Massless Exploration

atmosphere_sucker

NASA’s various technology programs are investing in a wide range of additive-manufacturing technologies. Some focus on the terrestrial problem of how to manufacture aerospace parts. Others focus on the NASA-unique problem of how to fabricate hardware in space. It’s not just NASA-unique. It’s also revolutionary. If done right, these technologies may revolutionize space science and human exploration.

timthumbThe image above is from Deep Space Industries. It’s a concept in which a sort of 3D printer sucks mass out of an asteroid and prints it into a deep-space habitat. That would be revolutionary, no doubt about it.

There’s a larger point to be made here, one beyond designing a single spacecraft a week (which is this blog’s charter, remember). So, let me start with this bigger picture, something a little polemical, which I think will motivate the spacecraft I have in mind.

A little recent history, first. In 2012 the National Research Council identified the top technology-development priority for NASA: improving access to space. So, late last year Air Force Space Command, the Air Force Research Laboratory, and NASA partnered to sponsor a study at the NRC with the following goals:

      1. Lower the cost of space research and exploration in the long term through targeted, sustained investments that start immediately.
      2. Identify new space-system architectures that can be realized only if in-situ manufacturing is possible.

For this first goal, even with a new generation of lower-priced launch vehicles, e.g. from SpaceX, the economics of space will continue to deter most commercial and government organizations from using space for the nation’s scientific and economic benefit. Unless someone creates a killer app to kickstart commercial use of space, we will need a paradigm shift.

That new paradigm is what some of us call Massless Exploration: change the ratio of mass launched from earth to mass used in space. In the limit, the mass we use in space would all come from space. So, we would be exploring space without mass from Earth, i.e., masslessly—at least from the launch perspective. But you see that this perspective gets around the access-to-space barrier, if it could be made real.

As for the second goal, imagine if we could fabricate in space all the spacecraft components, structures and instruments for human exploration, and expendables (such as propellant, food, and oxygen) to support those efforts. In such a future, what would space-system architectures look like? What would we be fabricating if we had the means to do so? Spacecraft, habitats, even human-specific operations would likely look very different and be composed of unfamiliar materials. And for the U.S. to realize such architectures, what are the advanced-manufacturing technologies we must develop now? That’s the real question, in my opinion.

Massless Exploration provides a purpose, a direction for what are at best uncoordinated technology-development activities in additive manufacturing across various space agencies. At worst, some of them are duplicative or poorly motivated. We need a substantive roadmap that takes us from where we are now—3D printed plastic—to space-systems architectures conceived in a way that exploits what’s novel in an in-orbit manufacturing capability.

So, let me try to state it again succinctly. Massless Exploration is the working title for the paradigm that answers this unique question:

“What science and exploration architectures are made possible by in-situ fabrication and assembly of space systems, whether from new raw material brought from earth, unused components already in orbit, or in-situ material, and what advances in additive-manufacturing technologies must be achieved in order to lower the ratio of mass launched from Earth to mass used in space?”

As we learn to reuse and extract resources from the space environment, we may be able to increase this ratio to the point where access to space is no longer the driver for the size, weight, and power of spacecraft. At that point, we may be launching only people and the particularly hard-to-manufacture components, such as integrated circuits and exquisite components for scientific instruments. I joked about this idea in a Reddit AMA I did a few months ago, and the humor associated with manufacturing humans got taken seriously. It would be an interesting and familiar science-fiction story, though, printing up humans. Or maybe it’s too real to be funny. But I digress.

NASA’s current portfolio has a coordinated vision for an agency-wide path to the future. Additive manufacturing needs connectivity to other activities at the agency and elsewhere at a strategic level. If the NRC points the way, it is my hope that NASA and the Air Force will take on the much harder problem of developing science- and exploration-unique capabilities that will end NASA’s, and the nation’s, dependence on high-cost space launch. In doing so, I expect that transformational new technologies will spin off to the benefit of sectors of the economy beyond aerospace.

In this time of declining budgets for technology research, NASA has to focus and synergize its technology investment dollars on high-priority areas that produce fundamental and required capabilities that NASA cannot acquire through other means. NASA cannot justify investing resources in capabilities already being advanced by others. That need for focus motivates this NRC study.

What_Is_What_Could_Be_Massless

Image Courtesy of NASA

This image shows just a few of the ingredients of Massless Exploration that are already being brought together. Whether it’s painting lunar habitats into existence with a sort of toothpaste-like lunar-regolith cement or simply fabricating CubeSat components with the goal of doing so in orbit, there is a wide range of applications and solutions. I’m not alone in thinking about this problem.

I believe that the Maker Community has a big role to play here. We’ve reached a point in history where an individual can hope to build and launch his or her own spacecraft. The impulse to make space, or make space work for us, informs Massless Exploration as well, whether through business-development incentives as well as simply the desire for adventure. The role of government is to establish and nurture these grand visions for the sake of the nation’s citizens and businesses. If the right policies are in place, if we can consider space more of a national park (a “land of many uses”) than a sacred shrine, an object of mere detached scientific study, or the military high ground, we’ll see Massless Exploration all the sooner.

So, that’s the big picture. Now here’s an idea for a spacecraft I don’t think you’ve seen before.

Let’s agree that it’s hard to gather mass from the moon, say, even though it’s relatively nearby. You would need enough energy to change the velocity of a spacecraft by thousands of meters per second to go to the moon, secure regolith, and bring it back to low Earth orbit (LEO). It’s probably about as hard as gathering it from asteroids, although for different reasons. So, let’s pull it out of Earth’s atmosphere instead.  How about a spacecraft that slowly collects ions hovering in low Earth orbit until there’s enough mass to feed into a 3D printer?  Or a greenhouse?

Here’s roughly what a spacecraft rams into at 300 km altitude, just below the International Space Station’s orbit, if the sun activity is low.  If the sun is acting up, there’s about ten times more:

  • 1×1014 oxygen atoms (O) per cubic meter
  • 5.6×1012 hydrogen molecules (H2) per cubic meter
  • 3×1012 helium atoms (He) per cubic meter
  • 1.8 x1012 nitrogen molecules (N2) per cubic meter
  • 5.6×1010 oxygen molecules (O2) per cubic meter
  • A little argon, too, but I don’t really care about argon.  Do you?

The ratio is about right for making ammonia (NH3), e.g. by the Haber process. Then we would have fertilizer. And there’s more than enough oxygen to collect and use as an oxidizer, with the goal of nitrification. So, our spacecraft would provide water, which may be the key to everything. The image at the beginning of this post shows a satellite (adapted from IBEX, in this case, courtesy of NASA, just to show something modest in size). It extends a boom that collects ions sort of like dipping a candle in molten wax, or maybe making rock candy. Electrostatic charge attracts some ions. A chemical catalyst might help, too.

As this wick—this ion collector—orbits the Earth, a combination of ram effects and electrostatic attraction pulls in particles from the ionosphere. There’s a lot to this. Let’s not worry about the details of the plasma dynamics right now. For simplicity, let’s say that this collector sweeps out 10 square meters’ worth of area as it goes. A year’s collecting mass in this orbit yields mass that corresponds to between 80 and 800 grams of ammonia, depending on solar activity. That’s enough nitrogen for a large garden.

For this design to be worth the effort, it needs to produce enough fixed nitrogen to justify launching the satellite in the first place. If you can simply launch the nitrogen fertilizer to your orbiting colony, don’t bother with the satellite to collect it from Earth’s atmosphere, right?  If a 3U CubeSat (traditionally 4 kg) with a 10m long, electrically charged tether can accomplish this task, the spacecraft would justify its launch cost in about 9 years. If there’s a market for helium in space, and/or a way to use that extra oxygen, the break-even point arrives sooner.

And we’ll have to come up with a way to make this satellite stay in orbit, not drag down into and burn up in the very atmosphere it is trying to collect. But that’s a post for another day.

The larger point here is that we should be exercising our imaginations to come up with new ways to explore sustainably. All the mass we need to establish permanent human colonies throughout the solar system is already in orbit. It’s just in the wrong shape.

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