It’s been more than 40 years since the first successful space shuttle launch. However, as we saw with the recent NASA launch, we still have launch failures. Why is it so tough to achieve reliability in space shuttle launches? Does this apply to all space technology?



It’s been more than 40 years since the first successful space shuttle launch. However, as we saw with the recent NASA launch, we still have launch failures. Why is it so tough to achieve reliability in space shuttle launches? Does this apply to all space technology?


“It’s Rocket Science” is a meme for a reason. To get maximum efficiency, rocket designers are pushing the limits of human technology. Sure, we could more reliably use old technology, but it’s not affordable.

The reason why we have failures so often is because the technology and the physics are incredibly complex. When you’re launching a rocket, you need to make sure that the three ignition systems are working perfectly, that there isn’t a single screw out of the tens of thousands loose, that the weather could not possibly pose a problem. There is so much that could go wrong, and so much at stake (even if there aren’t people on board, launches are unbelievably expensive) that launches get cancelled quite frequently. However, there are so many variables that sometimes one gets missed, something goes wrong, and the launch fails

Part of the issue is that NASA is involved. Any time a government agency gets involved, the project costs 100x more and always has issues. Not saying the people doing the actual work are bad, but communication between outsourced parties is horrendous.

Now imagine SpaceX. All their fabrication and building is in house, meaning everyone involved can meet with everyone else involved. The only reason they talk to NASA is because… well I don’t know why they even keep talking to them. But you can’t go wrong with their rockets these days.

Rockets are extremely restricted by weight, much more than most other technologies. IIRC the Saturn V was something around 3000tons and only delivered a payload of a few single or double digit tons. If the rocket was 1% more heavy it would have basically lost all its cargo potential.

The result is that rockets operate on much lower safety margins than other means of transport. Everything is designed to be just barely strong enough for the expected loads and redundant systems aren’t always possible or particularly practical. A single sensor failure can lead to the loss of the entire vehicle. IIRC there was a proton rocket that just flipped upside down and exploded because a sensor was mounted the wrong way around.

Another aspect is that there is only limited ways to test your product in realistic scenarios. Rockets are crazy expensive and until recently they were entirely expendable devices. „Test flights“ aren’t really a thing when your vehicle has no way to land. The engineers must rely on in flight telemetry which makes it hard to spot faults unless you have a sensor specifically monitoring that part. There was an arianna rocket which exploded because its control software was partially copied from an earlier generation of the rocket. The newer rocket was faster and as a result a sensor ( I think it was an altimeter) exceeded its range of valid values during the early phases of the launch. This wasn’t an issue on the old slower rocket because the system was shut of before it ever flew that high. It never happened during tests because all tests were performed on the ground.

And lastly rocket failures are always spectacular because rockets are basically a giant fuel tank with some high tech strapped on the top and bottom. If it goes wrong it goes wrong with a big boom. In retrospect it’s often a small „silly“ thing, but every part is critical in the rocket.

Take a really big bomb…put it in a big trash can…cut a hole in the bottom …and put a seat on the lid and blow it up. Did it work? Kind of… it did launch the chair 30,000 feet in the air…hmmmmm…were going to need 211.2 times bigger trashcan/bomb to hit LEO. Rinse & Repeat.

Rockets are very complex and operate as close to the limit of their materials as we can. That means there are both more things that can break and they’re more likely to break since they’re under a lot of stress. That’s why we have so many launch aborts. If there’s a minor failure that mission control can’t work around, it’s better to scrub the mission and try again later. Otherwise, it risks a failure in flight which is often catastrophic. A rocket isn’t like an airplane that can fly with an engine out or an instrument failure.

When/if you watch programs showing factories producing things you rarely, if ever, see anything going wrong. In reality, there are problems ALL the time, and things are having to be corrected on a regular basis.

Stands to reason things will go wrong with rockets aswell. Only difference is, instead of a small pile of food on the floor, you get an impressive big bang.

For uncrewed launchers, you wouldn’t want extremely high reliability. Extremely high reliability means making things more robust and heavier. It means adding redundant systems that weigh a lot. Weight that you add to the launcher is weight you have to remove from the payload.

I’ve no idea how the economics pay out for any specific launcher, but if they just plain never fail you’ve built them too strong.

Obvs all this goes out the window for crewed launchers.

“However, as we saw with the recent NASA launch, we still have launch failures.” – What launch are you referring to?

Global / planetary entropy means there are always variables independent to the launch parameters, which cannot all fully and explicitly be accounted for ahead of launch.

Because there is so much data available at the time of launch and we only know where to apply human focus when a problem arises.

One of the reason humans consider hindsight 20:20; you only get the complete data set when you are observant

There are some quality responses here; but a point the other posts dont emphasise is the very narrow specialist nature of the technology.

While there is some overlap with military applications – which have tens of trillions of dollars thrown into them over the last five decades.

Arguably up until recently, **manned space flight is not actually a well funded mainstream industry.** It has a (proportionally) tiny budget, for what is effectively a continued series of research experiments (the launches included).

If major world economies *chose* to throw more time, money, and effort at the technology – you would rapidly see a significant reduction in cost, and an increase in reliability (all the listed problems notwithstanding).

This is what we are finally starting to see with the privatisation of space flight.

Isnt there some thing with the chaos theory being more prevelant the more you scale something up?

The forces involved are huge, and the machines have to be as light as possible. You can’t “over engineer” due to the weight requirements, and even slightly “under engineered”, or even a tiny flaw in the materials, can cause failure. “Just right” is a thin line.

Pretty much every rocket launch is it’s maiden voyage. Sure space x can reuse the rocket, but every component has to be inspected, and possibly replaced. Gaskets, pumps, valves, etc.

It’s fairly easy to build a reliable component that never leaves earth. There are many types of rocket fuels, some of them are toxic, corrosive or kept at extremely low temperatures. All of which wreck havoc on seals and gaskets.

Then during the launch, the rocket is exposed to intense forces, near constant acceleration, the vibration and shockwave from both the fuel burning, and supersonic flight.

Many people here are talking about the difficulty of rocketry, which is huge, but I think many people are forgetting a big piece: sample size.

There are very very few things in this world that happen as infrequently as a space launch. There have only been ~200 crewed flights by NASA and ~5,000 orbital launches by the world.

Cars produced: over 1 billion

TVs produced each YEAR: ~200 million

Aircraft flights per year: ~10,000

No matter what you are doing, if you don’t do it enough, you’ll never become an expert at it, and until you become an expert at it, you can be rest-assured you will have issues.

Read Failure is not an Option. I don’t think there was ever a launch in the Saturn series that didn’t have an issue. There was great Engineering but we got very lucky.

For a successful rocket launch, a million things have to go right
For it to go wrong, only one thing has to fail

In a rocket you will have a couple of thousand parts that each have to work in order for the whole thing to function.

Now imagine you can achieve a failure rate of only 0.1% through good engineering.

That still means a couple of parts on average will fail per launch.

Of course you can spend a lot of time and money to make everything more reliable on its own, but thats greatly diminished returns at some point.

The better way to solve that is redundant systems, so a single failure will have none/only minor consequences

I feel like most professions are like this. Routine surgeries can go wrong. Hard drive manufacturing still produces defective drives. Database conversion always have some unforeseen error after the fact. Bone grafts by my dentist don’t always work. Etc etc etc…

One big consideration is weight vs fuel. If 90% of a rocket is fuel, just to get to near earth orbit, every pound of structure needs 9 pounds of fuel. So the fuel tank needs to be bigger, etc etc etc. Going to Geostationary orbit? More fuel, so more weight. Moon? Mars? Things get heavy really fast.

You can build a bridge to 150% of strength as a back up for worst case situations and aging, and the bridge won’t be that much bigger. It will be heavier, and a rocket fuel/energy budget can’t afford that. That means everything needs to be built – just strong enough – to do the job, and maybe just a little bit more, but no more.

At that point, then you’re into the weeds of vibration, wind shear, rain, turbulence, and other factors that could go past that little bit more. That’s the engineering challenge.