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A Boost for Ion Propulsion

The European space agency is ramping up expectations for its Dual-Stage 4-Grid (DS4G) ion thruster. Using a concept developed by UK propulsion theorist David Fearn, the agency’s test model, designed and built by a team from Australian National University, is said to be ten times more fuel efficient than the ion engine used on the SMART-1 lunar mission. In fact, says Roger Walker of ESA’s Advanced Concepts Team, who is technical manager of the project, “Using a similar amount of propellant as SMART-1, with the right power supply, a future spacecraft using our new engine design wouldn’t just reach the Moon, it would be able to leave the Solar System entirely.”

Walker calls the design “an ultra-ion engine,” and ESA talks about using flight models to push into the Kuiper Belt and beyond, or deploying clusters of higher-power versions of the engine on manned Mars missions. All of which is exciting stuff, though it comes with a needed caveat. Currently at the stage of laboratory experiment, the DS4G thruster must now evolve into a flight-ready device, and that means not only intensive design work but thousands of hours of ground testing. Ion engines operate continuously, and must burn in a vacuum at low thrust for long periods to be viable for deep space missions.

The key difference between DS4G and earlier ion designs is that it seems to resolve an issue that limited engine lifetime. Normally, a voltage difference between two perforated grids creates an electric field that extracts and accelerates ions. But the accelerating ions can damage the second grid when voltage differences are high. DS4G uses a two-stage process to extract and accelerate the ions that has produced impressive results without resultant damage to the grid. Here’s what an ESA news release has to say about the early findings:

The test model achieved voltage differences as high as 30kV and produced an ion exhaust plume that travelled at 210,000 m/s, over four times faster than state-of-the-art ion engine designs achieve. This makes it four times more fuel efficient, and also enables an engine design which is many times more compact than present thrusters, allowing the design to be scaled up in size to operate at high power and thrust. Due to the very high acceleration, the ion exhaust plume was very narrow, diverging by only 3 degrees, which is five times narrower than present systems. This reduces the fuel needed to correct the orientation of spacecraft from small uncertainties in the thrust direction.

Centauri Dreams note: Their high specific impulse makes engines like these of great interest for long duration missions (and be sure to compare this work with ESA’s Helicon Double Layer Thruster (HDLT) drive, described here in an earlier post). But electric propulsion systems are not new. In fact, geostationary satellites have used them for orbital maintenance since the early 1980s, and the methods have also been applied to low Earth orbit satellites. Their use as a primary means of propulsion wasn’t demonstrated until NASA’s Deep Space One mission, which used a xenon-based ion engine; ESA’s SMART-1 has been an outstanding proof of concept in its own right.

And then there’s the Japanese Hayabusa, which put four ion engines to work in 20,000 hours of cumulative operation. We’re learning huge amounts about making ion engines better, but even greater changes are clearly in the offing. Electrical power to operate these devices normally comes from solar panels. If we ponder deep space missions, nuclear electric options will have to come into play, and so will a host of new engine designs.

Comments on this entry are closed.

  • tmayes1999 February 18, 2006, 20:16

    An ion engine is capable of generating an exchaust velocity approaching
    the speed of light if you use an advanced enough engine design,
    and you have enough nuclear electric power to run it.
    Tim

  • george scaglione November 18, 2006, 14:12

    tim that does indeed sound like a good idea to me.but answer me this if you happen to read this comment anytime soon….please… as a matter of fact anybody please feel free to answer this question: why was there 1 response on feb 18th to which i am now the sole respondant on nov 18th !! gadzooks!! 9 months for one interchange!! thanks in advance george ps… hulloooooo! anybody!!!!!! ;) g

  • Vishaque December 18, 2006, 2:07

    Recent practical developements as I’ve noticed in PP is, of DS4G Engine; they achieved a thrust of 1mN (don’t laugh) till 15 minutes, at ESA. Indeed, quite remarkable, when compared to other theories. And as far as, HDLT’s concerned; its indeed very practical plus, genuine idea. Relatively. Moderated. ;)

  • Timothy J Mayes January 19, 2007, 2:41

    Electric propulsion in the form of nuclear electric propulsion rockets,.and nuclear electric propulsion ramjets can get us to the stars. All that is required to achieve it is the availability of the necssary large scale electric power sources for use in space flight. These can be on board electric power sources , or beamed power electric sources or any combination of them .
    tim

  • Adam January 19, 2007, 3:58

    Hi Tim

    Electric propulsion is hobbled by the mass of its generators or the mass of the collection system for beamed propulsion. Geoff Landis analysed the ion-drive laser-sail and found it was more efficient than a pure laser sail up to about 0.2c, but after that the relative advantage declined due to red-shift.

    All the high exhaust velocity rocket designs try for direct ejection of fuel-particles – fission fragment rockets, fusion-pulse rockets, and the like don’t muck about with the additional mass-cost of power-conversion and heat-rejection systems. Arguably all those systems are “ion drives” because the exhaust is ionised and directed via magnetic fields, but that’s hair-splitting.

    Adam

  • Timothy J Mayes June 25, 2007, 22:53

    yes electric propulsion is a power limited system . Current or near term atomic power reactor technology can give us up to 2200 watts of electric power generation per kilogram of the mass of the onboard power pource .Fusion reactors may provide up to 22000 watts per kilogram ,and antimatter-matter annhilation could provide up to 2,200,000 watts of
    power kilogram of mass . Direct thrust is also more efficient at converting
    the energy of the fuel into thrust also.Ion drives require optimization
    of the exchaust velocity, relative to mass of propellant accelerated .
    The maximium otimized ion exchaust velocity for fission powered ion drives
    is usuually about 3,000,000 m/sec, or 3000 km/sec which is 1 % of light velocity . The typical maximium mass accelerated of the optimized fission
    powered nuclear electric ion drive is about 1 gram of ions per second.
    This is sufficient to operate a nuclear electric ion ramjet drive ,that is
    capable of accelerating at a few thousands of a G which is 9.81 m/sec.
    The best method of electric propulsion for powering an interstellar vehicle
    is a NUCLEAR ELECTRIC ION DRIVE INTERSTELLAR RAMJET ASSISTED INTERSTELLAR ROCKET.

  • Timothy J Mayes June 25, 2007, 23:11

    Applying the kinetic energy formula and an ion drive efficiency of
    90% at converting the on board electric power into ionic thrust :
    Ke = 1/2 M* V^2 and solving the eqaution for the amount of energy
    required to accelerate a given mass of ions to exchaust velocity Ve
    we calculate that 450,000,000 joules is required to accelerate
    1 gram of ions to 3,000,000 m/sec which is 1 % of light velocity .
    Assuming 90 % efficeiency then we need 500,000,000 joules to do
    that. 1 watt of electricity is a current of 1 amp and 1 volt past
    a point per second in a circuit . If the power source is a fission power
    reactor that can generate 2200 watts of electric power per kilogram of
    mass then the required fission reactor or reactors will mass
    227,272.72 kilograms . This would deliver 3000 newtons of thrust .

  • Timothy J Mayes June 25, 2007, 23:28

    Comparing Ideal Rocket exchaust velocitys :
    1. H2 + O2 chemical rocket: 5000 m/sec
    2.Solid core nuclear fission thermal rocket
    : 10,000 m/sec
    3.Direct Thrust Nuclear fission pulse rocket ,or fission
    fragment rocket : 12,000 km/sec or 12,000,000 m/sec
    which is 4% of light velocity
    4. Nuclear fission powered electric ion rocket
    : 3,000,000 m/sec which 3000 km/sec or 1 %
    light velocity .
    5. Nuclear fission powered electric plasma rocket
    : 2000 km/sec or 2,000,000 m/sec
    6. Direct thrust steady state fusion , or fusion
    nuclear pulse rocket.: 30,000,000 m/sec or
    30,000 km/sec which is 10% light velocity.
    7. Matter antimatter annhilation powered rocket
    with photonic engine : C 300,000 km/sec or 300,000,000
    m/sec
    8. Beam core type matter antimatter annhilation powered
    pion rocket : 282,000 km/sec or 282,000,000 m/sec
    which is 94 % of light velocity .

  • Konstantinos December 8, 2009, 2:41

    Does anybody knows how many satellites incorporate ion engines? Of course it is not easy to knowthis figure for the Soviet Union/Russian satellites but it should be known for the Western ones.