June 13 (UPI) -- Space travel technology may seem to have stalled since the Apollo and space shuttle eras, but private industry is now fueling rapid innovation.
Reusable rockets, commercialized by SpaceX and under development by others in the last few years, have dramatically lowered the cost of reaching space, along with other advances. Lessons learned from 135 shuttle missions and almost 20 years at the International Space Station have boosted knowledge about working and living in space.
The surge of innovation leading to the Apollo 11 moon landing 50 years ago was unprecedented, historic and fueled by the Cold War. As the nation looks back on five decades of space exploration since then, many have wondered why we aren't on the moon or even Mars.
"The innovation is coming along now because private industry is coming along now," retired shuttle astronaut and businessman Sid Gutierrez said. "Now you have people like Elon Musk and Jeff Bezos who got in there and shook things up. After they shook it up, that opened the door for more people to come in."
Few people alive have Gutierrez's grasp of the evolution in rocket technology. Not only has he flown to space on top of a rocket, but he's also CEO of a new company called Rocket Crafters. And his father was part of the U.S. Army's special operation to recruit German rocket scientists after the Nazi defeat in World War II.
The Germans were the first to reach space with their V-2 rocket, designed to bomb Allied cities. Operation Paperclip is what brought the leader of Apollo rocketry, Wernher von Braun, from Germany to the United States.
"War is historically what drove innovation," Gutierrez said. "In the Cold War, we didn't really care that much about cost or even safety after launch if it was carrying a weapon. And money was essentially unlimited for the Apollo program."
Quest for reusability
Apollo's Saturn V rocket system was entirely disposable. Stages of the rocket either burned up in the atmosphere, crashed into the ocean, crashed into the moon or entered orbit around the sun or Earth.
The space shuttle was all about being reusable, but the shuttle never got to the frequency of launches that was originally envisioned, and the main fuel tank was never reusable -- it simply dropped into the atmosphere and burned up into small pieces over the ocean.
Shuttle boosters were reusable, but only after they fell into the ocean, which added a lot of other risks of damage.
In 2015, Blue Origin and SpaceX perfected landings of rocket boosters that actually fly back to Earth and land, making them less expensive and quicker to refurbish and turn around for another launch. SpaceX says its Falcon 9 Block 5 can be refueled with little need for any refurbishment.
In a 2017 presentation, Musk said throwing away rockets after one use is crazy.
"It is really crazy that we build these sophisticated rockets and then crash them every time we fly," he said. "This is mad. I cannot emphasize how profound this is and how important reusability is."
Today, a launch on a SpaceX Falcon Heavy, essentially three Falcon 9's strapped together, is advertised for $90 million. That compares to $350 million for a launch on its main competitor, a Delta IV Heavy by United Launch Alliance.
ULA says its long-standing success record for launches makes the extra cost worth it. But it also is developing a new rocket, the Vulcan, that will include reusable engines.
NASA, meanwhile, is developing the Space Launch System with an SLS rocket, solid rocket boosters and the Orion spacecraft.
"The good thing about the new space companies and the venture capital involved is you are now putting a lot of new money into it," said Mitchell L. R. Walker, professor of aerospace engineering at the Georgia Institute of Technology.
SpaceX has proven regular, commercial usage of concepts with which others had tinkered, including the landing of a first-stage booster and use of supercooled liquid oxygen, Walker said. Recovering a second stage is proving more difficult, although Musk tweeted out ideas in 2018 for an inflatable heat shield.
"It's great, but they're still on the path to proving total reusability over the long haul, and with a reliability needed to carry people," Walker said. "It has the potential to save taxpayers a lot."
Advances in fuel
The liquid fuel used in rockets hasn't changed much since the Apollo era. The basic liquids involved are liquid oxygen, liquid hydrogen and rocket-grade kerosene.
To make oxygen usable in a rocket, it has to be condensed and cooled below -297 degrees Fahrenheit. SpaceX took that one step further by cooling it more into "deep cryogenic" liquid oxygen. That makes it more dense, so it would take up less room in the rocket, leaving it lighter or with more room for other things, Walker said.
Methane now is being included in development of next-generation rocket engines -- the BE-4 from Blue Origin and the Raptor from SpaceX -- in a bid for more efficiency. Methane also is considered to be something that could be produced on Mars -- the working target for a new generation of space exploration.
Seetha Raghavan, associate professor of aerospace at the University of Central Florida, noted that the shuttle had several reusability problems -- like heat shield tiles that needed to be replaced repeatedly.
"We've definitely come a long way," she said. "Rocket technology is more efficient and manufacturing is more cost-effective. Reusing a booster by having it fly back to the launch pad, without having to recover it, is very big."
Lunar pit stop
Other advances have been made in learning about the surface of the moon and asteroids, allowing the moon to be a stopover on the way to Mars, Raghavan said.
"The combustion process is not that much different, but there's more going on than you can see," she said. "We know more about how these materials behave in extreme environments now, and we have a lot of experience and technology to help us test them."
The drawback to chemical, liquid rockets is painfully obvious looking at the history of rocketry: explosions.
Hybrid fuel systems are being attempted by Gutierrez's Rocket Crafters and by Richard Branson's Virgin Galactic. They use a solid fuel with a liquid oxidizer.
Rocket Crafters' solid portion is basically Lego-type plastic mixed with powdered aluminum, which only burns under precise conditions. The company says it is far more stable and less dangerous than a liquid-only rocket system.
"SpaceX is doing a lot of nice innovation," Gutierrez said. "But given that they are still using liquid bi-propellant, there may be only so far they can go with that."
Mitchell also said he thinks more than chemical rockets will be needed if Mars really is a target.
"We need to get an electrical propulsion system with higher power to start pushing stuff off to Mars," he said.