I understand that the static test is a general test of pre-launch procedures, but risking a multi-million dollar payload for a test seems remarkable. Couldn't they use a mass simulator or something? Do they fuel the payload as well for the test, and couldn't that be done separately?
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$\begingroup$ I was wondering this myself! $\endgroup$– Organic MarbleCommented Sep 2, 2016 at 2:13
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1$\begingroup$ I think we are missing the point. The explosion seems to happen during fuelling upper stage and not during the test. In other words, the explosion would have happened either way. $\endgroup$– ZeezerCommented Sep 2, 2016 at 9:05
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$\begingroup$ SpaceX prides themselves in lateral loading. It'd be prohibitively expensive to static fire, then raise the payload vertically. $\endgroup$– TylerHCommented Sep 2, 2016 at 14:30
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$\begingroup$ This saved them a day, a week and 500,000 bucks $\endgroup$– IsrorianCommented Sep 4, 2016 at 18:55
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3 Answers
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The static test wants to be done relatively close to launch day, to minimize the likelihood of anything happening to the engines between the test and the launch.
The more conservative procedure is to attach the payload after the static test, but they'd have to lower the rocket, move it back indoors, stack the payload, take it back out and reelevate it.
Static firing after payload integration saves a day or two, but puts the payload at risk if something like this happens.
answered Sep 2, 2016 at 1:00
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$\begingroup$ Thanks. That sounds much more sensible now, as far as calculated risks go. $\endgroup$ Commented Sep 2, 2016 at 2:34
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2$\begingroup$ It's also an opportunity to validate the entire stack and shake out any issues. $\endgroup$ Commented Sep 2, 2016 at 3:02
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2$\begingroup$ @JohnBode Especially the 'shake out' (literally) $\endgroup$– user10509Commented Sep 2, 2016 at 6:54
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5$\begingroup$ I vaguely remember seeing something yesterday that claimed they actually used to do the static fire without the payload but changed the procedure specifically in order to shave 1 day off the launch prep. Remember: they're all about rapid re-usability. They want to get to the level of airplanes: land, refuel, stick another payload on top (possibly while refueling), launch. $\endgroup$ Commented Sep 2, 2016 at 14:50
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2$\begingroup$ Apparently, SpaceX used to do "topless" static fires, but started offering static fire with payload this year as an option. In other words, the customer explicitly opted into the static fire with payload in order to shave one day off the launch campaign. They had the option to order (and pay for) a topless static fire but chose not to. $\endgroup$ Commented Sep 4, 2016 at 8:55
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The Transporter/Erector can only lift a complete first and second stage. That is not to say it requires the payload, but to say it requires the second stage.
Taking your question to next logical step, why do a static fire of the first stage engine with a $20 million second stage on board?
Well, they need it so the T/E can grab it and hold the complete stack.
A better question might be, for a Static Fire, why were they fueling the second stage at all?
Having said all that, there is an additional reason to test fire with the second stage, fueled, and with the payload attached is that the vehicle behaves different fully configured than in pieces, and this is a static test of the entire vehicle.
From Reddit:
According to Peter B. de Selding on Twitter, SpaceX implemented an optional policy of attaching the payload to the vehicle earlier this year with some “insurer upset”, as it saves about a day during of launch preparations, and allows SpaceX to monitor the payload’s interaction with the vehicle. The customer can decline this option if they wish.
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6$\begingroup$ I don't see how this answers the question. The question asks why the payload was there but you only address why the second stage was there. $\endgroup$ Commented Sep 2, 2016 at 9:49
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SpaceX performs a test fire of all their rockets at the pad, lasting for a few seconds. There is an option to place the satellite on top of the rocket, or to delay the launch by a single day. As the static fire test has been considered a low risk to the spacecraft, this has often been done, as a day can cost the commercial operators lots of money, and there has been low risk. Furthermore, it provides a realistic test of what the spacecraft will do on launch day. They can determine what the thermal environment will be like on the fairing, which might need to be adjusted for flight day. It also is a good chance for the satellite team to have a dress rehearsal.
As I understand it, there is a cap that is placed on the rocket if it doesn't have the payload. That cap needs to be removed, and the fairing attached, which takes a day.
answered Sep 3, 2016 at 21:32
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$\begingroup$ This "test" of what could go wrong was certainly realistic alright! But what good did it do to lower the risk to the payload? As a matter of fact, these "tests" have increased the loss of payloads by 100% thus far. Thoughts go to the Soviet Nedelin catastrophe in 1960. Since then people are kept away from launch pads during fueling, so that the engineers don't have to run away burning. Maybe payloads should be kept out of the way too. $\endgroup$ Commented Sep 4, 2016 at 8:01
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$\begingroup$ Mating the payload takes a day and dozens of engineers. Keeping the payload away during fueling means that it needs to be mated after fueling. So, you want to have a team of dozens of engineers working on a fully-fueled rocket for an entire day? How is that going to be safer? In fact, it isn't even possible: there is no such thing as "after fueling". There is no way to keep the fuel cold enough and pressurized enough for even one second, let alone a day. Fuel constantly boils off and needs to replaced. "After fueling" is "during fueling". $\endgroup$ Commented Sep 4, 2016 at 8:48
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$\begingroup$ @JörgWMittag Doing it once instead of twice should halve this kind of risk. When the payload is mounted, then maybe "testing" isn't a good idea. Doing the test (or dress rehearsal) with the payload is optional and up to the satellite company, AFAIK. And wasn't this payload owned by an Israeli company which is now negotiating being sold to Chinese investors? Sounds like bad timing for taking additional risk. $\endgroup$ Commented Sep 4, 2016 at 9:29
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$\begingroup$ For the record, after a static fire the rocket is defueled before it is used. It is up to the satellite company. It has never really been considered an additional risk until this incident. $\endgroup$– PearsonArtPhoto ♦Commented Sep 4, 2016 at 10:01