SpaceX Falcon 9 : Iridium NEXT Flight 2 (June 25, 2017) : Discussion

[Welsh Dragon]

Concur with those that observed it seemed to reach 0 velocity a few feet above the deck and drop the last couple feet after cut off.

Impressive sleuthing from a terrible angle. :p Don't quit your day jobs, people.

Definite vertical movement after engine cutoff, and no leg movement relative to stage body until after engine cutoff. Both suggesting cutoff before leg contact. Like you say, always need a second angle, but it does seem like it was a bit off. Not a big deal if it is though. Just replace the crush cores.

[Herb Schaltegger]

Concur with those that observed it seemed to reach 0 velocity a few feet above the deck and drop the last couple feet after cut off.

Impressive sleuthing from a terrible angle. :p Don't quit your day jobs, people.

Pause the YouTube video (<space>), then advance slowly with > (go back with >) and you'll see the engine glow stop about 0.5 seconds before the legs move on impact with the deck.

Probably due to a pitching deck or swell ... the video of the landed stage from JRtI showed a large break aft (?) of the deck a few seconds after landing. 

[sanman]

They really need to get better Hold Music 

[cebri]

Congrats SpaceX.

[Scylla]

operative @nullpointr
·
22m

Congrats on 2 successful landings in 2 days! One question: why are the fins not flat er the underside edges?


Elon Musk @elonmusk

Replying to @nullpointr
More aero effectiveness to create steep spires on windward side at the grid fin intersections
https://twitter.com/elonmusk/status/879086784969191424

[mvpel]

Novel High-Performance Grid Fins for Missile Control at High Speeds: Preliminary Numerical and Experimental Investigations

The numerical and experimental results show that the novel design of the lattice wings has distinct advantages in comparison to the conventional not-swept configurations. Compared to conventional lattice wings the maximum benefit e.g. of the zero-lift total drag for the investigated locally swept lattice wings is of the order of 30% - 40%.

[Edit: broken URL replaced]

[Silmfeanor]

The numerical and experimental results show that the novel design of the lattice wings has distinct advantages in comparison to the conventional not-swept configurations. Compared to conventional lattice wings the maximum benefit e.g. of the zero-lift total drag for the investigated locally swept lattice wings is of the order of 30% - 40%.

URL fixed - interesting paper. thanks for finding it.  Full of nice illustrations including some configs that really resemble the Falcon grids we saw today.

[sevenperforce]

Congrats to SpaceX! That was the shortest entry burn I've ever seen. Love the new grid fins.

Also, from earlier:

To the topic of re-entry profiles (from a few pages back)...

In situations where you have more than enough fuel for ASDS but not enough for a full RTLS, I don't think it would make any sense to do a "partial boostback" to kill horizontal velocity. The only reason for the immediate boostback is to decrease the amount of time you're headed downrange, saving boostback propellant. If they have extra prop, they'd save it for a longer entry burn. Oberth and all that.

Aaaaaand I'm immediately proven wrong.

[M.E.T.]

Any post launch press conference broadcast that we can get a live link to today?

[Lars-J]

Concur with those that observed it seemed to reach 0 velocity a few feet above the deck and drop the last couple feet after cut off.

Impressive sleuthing from a terrible angle. :p Don't quit your day jobs, people.

Pause the YouTube video (<space>), then advance slowly with > (go back with >) and you'll see the engine glow stop about 0.5 seconds before the legs move on impact with the deck.

The legs move out after landing to absorb impact/mass as well.

[Ben the Space Brit]

Both Bulgariasat-1 and Iridium NEXT-2 prove the robustness of the Falcon-9 core's landing struts. Both cores experienced seriously non-nominal landings but came to a rest stable and, from an outsider's perspective, in good overall condition.

[JamesH65]

Concur with those that observed it seemed to reach 0 velocity a few feet above the deck and drop the last couple feet after cut off.

Impressive sleuthing from a terrible angle. :p Don't quit your day jobs, people.

Pause the YouTube video (<space>), then advance slowly with > (go back with >) and you'll see the engine glow stop about 0.5 seconds before the legs move on impact with the deck.

The legs move out after landing to absorb impact/mass as well.

Er, yes, which is exactly what was seen, apparently after engine cut off. In prior landings the legs splayed out while the engines were still running. That and it does look like it is sitting lower than previous landings, but the angle is difficult. It even looked like it almost hovered over the deck for a moment...

However, it's all guess work from limited information. We'll know what happened soon enough.

[meekGee]

Both Bulgariasat-1 and Iridium NEXT-2 prove the robustness of the Falcon-9 core's landing struts. Both cores experienced seriously non-nominal landings but came to a rest stable and, from an outsider's perspective, in good overall condition.

Yup.  That's an inherently advantage of vertical landings - that they aim at a zero energy condition.

Horizontal landings, even when nominal are high energy, and so it's harder to recover from an off-nominal ones.

[joek]

Yup.  That's an inherently advantage of vertical landings - that they aim at a zero energy condition.

Horizontal landings, even when nominal are high energy, and so it's harder to recover from an off-nominal ones.

They all need zero energy at the end of the day (when they touch down on the landing platform, roll to a stop at end of runway, or whatever).  Only question is when and the cost of getting rid of that energy--and the associated risk (which might be included in the cost equation).

No objective evidence that one form of shedding energy is better or less risky than another.  If you want to argue that one form is more efficient than another... that's a different discussion.  Risk != Efficiency (at least to a first, and likely second or third order).

[meekGee]

Yup.  That's an inherently advantage of vertical landings - that they aim at a zero energy condition.

Horizontal landings, even when nominal are high energy, and so it's harder to recover from an off-nominal ones.

They all need zero energy at the end of the day (when they touch down on the landing platform, roll to a stop at end of runway, or whatever).  Only question is when and the cost of getting rid of that energy--and the associated risk (which might be included in the cost equation).

No objective evidence that one form of shedding energy is better or less risky than another.  If you want to argue that one form is more efficient than another... that's a different discussion.  Risk != Efficiency (at least to a first, and likely second or third order).

Horizontal landings do not have zero energy at the moment that counts - that of making contact with the ground.

This is where things are dicey.

Touch down that hard on a runway, blow a tire, and you'll realize those 200 MPH (+?) are not on your side.

Those last two landings demonstrated that.

You can crash any landing, but vertical ones are more forgiving.

[AC in NC]

Comparison of today's "Squat vs. a more nominal landing

[joek]

You can crash any landing, but vertical ones are more forgiving.

With respect to rockets given the current state of the art, I *might* agree.   However, as a general statement this fails.  You might want to do an FMEA before pronouncing vertical landings as less risky.  There are a lot of variables in play, of which energy-at-touchdown is only one.  Otherwise we would all be traveling on VL commercial aircraft.

[Norm38]

I expected to see some visual indication of grid fin heating during landing, but didn't see anything.  Very impressive. Wonder if we've seen the last aluminum fins.

[LouScheffer]

Elon has some free time to spend on twitter:

Slightly heavier than shielded aluminum, but more control authority and can be reused indefinitely with no touch ups

No, but shielding got fragged every flight. More control authority is for Falcon Heavy, but also enables Falcon 9 to land in heavier winds.

Interesting that they need more control authority.  On landings to date you can barely see the grid fins move, much less approach maximum travel for any period of time.   Must be planning for quite a bit worse conditions than we've seen them land in so far.

[AC in NC]

Best attempt with weak image skills to overlay the nominal angle to this landing.