Two prominent ones come immediately to mind, not at all an exhaustive list:
Destroyed shortly after launch due to an cracked casing in a "so reliable they don't need to be test fired" GEM-40 booster:
Blew up on the pad as people were working on it, leveling the pad and killing 21 people (they seem to have moved on to largely liquid-fueled systems now):
Manufacturing solids is a hell of a lot more than "a giant Magimix with extra safety precautions", it requires extremely good process control and very detailed inspection of the end product with a lot of expensive equipment, and entails a tricky disposal issue with all the castings that fail QC and huge amounts of hazardous materials to handle all along the supply line.
Ares was canceled, in large part due to being unaffordably expensive yet underperforming. Epsilon and Vega are tiny, Ariane 6 is a big step back in capability and not particularly cost competitive, and there's a lot of industry support for a change in direction to liquids. The Russians and Chinese primarily use liquid boosters, there were proposals to replace the Shuttle's solid boosters with higher-performing liquids (the performance benefit is actually quite substantial, this being the reason almost all launchers use liquids), and Aerojet is developing liquid boosters for the SLS Block IA and Block II as an upgrade from the Block I's Shuttle-derived solids (which may see use as launchers themselves, as the Energia's Zenit boosters have).
And again, SpaceX keeps demonstrating the advantages of liquids: the vehicle is safer to work on, engines can be properly tested prior to use, the vehicle can be shut down on the pad after ignition if problems are found, it can continue on to orbit even after losing an engine in flight...and there's just no way a solid first stage can come back and land for reuse like the Falcon 9-R. Liquid systems easily beat solids in cost, SpaceX's Falcon 9 is far cheaper than any solid system even without reusing the first stage.
It's not even helpful to astronomers. Your telescope's direction will jump by 15 arcseconds for every leap second applied. If you want precise pointing, you'll use a rotation model based on more detailed data on Earth's rotation with a timebase that's actually real time, not some mostly-increasing number with arbitrary jumps forward and back.
As others point out, things don't lose their mass just because they're in space.
However, the problem with reactors isn't that they're "too heavy", they're lighter than an RTG with equivalent power output would be. The problem is that they're too big. An RTG is a lump of passively decaying material surrounded by thermoelectric converters and heat sinks, there's no hard lower limit in size. A reactor has to have enough material to sustain a chain reaction, which imposes a stricter minimum mass.
If your mission's big enough to use one, a reactor makes much more sense than an RTG, but they only make sense for big missions. One example is the SAFE-400, which masses 512 kg but puts out 400 kW thermal and 100 kW electrical. A GPHS-RTG masses 57 kg and produces 4.4 kW thermal, 300 W electrical at the start of the mission. The reactor's a lot lighter for its output, but if you need 1 kW, what do you choose?
And if they'd been using a solid? They'd have been unable to do a hot fire test, and might have attempted to launch with a faulty vehicle, leading to a messy failure rather than a 2 week delay due to range contention. They've repeatedly demonstrated the benefits of being able to shut the vehicle down on the pad, among other advantages of liquids. (You can't make a launcher with engine-out capability using solid rockets, for example.)
Solids are a lot more trouble to manufacture, transport, and work around, can't be test fired or shut down when problems are encountered, have a nasty habit of exploding, are very difficult to scale up, and their performance sucks. In addition, just try restarting a solid and performing a precision landing as SpaceX intends to do with the Falcon 9-R. Even without that, SpaceX is launching for far lower prices than those other rockets.
Launch vehicles based on solid rockets are a dead-end carried over from and kept on life support by the ICBM industry, where they are required for their ability to sit in a silo for years and be ready to fire.
In fact, 1 billion dollars would fuel around 5000 Falcon 9 launches, each lifting 13 metric tons of payload to LEO, for 65000 metric tons total. For the Falcon 9 (one of the lowest cost launchers), propellant is about 0.4% of the launch cost.
The real costs are in the hardware and in operations. The problem is that there really hasn't been a huge amount of incentive to reduce costs. Especially in NASA's launcher programs, where things like Constellation and the SLS are specifically intended to keep Shuttle personnel employed and funds going to the important Congressional districts. This is just not an approach that will reduce costs.
The COTS effort is shaking things up a bit. SpaceX's prices are a lot lower than the competition's, and they are working on recovery and reuse of as much of the vehicle as is economical.
Perchlorate is a reactive and unstable anion that can easily be washed out of regolith, thermally decomposed by baking in an oven, or removed using chemical or microbial treatments. Similar treatments are likely going to be required anyway if you're going to be growing plants in it.
It's also not actually all that toxic. The thyroid absorbs it in place of iodine, reducing the amount of iodine absorbed...it has no other effects, and the iodine uptake interference stops when exposure to perchlorate stops...chronic ingestion is required to make it a problem, an acute exposure will only have a brief effect.
Basically: don't make a habit of eating untreated dirt, and monitor drinking water contaminants. Nothing they shouldn't already be doing. Iodine supplements might be a good idea in case drinking water becomes contaminated and it takes some time to correct.
You're missing the point. You have to make basically the same velocity change (somewhat more to actually rendezvous), but *you don't have to carry your radiation shielding while doing so*. A "cycler" carrying equipment and shielding only needed for the long duration port of the trip would only have to make minor maneuvers to maintain its orbit, the craft traveling to and from it could be much lighter because they only need to support their passengers for a relatively short trip.
"astronauts on even the shortest roundtrips to Mars would get radiation doses of about 662 millisieverts"
That is simply *not* the "huge amount of radiation" the article claims. It won't even cause any effects that can be tied to the radiation...it'll increase the long-term risk of fatal cancer by a few percent (for the 1000 mSv, 5% increase in cancer risk limit, that means you're still 20 times more likely to die of cancer from something else), provided the models are even accurate for such low exposures. Radiation exposure is something we'll obviously want to minimize, but this article is just radiophobic fearmongering.
They grind the plants up, extract the thylakoids from the chloroplasts in the plant's cells, and somehow bind them onto a base electrode covered in carbon nanotubes (it's not clear where the other electrode is). So no, the plant is not going to be doing anything with the energy produced. It's also not going to be doing any repair or replacement work on those extracted bits of cellular machinery, or reproducing, etc.
The "nearly 100 percent quantum efficiency" apparently refers to the fact that almost all of the energy of light of the appropriate wavelengths that is absorbed directly by a chlorophyll molecule ends up going into freeing electrons. The problem is that most of the light is of unusable or suboptimal wavelengths, a huge part of the remainder is reflected or absorbed by other things, and not all the freed electrons actually get put to useful work.
And they don't have anything that reproduces, they just use extracted plant bits as the active material in another type of PV panel. One that requires a large area carbon nanotube based substrate.
Except they're apparently harvesting the photosynthetic structures from plants and then incorporating them in something resembling a dye-sensitized solar cell using some exotic carbon nanotube substrate. That's not self-assembling, and given the lack of any cellular repair mechanisms, probably not very long-lasting.
Plants are nowhere near "the most efficient harvesters of solar energy on the planet". The most efficient plants, such as sugar cane, reach around 8%, on par with the very lowest efficiency photovoltaic modules. More typical efficiences are 0.1% to 2%.
Actually, it has a significantly better CPU. The Raspberry Pi CPU is an ARM11 (like the original APC) that, among other lacks, doesn't have hardware division. The Cortex A9 used in this thing is rather more sophisticated: http://en.wikipedia.org/wiki/ARM_Cortex-A9_MPCore#Features
These fish are apparently maintaining a constant level by feeding in contaminated sediments that replace the cesium as fast as it is excreted. Predators will only have elevated levels while actively feeding on these bottom feeders. However, with a 30 year half life, there aren't many plausible sources for the cesium, it pretty clearly came from Fukushima. Given that a major tsunami had just happened, it's not surprising that there's a layer of sediment trapping the cesium. Possibly something could be done to free up the cesium so it can dilute more thoroughly, or cover it in uncontaminated sediments so bottom feeders don't get into it so much.