For space travel to thrive, reusable rockets needed

The American physicist Robert Goddard launched the first liquid-fueled rocket in 1926, and nine decades later his experiments with controlled flight and multi-stage rockets remain the basis for how humans and satellites get into space.

This certainly speaks well for Goddard, but perhaps not so well for modern spaceflight as even today NASA and the world's other space agencies have not moved significantly beyond Goddard's principles of launching expendable rockets, and using chemical propulsion to power them in flight.

When considering the next 50 years of spaceflight, if humanity is really to spread deeper into the solar system, rockets and spacecraft will probably have to move beyond Goddard's basic principles by finding cheaper ways to access space, which likely means reusable rockets, and more efficient ways to move through it.

Both of these advancements would benefit Johnson Space Center, as the home of astronaut training and mission planning. More people in space, and using better propulsion to go deeper into space, would give the home of human spaceflight renewed purpose. As it stands now, there are only a handful of NASA astronauts training for a specific mission at any one time.

From the very first moments of human spaceflight, beginning with Yuri Gagarin and Alan Shepard, the boosters that launched humans into the heavens were expendable. The stack on the launch pad included a powerful first stage, an upper stage, and a capsule on top. Only the capsule returned - everything else was thrown away.

NASA sought to change this paradigm in the 1980s with the space shuttle, but that initial approach to reusability, which preserved everything but a large, external fuel tank, proved to be too costly. So with its latest human-rated rocket, the Space Launch System, NASA has gone back toward expendable boosters. (Ironically, old shuttle engines that were used on multiple flights will power the SLS rocket into space once, and then be lost). Other countries, including France, China and Russia, are sticking with expendable launchers, too.

But if the goal is to launch lots of people and many payloads into space, which any journey to Mars or elsewhere will require, expendable rockets quickly become very expensive, with the need to build new engines and hardware for every launch.

Theoretically, a reusable booster could slash launch costs by as much as 90 percent as fuel costs are a negligible fraction of the expense. Accordingly, some space entrepreneurs have not given up on the possibility of reusable boosters.

Elon Musk and SpaceX have gotten the most attention when it comes to trying to master the practice of reusability by landing his large Falcon 9 booster on both a barge at sea as well as a land-based landing site.

But his vision of reusable rocketry is shared by another tech mogul, Jeff Bezos, who founded Blue Origin. Bezos' rocket company has had success with a small, suborbital rocket that can take off, land, and then fly again after several weeks with only minor refurbishment. Bezos intends to take those principles and apply them to a larger orbital rocket, New Glenn.

Unlike the national space agencies, both Musk and Bezos believe reusable rocketry is the only way to cut costs, and push more people into space, and aren't afraid to say so.

Last November, after his New Shepard suborbital launch system took off from near Van Horn, in West Texas, and landed beside the launch pad for the first time, Bezos said he could not understand why government agencies had stuck with expendable launch vehicles in the 21st century. "The holy grail of rocketry is full reusability," Bezos said.

He then recalled Wernher von Braun, the German rocket scientist who defected to the United States at the end of World War II. Later, von Braun would design the Saturn V rocket that blasted Neil and Buzz to the moon. The German would be shocked, Bezos said, that NASA is still flying essentially the same hardware he designed in the 1960s.

"If von Braun came back from the dead and looked around at our current fleet of rockets he would recognize them all," Bezos said. "He'd say 'Oh, you're still throwing them in the ocean. I thought by now you'd be reusing them.'"

It seems reasonable to conclude that if private companies are able to master reusability, both in terms of landing and refurbishing rockets at low cost, they can launch a lot more people into space, moving beyond NASA's existing paradigm of a few, carefully selected astronauts.

Propulsion is a second key technology to watch. Now, spacecraft typically use chemical propulsion to fly through space, which has two primary drawbacks.

One, it's slow. At best chemical propulsion can get humans to Mars in about six months, which is a long time to survive in microgravity, outside of Earth's natural radiation protection. Getting humans to Mars quickly also means the astronauts will be healthier when they reach the surface of the red planet. Moreover, chemical propulsion is a non-starter for human transport when considering destinations further than Mars.

A second factor drawback comes from the amount of propellant required, literally tons of the stuff, to move large distances through space. Such propellant is very expensive to deliver into orbit, especially with expendable rockets.

NASA has begun to develop some alternative propulsion concepts, such as solar-electric propulsion, in which solar energy powers the ionization of a gas to create thrust. Little propellant is needed. This may prove useful for moving large amounts of cargo through the solar system, but solar panels can't collect enough solar energy to provide sufficient speed for human travel.

To really open up the solar system to human exploration NASA is going to need faster propulsion, and in the coming decades the most viable technological option is nuclear thermal propulsion.

With such a spacecraft, a nuclear power plant would provide energy to an ion thruster or similar concept. One such engine is the VASIMR plasma rocket being developed by former astronaut Franklin Chang-Diaz, in Houston.

The big hurdle with this technology isn't the engine, but rather the potential political push back against launching and using a nuclear reactor in space. Nevertheless, for the foreseeable future, nuclear thermal propulsion this remains the most promising option for moving humans quickly around the solar system, to Mars and beyond.