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I never understood how we launch to earth sun langrange points? By starting from earth we’re already at the correct orbital velocity around the sun so do we ju

I never understood how we launch to earth sun langrange points? By starting from earth we’re already at the correct orbital velocity around the sun so do we just cruise out there and cancel out the delta v we used to get there?

mabbo 5y ago
Remember that no matter how far from the earth you get, you're always being pulled by it, decreasing velocity. The Webb left earth moving at 7km/s, but now is going less than 1km/s. It's going to let Earth's gravity slow it down so that it reaches (effectively) zero at exactly the right spot. It's literally rocket science to do the equations to make it work, but by God we've gotten pretty good at it.
- BbzzbB 5y ago
  Zero? Won't it keep spinning on a plane perpendicular to our orbit and "pointing" the Earth and Sun?
  - jacquesm 5y ago
    Yes, but that's 90 degrees to the current direction of travel. The L2 orbit insertion burn will achieve that.
    - BbzzbB 5y ago
      Oh, right. Makes sense thank you.
kibwen 5y ago
Take a look at the dashboard and note the current speed: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html Right now it's traveling at about 0.55 miles per second. When I checked the other day that was over 0.7, and a bit after launch it was over 1. Putting JWST into L2 is essentially the world's biggest curling toss ( https://en.m.wikipedia.org/wiki/Curling https://en.m.wikipedia.org/wiki/Curling ). As the OP alludes to, JWST's operational life is hard-limited by its fuel capacity. L2 (like L1 and L3, but unlike L4 and L5) is an unstable orbit, and without regular corrections it will drift out of position. This means that you want to save ALL your fuel for making those corrections, and thus spend as little of it as possible on getting there in the first place. So over the next month it's going to slowly crawl into place, cruising on no power other than what the Ariane initially gave it, getting continually slower and slower via the effect of the earth and sun's gravity until it stops perfectly in position.
- vidanay 5y ago
  If curling stones had attitude adjustment thrusters and PID control loops and astronomical observations and precision on-board time keeping.
  - mattmoose21 5y ago
    wouldnt those be the brooms?
  - blacksmith_tb 5y ago
    Automation is coming[1] (though presumably only as a fun challenge). 1: https://www.smithsonianmag.com/smart-news/curly-curling-robot-can-beat-pros-their-own-game-180975951/ https://www.smithsonianmag.com/smart-news/curly-curling-robo...
- khuey 5y ago
  > cruising on no power other than what the Ariane initially gave it Webb has already done multiple burns to get to L2 after being released from the Ariane upper stage. Preserving time on orbit is important but the bigger issue is that Webb can only fire its thrusters in one direction (because it can't point the optics at the sun) so any overshoot is catastrophic. Ariane thus was set to intentionally undershoot L2 and Webb is making up the difference with its fuel.
- deleted 5y ago
  [deleted]
- Dayshine 5y ago
  > and without regular corrections it will drift out of position How significant is that drift? Over 1 year how far out of position would it get? How many days/months/years would it take before it started being too far from earth or had an orbit that was dangerous? I've never been able to find any answers to this question. The internet is covered in people repeating that L1, L2 and L3 are unstable, but never explain the impact.

mabbo 5y ago

Remember that no matter how far from the earth you get, you're always being pulled by it, decreasing velocity. The Webb left earth moving at 7km/s, but now is going less than 1km/s. It's going to let Earth's gravity slow it down so that it reaches (effectively) zero at exactly the right spot. It's literally rocket science to do the equations to make it work, but by God we've gotten pretty good at it.

BbzzbB 5y ago
Zero? Won't it keep spinning on a plane perpendicular to our orbit and "pointing" the Earth and Sun?
- jacquesm 5y ago
  Yes, but that's 90 degrees to the current direction of travel. The L2 orbit insertion burn will achieve that.
  - BbzzbB 5y ago
    Oh, right. Makes sense thank you.

kibwen 5y ago

Take a look at the dashboard and note the current speed: https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html https://jwst.nasa.gov/content/webbLaunch/whereIsWebb.html Right now it's traveling at about 0.55 miles per second. When I checked the other day that was over 0.7, and a bit after launch it was over 1. Putting JWST into L2 is essentially the world's biggest curling toss ( https://en.m.wikipedia.org/wiki/Curling https://en.m.wikipedia.org/wiki/Curling ). As the OP alludes to, JWST's operational life is hard-limited by its fuel capacity. L2 (like L1 and L3, but unlike L4 and L5) is an unstable orbit, and without regular corrections it will drift out of position. This means that you want to save ALL your fuel for making those corrections, and thus spend as little of it as possible on getting there in the first place. So over the next month it's going to slowly crawl into place, cruising on no power other than what the Ariane initially gave it, getting continually slower and slower via the effect of the earth and sun's gravity until it stops perfectly in position.

vidanay 5y ago
If curling stones had attitude adjustment thrusters and PID control loops and astronomical observations and precision on-board time keeping.
- mattmoose21 5y ago
  wouldnt those be the brooms?
- blacksmith_tb 5y ago
  Automation is coming[1] (though presumably only as a fun challenge). 1: https://www.smithsonianmag.com/smart-news/curly-curling-robot-can-beat-pros-their-own-game-180975951/ https://www.smithsonianmag.com/smart-news/curly-curling-robo...
khuey 5y ago
> cruising on no power other than what the Ariane initially gave it Webb has already done multiple burns to get to L2 after being released from the Ariane upper stage. Preserving time on orbit is important but the bigger issue is that Webb can only fire its thrusters in one direction (because it can't point the optics at the sun) so any overshoot is catastrophic. Ariane thus was set to intentionally undershoot L2 and Webb is making up the difference with its fuel.
deleted 5y ago
[deleted]
Dayshine 5y ago
> and without regular corrections it will drift out of position How significant is that drift? Over 1 year how far out of position would it get? How many days/months/years would it take before it started being too far from earth or had an orbit that was dangerous? I've never been able to find any answers to this question. The internet is covered in people repeating that L1, L2 and L3 are unstable, but never explain the impact.