Chances good for NASA Artemis SLS Moon launch on Saturday NASA will try to launch its Space Launch System (SLS) rocket to the Moon on Saturday after its first attempt on August 29 was scrubbed due to what turned out to be a faulty sensor on one of its core engines. The flight is the first-ever proper trial of the super heavy-lift rocket. It was designed for the US space agency's …
It's not flight-critical because it's not for flight... it's for getting the engines cold enough that running large amounts of cryogenic oxygen/hydrogen through it won't do bad things.
It's the primary sensor, but it's not the only sensor. There's also temperature sensors in the tank and the vent, so that's how they know the sensor's "off" because it doesn't match the temperature it should be between those 2 points.
The problem is, it's an integral part of the engine. It would require rolling back and a lot of time pulling the engine and either putting a new one in, or disassembling it and replacing the sensor. Then after you do that, you've got to do another "wet dress" to qualify it for flight.
That would be 3 months of delay at least, because it's a lot of work.
Whether 'tis nobler in the mind to suffer the doubt and uncertainty of unknown temperatures, or to take Artemis to the vertical assembly building, and by fitting a new temperature sensor end them.
The solid rocket boosters were stacked 2021-01-07 which started the clock on the 12 month certification validity. That 12 months figure is based on limited data as no-one has kept a large number of SRBs stacked and idle for years just to see how long they last. At some point the propellant is going to sag and crack. Cracks will cause the propellant to burn more rapidly than required leading to a pressure build-up and RUD. The propellant is measured regularly and so far those measurements have shown the SRBs are as safe as ever. Adding an extra few months delay risks the SRBs dying of old age and that would come at a steep cost.
There are plenty of SRB segment casings. These were re-usable parts that have flown on several space shuttle missions. Another set could be filled with propellant, transported across 5 states, recovered from a collapsed rail bridge, sent back for re-certification then brought to the VAB for stacking which would reset the 12 month counter. The launch abort system, Orion Capsule, service module, and upper stage could all be de-stacked so the core stage can be removed from the old SRBs which could then be replaced.
SLS was constructed from components that were known to be difficult to operate and the design has been thoroughly optimised for cost plus delays. Now that there is some kind of deadline, launch/delay decisions have become really difficult and will be far tougher when Artemis 2 is ready to be delayed in May 2024.
@Gene Cash: I think "not exploding prematurely" is a flight-critical element, but I understand the distinction you're making.
@Gene Cash and Flocke Crowes: thanks for the education on this!
My I.T.-based paranoia/experience makes me wonder things such as, "Is the sensor truly-bad, or is there a physical issue, e.g. a backwards-installed bolt+nut combo abrading insulation from a wire and causing an intermittent, partial short-circuit which could cause other system failures, or is there a software fault which manifests only under certain conditions, and which could cause other system failures?". Kudos for them using a design which has backup sensors, and kudos for them noticing somerhing was wrong.
Presuming they launch without noticable problems, I hope they recover the unit postflight, disassemble it, and find the truth of the matter.
The whole thing is now disposable.
This is the last hurrah of the Shuttle engines and SRBs.
One bit I really don't understand is why they're not recovering the SRBs. They even had to make new endcaps specifically to remove the capability.
There was early talk of catching a detachable engine block using a helicopter, but that was unsurprisingly quietly dropped.
TBH, a lot of the design feels very much like they know damn well the SLS will be cancelled before they've used up the warehouse full of Shuttle main engines and SRB casings, and don't care that they'll have learned nothing about engine design and precious little about anything else by then.
On the other hand, it'll be spectacular, and will hopefully inspire more people to keep funding NASA et al so the Moonbase and Mars trips happen anyway using the commercially viable launchers later on.
So, launch critical? If it does "bad things" like a crack or burn a hole through the nozzle at launch causing a RUD it would still be a big setback. One that I would think they would like to avoid at all costs. The statement from the NASA chief engineer reminds me too much of previous statements made about well known problems with the Space Shuttle. Like I said in a previous post I am very conflicted about the usefulness of the SLS for the proposed space missions for it, SpaceX's approach is much, much better in every way. But I still want it to succeed mainly to get some value for the money we spent on it. I was lucky enough to watch the first time we landed on the Moon and I would like to see us go back to establish a more permanent presence around and on the Moon. Then, Elon willing, on to Mars. Unfortunately I will probably not be around to watch that.
The bloody thing had better take of tonight.
I'd arranged for a drinks and nibbles party at the Meldrew residence and we had to call the whole match off!
The "Extra Special" sausage rolls bought by Margaret and Mrs. Warbouys expire tonight at midnight!
If that bloody craft hasn't blasted of by then, then NASA better start praying, we shall be suing for the cost of rolls and disappointment, we estimate a law suit of at least 22 USD.
Seriously though cannot wait to see this launch.
Leaving things like that to chance is too risky.
Instead since we know that the majority of Shuttle launches weren't catastrophically destroyed by falling ice we will install special ice cannons to launch lumps of ice at the aerodynamic surfaces, thus reducing the risk of destruction to <1%
Basically persistent leaks that lasted IIRC about 18 months.
Root cause. Rocketdyne (the SSME contractors) used LN2 to simulate LH2 at 4x the operating temperature of LH2
No leaks at 80K. Only when they tried the tests (eventually) at LH2 temps did they find the leaks. :-(
Nothing simulates LH2 except a)LH2 or b)GHe.
BTW North American Aviation (Rocketdyne's parent) who also built Shuttle built like a warplane. IOW you have so much redundancy you fly the mission anyway if 1 sensor's a dud and you have 2 others (as they had in the base of the ET LH2 tank) and a sensor in the downpipe and a timeout coded into the engine management (so the SSME's never ran O2 rich) launch the f**king mission. It's got to hold its s**t together for about 6 minutes (like the booster on SLS in fact) and like the booster it's completely expendable
Is anyone else wondering if SX is holding off trying to launch SS to orbit before NASA because it's bad policy to embarrass the customer who's missions are probablly much more profitable than their regular lauches?
Including it's pre-history as part of the Constellation Programme Aries V this thing has been under continuous funding since 2004. IE 18 years.
And note the con-tractors on the Orion capsule sucked up so much cash that the only way NASA could get what is the Service Module done was to get ESA to supply it as their fee for access to the ISS
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