Getting humans to Mars will require overcoming a number of technological hurdles. (credit: NASA)
The second fifty years: expanding human presence on the space frontier
by Doris Hamill
NASA's mandate to open space for civilian use has three elements:
Explore space to gain scientific knowledge.
Expand human presence in space through technology development.
Exploit space for human benefit by developing engineering and operations practices.
The choices and challenges of exploring space scientifically are logically arrayed and wait only to be prioritized. The other two elements of the mission are ripe for rethinking as the agency moves into its second half century. NASA can build systematically on its history to expand human presence out from its toehold in low Earth orbit and prepare to reap whatever benefits space may offer.
Achieving Mars
No one doubts that the next major milestone in expanding human presence in space focuses on Mars. Twice now, political leaders have pushed NASA towards an aggressive program to achieve a manned landing there, but studies growing out of those efforts showed that acquiring the knowledge and technology for this endeavor will be the work of decades. Even an aggressive program will require decades of development, requiring a national commitment that will be difficult to sustain as other national priorities come and go. But even without an aggressive program, a manned landing on Mars can serve as an organizing theme for expanding human presence in space. This distant goal should focus our efforts in human spaceflight.
Let us not stumble over the question of why we should go to Mars or what people might do there that robots cannot. If humanity is to continually expand out into space, Mars will be the next planet we step on. It is too early to even guess what practical benefits would result. People learned to live and work on the sea floor before there was any though of extracting oil from it. Otto Lilienthal launched his gliders without envisioning the airline industry. The first computers were connected across a telephone line without anticipating web commerce. People did these things from a conviction that they ought to be done. Similarly, the nation has expressed a conviction that the space frontier ought to be opened, tamed, and brought under human hegemony. As long as this conviction lasts, a manned landing on Mars is the next logical goal for expanding human presence.
If humanity is to continually expand out into space, Mars will be the next planet we step on.
If Mars is the goal, the Moon becomes a means to that end. On the path to Mars, we will need to test out many designs and operations, and the Moon can provide a unique proving ground for them. Along the way, we may uncover other benefits from going there or worthwhile activities we can do there. The International Space Station is a model for this. The real purpose of the Space Station is to help us learn how to live and work in space. The work we choose to do while we learn is scientific research because it's worthy and relevant, but the enormous cost of ISS is ultimately justified by its role in helping us to expand into space, not by whatever research results might flow from it. ISS also had the explicit goal of pioneering an international approach to human expansion into space. Building international cooperation has been every bit as challenging and rewarding as building space hardware, and the lessons learned from the international aspects of ISS will certainly be as important to achieving Mars as whatever knowledge, technology, engineering, and operations ISS develops.
For a will, a way
Producing a credible technology roadmap to achieve Mars will require serious studies and analyses, but a way forward can be more easily grasped through specific examples of what such a roadmap might contain. Here are a few such examples.
A Mars transit vehicle is likely to be assembled in orbit. The technology and operations to do this will build upon the lessons learned from ISS assembly. Moving beyond the EVA-intensive approach used on ISS will certainly require autonomous rendezvous and docking. Experience with autonomous rendezvous and docking can be gained supporting activities on the Moon, since payloads are likely to be handed between ascent, transfer, and landing vehicles. On-orbit operations should also establish the realistic boundaries between autonomous, remotely-controlled, and manual assembly of space structures. This understanding might be built by constructing a space-assembled MEO or GEO space station that would provide a habitat outside the protection of the Van Allen belts to test approaches to mitigating the effect on crews of deep space radiation and long-duration microgravity. Such a station would also provide next-generation lessons about the operations needed to support and sustain isolated crews.
A Mars surface habitat would have to be assembled and begin operations before the crew arrives. The technology for this will grow from work in high-mass Mars entry and pinpoint Mars landing to support robotic exploration. Robotic exploration will also advance the technology for Mars surface mobility, while habitat assembly gains from advances in autonomous assembly of space stations. Remote surface assembly should be proven in a lunar scenario, perhaps in the form of a remotely assembled radio telescope on the back side of the Moon. This would require a communications relay satellite, perhaps orbiting L2, which could also reduce the risk for a similar satellite at Mars.
In situ power generation on Mars is another pacing challenge. Because a nuclear unit may pose prohibitive challenges and hazards, the best alterative will probably involve solar power. But the solar constant on Mars is half that on Earth, so surface-based photovoltaic arrays are likely to be extremely large and require maintenance in the dust and wind environment. Cooling them is also problematic. A better alternative may be an orbiting solar array with space-to-surface power beaming. This technology can be developed for applications nearer to earth, first as space-to-space power beaming for ion-propelled LEO-GEO tugs, then as space-to-surface power for a lunar installation. Long before humans arrive at Mars, an orbital power station there could support robot systems.
The risks of spaceflight have made the space community technologically conservative in recent decades. NASA must rededicate itself to finding and maturing technology advances for human spaceflight.
Getting mass to Earth orbit, though not inherently constrained by technology, poses a cost barrier at the scale that will be required to achieve Mars. NASA should continue to seek technology to break the cost curve, but some cost reduction can be achieved without a breakthrough by fostering a competitive commercial launch services industry. When industry competes to support NASA on a commercial business model, it has an inherent incentive to reduce operational costs. Presumably, reduced launch costs will stimulate commercial applications of space that could achieve the economies of scale needed to ignite a virtuous cycle. A commercial market for launch services could be stimulated by transitioning ISS research and operations support to a commercial business model in the next decade. This would encourage companies to find commercial research customers to add to their business base, commercial customers that will require commercial launch services. In time, this business might outgrow ISS to include orbital facilities specifically built for commercial uses. This approach would stimulate the exploitation of LEO for economic benefit while allowing NASA to transition its workforce to the technology challenges of achieving Mars.
Many paths up the mountain
The technology vision just sketched describes one scenario that could build to a human landing on Mars in NASA's second half-century. It encapsulates a number of challenging elements, any one of which promotes the goal of extending human presence in space. Because previous aggressive attempts to push for Mars have proven to be unready technologically and unsustainable politically, a new focus on achieving Mars should implement a flexible approach that can be adjusted to whatever technological, fiscal, and political circumstances emerge in the unforeseeable future. NASA should describe programs that are within the reach of technology and pursue them methodically, at a rate dictated by the opportunities and constraints of their time.
The risks of spaceflight have made the space community technologically conservative in recent decades. Achieving Mars will require new technologies, not just clever engineering with old technologies. NASA must rededicate itself to finding and maturing technology advances for human spaceflight. The agency should develop a systematic way to advance promising technologies through the Technology Readiness Levels (TRLs). The mid-TRL "Valley of Death" will be easier to bridge once conceptual designs have been sketched. For example, the needs of a conceptual MEO space station, orbital solar power plant, or lunar radio telescope can provide the basis for evaluating the potential of new technologies and competing them against each other. The experience of the Defense Department's premier technology development agency, DARPA, has demonstrated beyond argument the importance of developing technology in the context of a challenging conceptual system.
A sustainable path through NASA's second fifty years requires that the agency build a culture of embracing then reducing risk. Extending human presence toward Mars provides an unlimited source challenges that can keep NASA fresh and relevant indefinitely.
Doris Hamill is a technology manager working for NASA Langley Research Center. The opinions expressed in this article are her own and do not represent the views of any organization or government agency.