Seems pretty irresponsible of them to write it up like that. Some kind of intentional damage–whether by a competitor or just an idiot with a high-powered rifle–has to be on their fault tree, so it’s not surprising that they would be chasing down any leads in that direction. But yeah, putting “sabotage” right in the title is just stoking the rumor-mill. I guess we live in the age of clickbait titles.
Yes, we do.
Yet another sabotage article. Please don’t click on the link; you’ll only encourage them. Instead, enjoy this music video.
Even if it was their primary theory, which I doubt, no good can come of this rampant media speculation. On the other hand, I don’t really see any means of them shutting it down. Bleh.
Relatively small update here. This bit seems most significant:
No true root cause yet, though it’s not clear if that’s because they haven’t quite confirmed that their recreation had exactly the same conditions as the failure scenario, or whether they haven’t yet ruled out all other possibilities.
I wonder if this will prove to be something that escaped their qualification process because of too many dimensions. They obviously can’t test every combination of LOX pressure, LOX temperature, He pressure and He temperature (where one might wish to try 10 values of each)–not to mention variations in duration. Perhaps they used sparse sampling across the range, or picked a handful of what they thought were the worst-case conditions. That might leave certain bad combinations untested.
There’s been some speculation that SpaceX was testing new LOX and He filling procedures during this static fire. That aligns with some of the comments by Shotwell about the fix being “business process” related, e.g. “stop testing new procedures when your customer’s payload is sitting on a GIANT BOMB.” If true, that’s pretty damning… and yet, SpaceX is advancing so rapidly in part because they are squeezing a lot of testing and development around paying missions. In the short to medium term, they might get away with continued low reliability if they can keep learning valuable things (besides “someone figured out a new way to hammer in a sensor… backwards!”) while providing cost-competitive launch services.
Yeah–we know they’ve done that for their booster recovery efforts. One could argue that these efforts had zero impact on mission success, and naively that seems to be true, but there are always going to be small risks. The landing legs could have broken and caused instabilities; the extra helium lines could have burst; etc. So in some sense we already know that SpaceX is risking customer payloads to make their R&D cheaper.
It does seem a little irresponsible to do the same thing with propellant/helium loading, but maybe they thought the risk was infinitesimal.
At any rate, I don’t think they’ll be doing their pre-launch testing with payloads attached from now on.
Just a thought -
AIUI, the use of super-cooled fuel (and helium?) means that the window from fueling to launch is on the order of 30 minutes.
If they are using this extreme fueling procedure to get an extra X% thrust on the Falcon 9, could they use stable fuel and get the extra boost required by strapping on solid rockets?
Yeah, they’d have to go outside to buy the boosters (or buy somebody who already builds motors), and they need to do something to jettison the boosters if they want to land the first stage. That should not be difficult.
How common are such push-the-envelop technologies used?
For that matter: could they get this “Extra X%” by simply using all fuel aboard the booster and sacrifice the booster? How much fuel is used for the recovery? If you are willing to burn that fuel to deliver the payload, could you use ambient-temperature fuel?
Alternately, they could come up with payload “fairings” with Dragon-style escape boosters and parachutes. j/k
My information comes from some of Stranger’s posts on earlier SpaceX flights using densified O2. As I remember it, the concept was considered as far back as the 60’s and rejected as being impractical/not worth the effort. So I believe no one else besides SpaceX has tried this technique. A major problem with it is the very short time window inherent in the technique. One has be launch very soon after fueling, if something goes wrong (say an intrusion into the flight safety area), the launch has to be scrubbed.
It is worth noting that a recent review of launch procedures by a NASA panel of astronauts and flight experts was unanimous in rejecting the idea of having crew present during fueling. This last accident isn’t going to give the astronauts much confidence in the idea.
SpaceX isn’t the only one using densified propellants–the Antares rocket used sub-chilled oxygen, as did the Russian N1 rocket (which was where the Antares engines came from).
However, no one else has sub-chilled quite to the same degree, nor has anyone else used submerged carbon-fiber COPVs. It appears that this combination was what proved disastrous and led to the formation of solid oxygen. This reacted with the carbon, and… boom.
SpaceX seems to have a somewhat unusual approach to design. They take neither the “big dumb booster” path nor do they pursue delta-V at any expense. So they have a basic two stage rocket (when three stages would be more efficient for GTO missions) that uses kerosene (when a hydrogen upper stage would be a win). But on the other hand they really push the limits of what they have with densification and composites.
The payload increase from densification is certainly less than the payload hit from reusability. So they could make that tradeoff if they wanted. Densification gives more thrust as well, but that’s also not hugely important for them.
It seems to me that the “astronauts aboard during propellant loading” question does not have an immediately obvious answer. The risks during loading were certainly demonstrated, but simply being in the vicinity of a fully-loaded rocket is dangerous. So there are risks involved in just taking the elevator up to the capsule, among other things.
On the other hand, the capsule is arguably the safest place within a 1-mile radius. The escape system is operational during the whole process, so if the astronauts are already inside, there is no point where humans are nearby a skyscraper full of fuel and oxidizer while not also being protected by a safety system. The same can’t be said for late boarding.
I thought the helium tank’s placement within the tank the helium is to purge was a cute and efficient arrangement - no tubing, fewer/no fittings to fail.
But I see the liquid temp of helium (−269 °C) is lower than the Freezing point of oxygen (−218.79 °C) - if you want liquefied helium, you are risking solidified oxygen.
I really do hope they weren’t trying to inject liquid helium (does it even exist in commercial quantities?) into a tank buried in LOX.
Would the NASA manned shuttle to ISS require the super-densified fuels they were using for the failed test?
Yep, they were injecting liquid helium into a LOX tank.
It is now official: A chunk of solidified oxygen (!!!) bumped into the carbon-fiber overwrap of the helium tank, and ignited it. I don’t see anything resembling an ignition source.
On a wild guess, I’d think they’d know to ground all metal bits anywhere near LOX.
My mind is now (once again) officially blown.
Just found Ad Astra Rocket company. Warp drive coming up…
Would you like some oxygen ice cubes in that Hemlock?
The He in the second stages isn’t supposed to be liquid, the temperatures they are using are never supposed to be that cold. If there was indeed liquid He in the tank, then something very strange happened.
The working theory I’ve head is not that there was solid oxygen floating around, but that liquid oxygen soaked into the carbon overwrap on the helium tanks, then froze. As the tanks were pressurized, the solid oxygen was compressed as the carbon overwrapped stretched, and it was that compression that provided the ignition source.
Although the NK-33 engines used on the N-1 rocket and the later Antares do require LOx that is cooled below the liquid temperature of oxygen at standard pressure, it is only done to about -196 ℃ and is done to prevent LOx vaporization and combustion instability in the engine during operation. SpaceX is cooling their oxidizer down to -207 ℃ for the Falcon 9 specifically to densify the propellant, and in fact their performance margins for the uprated vehicle are dependent upon using densified propellants. The difference of -11 K may not sound like much but at those temperatures it is extremely difficult to keep the liquid insulated against conduction from the ambient environment, hence why SpaceX has experienced repeated aborts due to exceeding propellant temperature limits. This presents the sort of mission critical sequencing that stands in contradiction to making launches cheaper and less prone to error. As I’ve noted previously, densified propellants have been studied since almost the beginning of the space launch era (since at least the Titan I ICBM development) because they present the only practical way of getting higher performance from a size limited package due to the fundamental limitations of combustion chemistry, but they carry such severe constraints and risks that no one has implemented it in operation. As recently as the late 'Nineties, McDonnell Douglas (now Boeing) and Lockheed Martin both looked at using densified propellants to achieve better performance from existing designs and concluded it was not cost effective.
I’m not certain where the notion that there is liquid helium in the COPV tanks but this is not the case. SpaceX loads chilled gaseous helium into the COPVs which is heated and released for ullage (filling up the volume left by consumed propellants to maintain sufficient pressure) during stage operation. It is true that COPVs are not typically submerged into cryogenic fluid in operation, but one of the ways of testing COPVs that are used for low temperature operation is to thermal cycle them using a supercooled liquid nitrogen bath to ensure that they can endure sufficient temperature cycles without seeing liner separation or thermal stress cracking. The explanation for the failure appears to be an energetic reaction between the LOx and the carbon overwrap, presumably ignited by friction within the overwrap. SpaceX has not, as far as I am aware, presented evidence of testing or analysis to substantiate this but it seems like a plausible mechanism, albeit one that has potential design implications.
The claim that “The payload increase from densification is certainly less than the payload hit from reusability,” is very probably not true. The amount of propellant necessary to return the first stage back to a powered landing depends upon the trajectory but can be as low as 5% for a downrange (barge) landing, and even a return-to-launch-site landing is probably only ~15%, because the post-separation booster is so light and much of the energy to slow the stage is provided by atmospheric drag. Densification is giving SpaceX up to a 30% improvement in total impulse delivered to the payload and is absolutely crucial to achieving the upper range of the advertised capability for payload mass or GTO/GSO parameters. SpaceX would realize some amount additional delivered capability by removing the landing legs, attitude control system, and other hardware associated with the first stage return capability but that is actually a relatively small portion of the dry (unloaded) mass of the stage and is only represents a small fractional increase per unit mass of final payload.
The notion that it is ‘safe’ for the crew to be in the capsule during propellant loading because it has a launch escape system (LES) is equivalent to placing your faith in automotive airbags to allow you to drive recklessly down the highway. A LES is a last resort system to try to remove astronauts from a hazardous situation by subjecting them to accelerations and motion that is near human tolerance. There has only been one actual use of a LES in practice (Soyuz T-10-1) and in that case had sufficient information to actuate a couple of seconds before the rocket it was sitting on exploded. In the case of the F-29 failure, there was no warning of the imminent failure from instrumentation, and thus, the LES would have minimum time to respond. Fueling rocket launch vehicles is not like fueling your car, and it is always considered a hazardous operation to be done without people present on pad since the early days of rocketry after a few very near misses. A system that obligates the crew to be in capsule during the fueling operation is inherently risky to a degree that is beyond the normal tolerance for risk for crewed missions even by 'Sixties standards.
Although SpaceX has demonstrated the technical capability to recover the first stage, has successfully static fired the returned engines, and plans to refly a stage in the near future, the fiscal case for doing so remains unclear. Elon Musk and Gwynne Shotwell were originally promising order-of-magnitude reductions in cost (>90%), then 75% (the purported portion of cost of a Falcon 9 vehicle), more recently a modest 30%, and within the last month that discount dropped to 10%. They also continue to present the rationale that once a stage has been flown it is inherently more reliable by virtue of flight demonstration, which ignores the fact that modern rocket launch vehicles, including the Falcon 9, are not as mature or have sufficient ability to safely recover from a failure automobiles or airliners and just by virtue of operating near material capability limits under extremes of vibration and thermal stress have a very limited life under conditions in which the failure of a single subsystem can result in loss of vehicle.
The use of solid propellant boosters to augment liftoff thrust and get the vehicle moving (thus reducing gravity drag losses even though solid boosters have relatively poor propellant efficacy) as merit in general but would require structure to mount to the Falcon 9, and given their horizontal processing flow (vehicle is assembled laying on rails and then erected at the launch pad) is not really practical, nor does it really fit with SpaceX plans of high launch volumes. There are only two companies still producing large solid propellant rocket motors, and neither does so economically at high volume. Solid propellant motors also have significant logistical limitations that are not consonant with the way SpaceX operates so I doubt they would consider using solids for thrust augmentation even if it would work technically.
Stranger
SpaceX did achieve ~30% extra performance from their “Full Thrust” upgrade package, but not all of that is from densification. They stretched the second stage, reduced structural mass, and increased overall thrust. Some/most of the thrust was due to subcooling but it was partly just uprating. Saying that the full 30% is attributable to densification seems dubious, though I couldn’t say what the exact breakdown is.
SpaceX has said that the payload hit for barge landing is about 15% and 30% for return-to-launch. They could probably optimize that further but it increases their risk. They already failed one landing because the remaining fuel required a three-engine “hoverslam” that their control system couldn’t quite handle. They’d rather use a more comfortable but less-efficient single-engine landing.
So perhaps “certainly less” was stronger than is warranted; I’ll say “in the same ballpark of” instead.
That’s not quite my argument. There’s no doubt that fueling a rocket is a dangerous operation. But a fully-fueled rocket is also a danger. Not as much, certainly, but it is still a highly dynamic system and under the wrong conditions could easily fail.
Boarding a fueled vehicle is therefore a risk. This isn’t exactly controversial–the Shuttle famously had a tower escape system that transported the astronauts to a protected bunker in case of an accident. Obviously, this system had some limits and would probably only be effective when there was some kind of failure that hadn’t quite progressed to the giant fireball stage.
I’m just suggesting that, depending on how the numbers work out, it isn’t obviously wrong that the gains from protecting astronauts from “static” pad accidents could exceed the potential losses during fueling accidents.
To be more concrete (using some made-up numbers), suppose that rocket X fails 2% of the time during fueling and 0.5% of the time while fueled during the boarding process. The LES has a 95% success rate while the tower escape is 50%.
Late boarding thus has a 0.5% * 50% = 0.25% chance of crew loss. Half exposure to boarding failures but no exposure to fueling failures.
Early boarding would have a (2% + 0.5%) * 5% = 0.125% chance of crew loss. It has exposure to the more dangerous fueling operation but somewhat mitigated by the LES.
Like I said, made-up numbers, and I’d expect that both NASA and SpaceX have a more sophisticated performance model, but in any case I can see them coming to different conclusions even if both optimized for overall crew safety.
Yeah. Here’s a video of some LOX and oil being shocked by a falling weight. It detonates quite nicely. Trapped liquid oxygen would presumably be squeezed out from the COPV layers, but solid oxygen would be trapped and get squeezed at high pressure. I wonder if anyone’s characterized the reaction between oxygen and carbon at COPV pressures.
I wonder if SpaceX Martian ambitions are not, in part, behind their recoverable first stage business. As mentioned before they are not shy of piggybacking their R&D to commercial launches; as you say the economic case for reusability is sketchy but if they’d have a further incentive for developing technology that could be used on a rocket that can land and take off again in, oh let’s say Mars, it may explain why they’d pursue that path.
A rocket that can land and take off again, on Earth, is cool but arguably doesn’t make much sense (economically at least), but a rocket that can land and take off again from Mars is the only thing that would make sense.
In a little more detail, Musk stated that their leading hypothesis was that frozen oxygen formed between the fibers of the COPV. With expansion of the COPV, that could produce sufficient pressure for ignition.
However I’m not exactly clear on the temperatures and pressures involved. For that explanation to be true, clearly SpaceX believes that something is below the freezing point of oxygen. Liquid helium would be cold enough. But I’ve also seen COPV tank pressure figures in the several thousand PSI range. At the temperature of the surrounding oxygen, I believe that means the helium is a supercritical fluid.
I’ve also heard that helium in some phases will actually get colder as it is compressed, unlike most fluids. Though I haven’t seen any solid figures showing that this phenomenon is relevant at the temperature and pressures involved.
Can anyone shed a little more light on this?
I can see the grad papers now “Effects of interstitial compression on various crystallographic phases of oxygen”
IMO (and I doubt that is some great insight nobody else has noticed) is yes THAT is a major component of Musk’s plans.
And it probably makes more sense than a rocket with wings that lands like an airplane…
Probably the final anomaly update.
The helium pressure vessels (COPVs) have an aluminum liner which prevents the helium from escaping (the carbon-fiber overwrap, although it has a high tensile strength, is porous to helium). The update claims that it had “buckled”, which I suspect means something like the small creases you get when smoothing aluminum foil onto a curved surface.
The buckles alone aren’t a problem as the liner is not a structural component of the COPV; all that matters is that there are no breaks in the surface. However, they did allow a place for liquid oxygen to pool (since LOX can infiltrate the carbon overwrap as well).
The trapped oxygen was in contact with carbon fiber and the loading was a potential cause of friction, which can cause it to ignite. Worse, the temperatures were such that solid oxygen could form, which is more subject to ignition and would not get squeezed out.
A change to their loading procedure should eliminate the problem, although a COPV design change to eliminate the buckles is the longer term solution and will allow them to resume their fast loading method.
I’m a little surprised that SpaceX allowed these buckled liners to pass their QA, but maybe this is a known defect with COPVs and not traditionally considered a problem.