SpaceX space :-)

KarenRei

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For a land landing, I believe the landing pad *is* the safest crash location.
See: "At least there's not much around the pad, and one presumes that the ballistic trajectory after the reentry burn doesn't point to anywhere bad. But that just moves the safety responsibility to having proper failsafes for how to deal with an improper reentry burn"

If the reentry burn is normal but there's a problem in the landing burn, it'll likely crash somewhere on or west of the pad (but not far west, still in the general vicinity of the pad). But if the problem is a failure in the reentry burn, it could be on a much wider range of possible impact trajectories - generally significantly west of the pad. The dV from the reentry burn shifts the ballistic trajectory's impact point to the east in the process of reducing velocity, so if you have lower dV than intended, you have a further west impact.

There's an even worse possible failure case (excessive boostback burn), but it's not nearly as likely. Normally one's failure cases cause too little dV, not too much.

For sea landings, it could make sense to try to avoid drone ship damage, but I'm guessing that they don't want to bother putting in the engineering effort, at least not yet. There are so many ways that a rocket could fail to land.
And all need to be addressed to the degree possible. But some - like engine ignition failure - are really lowest-hanging-fruit cases.

I hope your assessment is correct, that it's just been lower on their priority list. But when it comes to land landings, proper detection of abort scenarios and handling of them simply can't be allowed to be lower priority. And the fact that they don't detect it for sea landings says they don't for land landings either; if they had the code for land landings, why would they deactivate it at sea?
 
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KarenRei

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ED: Based on some flight profile data I've looked at (such as this), I don't think a failed reentry burn could end up with the first stage reaching as far as Orlando (that would require an overly long boostback burn). But the Titusville to Rockledge area looks to possibly be in the potential impact area from a failed entry burn, depending on the profile. Certainly the Canaveral / Pine Island area is.
 

JWardell

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I've seen comments on reddit that say the center core actually performed as programmed. They intentionally aim to land off to the side of the drone ship, and only if everything is nominal toward the end of the decent it changes to the center of the ship. In this case it knew engines failed to light, so it did not change its course. Note it did not deploy its legs either.
 

KarenRei

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I've seen comments on reddit that say the center core actually performed as programmed. They intentionally aim to land off to the side of the drone ship, and only if everything is nominal toward the end of the decent it changes to the center of the ship. In this case it knew engines failed to light, so it did not change its course. Note it did not deploy its legs either.
I don't know who made said comments, but if the goal was to stay away from the ship, the last thing you want to do is to keep the rocket angled at the ship (rather than righting it with the nitrogen gas thrusters) and to keep the engine thrusting on max.

When only one engine lit, there was no chance it was ever going to reduce its velocity enough to land safely. This was obvious long before the craft came close to being in the closeup shot; a single-engine landing has to be started from a much higher altitude than a multi-engine landing to cancel out the dV. Yet you can watch the rocket try its hardest to get back to the drone ship in the distance shot, all the way up to impact. No nitrogen thruster righting of the craft. No shutdown of the engine. Just a continuous attempt to hit a drone ship it could not actually land on.

As for the legs, I don't know what is the actual triggering event for that. All I can comment about is what the rocket can be visibly seen doing in other regards.
 

KarenRei

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Lots of problems here. Let's start with that graphic.

2. The left and right side show two entirely different things. The right side contradicts numerous other graphics. The right side is also not remotely in-line with reality. Watch for yourself:


The stages are not coming in toward the landing pad vertically as drawn in that diagram, they're coming in at a significant angle. The engines light here:


There's no way that was aimed for the water like they're trying to draw it.

The drawing is just simply wrong. It's not even self-consistent.

You can see an entire landing burn from the side here:


That rocket is not in any remote way falling toward the ocean.

The rockets *are* aimed at the pad (actually toward the west side of the pad) when the burns start. And when the reentry burns start, they're aimed significantly further west.

I'm not sure who "JackONeill12" is. But he refers to SpaceX as "they", implying that he doesn't work for them.

Concerning the centre core landing: the rocket is not aiming for the ocean; it's coming in at an angle. It has to cancel out its horizontal momentum to reach the platform as close before landing as possible. To do this, the ballistic trajectory has to reach past the platform. It's not a safety measure, it's how the craft has to land.

By the time the craft comes into frame, even an engine relight (does the craft actually not know that it's out of TEA-TEB?) will not even come close to being able to avoid a collision with "something" (it hit the ocean at 300mph; any relight would have had to have occurred far higher). The only thing the rocket can control is how far away from the platform said collision is. It does nothing to maximize that distance.
 
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Michael Russo

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JWardell

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@KarenRei Those reddit comments are talking about the middle core landing on the drone ship in the ocean, not the two returning to land. Obviously they are programmed to target the concrete landing pads and not the buildings next to them.
 

JWardell

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Forgot about this thread...

A few weeks ago, I interviewed someone for work that had recently had a contract with SpaceX, but similar embedded systems experience as me. I dug a little and pretty much everything he said he did I said hey, I could have done that. I never thought I would be qualified to work there or they had a need for electronics stuff..
Then last week my good friend in LA just started working there, and he's already feeding me job openings to lure me over. Thanks but no thanks, I'm not moving way out there.
Yet there's some temptation...I think I need to go visit first :)
 

Bokonon

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Saw this “train” video of the Space X STARLINK satellites that were launched onboard Falcon 9, May 23rd. So cool!
This is awesome.... I can't wait to show this to my son, who is riding a train today with a train-obsessed friend "just because". Hey guys, you thought that train to Providence was cool? Check out this 🌠SPACE TRAIN🚀!!

Also, do we not have a dedicated Space X thread? Did some searches but admit I didn’t dig too much.
Found it and merged. The long-running "SpaceX Space" thread lives again!
 

Lovesword

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This is awesome.... I can't wait to show this to my son, who is riding a train today with a train-obsessed friend "just because". Hey guys, you thought that train to Providence was cool? Check out this 🌠SPACE TRAIN🚀!!



Found it and merged. The long-running "SpaceX Space" thread lives again!
Thank you sir!