5 ms·

Hershel operated 4 years and one month, but this was because it needed liquid helium coolant and it eventually ran out. Hershel was planned to operate 3.5 yea

by nabla9 5y ago

Hershel operated 4 years and one month, but this was because it needed liquid helium coolant and it eventually ran out. Hershel was planned to operate 3.5 years. btw. Hershel wast the first optical telescope placed in L2. It was also it was also the largest optical space telescope before JWST.

julienchastang 5y ago
"though many factors could ultimately affect Webb’s duration of operation." JWST also needs helium coolant with no possibility to recharge therefore limiting its lifespan to ~10 years, I believe. Interesting about Herschel and L2.
- bryanlarsen 5y ago
  IIRC, the helium coolant is only used on one of JWST's 4 instruments. So if they run out of helium the other three can still be used.
  - terramex 5y ago
    It does use helium only as refrigeration fluid in closed cycle, it does not get depleted. Building a cryocooler capable of achieving so low temperatures without boiling helium off was a major hurdle in JWST development.
    - vlovich123 5y ago
      Isn’t helium notoriously hard to contain without leakage even in a closed system?
      - dnautics 5y ago
        that's hydrogen. IIRC from my chemistry days, Helium is hard to contain in plastic closed systems, but "generally OK" in metal tubing.
- shepardrtc 5y ago
  It actually uses a closed system: https://webb.nasa.gov/content/about/innovations/cryocooler.html https://webb.nasa.gov/content/about/innovations/cryocooler.h...
  - deleted 5y ago
    [deleted]
  - jerjerjer 5y ago
    Doesn't liquid helium always evaporate?
Something1234 5y ago
Wait if Hershel was the largest optical telescope in orbit, how come it didn't catch the public imagination like Hubble did?
- nabla9 5y ago
  Because it must be American to catch attention in American media. Hershel took awesome images. For example: Galactic outflow with the Suzaku X-ray astronomy satellite https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2015/03/galactic_outflow/15327261-1-eng-GB/Galactic_outflow_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... Herschel’s view of new stars and molecular clouds https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2017/09/herschel_s_view_of_new_stars_and_molecular_clouds/17161676-1-eng-GB/Herschel_s_view_of_new_stars_and_molecular_clouds_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... The Little Fox and the Giant Stars https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2016/05/the_little_fox_and_the_giant_stars/15997422-1-eng-GB/The_Little_Fox_and_the_Giant_Stars_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... Star formation on filaments in RCW106 https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2017/02/star_formation_on_filaments_in_rcw106/16821984-1-eng-GB/Star_formation_on_filaments_in_RCW106_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... Feathery filaments in Mon R2 https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2015/08/feathery_filaments_in_mon_r2/15563621-1-eng-GB/Feathery_filaments_in_Mon_R2_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im...
- Gravityloss 5y ago
  Herschel was more modest in size, 3.5 meters vs JWST:s 6.5 meters. Also ESA PR is not as great as NASA. NASA is the gold standard in this regard.
  - jcims 5y ago
    Also because it was imaging far infrared with wavelengths 100-1000 times that of visible light, the resolution of the optics was much lower and yielded kind of bla images (with a few notable exceptions): https://www.herschel.caltech.edu/images https://www.herschel.caltech.edu/images
beezle 5y ago
I don't believe Hershel was optical at all - pretty certain it was far infra-red
- jacquesm 5y ago
  Infra-red is optical. Just not visible light but it uses lenses and mirrors like every other visible light telescope. The main difference is that those lenses are designed to be as transparent to IR as possible instead of accidentally filtering it out. The big trick for Webb is that it will allow for extremely red shifted IR to be received, which translates into 'light from very long ago and very far away'. To be able to do that the sensors are cooled to extremely low temperatures to ensure that the instrument noise level is brought down as low as possible, allowing for extreme sensitivity.
- nabla9 5y ago
  Optical refers to principles that work in visible, ultraviolet, and infrared light. JWST is also primarily infrared telescope. It as some capability in red and the yellow part of the visible spectrum.
  - wolverine876 5y ago
    > Optical refers to principles that work in visible, ultraviolet, and infrared light. Is there something qualitatively different about infrared and ultraviolet that they share with visible, that they are all grouped into 'optical'?
    - maxnoe 5y ago
      Yes, you can use normal mirrors and lenses for these wavelengths
      - wolverine876 5y ago
        Thanks. How is 'normal' defined?
      - 5y ago

by nabla9 5y ago

julienchastang 5y ago

"though many factors could ultimately affect Webb’s duration of operation." JWST also needs helium coolant with no possibility to recharge therefore limiting its lifespan to ~10 years, I believe. Interesting about Herschel and L2.

bryanlarsen 5y ago
IIRC, the helium coolant is only used on one of JWST's 4 instruments. So if they run out of helium the other three can still be used.
- terramex 5y ago
  It does use helium only as refrigeration fluid in closed cycle, it does not get depleted. Building a cryocooler capable of achieving so low temperatures without boiling helium off was a major hurdle in JWST development.
  - vlovich123 5y ago
    Isn’t helium notoriously hard to contain without leakage even in a closed system?
    - dnautics 5y ago
      that's hydrogen. IIRC from my chemistry days, Helium is hard to contain in plastic closed systems, but "generally OK" in metal tubing.
shepardrtc 5y ago
It actually uses a closed system: https://webb.nasa.gov/content/about/innovations/cryocooler.html https://webb.nasa.gov/content/about/innovations/cryocooler.h...
- deleted 5y ago
  [deleted]
- jerjerjer 5y ago
  Doesn't liquid helium always evaporate?

Something1234 5y ago

Wait if Hershel was the largest optical telescope in orbit, how come it didn't catch the public imagination like Hubble did?

nabla9 5y ago
Because it must be American to catch attention in American media. Hershel took awesome images. For example: Galactic outflow with the Suzaku X-ray astronomy satellite https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2015/03/galactic_outflow/15327261-1-eng-GB/Galactic_outflow_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... Herschel’s view of new stars and molecular clouds https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2017/09/herschel_s_view_of_new_stars_and_molecular_clouds/17161676-1-eng-GB/Herschel_s_view_of_new_stars_and_molecular_clouds_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... The Little Fox and the Giant Stars https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2016/05/the_little_fox_and_the_giant_stars/15997422-1-eng-GB/The_Little_Fox_and_the_Giant_Stars_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... Star formation on filaments in RCW106 https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2017/02/star_formation_on_filaments_in_rcw106/16821984-1-eng-GB/Star_formation_on_filaments_in_RCW106_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im... Feathery filaments in Mon R2 https://www.esa.int/var/esa/storage/images/esa_multimedia/images/2015/08/feathery_filaments_in_mon_r2/15563621-1-eng-GB/Feathery_filaments_in_Mon_R2_pillars.jpg https://www.esa.int/var/esa/storage/images/esa_multimedia/im...
Gravityloss 5y ago
Herschel was more modest in size, 3.5 meters vs JWST:s 6.5 meters. Also ESA PR is not as great as NASA. NASA is the gold standard in this regard.
- jcims 5y ago
  Also because it was imaging far infrared with wavelengths 100-1000 times that of visible light, the resolution of the optics was much lower and yielded kind of bla images (with a few notable exceptions): https://www.herschel.caltech.edu/images https://www.herschel.caltech.edu/images

beezle 5y ago

I don't believe Hershel was optical at all - pretty certain it was far infra-red

jacquesm 5y ago
Infra-red is optical. Just not visible light but it uses lenses and mirrors like every other visible light telescope. The main difference is that those lenses are designed to be as transparent to IR as possible instead of accidentally filtering it out. The big trick for Webb is that it will allow for extremely red shifted IR to be received, which translates into 'light from very long ago and very far away'. To be able to do that the sensors are cooled to extremely low temperatures to ensure that the instrument noise level is brought down as low as possible, allowing for extreme sensitivity.
nabla9 5y ago
Optical refers to principles that work in visible, ultraviolet, and infrared light. JWST is also primarily infrared telescope. It as some capability in red and the yellow part of the visible spectrum.
- wolverine876 5y ago
  > Optical refers to principles that work in visible, ultraviolet, and infrared light. Is there something qualitatively different about infrared and ultraviolet that they share with visible, that they are all grouped into 'optical'?
  - maxnoe 5y ago
    Yes, you can use normal mirrors and lenses for these wavelengths
    - wolverine876 5y ago
      Thanks. How is 'normal' defined?
    - 5y ago