back to article Grav-mapping satellite fires ion engines

The European Space Agency (ESA) has confirmed that both the electric ion propulsion engines aboard its Gravity Field and Steady-State Ocean Circulation Explorer (GOCE) satellite are "performing nominally". Artist's impression of GOCE orbiting over ice. Pic: ESA The "cutting-edge" drives - built by Qinetiq - are designed to …


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  1. Johnny G


    Why do boffins have to describe their gadgets as "performing nominally", when what they really mean is "performing normally" or "as expected"??

  2. Greg

    Coolest human space-thing ever

    Every time I see that satellite, I can't help thinking that it's the coolest looking thing we've ever put in space.

  3. zedee

    Range rather than defined point

    I think nominally refers to "within upper and lower acceptable limits" whereas normally would refer to a single "normal" state.

    But it does irk me slightly as well, the slow creep towards techspeak/management buzzwords etc becoming part of common vocabulary.

  4. Tim

    How high? How fast?

    So let me see if I have this right. A really cool looking bucket is an a kind of 'free fall', plumemting towards a hot and fiery death at the rate of 20.6096 double decker busses per day all because of a feeble blue flame engine that can only produce 0.0001 Norris since they only took up 9.5238 Jubs worth of Xenon.

    Seems to me that flying around a planet at about 0.1575% of the maximum velocity of a sheep in a vacuum at an altitude of 2024.8018 brontosaurus requires more energy than that.

    "All being well, the engines will - as part of the Drag-Free and Attitude Control Subsystem (DFACS) - automatically maintain GOCE's velocity and altitude while the scientists get down to the job in hand. ."

    What job is that then? Watching re-entry fireworks?

  5. Fluffykins Silver badge


    "velocity of a sheep in a vacuum"

    Sir - we salute you!

  6. Mike Richards

    @ Tim

    Thanks, I think we're all much more informed now. For sheer clarity that was worthy of a 1970s Open University programme - even if you didn't come equipped with a blackboard, kipper tie and oscilloscope.

  7. Wize


    ...when is this free-falling expensive brick going to plant itself in the ground? And where?

    Nice one Tim

  8. Robert Hill

    Clarity required...

    This article states both "This thrust represents a "fantastically small force" of between 1 and 20 millinewtons (mN), but that's enough to maintain GOCE's "free-fall" orbit - currently decreasing at a rate of around 190 metres a day from an altitude of roughly 280 km."

    and then goes on to say:

    "All being well, the engines will -... - automatically maintain GOCE's velocity and altitude while the scientists get down to the job in hand."

    OK, either this thing is in free-ball and losing altitude, or the engines are going to maintain a set can't be both, not correctly. (The engines COULD maintain the satellite's altitude LOSS to a given rate, but that is not the same as maintaining altitude.)

    Author, clarity please?

  9. Matt Symes

    'Currently' Decreasing altitude...

    @Robert Hill: I guess it's *currently* decreasing in altitude but once they're satisfied the engine's are working ok they'll have them fired up to *maintain* altitude.

    Paris, because this is my first time... oh hang on - that doesn't work does it :(

  10. breakfast

    A hot contender emerges

    Surely Rune Floberghagen is a serious contender for the much sought-after "Best Name In Science" award?

  11. Peyton


    Kind of interesting...

    From the OED: 6. orig. and chiefly Astronaut. Functioning acceptably, normal.

    From Merriam-Webster: 5: being according to plan : satisfactory <everything was nominal during the launch>

    Regardless of who you ask, this usage seems to be somewhat confined to 'rocket scientists'. I blame Mr. Spock.

  12. CypherDragon

    Obligatory Star Wars quote

    "Stand by Ion Control"

  13. Greg Trocchia

    @Robert Hill

    First off, in the context of orbital mechanics "free-fall" does not connote losing altitude. Orbits allow you to do what Douglas Adams suggested in "Hitchhikers Guide": "The knack lies in learning how to throw yourself at the ground and miss." When in orbit, you are constantly falling around the Earth and, hence, missing it and this is the essence of free-fall.

    As for the explicit statement that the orbit is "currently decreasing at 190 meters per day". The key word in the phrase is "currently" as in before the ion engines are fired for real (as opposed to test firing) in order to do the needed station keeping. The implication is that once the engines are continually firing, they will be enough to keep the orbit from degrading any further so long as they remain operational

    That said, I will agree that the phrasing in the article does not exactly help one to parse it correctly.

  14. Anonymous Coward


    Yeah, heaven forbid any of us should learn new words as we go through life. Let's dumb down everything, starting with El Reg! We're none of us really techies anyway, right? Just glorified typists really.

    This attitude amazes me most because when reading an internet article you have Google RIGHT THERE to look anything up. You don't even have to get up off your arse to look this shit up now.

    OTOH any of you guys fancy a game of Scrabble?

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