SpaceX Starship : First Flight : Starbase, TX : 20 April 2023 - DISCUSSION

[Alvian@IDN]

Is Elon Musk open to having the first orbital flight of the Starship make two or three orbits, given that the purpose of the first Starship launch will be to test the in-space behavior of the second stage of the Starship? This possibility shouldn't be ruled out because the first and only orbital flight of the Buran made two orbits before the Buran returned to Earth.

You don't want a 120+ ton space debris circling around and or raining down the populated areas just because the first-time space propulsion is having a failure at deorbit

There's plenty of next vehicles waiting in line to do that, once the orbital burn & reentry stage is more proven. It's afterall, still their objective

[Eer]

Is Elon Musk open to having the first orbital flight of the Starship make two or three orbits, given that the purpose of the first Starship launch will be to test the in-space behavior of the second stage of the Starship? This possibility shouldn't be ruled out because the first and only orbital flight of the Buran made two orbits before the Buran returned to Earth.

No, it is not given that the purpose of the first test flight is to test the in-space behavior of the second stage.

The purpose of the first flight is to test out the gse and first stage to get the stack off the pad and safely away from the gse. If that succeeds, try to make it to maxq. If it survives that, make it to MECO without tumbling out of control. Then stage separation. If it makes it that far it will be a stunning success for flight 1.

After that, if second stage engines light and doesn’t lose control, that’s a bonus, surely. Also, if booster reorienta itself and approximates a stable return trajectory…good. If the booster makes a soft approach to a zero vertical and horizontal vector some distance above the water, that is another huge success. Ditto Re-entry of the second stage towards the test range north of Hawaii. The whole idea of the low altitude perigee is to be absolutely darned sure it doesn’t get stuck in orbit if the engines can’t relight to bring it down.

Iteration is a different approach to retiring risk.

[TheRadicalModerate]

Is Elon Musk open to having the first orbital flight of the Starship make two or three orbits, given that the purpose of the first Starship launch will be to test the in-space behavior of the second stage of the Starship? This possibility shouldn't be ruled out because the first and only orbital flight of the Buran made two orbits before the Buran returned to Earth.

The reason not to do this is because you leave a big mess if the Starship can't deorbit or otherwise fails after getting to space.  If you're in a suborbital trajectory (even if you've achieved orbital energy--it's just a matter of eccentricity), then almost everything will reenter.¹  The suborbital trajectory also gives you a good chance of getting some hypersonic data even if the propulsion system doesn't restart.

The purpose of the test is not to test the in-space behavior of Starship.  The purpose of the test is to get Starship to space in the first place.  Anything beyond that is gravy.

_________
¹If the Starship explodes near apogee, then some debris will have its perigee raised enough to be in a stable orbit.  But explosions aren't very energetic, and most debris will decay fairly quickly.  If it collides with something, that's a different story.

[alugobi]

No.

The flight plan is already published.

[baking]

The purpose of the first flight is to test out the gse and first stage to get the stack off the pad and safely away from the gse. If that succeeds, try to make it to maxq. If it survives that, make it to MECO without tumbling out of control. Then stage separation. If it makes it that far it will be a stunning success for flight 1.

I've been trying to focus my thoughts on this flight in a similar manner.  Clearing the pad moving the debris field over water would be a success, in that the next launch could proceed without substantial rebuilding of stage zero.  Some repairs are to be expected, but we hope for no major delays.

Stage separation would be an unqualified success.  Everything after that is pure gravy.

My gut is telling me there is a 1/3 chance of failure at the pad or near the ground, 1/3 chance failure during ascent, and a 1/3 chance of making it to stage separation.  I hope I'm being too pessimistic, but I would like to hear some other educated estimates.

[daedalus1]

Is Elon Musk open to having the first orbital flight of the Starship make two or three orbits, given that the purpose of the first Starship launch will be to test the in-space behavior of the second stage of the Starship? This possibility shouldn't be ruled out because the first and only orbital flight of the Buran made two orbits before the Buran returned to Earth.

What for? It wouldn't be anywhere near a landing area.

[dnavas]

My gut is telling me there is a 1/3 chance of failure at the pad or near the ground, 1/3 chance failure during ascent, and a 1/3 chance of making it to stage separation.  I hope I'm being too pessimistic, but I would like to hear some other educated estimates.

Not to be a downer, but that seems to me an over-estimate of the likelihood of leaving the pad.
There hasn't been an entirely successful 33 engine start yet, and nothing anywhere close to full thrust.
We're talking about a repaired booster running engines that are regularly swapped out on a brand new architecture built by a company that prefers to fail fast.

I have every confidence that SpaceX will figure this out, but there will be a full exploration of the space of outcomes first.
All mho, and very definitely not an educated estimate!

[Jeff Lerner]

Does SpaceX commit to release of clamps and launch with less than 33 engines running at full power ??…

because if not, I suspect there will be several attempts/aborts, etc before we see liftoff .

For me, just getting off the pad and away from Stage 0 represents a huge success…having the OLM and GSE survive to live to fight another day is critical to keep the program moving along.

IMHO, anything positive that happens after that is gravy for this booster/ship combo…

[Lee Jay]

Does SpaceX commit to release of clamps and launch with less than 33 engines running at full power ??…

because if not, I suspect there will be several attempts/aborts, etc before we see liftoff .

For me, just getting off the pad and away from Stage 0 represents a huge success…having the OLM and GSE survive to live to fight another day is critical to keep the program moving along.

IMHO, anything positive that happens after that is gravy for this booster/ship combo…

Remember, booster hasn't flown at all.  Personally, I'd add a mostly-successful first stage flight to just getting off the pad as a measure of success, for at least two reasons.  First, booster needs to prove it can fly under control with Starship on top.  Second, if it just gets off the pad and nothing more, that means it could fall back fully-fueled onto the area and cause a lot of damage.

[daedalus1]

It doesn't need all 33 engines to climb from the pad. 2 or 3 less I  remember seeing somewhere.

[whitelancer64]

It doesn't need all 33 engines to climb from the pad. 2 or 3 less I  remember seeing somewhere.

If my math is right, Super Heavy could lose up to 8 engines at liftoff and still make it off the pad, i.e., TWR is >1

However, that would look a lot like that Astra launch that went sideways. It wouldn't get very far and there'd likely be considerable damage to the OLM and surrounding ground equipment.

It can lose 2 or 3 engines at liftoff and still make it to orbit. Losing engines later in the flight is less of an issue.

That said, I think that SpaceX will not release the hold-down clamps without all 33 engines running and healthy.

[matthewkantar]

If I recall correctly, all Raptor powered launches so far have nailed the going up part. I feel pretty good about their chances from liftoff to staging. Stage sep concept is new/never been done, if they get past that, man, they are in business.

[Alberto-Girardi]

If I recall correctly, all Raptor powered launches so far have nailed the going up part. I feel pretty good about their chances from liftoff to staging. Stage sep concept is new/never been done, if they get past that, man, they are in business.

I agree with you. If they launch it means that all engines have lighted correctly. Even the comparatively unreliable raptor 1 used in  the suborbital campaign has never had a failure (directly resulting in ascent failure) on ascent. This is because, i suppose, once the engine (and this might apply to a lot of systems in general) is in a stady state (eg full power) it is much less likely to have a failure than during a state transition (eg. engine ignition), but they will launch only after this "state transition". The staging worries me because it seems to involve a peculiar flip maneuver to separate the stack, given that there isn't any mechanical device to separate it.

We know that the stack is connected by protrusions on SH that fit in slots on the ship. Does anyone know if the system that keeps that connection firm is a kind of "claw" or pin in the ship or is a pin located in the protrusion?

edit: forgot what chopsticks later pointed out

[chopsticks]

If I recall correctly, all Raptor powered launches so far have nailed the going up part.

SN15 had an early shutdown on one of the engines. (The one that didn't relight)

SN11 had an engine fire which fried the avionics which led to a hard start and RUD. It kept running until shutdown though.

[joek]

It doesn't need all 33 engines to climb from the pad. 2 or 3 less I  remember seeing somewhere.

If my math is right, Super Heavy could lose up to 8 engines at liftoff and still make it off the pad, i.e., TWR is >1

However, that would look a lot like that Astra launch that went sideways. It wouldn't get very far and there'd likely be considerable damage to the OLM and surrounding ground equipment.
...

With or without nominal starship payload? Musk stated ~1.5 TWR; think we know "T" (give-or-take), but he did not state "W". Might be quite a bit more margin with zero starship payload, as we might expect for first test flight?

[DanClemmensen]

If I recall correctly, all Raptor powered launches so far have nailed the going up part. I feel pretty good about their chances from liftoff to staging. Stage sep concept is new/never been done, if they get past that, man, they are in business.

Reminder: reliability of .99 (example) for each engine is a reliability of .99^^33=0.71 that all 33 Raptors will start.

[sferrin]

If I recall correctly, all Raptor powered launches so far have nailed the going up part. I feel pretty good about their chances from liftoff to staging. Stage sep concept is new/never been done, if they get past that, man, they are in business.

Reminder: reliability of .99 (example) for each engine is a reliability of .99^^33=0.71 that all 33 Raptors will start.

If you go by the only example we have, where they succeeded in lighting 31/33, that gives it a 13% chance of lighting off all 33.  Of course they know why those two engines didn't fire, and have almost certainly mitigated those factors, so we'll see.

[joek]

Reminder: reliability of .99 (example) for each engine is a reliability of .99^^33=0.71 that all 33 Raptors will start.

True, and that undoubtedly will factor into their launch decision. Expect they have enough experience to determine start reliability to a high level of confidence. (Whereas we have only one public data point based on previous all-up test showing 31/33.)

Expect launch commit criteria is going to depend on several factors, of which number of engines starts is one, but not the only. That said, hope and expect they are shooting for 100%.

But we don't know what their test criteria-priorities are. Might be that they're ok with less than 100% if it accelerates starship tests. Or maybe getting the booster ironed out is a priority. Hard to tell from our (public) vantage.

[alugobi]

They're probably getting way tired of dealing with B7 by now and just want to get it out of there. 

[Alberto-Girardi]

Reminder: reliability of .99 (example) for each engine is a reliability of .99^^33=0.71 that all 33 Raptors will start.

True, and that undoubtedly will factor into their launch decision. Expect they have enough experience to determine start reliability to a high level of confidence. (Whereas we have only one public data point based on previous all-up test showing 31/33.)

I wonder if they could do a static fire as part of the launch rehersal. They haven't said "wet dress rehersal" which has a specific and established meaning.

AFAIK all the closures/notices for a static fire/wdr are the same, apart from the overpressure notice, which might not be necesary given that they might want to evacuate the village as it would happen during a real launch. So we can't rule that out yet.