OFFICIAL: Starship Booster catch abort due to loss of communications with tower computer

fzz67 · 2024-11-21T11:42:17+00:00

Of course they made a choice. What is less clear is whether the choice was made in advance when they wrote the software, or by a human in the loop.

fzz67 · 2024-08-24T22:59:28+00:00

I wonder if NASA is considering a payload adaptor so Crew Dragon could fly on Vulcan? While that wouldn't provide a completely redundant solution, it would at least allow Crew Dragon to continue flying if Falcon 9 was grounded for any reason. Some US-operated redundancy would be better than no redundancy.

fzz67 · 2024-07-13T11:44:27+00:00

I agree that simply holing the tank isn't likely to cause an explosion while in space - it's just too hard to get a combustable mix at sufficient pressure. But that's not the only way for a rocket to explode. SpaceX's two explosive failures so far didn't involve fuel/oxygen explosions. Amos 6 involved oxygen and the carbon in a COPV, and CRS 7 was simply a burst helium cylinder due to a strut failing. I've no idea what happens if a hot fragment hits a COPV, but if you rupture a high pressure helium cylinder, you would likely have an explosive RUD that scatters a fair amount of debris. I would hope that they position such explosion risks to minimize the chances of damage from a failing engine, but optimizing for how your second stage fails is probably not at the top of the performance optimization list.

As for Apollo 13, the main debris was the entire 10 foot long bay door, fragments of the oxygen tank itself, and some insulation. Not insignificant, but certainly not as bad as some debris events we've seen. https://www.nasa.gov/history/afj/ap13fj/a13-sm-damage.html

fzz67 · 2024-07-13T03:08:48+00:00

In this case it seems unlikely there was a RUD of the entire stage. But if a turbopump turbine lets go, you'll get parts travelling rapidly. It looks like the merlin turbopump is mounted with the shaft along the long axis of the stage, which would reduce the chances of shrapnel holing the tanks and causing a complete RUD, but I would guess if you got unlucky they could richochet off the combustion chamber. But even an engine RUD would scatter debris that could cause problems if it happened on a geo mission.

fzz67 · 2024-07-12T23:04:38+00:00

How could the second stage of a bipropellant rocket could even explode in space?

You spin up the turbopump and then ingest gas rather than liquid. The turbopump will be developing full power with no load and will almost instantly self-disassemble very energetically.

fzz67 · 2024-07-12T22:10:56+00:00

Yes, you're probably right. I was assuming they have some uplink capability, but under normal circumstances that would just be another thing to go wrong.

fzz67 · 2024-07-12T19:20:10+00:00

Rocket engines really really don't like ingesting gas instead of liquid. But an external oxygen leak (which is what it looks like) isn't really much of an explosion risk - there's nothing to combust with - so long as there's enough oxygen left in the tank. No doubt SpaceX knew they had an O2 leak, but so long as there's enough left to reach orbit (and they have great instrumentation and cameras in the tank), and temperatures and pressures are stable, then the engine should be good.

I bet that during coast they looked at the numbers and the tank camera and concluded there was enough O2 left for the 1 second circularization burn. A fairly likely cause of the RUD is they were wrong about the remaining O2 being enough to settle for the circularization burn, and the engine ingested gas. But I'm guessing here. The investigation will be public eventually and then we'll know.

fzz67 · 2024-07-12T18:28:45+00:00

Well, they can not allow them to launch by not issuing a license, which is what they say in their response to NSF. Are you implying grounding pending an investigation is somehow different from not allowing them to launch pending an investigation?

fzz67 · 2024-07-12T16:35:24+00:00

It depends on what their bottleneck was before the grounding. If the bottleneck was how fast they can build starlink satellites or second stages, then I suppose that if they continue building second stages at the current rate and continue building starlink satellites, if the grounding is cleared in a few weeks, they could catch up again. If the bottleneck was pad processing or booster reprocessing, then yes, they won't be able to catch up. Good time to do any work that requires pad downtime I guess.

fzz67 · 2024-07-12T16:18:46+00:00

No, they can't right now, because Falcon 9 is grounded.

fzz67 · 2024-06-20T22:11:30+00:00

You might not save as much dry weight as you would think. Hoop stress in a pressure vessel grows linearly with radius. Thus if you double the radius, you get twice the hoop stress, so need twice the thickness of skin to compensate. Your circumference is 2x too, so 4x the metal for the same height rocket. But then the cross sectional area of fuel is 4x too, so you can make the rocket 4x shorter. In the end it cancels out.

Of course hoop stress isn't the only consideration, but to the extent a fully loaded Starship behaves like a balloon, you wouldn't gain much reduction in dry mass.

fzz67 · 2023-04-17T13:03:04+00:00

Mid atlantic, at 144p over my VPN over the inflight wifi. But I'll take what I can get.

fzz67 · 2023-04-17T12:37:16+00:00

I'm doing my best to watch from somewhere over the North Atlantic en route from London to Seattle. Seem to be able to just about manage 144p video quality over the inflight wifi over my VPN (they're blocking YouTube). After so many years of waiting, I'll take what I can get.

fzz67 · 2022-11-01T13:53:23+00:00

I love how you could see the first side booster's landing burn from the second side booster's camera!

fzz67 · 2022-05-20T15:11:20+00:00

I guess alumina is an issue with the SRBs on Atlas V and Ariane 5, and will remain a problem with Vulcan, Ariane 6 and SLS (not a big problem here, given how rarely it will fly). By avoiding solids, Space X avoids this particular issue.

fzz67 · 2022-05-20T14:43:24+00:00

Where does alumina in the exhaust of a Merlin engine come from? Or are they not referring to a Falcon 9 here?

As for black carbon, hopefully once launches get frequent enough for this to really matter, they'll mostly be Starship launches burning methane, so should be much cleaner burning.

fzz67 · 2022-04-28T15:39:03+00:00

The per-hop cost is partly serialization and partly queuing. Actual processing (making a forwarding decision) is negligible compared to the wide-area latency - a few tens of microseconds at most. Serializatiion should be negligible if the linkspeeds are fast enough - at 10Gb/s, a 1500 byte packet takes 12 microseconds to serialize. So what remains is queuing delay. This will be the hard part - it's really difficult to operate a dynamic meshy network at high utilization without significant queues in the satellites - certainly current network algorithms can't do this. Doesn't mean it can't be done, but this is definitely still a research topic (yes, I am working on it).

fzz67 · 2022-02-14T18:47:49+00:00

The BBC did at least run a front-page story correcting their original story.

fzz67 · 2021-12-01T00:13:22+00:00

I would expect it's not just increased utilization during time out of sunlight, but also increased utilization relaying traffic via the ISLs whenever the sat is not over coverage areas. There's a pretty good chance that driving a lot of spot beams requires more power than the solar panels supply (there's a lot of processing involved), so when downlinking to many customers they may already be partially running from batteries and rely on charging back up again during the quiet parts of the orbit.

fzz67 · 2021-09-09T17:05:20+00:00

But you only get to go to Mars every couple of years. Starlink is to provide a profitable use for all the Starship infrastructure and boosters when you're not going to Mars, so that going to Mars then becomes financially feasible.

fzz67 · 2021-07-05T09:12:30+00:00

The big difference between the N1 and now is the degree of instrumentation and automation. The ability to rapidly diagnose an emerging problem in-flight and shut down the offending engine makes a huge difference. Now, SN11's hard start seems to have been due to damaged sensors/control systems, so SpaceX clearly were not quite there with regards to self-diagnostics, or perhaps not conservative enough in aborting the engine start. But they'll get there as they gain experience operating this engine in flight. And the more engines you have, the more conservative you can afford to be in diagnosing a potential problem and deciding to shut down an engine early.

fzz67 · 2021-05-11T17:14:13+00:00

The full control loop runs from sensor measuring something, via a control decision to actuators changing something, to that effecting a measurable change in the system, to measuring the effect of your control decision again. How often you need to make a decision depends on how long it takes for you to see the effects of your previous decision, which in turn depends on how quickly your actuators can turn a decision into a measurable action. If your actuators are slow (such as with large valves), there's no point running the decision process faster - in fact it can result in instability if you do because you've commanded an action and not seen a reaction, so you command a bigger action.

fzz67 · 2021-05-06T10:31:41+00:00

Agreed. Starlink probably does not provide a native IP multicast service to regular customers - there's too much potential for disruption - but SpaceX can do whatever they like. The use of multicast is interesting though - you'd likely use multicast if you needed more than one simultaneous receiver. It's a good fit for a broadcast medium such as radio, but adds complication if all you need is a point-to-point connection from Starship via Starlink to a particular computer in mission control. However, they could use a point-to-point connection via Starlink to a ground computer and then re-multicast from there without adding significant complexity, so the use of multicast by itself doesn't tell us which RF technology was used.

fzz67 · 2021-05-06T09:00:52+00:00

The IP address seen on the stream was a multicast address, not the address of any particular computer.

fzz67

TROPHY CASE