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NASA Unveils Two New Missions To Study Truly Strange Asteroids (space.com)
An anonymous reader quotes a report from Space.com: NASA's next low-cost planetary missions will attempt to unravel the mysteries of some seriously bizarre asteroids. The space agency has selected projects called Lucy and Psyche via its Discovery Program, which funds highly focused space missions to destinations throughout the solar system. The Lucy project will investigate the Trojan asteroids, which share an orbit with Jupiter, while Psyche will journey to the asteroid belt to study a huge, metallic asteroid named 16 Psyche that resides there. Lucy is scheduled to launch in October 2021. If all goes according to plan, the probe will visit an asteroid in the main asteroid belt -- located between Mars and Jupiter -- in 2025, and then go on to study six Trojan asteroids between 2027 and 2033, NASA officials said. There are two streams of Trojan asteroids. One trails Jupiter, and the other leads the giant planet around the sun. Scientists think both streams may be planetary building blocks that formed far from the sun before being captured into their current orbits by Jupiter's powerful gravity. Psyche will explore one of the oddest objects in the solar system -- a 130-mile-wide (210 kilometers) metallic asteroid that may be the core of an ancient, Mars-size planet. Violent collisions billions of years ago might have stripped away the layers of rock that once lay atop this metallic object, scientists say. Psyche is scheduled to launch in October 2023 and arrive at the asteroid in 2030, NASA officials said.
The "cleared" term is generally understood to have been poorly worded, with most preferring "gravitationally dominant" to be better. The Trojans are trapped in their location specifically because of Jupiter, not in spite of it.
Then again, if we want to get nitpicky, Jupiter fails the planet definition because the point it orbits (the Sun-Jupiter barycentre) is not inside the sun. They corotate an empty point in space rather than Jupiter simply "orbiting the sun" as the definition requires ;)
But that's being nitpicky. I have much bigger complaints with the planet definition than that.
For the love of Crom, am I the only one here who wants to keep the U.S. technologically competitive?
I was never really feeling NEOCam. It's not looking for earth-killers, just Tunguska-sized impactors. We've got LSST coming online in the early 2020s which will greatly increase our detection rate, and there will be more in the future. If anything, LSST is significantly better than NEOCam (p.38). A 5-10 years setback (counting for the complimentary nature of the two approaches - NEOCam is IR, LSST visible) is extremely unlikely to equate to "losing New York city" or anything of that nature. A Tunguska-scale impactor is a roughly one-in-400 year event, and overwhelmingly likely to impact few to no people. The odds of one hitting a major metropolitan area in that timeframe, which we could have stopped had we known about it, are one in millions. NeoCAM costs $500m. The delay seems acceptable to me, in an area where space budgets are tight.
If there is an imminent earth-killer out there, it's not in the inner solar system. It's a comet. And neither NEOCam nor LSST would likely see it until it was well on its way toward us. Smaller but still devastating comets? Even later. Hence, defense against large impactors has to be nuclear - as large of warhead(s) as possible, mounted to a storable rocket that can achieve significant delta-V. Nothing else but nuclear has the energy density to deflect in such a short time period, and you don't have the time to engineer your deflection craft from scratch and integrate it onto a stack when time is that short. So if we're serious about planetary defense, that's an approach we need to take.
All of this said: I do kind of look forward to the day when we know the orbits of a large chunk of the ~30-40m impactors and a fair minority of the ~20m (Chelyabinsk-sized) impactors. Because those hit often enough somewhere on the planet (generally very remote) that people could actually travel to see them, like people do with eclipses. And that would be a really neat experience :) And I can totally imagine meteorite hunters prepositioning hardware near the likely strewn field.
For the love of Crom, am I the only one here who wants to keep the U.S. technologically competitive?
The value of things mined from asteroids at present is zero. There is zero market. There is, however, a market for precious metals and gemstones here. Particularly if they're "exotic"
ISRU is something that could be very useful in the future, but first you have to develop the market for it. Meanwhile, in order to develop that market, people are working to undercut launch costs. Which undercuts the value of said resources being in space.
And ISRU is not nearly as simple as people like to think of it. Let's forget about some sort of "spacedocks" welding together spaceships out of asteroid nickel-iron for now, let's stick to the "easy" stuff, like water for a Marsbound spacecraft. Let's say that what you sinter together is only rock on the outside,but mined permafrost on the inside, so the rock can ablate and protect the sandy ice inside for aerocapture at Earth. Let's ignore how this is harder than just sintering regolith alone. How do you make use of what arrives at Earth? First you have to maneuver a spacecraft to dock with each chunk in LEO (after detecting them with radar), then drag it back to where you're assembling your spacecraft. You then need to drill/cut into each one in space. You then need to put it into a boiler to vaporize out the ice. The boiler needs to maintain a high enough internal pressure that water can exist in a liquid state (otherwise it'll just freeze out as ice and cause you difficulty in getting it into your tanks). So you have a condenser, and pumps connected to your tanks, and you fill them that way. If there's any other volatile chemicals in there that were in the rock (organics, ammonia, etc), you'll need to run your water through reverse osmosis or similar. And of course, any humans involved in this process have to be supported during all this time with consumables from Earth.
Or, you could save yourself all of the time, engineering expense, hardware launches, etc, and just simply launch the water to begin with.
When faced with such decisions, people usually choose the latter.
When it comes to sending mined material to the surface of the Earth, however, the situation is a bit different. Your asteroid still needs a regolith/rock gathering rover, a sinterer, a coilgun, and a power source, all delivered to an asteroid's surface. A project that's probably on the order of a few billion dollars when all is said and done. But all of your other costs are normal Earth costs, everything done on the surface of the planet. You have a chunk of land or sea where precious metal-rich rocks rain down from the sky every X months in a storm of fireballs. Radar tells you where they came in (yes, you actually can see meteors on radar!). A first generation mining operation (whether the landing site would be at land or on sea) would probably work with rocks that weigh just a tonne or less each, and would involve taking them back to a processing facility; however more advanced operations might involve rocks massing hundreds or even thousands of tonnes, and mobile processing facilities. It's not clear what the upper bound on survivable sizes would be, or whether there even really is one. Natural (aka, not optimally shaped, not optimally targeted) meteorites found on Earth get up into the dozens of tonnes each. And you can always include more void space into the sintered shape to increase your surface area to mass ratio and thus entry survivability
For the love of Crom, am I the only one here who wants to keep the U.S. technologically competitive?