SpaceX 'Star series' simulations

[Thrustpuzzle]

I'd love to see a simulation of the same cargo launch but with SH landing roughly 250km downrange (ie launch from Boca Chica, land on downrange platform).  The two interesting questions it would answer is 1) what the optimal downrange distance would be and 2) how much extra orbital payload mass it enables.

[steveleach]

Here is a simulation of an orbital Starship launch, updated to have a 28 engine Super Heavy. The payload is 150t to LEO, and I'm assuming Super Heavy has 8 x 210t thrust Raptors with gimbal and throttle, and 20 x 300t thrust Raptors without either.

Epic!

ISTR Musk commenting on a booster-catching animation once that SH will come in almost vertically, rather than at an oblique angle.

[soyuzu]

Here is a simulation of an orbital Starship launch, updated to have a 28 engine Super Heavy. The payload is 150t to LEO, and I'm assuming Super Heavy has 8 x 210t thrust Raptors with gimbal and throttle, and 20 x 300t thrust Raptors without either.

Nice job as always!

Have you considered shutting down Raptor SLs on Starship mid flight to gain more Isp? What is your assumption of stage empty mass and residual propellant? I’m also interested in simulation of 21t to GTO and Dearmoon launch without refueling.

[Aeneas]

Here is a simulation of an orbital Starship launch, updated to have a 28 engine Super Heavy. The payload is 150t to LEO, and I'm assuming Super Heavy has 8 x 210t thrust Raptors with gimbal and throttle, and 20 x 300t thrust Raptors without either.

Nice job as always!

Have you considered shutting down Raptor SLs on Starship mid flight to gain more Isp? What is your assumption of stage empty mass and residual propellant? I’m also interested in simulation of 21t to GTO and Dearmoon launch without refueling.

After burning 2/3 of the fuel, the switch likely increases payload by ~7 t. 21 t GTO is possible but dearmoon without refueling not at all.

[_MECO]

Here is a simulation of an orbital Starship launch, updated to have a 28 engine Super Heavy. The payload is 150t to LEO, and I'm assuming Super Heavy has 8 x 210t thrust Raptors with gimbal and throttle, and 20 x 300t thrust Raptors without either.

9 Gs of deceleration for Super Heavy. Is that going to wreck the engines or the engine bay? It takes a lot of hot wind to put the mass of a Super Heavy through 9 Gs.

[OneSpeed]

Out of curiosity, are you able to model performance to inclinations that would require dogleg maneuvers? Namely 53, 70, and 97.6 degrees for Starlink. Unclear if 97.6 degrees is even within the realm of possibility but that would be interesting to see

From KSC at 28.5° latitude, and using β = asin(cos(mi)/cos(ϕ)):

Orbital inclination (from East)	Launch azimuth (from North)	ΔV (km/s)
28.5°	90°	7.407
53°	43°	7.542
70°	22.9°	7.666
97.6°	-8.6°	7.888

So a 97.6° retrograde orbit requires 481m/s more than I modelled. If that's what you are after, I could model it.

I'd love to see a simulation of the same cargo launch but with SH landing roughly 250km downrange (ie launch from Boca Chica, land on downrange platform).  The two interesting questions it would answer is 1) what the optimal downrange distance would be and 2) how much extra orbital payload mass it enables.

I guess it's a trade, the further downrange you are prepared to go, the more payload you can loft. But if they are going to relaunch boosters in an hour, they need to RTLS.

ISTR Musk commenting on a booster-catching animation once that SH will come in almost vertically, rather than at an oblique angle.

Do you mean this one? If so, then yes, it's coming in like a javelin, not quite vertically, and no sky-diver or late flip like Starship.

https://twitter.com/elonmusk/status/1375510416994967552
Tweet Contents:  Super Heavy doing the flip maneuver
Heavy comes in more like a javelin. Similar to Falcon 9, but caught by the tower vs landing on legs.

Have you considered shutting down Raptor SLs on Starship mid flight to gain more Isp? What is your assumption of stage empty mass and residual propellant? I’m also interested in simulation of 21t to GTO and Dearmoon launch without refueling.

Certainly, but until you have reached orbital velocity, shutting down engines increases gravity losses, so it's another trade. Once in orbit, then Isp is king. For Starship I'm assuming 120t dry, and 30t of residuals, about 10t of which is ullage. For Super Heavy, 230t dry, also 10t of ullage, cutting it a bit finer.

9 Gs of deceleration for Super Heavy. Is that going to wreck the engines or the engine bay? It takes a lot of hot wind to put the mass of a Super Heavy through 9 Gs.

Sure, but this is a RTLS profile, and not nearly as challenging as landing downrange. As you can see from the video, the peak heat flux for Super Heavy is 68.6kW/m². By comparison, from my as yet unpublished Starlink L18 ASDS sim, I get a peak heat flux of 44.2kW/m², at a much higher altitude and velocity, and that figure doesn't include any additional heat flux from the three running Merlin plumes.

It will be interesting to see how much protection the stainless Super Heavy skirt provides for the Raptors on entry, but in any case it will be about an order of magnitude less than the heat flux Starship will have to endure from orbital re-entry.

Edit: put the numbers in a table.

[steveleach]

ISTR Musk commenting on a booster-catching animation once that SH will come in almost vertically, rather than at an oblique angle.

Do you mean this one? If so, then yes, it's coming in like a javelin, not quite vertically, and no sky-diver or late flip like Starship.

Tweet Contents:  Super Heavy doing the flip maneuver
Heavy comes in more like a javelin. Similar to Falcon 9, but caught by the tower vs landing on legs.

No, there was another one a while back where he was responding to someone's visualisation of the booster catching mechanism. If I recall correctly, the concept wasn't sufficiently open at the top, so Musk commented that the booster will be descending almost vertically as it reaches the tower, rather than approaching from the side.

It isn't in the main tweet index though, but I'll see if I can dig it out.

[sdsds]

Here is a simulation of an orbital Starship launch

Fantastic!

I'm confused about the numbers shown at the end. Altitude is 165.3, thrust is zero, yet perigee is 168.3. An orbiting object can coast up to its apogee, but how can it be lower than its perigee?

[OneSpeed]

This is a cross post from the Starship Engineering thread, where InterestedEngineer asked:

Are there any "good" estimates of the glide slope ratio for Starship?

Google returns a Reddit article that seems to guess at 1:1, but IANAAE (I am not an aeronautical engineer) so I have no way of telling how wild a guess that is.

and Pueo responded:

L/D should be equal to glide slope in steady state.  If the maximum L/D is 1.2 at 25° AOA then the Starship should only be pitched -14.8° when in a gliding configuration because the glide slope should be -39.8° in respect to the horizontal.  The trick is getting there because starting pitched -14.8° puts you at an AOA of 75.2° where you're certainly stalled.

Another consideration is that when Starship is not powered, it is only controllable by the body flaps in a small range of AoA. I've tried modelling this, and found I needed to limit AoA to no less than 60°, otherwise I lost control of the ship. Perhaps a Kerbal Space Program expert could do better than I did? Anyway the maximum downrange I could get from 12.5km with good control was about 8km, and Starship was completely stalled through the entire descent.

Regarding steady state, that only happened once, instantaneously at T+06:16, and I've annotated that frame below. The entire video of the sim is on YouTube:

[livingjw]

This is a cross post from the Starship Engineering thread, where InterestedEngineer asked:

Are there any "good" estimates of the glide slope ratio for Starship?

Google returns a Reddit article that seems to guess at 1:1, but IANAAE (I am not an aeronautical engineer) so I have no way of telling how wild a guess that is.

and Pueo responded:

L/D should be equal to glide slope in steady state.  If the maximum L/D is 1.2 at 25° AOA then the Starship should only be pitched -14.8° when in a gliding configuration because the glide slope should be -39.8° in respect to the horizontal.  The trick is getting there because starting pitched -14.8° puts you at an AOA of 75.2° where you're certainly stalled.

Another consideration is that when Starship is not powered, it is only controllable by the body flaps in a small range of AoA. I've tried modelling this, and found I needed to limit AoA to no less than 60°, otherwise I lost control of the ship. Perhaps a Kerbal Space Program expert could do better than I did? Anyway the maximum downrange I could get from 12.5km with good control was about 8km, and Starship was completely stalled through the entire descent.

Regarding steady state, that only happened once, instantaneously at T+06:16, and I've annotated that frame below. The entire video of the sim is on YouTube:

What was causing loss of control? Seems like there should be plenty of pitch authority.

John

[OneSpeed]

What was causing loss of control? Seems like there should be plenty of pitch authority.

John

It was tending to pitch down irretrievably. The body flaps have no authority once the AoA gets too small. They are simply behaving like fins with variable dihedral, and the aft flaps are quite a bit larger, so it becomes a dart. Of course a better pilot might help

[niwax]

This is a cross post from the Starship Engineering thread, where InterestedEngineer asked:

Are there any "good" estimates of the glide slope ratio for Starship?

Google returns a Reddit article that seems to guess at 1:1, but IANAAE (I am not an aeronautical engineer) so I have no way of telling how wild a guess that is.

and Pueo responded:

L/D should be equal to glide slope in steady state.  If the maximum L/D is 1.2 at 25° AOA then the Starship should only be pitched -14.8° when in a gliding configuration because the glide slope should be -39.8° in respect to the horizontal.  The trick is getting there because starting pitched -14.8° puts you at an AOA of 75.2° where you're certainly stalled.

Another consideration is that when Starship is not powered, it is only controllable by the body flaps in a small range of AoA. I've tried modelling this, and found I needed to limit AoA to no less than 60°, otherwise I lost control of the ship. Perhaps a Kerbal Space Program expert could do better than I did? Anyway the maximum downrange I could get from 12.5km with good control was about 8km, and Starship was completely stalled through the entire descent.

Regarding steady state, that only happened once, instantaneously at T+06:16, and I've annotated that frame below. The entire video of the sim is on YouTube:

I just noticed your last simulation of single stage P2P was using the old triple fin design. Do you have any ideas on how the new design might change this profile? A new simulation would be much appreciated.

[livingjw]

One speed,

- It appears that there is an error in your lift display when the AoA exceeds 90 degrees. Probably a sign problem.

John

[mikelepage]

This is a cross post from the Starship Engineering thread, where InterestedEngineer asked:

Are there any "good" estimates of the glide slope ratio for Starship?

Another consideration is that when Starship is not powered, it is only controllable by the body flaps in a small range of AoA. I've tried modelling this, and found I needed to limit AoA to no less than 60°, otherwise I lost control of the ship. Perhaps a Kerbal Space Program expert could do better than I did? Anyway the maximum downrange I could get from 12.5km with good control was about 8km, and Starship was completely stalled through the entire descent.

Regarding steady state, that only happened once, instantaneously at T+06:16, and I've annotated that frame below. The entire video of the sim is on YouTube:

Great work OneSpeed.

Not sure if this has been done elsewhere, but it occurs to me that if one can get 8km cross range in the final 12.5km of descent, one could probably get considerably more cross range you combined this with your atmosphere skipping approach upthread.

Some kludgy math:
Looks like you get a dV of about 1km/s in that first atmospheric bounce. Perhaps if one angled the starship to get sideways deflection during that bounce, so you halve the height of the bounce, but get maybe 500m/s sideways dV for 4 minutes or so before you went in for the next entry interface (which you do at the expense of downrange distance)? 

That works out to at least 120km or so of cross range when coming in from orbit - just on that first bounce.  Seems like there ought to be a way to get several hundred km of cross range on the way in, then use that final 8km of "glide" during the vertical descent to fine tune your landing location. Not quite STS's 2000km of cross range, but still plenty.

[OneSpeed]

SpaceX recently released some details of the first orbital test flight. In particular, they released an event timeline, which I have attempted to model.

Event	T+ time (seconds)
Liftoff	0
MECO	169
Stage Separation	171
SES	176
Booster Touchdown	495
SECO	521
Ship Splashdown	5420

They also stated that their objective is to collect as much data as possible during flight to quantify entry dynamics and better understand what the vehicle experiences in a flight regime that is extremely difficult to accurately predict or replicate computationally.

This model represents the minimum viable product that I think can deliver that objective. Landing the booster offshore allows a slight reduction in booster engine count from 19 to 18, which is a convenient subset of the current 28 engine Super Heavy design. If SpaceX do attempt to recover the Super Heavy by landing it on a drone ship or platform, then perhaps 10 legs of the same design already used by Starship could be fitted?

I have assumed three SL engines only for the Starship, and that works well for the published event timeline. If the Vacuum Raptor is ready for the orbital test, then a much shorter Super Heavy burn with fewer engines would suffice.

[oses]

Great work!

Is it reasonable to say that it seems that the timeline of events in the FCC briefing is seemingly incompatible with a full set of raptors on SS + SH?

I'd definitely be interested to see how much margin they gain by having a full set of raptors onboard, especially with Chris's report of that being the plan.

[OneSpeed]

Great work!

Is it reasonable to say that it seems that the timeline of events in the FCC briefing is seemingly incompatible with a full set of raptors on SS + SH?

I'd definitely be interested to see how much margin they gain by having a full set of raptors onboard, especially with Chris's report of that being the plan.

They may well install all 34 Raptors, I'm just saying that the minimum viable product has fewer than that. They go from about 10.6 km/s of ΔV with 18 + 3 to about 12.7 km/s with a fully populated stack. Maybe they just run all those engines at about 65% of full throttle for reliability, and have a partial propellant load? If so, the performance would be similar to the simulation above.

[gsa]

SpaceX recently released some details of the first orbital test flight. In particular, they released an event timeline, which I have attempted to model.

Thank you for your great work!
I'm sorry, I've got a very stupid question to ask. Acceleration on your graph is measured in dm/s². IIRC 1 dm = 0.1 m, so 1000 dm/s² = 100 m/s² ≈ 10 g. I'm not sure this is right. Am I missing something?

[OneSpeed]

SpaceX recently released some details of the first orbital test flight. In particular, they released an event timeline, which I have attempted to model.

Thank you for your great work!
I'm sorry, I've got a very stupid question to ask. Acceleration on your graph is measured in dm/s². IIRC 1 dm = 0.1 m, so 1000 dm/s² = 100 m/s² ≈ 10 g. I'm not sure this is right. Am I missing something?

You're correct, it should be cm/s².

[edzieba]

If the flight profile can be met with a significantly sandbagged configuration of Raptors, what size of mass-simulator could be added to Starship with a full complement of Raptors and still complete the mission?