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Different_Muscle_116 OP t1_j606ar9 wrote

Reply to comment by Waddensky in How come space probes generally take photos of moons or asteroids from several hundred (or thousands) of kilometers away from the object they orbit? by Different_Muscle_116

Okay Juno took photos of Io some of which were from several hundred to a thousand kilometers away.

I assume that IO has less gravity well than Earth. There are objects even smaller than Io that have had photos taken from orbits as well.

I always wonder why they can’t orbit closer and get even greater surface detail.

I’m basing an assumption that an object with less mass (like an asteroid or a moon) can be orbited much closer than a satellite around the Earth before the gravity well becomes an issue.

Are these missions at their absolute closest orbits possible given the fuel reserves?

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oalfonso t1_j60900b wrote

Juno main mission wasn't taking pictures, it was magnetosphere analysis to try to understand Jupiter's internal structure. The orbits were set for that mission, not pictures.

Also, any orbit on Jupiter and Saturn has to be carefully analysed to minimise the impact of the radiation on the spacecraft.

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Different_Muscle_116 OP t1_j60at10 wrote

That makes a lot of sense.

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oalfonso t1_j60b7o7 wrote

Take this with a pinch of salt because I don't remember when I heard it or read it. Juno originally wasn't going to have any cameras and NASA PR department demanded them to have something to show to the public because unless you are a scientist the telemetry data alone is not cool.

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sifuyee t1_j610i4u wrote

Mike Malin had proposed the Junocam instrument and been rejected. He will point out that JPL-run missions have a much higher than statistically expected predominance of JPL-developed payloads. However, Mike managed to convince enough folks to eventually get HQ to add Junocam to the payload suite anyway, partly by arguing that it would be a very effective way to engage the public in the mission.

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YesWeHaveNoTomatoes t1_j607oio wrote

If Io had been Juno's target, they would probably have calculated its trajectory and fuel needs to achieve either an actual orbit around Io or, if that wasn't possible, a closer flyby. But Juno's main target was Jupiter itself, so all photos of Jupiter's satellites were taken from the most fuel-efficient orbit around Jupiter.

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aztronut t1_j60d46i wrote

When the trade is between coverage and orbital altitude, coverage wins and closer is not necessarily better. It is also more dangerous to insert a spacecraft into such a close orbit, where it is also affected more by the perturbations induced by the body it is orbiting and thus more difficult to navigate. Look into the history of the MESSENGER mission and you'll see that once complete coverage of the surface was obtained the orbit was lowered progressively until impact was achieved at end of life, this seems to be the scenario you are asking for.

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[deleted] t1_j606qmv wrote

[deleted]

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djmustturd t1_j607dh3 wrote

Spacecraft like Juno have very specific orbits to follow that are planned very far in advance in order to maximize their mission time. If, say, Juno swings too close to Io, it might get a gravity assist that ejects it from Jupiter, in which case it’s no longer very useful is it.

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Hot_Egg5840 t1_j60dobt wrote

The closer to the object you are orbiting, the faster you need to go to stay in orbit. The faster you move, the more of an issue image blur is. Distant objects don't get much light. That means camera shutters need to stay open longer times, which also adds to blur. Yes, you would get better detail but it becomes useless because all the pixels are blurred.

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