Where will we get nitrogen in space?

Question

It's expensive to launch things out of a gravity well. So in the future, as we seek to manufacture things in space, it's worth exploring the possibility of harvesting them there as well.

In the interest of some degree of practicality, it seems to make sense to constrain the discussion to nitrogen that might be found within our solar system... maybe even especially close to Earth's orbit.

EDIT: To provide a little more practical context: one author (paper linked below) recently noted that Kevlar (which contains nitrogen) could maybe be used to construct the cable of a terrestrial space elevator if not for the prohibitive launch cost. So, I’m wondering how we might get around launching it out of earth’s gravity well. This was the train of thought that directly led to me asking the question. But the general discussion has been productive as well, IMO.

"[...] Additionally, although Kevlar was found to be strong enough to maintain reliability, its density remains prohibitively large to make it practical, given the massive volume of material which would need to be transported. On the other hand, carbon nanotubes already have the necessary strength, provided a repair mechanism can be incorporated to operate at higher working stress ratios.

Estimating the repair rates for carbon nanotubes remains an open question, contingent on the availability of data regarding their creep-rupture lifetime distribution, which has not yet been thoroughly studied to our knowledge"

From page 17 of https://arxiv.org/pdf/1804.06453.pdf (Building the Space Elevator: Lessons from Biological Design, Popescu/Sun, 2018)

EDIT 2 (5/18/20): In the interest of specificity, it seems like a wonderful idea to establish five particular regions of interest:

1. Near-Earth space
2. On the Moon
3. Near-Mars space
4. On Mars
5. In the Asteroid Belt

Answer 1

Nitrogen in space can come from several sources. Once we reach the stage of actually extracting resources from other planets and moons as the question seems to imply, we really should not have a problem with this element.

To name a few prominent sources:

As peterh mentions in the comments, there is four times as much nitrogen in the atmosphere of Venus as in the atmosphere of Earth. One possible reason for this is the fact that nitrogen is fixed in Earth's thunderstorms, forming nitrogen oxides from oxygen which then react with water to make nitric acid, then with rock to make nitrate salts.

Mars has nitrogen fixed into the soil as nitrates, found by Curiosity, as well as in the atmosphere. Unlike Venus or Earth, Mars has a much smaller gravity well making this nitrogen source easier to extract.

Ammonia and ammonium compounds are also known. McCord and Zambon report ammonium salts on Ceres. Saturn's moon Enceladus is reported to contain nitrogen compounds, labeled simply "biologically available nitrogen" in McKay et al. but identified as ammonia in Wikipedia. Ammonia as a solute lowers the freezing point of a possible submerged ocean in colder parts of the Solar System, and the presence of it's salts as minerals is indirect evidence for such an ocean as well as a nitrogen source.

Elemental nitrogen can also be found in the outer Solar System. Again peterh notes the case of Titan. Not only is nitrogen in the atmosphere of Titan, it may enter the hydrocarbon lakes as well. Nitrogen-rich ice is also present on most of the surface of the Neptunian moon Triton and in Pluto's famous "heart", although these are relatively far away and Pluto is more difficult to reach since a nearby giant planet is not available for gravity-assisted braking.

Answer 2

The upper atmosphere of Venus, of course, has a substantial nitrogen component that might be mined by orbit nuclear powered PROFAC vehicles. The nitrogen could then be transported back to cis-lunar space by light sails.

The martian atmosphere also contains nitrogen which could be extracted on the Martian surface and transported to orbit and then transported to cis-lunar space by light sails.

I think its likely that the lunar poles have significant quantities of nitrogenous materials. The LCROSS impact revealed the presence of ammonia at the lunar south pole.

For example, from Lunar Impact Uncovered More Than Just Moon Water:

In addition to water, the plume contained "volatiles." These are compounds that freeze in the cold lunar craters and vaporize easily when warmed by the sun. The suite of LCROSS and LRO instruments determined as much as 20 percent of the material kicked up by the LCROSS impact was volatiles, including methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide.

See also NASA Missions Uncover the Moon's Buried Treasures

Answer 3

As Marcel Williams mentioned, you can get nitrogen using PROFAC vehicles (they scoop gasses out of atmospheres.)

I would suggest that for the question of where to get nitrogen for space settlements near Earth (the Moon, Earth orbit, the Lagrange pts, etc), the best place is Earth itself. Except instead of launching it from the ground with big expensive rockets, use a PROFAC scooper to scoop gas from Earth's upper atmosphere - set the orbit so it dips to 80-120 mi altitude, and Earth's atmosphere has plenty of nitrogen. And oxygen if you're looking for propellant or something to breathe.

Put one in a figure-8 orbit between Earth and the Moon (similar to the trajectory of Apollo spacecraft), and you can scoop when it dips close to Earth, then have a nice cheap low-energy orbit that takes your cargo close to the Moon where a shuttle or lander can rendezvous and take it. Of course, every time the spacecraft scoops in atmosphere, it's going to lose momentum to drag, so it'll need a high ISP engine like an ion engine to correct for that without costing too much mass.