Satellites have an electric future

Ion thruster Thrust comes from a stream of charged atoms (ions) accelerated to very high velocities

One of the most interesting trends in satellite production in the next few years is likely to be the wide introduction of electric propulsion (EP).

More and more satellites will be launched not with chemical thrusters to manoeuvre them in space but with ion propulsion units.

We've seen electric engines fitted to scientific spacecraft in recent years, but not so much on commercial satellites.

Boeing has charged out of the box on this one, agreeing to build four "all electric" telecommunications spacecraft for Asian and Mexican operators.

The attraction is mass - or rather, lack of it.

Chemical thrusters require large tanks of propellant; electric engines, while they don't provide quite the same initial boost, do not need anything like the same volumes of fuel and can work for much longer.

The downside is that it takes you longer to put a satellite in its final orbital slot; the big plus, however, is that you get a much lighter satellite.

That weight saving can either be given over to more payload (transponders in the case of telecommunications satellites), or allow the satellite to squeeze on to a smaller, cheaper rocket.

The latter strategy is the one now being looked at seriously for the future of Galileo, Europe's new satellite navigation system.

It needs 30 spacecraft in orbit to operate a full network (with spares); and because Galileo will be an on-going service, there will be an on-going requirement for replacement satellites.

Galileo satellite A Galileo satellite can be produced now for a unit price of about 30m euros

Galileo, as we all know, is a hugely expensive project, costing billions of euros.

Part of that cost comes down to the price of the rockets used to get the platforms into the sky. If that could be tackled, our taxes would go further.

Currently, Galileo satellites are launched two at a time on a Russian Soyuz rocket.

It costs roughly as much to launch those two satellites as it does to build them. So, if you could get a third satellite aboard, you'd suddenly jump to a new cost regime.


Galileo constellation (Esa)
  • Galileo is owned by the EU but is being procured by the European Space Agency
  • Some 30 satellites are likely to be launched in batches in the coming years
  • Galileo will work alongside the US GPS and the Russian Glonass sat-nav systems
  • Europe's full system promises real-time positioning down to a metre or less
  • It should deepen and extend high-value markets already initiated by GPS
  • Some say economies are over-reliant on GPS; Galileo ought to make sat-nav more robust

This week, at the Farnborough International Airshow, the two companies making Europe's Galileo spacecraft put pen to paper on their contractual relationship.

OHB System of Bremen, Germany, and Surrey Satellite Technology Limited (SSTL) from Guildford, UK, can now turn out a Galileo satellite for about 30m euros.

That has come down from roughly 40m euros per spacecraft when they were first engaged to do the job by the European Commission and the European Space Agency.

But getting the cost down much further is really a launch issue, and electric propulsion could be the solution.

"It is feasible to take Galileo satellites up with electric propulsion, if the technology is available and mature enough," commented OHB's Ingo Engeln.

"You need more time to get the satellites in place, of course, but for the next generation this should be no problem."

And Giuliano Gatti, who works on the Galileo project for Esa, added: "It would mean you could get one satellite on Vega, three on Soyuz and up to six on the Ariane 5."

Europe has a lot of experience already in ion engines.

The concept is simple enough. Strip the electrons off a stream of xenon gas atoms so that they become charged (ions). Then put those ions in a magnetic field and accelerate them to extremely highly velocities in one direction to provide thrust for your satellite in the opposite direction.

You may be aware of Goce, the European Space Agency's gravity mapping satellite. This flies so low to make its maps that it must continually fire its ion engine to counteract the wisps of atmosphere still present at an altitude of 260km.

It was launched in 2009 with just a 40kg tank of xenon and is still working.

Goce satellite Gravity mapper Goce has been firing its electric engine non stop since 2009

Of course the penalty is that ion engines put you in the slow lane.

Chemical thrusters might not burn as long, but they give you great initial acceleration and a satellite can be ejected from its rocket and be ready for use in its correct position in the sky in a matter of weeks.

With electric propulsion, it would take months.

"Where the EP variant will come into its own is in the future, once the Galileo system is in place and you have to consider replenishment, perhaps of single spacecraft," commented John Paffett.

"At the moment, Soyuz and Ariane are quite efficient ways of populating a constellation; but what if you have a single spacecraft failure?

"It makes no sense to put an additional four or six spacecraft into an orbital plane. So the question then becomes: how cheaply can you acquire a small launch vehicle, drop a satellite off in any arbitrary orbit and have EP do the transfer from there?"

The contract signed between OHB System and SSTL brings another 80m euros' worth of work to the Guildford company.

OHB also signed a contract with Culham's ABSL at the show. The British company will be providing the batteries that go into Galileo satellites.

Jonathan Amos Article written by Jonathan Amos Jonathan Amos Science correspondent

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  • rate this

    Comment number 112.

    #111 Drunken Hobo
    "A nuclear reactor in space would be interesting!"

    The materials to build one and the fissiles to run it would be minable on almost any nickel-iron asteroid.

    It would have to be built in space. NERVA finally foundered on the risk of launching large amounts of nuclear material by rocket.

  • rate this

    Comment number 111.

    94 sporpo - The Stirling engine is such a beautifully elegant design, I'm surprised it's taken us as long to put it to use. However, I think using spontaneous fission rather than an induced nuclear reaction means it will only produce a watts rather than the kilowatts needed for an ion engine, and will likely be used to power instrumentation instead.
    A nuclear reactor in space would be interesting!

  • rate this

    Comment number 110.

    #108 Jonathon Amos

    I really hope VASIMIR is viable technology. Our current combustion based rocket technology is not really up to the job of turning a barely explored solar system into a solar civilization., or of herding asteroids as Planetary Resources and Spaceguard may require.

  • rate this

    Comment number 109.

    95 Philip Iszatt - The life expectancy since 1900 has doubled, also thanks to science.
    98 - If you wish to go for the "wonder" angle, is it not more wondrous to know that all we see around us is due to just 4 fundamental forces acting within matter? Compared to that, a god controlling everything is somewhat… tedious.
    If the universe would look the same with a god, then what exactly does he do?

  • rate this

    Comment number 108.

    @Entropic man. Ad Astra's work is very interesting. I've written about it here: because the Texas company has been making good use of some excellent British technology. Also here:

  • rate this

    Comment number 107.

    This is the sort of thing we should be looking for as a tool for expediting manned space flight.

  • rate this

    Comment number 106.

    My philosophy classes were a long time ago. I've been using "a priori" as a synonym for "assumption", not in Kant's sense of unquestionably correct knowledge for which no evidence is necessary.

  • rate this

    Comment number 105.

    I don't think that any of Philip's seven a priori assumptions are stated as being a priori, or even implied as being axiomatic, in science. We may consider them as such in order to have a starting point for rational enquiry, but I have certainly never considered any of them to be self evident.

  • rate this

    Comment number 104.

    #103 contd.

    A cosmologist can describe how our visible universe came into being and can speculate about the larger multiverse of which it may be part. He would see no reason to ask "Why?"

    Once again , your insistance that there is a purpose behind the universe is a priori, rather than necessary.

  • rate this

    Comment number 103.

    #110 Philip Iszatt
    "I think you mean circular rather than recursive"

    I did mean recursive.

    If your God is an ordered being he must be subject to the same requirement for a creator as his creation, leading to an infinite series of creators and no prime cause. If he is not ordered he cannot be regarded as a God.

    Your assumption of a prime cause is a priori and unnecessary.

  • rate this

    Comment number 102.

    Re 101.Entropic man
    A police inspector once came up with an explanation for a crime that fitted perfectly. Unfornutely in court the prosecution demonstrated four alternation explanatione that each fitted just as well. So your "why not" strategy is lazy. To "fit the evidence" is not to prove causality or why,

  • rate this

    Comment number 101.

    #96 David Butterfield
    "Science can tell us When, Where, What and How but not Why?"

    A university Philosophy Dept. once set a final exam. The paper asked one question - "Why".

    Anyone answering "Why not?" got an A grade.
    Anyone answering "Because" got a B.
    Any other answer got a C.

  • rate this

    Comment number 100.

    Re 99.Entropic man
    I think you mean circular rather than recursive. Moreover an arguement about order is quite different to one about design. But your problem is, if you believe in causality at all you cannot duck the question of prime cause. See the list of scientific assumptions @ 97. If you go with these and don't want to kiss your brains goodbye you are stuck with the probability of God.

  • rate this

    Comment number 99.

    #95 Philip Iszatt
    "the probability that an orderly universe could occur without the existence of God tends towards zero."

    The problem with your Argument From Design is that it is recursive.

    "Something as complex as Nature
    must have had a creator."
    This argument's odd.
    Who made the One God
    or created the Creator's creator?

  • rate this

    Comment number 98.

    Re 92.Drunken Hobo
    Don't worry about winning or losing an arguement, just imagine a fabulous life of science AND knowing a loving God.

  • rate this

    Comment number 97.

    Re 92.Drunken Hobo
    Just look at these 7 a priori assumptions of science and notice how close (if not identical) they are to faith in God:
    1 There is order
    2 There is causality
    3 There is one reality
    4 Time and logic are external to our minds
    5 Certainty is possible
    6 (Relatively) simple laws can explain an infinitely complex universe
    7 We can know something without knowing everything

  • rate this

    Comment number 96.

    I trained as an engineer, later gained a science degree but went to Church this morning to thank God for this beautiful World, spoiled only by some stupid and selfish humans. Science can tell us When, Where, What and How but not Why? I will continue in my belief until Dawkins et al stop their proselyting to sell books and prove "Why". I would volunteer to fly to the planets, though.

  • rate this

    Comment number 95.

    Re 92.Drunken Hobo
    We "got into this" because if science is pursued without reference to the meaning of life it can lead to disaster- as in the 200 million people killed last century in wars on a global scale enabled by science.
    As to God, in purely rational terms the probability that an orderly universe could occur without the existence of God tends towards zero.

  • rate this

    Comment number 94.

    Drunken Hobo
    14th July 2012 - 13:40
    I'm not sure the radioisotope generators would provide enough power to the engine; they're very primitive compared to a nuclear power station, just a hot bit of metal and a thermocouple!

    Stirling engines have been proposed to generate electricity from the heat of the radioactive material for long-duration space probes. Dont know if any launched yet.

  • rate this

    Comment number 93.

    When you start thinking big in space the numbers get out of control very quickly.

    Using ion propulsion to move a 1km asteroid enough to avoid a collision with Earth would need 50kN thrust applied for 30 years. This would need 500,000 Dawn thrusters working continuously for three decades and using 1.4 million tons of xenon.


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