One final thought on the Big Science/ Space Chronicles stuff from last week. One of the things I found really frustrating about the book, and the whole argument that we ought to be sinking lots of money into manned space missions is that the terms of the argument are so nebulous. This is most obvious when Tyson or other space advocates talk about the need for “inspiring” people, but it shows up even in what ought to be relatively concrete discussions of actual science.
Take, for example, the argument over humans vs. robots. Given the success of the robotic missions to Mars and other bodies, many people ask why we should bother to send people to any of those places. Tyson himself estimates the cost of sending a human to be around fifty times the cost of sending a robot, and says that “if my only goal in space is to do science, and I’m thinking strictly in terms of the scientific return on my dollr, I can think of no justification for sending a person into space.” But then, he turns around and tries to justify it on fairly standard grounds: that humans are more flexible, while a robot can only “look for what it has already been programmed to find.” Having humans on the scene would enable faster and more “revolutionary” discoveries.
This is an argument that sounds fairly convincing on a surface level, but on closer inspection it breaks down in two ways: it’s too generous to humans, and too hard on the robots.
One line of argument in favor of sending humans is that, being autonomous multi-function life forms, humans can notice things that robots wouldn’t, and adjust accordingly– Tyson cites the example of Apollo 17 astronaut Harrison Schmitt, a geologist by training, noticing some oddly colored soil that turned out to be interesting after he sampled it. The claim being that a robot, following a strict program, would not be able to adjust on the fly and sample that soil rather than some other soil.
Which would be true, if we were dealing with Apollo-era robot technology. But we’re not. In fact, the actual existing robot rovers on Mars have the capability to do exactly what he wants: they send back pictures of the surface of Mars to Earth, where human geologists study them. Based on the pictures, they select what targets to investigate on more or less the same criteria Schmitt used: that rock is an interesting-looking shape, or this spot is a different color than that other spot. That’s been the beauty of the robot rover program from the beginning.
And, in fact, if you go down the list of discoveries made by the Mars rovers, a large number of them have been serendipitous in exactly the manner that you’re supposed to be able to get from a human. The hematite “blueberries,” for example: scientists on Earth looking at the pictures sent back by Opportunity saw some odd little spherules on the ground, and directed the robot to investigate.
This also oversells human ability a bit– by definition, serendipitous discoveries have an element of chance. There’s no guarantee that even a human geologist would happen to notice everything interesting. In fact, tons of psychology research has shown that humans are just as susceptible to not noticing things as robots are supposed to be– people miss gorillas right in front of them, after all. A human geologist on Mars with limited time to work might well miss some things that would turn out to be interesting.
Another branch of the flexibility argument holds that humans could move more quickly past problems– Tyson cites the 12 hours that it took to navigate Spirit past the airbag from its lander, and says that a human could’ve cleared it in seconds– and make on-the fly repairs– “Give a person a wrench, a hammer, and some duct tape, and you’d be surprised what can get fixed,” he says. This again, is true to a point, but also elides a lot. For one thing, a mission including humans would be vastly more complicated than a robot mission, and a more complicated mission has many more possible failure points. So, yes, a human is less likely to be thwarted by an airbag on a ramp, but then a robot doesn’t have to worry about maintaining a pressurized breathable atmosphere, or securing supplies of food and water, or a comfortable temperature, or adequate radiation shielding, or waste disposal, or any of a host of other problems that preserving human scientists on Mars and returning them to Earth would entail. There are lots of possible failures that are just as stupid as an airbag on a ramp that could easily trap a human inside for as long as Spirit was stuck.
The repair argument also has its flaws, the most obvious being that any repairs would be limited by the available materials. Glib comments about duct tape are great if the only failures you worry about are gross mechanical ones, but nobody’s going to make a new Mössbauer spectrometer out of duct tape. Any Mars mission worth doing will include a lot of highly specialized components, and you can’t send spares of everything.
It also slights the ingenuity of the humans controlling the robots. Spirit famously had one of its wheels lock up in 2006, but the scientists “driving” it not only worked out a way to get around the stuck wheel (by driving the rover “backwards,” basically), but it turned out to be the vehicle for another of those serendipitous discoveries: the dragging wheel scraped away dust, revealing a silica layer underneath.
So, again, a lot of what appear to be more concrete arguments in favor of human space missions don’t seem to hold up very well, and end up turning on things that are as vague and unquantifiable as “inspiration.” There’s no question that certain things would go faster for humans than they do for robots, but then, they would need to go faster, because there’s no way we’d be able to leave a human on Mars for the nearly 3000 “sols” that the current robot rovers have been operating there. And it’s not at all clear that the small advantage in flexibility from having a human there rather than at the other end of a radio link would make a positive difference.
The one unquestionable advantage would be that a mission putting humans on Mars would eventually return to Earth, and could bring samples back that could then be subjected to a vast range of tests that can’t be done by a robot rover with a limited instrument set. Which is true, but then, you could get the same thing from a robotic sample return mission, at one-fiftieth the price.
So, while the pro-human arguments based on science sound convincing at first, they’re ultimately not that great, and fall back on the same sort of vague and airy platitudes as the general “inspiration” argument. And given the gigantic cost multiplier involved in sending humans rather than robots (or in addition to robots), I’d really like to see more than that.