Showing posts with label Small Bodies. Show all posts
Showing posts with label Small Bodies. Show all posts
3.8.11
3.7.11
30.8.08
Some Space News
Image source with more information
Credit: NASA/JPL/Space Science Institute
Credit: NASA/JPL/Space Science Institute
Cassini sends us this rather awesome image of Prometheus tugging at the thin F-ring. Far weaker than magenetism, images of gravity at work are rare and, I think, profound.
Rosetta, the ESA mission to orbit and place a lander upon a comet, is approaching its secondary target, the asteroid Steins.
Opportunity has succeeded in leaving Victoria Crater, and seems to still be going quite strong, save a few issues with her shoulder.
Finally, you may recall my fascination with (and unhappy ignorance of) orbital mechanics. The latest journal from Dawn Project System Engineer Marc Rayman serves up an entertaining and straightforward introduction to rocket science, so go read it right now.
16.7.08
Another Tiny World, Arbitrarily
Makemake, the second brightest Kuiper Belt Object after Pluto, has officially been categorized as a dwarf planet. As usual, I need to stress that this whole form of categorisation is completely artbitrary, not reflecting any kind of real attribute that these worlds possess or lack. I still think that Asimov came up with the only really valid categorisation for the worlds that orbit a star, dividing them up into gas giants (Jupiter, Saturn et al.) and 'debris' (everything else, including Earth).
But I do like the dwarf planet category, if only because it highlights worlds that might otherwise never make the spotlight. So: Makemake. It's bright. It's in the Kuiper Belt. At 1600 km across, we're confident that it's probably pretty round.
Not about to steal Best in Show from Ceres any time soon, methinks.
Hat tip: Planetary Society Blog
But I do like the dwarf planet category, if only because it highlights worlds that might otherwise never make the spotlight. So: Makemake. It's bright. It's in the Kuiper Belt. At 1600 km across, we're confident that it's probably pretty round.
Not about to steal Best in Show from Ceres any time soon, methinks.
Hat tip: Planetary Society Blog
28.11.07
Robot Story
Emily Lakdawalla reports that JAXA, the Japanese space agency, have released a strange and wonderful little CG movie telling the story of their Hayabusa probe. It's the tale of a lonely robot, tumbling through space after a difficult encounter with an asteroid, trying to remember how he got there, complete with a semi-original* jazz soundtrack and subtitles providing a bittersweet monologue from Hayabusa himself.
As Emily mentions, this is not something we could ever imagine being produced by the ESA or NASA. But you know what? I think it's great to see one of the space agencies promoting unmanned space exploration in artistic and emotional terms.
Watch or download the movie here.
*The music was composed for the mission, but before it launched. As such there's no, "I've damaged my fuel-lines and can't aim my antenna at home" tune.
13.6.07
The Wheel Spins YOU
Marc D. Rayman, 'Project System Engineer' for Dawn, which should be launching next month, has a couple of posts on the Planetary Society Blog, here and here, in fact he has an online journal here. If, like me, you're interested in figuring out how these crazy space machines actually work, you'll want to give that a good look.
A while back I wrote about Robbert Goddard and his contribution to the modern rocket. While Dawn will certainly be launched into space on a liquid fuelled rocket of the same basic design as Goddard's, once there, it will rely on a nifty ion propulsion system. This uses the same basic idea as the rocket - that if you throw something out of a spaceship, the spaceship will experience an equal force pushing it in the opposite direction - but differs in what is thrown, and how. At this point I'll borrow a technical looking diagram from the page on ion propulsion at the Dawn homepage:
Image credit: NASA
Which looks pretty scary (it is rocket science!) but is really just showing us that what we throw out of an ion thruster (that appears to be the actual name for these things, however science fiction-y that may sound) are electrically charged atoms ('ions'), and we 'throw them' by taking advantage of the way that they will move away from 'like' charges and towards 'opposite' ones.
Star Wars fans will be disappointed to learn that the ion thrusters we can currently develop probably wouldn't serve you very well in a space battle. They are very much the tortoise compared to the chemical rocket's hare - giving off a very small amount of thrust over a very long time. To quote the Dawn ion propulsion page:
How much longer a period of time? Well, according to Rayman (now that's a name for a rocket scientist!) Dawn would have to fire its ion engine for five solid years to exhaust all its propellant.
But what's the deal with the title of this post? Well, reading this post on Rayman's journal, I spotted something I'd never heard of, a mention of 'reaction wheels'. You wouldn't think that wheels would be much use on a spacecraft, and yet, in microgravity and a vacuum, spinning wheels has an interesting effect. Because of conservation of angular momentum, as you exert a force to change the speed a wheel is spinning at, the wheel will exert a force to turn you in the opposite direction. If you happen to be floating in microgravity, then you won't be able to stop this from happening as you would on the surface of a planet (for example, by bracing yourself on the ground), and as you change the wheel's rate of rotation, it will change your rate of rotation. This means that by sticking wheels in spaceships, we have a way to make them spin (or stop spinning) without using any propellant. That definitely wins my 'cool idea of the day' award.
(There's a larger and more complicated version of this called a 'control moment gyroscope' used by, for example, Mir and the Internation Space Station.)
A while back I wrote about Robbert Goddard and his contribution to the modern rocket. While Dawn will certainly be launched into space on a liquid fuelled rocket of the same basic design as Goddard's, once there, it will rely on a nifty ion propulsion system. This uses the same basic idea as the rocket - that if you throw something out of a spaceship, the spaceship will experience an equal force pushing it in the opposite direction - but differs in what is thrown, and how. At this point I'll borrow a technical looking diagram from the page on ion propulsion at the Dawn homepage:
Image credit: NASAWhich looks pretty scary (it is rocket science!) but is really just showing us that what we throw out of an ion thruster (that appears to be the actual name for these things, however science fiction-y that may sound) are electrically charged atoms ('ions'), and we 'throw them' by taking advantage of the way that they will move away from 'like' charges and towards 'opposite' ones.
Star Wars fans will be disappointed to learn that the ion thrusters we can currently develop probably wouldn't serve you very well in a space battle. They are very much the tortoise compared to the chemical rocket's hare - giving off a very small amount of thrust over a very long time. To quote the Dawn ion propulsion page:
Dawn's engines have [...] a thrust of 90mN. While a chemical rocket on a spacecraft might have a thrust of up to 500 Newtons, Dawn's much smaller engine achieves an equivalent trajectory change by firing over a much longer period of time.
How much longer a period of time? Well, according to Rayman (now that's a name for a rocket scientist!) Dawn would have to fire its ion engine for five solid years to exhaust all its propellant.
But what's the deal with the title of this post? Well, reading this post on Rayman's journal, I spotted something I'd never heard of, a mention of 'reaction wheels'. You wouldn't think that wheels would be much use on a spacecraft, and yet, in microgravity and a vacuum, spinning wheels has an interesting effect. Because of conservation of angular momentum, as you exert a force to change the speed a wheel is spinning at, the wheel will exert a force to turn you in the opposite direction. If you happen to be floating in microgravity, then you won't be able to stop this from happening as you would on the surface of a planet (for example, by bracing yourself on the ground), and as you change the wheel's rate of rotation, it will change your rate of rotation. This means that by sticking wheels in spaceships, we have a way to make them spin (or stop spinning) without using any propellant. That definitely wins my 'cool idea of the day' award.
(There's a larger and more complicated version of this called a 'control moment gyroscope' used by, for example, Mir and the Internation Space Station.)
22.1.07
Comet Halley
The nucleus of Halley's Comet as imaged by the ESA probe, Giotto. The nucleus is the bit on the far right, a dark and irregular (Arthur C. Clarke called it peanut-shaped) chunk of primordial ice and dust. Comets are believed to exist in vast numbers in parts of the solar system called the Kuiper Belt and the Oort Cloud, but when some event sends them careering through parts more local to us, they react pretty badly: coming to pieces as their ice sublimes away and forms a conspicuous cloud.
The picture above is a great example of robot bravery - Giotto was seriously knocked around by debris from the comet, including one impact that put it into a spin so that its Kevlar dust shield was no longer constantly protecting its sensitive bits. The camera that took this image was eventually destroyed by another impact.
17.1.07
The Future... in SPACE
While your tin-foil-suited life in a moon bubble may still be a long way off, there are some very exciting unmanned missions coming up over the next decade. All of the missions listed below have either already been launched or are launching this year.
Phoenix
August 2007: Launch
May 2008: Land on Mars
Phoenix is the latestrover lander mission to Mars, and it's heading to a radically new environment from the ones we've seen from landers so far. Phoenix will land on Mars' northern polar region, looking to understand the history of the ice there (and thereby also the history of Mars' climate) and also to search for microbial life. On top of that it has a really nifty set of fan-like solar panels.
Phoenix homepage
New Horizons
February 2007: Jupiter gravity assist
July 2015: Arrival at Pluto
New Horizons is the first mission to Pluto, and our first proper look at it. Next month, New Horizons will also become the latest mission to Jupiter, where it will hopefully do some science and get some pretty pictures. In the long run, New Horizons may also go on to visit other Kuiper Belt Objects.
New Horizons homepage
Dawn
Summer 2007: launch
March 2009: Mars gravity assist
September 2011: Arrival at Vesta
February 2015: Arrival at Ceres
Dawn is a spacecraft I find it easy to get excited about: a mission to Ceres and Vesta, the two largest bodies in the asteroid belt. Vesta seems to be a pretty standard potato as asteroids go, but Ceres is round enough to qualify as a dwarf planet and seems to have some interesting features, although we have no detailed images of it.
Dawn homepage
MESSENGER
June 2007: Venus gravity assist
March 2011: Mercury orbit insertion
The only spacecraft so far to vist the Sun's innermost planet was Mariner 10, probably because not only is it really hard to get to, so far into the Sun's gravity well, but once you're there you have to worry about intense heat and radiation. MESSENGER looks set to give us a good look at a planet that's been off the guest list for too long.
MESSENGER homepage
Phoenix
August 2007: Launch
May 2008: Land on Mars
Phoenix is the latest
Phoenix homepage
New Horizons
February 2007: Jupiter gravity assist
July 2015: Arrival at Pluto
New Horizons is the first mission to Pluto, and our first proper look at it. Next month, New Horizons will also become the latest mission to Jupiter, where it will hopefully do some science and get some pretty pictures. In the long run, New Horizons may also go on to visit other Kuiper Belt Objects.
New Horizons homepage
Dawn
Summer 2007: launch
March 2009: Mars gravity assist
September 2011: Arrival at Vesta
February 2015: Arrival at Ceres
Dawn is a spacecraft I find it easy to get excited about: a mission to Ceres and Vesta, the two largest bodies in the asteroid belt. Vesta seems to be a pretty standard potato as asteroids go, but Ceres is round enough to qualify as a dwarf planet and seems to have some interesting features, although we have no detailed images of it.
Dawn homepage
MESSENGER
June 2007: Venus gravity assist
March 2011: Mercury orbit insertion
The only spacecraft so far to vist the Sun's innermost planet was Mariner 10, probably because not only is it really hard to get to, so far into the Sun's gravity well, but once you're there you have to worry about intense heat and radiation. MESSENGER looks set to give us a good look at a planet that's been off the guest list for too long.
MESSENGER homepage
Subscribe to:
Posts (Atom)