Until today, Voyager 2 remains the only spacecraft to visit these planets. Are spacecraft visits to these planets hard to plan or develop?
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16$\begingroup$ Define "hard". You have to squeeze $4 billion plus out of governments, and that's before you get off paper, but after you have at least a partial design and detailed plan. Then you have to build stuff. And it has to work, because you don't get second chances. $\endgroup$– StephenG - Help UkraineCommented Mar 12 at 0:27
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7$\begingroup$ Voyager 2 was able to use multiple gravity assists. $\endgroup$– PM 2RingCommented Mar 12 at 1:28
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3$\begingroup$ space.stackexchange.com/a/45634/37747 $\endgroup$– Nilay GhoshCommented Mar 12 at 3:07
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1$\begingroup$ Setting a goal and planning is difficult, but it is possible. But what is the purpose of such a journey? $\endgroup$– ayrCommented Mar 12 at 10:15
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1$\begingroup$ Further to StephenG-HelpUkraine's excellent comment, can you also define 'plan'? Is that simply to plot the course, or does it include all the administration and logistics, as for instance what cargo is carried and even, how the cargo is distributed in the holds? $\endgroup$– Robbie GoodwinCommented Mar 15 at 21:13
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3 Answers
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Uranus and Neptune are far - in orders of light-hours away. It took Voyager 2 nearly a decade to reach Uranus since its launch, costing almost $1B to build it in the first place.
It's not that we can't launch another mission, we're more than capable of doing it again, especially with the evolution of technology - but rather that it is ludicrously expensive and time-consuming, so NASA chose to allocate capital to other projects.
Even if we chose to launch another mission to the ice giants, expect up to a decade for development (depending on how fancy they make the probe(s)), then another decade for arrival. Not very timely.
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23$\begingroup$ In addition, if we were going to send a mission to one of the ice giants, we'd probably want to drop into orbit out there and get an extended data collection period, which is really difficult. You can either get there in a relatively reasonable time and be going so fast that you can't stop, or you can get there at a reasonable speed and take so long that the probe might fail from general wear and tear before it arrives. $\endgroup$ Commented Mar 12 at 15:24
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8$\begingroup$ I would expect the delta V requirement for either kind of mission could be greatly affected by the relative positions of Earth, Jupiter, and Saturn in their orbits. The Voyager probes were launched when they were to exploit the particular alignment of the planets at that time; if you can readily find information about whether any future launch windows would be particularly advantageous, it might be useful to include it. $\endgroup$– supercatCommented Mar 12 at 17:41
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6$\begingroup$ @supercat, most of the Voyager boost came from Jupiter. An ideal Earth-Jupiter-Neptune or Earth-Jupiter-Uranus alignment happens about every twelve years; sub-ideal alignments happen almost every year. (The Voyager Grand Tour alignment happens every 175 years, but you don't need that if you're just going to a single destination.) $\endgroup$– MarkCommented Mar 12 at 22:48
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2$\begingroup$ @user253751 I'm not so sure about that. In a quick search it looks like the federal budget as a % of GDP has been relatively static, though overall trending slightly higher, for the last 50+ years. The definition of "public interest" has changed - NASA budget as % of federal budget peaked with Apollo and has been trending downward ever since (except for a slight bump early 1990s). $\endgroup$ Commented Mar 13 at 2:48
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They're expensive for sure, and you will be giving something up if you plan and build for such a mission. Since Voyager, the priorities haven't aligned for any such mission to be chosen over other alternatives.
However, the most recent Decadal Survey (which gives an idea to priorities that folks would like to see) has selected a Uranus orbiter and probe mission as the highest priority for flagship (big/expensive) missions.
So there is a reasonable chance of such a mission being funded this decade.
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No, it's not. You shoot a probe past Jupiter for a slingshot assist, and you reach Uranus in six, and Neptune in eight years or so. You can build that probe from old blueprints of Galileo and Cassini, and more recent Juno etc.
The problem is to plan and design a probe and mission that will show something we haven't seen and don't already know or can guess very well. If Cassini hadn't been more than a somewhat improved version of Galileo, it would have sent back nice pictures of Saturn with little scientific value. That would've been, paraphrasing Ernest Rutherford, "stamp collecting".
