Hi All
Well it’s been a while. Working full-time and four kids make regular blogging a tad irregular.
Just recently I bought a copy of Project Daedalus, the star-probe project of the British Interplanetary Society which went from 1973 to 1978, and has influenced space ethusiasts ever since. In summary the probe massed around 54-52,000 tons; used two stages and electron-beam fusion of deuterium-helium3 pellets to boost to 0.122c, and was famously targeted at Barnard’s Star because Kemp thought it had planets. Turns out he had been looking at slight shifts in the telescope’s drive system, a glitch discovered by the fact that no other telescope could produce the same results.
In reality the BIS was advocating a 100 year program to probe all the stars out to 12 ly – Barnard’s was conveniently close-ish at 5.91 ly. Alpha Centauri, Epsilon Eri and Indi, and Tau Ceti were all far more interesting for potential habitable planets, but at the time no one had detected the E.Eri planets and dust, Tau Ceti’s ‘roid belt, nor E.Indi’s twin brown dwarf companions. Barnard’s seemed the only close star with maybe planets.
Here’s a summary table of the basic details…
First Stage Second Stage
Propellant Mass 46,000 tons 4,000 tons
Exhaust Velocity 1.06E+7 m/s 0.921E+7 m/s
Stage Mass at cutoff 1690 tons 980 tons
Burn-time 2.05 years 1.76 years
Propellant tanks 6 4
Thrust 7.54E+6 N 6.63E+5 N
Pulse Rate 250 Hz 250 Hz
Payload Mass 450 tons
What’s cool about Daedalus is that the technology was conceivably ‘just around the corner’ and thus, given enough in-space assets, it could’ve begun in the middle 21st century. By 2100 we’d have flyby results from Barnard’s Star and probably Alpha Centauri – a bit far off for me personally, but kind of cool for my grand-kids I guess.
Ever since the study was published people have rightfully concluded that interstellar travel is a reasonable proposition – it is, if you can wait for the data. But what about going there in person? What would that take? A ‘slow’ Ark doing 0.005c would take 880 years to get to Alpha Centauri – a bit less since Alpha is getting closer to us all the time – and using the same 50,000 ton propellant budget the Ark could mass 150,000 tons, or about 300,000 if it used ultralight solar-sails to brake at Alpha Cen. That sounds huge, but we’re talking about spending nearly a millennium in a vehicle 300 metres long. Could be a bit cramped.
The original study called for mining the helium-3 from Jupiter because helium is pretty rare here on Earth and helium3 is only a tiny fraction of natural helium. Huge balloons 212 metres across, heated by a reactor on a gondola, would each sport a mini-factory extracting a few grams of helium3 a second. Problem is that Jupiter’s atmosphere is pretty turbulent, so the aerostat factories would be floating at the 0.1 bar level above most of the weather, but even then they might not survive. To extract the 30,000 tons needed (and deuterium) over 20 years some 128 aerostats would be dropped into Jupiter and a fleet of gas-core nuclear shuttles would pick up the processed helium to ship back to Callisto orbit.
Why not cut out the middle man and use nuclear-powered scoop-ships with their own mini-factories? These would fly fast enough to cut through the weather and simultaneously support a high flow of raw material to process. They would also tank up on hydrogen to then blast back into orbit to load up a tanker or the fuel-tanks directly on the probe. One problem is that Jupiter’s gravity is so damned strong. To get into a low orbit takes 42 km/s – 12.5 km/s is supplied from Jupiter’s spin, but 29.5 km/s remains. Plus the thrust has to be enough to counteract 2.3 gee dragging the scoop-ship back down.
Instead of fighting Jupiter there’s three other big planets also full of helium. Mining Saturn needs a mere 15 km/s to get to low orbit, Neptune takes 13 km/s and Uranus a measly 12 km/s – which are also re-entry speeds that we’ve had experience in protecting reusable spacecraft from the heat of ionised airflows. Also all three have much, much lower gravity levels. Saturn has a string of tiny moons and a big one for construction bases and probably extractable metals. Uranus’s moons are denser than Saturn’s and so might have more metals – the innermost, Miranda, is semi-shattered already. Neptune has Triton, but it also has an inner moon, Proteus, which is probably full of metals too with an easily accessible core.
Strange real estate, but that’s what building a Daedalus would take. Or maybe not…