Iodine propulsion

[Zermelo]

I just came across this:

https://www.insidescience.org/news/iodine-propulsion-systems-take-flight-space

which made me wonder about the implications for astronomical observation.

On the one hand, the ability safely to "de-orbit" at least some of these proliferating micro-satellites seems to be a positive. But are there any consequences of the vented iodine, which will presumably remain in orbit? I'm assuming that the ions will acquire electrons to leave either iodine atoms or (eventually) I₂ molecules, depending on the likelihood of collision. If enough of the stuff builds up in orbit, will the light absorption have any effect on ground-based spectroscopic work?
The article says that xenon has previously been used for this purpose, but in that case there is already a trace amount in the earth's atmosphere, unlike iodine.

[Xilman]

I would have thought it exceedingly unlikely to have a noticeable effect because only tiny amounts would be used.

Out in the mesosphere I would expect the main molecule to formed would be HI, as I_2 is more easily photolysed by solar UV. Even, so I would expect much more atomic iodine to be present than HI.

In the lower atmosphere all sorts of molecules, molecular ions and free radicals will be produced. Most of them react vigorously with water and would likely be washed out eventually. I do not have a feeling for what the mean lifetime might be.

Lighter halogens can catalyse dissociation of ozone, hence the recent restrictions on chlorofluorocarbons. Presumable Br and I would do this too but, again, I do not have a feeling for how well they do it.

Anyway, I repeat: only very tiny amounts would be used. In this context a hundred tons of the stuff is only a very tiny amount.

 

[saac]

I hope we don't find out ten years down the line that Iodine or any atmospheric compounds it may form are super greenhouse gases  

Jim 

[Xilman]

20 minutes ago, saac said:

I hope we don't find out ten years down the line that Iodine or any atmospheric compounds it may form are super greenhouse gases  

Jim 

I am pretty sure that the greenhouse effect of any plausible iodine compound is easy to calculate from first principles.

Once more: the amount of iodine used in these systems barely reaches negligible.

[saac]

1 hour ago, Xilman said:

I am pretty sure that the greenhouse effect of any plausible iodine compound is easy to calculate from first principles.

Once more: the amount of iodine used in these systems barely reaches negligible.

I'm pretty sure same stood for CO2 100 years ago .   I wasn't actually being serious Xilman  

Jim 

[Xilman]

9 minutes ago, saac said:

I'm pretty sure same stood for CO2 100 years ago .   I wasn't actually being serious Xilman  

Jim 

Indeed. Arrhenius did work out the greenhouse effect of CO_2_ over 100 years ago.

[Xilman]

5 hours ago, Zermelo said:

The article says that xenon has previously been used for this purpose, but in that case there is already a trace amount in the earth's atmosphere, unlike iodine.

I would expect trace amounts of iodine to be in the atmosphere for the same reason that chlorine and sodium are present --- sea water.

There is so much Na in the atmosphere that active optics lasers use it to form artificial stars.

No real idea about the relative concentrations of Xe and I in the upper atmosphere and can't comment on whether either or both are significant.

[saac]

Duplicate post.!

Edited November 21, 2021 by saac

[saac]

2 minutes ago, saac said:

It must be standard procedure to subtract an atmospheric background reading when processing any stellar spectrograph surely. So I would imagine the problem would not really present itself in future should iodine ion propulsion take off so to speak .  Of course hidden absorption may be a problem but then again I suspect that professional astronomy - exoplanet research etc will be using space based telescope for that .  Was/is HST fitted with a spectroscope package?

Jim 

 

Edited November 21, 2021 by saac

[Ags]

7 hours ago, Zermelo said:

which will presumably remain in orbit?

ION engines send their exhaust out at really high velocity. I'm not entirely sure the the Iodine would remain in orbit or would escape into space. Being ionized, Earth's magnetic field would also play a role.

A little Googling says Earth escape velocity is 11 km per second, while ion engines shoot out ions at 15 to 100 km per second.

Edited November 21, 2021 by Ags

[robin_astro]

16 hours ago, saac said:

It must be standard procedure to subtract an atmospheric background reading when processing any stellar spectrograph surely.

Correct. Spectra of so called telluric standard stars are recorded to correct spectra of the target for atmospheric absorption. (Absorption lines from the interstellar medium are also imprinted on spectra) You probably would not want to be observing directly through a cloud of Iodine though. Molecular Iodine has a lot of lines in the visible spectrum, so much so that Iodine cells are used to calibrate high resolution spectrographs. You might have difficulty "seeing the wood for the trees" !

http://spiff.rit.edu/classes/resceu/lectures/radial_vel/iodine_spec.png

Cheers

Robin

[robin_astro]

A quick search suggests naturally produced atmospheric I2  may impact  ozone levels though eg

https://www.pnas.org/content/114/38/10053

Robin

Edited November 22, 2021 by robin_astro
edited to clarify this is produced naturally

[Zermelo]

21 hours ago, Xilman said:

I would expect trace amounts of iodine to be in the atmosphere for the same reason that chlorine and sodium are present --- sea water.

This triggered a vague memory about one source ot atmospheric iodine I had read about - seaweed:

https://www.sciencedaily.com/releases/2008/05/080506103036.htm

and then clicking through to @robin_astro's link, it too says "In most midlatitude observations of I2 and IO, the source of inorganic iodine is believed to be macroalgae under oxidative stress, such as during low tide" (I wonder if the authors refer to it as "macroalgae" when they're out rockpooling with the family?)