Exploring Rocket Exhaust Plume Molecules in the Upper Atmosphere

[keithl]

TL;DR Summary

Imagine an isolated neutral molecule of CO2 or H2O, or an Argon atom 1AU from the Sun. Integrated over all wavelengths, what is the photoionization rate? What is the intercepted Raleigh scattering power per molecule?

I'm pondering the behavior and persistence of rocket exhaust plume molecules far above the atmosphere. For example, the plume from an apogee circularization thrust from GTO (Geosynchronous Transfer Orbit) to GEO (Geosynchronous orbit). CO₂ and H₂O are among the molecular species emitted by a hydrocarbon-fuel or hydrogen-fuel rocket engine. Argon propellant is favored for VASIMR and helicon thrusters. Very fast molecules might escape, very slow molecules might reenter, but for GTO to GEO thrust, many plume molecules will have retrograde velocities that put them in persistent elliptical (Kepler) orbits, intercepting the launch path they were emitted from once per Kepler orbit.

Rayleigh scattering will slowly diffuse the molecular Kepler orbits; photoionization will trap ionized molecules on magnetic field lines intercepting the radius at which they ionized. I hope to "factor-of-two" quantify this for crude system estimates.

At very high launch rates, this may someday cause huge problems, such as ram surface erosion and orbital decay for satellites, or diamagnetic reduction of Earth's magnetic field, increasing cosmic and CME radiation dose to the Earth's surface. Or not; no clue until I calculate.

Simple Rayleigh scattering peaks in the near ultraviolet, but the Rayleigh (1/λ⁴) law is accentuated by mid-UV resonances. Photoionization peaks just above the ionization energy. I have tables of space solar UV versus wavelength, and a few incomplete graphs of ionization cross sections, and static polarization for non-ionized molecules of interest.

But I would love to find the single numbers that someone else has computed from convolving these separate graphs ... or have measured empirically in simulated space solar UV. I don't trust my own (frightening!) estimates from partial data.

"Per molecular species" numbers might also be useful for computing the slow escape of the Martian atmophere, or water vapor from outer planet moons, but I have been unable to find simple numbers or references to them in journal papers about those processes. It is likely the numbers I want are in published papers, but I don't know the appropriate buzzwords to find them.

Photochemistry and collisions will create many more species, of course. The complete problem is huge; I'll worry about that after step one: starting with a few numbers and playing with roughly scaled, simplified models.

And if someone else wants to "snipe" the problem and publish first - be my guest. I just want to know, so I can invent mitigations if necessary.

 

[TeethWhitener]

There's a lot of information here, but I'm having trouble finding a question. Are you just looking for answers to the two questions in the summary? How much googling have you done for photoionization or Rayleigh scattering cross sections?
https://www.sciencedirect.com/science/article/abs/pii/S0065219908602195
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/19770012747.pdf
https://www.bnl.gov/envsci/pubs/pdf/2014/BNL-105434-2014-JA.pdf
Hopefully these can get you started.

 

[keithl]

Thank you for your answer. The question is in the title; I provided (too much?) supporting information in the body of the text.

"Solar Rayleigh scattering power per molecule, and photoionization rates for CO₂, H₂O" ... in average vacuum optical flux from the Sun.

The last part of the title was stripped when I posted it. Four numbers, essentially. Probably dominated by a few specific resonances in the far UV, 10 to 20 eV range.

Yes, those are interesting references, and I have read two of them and many like them, but ... they aren't the numbers I'm looking for, which would be numbers like those for isolated molecules (without Lambert-Beers pressure broadening) convolved with the Sun's average vacuum UV spectrum, producing two simple numbers per species - total power absorbed per molecule, and the photoionization rate.

Perhaps also the photodissociation rate for each species, with more numbers for each photodissociation product.

The problem I have with combining tabular data for cross sections with tabular data for "average" solar UV is that the tables are granular, with mismatched granularities.

Much of the important activity occurs close to the resonances, which cause asymptotes in the spectra and account for a dominating fraction of the total Rayleigh scattering and for all of the photochemical reactions. Depending on how I interpolate and combine cross section tables and spectrum tables, I get factor-of-two errors just from different interpolation choices. It's likely that there are many other errors in my reasoning due to my ignorance.

That's why I'm hoping to bypass all of that and find the totals somewhere.

I have made some progress since; similar H₂O molecular processes occur in the E ring of Saturn, and similar CO₂ processes strip atmosphere from Mars. The papers that model those processes may help me model vaguely similar processes, though I may need to contact the authors to get the actual computer models, not just the results. Those computer models are improved until they match observation, so they are probably doing something vaguely correct.

Thank your for taking the time to find those papers. I have dozens more. I'm also struggling though two books by Berkowitz (mostly >20eV), also Hargreaves and Rees and Baumjohann and a stack of old astrophysics books.

Extensive downloadable spectral tables at:
http://satellite.mpic.de/spectral_atlas

I'm learning much that is interesting but distracting. The long road to understanding is paved with confusion, and it seems easier to ask for directions from those who have already traveled it. The numbers I'm looking for (also for the decomposition products, and for other species like argon) are part of a much bigger puzzle I hope to solve.