| Do you know what the Uranus probe's goals are? They're laid out here [1]. It's to measure wind speed and atmospheric densities/temperatures. And that is typical. This is what I was getting at when I said that these probes do not achieve near what many people seem to think they can. We have a limited budget and I think this budget should be directed towards things that can advance us in the most meaningful ways possible. Measuring the wind speed and density on Uranus does not really fit the bill there. Think about SpaceX. What they've done should have been impossible. A private company operating on a shoestring budget revolutionized space in 15 years? That doesn't mean Musk is a genius, it means that our current space system is simply incompetent. There are certainly many reasons for this, including congress using NASA as a jobs program, but I think a lack of direction is also a major reason. 'Discovering how life began and evolved on Earth' as a mission statement is like a philsopher stating his goal is to 'discover the meaning of existence.' It's a goal that's so impossible and so broad that anything can be justified in its name. 'Easier' goals are in many ways much harder since you need to remain focused. And when NASA has focus they, at least in the past, have shown themselves capable of amazing things. Going from having never even put a man in orbit, to putting a man on the moon in a decade? Think about that, if you even can. In today's times that should seem completely unbelievable. And we should be capable of exponentially more now a days. And that is where we should set our sights. The point I'm getting at is that if you aim low, that's always where you're going to hit. Aim high and you might miss, but at least you're pointed in the right direction. --- As one brief aside, those mission statements immediately made me think of Oumuamua [2] -- that cylindrical weird interstellar object (it's exact nature is, and will likely remain unknown - the name translates to 'first scout', as the imagination might imagine) currently looping around the sun on its pass through and on its way out of our solar system. Being able to get ships and ideally humans onto that thing would be groundbreaking and actually go a long ways towards pushing those mission statements, abstract though they may be, forward. But our space program and technology is so backwards and dated that we're instead left watching jaws agape as arguably the single most relevant tracked celestial object lackadaisically (...as lackadaisical as 30km/s can be) laps us on its way on out of our solar system. It's again absurd that the primary interest in trying to perform an intercept with this object has come from the private industry. But hey, at least we'll know the wind speed in Uranus... [1] - https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/201700... [2] - https://en.wikipedia.org/wiki/%CA%BBOumuamua |
You mention the ambiguity of the animating goals. Part of this is just linguistic: of course you want to push down these top-level goals to more granular, 0/1 goals ("was there an ancient lake at this site on Mars?" Answer: yes). That's what the NAS report does. Now that we know how abundant water was on ancient Mars, we'd like to return samples to see if there was life. That's the next couple of missions.
You raise a worthwhile point, I think, about immediately-graspable 0/1 goals, like "man on moon". I see your point - but I'm really only here to talk about the unmanned program because my limited expertise covers part of that area.
You like SpaceX. So do I - two good friends left my lab to work there. But their achievement ("revolutionized space") is not unique. The little Mars pathfinder had about that much history. There are plenty of other examples over the same time period, like exoplanet discovery (as you noted), cosmology, and a host of Earth science stuff.