SpaceX Falcon 9 v1.1 - Jason 3 - SLC-4E Vandenberg - Jan 17, 2016 - DISCUSSION

[OxCartMark]

I liked that SpaceX closed out its webcast with the David Bowie words "The stars look very different today".

[TrevorMonty]

Congratulations SpaceX on successful launch.

Better luck next time with landings.

[Astromattical]

Add Automated spacecraft drone buoys (ASDB). Measure incoming wave height and predict elevation of barge at landing.

Right. But even if you get a good prediction for the drone ship movements, it's nontrivial to exploit this in the landing algorithm in a reliable manner.

Very true, but it wouldn't hurt, and it is something which doesn't require large hardware changes (though reliable radio comm uplink to stage is, as you say, nontrivial). It's possible that no "solution" will be found by the landing algorithm, but at least it will likely be better than going in completely blind to the droneship's state.

Is there no radar to determine altitude on the stage in the moments leading to touch down? I find this hard to believe, and it would certainly be easier to integrate that into the algorithm than wave prediction updates from buoys.

[PreferToLurk]

On the "optimistic for the future" side of things, this landing attempt was done with a smaller engine throttle range (non Full Thrust M1D having same lower throttle setting as Full Thrust M1D). Meaning that *potentially* a future landing with the same sea conditions *might* have better chances to land, given a more responsive engine.

Anyone know for certain whether this Falcon had the upgraded legs?  Don't see a reason why they wouldn't have the new legs unless they weigh more and didn't want to (or were contractually forbidden to) cut into their DV budget for Jason 3?

[Robotbeat]

Add Automated spacecraft drone buoys (ASDB). Measure incoming wave height and predict elevation of barge at landing.

Right. But even if you get a good prediction for the drone ship movements, it's nontrivial to exploit this in the landing algorithm in a reliable manner.

Very true, but it wouldn't hurt, and it is something which doesn't require large hardware changes (though reliable radio comm uplink to stage is, as you say, nontrivial). It's possible that no "solution" will be found by the landing algorithm, but at least it will likely be better than going in completely blind to the droneship's state.

Is there no radar to determine altitude on the stage in the moments leading to touch down? I find this hard to believe, and it would certainly be easier to integrate that into the algorithm than wave prediction updates from buoys.

I think there is radar. But you ideally need to know the full state of the barge, including pitch angle and its first time derivative.

[mme]

I liked that SpaceX closed out its webcast with the David Bowie words "The stars look very different today".

Me too, very poignant.  Actually brought a tear to my eye.

[JamesH]

Add Automated spacecraft drone buoys (ASDB). Measure incoming wave height and predict elevation of barge at landing.

Right. But even if you get a good prediction for the drone ship movements, it's nontrivial to exploit this in the landing algorithm in a reliable manner.

Very true, but it wouldn't hurt, and it is something which doesn't require large hardware changes (though reliable radio comm uplink to stage is, as you say, nontrivial). It's possible that no "solution" will be found by the landing algorithm, but at least it will likely be better than going in completely blind to the droneship's state.

Is there no radar to determine altitude on the stage in the moments leading to touch down? I find this hard to believe, and it would certainly be easier to integrate that into the algorithm than wave prediction updates from buoys.

I suspect (no evidence) that the radar altimeter gives one number, not 3/4 required to know the pitch/roll of the barge. But still not sure that would help - how do you pitch the rocket over to match the pitch of the barge?

[Robotbeat]

On the "optimistic for the future" side of things, this landing attempt was done with a smaller engine throttle range (non Full Thrust M1D having same lower throttle setting as Full Thrust M1D). Meaning that *potentially* a future landing with the same sea conditions *might* have better chances to land, given a more responsive engine.

Anyone know for certain whether this Falcon had the upgraded legs?  Don't see a reason why they wouldn't have the new legs unless they weigh more and didn't want to (or were contractually forbidden to) cut into their DV budget for Jason 3?

Jason 3 is like 550kg launch mass into LEO (polar). Performance was definitely not a problem, here. They would've had plenty of performance for a RTLS if they had been cleared to do so.

[ugordan]

This is going to be their longest 2nd stage coast to date correct?

The longest coast during the primary mission, yes. Deorbit burns in the past have happened at around this time, but they weren't primary mission critical.

I think this may also be the first three-burn MVac mission profile, 3rd being the deorbit burn.

[Robotbeat]

Just out of curiosity, is the parking orbit stable? And how much delta-v is needed to get into final orbit? And how much delta-v does Jason-3 have on-board?

Answering my own question, 12 second of Merlin 1D Vac firing time is like >700m/s of delta-v with such a lightweight payload (553kg) and upper stage (4500kg???), even if throttled down to 70klbf of thrust. Jason-3 is like 525kg dry, so assuming it's using hydrazine with an exhaust velocity of around 2km/s, Jason-3 only has like 100m/s of delta-v, not nearly enough to get into the final orbit.

I still don't know if the original parking orbit was stable or not.

[hrissan]

I've been thinking for a while that SpaceX needs something closer to an offshore drilling platform than a barge. With respect to timing the Falcon 9's hover-slam, it seems that the landing platform basically needs to be inert, rather than pitching and rolling with the seas.

Quick search gave me this site:

http://valm.no/stable/products/stable-deck/

The standard platforms have a diameter of up to 6 meters / 20 feet. Total payload is maximum 3 metric tons. The platform compensates for movements of up to +/- 6 degrees and builds a total of 43 cm/17 in above the original deck, or it can be integrated with the original deck construction.

The stabilization is achieved using 4 electrical servo motors. Standard power supply: 400 V, 50 Hz, 4 x 64 Amps fuses. Other options of power are available.

Scaling this solution 20x and running on hydraulic a la thrustmaster might be not that hard/costly?

[Astromattical]

Add Automated spacecraft drone buoys (ASDB). Measure incoming wave height and predict elevation of barge at landing.

Right. But even if you get a good prediction for the drone ship movements, it's nontrivial to exploit this in the landing algorithm in a reliable manner.

Very true, but it wouldn't hurt, and it is something which doesn't require large hardware changes (though reliable radio comm uplink to stage is, as you say, nontrivial). It's possible that no "solution" will be found by the landing algorithm, but at least it will likely be better than going in completely blind to the droneship's state.

Is there no radar to determine altitude on the stage in the moments leading to touch down? I find this hard to believe, and it would certainly be easier to integrate that into the algorithm than wave prediction updates from buoys.

I suspect (no evidence) that the radar altimeter gives one number, not 3/4 required to know the pitch/roll of the barge. But still not sure that would help - how do you pitch the rocket over to match the pitch of the barge?

Robotbeat and JamesH - you've both hit excellent points in that attitude and time derivative are needed, but those seem much easier than trying to integrate wave prediction; I can't imagine trying to determine what change wave A and wave B will have when they both arrive at the landing barge at nearly the precise same time but different angles.

You definitely do not want to pitch the rocket over prior to landing; the resultant change in horizontal velocity would ruin the landing. Need to find a way to compensate for the barge pitch with the stage vertical.

[sewebster]

They could build an ASDS simulator in Texas to practice in various simulated sea states. Could give them something to do with all the stages they'll be recovering soon

[AJA]

OK... this following idea is all sorts of crazy, but here goes anyway.


1. We know they can direct the stage back to a targeted location that isn't too big.
2. We know that the problems with splashdown involved the unacceptable entry of corrosive sea-water into the Merlin plumbing, maybe undesirable thermal quenching of the central Merlin engine bell; and maybe even the forces


So..why not splashdown into a controlled pool of some liquid...if that would indeed mitigate force issues rather than accentuating them? Heated freshwater maybe? You create a warm swimming pool IN the barge, and let the Falcon do a controlled "landing" in the water.


IIRC, they did do an ocean 'landing' during one of their previous (prior to the ASDSs)...did that stage break up on impact, or after toppling over? If it was the latter... then maybe it's something that the RCS at the top of the stage can help with...easing it into the water.


Yeah, I know it sounds ridiculous. But does anyone have more holes to poke?

[Space Ghost 1962]

Did anyone catch the actual staging velocity and altitude? Didn't hear it.

As to barge landing dynamics, doing repeated Monte Carlo's as a test might not be "good enough" due to the number of independent variables present. Terminal guidance for such landings have to model both barge and incoming stage independently with a joint momentum budget estimator that can have the "brake above and then drop" within the tolerance of the legs, which might not be that high...

add:

Likely not a guidance problem, more likely attitude/orientation and/or deceleration profile.

[Lars-J]

Yes, anything is possible with sufficient $$$ investment. But they are trying to do this within a limited budget.

It may be too ambitious a capability for the given launch vehicle and budget. 

You say it like it is a BAD thing. Don't we all often complain about how too much is spent to do too little? This is how you break new ground in *affordable* space access.

[PreferToLurk]

Anyone know for certain whether this Falcon had the upgraded legs?  Don't see a reason why they wouldn't have the new legs unless they weigh more and didn't want to (or were contractually forbidden to) cut into their DV budget for Jason 3?

Jason 3 is like 550kg launch mass into LEO (polar). Performance was definitely not a problem, here. They would've had plenty of performance for a RTLS if they had been cleared to do so.

So mass of legs is off the table.  question still though for new legs or old?  I could at least hypothesize a scenario where they had a contractually frozen launch vehicle configuration. Except, of course, for the safety upgrades from the CRS-8 investigation.

I think I remember reading that the assumption was on the new legs since a good reason to keep the old ones couldn't be thought up (for the record I don't think my hypothetical is a "good reason", merely plausible).  But if anyone *knows*, that would do wonders for my curiousity.  Thanks   

[Lee Jay]

I've been thinking for a while that SpaceX needs something closer to an offshore drilling platform than a barge. With respect to timing the Falcon 9's hover-slam, it seems that the landing platform basically needs to be inert, rather than pitching and rolling with the seas.

Yeah...this is the first thing that came to mind when I heard SeaLaunch was probably not coming back.  Buy Odyssey and strip the upper deck.

[mlindner]

<land in a pool of water>

This has been brought up here in the forums ad nauseum (along with nets, or controlled capture units or docking units). They don't work. The masses involved are too large.

[FutureSpaceTourist]

A slightly different tone than after ORBCOMM2?

Jeff Bezos on Twitter: "Impressive launch and @SpaceX will soon make Falcon 9 landings routine – so good for space! Kudos SpaceX!"

https://twitter.com/jeffbezos/status/688815223558410240