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A Fiery Finale for a Rocket That Brings the Heat

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Science|A Fiery Finale for a Rocket That Brings the Heat

https://www.nytimes.com/2024/03/28/science/delta-iv-heavy-rocket-final-launch.html

April 2: This article was updated to include a new launch date.

The ignition of the Delta IV Heavy rocket is perhaps the most visually striking liftoff you'll ever see — the rocket seemingly burns itself up on the launchpad before it heads to space. Now, the very last Delta IV Heavy ever is on the launchpad.

Liftoff was scheduled for 2:45 p.m. Eastern time from Cape Canaveral, Fla. Less than four minutes before the launch was to occur, flight controllers paused the countdown because of an issue with a component that provides pneumatic pressure to the rocket.

After a Friday launch time was announced, United Launch Alliance, the maker of the rocket, provided an update on Thursday night in a statement, saying that "more time is needed to instill confidence in the system," before another flight attempt. In an emailed announced on Tuesday, the company said it would attempt to launch the rocket again on April 9 at 12:53 p.m. Eastern time.

Before Thursday's scrubbed flight, U.L.A. officials shared their feelings about the Delta IV Heavy, which is to carry a secret spy satellite for the National Reconnaissance Office on its final mission.

"A bittersweet moment for us," Tory Bruno, the company's chief executive, said during a news conference on Wednesday. "This is such an amazing piece of technology. Twenty-three stories tall. Half a million gallons of propellant. Two and a quarter million pounds of thrust."

When it does launch, it will look as if it is catching on fire, with flames racing up the sides. That is by design.

Video

Fiery scenes from a Sept. 24, 2022, liftoff of a Delta IV Heavy rocket. Video by United Launch AllianceCreditCredit...

The Delta IV Heavy burns ultracold liquid hydrogen, which is a high-performance fuel. In the final part of the countdown, to cool down the engines and prevent a sudden temperature shock that could cause cracks, liquid hydrogen starts flowing through the engine into the flame trench.

But when the hydrogen warms above its boiling temperature of minus 423.2 degrees Fahrenheit, it turns into a gas. Hydrogen is lighter than air and rises upward. When the engines ignite, so does that cloud of hydrogen — like a space-age Hindenburg.

"A very dramatic effect," Mr. Bruno said.

The rocket designers of course took this into account and applied sufficient insulation to the boosters to keep the rocket from actually burning up. The orange shade of that exterior takes on a burned-marshmallow sheen as the rocket leaves the Earth.

"And away she goes," Mr. Bruno said.

Photographs by United Launch Alliance. Mobile photo illustration by Antonio de Luca.

A correction was made on 

March 28, 2024

: 

An earlier version of this article misquoted Tory Bruno, the chief executive of United Launch Alliance. He said in a news conference that Delta IV Heavy produces two and a quarter million pounds of thrust, not a quarter million pounds.

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