4 ms·

Since L2 is an unstable equilibrium, won’t there also need to be routine adjustments throughout the mission?

dredmorbius 5y ago
Yes. Those adjustments, as well as unloading of the reaction wheels used to position JWST, and the fuel burns reqiured for them, are the principle determinants of the JWAT's lifespan, estimated at 10 years. Nasa have lowballed such estimates for numerous missions in the past (Hubble and numerous Mars lander and rover missions come to mind), and it's possible JWST will exceed the planned lifetime, potentially by a wide margin. Initial indications are that the Ariane V insertion should have spared much potential fuel use in orbital corrections and insertion. I expect the space geek set will have speculation, hopefully reasonably informed, on this in the not-too-distant future.
- simonh 5y ago
  Apparently the launch and mid course burn were precise enough that it should have enough remaining propellant for a bit more than 10 years of station keeping.
- junon 5y ago
  Thought the same. The launch and everything went down so perfectly I bet it gets more than 10 years.
- weaksauce 5y ago
  I was under the impression that they were planning on making a drone that would refuel it in 10 years or so? Is that not correct?
  - dredmorbius 5y ago
    I've heard that the capavility exist but the mission is not planned. https://www.space.com/3833-nasa-adds-docking-capability-space-observatory.html https://www.space.com/3833-nasa-adds-docking-capability-spac... https://jwst.nasa.gov/content/about/faqs/faq.html#serviceable https://jwst.nasa.gov/content/about/faqs/faq.html#serviceabl...
  - phire 5y ago
    They have given it a 10 year lifespan. They have said that fuel is a major limiting factor and talked about a refuelling drone to extend life. But I don't think that means it only has 10 years of fuel, and I don't think they have ever said explicitly said that. I suspect it's more like 15 years in the best case. The fact that they aren't already planning a refuelling mission implies that it's not a critical limiting factor.
    - Ahwleung 5y ago
      Would I be wrong to assume that technological advances in the next 15 years would justify sending a second satellite? As in, instead of a refueling mission we'd be more likely to send a version 2 of the satellite with even better sensors/apparatus/whatnot?
      - foolfoolz 5y ago
        jswt was the version 2 satellite for hubble. turns out we were able to do 4 massive upgrades to keep hubble relevant before hubble v2 got anywhere
      - dredmorbius 5y ago
        It's helpful to think through what opportunities might exist. There are a set of telescope plans which are presently in consideration, including WIRST, the wide-angle infrared telescope; HabEx, the Habitable Exoplanet Imaging Mission; Lynx, a next-generation X-ray telescope; and the Origins Space Telescope, an infra-red telescope even larger than Webb. https://www.universetoday.com/139461/what-comes-after-james-webb-and-wfirst-four-amazing-future-space-telescopes/ https://www.universetoday.com/139461/what-comes-after-james-... For telescopes, among factors I'm aware of are: - The total number of devices. More 'scopes means more points of the sky which can be imaged at any one time. This permits detecting either rare or transient events. - Wavelength specificity. Infra-red, radio, visible light, UV, and X-Ray sensitivity all permit detection of different phenomena. Devices suited to one wavelength may not be suitable for others. Specific research goals may favour specific observational methods. - Other sensing modes. Gravity, gamma ray, and particle sensors (e.g., neutrino sensors, cosmic-ray detectors) may afford other options. There are proposals for space-based gravity-wave detectors, for example. - Compound devices. The HabEx system in particular has two components, the telescope itself, and a sunshield used to block the light of an observed star, which would operate at a separation of 100s of thousands of km. - Collector size. Larger mirrors permit gathering of more light. This permits shorter collection periods for brighter events, and imaging of previously undetectable phenomena. The Hubble Deep Field views are an example of the latter, and pushed the boundaries of known and and observable phenomena tremendously. - Storage, processing, and communications capabilities. I don't know how much this contributes to observation capabilities, though I suspect it has an impact. - Developments in phsyics, materials, and sensing, generally. Looking through lists of physics and chemistry Nobel awards since the 1970s, a surprisingly large number have concerned capabilities rather than fundamental characteristics or properties of matter or the universe. Many of these afford new capabilities in sensing and detection. - Probes. Rather than a single instrument which views distant objects, probes get close to a specific object, or set of objects, and make close or direct observations of these. Various landers, impactors, flyby, orbiter, and similar missions, to date all to objects within the Solar System, would be examples of these. These compete with other missions (manned, long-distance sensing). - Earth observation. Probably the largest class and most productive set of space-based observation platforms has been looking at our own planet. It's also worth thinking through what has made JWST possible, including launch platforms, experience with complex deployments, manufacturing, sensing, and control capabilities. These will have impacts on future missions, and further development might also extend their capabilities. Finally: most technological improvement tends to follow a sigmoidal curve: an early period of slow development, a period of rapid attainment, then a slower period of approaching theoretical maximum efficacy. New developments or combinations of technologies may restart that curve, but often 15 years doesn't deliver transformational development. Rather older technologies are refined, reliability improved, costs reduced, or flexibility increased.
- dev_tty01 5y ago
  They are already ahead on their fuel budget due to the accuracy of the Ariane launch process. NASA said it would "significantly" extend the mission lifetime. https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-excess-fuel-likely-to-extend-its-lifetime-expectations/ https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-exces...
stjohnswarts 5y ago
Of course, nothing is perfect they will have to adjust position over time and have accounted for all of it with possible robotic missions in the future to extend and refuel as necessary, although that is a "hope" rather a surety.
deleted 5y ago
[deleted]
Dayshine 5y ago
Does anybody know exactly how unstable L2 is? I've seen lots of people talk about how some Lagrange points are stable and others are unstable, but I've never been able to find a source for how much this matters. How long would it take for Webb to move so far off L2 that we can't communicate with it anymore, or for it to be at risk of being completely thrown out of orbit to the point that it would impact earth or the sun?
- andrewflnr 5y ago
  It matters enough that "over ten years" of fuel left (as we supposedly have now) is a really great outcome, as opposed to just five we might have form. Scott Manley on YouTube has a pretty good video on Lagrange points (and it's a topic where the video medium is actually pretty helpful).
- dTal 5y ago
  The failure mode of straying too far from L2 is the inability to shield the highly sensitive optics from both the Earth-Moon system and the Sun simultaneously.

Yes. Those adjustments, as well as unloading of the reaction wheels used to position JWST, and the fuel burns reqiured for them, are the principle determinants of the JWAT's lifespan, estimated at 10 years. Nasa have lowballed such estimates for numerous missions in the past (Hubble and numerous Mars lander and rover missions come to mind), and it's possible JWST will exceed the planned lifetime, potentially by a wide margin. Initial indications are that the Ariane V insertion should have spared much potential fuel use in orbital corrections and insertion. I expect the space geek set will have speculation, hopefully reasonably informed, on this in the not-too-distant future.

simonh 5y ago
Apparently the launch and mid course burn were precise enough that it should have enough remaining propellant for a bit more than 10 years of station keeping.
junon 5y ago
Thought the same. The launch and everything went down so perfectly I bet it gets more than 10 years.
weaksauce 5y ago
I was under the impression that they were planning on making a drone that would refuel it in 10 years or so? Is that not correct?
- dredmorbius 5y ago
  I've heard that the capavility exist but the mission is not planned. https://www.space.com/3833-nasa-adds-docking-capability-space-observatory.html https://www.space.com/3833-nasa-adds-docking-capability-spac... https://jwst.nasa.gov/content/about/faqs/faq.html#serviceable https://jwst.nasa.gov/content/about/faqs/faq.html#serviceabl...
- phire 5y ago
  They have given it a 10 year lifespan. They have said that fuel is a major limiting factor and talked about a refuelling drone to extend life. But I don't think that means it only has 10 years of fuel, and I don't think they have ever said explicitly said that. I suspect it's more like 15 years in the best case. The fact that they aren't already planning a refuelling mission implies that it's not a critical limiting factor.
  - Ahwleung 5y ago
    Would I be wrong to assume that technological advances in the next 15 years would justify sending a second satellite? As in, instead of a refueling mission we'd be more likely to send a version 2 of the satellite with even better sensors/apparatus/whatnot?
    - foolfoolz 5y ago
      jswt was the version 2 satellite for hubble. turns out we were able to do 4 massive upgrades to keep hubble relevant before hubble v2 got anywhere
    - dredmorbius 5y ago
      It's helpful to think through what opportunities might exist. There are a set of telescope plans which are presently in consideration, including WIRST, the wide-angle infrared telescope; HabEx, the Habitable Exoplanet Imaging Mission; Lynx, a next-generation X-ray telescope; and the Origins Space Telescope, an infra-red telescope even larger than Webb. https://www.universetoday.com/139461/what-comes-after-james-webb-and-wfirst-four-amazing-future-space-telescopes/ https://www.universetoday.com/139461/what-comes-after-james-... For telescopes, among factors I'm aware of are: - The total number of devices. More 'scopes means more points of the sky which can be imaged at any one time. This permits detecting either rare or transient events. - Wavelength specificity. Infra-red, radio, visible light, UV, and X-Ray sensitivity all permit detection of different phenomena. Devices suited to one wavelength may not be suitable for others. Specific research goals may favour specific observational methods. - Other sensing modes. Gravity, gamma ray, and particle sensors (e.g., neutrino sensors, cosmic-ray detectors) may afford other options. There are proposals for space-based gravity-wave detectors, for example. - Compound devices. The HabEx system in particular has two components, the telescope itself, and a sunshield used to block the light of an observed star, which would operate at a separation of 100s of thousands of km. - Collector size. Larger mirrors permit gathering of more light. This permits shorter collection periods for brighter events, and imaging of previously undetectable phenomena. The Hubble Deep Field views are an example of the latter, and pushed the boundaries of known and and observable phenomena tremendously. - Storage, processing, and communications capabilities. I don't know how much this contributes to observation capabilities, though I suspect it has an impact. - Developments in phsyics, materials, and sensing, generally. Looking through lists of physics and chemistry Nobel awards since the 1970s, a surprisingly large number have concerned capabilities rather than fundamental characteristics or properties of matter or the universe. Many of these afford new capabilities in sensing and detection. - Probes. Rather than a single instrument which views distant objects, probes get close to a specific object, or set of objects, and make close or direct observations of these. Various landers, impactors, flyby, orbiter, and similar missions, to date all to objects within the Solar System, would be examples of these. These compete with other missions (manned, long-distance sensing). - Earth observation. Probably the largest class and most productive set of space-based observation platforms has been looking at our own planet. It's also worth thinking through what has made JWST possible, including launch platforms, experience with complex deployments, manufacturing, sensing, and control capabilities. These will have impacts on future missions, and further development might also extend their capabilities. Finally: most technological improvement tends to follow a sigmoidal curve: an early period of slow development, a period of rapid attainment, then a slower period of approaching theoretical maximum efficacy. New developments or combinations of technologies may restart that curve, but often 15 years doesn't deliver transformational development. Rather older technologies are refined, reliability improved, costs reduced, or flexibility increased.
dev_tty01 5y ago
They are already ahead on their fuel budget due to the accuracy of the Ariane launch process. NASA said it would "significantly" extend the mission lifetime. https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-excess-fuel-likely-to-extend-its-lifetime-expectations/ https://blogs.nasa.gov/webb/2021/12/29/nasa-says-webbs-exces...

stjohnswarts 5y ago

Of course, nothing is perfect they will have to adjust position over time and have accounted for all of it with possible robotic missions in the future to extend and refuel as necessary, although that is a "hope" rather a surety.

deleted 5y ago

[deleted]

Dayshine 5y ago

Does anybody know exactly how unstable L2 is? I've seen lots of people talk about how some Lagrange points are stable and others are unstable, but I've never been able to find a source for how much this matters. How long would it take for Webb to move so far off L2 that we can't communicate with it anymore, or for it to be at risk of being completely thrown out of orbit to the point that it would impact earth or the sun?

andrewflnr 5y ago
It matters enough that "over ten years" of fuel left (as we supposedly have now) is a really great outcome, as opposed to just five we might have form. Scott Manley on YouTube has a pretty good video on Lagrange points (and it's a topic where the video medium is actually pretty helpful).
dTal 5y ago
The failure mode of straying too far from L2 is the inability to shield the highly sensitive optics from both the Earth-Moon system and the Sun simultaneously.