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.

67 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.

  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. 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.

  4. “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.

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