Wiki Super Heavy/Starship - General Development Discussion

[Electroman]

Finally some sense has dawned on Musk and SpaceX team on stage separation. They will be abandoning the crazy "twist, spin, jerk, wiggle, shake” method to separate , and instead will go for the proven Russian, “fire your engines and fly away” method.

This seems more reasonable and any damage to the top section of the booster should be marginal.

https://twitter.com/x/status/1672630597246926851

 

[JB47394]

Finally some sense has dawned on Musk and SpaceX team on stage separation. They will be abandoning the crazy "twist, spin, jerk, wiggle, shake” method to separate , and instead will go for the proven Russian, “fire your engines and fly away” method.

This seems more reasonable and any damage to the top section of the booster should be marginal.

Criminy. Ten percent improvement??

I suspect that they can easily mitigate damage to the top of the booster given that the sequence of events at staging is always the same. Perhaps they can put a tile at the center of each impinging engine flame from Starship and call it a day.

I'm a little disappointed that SpaceX isn't using some weirdly-effective and novel means of staging, but that ten percent improvement in payload performance is just tremendous.

 

[Cosmacelf]

From Ashlee Vance’s Twitter spaces interview of Elon Musk seven hours ago:

About 1,000 changes to Starshipfrom last attempt. Late stage change is hot staging. Light upper stage engines while some first stage engines are still on. Must protect top of booster from blast. Meaningful payload to orbit increase, roughly 10% to orbit from this. Need vents for upper stage engines to exhaust.

Launchpad upgrades and booster and ship will be ready in about six weeks. So Mid August right now.

Higher thrust to weight liftoff this time, so less time spent near the ground.

Engines on last rocket were a hodgepod. Built and tested over a period of a year. Hot gas manifold improvements to mitigate hot gas leakage (Expansion of materials can cause gaps). Tighter torques on bolts.

SpaceX has invested over $2B into Starship, $3B by end of year.

 

[ecarfan]

He estimates a ~10% increase in payload performance with this.

I don’t understand how changing the stage sep method accomplishes that.

 

[ecarfan]

Need vents for upper stage engines to exhaust.

I think I saw that in a NSF video recently of one of the boosters currently in the final stages of production. Will have to try and find the video.

 

[JB47394]

I think I saw that in a NSF video recently of one of the boosters currently in the final stages of production. Will have to try and find the video.

Here's a tweeted image speculating how cutouts spotted on a ring could be used at the top of the booster. Many thought at the time (3 weeks ago) was that it was not so much for hot fire but as a means of escape for Starship. There's also speculation that the ring with the vents would be added between Starship and the booster.

https://twitter.com/x/status/1664305744676519938

 

[mongo]

I don’t understand how changing the stage sep method accomplishes that.

The flip results in a higher crossection to the airstream which wastes velocity.
Unpowered flight sacrifices vertical velocity.
On the recent Starlink launch, it took 19 seconds from MECO until stage 2 had reachived that velocity ~190m/s
Booster lost 100 kph before stage 2 ignition ~27m/s.
So over 200m/s of deltaV to replace on a Falcon 9.

Reducing restarts reduces high pressure spin up gas mass.

 

[JB47394]

Unpowered flight sacrifices vertical velocity.

I think it's safe to say just "velocity". At staging, I would think that most of the vector is horizontal.

 

[Electroman]

The flip results in a higher crossection to the airstream which wastes velocity.

What airstream? At MECO there is no air.

 

[JohnnyEnglish]

Criminy. Ten percent improvement??

I suspect that they can easily mitigate damage to the top of the booster given that the sequence of events at staging is always the same. Perhaps they can put a tile at the center of each impinging engine flame from Starship and call it a day.

I'm a little disappointed that SpaceX isn't using some weirdly-effective and novel means of staging, but that ten percent improvement in payload performance is just tremendous.

In addition it is likely to be far easier to get Starship rated for human flight with a staging method which is independent of the booster performing nominally.

 

[mongo]

What airstream? At MECO there is no air.

There is not much air, but the rocket is moving through that not much very quickly.

Consider:
The fairing gets jettisoned after SES. 102km for Transporter-8. Note: only 83km for Starlink, so just after stage separation to avoid collision with booster.
F9 loses velocity with engines off
Sattelites naturally deorbit
'Space' defined as 100km (stage sep is ~80km)

Drag vs time plot in this thread:
Falcon 9 velocity/altitude values from webcast

 

[Electroman]

There is not much air, but the rocket is moving through that not much very quickly.

Consider:
The fairing gets jettisoned after SES. 102km for Transporter-8. Note: only 83km for Starlink, so just after stage separation to avoid collision with booster.
F9 loses velocity with engines off
Sattelites naturally deorbit
'Space' defined as 100km (stage sep is ~80km)

Drag vs time plot in this thread:
Falcon 9 velocity/altitude values from webcast

Nice graphs. I presume he got the acceleration data from the velocity values that SpaceX displays on their video feed.

Some questions:

- I see acceleration is quite squiggly, while the velocity graph is smooth. Which I thought was odd. There is no change in slope of velocity curve at MaxQ when the acceleration dips.

- I guess the M1D ignition point is not labelled correctly. How can the acceleration go from negative to zero before the engine ignites ?

- And as per this graph, Drag is pretty much zero at around 60 KMs.

- And most importantly how did he get the horizontal and vertical components of the velocity? I always wished SpaceX showed a downrange distance as much as the alititude. But without that data how does one compute the horizontal and vertical components of velocity?

It will be great to plot the same two graphs for Stage 1 after MECO all the way to touchdown,.

 

[mongo]

Nice graphs. I presume he got the acceleration data from the velocity values that SpaceX displays on their video feed.

Some questions:

- I see acceleration is quite squiggly, while the velocity graph is smooth. Which I thought was odd. There is no change in slope of velocity curve at MaxQ when the acceleration dips.

- I guess the M1D ignition point is not labelled correctly. How can the acceleration go from negative to zero before the engine ignites ?

- And as per this graph, Drag is pretty much zero at around 60 KMs.

- And most importantly how did he get the horizontal and vertical components of the velocity? I always wished SpaceX showed a downrange distance as much as the alititude. But without that data how does one compute the horizontal and vertical components of velocity?

It will be great to plot the same two graphs for Stage 1 after MECO all the way to touchdown,.

-they are screen scraping the video stream so sampling beat frequencies induces high frequency noise which shows up in acceleration as it is calculated as the derivative of velocity. One frame at 60Hz is 16mS in jitter. I ran into the same thing plotting Starship’s test flight. 5 second intervals looked much better.

-I don't follow, M1D ignition event goes from negative to positive acceleration. They are labeling the event, not the specific point on the line.

-Drag is not zero as indicated by both the drag plot and the loss of velocity. Starship drag during flip would be worse due to crossection, though mass inversely impacts velocity loss. It's planned to occur at around 64km also.

-I assume they used the derivative of altitude to calculate vertical velocity. That can then be removed from total velocity. Looks to be around 800m/s at the highest climb rate

 

[Grendal]

There is not much air, but the rocket is moving through that not much very quickly.

Consider:
The fairing gets jettisoned after SES. 102km for Transporter-8. Note: only 83km for Starlink, so just after stage separation to avoid collision with booster.
F9 loses velocity with engines off
Sattelites naturally deorbit
'Space' defined as 100km (stage sep is ~80km)

Drag vs time plot in this thread:
Falcon 9 velocity/altitude values from webcast

A whole lot has changed since Thiacom 8. That was the 25th F9 launch and used a Block 3 B1028 booster. It's still great data, just likely different from a modern Block 5 booster pattern. FYI.

 

[mongo]

A whole lot has changed since Thiacom 8. That was the 25th F9 launch and used a Block 3 B1028 booster. It's still great data, just likely different from a modern Block 5 booster pattern. FYI.

Sure, but the graph was there to show atmospheric effects exist. Current F9 diameter is the same, so variables would be altitude and velocity at stage separation (*maybe* grid fin shape) and those vary by mission anyway.

Other data point:
SpaceX lost 40 Starlinks in February last year from 210km when a geomagnetic storm increased atmospheric density 50%.

 

[Electroman]

Here's a tweeted image speculating how cutouts spotted on a ring could be used at the top of the booster. Many thought at the time (3 weeks ago) was that it was not so much for hot fire but as a means of escape for Starship. There's also speculation that the ring with the vents would be added between Starship and the booster.

https://twitter.com/x/status/1664305744676519938

This tweet thread dispels the notion that those cutouts will make it to production, and speculates how the staging will be done.

https://twitter.com/x/status/1673048849202683904

 

[Electroman]

Sure, but the graph was there to show atmospheric effects exist.

It is possible that Delta V between MECO and M1D ignition is primarily due to the reduction of vertical component of the velocity due to gravity and not any atmospheric effects.

 

[JB47394]

This tweet thread dispels the notion that those cutouts will make it to production, and speculates how the staging will be done.

Oh yeah? Well this tweet says that my dad can whip your dad.

That's an interesting find. I hadn't seen that ring section with the apparent vent holes. Leave it to SpaceX to take that captured exhaust and put it to good use. However, I think he's wrong about the direction of the vents. The images depict the exhaust vented towards the rear. Surely the vents will direct the exhaust forward so that it aids in slowing the booster and accelerating separation.

 

[mongo]

It is possible that Delta V between MECO and M1D ignition is primarily due to the reduction of vertical component of the velocity due to gravity and not any atmospheric effects.

Ah, great point!
I was incorrectly thinking the reported velocity was horizontal, but it isn't. The majority of velocity is horizontal so gravity loss shows up as less than a 9.8 m/s/s impact on total speed. Mass of stack minimizes impact of aero force, but gravity is always gravity.

From the recent Starlink launch, 4 seconds had 16 m/s velocity loss, 40m/s expected gravity loss.
8184kph=2273m/s = sqrt(X^2 + (813^2))
8123kph= 2259m/s = sqrt(X^2 + (813‐40)^2)
X=2123m/s
Y=813m/s

 

[Electroman]

Ah, great point!
I was incorrectly thinking the reported velocity was horizontal, but it isn't. The majority of velocity is horizontal so gravity loss shows up as less than a 9.8 m/s/s impact on total speed. Mass of stack minimizes impact of aero force, but gravity is always gravity.

From the recent Starlink launch, 4 seconds had 16 m/s velocity loss, 40m/s expected gravity loss.
8184kph=2273m/s = sqrt(X^2 + (813^2))
8123kph= 2259m/s = sqrt(X^2 + (813‐40)^2)
X=2123m/s
Y=813m/s

View attachment 950800View attachment 950801

This is also evidenced from looking at the 2nd graph in that page. If you look at that you can see the horizontal velocity does NOT dip but goes flat for a few seconds after MECO.

That small flat section tells us there is no reduction in horizontal velocity between MECO and Merlin ignition - Ergo no atmospheric effect