Scientific Method / Science & Exploration

The (current) future of human spaceflight: the Space Launch System

NASA just announced its new program for human spaceflight: the Space Launch …

In the wake of the end of the Space Shuttle program, and the effective cancellation of the Constellation program, Americans (and the rest of the world) have been wondering what comes next. On Wednesday, NASA announced the Space Launch System (SLS), a new heavy-lift launch vehicle that will carry astronauts and cargo to low-Earth orbit (LEO), initially, and eventually beyond. This new vehicle, planned for a 2017 launch at the earliest, uses some components from previous designs (for instance, the engines from the Shuttle program and the Orion crew vehicle from Constellation) but is a new design, and it will be the most powerful rocket yet built. Let’s go over some of the (announced) details, and see what exactly NASA has come up with.

First: the hardware. NASA focused on a design that would be both modular, combining different components for different missions, and reuse existing designs. The main engines will all be liquid-fueled, using hydrogen and oxygen (like the Space Shuttle main engine). To avoid the unnecessary expense of entirely new engines (see the Ares rockets), the new vehicle will use the RS-25 engines from the Space Shuttle main engines for the core stage and the J-2X, a variant of the J-2 engine from the Apollo-era Saturn V rockets, for the upper stage. The J-2X was originally designed for the Constellation program as a cheaper and more efficient engine compared to those used in the Space Shuttle.

The initial (announced) design will have a payload capacity of 70 metric tons (154,000 pounds), with a fully fueled liftoff weight of 5.5 million pounds (about 2500 metric tons), and use three RS-25 engines for a single stage, with solid rocket boosters similar to those used on the Shuttle. With additional boosters, this design could support 100 metric tons. Later, by adding two more RS-25 engines and an upper stage J-2X engine, the payload capacity will be upgraded to 130 metric tons (268,000 pounds). For some perspective, the three-stage Saturn V rocket used in the Apollo missions (the most powerful ever used, and hasn’t been used since 1973) has a maximum payload capacity of 119 metric tons.

For those unfamiliar with the concept of rocket staging, here’s a quick explanation. Chemical rockets basically generate thrust by expelling mass; in fact, the propellant mass is typically much larger than the actual payload and structure of the vehicle (for instance, propellant makes up 80 percent of the mass of the fully fueled Space Shuttle system at launch). In order to avoid carrying up unnecessary structural mass (which in turn requires additional propellant, and so on), rocket designers employ staging, where the entire vehicle is broken into self-contained stages that disconnect when their propellant is exhausted—think of the boosters and external tank falling off once the Shuttle gets to a certain altitude. Multiple stages increases complexity, but this is considered a worthy tradeoff when compared against considerable added propellant.

Now, where exactly is this vehicle going to take us? This part is a little more ambiguous. NASA plans on using the six-person Orion crew vehicle, now known as the Multi-Purpose Crew Vehicle (MPCV), with the SLS. The initial design could carry astronauts and cargo to LEO, where the International Space Station (ISS) and most satellite are located—but NASA is planning on using commercial spaceflight companies like SpaceX and Orbital Sciences to resupply the ISS, and their vehicles will be ready sooner than the SLS.

That leaves near-Earth asteroids, cis-lunar space, the Moon, and beyond (think Mars) for the SLS. I’m sure we’ll hear more about the destinations as the initial launch date (2017) approaches, but it is exciting to see that NASA has come up with a solid design, especially one that reuses known elements. The modularity of the design also allows for different missions, just by adding more boosters and an upper stage. Hopefully this pragmatism will allow this program to avoid the sweeping budget cuts of the current US government.

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