We'll smash probe into comet 300 million miles away for kicks, er, sorry, ... for science The European Space Agency (ESA) has set the date for the Rosetta probe's deathday and says that on September 30 the spacecraft will crash into the comet it has been orbiting for nearly two years. With Comet 67P/Churyumov-Gerasimenko more than 300 million miles from Earth and heading out toward Jupiter, the spacecraft's solar …
"Rosetta's companion craft, the lander Philae, is already on the comet's surface, but has produced very little science after a botched landing."
Maybe so, but it has produced a lot of data for the engineers to make the next one better.
All things considered, the whole mission is amazing, very successful and a huge step forward.
For orbit, you want gravity (GM/r² if we pretend the comet is round) equal to centripetal acceleration (v²/r if we pretend the orbit is circular). G=6.67x10⁻¹¹, M=1x10¹³kg, and r=2500m (probably above the surface most of the time) gives a velocity of about 0.5m/s (granny swims faster).
Rosetta's mass is 1230kg (small car), but its weight would be 0.13N (same as the weight of a £2 coin on Earth). Rosetta will bounce and slide until it finds some terrain that acts like a trap.
Bad landing wouldn't matter so much if they'd used a more constant power source like an RTG or two. Philae appeared to be still working even after the bounces, just couldn't get the juice to keep going.
Same for the Rosetta probe; loss of power because solar flux drops too low for its panels to be effective beyond Jupiter just wouldn't be an issue.
A very long mission failed to perform as expected under conditions where a couple of RTGs would be perfectly happy and chug on for years. Loss to science seems to vastly outweigh the slight risk of launching a few chunks of well protected Plutonium...
<quote>A very long mission failed to perform as expected under conditions where a couple of RTGs would be perfectly happy and chug on for years. Loss to science seems to vastly outweigh the slight risk of launching a few chunks of well protected Plutonium..</quote>
You can blame the ANTI-NUKE CROWD for that one.
I remember all of the noise they made over a previous launch (the Saturn probe Cassini), trying every legal trick to stop it. They failed, and it went up.
Philae's 32W solar panels could have been replaced with about 12kg of RTG. Stripping of the solar panels and replacing them with radiation shields the same mass changes nothing. Dumping the primary and rechargeable batteries saves (at a wild guess) 1.5kg and 1kg. Philae's mass is 21kg. Using an RTG would have cost several scientific instruments.
In hindsight, an RTG version of Philae would have been an interesting choice (fewer instruments require less power, so the RTG would not have been a whole 12kg). It looks like launch costs will fall quickly enough to allow launching multiple designs before politics can cope with nuclear power.
Pu-238* is about 8,000,000 USD per kg**, and for some years now there isn't that much of it to go around until someone makes some more. Which isn't trivial as you need Neptunium-237 and a nuclear reactor, hence the price tag. Right now a couple*** of kg Pu-238 is produced every year in the USA, after a break of 25 years.
The School of Nuclear Science and Engineering at OSU is working on a better method: Rebuilding the supply of Pu-238. Still in the theoretical / computer simulation phase, though.
* Other isotopes work too (Curium-244, Strontium-90, Polonium-210, Promethium-147, Caesium-137, Cerium-144, Ruthenium-106, Cobalt-60, Curium-242, Americium-241, Thulium), but if you want a small unit that lasts long, Pu-238 is the way to go. There once even was a series of cardiac pacemakers powered by Pu-238 RTGs (some of them still in use), that's how small you can make them.
** Probably not the deceiding factor. Cassini carried 32.7 kg of Pu-238 dioxyde.
*** Some sources suggest 1.5 kg, others 15 kg per year.
Bootnote: 1950ies Doc Brown was wrong. It's 2016, and we still can't buy Plutonium at the local drugstore. Time to invent Mr Fusion, so get cracking!
Solar power has its advantages, but the lost data from the lander show that it's really not always the best solution. A small radioisotope generator like Curiosity has would have saved the day and made the exact attitude of the landing far less important.
Yes, I know. The anti-nuke crowd. If the total lack of casualties at Fukishima wasn't enough to convince them, I can't imagine what would. Hopefully the more rabid of them will die off before too long.
Seeing how hamstrung the power companies are in Japan in restarting their power plants after the Fukushima incident by rampant radiophobia it's not just the "oldies" that fear anything nuclear. There are badly informed masses in all age groups. And once radiophobia sets in it becomes nearly impossible to get out of a persons mind again. Even Einstein realized this at the time of the Manhattan project, but "the powers that be" decided that the fear and unknown of radioactivity and fallout worked in their advantage. (an excellent article on the matter at Hiroshimasyndrome.com. In fact, that entire website makes for an interesting read and for those interested in the goings on at Fukushima features a great and informative blog without the bullshit)
Some of the more intelligent kids brought up in a very anti-nuclear weapon/power environment work out okay in the end.
Not that I'm hugely intelligent, however I've come to realise that nuclear power was unfairly demonised by many in the early days, most likely as an off-shoot of the dislike of nuclear weaponry (which was and is justified, IMHFO).
We need nuclear power (alongside advancements in sensible forms of renewables) in order to move forward as a species. weapons not so much. Bring on cheap and safe thorium reactors! :-)
What the 'phobes don't seem to get is that while a rocket carrying a RTG type payload going "poof" wouldn't be a particularly wonderful thing, it wouldn't be the end of civilisation as we know it that many make it out to be. The benefits to science and our understanding of the universe around us vastly outweigh the slight risk of such an accident.
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