Reusable Rockets and the Future of Space Flight

reusable rocket
SpaceX's reusable first stage rocket comes in for its second landing after its first reuse. SpaceX (used by permission)

The sight of a rocket coming down to make a soft landing is a common one these days, and is very much the future of space exploration. Of course, many science fiction readers are familiar with rocket ships taking off and landing in what is known as "single stage to orbit" (SSTO), which is relatively easy to do in science fiction, but not so simple in real life. Right now, launches to space are done using multiple-stage rockets, a technology embraced by space agencies around the world.

To date, there are no SSTO launch vehicles, but we do have reusable rocket stages. Most people have seen the SpaceX first stage settling down on a barge or a landing pad, or the Blue Origins rocket safely returning to its "nest". Those are first stages returning to the roost. These reusable launch systems (commonly referred to as RLS), are not a new idea; the space shuttles had reusable boosters to take the orbiters to space. However, the era of the Falcon 9 (SpaceX) and New Glenn (Blue Origins), is a relatively new one. Other companies, such as RocketLab, are looking at supplying reusable first-stages for more economical access to space.

There is not yet a completely reusable launch system, although the time is coming when such vehicles will be developed. In the not-too-distant future, these same launch systems will take human crews to space aboard capsules and then return to the launch pad to be refurbished for future flights.

When do We Get SSTO?

Why haven't we had single-stage-to-orbit and reusable vehicles before now? It turns out that the power needed to leave Earth's gravity requires staged missiles; each stage performs a different function. In addition, rocket and engine materials lend weight to the whole project, and aerospace engineering constantly looks for lightweight materials for the rocket parts. The advent of companies such as SpaceX and Blue Origin, who use lighter-weight rocket parts and have developed returnable first stages, is changing the way people think about launches. That work will pay off in lighter rockets and payloads (including the capsules humans will take to orbit and beyond). But, SSTO is very difficult to achieve and not likely to happen soon. On the other hand, reusable rockets are forging ahead. 

Rocket Stages

To understand what SpaceX and others are doing, it's important to know how rockets themselves work (some designs are so simple that kids build them as science projects). A rocket is simply a long metal tube built in "stages" that contain fuel, motors, and guidance systems. The history of rockets goes back to the Chinese, who are thought to have invented them for military use in the 1200s. The rockets used by NASA and other space agencies are based on the design of the German V-2s. For example, the Redstones that launched many early missions to space were designed using the principles that Werner von Braun and other German engineers followed to create the German arsenal in World War II. Their work was inspired by American rocket pioneer Robert H. Goddard.

A typical rocket that delivers payloads to space is in two or three stages. The first stage is what launches the entire rocket and its payload off Earth. Once it gets to a certain altitude, then the first stage drops away and the second stage takes on the job of getting the payload the rest of the way to space. This is a fairly simplistic description, and some rockets may have third stages or smaller jets and engines to help guide them to orbit or into trajectories to other places such as the Moon or one of the planets. The space shuttles used solid rocket boosters (SRBs) to help get them off the planet. Once they were no longer needed, the boosters dropped away and ended up in the ocean. Some of the SRBs were recollected and refitted for future use, making them the first reusable boosters.

Reusable First Stages

SpaceX, Blue Origin, and other companies, are now using first stages that do more than just fall back to Earth after their job is done. For example, when the SpaceX Falcon 9 first stage finishes its job, it heads back to Earth. Along the way, it reorients itself to land "tail down" on a landing barge or launch pad. The Blue Origins missile does the same thing.

Customers sending payloads to space expect that their costs for launch will drop as reusable rockets become more readily available and safe to use. SpaceX launched the first "recycled" rocket in March 2017, and has since gone on to launch others. By reusing rockets, these companies avoid the cost of building new ones for each launch. It's similar to building a car or a jet aircraft and using them multiple times, rather than building a new craft or auto for each trip you take.

Next Steps

Now that reusable rocket stages are coming of age, will there ever be a time when fully reusable space vehicles will be developed and used? Certainly there are plans to develop space planes that can leap to orbit and return to soft landings. The space shuttle orbiters themselves were fully reusable, but they depended on solid rocket boosters and their own engines to get to orbit. SpaceX continues to work on its vehicles, and others, such as Blue Origin (in the U.S.) to take future missions to space. Others , such as Reaction Engines (in the UK) continue to pursue SSTO, but that technology is still aways in the future.The challenges remain the same: do it safely, economically, and with newer composite materials that can withstand multiple uses.