james_nicoll

No, WE are just SLOW. "Space is Big" shouldn't apply at such short (cosmically speaking) ranges.

One would hope so.

Granted, there's something useful to be said for making sure that we've got everything we can find in Sol system catalogued, mapped and trajectory-tracked along the way...

I don't think we're in a great deal of danger from Ganymede.

Ganymede, probably not.

Something we don't yet know about en route between Jupiter and Earth, though?

I doubt there's much a Jupiter probe can do in this particular regard. Survey telescopes are more useful for tracking hazardous objects, though a probe can do science concerning the nature of an individual asteroid.

I worked on JGO trajectory modelling before it was JUICE as part of a fourth-year project: at that time there were no plans to do any flybys other than around planets on the way to Jupiter.

Thanks for this well-sourced information :)

This. And the main reason we are so slow is that we can't launch payloads heavy enough to provide our space probes with nice healthy sized rockets for getting from here to there. If and when SpaceX actually manages to turn their Falcon Heavy design into a working launcher, I expect the travel times for such probes will drop substantially because they'll be able to budget a bigger beefier rocket for getting the probes into Jupiter/Saturn/etc orbit.

I don't think rockets are the answer. ("Rockets Are Wrong") Using methods that cheat the rocket equation are what you want -- mass-beam systems, the Dusty Plasma approach that James pointed out to me and I used in Threshold, magsails or solar sails, etc., because they require much less expendable mass and produce low but constant thrust which adds way up after a while. For instance, accelerating at 1/1000th of a g constantly means you're gaining velocity of over 800m/s over the course of a day, if I do my math right -- 10m/s^2 *.001 = .01m/s^2, *3600*24sec/day = 864m/sec/day. That means you'll be over 300kps by the end of a year and have travelled over 4.7 billion miles.

If you can get a 1/1000th g constant acceleration, the whole of the main solar system is less than 1 year away, unless I'm f'ing up my math, which I suppose I may.

Rocket, ion drive, whatever, the main thing is that we can't lift a payload heavy enough to get our robots to orbit any planet other than Venus or Mars in a brief period of time, which puts a serious crimp on our ability to explore the outer solar system -- the longer it takes to get there, the more the robot costs, etc.

Probes can hibernate; it's not clear that a long coast phase makes a mission significantly more expensive - the PI goes back to her university during the cruise, and hires a new science team a year before Uranus orbit insertion. It does seem that you can do orbit injection with ion engines (though https://engineering.purdue.edu/people/james.m.longuski.1/ConferencePapersPresentations/2004PreliminaryDesignofNuclearElectricPropulsionMissionstotheOuterPlanets.pdf is using an unreasonably heavy spacecraft), if only you've got enough plutonium-238 to power the engines out in the dark.

http://arxiv.org/pdf/astro-ph/0409373.pdf has some preliminary numbers for a Pluto orbiter - 20kg of instruments, 500kg of probe structure including four ion engines and four RTGs, 350kg of xenon fuel, Ariane 5 launch and 18-year flight time.

I don't think rockets are the answer. ("Rockets Are Wrong") Using methods that cheat the rocket equation are what you want -- mass-beam systems, the Dusty Plasma approach that James pointed out to me and I used in Threshold (admittedly with some handwavy cheats for dramatics), magsails or solar sails, etc., because they require much less expendable mass and produce low but constant thrust which adds way up after a while. For instance, accelerating at 1/1000th of a g constantly means you're gaining velocity of over 800m/s over the course of a day, if I do my math right -- 10m/s^2 *.001 = .01m/s^2, *3600*24sec/day = 864m/sec/day. That means you'll be over 300kps by the end of a year and have travelled over 4.7 billion miles.

If you can get a 1/1000th g constant acceleration, the whole of the main solar system is less than 1 year away, unless I'm f'ing up my math, which I suppose I may.

It's all about the fuel economy. Besides, this IS a sightseeing expedition.

Voyager took about 18 months from Earth to Jupiter.

But it was a flyby mission so could be very light (815kg at launch) and it went up on a Titan IIIE + Centaur

Galileo is 2380kg at launch including 925kg of fuel, went up on an IUS from the Shuttle, and took just over six years from launch to JOI, using a Venus/Earth/Earth assist.

JUICE is about twice the weight of Galileo at launch (4800kg including something like 1700kg of fuel) and going up on an Ariane V with Earth/Venus/Earth/Earth assists over 7.6 years.

And JUNO - how did I forget Juno? Again it's quite big (1593kg vehicle + 1280kg fuel + 752kg oxidiser), Atlas V551+Centaur, single Earth flyby [set up by 345+388m/s], JOI 480m/s, make-orbit-usable 592m/s. Five and a half years to Jupiter.

New Horizons went past Jupiter; that's a tiny little probe (30kg of instruments, 360kg of probe structure, 80kg of fuel, not planning any large manoeuvres so it has teeny little hydrazine thrusters), launched by really quite a large rocket, and flew by Jupiter within thirteen months.

Basically, if you want to go into orbit, you have to carry a large rocket motor and more than half your launch mass has to be fuel for the go-into-orbit manoeuvre; gravity assists to speed you up are not that much use because, the faster you're going at Jupiter, the more fuel you need to be carrying to slow down.