Space Development Blog Haul for May 2017

Just recently the SpaceX Dragon cargo capsule has seen its first reuse. This is yet another stunning development toward a space transport system that has surpassed the economic tipping point.

Against that backdrop, I want to drop in my own throughs on a series of the space exploration blogosphere from the recent month-ish.

A Personal Space Program

This contains fanciful ideas about what the author would do if they had $1B to spend on space infrastructure projects. Some physical actionable things are found buried deep into the post.

I would start by having the librarians look for every potential revenue source that anybody has ever suggested. Everything from helium 3 mining, to tourism, to SPS, to interstellar probes, everything.

From my own personal perspective, I consider 1 of the 3 mentioned to be viable ideas. I agree with the sentiment that one should seek revenue-generating projects so that it may become self-sustaining. The problem is that none of these ideas (aside from tourism) have a snowball’s chance in hell of becoming self-sustaining with an initial investment to the tune of $1B.

Other ideas worthy of discussion are:

  • Partial gravity wheel
  • Greenhouse in LEO to study food production

To the gravity wheel, no. For some decades to come, private industry will have no business experimenting with artificial gravity. That is sufficiently distant in the future to be the domain of government research right now, and government is not researching it. However, the concept of microgravity food production is something that could absorb substantial contributions from interested private parties. This could have quick turnover for space tourism (not discounting the sheer novelty of space foods), as well as benefits for longer term missions, Moon bases, and Mars bases. The ISS has been making strides to the goal, but starting a program to aggressively provide more and more of an astronaut’s daily calories could validly be better suited to private investment. Whenever we get private space travelers up into space, this could be a substantial value-added investment that could be turned around and sold back to government agencies to reduce maintenance costs of the ISS.

New High-Rotation Type of Planetary Object

This subject is somewhat close to my heart, due to my own crazed endeavors of past to grok the toroidal equations for gravitational collapse of ring-like structures. It’s still true, to this day, that Andart did it best.

But this, on the surface this is very new and provocative research, going so-far as to claim that the Earth-moon system probably existed in such a state for something like 100 years before the instabilities actually broke it up into a 2-body system. At least, that’s the impression that the university press gives.

Color me skeptical on this one. The actual article looks somewhat less compelling, although I will admit to not having time to read this entire thing.

We should really just dive into the core of it here. As the press images suggests, they use multi-density regions to obtain the (entirely reasonable) result that a central massive object can cause a planetary ring to connect to the planet’s atmosphere and obtain a bulge in the north-south directions.

I come to this problem having produced and deeply troubled myself with similar math as the following before.

Figure 10 from cited paper

The problem here is the bulging yellow stuff to the right of all these graphs. With multiple layers of density you can absolutely obtain the structures illustrated, but you can’t sustainably put an atmosphere anywhere in there. An arcing mass-bridge from the central body to the ring can not be obtained without also having a significant mass-bridge from the ring into the great abyss of space. The rotation of the system will self-propel bits of atmosphere into space at an extremely high rate in these systems. Looking at the density graphs, it also seems paradoxical that center of the ring bulge is so much lower density than the central mass. It is true that Earth’s moon is lower density than Earth, but only by a factor of something like 3/5ths. The mathematical solutions don’t really help much with these situations, at least not the type of solutions portrayed in the above graphs.

Because of these issues, I have enormous hesitations believing that something like this might have applied for the Earth-moon system at some point. Intuitively I imagine that the flavor of it would have been entirely different from those press images. It would, at best, be a transitory shape that it pass through for a handful of rotations before it started looking like something much different, quickly transitioning into something more like Rocheworld.

Space Islands from Space Waste

There’s not a tremendous amount of depth in this article, and most of what I have to say is my own personal extrapolation.

Firstly, the near-term use case of space waste is obviously radiation shielding. Everywhere in cislunar space that is not the surface of either Earth of the Moon is inherently matter-poor. Radiation shielding can be done with any material, provided you have enough of it. Plus, waste will likely contain a mix of low-Z and high-Z elements anyway. Saving the waste for the purpose of radiation shielding makes a ton of sense. The one fairly major drawback is the added management challenge. You had to ship additional material that can act as the scaffolding on which to attach the space junk so that it will stay in place, even when it with micrometeorites.

Going much further than that, there will come a time when space junk can form a self-sustaining blob due to its own self-gravity, provided you have accumulated a sufficient amount in a single location. In this case, the burden of building your own container to hold the mass is eliminated, although this isn’t obvious compatible with radiation shielding. It could only be to maintain a reserve of solid material which could be called upon later. But again, we encounter a contradiction of requirements. Rebar is a relatively high-density thing, but a haphazard waste pile of rebar can be a very low-density thing due to empty space between the objects. The lower density of waste you have, the more you will need of it in order to create a self-gravitating blob. Because of this, higher-mass items will be more greatly prized, and lower, non-compactable items will be burdens.

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