No, hydrazine does not need an oxidiser: it's a monopropellant.
Schiaparelli had three 17.5 litre tanks, each filled with 15kg of hydrazine. There was also a 15.6 litre tank of high-pressure helium used to keep the hydrazine under pressure during firing.
Would it hurt people to occasionally do some research before contributing to the general drivel that Slashdot has become?
Speaking from the ESA team that co-published those MRO CTX pictures yesterday, your assertions are nonsense and need correcting.
There was a fully coordinated operation in place to track the lander during its descent, using the GMRT in Pune, India, our own Mars Express spacecraft, NASA's MRO, and the ExoMars Trace Gas Orbiter itself, while data came down through our ESTRACK network and NASA's DSN. The Opportunity rover also in Meridiani Planum took images during the descent, but it was known that that would only possibly work if the lander came down at the long end of the landing ellipse: in the event, the targetting was fine, and it came down within ~5km of the centre of the ellipse.
All agencies and partners cooperated fully, as we always do when it comes to Mars (and other solar system) operations, and all data were released as soon as they were available and analysed, including from our own assets. Nobody has been withholding anything beyond the reasonable time needed to analyse the data: we're less than 3 days past the Schiaparelli entry and descent, and a lot of information is already available. The various teams involved are working day and night to understand the complex data.
The MRO CTX images were pre-planned, regardless of a successful landing or not, and were made available by NASA to the ExoMars project team as soon as possible. A number of meetings and joint telecons were held yesterday to analyse and agree on their content to the extent possible (CTX is fairly low resolution: much better information will come via HiRISE when it targets the site next week), and to agree on a time to release them.
Indeed, at ESA, we were working very hard yesterday to publish them jointly as soon as possible, in order to make them available to the European media for last night's news. Due to the timezone different to California, it was challenging for NASA to get the images and accompanying text approved by then, but we're very grateful that they worked hard to make that possible.
Finally, remember that we deliberately sent Schiaparelli there as a test demonstrator. We successfully carried out the hypersonic entry and supersonic parachute deployment phases, prior to the apparent failure during the thruster phase, and telemetry during the whole descent down to the surface were recorded and are back on Earth. Yes, we're obviously very disappointed that we didn't manage the final phase, but we will learn from the data. We also successfully put the main scientific mission, the Trace Gas Orbiter, into orbit around Mars.
We have not withheld information: we've been as open as possible throughout. I'm sure that the truth of the matter won't dissuade you of your "NASA great, ESA bad" opinion, but sometimes it's important to lay out the real story for others to judge.
Bottom line is that Mars was, is, and will always remain hard.
Just because energy is on one side of the equation and mass on the other, that doesn't mean they are the same thing. There is an equivalence between them in the same that a certain amount of mass can be converted into a certain amount of energy (and vice versa), but it doesn't mean that they are the same.
And this equation is specific to the situation where the object with mass isn't moving (which is why E in this case is called the "rest mass energy"). More generally in special relativity, for an object that is moving and has a momentum p, the equation becomes:
I suspect that you have missed the point entirely: silentcoder made the correct distinction between "mass" (an inherent property that depends on the number of atoms etc. in an object and that is independent of where the object is) and its "weight", which in physics terms means the force exerted by that object on something, which is the mass times the local acceleration.
Thus a person with a mass of 80kg standing on the Earth exerts a force due to gravity pulling them down onto the surface, i.e. 80 kg x 9.8 m/s2 = 784 Newtons. But for all sorts of obvious reasons, we just use the shorthand version to say that the person "weighs" 80 kg.
On the Moon, their mass would be the same, because they'd have the same number of atoms in their body. But they'd exert much less force on the surface, because the gravity on the Moon is only 1/6th of that on the Earth. So, they would weigh less. It's at that point that the shorthand way of talking about weight becomes useless.
Take the person and stick them infinitely far from any gravitating body and there would be no acceleration and thus no force, so the person would be weightless, but not massless (same number of atoms still).
Of course, in low Earth orbit, you're right in pointing out that the Earth's gravitational acceleration has not diminished much. However, while you're falling freely towards the surface of the Earth under that acceleration, the spacecraft you're in is falling out from underneath you at the same rate, so you don't exert a net force on it. Thus you're effectively weightless.
(If you're both falling freely towards the Earth, why don't you hit it at some point? Because you're flying sideways at such a high speed that the Earth's surface curves away from underneath you at just the same speed as you're falling towards it, so you never hit.)
But here's another thing. Under general relativity, gravity is much better thought of as a curvature of spacetime and it turns out that the motion of even massless objects (photons) is affected by that curvature (think Einstein, Eddington, etc.). Indeed, given a very strong gravitational field / very high spacetime curvature, e.g. around a black hole, photons can go into orbit. This is because while they don't have any mass, they do have energy.
So, in a more correct general relativistic setting, even your basic assertion that "to be able to orbit, you must have weight/mass" is wrong.
Firstly, most of the detail is of relatively uninteresting bits of snow, rock, and ice: there's no real motivation to zooming in and poking around, as there is in a similar multi-gigapixel panorama of a city, for example.
As someone said above, the real grandeur of the scene comes in taking in the wider view, at which point the whole hi-res aspect is totally moot.
Plus the mosaic making sucks. Really, right from the get-go, the repeated features in the foreground snowfield are utterly distracting, followed by blurring in many areas when you zoom in a little.
Admittedly, such things are extremely difficult to do well / right (I know from experience), but I've seen plenty of other panoramas which are far better in post-processing.
Ultimately, the question becomes: why bother? Oh, because it's "the most pixelliferous image ever taken". Sigh.
Glad to see that you jumped in on this: good description.
Because the comet is so small, the gravity changes a lot with "altitude" from the surface. For a 2-km diameter sphere, say, then the difference in gravity between an altitude of 2-km and 6-km (i.e. between 4 and 8-km from the centre of the sphere) is a factor of 4. On the Earth, it barely changes at all between altitudes of 2 and 4-km, because this is a tiny change relative to the 6400-km radius of the Earth.
So, yes, at 100-km and 50-km, we'll be flying these hyperbolic arcs (slightly bent by the very weak gravity), using thrusters to "turn the corner" at the end of each leg. But at 30-km, we'll be on closed more-or-less circular orbits: I'm pretty sure that it is natural orbit though (and thus fairly long in duration), but not powered.
I do work on the project, albeit not on the flight dynamics side. One of our experts on this, Frank Budnik, did give a talk on this in the science session I moderated yesterday afternoon, starting at 11:28 into the recording of the live stream here:
Absolutely right: I was going to point out the same thing. It's many, many years away from any possible launch...
For reference, the James Webb Space Telescope (or NGST as it was then) was beginning to be picked up as a serious prospect by NASA, ESA, and the Canadian Space Agency in the late 1990's. It's due for launch now in 2018.
(This is not meant as a criticism: I've been closely involved with JWST since 1998 and know how hard it has been in terms of technology, programmatics, and politics to get the good state it's in today, namely mostly built and now entering the comprehensive integration and test phase.)
So, very crudely, I'd say that something like ATLAST might be launched after 2035, if it gets picked up as the highest priority in the next US astronomy decadal survey.
Good point; I did use the word "we" in a rather catch-all manner there, and I'd also agree that technologists are likely to have a much better record at predicting the future than journalists.
But I'd then turn the tables and say that it depends on the timescale implied by "future". On a ten-year horizon, I'd agree that technologists are likely to have a pretty good idea what's coming, in part because they're likely to be working themselves actively on new technologies and products for release on similar sorts of timescales.
But on a 100 or 50 or even 30 year horizon, as this article refers to? It seems clear to me that on some timescale, even technologists are unlikely to be that close, if only because they're probably called "futurologists" at that point, or "science fiction writers":-)
On some timescale, almost everyone is going to be pretty much guessing...
OK, now having read the linked article (oops), I do see that the author (Henry McCracken) realised that the cover painting had a humorous intent (not least that it was the April edition of BYTE), satirising the conservative opinion that future tech was likely to be an extension / miniaturisation of the then-prevalent PC paradigm.
C'mon, it's entirely obvious that that "PC on a watch" painting is a rather clever piece of irony or even satire, not a meaningful prediction of an actual future piece of technology.
That doesn't mean I disagree with the point of the discussion, namely that we're not that great at predicting the directions of future tech, but using this magazine cover as a direct illustration of that is, IMHO, rather disingenuous.
Actually, ESA built the Huygens lander which descended to the surface of Titan. It was carried there on the NASA-ASI Cassini orbiter after being launched by a NASA rocket, but Huygens was European-built, with instruments from Europe and the US.
Its the U-571 gambit: keep saying that things were achieved by the US independent of the truth of the matter, and pretty soon it becomes received knowledge.
Quite. Rosetta has been on a ten year journey around the Solar System, using Earth and Mars fly-bys to wind its orbit up to meet with 67P/Churyumov-Gerasimenko in August this year. At its most distant point from the Sun, it was beyond the orbit of Jupiter, but the comet rendezvous will take place at about 3AU, before the comet becomes active as it moves closer into the inner Solar System.
As for outer planet missions, the NASA-led and launched Cassini mission also carried ESA's Huygens probe, which performed the most distant ever landing in the Solar System when it landed on the surface of Titan in 2005.
But the elephant in the room here is ESA's JUICE mission, which is a real mission, not a study, already under implementation for a launch to Jupiter and its icy moons in 2022. JUICE will conduct a number of close fly-bys of Europa, but due to the dangerous radiation environment, will ultimately end up in orbit around Ganymede, another icy moon thought to host a deep ocean below the surface. And NASA are also involved in this mission, providing some of the instruments.
I was waiting for someone mention the (funded and being built) JUICE mission: it's astonishing to me that the "if it ain't NASA, it ain't worth jack" attitude generally persists, and that hardly anyone in the media (let alone on/.) bothers to do the slightest modicum of research.
JUICE is under development by the European Space Agency for launch in 2022 (not 2020 anymore) and arrival at Jupiter in 2030. It will tour the Jupiter system, including multiple fly-bys of the giant icy moons Europa, Callisto, and Ganymede. It will end up in orbit around Ganymede, where it will conduct a more detailed survey.
All three moons are thought to harbour giant water oceans under (probably) very thick icy crusts (~100km), although there are debates about which may be the most likely to provide potentially habitable environments deep in these oceans: it may depend on central heat flux from the moon's contraction, flexure due to Jupiter's gravity, heat from radioactive decay, and whether there's a water:rock interface which could provide minerals.
Why Ganymede as the final moon to be orbited? Because Europa is closer to Jupiter and suffers a much higher radiation dose due to high energy particles trapped in Jupiter's magnetic field. Not necessarily an issue for life(?) buried deep in the oceans, but certainly an issue for the survivability of a spacecraft. Through the US's, umm, extensive military experience, NASA has access to higher-grade rad-hard electronics components than ESA, and so JUICE will only fly-by Europa a few times instead of bathing itself in that radiation.
But NASA is involved in JUICE too: several of the (many) instruments on JUICE have US Principal Investigators, funded by NASA. So, NASA is already going to Europa in a very real sense.
I hate to rain on everyone's parade here, but this mission isn't likely to happen soon. The paper referenced in the original post is a write-up of a case made to the call for ideas put out by the European Space Agency for future large missions, specifically looking for one to be launched in 2028 and another in 2034 (L2 and L3, in ESA-speak, with L1 being a mission to Jupiter and its icy moons, selected a year or so earlier).
Problem is, the Uranus/Neptune case didn't win either the L2 or L3 slot. A wide range of scientific ideas and mission concepts were proposed, aired publically, and assessed by a senior survey committee, before the two top-ranked ideas were approved by ESA's Science Programme Committee in late 2013.
And those two future missions will be a new high-energy astrophysics observatory for L2 in 2028 and a gravitational wave observatory for L3 in 2034.
The senior survey committee liked the science case for Uranus and Neptune, saying "The SSC considered the study of the icy giants to be a theme of very high science quality and perfectly fitting the criteria for an L-class mission", but then went on to say:
"However, in view of the competition with a range of other high quality science themes, and despite its undoubted quality, on balance and taking account of the wide array of themes, the SSC does not recommend this theme for L2 or L3. In view of its importance, however, the SSC recommends that every effort is made to pursue this theme through other means, such as cooperation on missions led by partner agencies."
So, it certainly won't be an ESA-led mission in the foreseeable future, but ESA could participate in a wider international mission if someone else leads it.
His contemporary and science fiction novels have been an important part of my life for many, many years, and I shall miss knowing that his twisted and brilliant imagination is beavering away at new works.
But if nothing else, looking for a silver lining to this dark, dark cloud, I'm at least happy to have the chance to thank him publicly, before he's gone, for the great pleasure I've had in reading his books.
I'm sure he's greatly loved by many and I hope that that knowledge can go at least some small way to helping him and his wife through the months to come.
Problem is that Herschel's primary mirror was only polished to the level of surface roughness required for the telescope to be diffraction-limited (i.e. as good as it gets) at far-infrared wavelengths. It wasn't polished to the level necessary to form good images at optical wavelengths.
Just to put some numbers on that, Herschel's shortest operating wavelength is 70 microns (70 millionths of a metre), whereas the red end of the visible is around 0.7 microns, i.e. 100 times shorter.
Polishing the mirror to a factor of 100 lower surface roughness would have been far more expensive and perhaps even not possible using the underlying segmented silicon carbide technology. (SiC can be polished to optical tolerances, but I don't know if Herschel's substrate was made to the appropriate tolerances).
Space isn't really cold, not at least when you're close to a star like the Sun. After all, the Earth's isn't cold (well, relatively speaking), despite the fact that it sits in space. Sure, there's some internal heating from our molten core and some greenhouse effect from our atmosphere, but the underlying reason that the Earth is warm (again, relatively speaking) is because it's in thermal equilibrium with sunlight at a distance of 150 million kilometres from the Sun.
So if you stick something in space at L2, it's essentially at the same distance from the Sun as the Earth and thus, roughly speaking, it'll end up at the same temperature as the Earth.
The big difference, however, is that there's no atmosphere to transport heat by conduction or convection, so the side of the object that's facing the Sun will get hot and the other side, in the shade, will be colder. Of course, conduction by the object itself can transport heat from the hot side to the cold side, evening things out a bit. But if you can thermally isolate one side from the other, the side facing away from the Sun can get really, really cold, as it radiates any excess heat into the 3K "heat sink" of the Universe.
Which is exactly what spacecraft at L2 do. They have a hot side, facing the Sun and Earth, generating power to run the satellite and to communicate data back to Earth. Then they have a cold side, separated from the hot side by a sunshield and facing out into space, which can then get very, very cold, provided the two sides are thermally decoupled. You stick your telescope and instruments on that side and you can get nice and chilly.
(That said, you can only reach about 30–50K or so, which is fine for near-infrared observatories and their instruments, but the instruments used by far-infrared and sub-millimetre observatories need to be much colder, down around absolute zero, in order that their detectors don't blind themselves. That's why Herschel has liquid helium and why it will go blind when it runs out. Being at L2 is only half the story for Herschel.)
The beauty of L2 is that you keep the Sun, the Earth, and the Moon shining permanently on one side of the spacecraft, but never on the other side, if designed well. Spacecraft like Hubble in low-Earth orbit have to contend with half the sky being permanently filled with a big hot object called the Earth, and as you go around in orbit, the combined Earth and Sun illumination is constantly changing: not a good place to get a spacecraft really cold.
It's not being moved because it will clutter up L2. Indeed, such satellites don't sit exactly at the L2 point, but travel around it in orbits which are hundreds of thousands of kilometres wide. There's effectively no danger of any satellites at L2 hitting future ones.
No, the reason is that L2 isn't a stable location: the gravitational potential there is saddle-shaped. Very crudely, along the line of the orbit around the Sun, the satellite sits at the bottom of a curve. Move forward a bit and the Earth's gravity pulls you back. Fall behind a little bit and the same happens. However, perpendicular to the orbital track, in the plane of the ecliptic (the plane containing the planets), it's more like the top of a gravitational hill. Fall a little away from the Earth and bingo, the Earth is no longer strong enough to pull you back and you fall off, outwards.
But if you fall inwards, towards the Earth, the Earth's gravity gets stronger and pulls you even closer. So much so, that you might end up hitting the Earth.
So that's the reason why Herschel and other satellites there (WMAP in the past, Planck today, Gaia and JWST in the future) are pushed off L2 while the satellites still have propellant and are functional (if not scientifically) into heliocentric orbits, to prevent the possibility of the falling onto the Earth in an uncontrolled manner later.
Since you are posting as an AC, I have no idea whether you are one or two people, but under the assumption that the AC who posted this line:
Especially with the sky being blue from the full moon alone.
is the same as the AC who then posted this one:
I obviously didn't object to it being that hue, dumbass. I objected to it being *that* bright. It was a day shot. And obviously so.
then I'd say that's exactly what you did say.
And as for your assumption that I'm an American... well, you haven't got a clue, mate. You're many thousands of kilometres off. There are other countries in the world where English is the native language, after all. "We have 2013" indeed.
Sometimes I really do wonder whether/. is worth the trouble.
Err, of course the sky is blue under moonlight: it's just reflected sunlight, after all (but see below).
The problem is that the Moon is much fainter than the Sun and thus the overall light level is low. So low that it doesn't significantly activate the colour-sensitive cones in the human eye, meaning that you only really see with the rods in black-and-white.
But take a long exposure with a camera (or a video frame rate with this Canon sensor), and the blue will most definitely come through.
(Actually, the moonlight-illuminated sky is slightly bluer than a sunlight-illuminated one, as the Moon's slightly brown-ish colour first imprints its spectral dependence on the sunlight which bounces off it. That light is then Rayleigh-scattered off the molecules in the Earth's atmosphere, imprinting the well-known 1/lambda^4 dependence which makes the sky blue).
My thought entirely: it was in use as a scientific laboratory for many, many years prior to 2001 by Raymond Davis, Jr and colleagues to detect solar neutrinos. He identified a significant deficit in the number of neutrinos detected with respect to predictions and worked with John Bahcall for many years to demonstrate that his experiment was working correctly and the standard solar neutrino model was correct. Nevertheless, people doubted them for many years.
Later however, the Sudbury Neutrino Observatory in Canada and other experiments demonstrated that some of the electron neutrinos created in the Sun were mutating into muon and tau neutrinos (via "neutrino oscillation") en-route from the Sun to the Earth, providing an explanation for why Davis (whose experiment was only sensitive to electron neutrinos) was detecting only a third or so of the number predicted by the standard solar model.
Vindicated, Davis was then awarded part of the Nobel Prize for Physics in 2002, although unfortunately, Bahcall was not similarly rewarded. Neutrino oscillation and the direct implication that neutrinos have mass are profound discoveries, since they are inconsistent with the current Standard Model of particle physics. Many physicists are now working on further experiments and theory in this area.
Slashdot Mirror
No, hydrazine does not need an oxidiser: it's a monopropellant.
Schiaparelli had three 17.5 litre tanks, each filled with 15kg of hydrazine. There was also a 15.6 litre tank of high-pressure helium used to keep the hydrazine under pressure during firing.
Would it hurt people to occasionally do some research before contributing to the general drivel that Slashdot has become?
Schiaparelli's fuel tanks are filled
Hydrazine as a rocket fuel
Speaking from the ESA team that co-published those MRO CTX pictures yesterday, your assertions are nonsense and need correcting.
There was a fully coordinated operation in place to track the lander during its descent, using the GMRT in Pune, India, our own Mars Express spacecraft, NASA's MRO, and the ExoMars Trace Gas Orbiter itself, while data came down through our ESTRACK network and NASA's DSN. The Opportunity rover also in Meridiani Planum took images during the descent, but it was known that that would only possibly work if the lander came down at the long end of the landing ellipse: in the event, the targetting was fine, and it came down within ~5km of the centre of the ellipse.
All agencies and partners cooperated fully, as we always do when it comes to Mars (and other solar system) operations, and all data were released as soon as they were available and analysed, including from our own assets. Nobody has been withholding anything beyond the reasonable time needed to analyse the data: we're less than 3 days past the Schiaparelli entry and descent, and a lot of information is already available. The various teams involved are working day and night to understand the complex data.
The MRO CTX images were pre-planned, regardless of a successful landing or not, and were made available by NASA to the ExoMars project team as soon as possible. A number of meetings and joint telecons were held yesterday to analyse and agree on their content to the extent possible (CTX is fairly low resolution: much better information will come via HiRISE when it targets the site next week), and to agree on a time to release them.
Indeed, at ESA, we were working very hard yesterday to publish them jointly as soon as possible, in order to make them available to the European media for last night's news. Due to the timezone different to California, it was challenging for NASA to get the images and accompanying text approved by then, but we're very grateful that they worked hard to make that possible.
Finally, remember that we deliberately sent Schiaparelli there as a test demonstrator. We successfully carried out the hypersonic entry and supersonic parachute deployment phases, prior to the apparent failure during the thruster phase, and telemetry during the whole descent down to the surface were recorded and are back on Earth. Yes, we're obviously very disappointed that we didn't manage the final phase, but we will learn from the data. We also successfully put the main scientific mission, the Trace Gas Orbiter, into orbit around Mars.
We have not withheld information: we've been as open as possible throughout. I'm sure that the truth of the matter won't dissuade you of your "NASA great, ESA bad" opinion, but sometimes it's important to lay out the real story for others to judge.
Bottom line is that Mars was, is, and will always remain hard.
No it doesn't.
Just because energy is on one side of the equation and mass on the other, that doesn't mean they are the same thing. There is an equivalence between them in the same that a certain amount of mass can be converted into a certain amount of energy (and vice versa), but it doesn't mean that they are the same.
And this equation is specific to the situation where the object with mass isn't moving (which is why E in this case is called the "rest mass energy"). More generally in special relativity, for an object that is moving and has a momentum p, the equation becomes:
E^2 = m^2c^4 + p^2c^2
I suspect that you have missed the point entirely: silentcoder made the correct distinction between "mass" (an inherent property that depends on the number of atoms etc. in an object and that is independent of where the object is) and its "weight", which in physics terms means the force exerted by that object on something, which is the mass times the local acceleration.
Thus a person with a mass of 80kg standing on the Earth exerts a force due to gravity pulling them down onto the surface, i.e. 80 kg x 9.8 m/s2 = 784 Newtons. But for all sorts of obvious reasons, we just use the shorthand version to say that the person "weighs" 80 kg.
On the Moon, their mass would be the same, because they'd have the same number of atoms in their body. But they'd exert much less force on the surface, because the gravity on the Moon is only 1/6th of that on the Earth. So, they would weigh less. It's at that point that the shorthand way of talking about weight becomes useless.
Take the person and stick them infinitely far from any gravitating body and there would be no acceleration and thus no force, so the person would be weightless, but not massless (same number of atoms still).
Of course, in low Earth orbit, you're right in pointing out that the Earth's gravitational acceleration has not diminished much. However, while you're falling freely towards the surface of the Earth under that acceleration, the spacecraft you're in is falling out from underneath you at the same rate, so you don't exert a net force on it. Thus you're effectively weightless.
(If you're both falling freely towards the Earth, why don't you hit it at some point? Because you're flying sideways at such a high speed that the Earth's surface curves away from underneath you at just the same speed as you're falling towards it, so you never hit.)
But here's another thing. Under general relativity, gravity is much better thought of as a curvature of spacetime and it turns out that the motion of even massless objects (photons) is affected by that curvature (think Einstein, Eddington, etc.). Indeed, given a very strong gravitational field / very high spacetime curvature, e.g. around a black hole, photons can go into orbit. This is because while they don't have any mass, they do have energy.
So, in a more correct general relativistic setting, even your basic assertion that "to be able to orbit, you must have weight/mass" is wrong.
I have to say, this is borderline pointless.
Firstly, most of the detail is of relatively uninteresting bits of snow, rock, and ice: there's no real motivation to zooming in and poking around, as there is in a similar multi-gigapixel panorama of a city, for example.
As someone said above, the real grandeur of the scene comes in taking in the wider view, at which point the whole hi-res aspect is totally moot.
Plus the mosaic making sucks. Really, right from the get-go, the repeated features in the foreground snowfield are utterly distracting, followed by blurring in many areas when you zoom in a little.
Admittedly, such things are extremely difficult to do well / right (I know from experience), but I've seen plenty of other panoramas which are far better in post-processing.
Ultimately, the question becomes: why bother? Oh, because it's "the most pixelliferous image ever taken". Sigh.
Launch was March 2004, actually: it took a while :-)
Glad to see that you jumped in on this: good description.
Because the comet is so small, the gravity changes a lot with "altitude" from the surface. For a 2-km diameter sphere, say, then the difference in gravity between an altitude of 2-km and 6-km (i.e. between 4 and 8-km from the centre of the sphere) is a factor of 4. On the Earth, it barely changes at all between altitudes of 2 and 4-km, because this is a tiny change relative to the 6400-km radius of the Earth.
So, yes, at 100-km and 50-km, we'll be flying these hyperbolic arcs (slightly bent by the very weak gravity), using thrusters to "turn the corner" at the end of each leg. But at 30-km, we'll be on closed more-or-less circular orbits: I'm pretty sure that it is natural orbit though (and thus fairly long in duration), but not powered.
I do work on the project, albeit not on the flight dynamics side. One of our experts on this, Frank Budnik, did give a talk on this in the science session I moderated yesterday afternoon, starting at 11:28 into the recording of the live stream here:
http://www.esa.int/spaceinvideos/Videos/2014/08/Rosetta_at_comet_First_images_science_results
Ha ;-) From the live event at ESA's mission control centre in Darmstadt.
That said, there are some colleagues I tried to have volunteer to go ...
Our live webcast will be at www.esa.int starting at 10:00 CEST / 08:00 UT. Should be some cool new pictures of the comet to see.
(Disclaimer: I'll be one of the speakers :-)
Err, I think he was taking the mickey, surely. Or are these people really so dim?
Absolutely right: I was going to point out the same thing. It's many, many years away from any possible launch ...
For reference, the James Webb Space Telescope (or NGST as it was then) was beginning to be picked up as a serious prospect by NASA, ESA, and the Canadian Space Agency in the late 1990's. It's due for launch now in 2018.
(This is not meant as a criticism: I've been closely involved with JWST since 1998 and know how hard it has been in terms of technology, programmatics, and politics to get the good state it's in today, namely mostly built and now entering the comprehensive integration and test phase.)
So, very crudely, I'd say that something like ATLAST might be launched after 2035, if it gets picked up as the highest priority in the next US astronomy decadal survey.
Good point; I did use the word "we" in a rather catch-all manner there, and I'd also agree that technologists are likely to have a much better record at predicting the future than journalists.
But I'd then turn the tables and say that it depends on the timescale implied by "future". On a ten-year horizon, I'd agree that technologists are likely to have a pretty good idea what's coming, in part because they're likely to be working themselves actively on new technologies and products for release on similar sorts of timescales.
But on a 100 or 50 or even 30 year horizon, as this article refers to? It seems clear to me that on some timescale, even technologists are unlikely to be that close, if only because they're probably called "futurologists" at that point, or "science fiction writers" :-)
On some timescale, almost everyone is going to be pretty much guessing ...
OK, now having read the linked article (oops), I do see that the author (Henry McCracken) realised that the cover painting had a humorous intent (not least that it was the April edition of BYTE), satirising the conservative opinion that future tech was likely to be an extension / miniaturisation of the then-prevalent PC paradigm.
Good to see I got it, though :-)
C'mon, it's entirely obvious that that "PC on a watch" painting is a rather clever piece of irony or even satire, not a meaningful prediction of an actual future piece of technology.
That doesn't mean I disagree with the point of the discussion, namely that we're not that great at predicting the directions of future tech, but using this magazine cover as a direct illustration of that is, IMHO, rather disingenuous.
Actually, ESA built the Huygens lander which descended to the surface of Titan. It was carried there on the NASA-ASI Cassini orbiter after being launched by a NASA rocket, but Huygens was European-built, with instruments from Europe and the US.
Its the U-571 gambit: keep saying that things were achieved by the US independent of the truth of the matter, and pretty soon it becomes received knowledge.
Quite. Rosetta has been on a ten year journey around the Solar System, using Earth and Mars fly-bys to wind its orbit up to meet with 67P/Churyumov-Gerasimenko in August this year. At its most distant point from the Sun, it was beyond the orbit of Jupiter, but the comet rendezvous will take place at about 3AU, before the comet becomes active as it moves closer into the inner Solar System.
As for outer planet missions, the NASA-led and launched Cassini mission also carried ESA's Huygens probe, which performed the most distant ever landing in the Solar System when it landed on the surface of Titan in 2005.
But the elephant in the room here is ESA's JUICE mission, which is a real mission, not a study, already under implementation for a launch to Jupiter and its icy moons in 2022. JUICE will conduct a number of close fly-bys of Europa, but due to the dangerous radiation environment, will ultimately end up in orbit around Ganymede, another icy moon thought to host a deep ocean below the surface. And NASA are also involved in this mission, providing some of the instruments.
I was waiting for someone mention the (funded and being built) JUICE mission: it's astonishing to me that the "if it ain't NASA, it ain't worth jack" attitude generally persists, and that hardly anyone in the media (let alone on /.) bothers to do the slightest modicum of research.
JUICE is under development by the European Space Agency for launch in 2022 (not 2020 anymore) and arrival at Jupiter in 2030. It will tour the Jupiter system, including multiple fly-bys of the giant icy moons Europa, Callisto, and Ganymede. It will end up in orbit around Ganymede, where it will conduct a more detailed survey.
All three moons are thought to harbour giant water oceans under (probably) very thick icy crusts (~100km), although there are debates about which may be the most likely to provide potentially habitable environments deep in these oceans: it may depend on central heat flux from the moon's contraction, flexure due to Jupiter's gravity, heat from radioactive decay, and whether there's a water:rock interface which could provide minerals.
Why Ganymede as the final moon to be orbited? Because Europa is closer to Jupiter and suffers a much higher radiation dose due to high energy particles trapped in Jupiter's magnetic field. Not necessarily an issue for life(?) buried deep in the oceans, but certainly an issue for the survivability of a spacecraft. Through the US's, umm, extensive military experience, NASA has access to higher-grade rad-hard electronics components than ESA, and so JUICE will only fly-by Europa a few times instead of bathing itself in that radiation.
But NASA is involved in JUICE too: several of the (many) instruments on JUICE have US Principal Investigators, funded by NASA. So, NASA is already going to Europa in a very real sense.
I hate to rain on everyone's parade here, but this mission isn't likely to happen soon. The paper referenced in the original post is a write-up of a case made to the call for ideas put out by the European Space Agency for future large missions, specifically looking for one to be launched in 2028 and another in 2034 (L2 and L3, in ESA-speak, with L1 being a mission to Jupiter and its icy moons, selected a year or so earlier).
Problem is, the Uranus/Neptune case didn't win either the L2 or L3 slot. A wide range of scientific ideas and mission concepts were proposed, aired publically, and assessed by a senior survey committee, before the two top-ranked ideas were approved by ESA's Science Programme Committee in late 2013.
And those two future missions will be a new high-energy astrophysics observatory for L2 in 2028 and a gravitational wave observatory for L3 in 2034.
The senior survey committee liked the science case for Uranus and Neptune, saying "The SSC considered the study of the icy giants to be a theme of very high science quality and perfectly fitting the criteria for an L-class mission", but then went on to say:
"However, in view of the competition with a range of other high quality science themes, and despite its undoubted quality, on balance and taking account of the wide array of themes, the SSC does not recommend this theme for L2 or L3. In view of its importance, however, the SSC recommends that every effort is made to pursue this theme through other means, such as cooperation on missions led by partner agencies."
So, it certainly won't be an ESA-led mission in the foreseeable future, but ESA could participate in a wider international mission if someone else leads it.
You can read the whole report here.
As I posted a little earlier on The Guardian:
Desperately sad news.
His contemporary and science fiction novels have been an important part of my life for many, many years, and I shall miss knowing that his twisted and brilliant imagination is beavering away at new works.
But if nothing else, looking for a silver lining to this dark, dark cloud, I'm at least happy to have the chance to thank him publicly, before he's gone, for the great pleasure I've had in reading his books.
I'm sure he's greatly loved by many and I hope that that knowledge can go at least some small way to helping him and his wife through the months to come.
Problem is that Herschel's primary mirror was only polished to the level of surface roughness required for the telescope to be diffraction-limited (i.e. as good as it gets) at far-infrared wavelengths. It wasn't polished to the level necessary to form good images at optical wavelengths.
Just to put some numbers on that, Herschel's shortest operating wavelength is 70 microns (70 millionths of a metre), whereas the red end of the visible is around 0.7 microns, i.e. 100 times shorter.
Polishing the mirror to a factor of 100 lower surface roughness would have been far more expensive and perhaps even not possible using the underlying segmented silicon carbide technology. (SiC can be polished to optical tolerances, but I don't know if Herschel's substrate was made to the appropriate tolerances).
Space isn't really cold, not at least when you're close to a star like the Sun. After all, the Earth's isn't cold (well, relatively speaking), despite the fact that it sits in space. Sure, there's some internal heating from our molten core and some greenhouse effect from our atmosphere, but the underlying reason that the Earth is warm (again, relatively speaking) is because it's in thermal equilibrium with sunlight at a distance of 150 million kilometres from the Sun.
So if you stick something in space at L2, it's essentially at the same distance from the Sun as the Earth and thus, roughly speaking, it'll end up at the same temperature as the Earth.
The big difference, however, is that there's no atmosphere to transport heat by conduction or convection, so the side of the object that's facing the Sun will get hot and the other side, in the shade, will be colder. Of course, conduction by the object itself can transport heat from the hot side to the cold side, evening things out a bit. But if you can thermally isolate one side from the other, the side facing away from the Sun can get really, really cold, as it radiates any excess heat into the 3K "heat sink" of the Universe.
Which is exactly what spacecraft at L2 do. They have a hot side, facing the Sun and Earth, generating power to run the satellite and to communicate data back to Earth. Then they have a cold side, separated from the hot side by a sunshield and facing out into space, which can then get very, very cold, provided the two sides are thermally decoupled. You stick your telescope and instruments on that side and you can get nice and chilly.
(That said, you can only reach about 30–50K or so, which is fine for near-infrared observatories and their instruments, but the instruments used by far-infrared and sub-millimetre observatories need to be much colder, down around absolute zero, in order that their detectors don't blind themselves. That's why Herschel has liquid helium and why it will go blind when it runs out. Being at L2 is only half the story for Herschel.)
The beauty of L2 is that you keep the Sun, the Earth, and the Moon shining permanently on one side of the spacecraft, but never on the other side, if designed well. Spacecraft like Hubble in low-Earth orbit have to contend with half the sky being permanently filled with a big hot object called the Earth, and as you go around in orbit, the combined Earth and Sun illumination is constantly changing: not a good place to get a spacecraft really cold.
It's not being moved because it will clutter up L2. Indeed, such satellites don't sit exactly at the L2 point, but travel around it in orbits which are hundreds of thousands of kilometres wide. There's effectively no danger of any satellites at L2 hitting future ones.
No, the reason is that L2 isn't a stable location: the gravitational potential there is saddle-shaped. Very crudely, along the line of the orbit around the Sun, the satellite sits at the bottom of a curve. Move forward a bit and the Earth's gravity pulls you back. Fall behind a little bit and the same happens. However, perpendicular to the orbital track, in the plane of the ecliptic (the plane containing the planets), it's more like the top of a gravitational hill. Fall a little away from the Earth and bingo, the Earth is no longer strong enough to pull you back and you fall off, outwards.
But if you fall inwards, towards the Earth, the Earth's gravity gets stronger and pulls you even closer. So much so, that you might end up hitting the Earth.
So that's the reason why Herschel and other satellites there (WMAP in the past, Planck today, Gaia and JWST in the future) are pushed off L2 while the satellites still have propellant and are functional (if not scientifically) into heliocentric orbits, to prevent the possibility of the falling onto the Earth in an uncontrolled manner later.
Especially with the sky being blue from the full moon alone.
is the same as the AC who then posted this one:
I obviously didn't object to it being that hue, dumbass. I objected to it being *that* bright. It was a day shot. And obviously so.
then I'd say that's exactly what you did say.
And as for your assumption that I'm an American ... well, you haven't got a clue, mate. You're many thousands of kilometres off. There are other countries in the world where English is the native language, after all. "We have 2013" indeed.
Sometimes I really do wonder whether /. is worth the trouble.
Err, of course the sky is blue under moonlight: it's just reflected sunlight, after all (but see below).
The problem is that the Moon is much fainter than the Sun and thus the overall light level is low. So low that it doesn't significantly activate the colour-sensitive cones in the human eye, meaning that you only really see with the rods in black-and-white.
But take a long exposure with a camera (or a video frame rate with this Canon sensor), and the blue will most definitely come through.
(Actually, the moonlight-illuminated sky is slightly bluer than a sunlight-illuminated one, as the Moon's slightly brown-ish colour first imprints its spectral dependence on the sunlight which bounces off it. That light is then Rayleigh-scattered off the molecules in the Earth's atmosphere, imprinting the well-known 1/lambda^4 dependence which makes the sky blue).
My thought entirely: it was in use as a scientific laboratory for many, many years prior to 2001 by Raymond Davis, Jr and colleagues to detect solar neutrinos. He identified a significant deficit in the number of neutrinos detected with respect to predictions and worked with John Bahcall for many years to demonstrate that his experiment was working correctly and the standard solar neutrino model was correct. Nevertheless, people doubted them for many years.
Later however, the Sudbury Neutrino Observatory in Canada and other experiments demonstrated that some of the electron neutrinos created in the Sun were mutating into muon and tau neutrinos (via "neutrino oscillation") en-route from the Sun to the Earth, providing an explanation for why Davis (whose experiment was only sensitive to electron neutrinos) was detecting only a third or so of the number predicted by the standard solar model.
Vindicated, Davis was then awarded part of the Nobel Prize for Physics in 2002, although unfortunately, Bahcall was not similarly rewarded. Neutrino oscillation and the direct implication that neutrinos have mass are profound discoveries, since they are inconsistent with the current Standard Model of particle physics. Many physicists are now working on further experiments and theory in this area.