by STEVE WEINTZ
Hurling an object into space is certainly dramatic and risky. During its flight, a giant rocket burns hundreds of tons of fuel in a continuous explosion full of sound and fury, signifying human triumph over gravity.
All that power is dangerous. If the controlled explosion gets out of hand, people die and millions of dollars of equipment disintegrates into shrapnel. But no other technology can loft heavy payloads—like warheads and spacecraft—into orbit.
However, if you want to lift lighter loads, or ascend slowly to moderate altitudes, another method holds promise for safer, cheaper trips into space.
Improbable as it sounds, a rocket can hitch a ride on a balloon.
Balloon-launched rockets, or “rockoons,” sound crazy. Rocket scientist and entrepreneur José Mariano Lopez-Urdiales agrees. “Sometimes crazy is good,” he says. “If it sounds normal, everyone’s doing it.”
He’s getting two start-ups off the ground. Bloon want to take passengers into near-space for much less than other space-tourism companies. Zero 2 Infinity hopes to offer low-cost space-launch services.
Both companies plan to use balloons to get there.
Lopez-Urdiales is a native of Granada, Spain, and his father’s aerospace career inspired him to study astronautics at the Massachusetts Institute of Technology. He worked for Boeing after returning to his country.
Jose’s father studied a sample-return mission from Venus for the European Space Agency in the 1990s. Lacking NASA’s resources, the Europeans had to devise alternative methods of getting to Venus and back. At one point, the ESA considered rockoons.
Hitching a ride
The rockoon idea goes back to the early 1950s. Space scientist James Van Allen—working with the U.S. Air Force—used balloons to loft small instrument packages into the ionosphere.
At the time, rockets simply weren’t powerful enough to lift heavy payloads or send them into space. But they could lift 100 to 200 pounds to very high altitudes, especially if they traveled with a balloon.
Here’s how it works. In a rockoon system, a large plastic balloon carries an inert rocket mounted in a support structure 12 to 15 miles up into the stratosphere.
At that height, the rocket ignites and soars into space. The Air Force claimed its Project Farside rockoons reached an altitude of 4,000 miles high despite a two-in-six launch success rate.
For the balloon to get off the ground, the rocket and its payload necessarily can’t weigh very much. These weight and size limitations didn’t hinder scientific research, but it kept the rockoons away from military applications.
Nuclear warheads and reconnaissance satellites are far too heavy and bulky to ride in a rockoon. And it’s a slow trip—about an hour or more before the balloon ascends to the rocket’s launch altitude. During the opening stages of a nuclear war, that’s too slow.
Without interest from the military, intercontinental ballistic missiles and space boosters soon eclipsed rockoons. Small payloads—derided as “garage-sats”—also got little respect within the aerospace community.
Small payloads have to hitch rides on bigger boosters with their own agendas. Like human hitchhikers, they must go where the driver’s going—not to destinations of their own. They can’t look “dangerous.”
That means no propellants or classified missions.
But if you want to launch a small payload on your own, using a rockoon might be the way to do it. Launching from high altitudes simplifies rocket engineering, and frees designers from most aerodynamic problems, Lopez-Urdiales says.
The rocket’s shape and engines can be a lot simpler, as there’s no need to dead-lift the rocket against gravity or power through thick, sea-level air.
You don’t need thin, inefficient fuel tanks designed to knife through the air under great strain. Instead, you can use toroidal tanks shaped like tires, which are lighter and easier to recover.
Engineers can optimize the rocket engines for vacuum conditions, instead of having to work at both sea level and high altitude. That means simpler design—with vacuum sucking the propellants out of the tanks.
The machine doesn’t need turbopumps to create the necessary pressure differential between the combustion chamber and the outside atmosphere. You can hire half the engineers if you do away with turbopumps, Lopez-Urdiales adds.
Plus, a rockoon launches its rocket far away from human operators—a big plus for safety. On the ground, controllers oversee launches sometimes inside bomb-proof buildings.
You don’t want to be too close to a rocket launch … and its tons of chemical explosives. The Soviet Union, China and Brazil lost lots of rocket scientists to launch accidents.
Rockoons offer potentially massive reductions in launch costs. “Seventy-five percent of the cost of a satellite launch from the earth’s surface comes from the first 25 seconds of flight,” Lopez-Urdiales says. “The engineering, complexity and risk management necessary to fight through gravity and atmosphere during those first moments add up very quickly.”
“Most of our system’s costs are in the first and second stages of the rockoon,” he adds.
The toroidal shape generates shockwaves that should work like parachutes, slowing the stages’ descent. A rockoon also avoids the massive costs associated with traditional air-launch schemes. “Why pay 100 million euros for a big airplane you can paint your logo on?” he asks.
It’s a not-so-subtle reference to Virgin Galactic. He says that money is better spent on research and development. Avoiding the need to amortize an aircraft’s cost allows greater flexibility in launch scheduling.
But the rockoon’s limitations sidelined it as a launch system during the Cold War. Proliferation concerns have long stymied development of widespread, cheap access to space.
For one, North Korea’s supposed space program looks a lot like an ICBM program. In the 1970s, OTRAG—an ingenious German project to build low-cost space boosters—ran afoul of the U.S. government.
But Lopez-Urdiales says rockoons’ unsuitability as a weapons platform make them attractive to nations seeking access to space without strings. “It’s not an ICBM,” he says. He notes his companies’ rockoon system uses no export-controlled technology.
“No Arab nation can launch its own satellite, despite those nations’ wealth,” he says. “The United Arab Emirates thought its $390 million investment in Virgin Galactic would give them space access.”
“In the United States, the U.S. government—either the Pentagon or NASA—is the only real customer. In Russia, [Vladimir] Putin is the customer. There’s room for a truly independent space launch capacity.”
When asked, Lopez-Urdiales did think of one possible military application for rockoons. It’s pretty clever. Theoretically, he says, it could make a stealthy launcher for an anti-satellite weapon.
Here’s why—his companies plan to launch their balloon-borne vehicles from ships.
Sea launches allow for a greater choice of launch sites, cheaper facilities and the ability to match local wind speeds for easier take-offs. Though the rockoons’ flights are uncontrolled, it’s possible to accurately predict their flight paths thanks to decades of meteorological research.
Sea launches are also stealthy. Rockoons typically launch at night to take advantage of cool air and calm winds. The balloons are nearly invisible to radar—they need added reflectors if you want to track them.
Cooling the payload with cryogenic liquid propellants would also render it nearly undetectable to infrared sensors.
A rockoon can’t lift a heavy warhead or a bulky spy-sat, but it doesn’t take a big machine to kill a satellite.