How much does it cost to fill an ion thuster with Xenon for a spacecraft propulsion system?

Question

Ion engines are touted as a great source of propulsion for high deltaV missions that can afford an ample power supply and need low thrust maneuvers; and they are great. But I'd like to know how much they cost.

I can't seem to find any pricing details or indication on how much it costs to fill a spacecraft with Xenon, or even the pricing Xenon itself. A vague reference that doesn't seem right turns up \$120 for 100g of the rare noble gas. Alibaba is filled with prices for high purity quantities ranging from $15-300 per litre (and at STP, 5.98g/L makes that quite pricey!).

I ask because, today, NASA's Michele Gates gave a presentation that shows how they want to evolve SEP for Mars Exploration, and one proposal utilizes 16 metric tonnes of Xenon:

Chart from Michele Gates’ presentation shows how NASA plans to evolve solar elec prop technology from ARM to Mars:

- Jeff Foust on Twitter.

Which based on my calculations from Alibaba, would be between \$40m and \$815m; which seems just, wrong.

Dawn famously used 425kg of Xenon for its Asteroid belt exploration mission (Source), do we know how much it cost to fill her up? Other possible missions to check are Deep Space 1 and GOCE. But I cannot even find out how much Xenon they had on-board.

Fundamentally, I'd like to know how much it costs to fill a craft with Xenon, with evidence to support it.

Answer 1

A June 2005 paper Energetics of Propellant Options for High-Power Hall Thrusters (PDF) by Alex Kieckhafer and Lyon B. King, Michigan Technological University, published for the proceedings of the Space Nuclear Conference, San Diego, CA gives a cost of Xenon gas of \$US 850 / kg. That puts 16 metric tonnes of it at \$US 13.6 Million.

But that's free market price, as is evident from paper's:

Currently Xenon can be purchased for approximately \$5 per standard liter (\$850/kg).

From Capturing and Recycling of Xenon From A Cryopumped Vacuum Chamber (PDF) paper by Michael W. Swiatek, Sierra Lobo, Inc., published for the 46th AIAA/ASME/SAE/ASEE Joint Propulsion Conference in July 2010 in Nashville, TN (executive summary of it as it pertains to your question):

This gas [Xenon] is trapped by the cryopumps as part of the high vacuum pumping system and is normally discarded through venting after the testing is completed.

...

The need for an efficient method of recovering and recycling xenon became evident when the cost per liter increased 10 fold in a matter of eight years.

...

There have been previous attempts made at the NASA Glenn Research Center to capture and recycle Xenon gas. The typical commercially available process utilizes a cylinder cooled in a liquid nitrogen bath that acts as a cryopumping surface to capture the Xenon by having it solidify on the tank wall. This process was installed and tested but found to be ineffective due to conductance losses.

...

Initial estimates of the cost of refining the recycled xenon would be a fourth of the cost of purchasing new.

So NASA could find substantial savings in price of Xenon if they extracted it from cyopumped surfaces on their own, and the paper claims that's what NASA Glenn is already doing. I wasn't able to find any figure, precise or otherwise, on how much saving NASA does make with it and how much Xenon gas costs them, but it could go as low as roughly \$US 250 / kg (high estimate, bluntly amortizing initial investment costs et al., quoted as \$25,000 of hardware purchases to install [one of] the recovery system at GRC).

Or, in short, it could cost NASA as little as \$US 4 Million per 16 metric tonnes of Xenon gas because they have plenty of cryo-pumped surfaces on other systems where they could extract it from air on their own.

Answer 2

Xenon, as a rare gas, has high fluctuations in price over time. Factors including who sources it, what purity is required, and how much is being purchased at once will all impact the cost. For something like fueling an ion propulsion engine, my guess is there would be a large bulk purchase with specially negotiated rates directly from the air separation units. The general population can buy xenon by the liter in gaseous form from most compressed gas companies. Over the last 15 years that I have worked in the compressed gas and cryogenic liquid field, I have seen 1 liter of xenon sell at US\$5.50/L for industrial grade up to US\$19.50/L for grade 5.5 (99.9995% pure). I do not know what grade of material is required for these engines.

Answer 3

Can't add a comment, so here is an answer instead:

• Xenon grade is quite pure - research or the aptly named propulsion grade.
• Costs ~$15/liter. Some quotes can be higher. I would imagine if you were purchasing many 10's of kiloliters, you could get a price break.
• Xenon capture/recovery is for terrestrial testing. As Swiatek's paper details, NASA Glenn does this. During testing, the xenon is captured on the cryo surfaces. These panels do not work in atmosphere. The recovery process captures that xenon during the cryo pump regeneration instead of just discharging it to the atmosphere.
• Yes, xenon for a deep space mission costs a lot. It is also quite expensive for testing.
• As pointed out, these missions cost a lot, so the xenon cost is a small percentage.

Answer 4

In 1998, Xenon production was estimated at 5000-7500 m³/year. Going by this answer, 1 kg = 170 l, so 5000 m³ is 29.4 t. A mission that requires 16 t needs half the entire world's annual production, so you'd have to spread out our purchase over multiple years to avoid a price spike.

Answer 5

Probably worth adding that Xenon is expensive enough that less efficient alternatives are seriously considered. The Starlink constellation uses Krypton for it's ion thrusters. Alibaba shows Krypto at around ~$100 / cubic meter, which is less than a tenth of the of the price volume wise.