6

This answer to Why will Starlink satellites use krypton instead of xenon for electric propulsion? says:

I expect they did the math, and found that overall cost was less, even with reduced thrust/watt efficiency, reduced thruster life and increased tankage and solar string mass. The cost of xenon is huge, and supply is very constrained. When NASA builds a craft, they have to stretch their fuel purchase over several years. SpaceX probably can't afford to wait that long or spend that much. They may use xenon for a longer-lived, more slowly deployed second generation satellite.

Question(s):

  1. How much of the world's xenon supply has been used in spaceflight altogether? What's the total kilogramage sent above the karman line?
  2. Is it a lot? Does spaceflight make a dent in the amount of available xenon in the world?
  3. Did it cost a lot? Did NASA take out a mortgage in order to pay for its xenon, "stretch(ing) their fuel purchases over several years"?

Related and sources available in both posts and in comments; good info and links regarding the economics of xenon in spaceflight:

uhoh
  • 148,791
  • 53
  • 476
  • 1,473
  • 1
    While still new to matters chemical/physical, and despite my dad's foisting on me all manner of his employer's CANDU promotional materials, I still couldn't fathom why all the world's He hadn't boiled away megamillenia ago. This question may fall into the xkcd "what if" classical poser of what happens when you divide infinity by infinity. He's fallen silent of late. Ergo, +1. – Camille Goudeseune Jun 02 '21 at 03:21
  • @CamilleGoudeseune (w/empathy) I am always surprised that carbon dioxide geological sequestration, essentially pumping it underground and thinking "Okay, that solves that, it's gone forever!" is a thing. Luckily geological methane stays down there with the helium as well as it does otherwise we'd have both a hot planet and no balloons. – uhoh Jun 02 '21 at 03:41
  • 2
    @Camille There's a fair bit of He in the mantle, about 7% of it's primordial. See https://physics.stackexchange.com/a/548063/123208 & the attached comment thread. – PM 2Ring Jun 02 '21 at 11:45
  • 2
    Thank you for saying “kilogramage” and not “poundage”. Metricans of the world, unite :D –  Jun 03 '21 at 23:17
  • @user39728_i_said_user_39728_i_ thanks! Now I'm wondering if I should have actually said tonnage! – uhoh Jun 03 '21 at 23:21
  • 1
    No because kilogramage is much more obviously metric ;-) –  Jun 03 '21 at 23:26
  • 2
    Mars would be terraformed with a thriving civilization by now if we’d switched to metric two centuries ago, my metric calculations suggest. –  Jun 03 '21 at 23:27
  • 1
    That or we would have already self-destructed and gone extinct, our rate of technological progress would have been so rapid. Our adolescent cultures couldn’t have possibly dealt with the accelerated progress. We should still switch to metric and just accept the risk. –  Jun 03 '21 at 23:31
  • 5
    There is a simple English word instead of kilogramage : mass – Uwe Jun 04 '21 at 17:02
  • 1
    Here's a great article about noble gases in the mantle: Identification of chondritic krypton and xenon in Yellowstone gases and the timing of terrestrial volatile accretion. A lot of helium gets produced in the mantle & crust via alpha decay. Some xenon isotopes are produced by spontaneous fission, but that process is rare (eg U-238 is ~10⁸ times more likely to alpha decay than to fission). Xe-129 was produced in the young solar system via the decay of I-129 (half-life 15.7 million years). – PM 2Ring Jun 04 '21 at 21:08
  • 1
    FYI: Obtaining Kr & Xe from the atmosphere. – Fred May 13 '22 at 08:16

1 Answers1

10

According to Wikipedia's article about xenon, the gas occurs at 87 ppb (parts per billion) by volume in Earth's atmosphere. Earth's atmosphere weighs 5.15×1018 kg. Dividing this by the density of air (at sea level) gives us 4.207×1018 m3 of air if it were all concentrated at sea level. Multiplying this by the concentration of xenon leaves us with 3.65×1011 m3 of xenon gas. The density of xenon is 5.89 kg/m3, so we end up with 2.15×1012 kg of xenon gas in the air.

This is definitely enough for whatever you want, so what's the issue?

Well, it's still very rare. The only reason there is so much xenon is that there is so much air in general. If you collect 1000000 L of air, you only get 87 mL of xenon gas. This means that it is very slow to manufacture xenon. This probably accounts for its incredible price of 1800 USD per kilogram. It is produced as a byproduct of purifying N2, O2, Ar, and CO2. Krypton is far more common (~1 ppm, over 10x that of xenon), and is produced with similar strategies, so it is a lot cheaper than xenon, at 290 USD per kilogram. SpaceX is launching Starlink very fast, so they can't wait for a suitable xenon supply to show up. Xenon is commonly used only because it has a higher performance.

I had trouble finding exact numbers for the amount of xenon ever launched, but it is probably in the 1000-10000 kg range. The Dawn spacecraft alone used 425 kg of xenon, costing about 765 thousand dollars! Also all-electric propulsion communications satellites in GEO are becoming popular.

No Nonsense
  • 1
  • 2
  • 8
  • 21
flhl1010
  • 116
  • 1
  • 4