Thoughts on Antihydrogen and Propulsion

by Paul Gilster on March 14, 2012

Normally when we talk about interstellar sail concepts, we’re looking at some kind of microwave or laser beaming technologies of the kind Robert Forward wrote about, in which the sail is driven by a beam produced by an installation in the Solar System. Greg and Jim Benford have carried out sail experiments in the laboratory showing that microwave beaming could indeed drive such a sail. But Steven Howe’s concept, developed in reports for NASA’s Institute for Advanced Concepts, involved antimatter released from within the spacecraft. The latter would encounter a sail enriched with uranium-235 to reach velocities of well over 100 kilometers per second.

That’s fast enough to make missions to the nearby interstellar medium feasible, and it points the way to longer journeys once the technology has proven itself. But everything depends upon storing antihydrogen, which is an antimatter atom — an antiproton orbited by a positron. Howe thinks the antihydrogen could be stored in the form of frozen pellets, these to be kept in micro-traps built on integrated circuit chips that would contain the antihydrogen in wells spaced at periodic intervals, allowing pellets to be discharged to the sail on demand. The storage method alone makes for fascinating reading, and you can find it among the NIAC reports online.

Of course, we have to create the antihydrogen first, a feat achieved back in 2002 at CERN through the mixing of cold clouds of positrons and antiprotons. And it goes without saying that before we get to the propulsion aspect of antihydrogen, we have to go to work on the differences between hydrogen and antihydrogen, while investigating the various kinds of long-term storage options that might be used for antimatter. Does antihydrogen have the same basic properties as hydrogen? CERN is moving on to study the matter, with new work showing the amount of energy needed to change the spin of antihydrogen’s positrons.

The report comes from CERN’s Antihydrogen Laser Physics Apparatus (ALPHA) experiment, the same team that trapped antihydrogen for over 1000 seconds last year. Successful trapping now allows the analysis of the antihydrogen itself, applying microwave pulses to affect the magnetic moment of the anti-atoms. This BBC story quotes ALPHA scientist Jeffrey Hangst:

“When that happens, it goes from being trapped like a marble in a bowl to being repelled, like a marble on top of a hill,” Dr Hangst explained.

“It wants to ‘roll away’, and when it does that, it encounters some matter and annihilates, and we detect the fact that it disappears.”

Image: The ALPHA experiment facility at CERN. Credit: Jeffrey Hangst/CERN.

The work is part of a much larger program that will probe antihydrogen with laser light, the goal being to explore the energy levels within antihydrogen. What the work may eventually uncover, perhaps in addition to tuning up our methods of antihydrogen storage along the way, is whether there are clues in the makeup of antihydrogen that explain why the universe is filled with matter and not its opposite, given that both matter and antimatter existed in equal amounts in the earliest moments of the universe. The light emitted as an excited electron returns to its resting orbit is well studied in hydrogen and assumed to be identical in its antihydrogen counterpart.

These are early results that promise much, but the important thing is that the ALPHA team has demonstrated that their apparatus has the capability of making these measurements on antihydrogen. Uncovering the antihydrogen spectrum will take further work but could prove immensely useful in our understanding of the simplest anti-atom. We’re a long way from the antimatter sail concept, but Howe’s Phase II report at NIAC covered his own experiments with antiprotons and uranium-laden foils, critical work for fleshing out the architecture for a mission that may one day fly once we’ve mastered antihydrogen storage and learned to produce the needed milligrams of antimatter (current global production is measured in nanograms per year).

Antimatter’s promise has always been bright, given that 10 milligrams of the stuff used in an antiproton engine (not Howe’s sail) heating hydrogen through antimatter annihilation would produce the equivalent of 120 tons of hydrogen/liquid oxygen chemical fuel. But as soon as you start talking about the energy involved, the difficulty in producing and storing antimatter puts a damper on the entire conversation. That’s one reason why, at a time when antimatter costs in the neighborhood of $100 trillion per gram, finding natural antimatter sources in space is such an interesting possibility. It was just last year that we learned about the inner Van Allen belts’ roll in trapping natural antimatter, and James Bickford (Draper Laboratory, Cambridge MA) has been examining more abundant sources farther out in the Solar System.

The CERN work is reported in Amole et al., “Resonant quantum transitions in trapped antihydrogen atoms,” published online in Nature 9 January 2012 (abstract). For more on antimatter sources in nearby space, see Adriani et al., “The discovery of geomagnetically trapped cosmic ray antiprotons,” Astrophysical Journal Letters Vol. 37, No. 2, L29 (abstract / preprint). I discuss the recent results from the Pamela satellite (Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics) and provide sources for Bickford’s continuing work on naturally occurring antimatter in Antimatter Source Near the Earth.



Greg March 14, 2012 at 9:57

Paul, excellent article, it seems that the sun is a much better place to find antimatter as well,

One incidents it had approximately a pound of antimatter produced. Of course trapping it from there gives its own problems.

Mike Lockmoore March 14, 2012 at 12:08

MODERATOR: there is a small typo in the 3rd paragraph: “while investigating the various kids of long-term storage options that might be used for antimatter”

I assume Paul (you?) intended “kinds” not “kids”. Although I’m for anything that helps _kids_ properly store any kind of their matter, long or short term. :-)

jkittle March 14, 2012 at 12:36

I have though about storage of atomic hydrogen ( as apposed to H2, the molecule) . as a chemical rocket fuel, it would GREATLY improve on the performance of a rocket. Hydrogen atoms when released form storage can react to form H2 molecule releases a LOT of energy, and the resulting gas ( H2 ) has a very high velocity the specific impulse would be an order of magnitude better the H2 and O2 fuels. Storage would require high magnetic fields and some effective trapping system to keep the H2 from forming ( due to electron spin flipping) – this is not dissimilar to the anti hydrogee problem.

A.B. Samma March 14, 2012 at 14:10

If something is expensive to synthesis, it would be quite helpful to focus more on the possibility of harvesting antimatter it in the Van Allen belts and elsewhere. It might help to stimulate faster development in antimatter storage technology if you could show potential investors that the stuff can be harvested and used to propel ships (cargo ships carrying exotic materials from the outer planets ?) cheaply and effectively across the solar system and beyond.

Eric Rooney March 14, 2012 at 14:45

The world’s GDP is $63.12 Trillion US dollars so it will probably be mid-century before this technology becomes affordable unless the price decreases by an order of magnitude.

Paul Gilster March 14, 2012 at 15:47

Mike Lockmoore writes:


That one escaped me entirely! Thanks for the note — I went in and fixed the typo.

Alex Tolley March 14, 2012 at 16:45

IIRC, the article a while back on antimatter sources (planetary magnetic belts) suggested that full harvesting would more than exhaust the supply for just one interstellar flight.

Is there a better way to trap/harvest/create antimatter that could potentially bring down teh costs by orders of magnitude?

Interstellar Bill March 14, 2012 at 17:45

Is the number density of those antihydrogen atoms high enough that they collide and form the antihydrogen molecule? I would expect that the energy released would drive the molecule out of the trap. The only way that antihydrogen could be stored is as molecules in a cryogenic ice-speck. If there’s a fatal barrier to making the molecule then antimatter will stay in the dream factory.

It’s hard to picture us ever making higher atomic number antimatter, since we can barely get normal matter to fuse, and that’s starting out with deuterium, tritium, and helium-3. How do you make antineutrons and how do you use them to make anti-deuterium? Sounds highly unfeasible.

scott ryan March 14, 2012 at 22:12

good read thanks.

ps how can we say it will cost $100 trillion per gram of it?

Why and what is that figure based on?

scott ryan March 14, 2012 at 22:28

next question

if we can make it, why do we need to store it?

If they could make it and hold it for 1000 seconds, wouldn’t we use it right away to make a space ship move.

So once we make it & the antimatter hits matter that makes a powerful force, why do we need to hold it for a very long time?

What ever device is making it for 1000 seconds is put on the space ship. we will use it within seconds / instantly anyway.

Eniac March 14, 2012 at 22:38

I have never understood the synergy between antimatter and Uranium that is proposed for the sail. On one hand, antimatter could be seen as an ingenious way to get a fission fragment rocket, until you consider how much more difficult it is to get antimatter compared to several other ideas for fission fragment rockets. On the other hand, you could see the U235 as “reaction mass with a boost”, but given that the fission energy is actually less than that of the annihilation, it seems the U235 is redundant and some much lighter reaction mass could be used to produce much higher Isp.

Roger March 15, 2012 at 1:57

Antineutrons can be made in high energy Colliders:

Large amounts of antihydrogen could be stored in an antimatter propellant tank with walls made of antiberyllium, coupled magnetically to the vessel. A Kardashev Type I civilization could produce 1kg of antimatter per second. Totally doable.

Paul Gilster March 15, 2012 at 9:56

scott ryan asks:


Why and what is that figure based on?

To date, we can only make antimatter in nanograms per year quantities. The figure is based on the cost of production today extrapolated out to larger amounts. A good background source on antimatter is Frank Close’s book Antimatter (Oxford University Press, 2010).

Alex Tolley March 15, 2012 at 10:13

@ Scott Ryan

Suppose the efficiency of production of anti-hydrogen was 1% of the energy used. It is arguable that the best use of the energy would be some other means to accelerate the reaction mass, e.g. an ion engine. As the efficiency rises, at some point the on-board production mechanism may make sense, although this would depend on the mass of the anti-hydrogen factory. If it was the size of CERN, it wouldn’t make any sense unless you were talking about a seriously big ship.

ljk March 15, 2012 at 10:40

Although it is over two decades old, this book by the late great physicist Robert L. Forward – Mirror Matter: Pioneering Antimatter Physics (New York: John Wiley & Sons, 1988) – is a very good popular-level introduction to the subject of antimatter physics and propulsion.

Also see here:

Nick March 16, 2012 at 0:01

Long before we can store enough antimatter for a starship, terrorists will be able to carry around antimatter grenades with the power of a nuclear weapon. Putting the dreaded “suitcase nuke” to shame.

BTW, it’s a bit ironic that the spell-checking software for this blog doesn’t recognize “starship” as a legitimate word.

Ron S March 16, 2012 at 10:21

Is that worse than carrying around a nuclear weapon with the power of an antimatter grenade? (just kidding)

ljk March 16, 2012 at 11:31

Nick said on March 16, 2012 at 0:01:


We have had nuclear weapons since 1945. No terrorist group or individual has yet attained one for their own purposes, so how will an antimatter weapon be any different? Even more amazing, we are still here after the Cold War.

I know things could still go terribly wrong someday, but if we view everything as a potential weapon or threat we might as well just stay in our beds and let civilization stagnate.

A rock can be used either as a building block for a dwelling or an object to hurl at an enemy. There are those who fear that the technology to keep an NEO from impacting with Earth might also be used to aim a space rock right at our planet. It is not impossible, but I also doubt that such technology will not be simply lying around for anyone to pick and use as they please. The same will go for antimatter, which among other things requires a rather serious means just to keep the particles from touching the containment wall and going boom!

A brave fellow just coducted a test jump from a balloon at over 70,000 feet, something only two others have accomplished so far. He is trying to beat the altitude jump record of 120K feet which was set in 1960, just before we started sending humans into Earth orbit. It is nice to know that there are still a few people out there willing to be adventurous and take risks.

Nick March 17, 2012 at 20:45

ljk, that’s a nice sentiment, but the sad reality is that we already highly regulate nuclear power due to the threat of proliferation. There are even nuclear scientists being assassinated and frequent threats to bomb nuclear reactors because of this problem.

Such regulation and general climate of fear more than any other factor has limited entrepreneurial and less bureaucratic uses of nuclear power. How much more will antimatter sufficiently cheap for a terrorist weapon (far easier than antimatter sufficiently cheap for a starship) be regulated or just outright banned. Including, BTW, around the starship itself which would be a quite vulnerable terrorist target.

ljk March 19, 2012 at 11:02

The irony is that before the major earthquake and tsunami that hit Japan last year and damaged several of their nuclear power plants, several prominent environmentalists were starting to preach to their followers on the benefits of nuclear power over fossil fuels, citing the relative cleanliness of nuclear energy as opposed to oil drilling and coal mining among other examples.

The Japanese reactors were designs made over four decades ago, plus the “perfect storm” of a severe earthquake and tsunami probably would have overwhelmed even a new power plant. But no matter, nuclear energy remains an ecological villain no matter what the form it takes or how safely it is built and operated.

I think the only reason the RTG on the Curiousity rover heading to Mars was not protested like Cassini was in 1997 was due to the public having other things to worry about like the economy.

I have no illusions that human society is a safe utopia. If anything, the access current people have to various technologies and information which scientists, engineers, and government officials could only have dreamed about a mere few decades ago can be just as big a threat to our society and species as nuclear weapons were during the Cold War.

But there lies the rub: Do we stop advancing because some fanatic or group of like-minded people might use these tools against humanity, or do we keep striving ahead because the benefits will outweigh the negative possibilities?

This is similar to the attitudes and views on contacting ETI: Some see meeting up with an advanced species as our salvation while others think it will only spell our doom. Both sides have their merits, but the question remains: Can we stop everyone from conducting METI and SETI, and should we even if we could? Already there are those with the means who do METI precisely because they feel their freedom of expression is being repressed by those they feel do not have any real authority over them.

That is human nature, to defy the system sometimes because authority tells them they cannot do something. It often makes me wonder if other minds out there have similar attitudes, assuming not every being has evolved in very different ways from humans. And hasn’t most human progress come from those who bucked the system?

For me the biggest dangers to humanity are, in order of magnitude: Ignorance, primal fears, and overpopulation. The first two can be conquered by an improved education system – assuming we can find authorities who see the value of an educated populace rather than a threat to their positions of power (and such fears no longer seem confined to the outright dictators of totalitarian regimes).

As for overpopulation, there are still humane means for keeping the number of births under control.

However, if we don’t get serious about it starting yesterday, we can expect governments to institute draconian measures in their attempts to contain what may already be too late to resolve without major problems by then. I don’t know if we will end up with a Soylent Green scenario, but I would rather not test those limits.

The question remains: Can governments and society in general wake up from the fact that they are still acting like we are Cro-Magnons? Or are we going to keep pretending that Earth is infinite in land and resources until we damage things to the point that building starships and searching for ETI become moot points?

Modify what I have said above to include in this quote from Benjamin Franklin from 1775, and this sums up my views on why we as a society cannot hide under our beds or stay on our couches watching television if we really do want to reach the stars:


Tony Jarvis March 21, 2012 at 17:07

I will certainly agree with one point: our technology has certainly surpassed our humanity. As time rolls on, I assume antimatter will get easier to obtain and cheaper to manufacture. Assuming we havent destroyed our fragile planet and every carbon based life form on it.

charlie March 26, 2012 at 9:48

Hi, thanks for the post – fascinating stuff.
BTW have you seen this thesis about antimatter?

seems to be one of Bickfords students

Comments on this entry are closed.