Slashdot Mirror

← Back to Stories (view on slashdot.org)

Relativistic Navigation Needed For Solar Sails

Posted by Soulskill on from the i'd-rather-be-sailing dept.

KentuckyFC writes "Last year, physicists calculated that a solar sail about a kilometer across with a mass of 300 kg (including 150 kg of payload) would have a peak acceleration of roughly 0.6g if released about 0.1AU from the Sun, where the radiation pressure is highest. That kind of acceleration could take it to the heliopause — the boundary between the Solar System and interstellar space — in only 2.5 years; a distance of 200 AU. In 30 years, it could travel 2500AU, far enough to explore the Oort Cloud. But the team has discovered a problem. Ordinary Newtonian physics just doesn't cut it for the kind of navigational calculations needed for this journey. Because the sail has to be released so close to the Sun, it becomes subject to the effects of general relativity. And although the errors these introduce are small, they become magnified over the course of a long journey, sending the sail roughly 1 million kilometers off course by the time it reaches the Oort Cloud. What these guys are saying is that if ever such a sail is launched (and the earliest estimate is 2040), the navigators will have to be proficient in a new discipline of relativistic navigation."

11 of 185 comments (clear)

  1. Computers? by Extremus · · Score: 4, Insightful

    the navigators will have to be proficient in a new discipline of relativistic navigation.

    Probably you are trying to say that the computers will have to be proficient in this new discipline.

    1. Re:Computers? by FooAtWFU · · Score: 4, Insightful

      Probably you are trying to say that the computers will have to be proficient in this new discipline.

      It's not that hard, either. Just math. We have the equations. They're well-understood. Some physics grad students could probably write the basic engine for such an endeavour. I'd worry more about $UNKNOWN_EXOTIC_EFFECT pushing something off-course.

      --
      The World Wide Web is dying. Soon, we shall have only the Internet.
    2. Re:Computers? by TooMuchToDo · · Score: 4, Insightful

      Even if you get pushed off course, you get to discover $UNKNOWN_EXOTIC_EFFECT =)

    3. Re:Computers? by sabt-pestnu · · Score: 3, Insightful

      I'd be more worried about simple things like...

      Kilometers-to-AU translation errors (nobody would be using "miles" in their calculations, now would they?)
      cumulative floating point rounding errors
      antenna positioning failure

      There are more than enough problems that could re-occur, before you start looking for new ones.

  2. One part in 37 million... by argent · · Score: 5, Insightful

    One million kilometers sounds like a big number, until you realize that 2,500 AU is 3.7 * 10^11 kilometers. So that error is one part in thirty seven million. I suspect that accumulated errors from variations in light intensity due to sunspots and flares will be a bigger problem.

    1. Re:One part in 37 million... by CrimsonAvenger · · Score: 3, Insightful

      Unless we have some specific target in the Oort Cloud that we aim for at the beginning of the trip, with no course-corrections, this is pretty much meaningless.

      And with essentially unlimited ability to maneuver, course-corrections aren't going to be an issue, really.

      --

      "I do not agree with what you say, but I will defend to the death your right to say it"
  3. Re:Wont the accleration decrease with distance by UnHolier+than+ever · · Score: 3, Insightful

    The acceleration, yes, but not the speed. That is why the sail has to start so close ot the sun, it needs it to accumulate most of its speed.

    The reall question will be: how does it stops? I doubt it can use the gravitational slingshot trick at these speeds using only comets.

  4. Is this that important? by MiniMike · · Score: 5, Insightful

    sending the sail roughly 1 million kilometers off course by the time it reaches the Oort Cloud.

    Is there a specific part of the Oort Cloud they want to go to?
    If this ability is needed to travel to other planets accurately, then it seems important. For the Oort cloud, not as much.

    .

    Will this solar sail be going at a speed that will allow it to do any useful observations, or are we just going to watch for the flash when it 'finds' something at that speed?

  5. Mid-course corrections? by vrmlguy · · Score: 4, Insightful

    No space craft has ever been aimed accurately. At various times during the mission, you look at where you are and where you're supposed to be, and make a correction to your trajectory. Is there some reason why this won't work with a solar sail?

    --
    Nothing for 6-digit uids?
    1. Re:Mid-course corrections? by jpmorgan · · Score: 3, Insightful

      Of course there's resistive force. It's called gravity and most people, when they think about space travel, vastly underestimate it's strength.

      Do not forget for one instant that your solar-sailship is in orbit around something. You aren't using your solar sail to overcome the sun's gravity and drift off into the outer reaches of the solar system... there's a term what happens when a star is generating enough radiation pressure to overcome its own gravity: a supernova. Travel by solar sail (and any other modern propulsion system) is based on giving a gentle nudge to your orbit so that eventually you swing by where you want to be.

  6. Re:Just how big is the Oort Cloud? by larry+bagina · · Score: 3, Insightful

    No one has contradicted him? More like no one has any evidence whatsoever that there is an oort cloud, much less that his guess is right or wrong.

    --
    Do you even lift?

    These aren't the 'roids you're looking for.