Reusable Rockets: The Future Of Space Exploration

There is not one single specific reason for why space programs are so expensive, especially government funded programs like NASA. However, if one were to pinpoint what one of the biggest costs to a space program was, it would likely be launch costs.

Since the beginning of the space age in the 1950s one of the most difficult aspects of space travel was getting out of Earth’s atmosphere and into orbit. Science fiction author Robert Heinlein once said, “Reach low orbit and you’re halfway to anywhere in the Solar System.” This can be seen as a statement of how easy it is in terms of effort to go to another planet from Earth orbit, but it is also a declarative statement that getting into Earth orbit is just as difficult as traveling to other worlds. Today, the easiest way to do this is the same as it was at the beginning of the space age; to use a rocket.

There are many problems associated with sending a rocket into orbit however. Much of this comes down to material and propellant costs, which are based on the weight of the system. The lighter the rocket, the more you can send up with less fuel. Staging makes this easier, but it always comes back to the fact that most of the rocket is used to get to space and then discarded into the atmosphere to be destroyed by the elements. Therefore a lot of cost of space exploration is associated with building new rockets for future missions. The holy grail in rocket technology many have sought for decades is the idea of a fully reusable launch system to reduce launch costs by an order of magnitude.

StarBooster concept art from Buzz Aldrin's website showing an idea for a system where the booster rockets fly back to Earth like the Space Shuttle.

StarBooster concept art from Buzz Aldrin’s website showing an idea for a system where the booster rockets fly back to Earth like the Space Shuttle.

Back in the days of the Apollo Program the mighty Saturn rockets were built for only one use. Used stages fell back into the ocean or burned up in the upper atmosphere, never to be used again. The role of the rocket meant every Apollo mission needed a brand new rocket each time, which accounted for most of the costs, and part of the reason why the Apollo program was canceled after Apollo 17 even with three more Saturn V rockets already built. The three remaining rockets were later used for the Skylab mission and the rest divided up into museum pieces.

When the Space Transportation System was first envisioned in the 1970s it had a grand scope intended to greatly increase America’s access to space and the Solar System beyond what the Apollo program was capable of. However political and economic issues led President Nixon to cancel all but one part of the original STS design, that of the surface to orbit shuttle. This became what is today known as the Space Shuttle, which inherited the official title of Space Transportation System. NASA decided that the optimal thing to do would be to create a mostly reusable spacecraft capable of multiple launches a year that could be the workhorse for all of America’s space needs. This would make the program cheaper through amortization — paying for itself over time — and enable it to do multiple tasks in orbit.

A Space Shuttle SRB being towed back after recovery in the ocean.

A Space Shuttle SRB being towed back after recovery in the ocean.

However, history has taught us that even the best plans don’t always work out as intended. The cost of the space shuttle became much higher and its ability to do rapidly successive launches never reached the potential envisioned. If it was reusable, why did this happen? The answer is the space shuttle was ultimately not as reusable as originally planned because the program was never fully funded. While the solid rocket boosters could be recovered and set up for future launches, the biggest issue was the Orbiter. After returning from each mission the original plan was for it to be inspected, undergo quick maintenance and then be reset to a new launch stack and be ready to go again within two weeks. However, the maintenance turnaround time on the space shuttle was grossly underestimated, often taking months, with Space Shuttle Atlantis setting the record for two launches in 54 days.

The reason maintenance turnaround was so long for the space shuttle was mostly due to the fact that a large part of the reusable spacecraft needed to be overhauled and replaced after each flight. The thermal tiles on the Orbiter often took a long time to inspect with each of the 35,000 tiles manufactured for a specific spot on the space shuttle, thus requiring individual testing. The Space Shuttle Main Engines, despite being very advanced for liquid engines at the time, were still very complex, requiring removal, inspection, and the replacement of several parts after each flight. Before the Block II upgrade, the turbopumps, one of the most important components, needed to be completely overhauled each flight due to the light weight hydrogen fuel burning them out. The toxic propellants used in the thrusters required special handling which meant no other activities could be done at the same time. As seen in the pictures below, the planned ground processing was to be in a simple hanger like an airliner, but the actual ground processing complex ended up vastly more complex. Often the entire avionics system had to be overhauled and replaced as well. In the end the most reusable part of the orbiter was the primary structure.

Envisioned ground processing for Space Shuttle

Envisioned ground processing for Space Shuttle


Actual ground processing for a Space Shuttle

Due to funding limitations the re-usability plan for the space shuttle was drastically scaled back. The space shuttle was a very complex vehicle, and the idea for using it for everything NASA originally wanted it to do did not pan out. This lead to expendable launch vehicles coming back into use for orbiting satellites, robotic probes, and other unmanned cargo as it was cheaper and more reliable.

This does not mean re-usability is a bad idea though, however it does mean the concept of a reusable spacecraft may need to be re-evaluated. Recently NASA revealed that their new spacecraft intended for use in manned missions, called the Orion Multi-Purpose Crew Vehicle, is intended to be reusable. However unlike the space shuttle, this time they are only intending the re-usability to be for a specific part of the vehicle, the re-entry capsule that returns to Earth. The capsule, which is more like the original Apollo capsules than the Space Shuttle, will return to Earth and make water landings aided by parachute descent. A problem with water landings though is that salt water is very corrosive to on board electronics.

Part of Orion’s re-usability is that the majority of the electronics are in the crew capsule itself unlike Apollo, and are not intended to be replaced after each flight. This is done by placing the electronics in the pressurized section of the capsule that the astronauts ride in to protect them from the salt water. Exterior equipment will be sealed to protect them from water and other hazards like dust and micrometeors. The electronics will also be very simple so that they can be upgraded over time as needed, and thus require fewer replacements for different missions. The only part of the capsule that is not reusable is the ablative heat shield which will melt away during re-entry. While needing replacing for a new mission, it will require less effort than inspecting thermal tiles such as on the space shuttle, despite the weight cost of ablative shielding.

This leads to an obvious question, what about the rest of the Orion spacecraft, or of the Space Launch System rocket that will carry it as a whole? The service module for the Orion spacecraft is, for the foreseeable future, not going to be reusable. The Orion service module, which is designed after the ATV cargo vehicle used by the European Space Agency, will be detached before re-entry and burn up in the atmosphere. However, NASA has not discounted the idea of reusing the service module in the future by leaving them in orbit as satellites to be refueled so that future crew modules could be sent up alone and docked with them. This is still a speculative idea though as an on orbit refueling system does not yet exist. As for the rest of the Space Launch System rocket, the solid rocket boosters would be reused from the Space Shuttle Program. Future variants based on the same technology would also likely be reusable. However, the rest of the rocket would likely be made as an expendable launch system for increased reliability and lower maintenance costs much like the current class of expendable launch vehicles.

The cylindrical service module will not be reusable unless it can be re-purposed in orbit by future refueling techniques.

The cylindrical service module will not be reusable unless it can be re-purposed in orbit by future refueling techniques.

The increased use of expendable launch vehicles for reliability has happened in part due to the fact that the space shuttle’s long turnaround time in processing made it unfeasible to be used for all launches into Earth orbit. More frequent and less risky unmanned launches could be made with expendable rockets like the Atlas V and Delta IV while the space shuttle became a dedicated manned vehicle, which decreased the usefulness of its design. In many ways the space shuttle became a symbol of the spacecraft we deserved, but not the one that we needed anymore due to the reduced scope of the original Space Transportation System plan and the post-flight processing issues inherent in the reusable design. Future rockets will likely look at re-usability more like what is being done with Orion and SLS with the main rocket sacrificing re-usability for safety and reliability and the main spacecraft being more reusable.

The dream of a fully reusable rocket system is not entirely dead. The Falcon 9 rocket developed by SpaceX is currently an expendable launcher. However, ambitious plans are in the works to eventually upgrade the rocket to become mostly reusable to the point where entire rocket stages will return to Earth and land themselves back on the pad. Current feasibility testing is underway, but this is an ambitious plan which presents great possibilities for the future of space exploration. Since NASA is intended to be one of SpaceX’s primary customers it could one day have access to a cheap reusable launch system if everything goes as planned. If so the precedent may be set for a future of more robust and reusable launch vehicles, enabling humanity to finally achieve cheaper access to space.

Watch the video below to see the testing of SpaceX’s Grasshopper rocket, the first step toward a reusable rocket system.

A future for humanity in space relies on such innovative ideas. But this cannot be achieved without proper funding. NASA can do a lot more with an increased budget that wouldn’t require much sacrifice from elsewhere. If you think NASA deserves a bigger budget, let your representatives in Congress know by using this tool: