After eight years, NASA's Dawn probe brings Ceres into closest focus More than a thousand times farther from Earth than the moon, farther even than the Sun, an extraordinary extraterrestrial expedition is taking place. NASA’s Dawn spacecraft is exploring dwarf planet Ceres, which orbits the Sun between Mars and Jupiter. The probe has just reached the closest point it ever will, and is now …
I feel very conflicted about living in this period of history.
On the one hand, awesome stuff like this.
But on the other hand, anthropogenic global climate change.
On a related sidenote: sci-fi loving types would do well, I think, to take a look at SyFy's (Sigh-Fy, amirite...?) "The Expanse". The book is naturally better, so far. But considering it's TV, it's not that bad.
"Gravity on Ceres is 3% of Earth's".
The Expanse's Ceres has apparently somehow been spun to create artificial gravity. So more of a really large space station than a planetoid.
I am hoping the book(s) -- which I started to read after seeing the series, BTW -- will explain how this could be achieved without scattering the thing to dust. Considering the relative accuracy of the physics so far (I didn't do the math. But I didn't get the urge to bang my head on the nearest solid surface in frustration, either), I am hopeful.
I've read them and from what I can recall they reference Ceres being spun up as one of mankinds major engineering achievements and refer to a long slow process, more of a side note, but I agree their approach to the physics and explanations aren't bad and well ahead of a lot of stuff.
"they reference Ceres being spun up as one of mankinds major engineering achievements and refer to a long slow process".
Ah! I see... Please excuse me while I find the nearest solid surface I can bang my head against.
I already came across that bit and was hoping for more.
The problem I see is that regardless of how slowly and carefully you do it, if you spin up something like Ceres with enough angular velocity to create a radially outward acceleration that would exceed its own gravitational acceleration, then it will fly apart. Probably long before you got to that point, in fact. After all, it's essentially just a pile of rubble held together by gravity.
"But the ship will remain in orbit around Ceres as surely as the moon remains in orbit around Earth and Earth remains in orbit around the sun"
So after we finish littering our gravitational sphere with scrap, we start doing it to other worlds
Won't the interstellar travellers see us as the "Pikey's" of an inhabited solar system?
If it weren't for Assyrian, Indus Valley, Meso-American, Chinese and Egyptian 'pikeys' we would know a lot less about our ancient past than we actually do.
What's worrying is not so much that we've left a lot of stuff in orbit around Earth; it's that some irresponsible idiots in both China and the US deliberately created large debris fields that threaten near-Earth orbits, and that it wasn't mandated early on that any entity lofting a sattelite into Earth orbit should have built in the means or otherwise have doable plans and the ability to de-orbit it safely too.
Fingers crossed someone comes up with a solution to the current mess up there before kessler Syndrome starts biting too hard, its already at a worrisome point.
"Fingers crossed someone comes up with a solution to the current mess up there before kessler Syndrome starts biting too hard, its already at a worrisome point".
Look t it this way: this future solution will certainly require significant technological, if not scientific, advancement. Challenges present opportunities to advance. Even those challenges that we ourselves needlessly create.
we already have part of the answer to the space debris - the returnable rocket. Now we will see what Space X does with the 2nd stage of the Falcon system. The DSCOVR mission will be the 1st time a Falcon 2nd stage left earth orbit - sounds like the safest plan ever! Eject them into the Sun!
"we already have part of the answer to the space debris - the returnable rocket. "
The returning of the first stage has nothing to do with space debris. Prior to this (and Bezos' earlier equivalent - but much smaller scale, sorta like getting the scooter to come back vs the Heavy Truck of Space X) feat, the first stage did not become space debris. It became ocean (or in the case of Russia/Soviets Siberian) debris. The first stage of a multi-stage to orbit rocket would never reach space. It would splash down in the Atlantic Ocean and (mostly) break up and sink to the ocean floor.
once we're all over the asteroid belt, as we should be, early spacecraft (like this) are going to turn up from time to time
Presumably those times will be pretty far apart, since 1) there aren't likely to have been a whole lot of said "early spacecraft", and 2) the asteroid belt, is, um, a fairly large place. Quite a few of "us" could be "all over" the asteroid belt and miss a lot of stuff (and not be particularly easy to find ourselves); there are around a million asteroids with a diameter of a kilometer or more.
Of course, the belt is mostly full of nothing, which presumably makes anything that's something easier to find. But I'd think little probe spacecraft will either be pretty straightforward to find because they're still broadcasting a strong signal, or pretty damn hard to find because they aren't.
This site estimates the volume of the belt at around 6x1023km3. (Or a bit less than a mole of cubic kilometers, in one of those completely irrelevant coincidences.)
Actually rocket engines in general are more efficient than the IC engines in cars, otherwise in Randall Munroe's words, you will not go to space today. Although car engines can be as much as 35-40% of the Carnot efficiency, all the added mass means that, in terms of moving the human payload, the average US car efficiency is about 0.5% and the average European/Far Eastern car is around 1% (these figures from an article in Scientific American.)
Real ion engines are very low thrust, which makes sense if you think about the electric charge that would need to be transferred to create a TIE fighter. As the ions come out the back at speed, they have to recombine with an electron supply so the spacecraft stays overall neutral. I haven't calculated the current necessary for a TIE fighter (perhaps I will if I can summon up the enthusiasm) but solar panels won't cut it; it's going to be on board nuclear or fusion reactor order of magnitude. Perhaps in that galaxy very long ago and very far away the laws of physics were different.
Let's assume a mass around 10t and a maximum required acceleration of 8g. No air in space so this has to come entirely from propulsion. To give 8g to a 10t mass requires about 800kN. The peak power is thus 0.5 * 80 * 800 000 or approx. 32MW.
Thrust is roughly equal to flow rate * exhaust velocity. 90 000mph in the example is roughly 40kM/s in real units, so to get 800kN we need to output 20kg/s of gas. That actually isn't too bad.
The atomic weight of xenon is about 131 so 20kg is very roughly 1/6th of a mole. That means that the charge transferred per second is 1/6th of a Faraday or approx. 16000A, and for a perfectly efficient ion engine this would involve a PD of about 2kV.
Ion engines have been built with higher velocities than those in the article, so at 4 times the velocity we might get that down to 5kg/s, 4000A and 8kV.
The gen4energy proposed portable nuclear reactor produces about 25MWe so it is in the ballpark, but all I can find about the weight is that it is "under 50t". Unfortunately the ancillary equipment is an awful lot bigger than that. One major problem with a TIE fighter is going to be cooling.
tl;dr is that to make it work we need a way of removing an awful lot of mass and heat.
"To give 8g to a 10t mass requires about 800kN. The peak power is thus 0.5 * 80 * 800 000 or approx. 32MW."
I don't understand that equation. Power has dimensions of m2⋅kg⋅s-3 But your equation seems to be "dimensionless constant (0.5) × acceleration (80m⋅s-2) × force (800,000 m⋅kg⋅s-2) = 32×106 m2⋅kg⋅s-4" making the "units" MW/s.
I accept that an acceleration of 80m⋅s-2 produces a change in velocity of 80m/s in unit time (v=u+at). So, if and only if, the ship's velocity was initially 0, then a 10Mg ship has gained 32MJ of kinetic energy in unit time (via ½mv2). (And note it gains 96MJ in the second second.)
However this neglects the energy given to the propellent. We know the change in momentum of the ship in unit time is 800kNs (Δp=FΔt); conservation of momentum requires the propellant be given the same momentum. I agree that 20kg at 40km/s produces 800kNs of momentum (p=mv) so the kinetic energy given to the propellent, via ½mv2, is a whopping 0.5*20*40E3*40E3 = 16GJ
So your power plant needs O(16GJ). And a loss of 20kg/s is non trivial: in one minute you've lost over 1Mg of your 10Mg ship.
The corrector's law says I will have gone horribly wrong somewhore.
The VASIMR engine appears to be the champ for specific impulse and thrust to weight, yes. And yes, at 200KW you are probably going to need a fusion power plant. And at that point, why not just use the bare fusion for thrust and skip the energy conversion losses, the heating and so forth?
We have a ways to go, but we will solve this star travel problem eventually now that it's "finder's keepers for as long as you can maintain possession" for everything off of Earth. As if it wasn't always that way down here too.
To the people who would call me a "space nutter": a homeless disowned 18 year old refugee from South Africa grew up, challenged your preconceptions, and just took ownership of all the world's space launch business by inventing something you said wasn't worthwhile - a reusable rocket. Now he's got a dozen launches scheduled in the next year that are already paid for, and he gets to keep all those rockets for free! Remember that to the buyer a proven rocket is $80M with of critical delivery. To the manufacturer it's $8000 worth of scrap metal, some plant, some IP, and some labor. And the plant and IP is paid for. And that kid? Why? He wants to go to Mars, personally, and the $3B he got for inventing PayPal wasn't enough to get him there without smashing your despair meme.
Lockheed Martin thinks they have Fusion sorted, and are developing the commercial product. Unless they've been smoking dope, we're on our way. And these are the people who invented the SR71.
The rest of the world, on notice that this is actually possible, is now on a nation-state funded race to compete because apparently all the money on Earth ain't a grain of sand on the beach of the Cosmos.
Mikel "The VASIMR engine appears to be the champ for....thrust to weight..."
I'm pretty that it's not 'the champ' in thrust to weight, as the thrust is so tiny. Ion engines make very poor 1st stage boosters for this reason.
"Lockheed Martin thinks they have Fusion sorted."
LM made the obviously-BS claims that a 100MW fusion plant could "fit on the back of a truck." That sound-bite claim sets off all sorts of alarm bells. Just the plumbing to move 100MW of heat, the steam plumbing, turbine, cooling towers, generators, switch yard, control systems, canteen, offices, ...must be a pretty big truck.
Not to mention the radiation alarm bells because their "truck" is spewing neutrons due to lack of shielding.
Obvious BS.
"More than a thousand times farther from Earth than the moon, ..."
Roughly 245,000 miles x 1000 = 245 million miles. Okay.
"...farther even than the sun..."
Roughly 93 million miles. ...Huh? That's LESS than the first phrase.
Bad style to have such comparisons (of vastness) in decreasing order by magnitude.
Downvote?
So this is okay? "More than a thousand times farther from Earth than the moon, farther even than the sun, even further (amazingly) than the chemist down the street; astoundingly this is further away than your kitchen (in case we've not established that already). More than a foot, more than an inch, and - OMG yes! - more than a millimeter..."
It's fundamentally-incorrect Writing 101.
You're probably right, but I downvoted you for using non-SI units. I know the earth-moon distance and the AU off the top of my head in metres (384km and 0.150Tm). I haven't a clue what they are in miles.
Note: I would have also accepted AU, parsecs, and lunar or terrestrial radii.
"I'm old enough that we had material presented in Imperial, cgs, MKS and SI. I never did like cgs."
Astronomers haven't outgrown cgs. My reaction on first encountering an erg was priceless. "What the FUCK is an erg?!" ;) It's not as if the distances, masses or energies need to be magnified.
I still cook in ounces and pints. So if there's a serious point---and there wasn't---it's picking the right unit for the field. Converting light years to parsecs can be done roughly by multiplying by three; converting miles to km is horrible.
Converting light years to parsecs can be done roughly by multiplying by three; converting miles to km is horrible.
Divide by 6, multiply by 10. Really not that bad, particularly since the former can be reduced to "divide by 2 then divide by 3" and the latter is just adding one to the exponent. It doesn't strike me as "horrible" compared to the times-three approximation for parsecs-to-light-years.
swm pointed out "Miles and Kilometers are in the golden ratio."
Nice. Accurate to about 0.5%. I never noticed that factoid in my entire life. Thank you.
So you just extract the square root of 5 (in your head), subtract 1, and divide by 2, then multiply miles to get km. Or inverse (which is +1) as needed.
(The definition is 2.54 cm *exactly* = 3 barleycorns, then of course 8 furlongs to get the precise mile-km conversion factor.)
"It's fundamentally-incorrect Writing 101."
Ignoring that the moon is closer than the sun, (yes, I know 20 times the distance isn't)
I'll refer to a better writer than I...
"Space is big. You just won't believe how vastly, hugely, mind- bogglingly big it is. I mean, you may think it's a long way down the road to the chemist's, but that's just peanuts to space."
Edit: You do seem to be channeling DNA with the chemist reference. This is The Reg, not The Times. Next you'll be banishing the hard-won title Boffin.
"Once the spacecraft exhausts the small supply of conventional rocket propellant it squirts through thrusters to control its orientation in the zero-gravity, frictionless conditions of spaceflight, it will no longer be able to point its solar arrays at the sun"
No gyros then I suppose? While you can't really change your trajectory in space with nothing but electricity at your disposal, you certainly can change your attitude...
Were it my engineering, I'd have to examine the mass-energy trade-offs between a system of thrusters against a gyroscope based system. Don't forget to include the requisite batteries, preferably redundant, in your calculations as well as recharging cycle times. Sometimes (often!) what seems the reasonable choice to make in the design phase turns out unreasonable when compared to budget constraints and/or requirements.
Gyros (reaction wheels) are good for a while... but over time they can accumulate stored momentum until they are spinning at maximum, at which point they are no longer useful. Of course you could add another mechanism (e.g. rockets) to move the craft so you can dump that momentum, but now you have two systems instead of one and therefore everything is heavier.
So why do some craft use reaction wheels? Because they are really good at making very tiny attitude adjustments, so you can keep the craft pointed accurately at a distant target. Not all craft need that accuracy.
>In 2007, we launched Dawn from Cape Canaveral, and it will never again visit its erstwhile planetary home.
I wouldn't be too sure about that. Ceres is the most valuable object in the Solar System that isn't the sun or a planet. No doubt someone will be out that way shortly, and returning NASA's spy satellite and eradicating its priority claim to ownership will be a priority. In the name of its historical and cultural value as a museum piece of course, and as a signal of goodwill from the people of Free Ceres.
I was about to point out NASA's prior claim before I read the rest of your post. Even though your tongue in cheek is evident, I feel compelled to remind people that the US genuinely considers their jurisdiction to extend as far as they care to say it does, hence the US vs MS over Irish servers, and therefore future US vs anybody trying to claim their space junk.
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