'm not sure how they solve the ullage problem.

[annodomini2]

RizzoTheRat said:

annodomini2 said:

The Space Shuttle used a similar system, the fuel is chilled to get more in the tank.

Once some of it is used, space begins to appear and so they fill it with fuel that has been used to cool the combustion chamber and nozzle. A valve will direct some to the engines and some to the tank.

This maintains the pressure in the tank and stabilises the flow to the turbo pumps, the trick is regulating the flow into each tank to maintain the correct pressure.

Presumably the bigger trick is getting the fuel in to the fuel lines. The shuttle never restarted it's engines did it? Meaning there was always acceleration to push the fuel to the back of the vehicle. Starship switches to different tanks for the restart but I'm not sure how they solve the ullage problem.

If they have a solution it's not public yet, at them moment they've had to revert to helium for the landing tanks.

I'm guessing the lag in the flow is currently too long for the landing tanks to achieve stable pressure.

For the launch they have small amounts of LCH4 and LOX in the COPV's in the engine skirt to start the turbopumps, which when running will serve to pressurise the main tanks.

Maybe the could use heaters on the tanks to induce pressure.

[MartG]

annodomini2 said:

RizzoTheRat said:

annodomini2 said:

The Space Shuttle used a similar system, the fuel is chilled to get more in the tank.

Once some of it is used, space begins to appear and so they fill it with fuel that has been used to cool the combustion chamber and nozzle. A valve will direct some to the engines and some to the tank.

This maintains the pressure in the tank and stabilises the flow to the turbo pumps, the trick is regulating the flow into each tank to maintain the correct pressure.

Presumably the bigger trick is getting the fuel in to the fuel lines. The shuttle never restarted it's engines did it? Meaning there was always acceleration to push the fuel to the back of the vehicle. Starship switches to different tanks for the restart but I'm not sure how they solve the ullage problem.

If they have a solution it's not public yet, at them moment they've had to revert to helium for the landing tanks.

I'm guessing the lag in the flow is currently too long for the landing tanks to achieve stable pressure.

For the launch they have small amounts of LCH4 and LOX in the COPV's in the engine skirt to start the turbopumps, which when running will serve to pressurise the main tanks.

Maybe the could use heaters on the tanks to induce pressure.

Heaters would take a lot of energy to heat the mass of fuel by any measurable degree - and the last thing the engines need is fuel or lox arriving in semi-gaseous state.

Maybe burn some propellants in a gas generator and feed the exhaust to the tanks ?

[annodomini2]

MartG said:

Heaters would take a lot of energy to heat the mass of fuel by any measurable degree - and the last thing the engines need is fuel or lox arriving in semi-gaseous state.

Maybe burn some propellants in a gas generator and feed the exhaust to the tanks ?

This what they are doing with the main tanks, known as Autogenous pressurisation, which would result in gas in the tank, if the engines could not handle it, they would not be using it.

They tried this with SN8, look how that worked out.

You don't need to heat all the fuel, just enough to induce the required pressure.

https://en.m.wikipedia.org/wiki/Autogenous_pressur...

[MartG]

This morning's Starlink launch aborted with just over a minute to go in the countdown