Two Small Unrelated Stories

So Why Did the Delta IV Heavy Set Itself on Fire at Every Launch?

Even Tory Bruno, CEO of ULA, referred to the Delta IV as "the most metal of all rockets, setting itself on fire before it goes to space." Setting itself on fire was because of a design choice, but what was it? And why was it?

A shot of a Delta IV Heavy launch in 2014, found with a web search for "delta iv sets itself on fire." Image Credit: United Launch Alliance

The answer is in the engines used on all three core boosters, the massive RS-68 rocket engines, were developed during the 1990s by Rocketdyne, the same company that developed the Space Shuttle's (and now Artemis') RS-25 engines. These expendable engines were designed to be cheaper and more powerful than the reusable RS-25 engines while running on the same fuel mix of liquid hydrogen and liquid oxygen. 

The fireball phenomenon manifests because of design differences between the RS-68 and the Shuttle main engines and because the RS-68 propellant valve is open longer before the oxidizer starts flowing. Essentially, at engine startup, only liquid hydrogen is running through the engine because it is less chemically active than oxygen.

This hydrogen flows out of the engine, and because hydrogen is very light compared to ambient air, it rises up the outside of the rocket. When the liquid oxygen flow begins, the excess hydrogen is ignited into a fireball. This occurs within the last five seconds of the countdown. This design trade was intentional, and the exterior of the rocket is configured to withstand the fireball.

An imposing fireball during the first moments of flight? I remember people talking like they expected the rocket to explode on its own. That fire is a design feature, not a bug.

A Giant of Theoretical Physics Passed Away This Week

On April 8th, British theoretical physicist Peter Ware Higgs passed away at the age of 94. It was three months short of 12 years ago, on July 4, 2012, when Higgs achieved the practical immortality in theoretical physics. 

That was the day it was announced that collisions between particles at the Large Hadron Collider (LHC) facility — arguably the most ambitious and audacious science experiment ever — revealed the existence of the Higgs Boson.

The discovery of the Higgs boson, named for Higgs himself, has been vital for the field of particle physics. It was the last occupant of the particle zoo that's needed to complete what's known as the "Standard Model of particle physics," the best description we have of the universe on the smallest of scales.

The Higgs Boson, also called the God particle, is generally credited as having been derived in work Higgs was doing in the 1960s. The Higgs field is what gives mass to the other subatomic particles.

I'm going to go out on a limb and say more people who read here regularly will be familiar with the Higgs Boson than a similarly sized readership at the vast majority of other blogs. Not that there's anything wrong with them.

EDIT 4-11-24 0930 EDT: Forgot the link to the source at the top of the second section - on the notice of Higgs' passing.