totm nov 2023 SpaceX Discussion Thread

[Flavio hc16]

4 minutes ago, magnemoe said:

Add some extra information from an fast google. 
An minuteman ballistic missile has an maximum velocity of 24000 km/s who was the velocity Starship had at cutoff.  has an max range of 6000 miles or 9600 km, it however has an ceiling of 1,120, this improves accuracy as less time in the atmosphere and Starship AP was 250 km, but ignore this and focus on 9600 km  who is around 1/4 of the earth diameter. 
https://www.atomicarchive.com/almanac/forces/minuteman-III.html

Note I does not discredit source, but people make mistakes making posts. Myself did not know they blew up Starship until reading it here. 

 

Angle of ballistics makes this wildly differently, starship has basically no Y vector speed when going for orbit, and it's very close to the atmosphere, a minutemen is going to 1000 km, and actually more if you consider that it's using the earth curvature to it's advantage. If it was going at a 45° angle it will go even further. 

This is a graph of range of a projectile with the same speed, but different angles, and this get actually improved when we are talking about orbital/semi orbital velocities

https://upload.wikimedia.org/wikipedia/commons/6/61/Ideal_projectile_motion_for_different_angles.svg

 

 

[RCgothic]

1 hour ago, mikegarrison said:

The ship was not headed for an orbital trajectory anyway, even if it had completed its burn.

Theoretically pieces of a ship on a near-orbital trajectory could be converted onto an orbital trajectory by an energetic explosion event, but as Jonathan said it wasn't close enough.

[tater]

48 minutes ago, CatastrophicFailure said:

OMG. What a shot!

Needs full size,

 

A render

 

[CatastrophicFailure]

1 hour ago, Flavio hc16 said:

Then you haven't  played KSP enough: try to reach 88% of orbital velocity in KSP, and you will see that you will cover less than 20% of the planet. It's the last few hundreds m/s that makes you go places. And this is eve more pronounced with a bigger Kerbing, aka Earth.

I just tried this in RSS, not surprisingly it confirms reality.  On a less-lofted trajectory (AP=156km), destructive reentry began about 3500km downrange. Puerto Rico is about 3300km from Boca, and Starship AP=250-ish km at FTSECO.

So, Math=KSP_Confirmed. 

 

1 hour ago, tater said:

A render

[JoeSchmuckatelli]

1 hour ago, tater said:

OMG. What a shot!

Needs full size,

 

A render

 

You know - without knowing it was a render - I knew something was off.  The video / tweet that @taterposted showing the staging surprised me with how much frost still clung to both vehicles. 

I'm still amazed at the quality of the photo / frame of the separation - that is amazing image quality for something at that distance / altitude. 

Props to the artist, btw, for such an excellent rendering! 

4 hours ago, tater said:

 

Question about this - the Booster rotation, specifically. 

It looks like the engine compartment is the COG - as it pretty much stays in line with Ship as it begins to flip.  (or rather, the COG is just above the rockets) is that correct or likely something from the angle? 

[darthgently]

32 minutes ago, JoeSchmuckatelli said:

Question about this - the Booster rotation, specifically. 

It looks like the engine compartment is the COG - as it pretty much stays in line with Ship as it begins to flip.  (or rather, the COG is just above the rockets) is that correct or likely something from the angle? 

Speaking from mostly KSP experience, ha ha, with only a small amount of fuel left for burn back and landing, the mass of the engines and reinforced thrust puck area will very much dominate the mass.  Also strengthening stringers, ribs, and bulkheads will typically be more of the mass lower on the stage as there is more load above the area.  Seems legit.

Also, consider the aero drag on the grid fins  up high on those mostly empty tanks

Edited November 20, 2023 by darthgently

[mikegarrison]

27 minutes ago, JoeSchmuckatelli said:

It looks like the engine compartment is the COG - as it pretty much stays in line with Ship as it begins to flip.  (or rather, the COG is just above the rockets) is that correct or likely something from the angle? 

With most of the fuel burned, almost certainly the rockets make up the bulk of the remaining mass of the booster.

[tater]

 

[darthgently]

2 hours ago, Flavio hc16 said:

Then you haven't  played KSP enough: try to reach 88% of orbital velocity in KSP, and you will see that you will cover less than 20% of the planet. It's the last few hundreds m/s that makes you go places. And this is eve more pronounced with a bigger Kerbing, aka Earth.

How aggressive the pitch over is can be a big factor also.  IFT-2 seemed to pitch fairly conservatively early on and achieved a high AP fairly quickly, but did seem close to horizontal at stage sep (within 10 or 15 degrees of zero pitch?  Just guessing obviously)

[darthgently]

 

 

[darthgently]

 

 

[tater]

 

[tater]

 

 

(superior to the slo-mo, IMHO)

[JoeSchmuckatelli]

Why does the vapor falling down the sides seem to corkscrew around the craft? 

Coriolis? 

[darthgently]

7 hours ago, tater said:

(superior to the slo-mo, IMHO)

I agree.  It really leaps off the pad and that is awesome to see

5 hours ago, JoeSchmuckatelli said:

Why does the vapor falling down the sides seem to corkscrew around the craft? 

Coriolis? 

Breeze I'd imagine

Edited November 20, 2023 by darthgently

[Superluminal Gremlin]

15 hours ago, Flavio hc16 said:

truly hope they start to push hard for a December launch, as they are limited by 5 test/year.

So do I, might even land on my birthday (late december).

Or a Christmas Miracle. Have the authorities paused SX's ability to launch or can they go again as soon as they can.

[mikegarrison]

7 hours ago, JoeSchmuckatelli said:

Coriolis? 

Coriolis has approximately zero effect on such scales.

[JoeSchmuckatelli]

50 minutes ago, mikegarrison said:

Coriolis has approximately zero effect on such scales.

I figured - but 400 feet and slow vapor = maaaybeee? 

Ah, but no.  My 'water swirling down the drain = Coriolis' is clearly an urban myth.  https://www.nsta.org/journals/science-and-children/science-and-children-february-2019/why-does-water-swirl-when-it-goes

So... Breeze 

[sevenperforce]

22 hours ago, Exoscientist said:

On 11/19/2023 at 8:19 AM, darthgently said:

the vacuum engines were burning continuously  from stage separation on, so not sure about your conclusion.

 

  On the 1st test flight some booster engines worked fine at launch, but failed later on in the flight. The same could have happened with the vacuum Raptors, in regards to failing later in the flight. I have no information to confirm that, though. Whenever a rocket stage fails, the engines are the first thing focused on. Since the sea level engines worked fine, that leaves the vacuum engines to be scrutinized.

On the first flight, hydraulic fluid leaks in the engine bay led to fires which caused a rapid cascade of knock-on failures of other engines. There's no indication of any engine bay fires in the second stage, and any such failures (if they were similar to the ones in the first flight) would have taken place earlier in the six-minute burn.

18 hours ago, Deddly said:

On 11/19/2023 at 8:55 AM, Mikki said:

I just re-read Alemberts gyroscopic theory and it states that fast rotating bodys exert unusual very high counterforce (torque) tangential to a second applied rotation (force vector), which are unpredictable and surely very uneven on complex shapes like pumprotors.

You can calculate this force on a fast rotating straight rod, but a pumpshaft with curved blades and impellers  is just structural chaos. 

Don't/can't they have booster rotation on the same axis as the pump rotors? 

They don't; Raptor 2 has inline pump rotors that rotate along axes parallel to the thrust vector:

Spoiler

Even if they did a complete redesign of Raptor just for this specific problem, it still wouldn't work because there are 33 different engines on the first stage that are all oriented in specific ways to allow for plumbing, etc. to work properly. If the Raptor engines had pumps with rotation axes at 90 degrees to the thrust vector, each Raptor engine pump would have a slightly different rotation axis, meaning that you'd never be able to get the flip maneuver to align with more than a few rotational axes max.

Someone upthread asked how Falcon 9 manages the flip. Falcon 9 flips by first shutting off the first stage engines entirely, then using a pusher rod to achieve stage separation, then using nitrogen cold-gas thrusters to initiate the booster flip, then using nitrogen cold-gas thrusters to resettle the booster propellant, then restarting the central booster engine, then restarting two additional booster engines. Starship is too large to use pusher-rod separation. I imagine that depending on lessons learned from this launch, SpaceX might revisit using gas-gas hot thrusters on Superheavy to provide stability during hot staging and to perform the flip and ullage burn, with a complete MECO. Lower thrust from hot-gas thrusters might even allow for a more gentle hot staging (e.g. central Raptors only) which could both reduce the weight of shielding on Superheavy and reduce any potential engine bay damage to Starship.

17 hours ago, magnemoe said:

Second was flying at almost orbital velocity at +150 km with an AP of 250 km, blowing it up in vacuum would not affect the trajectory a lot, yes it will spread out the debris field quite a lot over the distance so would drag from the air. 
But if this is debris field from starship the telemetry was an obvious lie. 

@tater already addressed this, but you'd be surprised at just how much extra umph you get from the very end of a burn, as @Flavio hc16 and @CatastrophicFailure pointed out. At a near-circular orbit with ~150 km apogee, a difference of 830 m/s at apogee is a difference of 2,184 km at perigee (graphic to scale):

Spoiler

 

17 hours ago, magnemoe said:

An minuteman ballistic missile has an maximum velocity of 24000 km/s who was the velocity Starship had at cutoff.  has an max range of 6000 miles or 9600 km, it however has an ceiling of 1,120

The LGM-30 Minuteman most certainly does not have a maximum velocity of 24,000 km/s, and this was most certainly not the velocity of Starship at cutoff.

ICBMs travel along highly eccentric trajectories. The velocity of an object at any given point along an eccentric trajectory is not in any way comparable to the velocity of an orbit along a near-circular trajectory.

11 hours ago, tater said:

 

(superior to the slo-mo, IMHO)

Ooof, that baby is MOVING.

[mikegarrison]

6 minutes ago, sevenperforce said:

The LGM-30 Minuteman most certainly does not have a maximum velocity of 24,000 km/s, and this was most certainly not the velocity of Starship at cutoff.

I assume he was confusing km/s with km/h.

[tater]

Another routine trip to space happened 4 hours ago, apparently.

[AckSed]

My goodness, the announcer actually sounds bored. Amazing.

[Exoscientist]

On 11/19/2023 at 4:38 AM, darthgently said:

FTS on SS may have been incomplete.  I'm wonder if something like integrating an off the shelf (or custom probably) black box on the second stage could over time make situations like this, and Rocket Labs recent situation, less mysterious.  Of course they'd need to be very tough and recovered.

 

 Could the payload bay have survived reentry? The canards at top could help with streamlining during reentry. 

 For the Starship, the payload bay is different than just the fairing of a normal rocket.  The rings and the nose cone are welded together steel, rather than only a fairing designed to separate apart when jettisoned.

  Bob Clark

Edited November 20, 2023 by Exoscientist

[sevenperforce]

12 minutes ago, Exoscientist said:

Could the payload bay have survived reentry? The canards at top could help with streamlining during retry. 

 For the Starship, the payload bay is different than just the fairing of a normal rocket.  The rings and the nose cone are welded together steel, rather than only a fairing designed to separate apart when jettisoned.

It definitely has a heat shield, but the question is whether the intact section would have had passive aerodynamic stability. I think the answer is almost certainly no. Starship achieves shield-first aerodynamic stability during re-entry using active control of all four drag flaps, but without only two flaps and no active control I don't see how any orientation provides passive stability. The center of mass and the center of drag will be very close to each other which would likely induce either a tumble or a flat spin, either of which would result in the vehicle being ripped apart by aerodynamic forces.

^{(This was the same fate for both Challenger and Columbia. Although Challenger is often said to have "exploded" and Columbia is said to have "burned up", both orbiters were ultimately destroyed by aerodynamic forces while tumbling: Challenger when the loss of active engine control could no longer keep the stack oriented and Columbia when differential drag on the half-melted wing caused roll and yaw deviations too great for the control surfaces to counteract.)}

It is very unlikely that the intact-but-tumbling payload bay of Starship would achieve ANY passively-stable orientation, let alone one in which the heat shield was properly pointed into the airstream.

[tater]