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On 2018-05-26 21:16, Jeff Findley wrote:

No. SpaceX cools the LOX almost to the point where it would start to
become solid. They call it "sub-cooled".

thanks. Knew about kerosene being cooled, didn't realize they did that
to LOX too.

How long does SpaceX take to load rocket with both LOX and kerosene? And
how long before launch does SpaceX expect crews to be strapped in, hatch
closed?

You can Google this yourself. Look for the time-lines of one of the
launches. It's surely called out in the launch videos on YouTube.

It's Memorial Day, so I'm thinking more about my family members who have
served their country.

The "conflict" may exist because SpaceX wants the extra "cold"
performance to raise odds of successful landing whereas NASA isn't
inteested in that part, only interested in getting crew to ISS. (which I
assume is not straining performance and may not require the "extra cold"
fuel. (I have no data on this, just theory/speculation).

It gives them a higher fuel load (higher density means higher mass for a
given volume) so the performance is higher. This does allow for more
fuel to land the stage. But that's not really the primary reason.

The primary reason is to keep the crewed launches the same as all the
other launches in the way that the Falcon 9 is fueled, launched, and
flown. When you make things different you introduce the possibility
that there could be an error, anomaly, or other such issue with the
crewed launch because it's the exception, not the rule. In other words,
you could actually be increasing the chance of failure by doing things
different for the crewed flight than for the more numerous uncrewd
flights.


You raised ground crew safety. There is a corollary to this: it is safer
to have a rocket being fueled with no activity near pad, no equipment
moving, no motors starting/stoppiong, no cars/trucks etc. So it isn't
just the lived of ground crews, but also not having them there likely
reduces risks of things going kablouee.

Yes. We don't need any of that activity around a vehicle being loaded
with LOX/kerosene.

Note: comemrcial aircraft have various restrictions on fueling aircraft
when there are passengers on-board vs boarding/deplaning vs empty. (and
these vary depending on fuel being used).

Cite?


Google FAA aircraft refueling regulations.

In the case of a Falcon 9, the concern is with the LOX (which makes
pretty much anything burn) and helium (extremely high pressure) than
with the kerosene fuel. In fact, fueling of aircraft with kerosene type
fuels with passengers on board is permitted by the FAA. Gasoline type
fuels, on the other hand, is more dangerous, so it's not permitted to
fuel an aircraft with such a fuel with passengers aboard.

Jeff
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