Project SpaceX SuperHeavy

[sberinde]

Hi,
I don't know the coordinates in the Indian Ocean but I did some guess. However, based on [1] and [2] I know the following data

Launch time: 1325 UTC Mar 14
Orbit incl: 26.5deg
Booster max_alt: 105km
Booster splashdown distance (from launch site): 85km
SECO_1 alt: 150km
SECO_1 orbit: -50 km x 234 km
SECO_2: intended but not performed
SECO_2 orbit: 50 km x 234 km (not reached)

I prepared a scenario (attached) where I moved LZ_TX at 80km downrange and created LZ_IND in the Indian Ocean. I launched with autopilot.

After MECO the booster fails to reach the intended apogee by few km and also it fails to stop the engines. Maybe a problem with the guidance, since in manual mode I can approach LZ_TX with the right amount of boostback speed.

I let autopilot drive the second stage until at 140km in altitude. With manual control I put the spacecraft roughly in SECO_1 orbit and after a final burn at apogee I reached SECO_2 orbit. I did a fuel dump till 3-4k left. I activated reentry autopilot and I noticed it uses left and right hard turns to disipate energy. To my surprise it landed at LZ_IND! Too bad it was very dark in the area and nothing to see. Congrats for the guidance.

[1] Starship IFT3 flight data estimated from livestream telemetry,
[2] Jonathan's Space Report No. 831

 

[BrianJ]

Hi,
thanks for the scenario. Yes! The booster guidance fails for that location of LZ_TX. Thats interesting
Cheers,
Brian

 

[sberinde]

I continue my quest of simulating IFT-3 flight as real as this addon allows. Based on this guesstimate by someone on reddit I adjusted LZ_IND location and also corrected its orientation (I just noticed its red beacons at night).

Since MECO happens at 150km altitude, I set up autopilot target orbit to 148km x 148km. However, this is not possible via console. Only by hand.

Next is an operation timeline without using sophisticated instrumentation. Please use attached scenario (updated) if you want to play along.

13:25 start autopilot

after MECO continue to use autopilot​

forget about booster, it will have a malfunction anyway ​

at exactly 147.0 km in altitude stop autopilot and do killrot, but do not stop engines​

gradually throttle back to keep ACC < 35​

stop engines when apogee is at 234km​

If everything went good the spacecraft has just passed 150km in altitude and its orbit perigee is around -45km.

13:48 apogee passage (enjoy the ocean view)
14:00 passing over Namibia

you have two options here (red or green)​

do nothing, pretend a malfunction​

uncontrolled reentry, beautiful plasma with a sunset​

-13g !​

over Namibia perform a second burn in prograde direction until perigee rises to 50km​

fuel dump till 3-4k left​

at 120km in altitude (south of Madagascar) start reentry autopilot​

at 25km in altitude activate landing reserve fuel (or sooner if main prop gets empty)​

14:29 landing at LZ_IND

I'm still amazed how beautiful reentry autopilot performs. It has a good margin for success. Deceleration was below 2g.

 

[sberinde]

I want to report a problem. If setting BocaChica as the base landing target for booster I get CTD (just before landing burn).
Is not possible to land over normal bases? I attach a scenario for convenience.

 

[Donamy]

Sounds accurate for IF3 to me.

 

[sberinde]

The tower is about to catch the ship but it fails. This is scenario "25k RTLS test" after a complete orbit and reentry.

 

[BrianJ]

The tower is about to catch the ship but it fails. This is scenario "25k RTLS test" after a complete orbit and reentry.

It does (just) catch the ship for me if "Wind Effect" is on - but not if wind is off.
The backflip landing algorithm is not very robust.
But worse, the Tower "Chopsticks" are not in the correct position for receiving the ship. Bug.

I think I improved the Boostback burn algorithm so the engine cuts off more reliably.
Fixed the CTD-landing-burn-at-base bug.

Also, am implementing "hot staging" (or something similar!).

Thanks for the test reports.
Brian

 

[barrygolden]

Sharing with you that I am at Boca Chica and sharing these pictures of IFT 4 on the pad.

Space X has built a new road to the port of Brownsville and a dock on the south side of the channel to bring stuff in to the launch site .They have bought more land north east of Hwy4 to swap to Texas for the beach area so they can close the road to Boca Chica beach off for good

 

[BrianJ]

Hi Barry,
thanks for sharing the pics. Lucky man!
Brian

 

[sberinde]

It does (just) catch the ship for me if "Wind Effect" is on - but not if wind is off.
The backflip landing algorithm is not very robust.
But worse, the Tower "Chopsticks" are not in the correct position for receiving the ship. Bug.

The bugs in tower landing scenario can be overcomed as follows:

1. Select 3 Raptor engines on the ship (only 2 were selected)
2. Arms will fully open if tower catch is enabled at the last moment

Hope it helps.

 

[BrianJ]

The bugs in tower landing scenario can be overcomed as follows:

1. Select 3 Raptor engines on the ship (only 2 were selected)
2. Arms will fully open if tower catch is enabled at the last moment

Hope it helps.

Hi, thanks for testing

1. Ah! I'm quite surprised it works as well as it does with only 2. The backflip sequence does expect 3 engines though
2. Not a bug! I noticed the Booster stage is landed close by in your scenario - the arms are targeting that, until Starship comes within range (1km). You can fix this by:
a) Entering BC_TOWER target name "Starship" [P]
or
b) deleting Booster from scenario.
Anyway, new BC_TOWER module will ignore landed vessels, so no longer a problem.

Attached is "starship_patch_240605.zip" with new modules (Starship, Tower , Booster and HSR (Hot stage Ring) )
meshes (HSR, Tower) and .cfgs for D3D9 GC and HSR vessel.

Hope I have fixed the Boostback-engine-shutdown problem and Base-landing-burn-bug.
Added HSR to meshes and Hot Stage engine sequence (well, more like instantaneous staging).

Its nice being able to keep the Booster engines on while staging - it speeds up the flip to boostback attitude.
Are they really going to jettison the HSR after Boostback? That's what I saw on the interweb, so I've made it - but it looks.....not..very..safe!

Lots more work to do, especially the fuel reserve estimate (depends on payload, azimuth, apogee, landing target pos).
But thought I would put up this patch in the meantime.
I haven't tested the .zip - let me know if it doesnt work!

OK, hope all goes well for IFT4
Brian

 

[DaveS]

Are they really going to jettison the HSR after Boostback? That's what I saw on the interweb, so I've made it - but it looks.....not..very..safe!

Yes, here's official IFT-4 page, scroll down to Flight Test Timeline for the note of Hot-stage jettison at 03:54: https://www.spacex.com/launches/mission/?missionId=starship-flight-4

 

[BrianJ]

Well, IFT-4 was quite a show!
HSR jettison is only temporary then.
Re-entry profile was an eye-opener for me.
Very interesting

 

[Urwumpe]

I fear you will get more work for IFT-5 because of the redesigns needed.

 

[sberinde]

Well, IFT-4 was quite a show!
HSR jettison is only temporary then.
Re-entry profile was an eye-opener for me.
Very interesting

Indeed, spectacular show with lots of valuable data for you!
Ship reentry was smooth and without noticeable bank turns. Maybe they targeted a wider area, not a fixed point.
I plan a fly-by-wire sim of this flight.

 

[BrianJ]

I fear you will get more work for IFT-5 because of the redesigns needed.

Undoubtedly. Fie! upon Spacex and their iterative developement process!

Indeed, spectacular show with lots of valuable data for you!
Ship reentry was smooth and without noticeable bank turns. Maybe they targeted a wider area, not a fixed point.
I plan a fly-by-wire sim of this flight.

Yes, lots of new info for me to play with.
13->3 engines landing burn, very smooth and stable reentry, etc.
Hope the fly-by-wire idea works!

Cheers,
Brian

 

[sberinde]

I noticed an inconsistency in the starship ascent profile when setting 1st stage apogee at MECO at higher altitudes (130km in this case). The starship will throttle down during mid-flight. See attached scenario.

In the IFT4 case, the booster max altitude was 109km and starship stayed below 150km upto SECO. So far I cannot reproduce that profile without breaking the ascent autopilot on starship.

P.S. Maybe the booster is trying to cancel out its VS speed too agressively?

 

[barrygolden]

Hey Brian thanks for all you have done not only for me but for all of the orbiter family.
wish you were here so I could show you these places like JSC and Boca Chica

 

[BrianJ]

I noticed an inconsistency in the starship ascent profile when setting 1st stage apogee at MECO at higher altitudes (130km in this case). The starship will throttle down during mid-flight. See attached scenario.

Hi,
ah yes, thats a bit of old code inherited from Falcon9 for improving fuel efficiency on very high altitude orbit insertion.
Autopilot doesn't expect a shallow "up-and-over" (orbit insertion during descent) profile. Probably irrelevant for Starship anyway. I'll fix it.

In the IFT4 case, the booster max altitude was 109km and starship stayed below 150km upto SECO. So far I cannot reproduce that profile without breaking the ascent autopilot on starship.

The ascent autopilot, simple as it is, can't really handle sub-orbital trajectories - its for going to LEO.
I've reduced the minimum orbit altitude to 150km, if that helps at all.

P.S. Maybe the booster is trying to cancel out its VS speed too agressively?

There are an infinity of ballistic trajectories the booster could use to RTLS.
I chose the "minimum energy ballistic trajectory", but SpaceX may have different constraints(reentry angle, etc.) and much cleverer algorithms. My crazy boostback algorithm kind of works OK, so I'm going with that

Hey Brian thanks for all you have done not only for me but for all of the orbiter family.
wish you were here so I could show you these places like JSC and Boca Chica

Hi Barry,
hey, thanks for the kind words. One day I'll make it over "the pond" to see some rockets go up!
Cheers,
Brian

 

[barrygolden]

If you can make it lets meet up and start in Alabama and you will see a Saturn 5 standing up, it will take your breath away
I think this was Saturn 502 used as a fit check during the Gemini 11 launch