Space Vehicles Go Green – Reusable Launch Vehicle Concepts

In launch vehicles these days, it’s all about reusability. SpaceX recently tried to reignite its first stage booster, which is the initial step toward landing it vertically on the ground. If this first stage is landed successfully, it can be used again and again. DARPA is calling for proposals for a “reusable hypersonic vehicle with costs, operation and reliability similar to traditional aircraft.” Companies will propose their ideas on Monday October 7th.  Across the Atlantic, Reaction Engines is developing the SABRE engine, a radical engine for the Skylon spaceplane. Each design has the same intention, lowering the cost of access to space by reusing vehicles over and over again.

SpaceX has taken the most traditional approach to launch vehicles, using a vertical launch system and powerful rockets to get payloads into orbit. However, this system has not been reusable in the past. To add reusability to their system, SpaceX intends to have the massive first stage of the rocket land itself on the launch pad. The company is currently exploring the vertical landing technique through the Grasshopper research project, which completed a 325 meter leap test on June 14. While SpaceX’s system is not fully reusable, they are working toward that goal.

On the opposite extreme, Reaction Engines in the U.K. is developing a fully reusable spaceplane known as Skylon. Unlike SpaceX, which uses multiple stages of rockets to get into space (dropping used ones, such as the first stage, along the way), Reaction Engines wants their spaceplane to get into orbit using a single stage. To achieve this lofty goal, Reaction Engines is developing SABRE (see picture), a revolutionary rocket engine that uses atmospheric air as rocket oxidizer for a portion of the trip. Reaction Engines explains that SABRE sucks in atmospheric air through an inlet and then cools it to nearly liquid, basically generating its own oxidizer. However, once the Skylon exceeds Mach 5, the engine morphs into a typical rocket engine, using its own oxidizer stored onboard. This design allows Skylon to carry less liquid oxygen than a typical launch vehicle, saving space and weight for other essentials. With this radical engine, Skylon could be the start of a whole new family of launch vehicles.

In contrast, DARPA’s XS-1 spaceplane design concept seeks to be a melding of the traditional and radical. The radical part of the design is a suborbital spaceplane that can launch just like an aircraft, from the ground. This distinction is important because SpaceShipOne, a successful suborbital spaceplane, launched from a flying “mothership” airplane in 2004. The XS-1 concept, according to the proposer’s day announcement, is a reusable suborbital space plane with a (more traditional) secondary stage that would launch payloads into their required orbit. DARPA’s goal is ten flights in ten days, which would be a radical departure from current launch timeframes.

Although the goal of reusability is shared across these programs, the designs are completely different. They each also have their own timeframe. SpaceX is already conducting preliminary tests. The other two space planes are still in the concept phase. While parts of SABRE, such as the precooler system, have been tested, the Skylon system is years from launching. The XS-1 design is still flexible, so there’s no telling when it may be ready to fly. This flexibility shows how DARPA recognizes that they are many different ways to make reusable launch vehicles. The plethora of designs in development right now shows that reusable space vehicles are likely to be the next way to access space.

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Repurposing Spacecraft not a Novel Idea, but a Cost-Effective One

On August 15th, NASA officially issued a call for help, in the form of scientific white papers, in hopes of repurposing the crippled Kepler spacecraft. The telescope, which had led the charge in finding exoplanets, planets orbiting distant stars, has been unable to function due to issues with two of its four reaction wheels. These wheels, which, NASA explains, are used to point to distant galaxies, are vital to Kepler’s scientific mission, studying distant stars for the changes in light intensity that would signal a planet passing between Kepler and the star. Without the ability to point correctly, the spacecraft’s main mission is compromised. Rather than letting it drift in space, NASA is trying to repurpose the satellite to save money, a strategy that the space agency has used in years past.

NASA had success with repurposing two of the THEMIS spacecraft in 2010, according to an old press release. Originally intended to study the magnetosphere, the little understood magnetic field that surrounds the Earth, two THEMIS spacecraft were diverted toward the moon after finishing their original mission. Once in lunar orbit, the spacecraft began a new mission, ARTEMIS, studying the effect of solar wind on the moon’s surface. By simply sending the fueled spacecraft to another location, NASA scientists were able to get valuable new data, without spending much extra money.

“Using two repurposed satellites for the ARTEMIS mission highlights NASA’s efficient use of the nation’s space assets,” said Dick Fisher, director of the Heliophysics Division in NASA’s Science Mission Directorate at the agency’s headquarters in Washington. With its budget shrinking, NASA is doing all that it can to avoid the high cost of building and launching spacecraft.

NASA is not alone in trying to save money through repurposing satellites. John Keller reported in late January that the U.S. Defense Advanced Research Projects Agency, aka DARPA, is also looking to repurpose spacecarft, by recycling components from non-operational satellites. Defunct spacecraft often have still useful antennae and sensors. Building and launching these components is costly, in terms of both manufacturing and fuel. By recycling parts already up there, DARPA can lower the cost of a new satellite.

Using new ideas and clever innovations to repurpose or recycle spacecraft is both cost effective and a strong move toward sustainability. The junkyard of decommissioned satellites can instead become a useful tool shop for those with innovative ideas.