Travel To Mercury On Ion Power

Star Trek — as much as we love it — was guilty sometimes of a bit of hyperbole and more than its share of inconsistency. In some episodes, ion drives were advanced technology and in others they were obsolete. Make up your mind!

The ESA-JAXA BepiColombo probe is on its way to Mercury riding on four ion thrusters developed by a company called QinetiQ. But unlike the ion drive featured in the infamous “Spock’s Brain” episode, BepiColombo will take over seven years to get to Mercury. That’s because these ion drives are real.

The craft is actually two spacecraft in one with two different Mercury missions. The Mercury planetary orbiter will study the surface while the magnetosphere orbiter will study the little planet’s magnetic field. Check out a video about the mission, below. The second video shows [Neil Wallace] talking about how the ion propulsion — also known as solar electric engines — differ from traditional chemical thrusters.

According to [Wallace] the higher efficiency of the ion motors makes the mission feasible. A 6.5-meter tall vehicle that weighs about 9,000 pounds at launch would not be workable without the ion propulsion. The craft will also use gravity assists from Earth, Venus, and Mercury.

The ion engines are only about nine inches around and use xenon gas. Solar energy provides 4.5 kW to ionize and accelerate the xenon to over 100,000 miles per hour. Of course, xenon atoms don’t weigh much, so the thrust is only 145 mN. For point of reference, ANSI A117.1 (Standard on Accessible and Usable Buildings and Facilities) calls for interior doors to require no more than 22.2 N — that’s 22,200 mN — to open or close. That’s only five pounds of force, so the engines aren’t producing enough to open your bedroom door. However, in space, those tiny forces add up and over time they will act on the massive spacecraft and provide continuous braking against the sun’s pull until the craft orbits Mercury.

Chemical rockets, obviously, have a much greater thrust but use 10 to 20 times the fuel to get the same job done. It is also difficult to keep a highly energetic chemical rocket running for thousands of hours without failing. Additionally, that fuel adds to the weight of the craft. Ironically, NASA’s SERT ion engines, tested in the 1960s and 1970s used mercury as a propellant. Xenon, however, is much less prone to wear out the acceleration grids.

Sometimes in spaceflight, less is more. For example, an Electron offers an easier way to lift smaller satellites into orbit. If you want a more conventional rocket propulsion system, do like we did as kids and use water.

69 thoughts on “Travel To Mercury On Ion Power

    1. Edward’s got it: it’s all about orbital energy (and momentum vector) management, whether the initial chemical burn to drop it down-well, the momentum transfers with planets at the gravity assists, or the long ion burns to kill orbital energy and slow down enough to slip into the tiny dimple of an energy well of Mercury.

      If HaD’s that loosey-goosey with the units, we’ll give them the metaphor of “braking against the sun’s pull”.

      The engines are pretty darned efficient about propellant use: specific impulse is about 10x that of chemical fuel. It’s really too bad Xenon is so bloody expensive and the thrusts are so low. It just won’t scale to human missions.

      If BepiColombo paid industrial rates for their 580 kg of Xenon, the propellant alone would have cost more than $20 million. Compare that to the $200k that Musk says it costs to fuel a Falcon 9, which can lob 10 times the payload to 50% higher speed than those ion engines do. The snag, of course, is first getting a fully-fueled Falcon 9 into interplanetary transfer orbit…

      1. If we had the technical chops to put something as massive as a Falcon 9 into orbit. We wouldn’t be having this topic for discussion.

        Sadly we don’t have the capability. For all intents we’ve regressed – at least here in the West to 1950’s level rocket tech. Maybe even earlier since we lack the capability of putting a man into orbit. It’s really pretty pathetic.

        All Space X is doing is reinventing what’s already been done and lost by the idiots at NASA, Lockheed and Boeing in the last 40 years.

        As it stands Congress may as well shut down the space program for what little we get for the billions we put into it.

        1. “All Space X is doing is reinventing what’s already been done and lost by the idiots at NASA, Lockheed and Boeing in the last 40 years.”

          If you’re doing it right, 90% of engineering is reinvention, i.e., adapting old designs to new sets of requirements. What SpaceX is doing is applying knowledge gained from old programs to building spacecraft for the ’10s and ’20s.
          And by the way, this was NASA’s reason for existing. It wasn’t to produce spacecraft, but to facilitate spaceflight research and development.

        2. “For all intents we’ve regressed”


          “All Space X is doing is reinventing what’s already been done and lost by the idiots at NASA, Lockheed and Boeing in the last 40 years.”

          Uh. So SpaceX is doing what we did in the 1950’s for a much lower bill of materials. So for all intents we’ve actually progressed. It’s becoming economically viable right now.

          I don’t even think you’re right about the lost billions that were put into NASA. Yes, a lot of billions were lost. But that’s the price you have to pay if you want to learn how to make space travel economically viable *the hard way*. Those billions are only lost because the space race grossly jumped the gun.

      2. >” Compare that to the $200k that Musk says it costs to fuel a Falcon 9″

        When Elon Musk talks about prices, you have to remember that he uses what he calls “First Principles analysis”. It’s a method of approaching problems like a child would, rejecting any detailed knowledge and building a solution from the ground up: just take the question at face value, and answer it at face value, and only then you start to think about what it would actually take to pull it through.

        That means, you take the cheapest wholesale market price of something, like kerosene or jet fuel of any grade, anywhere you can find it, and then assume no other costs apply to put that fuel into a rocket and launch it. Then you shake some sort of “learning curve” from your sleeve by applying some form of Moore’s Law argument, and claim that after such and so many years, your engineers should be able to reach that price.

        Then you set up a press conference where you promise to deliver this product at that price, take a huge government loan, collect subsidies by promising to set up the factories in key voter states/districts, and release more stock onto the market. You tell everyone it’s going to happen according to your master plan, and then when it eventually fails to come true and you’re only half-way to the target at the end of your “roadmap” – no worries, nobody remembers what you originally promised anyhow. Everybody’s still shoveling good money after bad money in hopes of it actually coming true, maybe, one day…

        1. Example:

          “Imagine you have three things: (…) Now, let’s break these items down into their constituent parts:

          Motorboat: motor, the hull of a boat, and a pair of skis.
          Tank: metal treads, steel armor plates, and a gun.
          Bicycle: handlebars, wheels, gears, and a seat.

          What can you create from these individual parts? One option is to make a snowmobile by combining the handlebars and seat from the bike, the metal treads from the tank, and the motor and skis from the boat.

          This is the process of first principles thinking in a nutshell. It is a cycle of breaking a situation down into the core pieces and then putting them all back together in a more effective way. Deconstruct then reconstruct.”

          Alright, so that’s First Principles in action. But then, a commentator could ask whether you’re supposed to merely take the abstract concepts, or the actual parts of a motorboat, a tank, and a bicycle, because the latter case which is closer to the situation you’re actually in, would produce a rather shitty snowmobile because the parts simply don’t fit.

          And now you know what sort of logic is driving multi-billion dollar ventures in the modern world.

      3. Xenon is pricey, but not that pricey. It’s less than $1200/kg . (Alibaba has ads at $6.80 / liter; 22.4 liters/mole at STP, atomic weight 131 g/mole) so $675k for BepiColumbo’s load.

    2. I would hate to argue with your KSP education and despite having designed a good bit of space avionics over my career, I can’t really authoritative say if you are right or wrong. However, my old friends at ESA had this to say on the vehicle’s public home page:

      The way the journey from Earth to Mercury will be carried out will also be a first. After launch into Earth-escape orbit, the MCS will undergo a near-Earth commissioning phase. Leaving Earth on its way to Mercury, the spacecraft must decelerate against the Sun’s gravitational attraction, which increases as it approaches the Sun. This is in contrast to accelerating away from the Sun, as is the case with journeys to the outer Solar System. In addition, the spacecraft orbital plane shall be changed to that of Mercury. BepiColombo will accomplish this deceleration and plane change by making clever use of the gravity of the Earth, Venus and Mercury itself, and by using solar-electric propulsion (SEP). ESA’s technology mission, SMART-1, has demonstrated this innovative combination of low-thrust space propulsion and gravity assist.

      Last time I was at ESTEC they seemed to know what they were talking about ;-)

      1. I’m sure their scientists and engineers do. Their PR copy writers either don’t, or care so little that they’re willing to dumb it down to the point of being actually wrong. You’re writing for a technically literate audience; you don’t have to follow their bad example.

  1. ion engines are nothing new. where i want to see advances are in space power. solar/nuclear/rtg, and with the exception of solar all neglected technology that is progressing at a snails pace. beamed power would be nice too but nobody wants to touch that.

    1. Well, they are pretty new considering that only 4 missions used them until BepiColombo. Nuclear is pretty useless in space, because it is based on thermcouples, which arent exactly high-power devices. As for beamed power, it takes a lot of resources and gives little back.

      1. “Nuclear is pretty useless in space”
        Really? So why are there several dozen genuine nuclear reactors currently in space, along with many other nuclear (but technical non-reactor) RTGs? The Russian Topaz reactors, for example, produce (a measly) 10 kW. Compare that to the (quite large) 4.5 kW solar panel the BepiColombo has.

      2. The low efficiency of thermocouples is why current work is focusing on using Stirling or Brayton cycle engines powered by nuclear heat sources. The real problem with nuclear-powered spacecraft is political — people are scared of the N-word no matter what the actual technology is like, and nobody wants to explain to the public why they’re supporting the idea of launching radioactive things on rockets.

        Solar would be the right answer for a mission to Mercury anyway; 1/r^2 makes those panels very, very effective.

        1. I remember the uproar and panic over Cassini prior to it;’s launch. The Greenies went out of their way to panic people over it so it would be cancelled.

          I’d say Nuclear power is dead in the West. The Luddite Greens and Liberals killed it. What progress that will be made will by Russia, China and India as they are not ruled by luddites-Greenies.

          1. I’m a little concerned about putting large quantities of radioactive material on a rocket. Sometime a launch doesn’t go off as planned. Living so close to the Space Coast, I wouldn’t it to explode on the launch pad, or have it go off course, and need to be destroyed. We’ve been dumping a lot of bad stuff in the oceans, don’t think radioactive debris would be a good thing. There’s a reason why no country ever uses nuclear weapons, but have had them sitting around for decades…

      3. Nuclear is pretty useless in space? That’s just wrong. Bear in mind that nobody is advocating that we bundle up an everyday terrestrial nuclear powerplant and launch it on a rocket. There are specific designs that bear enormous advantages in space. Brayton cycle generators handle plenty of power to run an in engine or MHD, and if you need more power than that you can always use nuclear propulsion directly.

        Check out Winchell Chung’s website if you want to learn all about it. It’s amazing the number of creative solutions that have been sincerely researched and developed in the last century.

      4. “Well, they are pretty new considering that only 4 missions used them until BepiColombo.”

        Well, I worked for a company 25 years ago that made electric thrusters, and they WERE used on actual spacecraft. Not as the primary propulsion, but these were (and are) great for stretching your propellant budget for stationkeeping and other low-thrust maneuvering needs.

        1. Meanwhile, all metric countries use non-SI units like the liter and the hour, which are merely “convenience units” just like the foot, pound, and gallon.

          If you want to stick to SI, you should be using only seconds, meters, and cubic meters to describe time, distance and volume. That means no 26″ wheels for your bicycle, clocks would read in kiloseconds, and soda bottles would come in cubic decimeters. Obviously this is too awkward, so we’re graciously “allowed” to use whatever is historically convenient and popular.

        2. @Luke: uhm…you do realize that a cubic decimeter is exactly one litre, right? And litre is an SI accepted unit of measurement for volumes of fluids.

          But that’s not even the point. The point is that some people for some reason prefer using units of measurement that are best described as an emotional rollercoaster. Converting from one magnitude (e.g. inches) to another (e.g. feet) is a relatively complicated matter. While when using the metric system, all you have to do is move the decimal point a few digits over.

        3. @Luke: Most of your electronics units are derived units of the kg

          newton N force, weight kg⋅m⋅s−2
          pascal Pa pressure, stress N/m2 kg⋅m−1⋅s−2
          joule J energy, work, heat N⋅m = Pa⋅m3 kg⋅m2⋅s−2
          watt W power, radiant flux J/s kg⋅m2⋅s−3
          coulomb C electric charge or quantity of electricity s⋅A
          volt V voltage (electrical potential), emf W/A kg⋅m2⋅s−3⋅A−1
          farad F capacitance C/V kg−1⋅m−2⋅s4⋅A2
          ohm Ω resistance, impedance, reactance V/A kg⋅m2⋅s−3⋅A−2
          siemens S electrical conductance Ω−1 kg−1⋅m−2⋅s3⋅A2
          weber Wb magnetic flux V⋅s kg⋅m2⋅s−2⋅A−1
          tesla T magnetic flux density Wb/m2 kg⋅s−2⋅A−1
          henry H inductance Wb/A kg⋅m2⋅s−2⋅A−2

    1. The US adopted the Swedish/Johansnen definition of the inch=2.54cm exactly a long time ago. Henry Ford adopted it before it was official. Everything in the US is based on Metric standards.

      I don’t see any problem with knowing both and mixing them for convenience. The Metric factors of 10 are steps that are too big. Look at the dials on a scope for example 1 – 2 – 5 – 10 – 20 – 50 – 100 etc. and ask yourself why? Or try to just use 1 – 10 – 100 scales. And nobody uses decimeters. A meter is always 100cm or 1000mm. Ridiculous to work with especially for estimating areas and volumes.

  2. I wish Abraham & Franck could use their “Expanse” profits to fund Epstein drive development. Franck has seen the research work, Abraham says “It works really well” and others say “it’s very efficient.”

  3. It’s funny how intellectually inflexible nerds really are. They have no problem learning multiple programing languages, different forms of math. But heaven forbid they are forced to know two different measurement systems.

    Then they curl up into a ball and cry.

    1. Oh, metric users do indeed know how to use two measurement systems. One that is useful and one that is utterly moronic. It’s not like learning python and also learning c++. It’s more like programming using a keyboard versus typing on turd with a USB cable sticking out of it.

      People who use the old imperial systems are absolutely the ones that flat refuse to learn another system. The metric world puts up with the proclivities of US laymen and consumers because they have to. If people who were raised on imperial bothered to learn metric, they’d make the obvious choice and switch over because it’s much more intuitive and saves enormous amounts of time. Even when you use it in an imperial-dominated environment. Ask me how i know. I was raised on imperial myself. Scientists and engineers in the US all made the switch–shouldn’t that speak for itself?

      Defense of it isn’t intellectual flexibility, it’s just ignorance.

      1. American units have the tremendous advantage that while on the Earth’s surface, pound-force is closely equivalent to pound-mass. Specifying force in Newtons and weight in grams or kilograms is a damned nuisance.

        1. “Pound force should not be confused with foot-pound, a unit of energy, or pound-foot, a unit of torque, and may be written as “lbf⋅ft”. They should not be confused with pound-mass (symbol: lb), often simply called pound, which is a unit of mass.”

          How on earth is THAT not a nuisance?

          “while on the Earth’s surface”

          Ballsy thing to say in a time when we’re constantly shooting people out into space.

        2. John, no. There are differences and IIRC the US adopted 2.45cm=1inch before Britain. The math and science/engineering literate don’t care. And how will yoots of today read primary sources of the past?

  4. Yes, please use metric. I know it seems like sophistry sometimes, but pieces of culture like this blog are essential in defeating that inertia and getting the last few holdouts to stop using sixty-fourths of the length of a thumb, or however many damn ounces there are in a pint, or what crazy random number of yards there is in a mile. That shit needs to die. It’s not cute anymore. Nobody else is having a problem with this stuff.

    1. How about for heat? Celsius requires finer precision to punch in specific temperatures while Fahrenheit offers more whole number values for the same temperature range. Might sound stupid but consider your typical digital input that limits you to whole numbers or just 2 decimal places.

      Also cars from any country tend to mix Imperial and Metric measurements. You can’t find any car currently or previously in production that uses entirely Imperial or entirely Metric sizes for bolts and nuts. Comes back to what is available, either you wind up stocking some fractional sized Metric sockets or you mix and match to get precise measurements.

      1. Add a decimal to Celsius and it’s fine. It also has the bonus of not being based on an inaccurate measurement of human body temperature on one end and a random winter day in northern Europe on the other. I mean seriously, it’s like throwing darts or something to figure out what everything’s base is.

        The second issue is purely caused by one single country dragging its feet. Hint: it’s not Liberia or Myanmar.

        1. I assume you’re talking about the country whose civil aviation authority insists on specifying altitudes in feet, and speeds and distances in, what’s that? Nautical miles? Seriously?

  5. Not to nit pick, but having been a designer on two space stations, an international docking standard, and one spacecraft, I can tell you that most of the engineering is done in metric but most of the pilot/crew displays are in Imperial, although that varies too based on preference. I once tried to get everyone to standardize on one system throughout the cockpit and got my *** handed to me so hard that I just gave up and resigned myself to mental conversions. My arguments? The Mars probes and the Glimli Glider didn’t hold much weight in those circles. But, honestly, it isn’t hard to convert and given that this is a post about a news release, I’m pretty sure I was quoting and not doing the conversions myself.

    1. Most commenters here have latched, seemingly reflexively, onto the unit system issue. It’s not that. It’s the clarity in writing.

      Al, you have my deepest respect for your career and accomplishments, and the experience your bring to this forum. But, like an engineer or designer, a writer’s job is to communicate concepts clearly and unambiguously. Requiring a reader to do a conversion because of a jarring mismatch of unit systems — and an unnecessary one at that — breaks the flow of the narrative and distracts the reader from your objective.

      We understand the pressure to get an article out in a time-efficient manner. We understand it’s more efficient to grab existing content and regurgitate it. But it’s a disservice to your readership to distract them from your message by making them do unnecessary mental gymnastics while reading. I’m sorry to say it: I’d even go so far to say it’s sloppy and unbefitting of an engineering writer.

      1. My 2 bits is first, use the units of the source material. If you can’t, use the common units in the country where the story occurs.

        Please don’t use both American Standard and French Metric (like so many publications) for everything (with one in parens). That is as bad as all the editors who show pictures of tweets and repeat them in the main text to make stories longer.

        And try not to call American standard “Imperial”. They are not the same.

      2. NASA is one of the worst offenders in the SI/customary battle. They seem to love mixing units in their press releases, pissing off people on both sides. They must have a directive that covers this, like, “If the quantity is something used by common people, like volume, mass, force, or distance, use pounds, gallons, and feet or miles. At all other times, use SI units.” Or maybe it’s just a rounding thing – if you are describing a rocket with a 5-meter payload fairing, “5 meter” is a whole lot better, from a “keep it simple” principle, than “16 ft., 4.85 inch.”

        1. Like I said, it is engineers vs pilots and we all got tired of arguing about it. What’s worse is when you start working with ESA or ROSCOSMOS and you have AWG wires vs their wires and then the specification of connectors in inches and how you round the conversions to metric…. So for a crimp connector do you want the closest size, the next largest size or the next smallest size? Or does it matter? Oh wait, the Russians don’t crimp, they solder. We don’t solder, we crimp. So many little details like that.

  6. I guess most of you guys that use metric exclusively, don’t work on many cars, Never in my who life have I ever seen more type of nuts and bolts used. Unless you both sets of tools you are going to get very far.

    1. Worked on cars my whole life, only time i needed anything else than metric was when working on an old fordson major 4000. British cars are rubbish, american classic cars are rare, american present day cars, the less said, the better.

  7. “Star Trek — as much as we love it — was guilty sometimes of a bit of hyperbole and more than its share of inconsistency. In some episodes, ion drives were advanced technology and in others they were obsolete. Make up your mind!”

    Caveman: “This cellphone is advanced technology”.
    Vulcans:”This cellphone is stone knives and bearskins.”

    1. Is that weird packaging standard for space-rated hardened chips, or are they quite exotic components?

      Hope they let you use lead in the solder! Nobody on Mercury will give a shit about heavy metals.

    1. These images are all gone now, only 2.5 years later. If you still have them, could you reupload them somewhere else such as Flickr, Imgur, or your personal website (or even (I’m guessing they might have gotten deleted for not being Hyundai-related?)

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