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Space is still hard

The folks at NASA had hoped to send astronauts into space on an orbit that would have seen them disappear around the far side of the moon this month.

Sadly, that is not to be.

As if to prove just how hard rocket science really is, the launch of the Artemis II mission, planned for later this month, has been scrubbed.

Despite the huge sums of money that have already been spent on this mission, the chances of a February launch are now zero and we're told that it won't be until March at the earliest before a launch is possible.

The cause of the hold-up is a perenial one -- leaking hydrogen.

Ever since the Space Shuttle, hydrogen has become one of the key fuels for manned space missions conducted by NASA. It's cheap, it's light (which gives it a great energy-density when liquified) and it's non-polluting.

Even the upper stages of the beloved Saturn V booster used hydrogen as the fuel, but the first stage used kerosene and liquid oxygen -- making fuel leaks much less likely.

Unfortunately, due to the very small size of hydrogen molecules, it tends to escape very easily from containment, especially where there are fittings and fixtures involved.

Adding to the problem is the cryogenic form in which the fuel is kept when the rocket is being fueled. This means that pipes, flanges, mating surfaces and gaskets all undergo significant changes in physical dimensions as the chilly (-253 deg C) fuel is poured into the tanks of the rocket. Maintaining a gas-tight seal under these conditions is nigh on impossible, despite our best efforts.

Given the futility of attempting perfect containment, engineers have set a maximum allowable rate of leakage at four percent. If things go above that then there's a very real risk of explosion in the vicinity of the rocket as gaseous H2 mixes with regular air during the refueling process.

When you consider that the main SLS (space launch system) rocket holds over two million litres of liquid hydrogen, even a small leak (percentage wise) means a massive volume of highly explosive gas being liberated into the nearby vicinity.

It's worth remembering that the recent aborting of the NASA Starliner capsule's mission to return astronauts from the ISS was as a result of helium leaks in the thruster units on that craft. If they can't keep the comparatively much larger helium molecules confined, what chance hydrogen?

Once again I find myself marvelling at the way NASA made space look so easy back in the 1960s and 1970s. They sent men to the moon six times with no loss of life, despite major issues with Apollo 13. These days, we're having trouble even getting off the launch-pad.

Carpe Diem folks!

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