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

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:

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.

• My Googling shows the same price levels from multiple sources. – user8406 Apr 9 '15 at 8:20
• A ha! I saw this question on the list, and immediately thought, "That sounds just like EchoLogic (from Reddit)". And lo and behold ;-) I do think that, at the end of the day, the cost of the Xenon is going to be pretty trivial compared to the cost of putting it into orbit, and the cost of the thrusters themselves... – Kirkaiya Apr 9 '15 at 20:47
• @Kirkaiya, yeah, it got raised as a point that on my Twitter account, I couldn't find any decent answers, so here we are! – ReactingToAngularVues Apr 9 '15 at 21:02

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. • There's also a supply & demand/economy of scale factor involved. If there's not much demand for pure xenon (or whatever), not many sources will bother to produce it, even though it could fundamentally be produced by any company producing liquid oxygen & nitrogen from the air. – jamesqf Apr 9 '15 at 18:42 • That paper is about recapturing and recycling Xenon from vacuum systems where it's used (e.g. in thruster tests), and it's claiming that could be done at about 1/4 the cost of just buying more Xenon. It's not saying you can extract Xenon from the atmosphere at that price. – pericynthion Oct 26 '17 at 18:17 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. • Hi Indigo's Child, welcome to space exploration. Do you know of a reference online that you could use to back this up? By the way, you can put$ in a post by putting a \ in front, otherwise, if there are two in an answer, it is assumed that what is between is MathJax formatting for writing math expressions. – kim holder Mar 16 '16 at 15:41
• @Indigo's Child Just to understand your answer better, is it taken for granted that prices per litre are quoted for standard temperature and pressure? Hence does the 6g per litre assumption in the original question apply here too? – Puffin Mar 16 '16 at 21:54

• 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. • As this isn't a comment, please try to write it as a fuller answer rather than a set of disconnected notes. – user20636 Oct 29 '17 at 10:07 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. 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.