The Decatur Daily December 10, 2006
Hydrogen vs. kerosene
Type of fuel to make major difference for Decatur-built rockets
By Eric Fleischauer
What do liquid hydrogen, kerosene and assured access to space have to do with Decatur?
Lots, now that Decatur is home to the sole production facility for the Atlas V and the Delta IV.
“Assured access to space” is a mantra that served as the main driver for the Pentagon’s support of the United Launch Alliance, a joint venture that consolidates former Lockheed Martin Corp. Atlas rocket production and Boeing Co. Delta rocket production in Decatur. The same mantra will control the internal workings of the ULA plant.
The Pentagon is convinced that the status quo — two separate families of satellite-launch vehicles — is the best way to maintain assured access to space. Problem is, the economy has not supported the luxury of separate and largely duplicative launch production at Boeing and Lockheed.
As Kenneth Krieg, U.S. undersecretary of defense, explained in an August letter to the Federal Trade Commission, “The current and future commercial launch market, ... coupled with the low number of national security launches, makes it extremely difficult for two competing U.S. providers to maintain separate, competing, experienced work forces.”
Stated more bluntly: Atlas might have survived its financial bludgeoning, or Delta might have, but one of the programs was doomed. That expected result was unacceptable to the Pentagon as undermining the goal of assured access.
The same assured-access motivation for ULA’s formation also dictates how the launch company will proceed. While the Pentagon is for sharing information between the two programs in their new ULA home, it is adamant that the products remain fundamentally distinct.
“Economically, combining production makes sense,” said Charles Vick, a senior fellow at GlobalSecurity.org in Washington. “We have to realize how much the launch industry has collapsed since the Cold War.”
And that’s where liquid hydrogen and kerosene — competing fuels in the launch business — come into play.
The Delta IV and the Atlas V, like all rockets, rely on Isaac Newton’s third law of physics: For every action, there is an equal and opposite reaction. Using a controlled explosion in their bottom (first) stage, both rockets move in one direction by expelling exhaust gases in the other.
The more gas it spits out, and the faster it spits it out, the more thrust it has to carry it beyond earth’s atmosphere.
Both rockets also carry liquid oxygen in their first stage. Just like a campfire needs oxygen, the fiery combustion in a rocket’s belly needs it.
Unlike a jet, which uses oxygen in the air to keep its fires burning, a rocket must carry the oxygen with it so it still has a supply when it leaves the Earth’s atmosphere.
The fuel is what makes the Delta IV and Atlas V different animals, and what leads the Pentagon to the conclusion that keeping them distinct is essential to assured access.
Vick said the Delta IV is probably the most reliable vehicle, but it and the Atlas V have unique problems that make maintaining both products important to assured access.
The Delta IV, produced in Decatur for the last eight years, uses cryogenic fuel. “Cryogenic” is a fancy term for “seriously cold” — so cold that gases transform into liquids.
The Delta IV uses hydrogen to fuel its combustion. A tank filled with enough gaseous hydrogen to make the long journey satellites require for Earth orbit would be too large to permit flight, so the hydrogen must be condensed into a usable form by keeping it at a temperature of minus 473 degrees Fahrenheit.
That cooling requirement is one of the shortcomings in the Delta IV that led the Pentagon to insist on a separate rocket family.
Long-term storage of liquid hydrogen is expensive and impractical.
Even in liquid form, hydrogen is less dense than other fuels, meaning it requires a larger tank to hold it.
A larger tank means more weight and more friction during the launch.
To maintain the low temperature of the hydrogen, the manufacturer must coat the tank and all plumbing with insulation, which also adds weight.
The Atlas V uses refined kerosene as its Stage 1 fuel in a Russian-built — and less reliable, said Vick — engine. Kerosene has the advantage of being more dense than liquid hydrogen, thus requiring a smaller and lighter tank, but it packs less energy than hydrogen. It also produces residue that can clog rocket components.
While most differences between the Delta IV and Atlas V stem from their different fuels, Vick said other differences also support the maintenance of separate lines.
Most important, he said, is that the Delta IV uses an open-cycle engine.
That means its exhaust is released rather than used for additional power, thereby reducing efficiency.
The Atlas V uses a closed-cycle engine, using the exhaust to increase power.
“The open cycle is cheaper and requires less maintenance,” Vick said, “but the closed cycle is much more efficient.” He would like to see accelerated development of a closed-cycle engine for the hydrogen-based Delta IV, something he fears is less likely given ULA’s monopoly on government launches.
Ominously for Decatur, Vick points out that combining production facilities may serve the national security interest of assured access from an economic perspective, but it leaves the space program more vulnerable to intentional attack.
Aside from how it would impact people in Decatur, the ULA provides enemies a single target that would effectively close U.S. satellite-launch capabilities.
With the coming of ULA, “assured access to space” is a term that those in Decatur will hear a lot in coming years.
Decatur residents may also find themselves increasingly interested in what was once a debate limited to aerospace engineers: the respective merits of liquid hydrogen and kerosene as the fuel of choice for rockets.
© Copyright 2006, The Decatur Daily