[oconnor663]

I don't know anything about this particular launch, but one reason static fires sometimes load more fuel than you'd think is that the hold-down clamps aren't rated for the total thrust of the vehicle. Launch thrust is usually 1.2-1.6x the launch weight (if it's <1x you will not go to space today), so after subtracting gravity you've got 0.2-0.6x the weight acting upwards on the clamps. But rockets are mostly fuel by weight, so if you static fire it nearly empty, then that gravity term goes to ~zero, and the clamps have to hold the full 1.2-1.6x. You could overbuild them to handle that -- which isn't the end of the world, because they don't need to fly -- but it can be easier to just add extra fuel and detank it afterwards.

[HarHarVeryFunny]

I don't know if it'd be a factor for BO, but doesn't the ignition sequence sometimes use gravity feed to begin with, before the turbo pumps kick in, with the height of the fuel tanks meaning that full tanks add a few atm of pressure. Therefore, a test without full tanks isn't exactly replicating the normal ignition sequencing conditions.

[angled]

Why use fuel, though? Is there something about its specific density and weight distribution that rules out using other types of ballast?

[Polizeiposaune]

Where would you put the other ballast?

You've got two large tanks making up the bulk of the stage's structure - one for oxidizer, one for fuel. They have large diameter pipes that feed propellant to the engines. You can't mix the ballast with either the oxidizer or fuel, and you can't feed the engines from anywhere but the propellant tanks...

[gorgoiler]

If you are writing an integration test for some new and potentially bug-ridden code then you might opt to mock, say, the database connection.

Doing so risks having to write so much database logic — with all the potential for getting that code buggy as well — that it’s often better to avoid the mock and test the entire system, end-to-end.

This was an end-to-end rocket test.

[oconnor663]

The vehicle is designed to hold all that fuel, plus whatever payload it carries on top, but it's not designed to have heavy loads attached to it in any other way. Rockets are so intensely optimized for weight that sometimes they're barely strong enough to stand upright if you fuel them the wrong way: https://www.youtube.com/watch?v=imkdz63agHY.

[arjie]

That's a great video! Thank you for sharing it. A rocket is more like a soda can than a building but it's hard to relate when you see such a massive object!

[oconnor663]

You can see a similar effect after the explosion at the end of last week's Starship test flight. If you look at where the flames are coming out after the first fireball clears, it kind of pancakes under its own weight there: https://www.youtube.com/live/Zi2SU98BAD8?t=5735s

[arjie]

Oh huh. You really can. I didn't pick up on that the first few hundred times I watched it. That's really cool. It kind of splats down into a 2-d rectangle.

[AceyMan]

It's been said that the most amazing engineering of the whole Shuttle program was the external fuel tank (and there is one with the static display of Endeavour here at the California Science Center in LA).