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According to the BBC's Nasa confirms ocean moon mission:

Europa's orbital path takes it deep into belts of intense radiation that surround the giant planet. This radiation fries spacecraft electronics, which limits the durations of prospective missions to months or even weeks.

So rather than orbiting Europa, Clipper will make repeated close flybys of the moon, to reduce its exposure to the energetic particles trapped by Jupiter's magnetic field.

If Clipper orbited Europa then every moment that it was in the high radiation environment it would also be taking data on Europa.

But since Jupiter's radiation field is much, much bigger than Europa, each hour-long (or less) flyby would involve an orbit around Jupiter and probably would involve tens of hours of radiation exposure during it's perijove.

Question: How does not orbiting Europa maximize Clippers coverage of Europa for a given radiation dose? This seems backwards to me.

Related items involving spacecraft passing through Jupiter's radiation field:

enter image description here

above: "Animation of Jupiter's Synchrotron Radiation Torus. Credit: NASA/JPL - Caltech". From the Vatican Observatory Blog

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1 Answers1

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It seems to be a duty cycle thing:

Because Europa lies well within the harsh radiation fields surrounding Jupiter, even a radiation-hardened spacecraft in near orbit would be functional for just a few months. Most instruments can gather data far faster than the communications system can transmit it to Earth because there are a limited number of antennas available on Earth to receive the scientific data. Therefore, another key limiting factor on science for a Europa orbiter is the time available to return data to Earth. In contrast, the amount of time during which the instruments can make close-up observations is less important.

(From Wikipedia quoting a Planetary Society article)

Flybys intermixed with time spent sending back data maximizes the data sent back because you can send for longer.

The article provides a numerical example:

Studies by scientists from the Jet Propulsion Laboratory show that by performing several flybys with many months to return data, the Europa Clipper concept will enable a \$2B mission to conduct the most crucial measurements of the cancelled \$4.3B Jupiter Europa Orbiter concept. Between each of the flybys, the spacecraft will have seven to ten days to transmit data stored during each brief encounter. That will let the spacecraft have up to a year of time to transmit its data compared to just 30 days for an orbiter.

I can only speculate why a “sit until your electronics is not quite dead, then fly out to a safe distance and transmit” isn’t used, but I suspect the “not quite” part is nerve wracking: guess wrong and you lose the bulk of the mission data. The flybys are being done via gravity assists from other moons, so it’s also possible this takes less fuel than going into and out of orbit.

Bob Jacobsen
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