Author: Adam

Photosynthesis powers our biosphere and without it we’d be rather short of breath, but oxygenic photosynthesis is a tiny subset of what life has tried. In bacteria there are many different photoreactive molecules and several different photosynthetic processes – some use water as the reductant (hydrogen source), some use hydrogen neat, and some use hydrogen sulphide. Also the photosynthesis we know and love in familiar plants is quite fond of two rather narrow frequencies of visible light, but it’s possible for biomolecules to grab several photons of light to get their power-boost from near-infrared (NIR) in the 1000 to 1400 nanometre wavelength range.

So what does this imply? According to these two studies…

Spectral signatures of photosynthesis I: Review of Earth organisms

…and its follow-up…

Spectral signatures of photosynthesis II: coevolution with other stars and the atmosphere on extrasolar worlds

…it means that M-dwarf stars can sustain oxygenic photosynthesis and might even allow land-based life, if their flares are of the milder variety. Most M-dwarfs flare – rapidly increase in x-ray and UV brightness for brief periods – but some flares are milder than others. A proper atmosphere is quite able to absorb harmful x-rays, but a bit of UV gets through, enough to inhibit life – but even the largest flares will only penetrate about 9 metres into water with their UV, so oceanic life is quite safe.

An who’s to say that life can’t adapt to UV and even find it useful? Perhaps by incorporating more metals into their metabolism organisms might usefully trap UV energy for biological processes?

In more immediate terms what it means is that we can fairly confidently hope to find habitable planets around even the smaller variety of stars – and since M-dwarfs make up 75% of stars in our immediate neighbourhood that’s a good thing.

Adrian Mann is an awesome digital artist who has visualised some of the classics of spaceflight studies of the last 35 years…

This is Rocket Science

…some notable creations are Starship Daedalus

Starship Daedalus

…which is very cool. And another ‘blast from the past’ is Project Orion

Project Orion

And the ultimate starship design, the interstellar ramjet

Bussard Ramjet

But there’s some near-term designs from the 1960s, aka the Nerva nuclear thermal rocket and its associated Mars Mission

Project NERVA

A PROFAC (Propellant Factory) from the early 1970s (studied by ELDO, the European Launcher Development Organisation, parent of the ESA)

PROFAC and Space Tug

…the Space Tug design is from a European study on early Lunar access using European and NASA hardware. In Adrian’s visualisation we’re seeing the Luna Landing kit deployed, plus an add-on Crew Mission Module. For interorbit operations the Space Tug would have neither and would dock to a cargo module or another Space Tug operating as a booster stage. Fully fuelled a Tug would mass 12.5 tons, with a burn-out mass of about 1.8 tons. According to Marcus Lindroos this is well within state of the art. By comparison NASA-studied Tugs massed 2.5 tons dry and 20.8 tons fully fuelled, with an extra 4.4 ton CMM for a 3-man 50 day mission.

Hitachi have developed a brain-reading device which uses near-IR light to watch blood-flow in the brain – a proven proxy for simple, strong thoughts.

Hitachi’s Brain-Scanning Remote

In essence you’d wear a near-IR pick-up as a head-band and it would allow you to think simple commands on a remote control. They’re hoping to market to disabled people, but I can see the idea spreading and being refined to give us ‘thought recorders’ and the like. The US DARPA worked on sub-vocal communicators for a while which sensed the impulses to the vocal-cords which occur when we’re “talking in our heads” – I’m not sure how well that project went, but it would also allow for ‘thought recording’ or at least a sub-vocal Dictaphone.

Will we have it first appearing as a hobbyist craze – ‘stick to your head Thought-Buttons’ – advertised with telescopes and computer projects?

Space.com has a news article covering the claim that we’ll soon be able to “eavesdrop” on ETs…

Eavesdropping on ET soon

…which would be fantastic if it happens and disquieting if it never happens. But detection may not be easy. Even the Square Kilometre Array will be hard-pressed to pick a signal from more than a few hundred light years away unless it’s a tight beam, so if ET is thinly spread out They will be drowned out by the Galaxy’s natural radio ‘noise’.

To make ET more prevalent, the argument goes, we might assume they’ll go on to colonise the Galaxy. Galactic colonisation and exploration has rather glibly presumed to be ‘easy’ – even by this author – but without incredibly unlikely FTL travel the project will take at least a hundred thousand years and potentially much, much longer. Possibly the current age of the Galaxy…

Exploring the Galaxy using space probes

Many assume that as soon as intelligences can make autonomous self-replicating robots then that’s what they’ll do, sending them forth with a ‘mission’ to colonise the galaxy with their kind of intelligent life. A self-replicator smart enough to be called ‘intelligent life’ is a ‘person’ in my view, but an arguably important aspect of personal identity is freedom and creativity, and I suspect even the longest-lived ‘persons’ will fatigue in the face of a task like colonising every star in the Galaxy. A more organic expansion will be what eventually completes the task and there’s no easy way of estimating how long, or how thorough, such an expansion will be.

And why should self-replicating probes colonise at all? They’re intelligent enough to decide that for themselves, but such vastly long-lived entities may well develop a wholly different set of motivations to us organic beings. Perhaps they will rest content with lightly touching on every star, leaving a ‘clone’ to thoroughly explore and monitor every system while venturing ever onwards to new stars. Years ago Chris Boyce computed that even if the probes weighed a million tons each, a new one arrived every decade, and made a copy every decade to send off, then after 4.5 billion years they would have consumed at most the mass of Neptune. That might sound like a lot, but the Kuiper Belt is assumed to have massed maybe 100 Earths in its early days – more than enough mass for making probes, in bite-sized chunks.

And that’s with gargantuan megaton probes. Frank Tipler has spoken of 0.1 kg ‘probes’ running a virtual city of 10,000 people as software. At the same pace of replication they’d mass 1/10,000,000,000 th of Neptune by now – a smallish asteroid.

With that in mind read Gregory Matloff’s essay from a few years ago…

Re-enchantment of the Solar System

…in which he discusses ETs living quietly in space-arks in our Kuiper Belt. His case is plausible – he even provides a means of detecting ET’s heat emissions – and, if ETs are real and long-lived, then They’re almost certainly ‘here’ on the fringe of our Solar System.

That still doesn’t mean UFOs are really ET space vehicles, but it does mean some might’ve been, just maybe.

Massive radio telescope arrays are soon to be built around the world – notably, for me as an Aussie, the Square Kilometre Array, and other systems around the globe. Such incredibly sensitive radio telescope clusters will allow direct detection of electromagnetic leakage (RADAR, TV, and radio) from star systems within 30 light years or more for tight beams…

Eavesdropping on Radio Broadcasts from Galactic Civilizations with Upcoming Observatories for Redshifted 21cm Radiation

…so before long we might be able to say if there’s Anyone nearby with technology akin to our own. Perhaps they all use lasers, neutrinos, gravitons or even tachyons? Maybe. Or maybe they use radio too.

The Integral Fast Reactor is so named because it handles all its fuel reprocessing on-site which does tell us much more about just what it does. Here’s a link to a very good Wikipedia article

Integral Fast Reactor

The external links are worth checking out too. I was put on to the design by a write up in Scientific American…

Smarter Use of Nuclear Waste

…(PDF warning) the title being the obvious selling point. An Integral Fast Reactor uses fast neutrons to make more fuel out of natural uranium mixes. Regular reactors extract fissionable U235 to ‘enrich’ the more reluctant U238. What used to be normally fired from tanks in armour-piercing rounds as ‘depleted uranium’ is U238 after the U235 has been extracted.

A Fast Reactor can also burn ‘nuclear waste’ – because it isn’t really waste. About 97% of the energy potential of uranium is still locked up in such ‘waste’ so in reality all those tens of thousands of tons of ‘waste’ sitting around current reactors waiting for ‘disposal’ are a potential source of uranium for about 300 years worth of power at current usage.

The final advantage – on top of mining less uranium for the same return, producing no long-term waste (which is really potential fuel like plutonium), and burning up all the current ‘waste’ – is that the waste products eventually produced become safe after 300 years storage – not the 10,000 or so that long-term ‘waste’ commits us to. Storage of such fission-products is pretty straight forward and the total mass is 3% of current long-term ‘waste’ for the same energy return.

So why hasn’t the technology been exploited to the full already if it eats up waste? Firstly the specific approach uses metal fuel elements, not oxides, and that’s an area that has been under-explored. Secondly, the design uses liquid metal working fluid, not water or gas, and that’s another under-explored avenue. Sodium – the metal of choice – is also highly reactive, but no more so than lots of other nasty stuff regularly handled in huge quantities day-to-day world-wide without mishap.

Finally, and this is the cynical part, a fast reactor destroys uranium mining on the obscene scale it has grown to. There’s a few mining bucks tied up in using just U235 because it’s so rare (0.72% of uranium is U235.) There’s 1.5 million tons of uranium in proven resources, about double that in estimated, but unprospected resources. Thus there’s only 21,600 tons of usable U235 in all those millions of tons of ores – lots of mining profit and mess-making for not a lot of useful material. A gigawatt reactor uses 100 tons of 3%-enriched uranium per year. That means 720,000 tons of enriched uranium (and 2.3 million tons of depleted) represent some 7,200 GW-years of power. Earth uses 15,000 GW-years and demand grows all the time. A Fast Reactor would burn 1 ton to produce 1 GW-year, thus all estimated economical uranium represents 200 years of World-Energy demand. That’s total demand, currently provided by coal, oil and gas, plus a pittance by nuclear.

Uneconomical uranium becomes ‘economical’ with Fast Reactors because they can burn the uranium straight – it’s feasible to extract it from seawater then and that source is at least enough for several million years at World-Demand levels.

Also U235 makes bombs, but U238 doesn’t – and integral fast reactor fuel-reprocessing doesn’t make bomb-ready material either. A metal alloy of uranium/plutonium might sound like bomb-stuff, but the isotope mix is all wrong and the stuff needs industrial scale handling facilities – easy for a reactor to supply, utterly ludicrous for wannabe bomb-makers in Third-World nations. Fast Reactors are inherently a Non-Proliferating technology when using mixed-alloys. Note that.

On the flip-side enriched uranium reactors commits us all to sustaining the bomb-makers.

Don’t know if you’ve seen this rendering work by Rhys Taylor of Orion before, but I’m gob-smacked…

http://rhysy.plexersoft.com/orion/index.html

…and his fictional Orion-powered space-fleets around Callisto…

http://rhysy.plexersoft.com/Deep%20Space%20Force%20Gallery/

…plus a 3-D animation of an Orion launch…

http://www.nuclearspace.com/gallery_orion_movie.htm

…quite impressive really. Quite dire in other respects – nuclear Cold-War space-fleets have an Apocalyptic feel.

Another link is an interview with Steve Howe discussing his nuclear rocket work and his antimatter sail concept for a very light probe (10kg) to Alpha Centauri…

http://www.nuclearspace.com/article/Sview/HOWE_view.htm

…needs 0.017 kg of antimatter which is a BIG ask presently, but doable given some dedicated accelerators on the Moon *sigh*

One big topic of perennial interest is interstellar travel and all its sundry issues. I’ve fiddled with a few equations for relativistic rockets and produced some interesting results – at least to me. For example, the regular equation for motion under continuous, unvarying acceleration is usually written like so…

s = Vo.t + 1/2.a.t^2

…where s is displacement (distance), t is acceleration time, Vo the initial velocity (can be 0 or even negative.) For a complete journey where you accelerate and deccelerate (which is negative acceleration, really) from one location to another, the equation simplifies to…

s = 1/4.a.t^2

and the amount of time you travel is…

t = [4.s/a]^0.5

Now the interesting relativistic thing is that time becomes a dimension as well, and your time displacement is calculated like so…

t^2 = 4.s/a + (s/c)^2

…c being the speed of light. Notice how it’s just like the Newtonian equation, plus a component for light’s journey as well. In this case all the units are standard SI, metres, seconds, their combinations and c = 299,792,458 m/s exactly. If we use years for time and lightyears for distance a constant, k, comes into play like so…

t^2 = 4.s.k/a + s^2

…k is c/yr, where ‘yr’ is the standard tropical year of 1900, what’s used to calculate an official light-year, some 31,556,925.9747 seconds. But the difference between a tropical year from 1900 (365.2421987 days) and a standard Julian year (365.25 days) is negligible for most purposes, so in either case k is 9.5.

Notice, however, that the time displacement we calculated is for observers at rest relative to the destination. On-board ship the time observed is more complicated and requires hyperbolic equations, oddly enough…

t = 2.s/a.arcosh[1 + a.s/2.c^2]

…which I’ll go into some more next time.

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…