Look at it from the other point of view. If something has an orbital eccentricity of more than 1, then we get one chance to see it (one "apparition"). But if something is perturbed into an orbit with an eccentricity of 0.96 (eg Halley's Comet), we'll get multiple chances to see it (30, so far, for Halley).
To have lower eccentricity and be close enough to the Sun to be seen through much of it's orbit ( e.g 67P/Churyumovâ"Gerasimenko, eccentricity 0.64, perihelion 5.7AU, aphelion 1.2AU) required multiple interactions with Jupiter. It's not got a long life expectancy either.
It is possible to get a fair-quality orbit from one night's observations - at least, good enough to know where to point the CCD for follow-up observations the next night. And the industrial-scale data pipelines will be back to photograph (well, "CCD") the same regions of sky repeatedly over the next few nights. So if the body is large enough (or bright enough at some points in it's light curve - which you're already starting to record), you'll know about it a long long way out. IIRC, comet Hale-Bopp was discovered when it was somewhere out near Saturn's orbit. But that was 40-80km diameter, compared to Pluto's 2400km diameter.
The inner boundary of the Kuiper Belt is typically taken at Neptune's orbit. But it is rather fuzzy. Once a body evolves to high enough eccentricity(*) to start crossing Neptune, then it's increasingly likely to come close to Neptune, which is pretty unlikely to result in the eccentricity decreasing. Things start to happen rapidly then, and within mere tens of thousands of orbits it's likely to meet Jupiter. SL-9 did that in about 1970, did about 10 orbits of Jupiter, fragmented under the tidal stress in 1992, and impacted in late 1994. Comets evolve fast once they start to reach the inner Solar System.
(*) It's average kinetic energy, proportional to it's semi-major axis "a" changes much more slowly, because that energy has to go somewhere. Which is why a-e diagrams encapsulate so much about a population of bodies.
I'm no professional in these matters - just an interested amateur.
I'm not sure that I understand what you're trying to say then. Why the interest in "escape speed" (nb: it's a speed, not a velocity - https://en.wikipedia.org/wiki/... paragraph 2), which varies at different heliocentric distances, over eccentricity (which is a property of the entire orbit, and doesn't matter where in the orbit the object is when you measure it. If you're interested in the escape speed, then you first need to determine the orbit (boing! you've got the eccentricity!) then work out where on the orbit the object is, and what the heliocentric escape speed is at that distance, then calculate the object's speed at that distance... several additional steps, increasing the error bars.
There were numerical techniques used back in the days of slide rules and log tables where you could shorten the calculation by initially assuming an eccentricity of 1 (if you thought your object was a comet) or 0 (if you thought it was in a circular orbit). But once you've got your initial orbit you need to do a couple of rounds of refinement of the orbit to improve the quality of fit - and you'd get to a true estimate of eccentricity then. If your orbit wasn't converging to a valid solution with each round... you've got trouble. But that excuse was dieing by the end of the 1950s - you might have to wait a week or two to get your printout back from the computing centre after you set up the observations onto cards (hint : the standard format for reporting observations is still 80 columns wide!) and drop the cards into the internal mail, but you'd still get your computer-calculated orbit back while you're typing up your paper.
Nope. Ever since Gauss's work on the determination of the orbit of Ceres (the discoverer Piazzi only got 41 a day long arc of observations before Ceres got too close to the Sun - turning those data into an orbit was suddenly urgently necessary to "recover" the object when it came back out of the Sun's glare. As a part of that calculation, the eccentricity of the (calculated) orbit pops out. The maths goes over my head, but there is no shortage of descriptions of it (e.g. http://sce.uhcl.edu/helm/Space...) and there are commercial and freeware packages for doing the calculations for you (e.g. https://www.projectpluto.com/f... which includes other useful stuff too).
In practice, it is sufficiently automated that, for example, if you do Mike "@plutokiller" Brown's MOOC on the formation of the solar system (harder than your average MOOC ; strongly recommended) you'll be seeing and using plots of thousands of KBOs in "a:e" space. If you've got three observations, you've got an orbit. But if you've got four observations, you've got three orbits and you've got to be looking at the internal consistency of the data sets. Which is why TFP is complaining about the poor quality of the data in the sense of "high residual errors". The intrinsic problems of determining orbits in the Kuiper Belt are as they'll always be - faint objects (meaning noisy data) and slow movement (because the longer the arc between your first and last observations, the more accurate your orbit). But if you stick at it, and in particular, if your first orbit is good enough to collect the object a year later (when it's next in a good position in the night sky for observation - far from the Sun, far from your observatory's horizon at midnight), you'll get a reliable orbit. Unless of course, there is something like fragmentation, or gas ejection (propulsion) going on which you don't notice, and there is no single orbit for your object.
I take it that you didn't actually read the fucking paper? They're fully aware that the data set is poor. But that doesn't mean that the data is invalid. You might, for example, have done the two bouts of observation on either side of a large lump (but still too small to show up in the telescopes) falling off from a rotating and warming up body. There isn't enough data to decide, and there never will be. Which is the reason for stressing the need for prompt reporting of orbits and the prompt targeting of unusual orbits for additional follow-up.
No wonder you're an AC. I'd be ashamed to put my name to such an admission of incompetence.
Apparitions of "first appearance" comets didn't all produce eccentricities of 1.0000. - I recall for example reading papers by Opik (grandfather of the MP who promoted the UK actually investing money in planetary protection. Before getting "involved" with a pop starlet and losing his seat.) from the late 40s or mid-50s when for plotting and comparison purposes he worked on the semi-major axis of the reduced orbits because it made the small differences more obvious. That's what gave evidence for the Oort cloud - which we're still at the very edge of being able to directly observe.
But these days we're spending a lot more time observing with a lot bigger "light buckets", and reducing the data astrometrically to orbits a lot faster - which makes the recent discoveries (putative) much less surprising. We can look forward, on this basis, to seeing yearly or more frequent discovery of interstellar objects - exactly as we did with pulsars when I was a school kid and we've done with gravity wave astronomy in the last couple of years.
I think getting to 0.2c is the first problem to address. Then the problem of a 20-year voyage in a closed ecosystem with no resources you didn't accelerate to 0.2c (caveat : you might catch up with stores you dispatched 5 years ago at 0.18c - read any book on the logistics of "Expedition" style mountaineering for examples).
Actually, my first guesstimate is that if confirmed, this second pre-covery would generally agree with the estimate that there are of the order of 10000 such objects within the orbit of Neptune at any one time. The estimate of the number of interstellar objects hasn't changed much - just your knowledge of that flight hazard.
Yeah, that's the sort of numbers I was getting. TFS isn't at all clear on whether or not the bills are purely for supplying the hardware, or for supply and installation. If it's just for the hardware, weatherproofed and batteried (so they'll still work when the light isn't powered up)... you might cover a hundred or so of these. If it's to supply and install, then it's probably a couple of dozen only. Putting a man up on a cherry picker isn't exactly cheap. and sparkies ticketed to work on public utilities cost too. Even without getting any landsharks involved.
Oh, sorry, after introducing C/2014 W10 PANSTARRS, I forgot the original point. They (K&D) made a number of attempts to get a coherent solution for the orbit (the details are in the paper, see links already posted), which gave wildly divergent dates of perihelion dates and distances :
perihelion passage date: 2015 Feb. 9.246 ; 2014 Feb. 06.757 ; 2014 Feb. 07.6 ±979 days ; 2016 Aug. 17.267 ; 2013 Aug. 29.115 ; 2016 Jul. 15.6 ±211 days ; 2013 Jul. 3.8 ±102 days ; 2013 May 16.2 ±42 days
perihelion distance [AU]:7.4247577 ; 7.9952199 ; 8.00 ±0.75 ; 6.51927 ; 7.7604333 ; 4.40 ±2.26 ; 7.575 ±0.43 ; 7.279 ±0.40
(Sorry for my presentation ; I've not had a lot of luck with tables in Slashdot previously. RTFP, that's why they PublishedTFP.)
Which gives two points : they couldn't even be sure if the comet was coming or going at the times of observation (3 years uncertainty in perihelion date, in bold above, extending outside the window of observations); and several of the possible orbital solutions are "robustly hyperbolic". Also, in comment on your original point, most of those perihelion distance solutions are outside the orbit of Jupiter - giving fair grounds to the habit originally noted of doing the statistics for the count of interstellar bodies within the orbit of Neptune.
And now that they have found this in the archives... the object is out in the dark depths and no longer available for interrogation, even with our biggest telescopes.
Exit stage, left, followed by quiet muttering "submitted a damned interesting bit of science geekery, bloody stupid Slashdot didn't even notice ; why effing bother?"
If you RTFA'd on 'Oumuamua as it was happening (which I do to a degree by at least reading the abstracts as they go past on the Arxiv mailing list, one email a day, and fully reading interesting papers), you'd have seen that the normal unit of measure for "interstellar objects passing near the Sun" is actually to count "bodies within a sphere containing Neptune". Quite what the logic behind that is, I'm not sure, but it's a volume of about 3.80E+29cu.km. If they looked at bodies within the orbit of Jupiter... well, that's 1.98E+27 cu.km. They may have chosen that metric as the orbit of the largest body with a significant perturbing cross section. Or chosen it to get manageable integers. I don't know.
The estimates at that time (number of stars in the galaxy, guess at number of small bodies ejected from the Solar system) were that at any random day there should be about 10000 bodies of a km diameter within that "orbit of Neptune" metric. However, of that number, only a small proportion would be bright enough (in reflected light) to see, and the overwhelming majority of the search effort (for comets, NEAs, PHAs) is confined to the plane of the ecliptic. So... it wasn't wildly surprising that none had been detected before. Given that search depth (i.e. brightness * exposure) and search plate count are going up all the time, it wasn't terribly surprising that the first discovery came during a time of increasing search effort.
Everyone in the sane universe is highly suspicious of doing statistics on a sample of one. Which is precisely why my eyebrows went skywards and my mouse crept to the "Submit" button when I read KrÃlikowska & Dybczynski 's paper a couple of days ago. Because, if it's analysis is true, it doubles the size of the catalogue of interstellar objects observed telescopically in the Solar System. If the analysis is correct. Anyway, I submitted it for/., but the editors don't seem interested.
I'll stress it again - because some of Slashdot's readers don't seem to get the idea - that this sort of paper is not a report of a definite discovery, but reports for consideration and checking. Indeed, the authors stress that point themselves:
Our main purpose is to show that similar cases should be treated in future with greater care by more reliable preliminary orbit determination and alerting observers about the importance of the object to initiate more follow-up observations.
Any way, I said my thing on the submissions page. No reason to repeat myself.
To compound my sin of RTFAing, I'll note that there is a revised version of the paper out. As far as I can tell the changes are that they've changed the header to the "ACCEPTED FOR PUBLICATION IN THE ASTROPHYSICAL JOURNAL LETTERS" statement, and added a reference at the end. The rest of the contents look essentially the same.
I wondered if it was Slashdot's editors, or the original article. But the closest TFA comes to that phrase is "Whether she is independent enough to rein in public outbursts by Musk" - which is correct, even if you don't know which end of the horse to insert the bit and attach the reins to.
In slight defence of Slashdot's editor "BeauHD", the original submission had the error. But they still passed eyes over this before accepting it, which is almost as bad. My old redaktor (en_gb: editor) wouldn't have let me get away with this sort of stuff, and he wasn't even a native English speaker. Though I'd hardly call his native Norway a "third world" country. Britain, maybe. But he'll be leaving with Brexit.
There, you'd need gravity. If you're opting for hydroponics, why bother? The plants won't care.
Plants grow well without a gravity feed? Well, if you're growing algal feedstock for a "food synthesiser" (what is the Unobtanium budget for one of those? Or does it use Handwavium?), maybe not. Otherwise, for something resembling a balanced diet for the crew (assuming most of the colony-building animals are shipped as gametes, and a small number of live animals for use as wombs on arrival), you're going to need a variety of plant types.
Unless you have a drive of novel physics (again, what is the Handwavium/ Unobtanium ratio?), the only pseudogravity you're going to get is by rotating. So... it's either the inside of a sphere or a cylinder (or several cylinders, for isolation in the event of leaks/ disease outbreaks). How much you allocate to agriculture and how much to inhabitation / maintenance is where your optimisation options lay.
Whether you could pull off a Rendezvous With Rama-style dormancy is unclear
Is there any significant biology to support this being possible for large (centimetre-plus) organisms. I've been watching the science press for about 4 decades now, and seen nothing that classifies as "science" rather than "fiction". It's dead popular in fiction, I agree. In something resembling the real world, I see no evidence that it would be possible. Which leaves doing it the slow, generation-ship way as the available option. With a fusion power plant (itself pretty hairily close to Handwavium-plated Unobtanium) and something on a Rama-esque scale, it's doable. But the original departees would have been forgotten by the ship residents (along with this "living on a planet" lark) long before arrival at anywhere. Not good fiction material.
I'm thinking of casually stealing your idea for a short story, though, as that's probably one one the best solutions I've seen. That ok?
I've lifted most of it from the 1975 NASA report on space habitats. (Various places. Try http://www.nss.org/settlement/... ) Steal away, I did.
If you've that much shielding, then your primary problem is getting rid of excess heat.
"That much shielding" is equivalent to about an Earth atmosphere - which is the only shielding system with a million-year testing programme behind it. Unless... you've got a shielding system with a two million-year track record? Tell me more!
The inner surface of the shielding will all be in contact with the bags of water and/or rock which initially be at Asteroid Belt temperatures. Say, 100K. As it warms up (during construction/ flight trials) you'll get the thermal balance checked out. You might need active heat dumping (radiators and... maybe ammonia/CO2/water coolant fluid? Extract from some of the shielding if you need top-up en route, but you should be able to out-engineer that sort of problem. Minor leaks your biosphere microbes should be able to process into crops.) I doubt that excessive heat buildup or loss would be major issues, but again that's something you'd address in detail engineering. This is more like nautical science (I've sweltered and frozen inside different vessels from the sub-Arctic to the Tropics.) than rocket science. Insulation adjustment on the skin when vacuum is free and your shielding is cold and attached in relatively small lumps, multiply layered isn't challenging.
I wonder if that could be used, in some way. Just direct the IR in a relatively tight beam.
Not with any physics I know of. Or that I can bring to mind in several years of thinking along these lines.
Regardless, [...] If the minimum exceeds the maximum, the design is impossible with that technology.
That is part of the question which will be addressed by this conference (amongst others). The decision that the "standard mass" is inadequate for current and predicted uses has already been taken. The remaining questions are
Firstly - is the "Watt balance" approach currently better than the "standard mass"; if so by how much, and how long on current trends is it likely to remain good enough?
Secondly - is the "atom count" approach currently better than the "standard mass"; if so by how much, and how long on current trends is it likely to remain good enough?
Thirdly - is the "atom count" approach currently better than the "Watt balance"; if so by how much, and how long on current trends is it likely to remain good enough?
Those questions between the two systems, and the predictions about the future are likely to be the thorny ones.
You're indulging in a decades-long free-space rebuilding of an asteroid. You've got in-space engineering down pat long before you do that.
And you'd not move most of the material more then a few km while building your spacecraft. You'll also be building motors at the same time and place. And turning the volatiles of the "donor" asteroid into pumpable reaction mass. For the engines. Which will need testing.
To "remove" mass implies giving it enough energy to move it out of the gravity of the rest of the asteroid. Why waste that energy? Literally.
That is the gist of a proposition published by Ryan and Pitman in 1997. They proposed it on the basis of finding a couple of deeply-incised channels in the sediment and bedrock (their interpretation, not accepted by everyone) near the mouth of the Bosphorous.
But, with more work (seismic survey boats don't come this way very often, and cruising slowly across an extremely busy shipping lane will get you arrested, your vessel impounded, and probably the vessel master appearing in court after several days in a Turkish prison. Imagine trying the same in New York or Rotterdam harbour mouths.), there are more like half a dozen such channels. Some of them penetrate bedrock, some don't and some you just can't tell (got a boat with a saturation or mixed-gas dive spread on board? And permission to dive?). You also can't tell if they happened one after the other, all at the same time, or every decade and a half over a century - which would put extremely different "human scale" interpretations on the events.
Producers of hour-long (less advertising time) TV programmes like nice simple narratives. I'm not a TV producer, and I had several days of "waiting on materials" while bobbing around on a boat in the Black Sea, so I read up on the technical literature on the question, as well as viewing the ROV's pre-operations survey of the sea bed around the location (just in case there was anything archaeological 2+ km below us. Within the shallow-seismic (includes laying pipelines) community and the deep seismic (oil exploration) communities, Ryan and Pitman did not present adequate data to convince the majority of people of their case. Which is not a TV-friendly simple story.
One of "Ryan and Pitman" has stopped writing on the subject - which in science is tantamount to saying "I think I got it wrong that time". The other still raises the subject from time to time.
Size estimates for 'Oumuamua range from 230m to 1000m - 240m being the commonest. Rotation periods are given as 6.96 and 8.1 hours (that's 417.6 and 486 minutes respectively, because my space-station designing toolbox works in RPM). For 230m, the rotation rates give 7.4*10^-07 and -5.4*10^-07 g. For 240m, the rotation rates give 7.7*10^-07 and 5.7*10^-07 g. For 1000m, the rotation rates give 32.1*10^-07 and 20.4*10^-07 g.
So, we can deduce using your argument that the 'Oumuamua-ians developed their physiology in micro-g gravity fields. That's down in the "ISS during tepid manoeuvrers" level.
it can include details like their name, address, phone number and party affiliation
What the flying fuck business does the state have in knowing which one of the 8 significant political parties you're affiliated to? If any. Or several. I mean, it's perfectly possible for you to have valid grounds for affiliation to 4 political parties here, without one word of hypocrisy and only considering where you grew up and where you live now. If you've had a more mobile history, it could be 5, easily.
But hey, America's problem, so there's no reason to expect a solution. It's obviously convenient for the "powers that be", so the voters can go hang.
4. TENSILE STRESSES
A thin object can be torn apart by centrifugal forces or tidal forces if its tensile strength is not sufficiently strong. [...]
4.1. Rotation
Works out to around 0.65 dyne/sq.cm. depending on your assumption for the material density
This is much smaller than typical tensile strengths of normal materials, and even of that of the comet 67P/Churyumov-Gerasimenko (see Table 1). Thus, even when self-gravity is ignored, âOumuamua can easily withstand its centrifugal force.
Interesting. Of course, we knew that because it hadn't fallen apart in the last several million years of it's flight.
The assumption that the relatively small non-Keplerian component to the course of 'Oumuamua is due to light acceleration from the Sun seems unwarranted, when the possibility of it being due to outgassing remains credible, seems... well, overblown. IMO. Worth discussing as an option, in the same way that reductio ad absurdam remains a valid form of argument.
If you wanted to fly to the stars, you'd need a ship with a very thick hull to handle galactic background radiation.
Only about a dozen metres of water-ice. Down to around 5m for a 50-50 ice-rock dust mix. Not trivial, but not horrendous.
The odds of meeting something large enough to fragment... well, 'Oumuamua got here after an uncertain (but probably very long) travel, so... low enough. Send two, travelling outside their mutual ballistic debris cones.
Walls already made for you, and you've extracted ore you can use to make floors, engines, etc.
My suspicion would be that you'd have to do so much mining and making space to actually build things inside your putative asteroid... that demolishing the original asteroid and completely rebuilding it would be quicker. You could then engineer for rotation sufficient to give an endurable pseudogravity for indefinite travel.
Thank you, American tax payer. Arthur C. Clarke would have been fuming.
But he'd do it politely and sarcastically. Being a British WW2 radar developer.
The good news is that the builders of Rama do everything in threes.
So, on the way in 'Oumuamua dropped two von Neumann factories, and will drop another on the way out. Give it a couple of thousand years for them to make the system habitable (for not-necessarily-human values of "habitable") and the next ship will be along.
Stars move. Our distance estimates have uncertainty to them, and the glare of each star's light introduces an uncertainty in their angular position measurement. In short, over the many millennia of travel, we don't know the previous positions of nearby stars well enough to constrain 'Oumuamua's path well enough. Yes, astrometry is improving (see, for example, Gaia data release 2). No, it is not adequate to that task, and probably never will be, because there is dark (sense : not luminous) stuff too, in sufficient quantities to render the project... impracticable.
Yeah. Uh, there is a lot of discussion on that suggestion. Whether the seismic (you know, the original data on which the whole proposition is based) actually supports Ryan and Pitman's original interpretation of one catastrophic flooding event remains very much a topic of debate. There are certainly multiple scour channels on the Black Sea side of the Bosphorus, though what the levels of the Bosphorus were for each scouring event is... very debatable. Let alone their dating, absolute and relative.
Yeah, it's an interesting question. I spent some days on it while working in the Black Sea a couple of years back. As far as I can tell (and I am tens of thousands of hours of experience short of claiming to be an "expert" in seismic interpretation), the data just isn't sufficient to decide if there was one flood event, or many smaller ones. Feel free to upfront the costs for a seabed corer, boat, crew and permission to block the traffic of one of the most congested sea lanes of the world. The permission would be the hard bit. And very expensive.
Oh, by the way, if it happened, it probably didn't affect the development of civilisation in China, India, or Central America very much. Fertile Crescent - much more credible. Egypt, so-so.
Slashdot Mirror
To have lower eccentricity and be close enough to the Sun to be seen through much of it's orbit ( e.g 67P/Churyumovâ"Gerasimenko, eccentricity 0.64, perihelion 5.7AU, aphelion 1.2AU) required multiple interactions with Jupiter. It's not got a long life expectancy either.
"A chance no astrophysicist could pass up."
"I am sorry, Louis Wu. I do not understand."
"The opportunity to study the underside of sunspots."
The inner boundary of the Kuiper Belt is typically taken at Neptune's orbit. But it is rather fuzzy. Once a body evolves to high enough eccentricity(*) to start crossing Neptune, then it's increasingly likely to come close to Neptune, which is pretty unlikely to result in the eccentricity decreasing. Things start to happen rapidly then, and within mere tens of thousands of orbits it's likely to meet Jupiter. SL-9 did that in about 1970, did about 10 orbits of Jupiter, fragmented under the tidal stress in 1992, and impacted in late 1994. Comets evolve fast once they start to reach the inner Solar System.
(*) It's average kinetic energy, proportional to it's semi-major axis "a" changes much more slowly, because that energy has to go somewhere. Which is why a-e diagrams encapsulate so much about a population of bodies.
I'm no professional in these matters - just an interested amateur.
There were numerical techniques used back in the days of slide rules and log tables where you could shorten the calculation by initially assuming an eccentricity of 1 (if you thought your object was a comet) or 0 (if you thought it was in a circular orbit). But once you've got your initial orbit you need to do a couple of rounds of refinement of the orbit to improve the quality of fit - and you'd get to a true estimate of eccentricity then. If your orbit wasn't converging to a valid solution with each round ... you've got trouble. But that excuse was dieing by the end of the 1950s - you might have to wait a week or two to get your printout back from the computing centre after you set up the observations onto cards (hint : the standard format for reporting observations is still 80 columns wide!) and drop the cards into the internal mail, but you'd still get your computer-calculated orbit back while you're typing up your paper.
In practice, it is sufficiently automated that, for example, if you do Mike "@plutokiller" Brown's MOOC on the formation of the solar system (harder than your average MOOC ; strongly recommended) you'll be seeing and using plots of thousands of KBOs in "a:e" space. If you've got three observations, you've got an orbit. But if you've got four observations, you've got three orbits and you've got to be looking at the internal consistency of the data sets. Which is why TFP is complaining about the poor quality of the data in the sense of "high residual errors". The intrinsic problems of determining orbits in the Kuiper Belt are as they'll always be - faint objects (meaning noisy data) and slow movement (because the longer the arc between your first and last observations, the more accurate your orbit). But if you stick at it, and in particular, if your first orbit is good enough to collect the object a year later (when it's next in a good position in the night sky for observation - far from the Sun, far from your observatory's horizon at midnight), you'll get a reliable orbit. Unless of course, there is something like fragmentation, or gas ejection (propulsion) going on which you don't notice, and there is no single orbit for your object.
No wonder you're an AC. I'd be ashamed to put my name to such an admission of incompetence.
But these days we're spending a lot more time observing with a lot bigger "light buckets", and reducing the data astrometrically to orbits a lot faster - which makes the recent discoveries (putative) much less surprising. We can look forward, on this basis, to seeing yearly or more frequent discovery of interstellar objects - exactly as we did with pulsars when I was a school kid and we've done with gravity wave astronomy in the last couple of years.
Actually, my first guesstimate is that if confirmed, this second pre-covery would generally agree with the estimate that there are of the order of 10000 such objects within the orbit of Neptune at any one time. The estimate of the number of interstellar objects hasn't changed much - just your knowledge of that flight hazard.
Yeah, that's the sort of numbers I was getting. TFS isn't at all clear on whether or not the bills are purely for supplying the hardware, or for supply and installation. If it's just for the hardware, weatherproofed and batteried (so they'll still work when the light isn't powered up) ... you might cover a hundred or so of these. If it's to supply and install, then it's probably a couple of dozen only. Putting a man up on a cherry picker isn't exactly cheap. and sparkies ticketed to work on public utilities cost too. Even without getting any landsharks involved.
... which takes some skill, since the profit margin is literally built into the rules of the game.
perihelion passage date
perihelion distance [AU]
(Sorry for my presentation ; I've not had a lot of luck with tables in Slashdot previously. RTFP, that's why they PublishedTFP.)
Which gives two points : they couldn't even be sure if the comet was coming or going at the times of observation (3 years uncertainty in perihelion date, in bold above, extending outside the window of observations); and several of the possible orbital solutions are "robustly hyperbolic". Also, in comment on your original point, most of those perihelion distance solutions are outside the orbit of Jupiter - giving fair grounds to the habit originally noted of doing the statistics for the count of interstellar bodies within the orbit of Neptune.
And now that they have found this in the archives ... the object is out in the dark depths and no longer available for interrogation, even with our biggest telescopes.
Exit stage, left, followed by quiet muttering "submitted a damned interesting bit of science geekery, bloody stupid Slashdot didn't even notice ; why effing bother?"
If you RTFA'd on 'Oumuamua as it was happening (which I do to a degree by at least reading the abstracts as they go past on the Arxiv mailing list, one email a day, and fully reading interesting papers), you'd have seen that the normal unit of measure for "interstellar objects passing near the Sun" is actually to count "bodies within a sphere containing Neptune". Quite what the logic behind that is, I'm not sure, but it's a volume of about 3.80E+29cu.km. If they looked at bodies within the orbit of Jupiter ... well, that's 1.98E+27 cu.km. They may have chosen that metric as the orbit of the largest body with a significant perturbing cross section. Or chosen it to get manageable integers. I don't know.
The estimates at that time (number of stars in the galaxy, guess at number of small bodies ejected from the Solar system) were that at any random day there should be about 10000 bodies of a km diameter within that "orbit of Neptune" metric. However, of that number, only a small proportion would be bright enough (in reflected light) to see, and the overwhelming majority of the search effort (for comets, NEAs, PHAs) is confined to the plane of the ecliptic. So ... it wasn't wildly surprising that none had been detected before. Given that search depth (i.e. brightness * exposure) and search plate count are going up all the time, it wasn't terribly surprising that the first discovery came during a time of increasing search effort.
Everyone in the sane universe is highly suspicious of doing statistics on a sample of one. Which is precisely why my eyebrows went skywards and my mouse crept to the "Submit" button when I read KrÃlikowska & Dybczynski 's paper a couple of days ago. Because, if it's analysis is true, it doubles the size of the catalogue of interstellar objects observed telescopically in the Solar System. If the analysis is correct. Anyway, I submitted it for /., but the editors don't seem interested.
I'll stress it again - because some of Slashdot's readers don't seem to get the idea - that this sort of paper is not a report of a definite discovery, but reports for consideration and checking. Indeed, the authors stress that point themselves :
Any way, I said my thing on the submissions page. No reason to repeat myself.
To compound my sin of RTFAing, I'll note that there is a revised version of the paper out. As far as I can tell the changes are that they've changed the header to the "ACCEPTED FOR PUBLICATION IN THE ASTROPHYSICAL JOURNAL LETTERS" statement, and added a reference at the end. The rest of the contents look essentially the same.
In slight defence of Slashdot's editor "BeauHD", the original submission had the error. But they still passed eyes over this before accepting it, which is almost as bad. My old redaktor (en_gb: editor) wouldn't have let me get away with this sort of stuff, and he wasn't even a native English speaker. Though I'd hardly call his native Norway a "third world" country. Britain, maybe. But he'll be leaving with Brexit.
But I'm sure I saw Madame Miss Pelling in a Voltaire play. Or was it Rabelais?
Plants grow well without a gravity feed? Well, if you're growing algal feedstock for a "food synthesiser" (what is the Unobtanium budget for one of those? Or does it use Handwavium?), maybe not. Otherwise, for something resembling a balanced diet for the crew (assuming most of the colony-building animals are shipped as gametes, and a small number of live animals for use as wombs on arrival), you're going to need a variety of plant types.
Unless you have a drive of novel physics (again, what is the Handwavium/ Unobtanium ratio?), the only pseudogravity you're going to get is by rotating. So ... it's either the inside of a sphere or a cylinder (or several cylinders, for isolation in the event of leaks/ disease outbreaks). How much you allocate to agriculture and how much to inhabitation / maintenance is where your optimisation options lay.
Is there any significant biology to support this being possible for large (centimetre-plus) organisms. I've been watching the science press for about 4 decades now, and seen nothing that classifies as "science" rather than "fiction". It's dead popular in fiction, I agree. In something resembling the real world, I see no evidence that it would be possible. Which leaves doing it the slow, generation-ship way as the available option. With a fusion power plant (itself pretty hairily close to Handwavium-plated Unobtanium) and something on a Rama-esque scale, it's doable. But the original departees would have been forgotten by the ship residents (along with this "living on a planet" lark) long before arrival at anywhere. Not good fiction material.
I've lifted most of it from the 1975 NASA report on space habitats. (Various places. Try http://www.nss.org/settlement/... ) Steal away, I did.
"That much shielding" is equivalent to about an Earth atmosphere - which is the only shielding system with a million-year testing programme behind it. Unless ... you've got a shielding system with a two million-year track record? Tell me more!
The inner surface of the shielding will all be in contact with the bags of water and/or rock which initially be at Asteroid Belt temperatures. Say, 100K. As it warms up (during construction/ flight trials) you'll get the thermal balance checked out. You might need active heat dumping (radiators and ... maybe ammonia/CO2/water coolant fluid? Extract from some of the shielding if you need top-up en route, but you should be able to out-engineer that sort of problem. Minor leaks your biosphere microbes should be able to process into crops.) I doubt that excessive heat buildup or loss would be major issues, but again that's something you'd address in detail engineering. This is more like nautical science (I've sweltered and frozen inside different vessels from the sub-Arctic to the Tropics.) than rocket science. Insulation adjustment on the skin when vacuum is free and your shielding is cold and attached in relatively small lumps, multiply layered isn't challenging.
Not with any physics I know of. Or that I can bring to mind in several years of thinking along these lines.
Firstly - is the "Watt balance" approach currently better than the "standard mass"; if so by how much, and how long on current trends is it likely to remain good enough?
Secondly - is the "atom count" approach currently better than the "standard mass"; if so by how much, and how long on current trends is it likely to remain good enough?
Thirdly - is the "atom count" approach currently better than the "Watt balance"; if so by how much, and how long on current trends is it likely to remain good enough?
Those questions between the two systems, and the predictions about the future are likely to be the thorny ones.
So?
You're indulging in a decades-long free-space rebuilding of an asteroid. You've got in-space engineering down pat long before you do that.
And you'd not move most of the material more then a few km while building your spacecraft. You'll also be building motors at the same time and place. And turning the volatiles of the "donor" asteroid into pumpable reaction mass. For the engines. Which will need testing.
To "remove" mass implies giving it enough energy to move it out of the gravity of the rest of the asteroid. Why waste that energy? Literally.
That is the gist of a proposition published by Ryan and Pitman in 1997. They proposed it on the basis of finding a couple of deeply-incised channels in the sediment and bedrock (their interpretation, not accepted by everyone) near the mouth of the Bosphorous.
But, with more work (seismic survey boats don't come this way very often, and cruising slowly across an extremely busy shipping lane will get you arrested, your vessel impounded, and probably the vessel master appearing in court after several days in a Turkish prison. Imagine trying the same in New York or Rotterdam harbour mouths.), there are more like half a dozen such channels. Some of them penetrate bedrock, some don't and some you just can't tell (got a boat with a saturation or mixed-gas dive spread on board? And permission to dive?). You also can't tell if they happened one after the other, all at the same time, or every decade and a half over a century - which would put extremely different "human scale" interpretations on the events.
Producers of hour-long (less advertising time) TV programmes like nice simple narratives. I'm not a TV producer, and I had several days of "waiting on materials" while bobbing around on a boat in the Black Sea, so I read up on the technical literature on the question, as well as viewing the ROV's pre-operations survey of the sea bed around the location (just in case there was anything archaeological 2+ km below us. Within the shallow-seismic (includes laying pipelines) community and the deep seismic (oil exploration) communities, Ryan and Pitman did not present adequate data to convince the majority of people of their case. Which is not a TV-friendly simple story.
One of "Ryan and Pitman" has stopped writing on the subject - which in science is tantamount to saying "I think I got it wrong that time". The other still raises the subject from time to time.
Size estimates for 'Oumuamua range from 230m to 1000m - 240m being the commonest. Rotation periods are given as 6.96 and 8.1 hours (that's 417.6 and 486 minutes respectively, because my space-station designing toolbox works in RPM). For 230m, the rotation rates give 7.4*10^-07 and -5.4*10^-07 g. For 240m, the rotation rates give 7.7*10^-07 and 5.7*10^-07 g. For 1000m, the rotation rates give 32.1*10^-07 and 20.4*10^-07 g.
So, we can deduce using your argument that the 'Oumuamua-ians developed their physiology in micro-g gravity fields. That's down in the "ISS during tepid manoeuvrers" level.
Nice idea. I don't think it helps though.
What the flying fuck business does the state have in knowing which one of the 8 significant political parties you're affiliated to? If any. Or several. I mean, it's perfectly possible for you to have valid grounds for affiliation to 4 political parties here, without one word of hypocrisy and only considering where you grew up and where you live now. If you've had a more mobile history, it could be 5, easily.
But hey, America's problem, so there's no reason to expect a solution. It's obviously convenient for the "powers that be", so the voters can go hang.
Interesting. Of course, we knew that because it hadn't fallen apart in the last several million years of it's flight.
The assumption that the relatively small non-Keplerian component to the course of 'Oumuamua is due to light acceleration from the Sun seems unwarranted, when the possibility of it being due to outgassing remains credible, seems ... well, overblown. IMO. Worth discussing as an option, in the same way that reductio ad absurdam remains a valid form of argument.
Only about a dozen metres of water-ice. Down to around 5m for a 50-50 ice-rock dust mix. Not trivial, but not horrendous.
The odds of meeting something large enough to fragment ... well, 'Oumuamua got here after an uncertain (but probably very long) travel, so ... low enough. Send two, travelling outside their mutual ballistic debris cones.
My suspicion would be that you'd have to do so much mining and making space to actually build things inside your putative asteroid ... that demolishing the original asteroid and completely rebuilding it would be quicker. You could then engineer for rotation sufficient to give an endurable pseudogravity for indefinite travel.
But he'd do it politely and sarcastically. Being a British WW2 radar developer.
So, on the way in 'Oumuamua dropped two von Neumann factories, and will drop another on the way out. Give it a couple of thousand years for them to make the system habitable (for not-necessarily-human values of "habitable") and the next ship will be along.
Stars move. Our distance estimates have uncertainty to them, and the glare of each star's light introduces an uncertainty in their angular position measurement. In short, over the many millennia of travel, we don't know the previous positions of nearby stars well enough to constrain 'Oumuamua's path well enough. Yes, astrometry is improving (see, for example, Gaia data release 2). No, it is not adequate to that task, and probably never will be, because there is dark (sense : not luminous) stuff too, in sufficient quantities to render the project ... impracticable.
Yeah, it's an interesting question. I spent some days on it while working in the Black Sea a couple of years back. As far as I can tell (and I am tens of thousands of hours of experience short of claiming to be an "expert" in seismic interpretation), the data just isn't sufficient to decide if there was one flood event, or many smaller ones. Feel free to upfront the costs for a seabed corer, boat, crew and permission to block the traffic of one of the most congested sea lanes of the world. The permission would be the hard bit. And very expensive.
Oh, by the way, if it happened, it probably didn't affect the development of civilisation in China, India, or Central America very much. Fertile Crescent - much more credible. Egypt, so-so.