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They do the tests to validate that this rocket won't turn into a cruise missile, headed for the nearest residential area. Not an impossible scenario. Lots of en
by mabbo 10y ago
They do the tests to validate that this rocket won't turn into a cruise missile, headed for the nearest residential area. Not an impossible scenario. Lots of energy stored up in one of those rockets.
Just like when we test software, they want to have everything as close to what they would expect on launch day as possible (2 days from now). All the stresses, the structure, etc. That means putting stage 2 and the payload on top of the main rocket before the test starts. They probably did a lot of tests before the payload was on board as well, and those didn't reveal whatever flaw has caused this issue.
Yes, it sucks that the payload was lost but there will have been insurance to cover the loss. No human lives lost, no cruise missile scenario, no out of control fire... this is the best case scenario for a rocket failure.
- ygra 10y ago> They do the tests to validate that this rocket won't turn into a cruise missile, headed for the nearest residential area. In that case the rocket has a flight-termination system, though, which should activate as soon as it veers too far outside the planned/expected parameters of the flight.
- Gracana 10y agoThis discussion reminds me of the failure of the first Ariane 5 launch. The flight-termination system was activate erroneously, and the payload was not insured. Ouch. http://www.esa.int/esapub/bulletin/bullet87/cavall87.htm http://www.esa.int/esapub/bulletin/bullet87/cavall87.htm https://around.com/ariane.html https://around.com/ariane.html https://en.wikipedia.org/wiki/Cluster_%28spacecraft%29 https://en.wikipedia.org/wiki/Cluster_%28spacecraft%29
- twic 10y agoThat's not what happened - the rocket went out of control due to a software bug allowed by over-reliance on unit testing, and was quite properly deliberately destroyed. But yes, Cluster was run on the cheap, hence the use of the Ariane 5 test flight, and didn't have insurance.
- dalke 10y ago"Over-reliance on unit testing"? I have a somewhat different read from the inquiry board report, which says it was a "systematic software design error." Yes, inadequate testing, and a belief the working code for Ariane 4 meant it was validated for Ariane 5 were certainly contributory, but I think it's unfair to single out an over-reliance on unit testing. The board argues that there was a bias towards believing the software does not have an error. Thus, any out-of-range value is interpreted as a hardware error, which means the CPU should shut down. There was a decision to not include Ariane 5 trajectory data in the SRI requirements and specification. Thus, while tests were rigorous at the equipment ("unit") level, and there were system tests, they didn't test that case. This is test design failure. In addition, the board says "the review process was a contributory factor in the failure." I can see how those can be aspects of "over-reliance on unit testing", but it doesn't explain, for example, how some of the variables from Ariane 4 were protected from overflow exceptions but others were not.
- twic 10y agoYou have quite fairly picked me up on a cheeky exaggeration. Lots of things had to go wrong to cause the Ariane 5 failure - including bad handling of overflow, as you mention. But to my mind, the universal last line of defence against any kind of mistake is an integration test: put all of the parts of the system together, feed them real input, and verify that you get correct output. Arianespace did not do that. Well, until they actually launched it. It was a test flight, right? It proved to be an essential and very effective test.
- dalke 10y agoThat means there was an under-reliance on system testing, which I agree with. It doesn't imply there was an over-reliance on unit testing any more than it implies there was an over-reliance on analysis or over-reliance on the expectation of developing bug-free software.
- david-given 10y agoIf anyone's at all interested in risk analysis or robust software, it's totally worth finding a decent writeup on the Ariane 5 failure --- it's a fascinating postmortem in just how many unexpected little things together added up to a big boom. Everything is incredibly obvious in hindsight, of course, but making things obvious is largely what hindsight is for. And once you've finished reading that, go look up the Therac-25...
- Phlarp 10y agoFor more context, all (edit: American!) rockets for decades have had onboard self destruct systems and a "Range Safety Officer" on the ground whose entire job is to determine if and when to deploy this self destruct system. The cruise missile scenario is highly unlikely as the rocket itself would be destroyed soon after leaving its intended trajectory.
- cstross 10y agoNot all rockets: https://en.wikipedia.org/wiki/Intelsat_708 https://en.wikipedia.org/wiki/Intelsat_708 (China, CZ-3B, Intelsat 708 payload, the launcher flew off-course and crashed on a village in 1996: by some estimates 200-500 civilians were killed.)
- ygra 10y agoAll rockets launched in the US have to have one, though :-)
- dalke 10y agoThat links to http://www.thespacereview.com/article/2323/1 http://www.thespacereview.com/article/2323/1 where one of the comments is: > Like Russian vehicles, there is no flight termination system that receives ground commands onboard Chinese launch vehicles. Only US and ESA launch sites have such a system. Correction, Falcon 1 did not have such a system for launching on Kwaj.
- dogma1138 10y agoThat's because usually the US and ESA/France launch from densely populated areas. The launch pad at the Kennedy Space Center/CC is effectively about 50 mile from downtown Orlando, Baikonur is in the middle of nowhere.
- T0T0R0 10y agoOkay, rockets that can go very high, can still crash very far away. An unpredictable, malfunctioning rocket could still million-to-one itself onto a school bus filled with children, halfway across a continent.
- deleted 10y ago[deleted]
- TrevorJ 10y agoThat doesn't mitigate the danger really.
- mabbo 10y agoIt too should work. Just like rockets shouldn't explode while loading fuel before a test firing. But of all systems I never want to have to test in production, the flight-termination system is at the top of my list.
- dTal 10y agoNitpick: you're thinking of a ballistic missile. Cruise missiles are more like exploding fixed-wing drones. The V-1 flying bomb was a cruise missile, and the V-2 rocket was a ballistic missile.
- Phlarp 10y agoIf a fully loaded (cryogenic fuel + oxidizer) SpaceX rocket did a belly flop into downtown Orlando I suspect this distinction would be quite meaningless to the locals!
- fizzbatter 10y agoSure but wouldn't most things be meaningless to them at that point? S/he said it was a nitpick, i appreciate the info.
- mabbo 10y ago'Cruise missile' has always sounded cooler than ballistic missile, imho. But you are 100% correct according to Wikipedia.
- izacus 10y agoNot sure what exactly are you nitpicking here - ballistic missiles have propulsion for a short time after lunch and afterwards continuing on a ballistic (hence the name) trajectory towards the targets. Cruise missiles have propulsion usually during most of the flight. A rocket straying off course could either smash into city under full power (thus being a cruise missile) or have its propulsion cut off remotely beforehand (thus being a ballistic missile), depending on a scenario. What kind of a correction were you making?
- caf 10y agoCruise missiles are designed to rely on aerodynamic lift (and typically use air-breathing engines, although there have been some "boost-glide" weapons that used rocket engines).
- tamana 10y agoInsurance isn't magic pixie dust, it just moved the cost around.
- stcredzero 10y agoThey do the tests to validate that this rocket won't turn into a cruise missile, headed for the nearest residential area. Not an impossible scenario. Lots of energy stored up in one of those rockets This is a big plot point in the "Twin Spica" series.
- _puk 10y agoCould they not have mocked the payload?
- MicroBerto 10y agoThe question nobody is answering....
- mandevil 10y agoMocking a six ton payload is actually fairly expensive, to get the cg, vibration etc. right. A lot more difficult than payload = mock(satellite); NASA did it for the Hubble but so the ground crew could practice operations and not drop the billion dollar space observatory, not to try and save some money if something blew up during testing.
- xwvvvvwx 10y agoSurely still much cheaper than a two hundred million dollar satellite?
- mandevil 10y agoAnd at what frequency would it save the payload? In 85-95% of cases, payload is safely delivered to space, so the dummy just slows things down. In most of the remaining cases the payload is lost on it's actual ride into space (e.g. the last time SpaceX had a problem, CRS-7) where a dummy can't help. There have been a handful of pad accidents involving loss of payload, but they are very much the exception to the rule about the exception to the rule.
- TrevorJ 10y agoIt is possible to damage the rocket and systems when mating the payload in the faring, which would not become apparent without further testing and somewhat negates the purpose of this test itself.
- grkvlt 10y agoThe payload is mated early to save time by speeding up the launch schedule [1] so a mock payload would have the opposite effect - it would need mated and then removed after the test fire. [1] https://twitter.com/pbdes/status/771411924907094016 https://twitter.com/pbdes/status/771411924907094016