posted February 21, 2012
Heavy-lift vehicles helped humans reach the moon and may one day help us get to Mars; their story is one of politics, engineering triumphs, and the fancy of the space age.
There is no standard, industry-wide definition of what constitutes a heavy-lift vehicle. This is because there are so many variables that can affect how powerful a rocket needs to be in order to launch a payload in to space. According to Edward Ruth, principal director, Launch Systems Engineering, any launch vehicle that can lift a payload of 20 metric tons or more into low earth orbit (LEO) can generally be considered as a heavy-lift vehicle. A super-heavy launch vehicle is able to lift a payload of about 100 metric tons or more to LEO. No super-heavy is currently in production or use.
These enormous vehicles are needed because they are the only ones that have the sheer power necessary to carry large payloads into orbit and to reach the moon or Mars.
“To go to low earth orbit, you need to change the payload’s velocity by nearly 10 kilometers per second,” Edward Ruth, principal director, Launch Systems Engineering, says in explaining how powerful heavy-lift vehicles are. “You start from zero and rapidly accelerate to those speeds. You are moving so fast that gravity cannot pull you back down.”
Heavy-lift vehicles are excruciatingly complex. They are not simply a smaller rocket scaled up, but instead are usually combinations of multiple propellant tanks and engines. Sometimes heavy-lift vehicles are created by clustering a number of smaller launch vehicles into one heavy booster as is done with the heavy-lift version of the Delta IV. The Soviet N1 rocket, Russia’s Saturn V counterpart, had a total of 38 engines between its upper and lower stages. After a series of launch failures the N1 was canceled.
“When you add complexity, reliability becomes more difficult to achieve,” Ruth says.
The Delta IV Heavy is so complex it is almost like flying three missions. There are nearly three times as many rocket components in the Delta IV Heavy as compared to an average rocket.
Heavy-lift vehicles can be surprisingly fragile for their size. As with most rocket designs, their fragility comes from the requirement that their dry mass be as low as possible in order to get the most structural efficiency out of the vehicle.
Ruth explains, “every part of the rocket is usually so close to its breaking point that any imperfection or flaw can lead to a catastrophe.”
An added complication of large rockets is that their size makes transportation and storage especially challenging. For example, the Saturn V was so large that it had to be assembled vertically in what was then the world’s largest building by volume. After it was assembled, a specially built crawler was needed to carry it to the launch pad.
The Saturn V is the most well-known heavy-lift vehicle ever built in the U.S. It has a noble pedigree — it was developed by German rocket scientist Wernher von Braun and his team — and an unbeatable resume: it took the Apollo astronauts to the moon.
The Saturn V remains by far the largest and most powerful launch vehicle ever flown by the United States and is the only launch vehicle to have ever carried humans beyond low earth orbit. Sitting on the launch pad, fully fueled and carrying a payload, it weighed in at about 6.5 million pounds or 3,000 metric tons and was taller than the Statue of Liberty. Its first stage powered by a cluster of five F-1 engines, the Saturn V developed 7.8 million pounds-force of thrust on liftoff. (The space shuttle, by comparison, developed 6.8 million pounds-force.)
The legacy of the Saturn V is significant to Aerospace because the groundwork for much of the mission assurance work done on rockets today was laid down during the development of the vehicle. Systems engineering, checks during manufacturing, and testing and retesting processes all played a significant role in the design and production of the vehicle.
According to Ruth, the Saturn V was one of the most successful launch systems ever flown.
Politics and a push to pave the way for the space shuttle program eventually spelled the retirement of the Saturn V launch system.
The space shuttle followed Saturn in the heavy class of U.S. spaceflight vehicles. It was designed to replace Saturn as both a human and cargo transportation vehicle.
Ruth recounts what it was like to see the shuttle in person:
“I drove up to Vandenberg on a Sunday evening to get involved in some testing. As I started to walk up there, I saw for the first time the launch pad with the Enterprise on it. It was like walking into a Star Wars movie. It was the biggest thrill I’ve ever gotten in my career at Aerospace.”
With the shuttle now retired, the heavy lifting of the U.S. space program now falls to the Delta IV vehicles.
For the United States space program, the future of heavy lift vehicles lies in the Space Launch System (SLS). SLS is still in development, but, when finished, it will be used for human exploration of space beyond Earth orbit and as an alternative vehicle to reach the International Space Station. There are several configurations of SLS, but at its largest it would stand 380 feet tall to Saturn V’s 363 and would be more powerful than the Saturn. It will use a liquid hydrogen and liquid oxygen propulsion system and strap-on solid rocket boosters.
At this stage of the process, Aerospace is involved in several aspects of the project. Aerospace is evaluating launch processing architectures and is also working on integrating an interim cryogenics propulsion stage onto SLS’s existing upper stage.
Beyond the SLS, proposed large rockets become the stuff of dreams. The speculative Project Orion heavy launch vehicle would have used nuclear bombs for propellant and would have been as large as a battleship.
But in whatever form they take, there will be a need for heavy-lift launch vehicles — as long as humans plan on exploring space beyond Earth’s orbit.