Space-Based 3D Printing Tweaks ASEB's Interest

Space-Based 3D Printing Tweaks ASEB's Interest

Space-based additive manufacturing – better known as 3D printing – was one of many technologies discussed at Friday’s meeting of the National Research Council’s (NRC’s) Aeronautics and Space Engineering Board (ASEB).  Entry, Descent and Landing (EDL) technologies and solar electric propulsion were also on the agenda.

Additive manufacturing is a process where a product is built by assembling material, usually layer upon layer, from a 3D digital design.  Bhavya Lal of the Science and Technology Policy Institute presented an update to ASEB of an ongoing NRC study on space-based additive manufacturing of space hardware. Although it has gained headlines recently, additive manufacturing dates back to the 1980s when it was developed by industry and academia with the support of several federal agencies including the Office of Naval Research (ONR), the Defense Advanced Research Projects Agency (DARPA), and the National Science Foundation (NSF).

In response to a question, Lal expressed her personal observations that NASA and the Air Force are showing interest in the technology, but are operating on different timescales.  She explained that, at the moment, NASA appears to have a short term vision of the technology.  It is cooperating with the company Made in Space Inc. to launch an additive manufacturing system to the International Space Station (ISS) next year to assess its capabilities to print tools and spare parts.  The Air Force, however, has a more long term vision — to print a small spacecraft several decades from now. The NRC study, which is expected to be released in the early summer of 2014, will assess the current state of the technology and focus on the feasibility of space-based additive manufacturing and its possible implications 20 to 40 years from now.

Entry, Descent and Landing (EDL) technologies for landing a spacecraft on a planetary surface were the next topic at the ASEB meeting.  Jim Masciarelli of Ball Aerospace and Technology Corporation and Suraj Rawal of Lockheed Martin Space Systems explained that these technologies are used for a spacecraft entering the atmosphere of a planetary body at hypersonic velocities, descending and decelerating below supersonic velocities in the atmosphere, and landing on the surface. Each of these steps usually requires different technologies. The successful Curiosity rover’s landing on Mars used a rigid-body aeroshell to enter the atmosphere, supersonic parachutes to slow down, and a sky crane to lower the rover onto the surface. These technologies are limited to payload masses around one ton, while future payloads for a human expedition to the surface of Mars are likely to be about 40 tons.   Masciarelli told the ASEB that a deployable aeroshell with a large surface area may be a key technology for larger payloads as well as for slowing smaller vehicles through the supersonic stage of EDL. Rawal spoke on aerobraking, where a rigid-body aeroshell system skims the atmosphere on multiple passes to slow the vehicle down enough for landing.

ASEB also received an update from Alex Galimore, University of Michigan, and Roger Myers, Aerojet Rocketdyne, on solar-electric propulsion (SEP).  SEP is receiving increased attention as a technological centerpiece of NASA’s proposed Asteroid Redirect Mission (ARM).  SEP offers an advantage over chemical rockets by using its propellant mass more efficiently.  Propellant used in SEP is accelerated to more than five times the velocity of rocket propellant.  The drawback is that the amount of propellant mass being expelled by SEP at any given second is much smaller than in chemical propulsion systems.  This then requires more time to accelerate the spacecraft to the velocities needed for its mission. The advantage of using propellant more efficiently is that SEP systems can be less massive and have a smaller volume than chemical propulsion systems. Current challenges for producing more powerful SEP systems include lifetime testing, solar array technologies, power electronics, and thermal control. Gallimore mentioned that academic research in this field tends to be thruster specific, while Myers recommended that future research focus on electric propulsion’s power electronics and solar arrays.

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