A Rational Defense of Manned Spaceflight

This is a quick essay I wrote recently to explain why the scientific community should not turn its back upon manned spaceflight. Interestingly, the same arguments also address why and when I see manned space travel becoming more commonplace in all kinds of fields, especially economic, with increased in situ resource utilization. There’s really nothing to do with writing here, but I promise next week’s post will be more literary. For now, I hope you find this essay interesting.

As computers have become more advanced, faster, and more capable, the arguments in favor of manned spaceflight have become weaker, and space travel has increasingly become the domain of machines.  Long before the invention of the microchip, Isaac Asimov proposed exactly this, describing unmanned, computer-controlled space exploration vehicles that would be able to venture into territories too extreme and too dangerous for humans.  That vision has come to pass, and it is now commonly argued that humans are indeed too soft, vulnerable, and unreliable to utilize in spaceflight, and that removing them from the paradigm removes the weakest link.  Manned spaceflight has largely been relegated to an oft-maligned holdover of Cold War international competition and patriotism.  This is a mistake.

Humans, it is true, are soft, vulnerable, fragile vessels full of unpredictable emotions and biological reactions arising from the incompletely understood complexity of their biological systems.  Despite that, they are stupendously capable and adaptable, beyond the capacity of any computer we can currently construct.  Furthermore, the computers that we can currently construct that approach or surpass the purely computational abilities of the human brain are largely more delicate than the humans they are intended to replace.  Artificial intelligence cannot effectively replace the human in spaceflight or any other situation without becoming an independent lifeform.

It is not artificial intelligence, however, that has enabled much of the unmanned exploitation of the space environment that we have so far executed, but remote operations, allowing a human being and all of its attendant advantages to control a spacecraft operating in a hostile environment from the safety of spaceship Earth, that environment to which the species is best adapted.  This has served well for many purposes, and appears to offer an ideal hybrid approach to spaceflight: the intellectual flexibility and agility of a human, paired with the durability, resiliency, and risk tolerance of a machine.  For many mission sets, that holds true, but there is a major kink that prevents this paradigm from being the utopic solution it seems: lightspeed.

Einstein’s theory of relativity presents the idea that there is a maximum velocity at which anything in the universe can move, which is the speed of light through a vacuum.  Everything, from electrons to photons to elephants, cannot exceed this ultimate speed limit.  Assuming that relativity holds true and that the lightspeed barrier remains immutable, it presents a frustrating and pivotal limitation to the capabilities and potential of the hybrid, unmanned approach to spaceflight.  In order to execute unmanned exploration not entirely reliant on advanced artificial intelligence systems that do not yet exist, bidirectional communication between the spacecraft and the operator must exist.  That communication, that exchange of information, is limited by lightspeed.  No information can be communicated between the two entities at any velocity greater than c, approximately 186,363 miles per second.

This may not seem significant, or at least it may not seem insurmountable.  After all, the Voyager probes have been operated under this paradigm for nearly fifty years as of this writing, and they currently are experiencing a one-way lightspeed delay of almost a whole day, twenty four hours.  Accounting for a data rate of barely one kilobit per second, it can takes weeks just to send a single command and receive confirmation that it was received and executed successfully.  Downloading data from the probes has become even more tedious than that, but this discussion is focused on the commanding side.  The Voyager mission can still work with that lightspeed delay because it can afford a reaction time measured in days or weeks as the spacecraft drift through the interstellar medium.  Many other missions could not survive with such a delay.

Consider a mining or exploration mission to the surface of one of Jupiter’s moons.  Assuming that constant communications could be maintained, which is itself an enormous technical challenge, and that Jupiter and Earth are at a minimum separation distance, the one-way lightspeed delay would be approximately half an hour.  If something were to go wrong during a surface operation that endangered the spacecraft or its mission, it would take at a minimum a full hour for the spacecraft to report what it was experiencing, the crew on Earth to develop and implement a solution, and the instructed response to return to the spacecraft.  Imagine seeing a fire sweeping towards you, and having to stand there for an hour before you can move away from it.

It is worth noting that modern artificial intelligence and algorithmic programming can address some of these extreme situations.  The landing sequence for the most recent of NASA’s Mars rovers was entirely computer-controlled, because by the time a signal about something going wrong would reach Earth, the landing would be over: this is referred to as the seven minutes of terror, because the lightspeed delay is seven minutes and the landing sequence takes seven minutes.  Programming specific sequences and allowing the system some programmatic flexibility to make its own “decisions” helps mitigate the effects of the lightspeed barrier, but as the tasks for unmanned systems become more complex, the reaction time and the need for the full adaptability and imaginative problem solving of an on-site human becomes insurmountable.

This is not an argument for only manned spaceflight, but rather for a modification of the hybrid approach currently being pursued.  Instead of unmanned spacecraft commanded from Earth, consider further hybridization, manned missions that travel with a complement of robotic explorers.  A crew controlling a mission on Io from Jupiter’s orbit would have a lightspeed delay on the order of seconds, rather than half an hour to an hour.  This better unites the advantages of both manned and unmanned spaceflight.  As long as the spacecraft we build require any human input, there will be a place for manned spaceflight.