In the section about Orbit and Environment the Wikipedia article about the Juno spacecraft says:

In comparison, Juno will receive much lower levels of radiation than the Galileo orbiter at its equatorial orbit.

The reason is partly because Galileo had a more equatorial orbit, in order for it to execute a large number of close flyby's of the Jovian moons for data collection. Juno carefully avoids that by remaining in an essentially polar orbit that mostly avoids the intense radiation belts, at least in the beginning of the mission.

Galileo operated for roughly seven years. It was inserted into Jupiter orbit December 1995, the camera operated until January 2002, and the spacecraft was de-orbited - still under control - in September 2003.

If Juno will receive less radiation than Galileo and yet it's systems will start failing within a few months and it seems mostly within one year, even with the electronics in a titanium radiation vault, why would it fail so much faster?

My guess is that it's a side effect of Moore's law. Pixels are much smaller, and transistors are much much smaller 20 years later, perhaps 100 to 1000 times smaller volume per element, so while it's much faster and more powerful, it's much, much more sensitive to radiation. But that's only a guess.

If Juno will get much less radiation than Galileo did, why is it expected to fail so much faster?

  • 2
    $\begingroup$ What was the expected liftetime of Galileo? Your question needs an update because it now seems your are comparing Juno's expected lifetime with Galileo's actual lifetime. $\endgroup$
    – user10509
    Dec 2, 2016 at 14:30

1 Answer 1


It looks like Juno has a much lower apoapsis (e.g., http://spaceflight101.com/juno/juno-mission-trajectory-design/) than did Galileo (e.g., http://solarsystem.nasa.gov/galileo/mission/journey-orbital.cfm). However, Juno is only scheduled to undergo 36 orbits while Galileo went through 34, so similar but the higher apoapsis of Galileo resulted in a longer duration.

It is not clearly stated on the mission website or elsewhere (that I could find) why Juno would last for a shorter period of time than Galileo but I have a few guesses, in no particular order:

  • Galileo did not rely upon solar arrays which degrade under such harsh radiation environments.
  • Galileo used older electronics (e.g., much larger transistors) which by their size alone makes them more robust to harsh radiation environments.
  • The larger apoapsis, as stated above, would result in a longer mission duration than Juno for the same number of Jovian orbits.
  • (This one is purely speculation.) Fuel may also be a constraint since one of the primary mission requirements is a deorbit that will cause Juno to burn up in the Jovian atmosphere.

I should also note that many of Galileo's instruments had failed (due to radiation damage, among other things) prior to the deorbit into the Jovian atmosphere.

  • 1
    $\begingroup$ @uhoh - So I went digging and no one is clearly stating why but I have three guesses. One is that Galileo did not rely upon solar arrays which degrade under such harsh radiation environments. Two, Galileo used older electrons (e.g., much larger transistors) which by their size alone makes them more robust to harsh environments. Three is my answer posted above, namely, that just by its orbit the mission would take longer to complete ~36 orbits (many of Galileo's systems were failing prior to mission end, by the way). $\endgroup$ Nov 30, 2016 at 14:18
  • 1
    $\begingroup$ If somebody wants to dig deeper into the electronics aspect: it looks like Galileo used radiation hardened 1802s and 2901s (see Galileo - True distributed computing in space) and Juno uses RAD750. $\endgroup$ Jul 15, 2019 at 12:24

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.