SpaceX FH: STP-2 : LC-39A : June 25, 2019 - DISCUSSION

[JamesH65]

One could argue that the added complexity of landing three stages pushes it past some arbitrary level. The complexity of the entire mission should probably include those features.

[intelati]

One could argue that the added complexity of landing three stages pushes it past some arbitrary level. The complexity of the entire mission should probably include those features.

Even subtracting the first stage considerations, it's a complex mission on its own. That's my view of the launch anyways.

Add in the booster seperations and landingS...!!!

[abaddon]

One could argue that the added complexity of landing three stages pushes it past some arbitrary level. The complexity of the entire mission should probably include those features.

...catching one of the fairing halves, recovering the other one, drone ship, landing pads...

Yeah.

[Lar]

What happened to the spent second stage?  There is no mention of it’s final disposition in the press kit:  https://www.spacex.com/sites/spacex/files/stp-2_press_kit.pdf

Propulsive depassivation and it has been left out in a graveyard orbit.

What is propulsive DEpassivation? Is that like activation?

It still has throttle authority, so even with no effective directional control it could still have attempted some kind of abort.

If you have thrust off center and you want to control which direction you skitter off in (to abort more safely, say, deliberately avoiding travel in the direction of support vessels for example) rather than a random direction, doing a roll with the nitrogen thrusters might be a way to choose your direction. Roll till the off center thrust is diverting you in the direction you want to go, then stop rolling.

Actually landing by using fancy rolls to make your off center thrust cancel out over time seems a stretch but not completely impossible. The booster would appear to be gyrating wildly.

In both cases you'd have to have programmed that failure mode in though I think.

[Kansan52]

My understanding of "propulsive DEpassivation" is placing the stage in the chosen orbit and venting fuel and oxidizer to reduce the chance of explosion and debris cloud later.

[Prettz]

twitter.com/elonmusk/status/1143686587877691392

Yes, but we couldn’t take a chance on 2nd stage failing it’s 4th maneuver. This mission was more complex than anything I’m aware of in history of rockets. RIP center core, you did your duty well.

I believe Proton-M/Briz-M missions are more complicated. The Briz-M does five burns plus a tank separation (parking orbit insertion, intermediate orbit insertion, transfer orbit insertion 1, tank separation, transfer orbit insertion 2 and geosynchronous transfer orbit insertion). Mission duration is 11 hours. In comparison, the FH second stage only did four burns and had a mission duration of 3.5 hours.

http://www.russianspaceweb.com/mexsat1.html

So the most complex mission done with cryogenic propellants then? Briz-M is a hypergolic tug, so multiple relights with coasts in between isn’t really that impressive because hypergols don’t suffer from the same problems cryos do when stored on orbit for lengthy periods e.g. boil off. These aforementioned problems are what makes STP-2 such a complex mission.

And don't most(all?) hypergols have bladders?
So no fuel settling.

Isn't it that only spacecraft use bladders for hypergolic tanks? I can't think of any hypergolic rocket stages that use that. You've got Delta K, Ariane 5 EPS, the Agena family, Transtage, etc. Unless Russian tug stages do use it.

[Kabloona]

My understanding of "propulsive DEpassivation" is placing the stage in the chosen orbit and venting fuel and oxidizer to reduce the chance of explosion and debris cloud later.

Lar was asking a rhetorical question about "DEpassivation," which is the grammatical equivalent of "irregardless."

What Alexphysics meant to say is "propulsive passivation."

[Kansan52]

Ahhh.

[Lar]

My understanding of "propulsive DEpassivation" is placing the stage in the chosen orbit and venting fuel and oxidizer to reduce the chance of explosion and debris cloud later.

Lar was asking a rhetorical question about "DEpassivation," which is the grammatical equivalent of "irregardless."

What Alexphysics meant to say is "propulsive passivation."

Exactly. I know what passivation is. Make the stage passive!

I'm not clear on how to DEpassivate something after you passivated it (unless you have on orbit refueling and battery recharging to undo the passivation you did by venting and discharging... that day is coming but not here yet) Hence my question to Alexphysics

[ZachS09]

Would it have been possible for the center core to be expended while the side boosters still returned to LZ-1 and LZ-2?

Why wouldn't it be possible? What the center core does after BECO is of no consequence to booster RTLS, at that point it would behave just like an expendable F9 launch and just provide more margin to the 2nd stage.

My logic is so that we wouldn’t have to worry about a potential landing going awry. But then again, maybe SpaceX wanted to recover the center core to reuse it.

Of course they wanted to recover it. If not to reuse it, at least to inspect for potential weak points during high energy returns.

What I meant by "is it possible" is because of your answer: providing more margin for the upper stage to complete the mission without running out of delta-v.

However, another factor to that question is what if the side boosters did not have enough delta-v to return to the Cape since there is not a second drone ship for one of the side boosters. Even though expending the center core provides more margin, they would still want to recover the side boosters using the right amount of delta-v.

[whitelancer64]

My understanding of "propulsive DEpassivation" is placing the stage in the chosen orbit and venting fuel and oxidizer to reduce the chance of explosion and debris cloud later.

Lar was asking a rhetorical question about "DEpassivation," which is the grammatical equivalent of "irregardless."

What Alexphysics meant to say is "propulsive passivation."

Exactly. I know what passivation is. Make the stage passive!

I'm not clear on how to DEpassivate something after you passivated it (unless you have on orbit refueling and battery recharging to undo the passivation you did by venting and discharging... that day is coming but not here yet) Hence my question to Alexphysics

It's obviously a typo. Don't be a jerk about it.

[ugordan]

Would it have been possible for the center core to be expended while the side boosters still returned to LZ-1 and LZ-2?

Why wouldn't it be possible? What the center core does after BECO is of no consequence to booster RTLS, at that point it would behave just like an expendable F9 launch and just provide more margin to the 2nd stage.

What I meant by "is it possible" is because of your answer: providing more margin for the upper stage to complete the mission without running out of delta-v.

However, another factor to that question is what if the side boosters did not have enough delta-v to return to the Cape since there is not a second drone ship for one of the side boosters. Even though expending the center core provides more margin, they would still want to recover the side boosters using the right amount of delta-v.

I'm not sure what you're getting at here. Why would the fate of the center core have any direct say in what happens to the boosters?

The center core pretty much runs at lowest throttle the whole time shortly after clearing the pad until BECO and so whether or not the center core is expended afterwards, it does not change the staging point of the boosters (neglecting the modest mass of recovery hardware on the center core) if they were to RTLS. The subsequent burn time of the center core does not play into that trade.

There is nothing practical that prevents a combination of 1) booster RTLS and 2) center core expenditure.

Now, whether or not SpaceX would ever choose to fly such a profile or if it makes sense for one reason or another is a different question.

[ZachS09]

Would it have been possible for the center core to be expended while the side boosters still returned to LZ-1 and LZ-2?

Why wouldn't it be possible? What the center core does after BECO is of no consequence to booster RTLS, at that point it would behave just like an expendable F9 launch and just provide more margin to the 2nd stage.

What I meant by "is it possible" is because of your answer: providing more margin for the upper stage to complete the mission without running out of delta-v.

However, another factor to that question is what if the side boosters did not have enough delta-v to return to the Cape since there is not a second drone ship for one of the side boosters. Even though expending the center core provides more margin, they would still want to recover the side boosters using the right amount of delta-v.

I'm not sure what you're getting at here. Why would the fate of the center core have any direct say in what happens to the boosters?

The center core pretty much runs at lowest throttle the whole time shortly after clearing the pad until BECO and so whether or not the center core is expended afterwards, it does not change the staging point of the boosters (neglecting the modest mass of recovery hardware on the center core) if they were to RTLS. The subsequent burn time of the center core does not play into that trade.

There is nothing practical that prevents a combination of 1) booster RTLS and 2) center core expenditure.

Now, whether or not SpaceX would ever choose to fly such a profile or if it makes sense for one reason or another is a different question.

You're right. I guess my theory didn't make sense in the first place.

[Star One]

How many more flights does FH have to do to be certified to carry the various classes of NASA science payloads?

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20180007026.pdf

[vanoord]

Would it have been possible for the center core to be expended while the side boosters still returned to LZ-1 and LZ-2?

My logic is so that we wouldn’t have to worry about a potential landing going awry. But then again, maybe SpaceX wanted to recover the center core to reuse it.

The justification to expend the centre core for this mission would (presumably) have been to enable the second stage to retain enough fuel for a de-orbit burn.

However, the opportunity existed to bring a centre core home for the first time; and to subject a core to the most extreme heating one has yet endured and see what happened.

This time, the core didn't survive. Next time it might - and the lessons learned, even from a core that might not fly again, may be invaluable.

*If* SpaceX had got this core back and it turned out it had only just made it back but was in very bad shape, that might have increased the odds of the next Falcon Heavy with this sort of flight profile flying in expendable mode to negate the risk of losing the grid fins and legs etc. - but we won't know until they have got one back after this sort of punishment.

[Alexphysics]

My understanding of "propulsive DEpassivation" is placing the stage in the chosen orbit and venting fuel and oxidizer to reduce the chance of explosion and debris cloud later.

Lar was asking a rhetorical question about "DEpassivation," which is the grammatical equivalent of "irregardless."

What Alexphysics meant to say is "propulsive passivation."

Exactly. I know what passivation is. Make the stage passive!

I'm not clear on how to DEpassivate something after you passivated it (unless you have on orbit refueling and battery recharging to undo the passivation you did by venting and discharging... that day is coming but not here yet) Hence my question to Alexphysics

It's obviously a typo. Don't be a jerk about it.

Yep, a typo, don't know what I was thinking about. Sorry for the confusion

[punder]

How many more flights does FH have to do to be certified to carry the various classes of NASA science payloads?

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20180007026.pdf

Sometimes I wonder if NASA even knows the FH exists.

And yes, that's unhelpful cynical fanboi sarcasm. What I really meant to say was, Congrats SpaceX! What a spectacular mission. And bonus, a solar sail. Sure hope it works.

[XenIneX]

If you have thrust off center and you want to control which direction you skitter off in (to abort more safely, say, deliberately avoiding travel in the direction of support vessels for example) rather than a random direction, doing a roll with the nitrogen thrusters might be a way to choose your direction. Roll till the off center thrust is diverting you in the direction you want to go, then stop rolling.

Actually landing by using fancy rolls to make your off center thrust cancel out over time seems a stretch but not completely impossible. The booster would appear to be gyrating wildly.

In both cases you'd have to have programmed that failure mode in though I think.

Too complicated.  Just push TVC and RCS over to one side and throttle up.  Between them, they should overpower the malfunctioning engine -- and the rocket would be unstable anyway.  The rocket will tumble, arcing several hundred feet away from the ASDS, and since the support ships are miles away, they're perfectly safe.

[cscott]

Don't forget that even though the center core missed the drone ship, SpaceX got full telemetry from it: the drone ship acquires signal from the booster, and I believe several of the GO sisters can as well. It's recorded, not real time, so SpaceX likely won't have the full data for a week or so yet until the fleet returns (it took six days for OCISLY to get on station).  But there's a lot of data coming back from this attempt.

[Okie_Steve]

Given how close it got to the "X" on deck before aborting I have to wonder when the TVC failed and how. It would not surprise me if boostback and entry have the engines at dead center and the landing burn starts that way. So, was the TVC fried earlier and not noticed or was it damaged earlier and gave up the ghost at the very end? It looked like it might have made it to somewhere on the deck it it had not aborted. I wonder what the lawn dart damage cost last time vs getting the stage back intact. Interesting trade off.