This was originally the content of the details for the project, but the focus and angle described here has been set aside for the time being so I've turned it into a project log instead.

Transporting fleshy, vulnerable humans through space requires a lot of shielding. We have to be protected from the vacuum of space and the radiation that fluxes through it. Minimizing the mass required for shielding is going to be a key engineering challenge for future space missions. Water works great as a radiation shield and is relatively easy to deal with (can be pumped into inflatable structures) but it's very dense. Smarter materials can block more radiation with less mass. It turns out that there are some living organisms that fall into this category. These living radiation shields use ionizing radiation for nourishment. One example of such an organism is cryptococcus neoformans which can be found growing both in bird poop and the reactor vessel at Chernobyl. A similar lifeform was taken aboard the International Space Station to examine the potential for engineering living radiation shielding for future space missions.

Humans might be a small part of a dense ecosystem aboard space craft of the future. Besides shielding there are benefits in using living organisms to produce food and medicines en route, to help clean the air, alleviate human stress, and potentially more exotic applications like in self-healing composite structural components or helping to monitor for environmental contamination. As we get better at creating synthetic biology it's likely that we replace more and more of our current dead technology with new and improved living equivalents. After all, finding general methods for convincing biological systems to do our bidding would be equivalent to stealing fire from the Gods - the constructs of biology can be viewed as a fantastically advanced form of technology of non-human origin.

Space flight is a uniquely constrained problem space because of the high cost it assigns to the mass of the system doing the flying. Every bit of mass has to be accelerated, and we accomplish acceleration by flinging mass opposite where we want to accelerate. That double cost from mass creates the tyranny of the rocket equation. Mass makes it hard to get where you are going, but it also makes it hard to stop once you get there. As a result the engineering game is both about reducing the amount of mass launched and getting rid of it as efficiently as possible along the way.

An interesting consequence of these constraints for future human colonization of the solar system is that we are going to generate a lot of waste, and a lot of trash. When we launch our rockets we'll leave most of their mass on Earth in the form of hot exhaust gases. When they arrive at their destinations they will either jettison or park most of their mass before landing their cargo and/or crew. For reasons I'll get into elsewhere I guesstimate that humans will be spewing bits of spacecraft around the solar system for around a few hundred years (assuming we survive at all and don't send ourselves back to the stone age). The clock started with Sputnik 1 (or maybe that steel cap from Operation Plumbbob) and ends at some arbitrary point along a curve rapidly approaching its asymptote at zero. That end will come about when we are able to package up the stuff we really care about sending into space (self-replicating systems and a lot of information, I think) without a ceiling of efficiency set by the mass of a human body.

So what happens to all that space junk? What does it look like? If the observations above about the potential utility of living spacecraft are on the mark then the space trash of the future is going to look something like a well-used refrigerator designed by Zaha Hadid and engineered by an artificial intelligence trained on the hallucinated imaginations of John von Neumann left to sit broken for a few summer months in a damp corner of a tropical rainforest. Very likely there will be living systems, engineered materials, and active artificial systems mixed together in these castoffs. And once we've sufficiently bent physics to our will we may have room to throw aesthetic considerations into the mix too.

Given an optimistic future (or a pessimistic one, for the fellow misanthropes out there) where humanity continues to grow in scale and reach there is going to be an enormous amount of this kind of trash thrown into interplanetary space. In a way that future will be a repeat of what we are already doing to the oceans of Earth, but grander. Space is vaster than the oceans but the oceans are still really vast relative to us, and yet all the stuff we chuck into the oceans doesn't just disappear because the ocean is a dynamic and chaotic environment that pushes stuff around but also hosts stable equilibrium points where stuff accumulates. The most famous example of such a stable point on present-day Earth is the Great Pacific garbage patch. In our spacefaring far future the same kind of aggregations may find homes in the Lagrange points of gravitational dynamics. What do those garbage patches look like? What lives there?