Category: Starflight

All matters interstellar

Daedalus Component Masses… part 2

(all masses in kg)

PROPELLANT SYSTEM
1st Stage 47400000.00 4228190.00
Helium-3 Fuel 27600000.00 2nd Stage Helium-3 Fuel 2450000.00
Deuterium Fuel 18400000.00 Deuterium Fuel 1630000.00
Insulation Insulation
Fuel Tanks 31500.00 Fuel Tanks 19500.00
LH2 Tanks 407.00 Manoeuvre Tanks 460.00
LH2 Tanks 360.00
Fuel Tanks 98500.00 Fuel Tanks 8870.00
Uncommitted Mass (V.O.) 1300000.00 Uncommitted Mass (V.O.) 119000.00
Total= 5.16E+07
PAYLOAD BAY 507000.00
Committed Bay Structure 50000.00
Sensing and Communications (V.O.) 110000.00
Subprobes(V.O.) 245000.00
Service Wardens (V.O.) 45000.00
Shield Cloud (V.O.) 5000.00
Dust Bugs (V.O.) 2000.00
Beryllium Payload Shield 50000.00
TOTAL MASS ESTIMATE 54670415.61

Daedalus Component Masses… part 1

Daedalus Starprobe Component Data…

(all masses in kg)

DAEDALUS
Starship Component  Masses (kg)
PROPULSION SYSTEM 1544427.51
1st Stage 1229636.60 2nd Stage 314790.91
Reaction Chamber(s) 219000.00 Reaction Chamber(s) 22100.00
Excitation Field Coils 125000.00 Excitation Field Coils 43600.00
Titanium Coil Supports 241000.00 Titanium Coil Supports 90600.00
Ignition Assembly 307000.00 Ignition Assembly 81000.00
Charging Circuit Supports 21000.00 Charging Circuit Supports 5900.00
Pellet Injector Pellet Injector
Capacitors 29600.00 Capacitors 790.00
Al Superconducting Coils 36.60 Al Superconducting Coils 0.91
Uncommitted Mass (V.O.) 287000.00 Uncommitted Mass (V.O.) 70800.00
THRUST STRUCTURE 75000.00
1st Stage 50000.00 2nd Stage 25000.00
SERVICE BAY 915798.10
1st Stage 740468.00 2nd Stage 175330.10
Core 645000.00 Core 132000.00
Thermal Shielding Thermal Shielding
Gold 578.00 Gold 55.10
Rhodium 2890.00 Rhodium 275.00
Iconel Base 2000.00 Iconel Base 2000.00
Power Supplies Power Supplies
Buffer Capacitors 30000.00 Buffer Capacitors 3000.00
Nuclear Reactors (V.O.) 60000.00 Nuclear Reactors (V.O.) 38000.00
Total 9.16E+05

The Choice

Alan Boyle posted some thoughts on the next 50 years of spaceflight at his MSNBC CosmicLog. The comments were what I’d expect from enthusiasts and cynics. A lot of doom & gloom, plus runaway enthusiasm.

I am not a moderate on the importance of spaceflight, interstellar colonisation.

Is there a middle ground? Or is there a BIGGER reason for spaceflight? How about the survival of the Universe?

Life is insignificant NOW, but in a few billion years our descendents could be shaping entire segments of the visible universe. And in a few trillion years, as the last stars die, they’ll be doing even more dramatic things to sustain Life.

One possibility is that, left to itself, the Universe will “crash” because all the quantum information that makes the laws of physics possible will be erased by black hole decay – if the Universe expands forever. Can we stop the expansion? One theory is that the current acceleration is caused by the Higgs field not being in its true vacuum state, due to the presence of baryonic matter. If Life uses baryons, via reverse baryogenesis, for power then the Higgs field will cancel out and the Universe will recollapse.

Now a Big Crunch sounds bad, but guided by Life shifting mass around on a cosmic scale, the recollapse can both provide energy for Life and a heat-sink to make that energy usable. And that infinite recollapse energy can power infinite experiential states – infinite subjective time for an infinite number of beings – between Now and the End Point.

Thus Life doesn’t have to end – if we set out and “conquer” the Universe. Don’t worry about wars between intelligent life elsewhere in the cosmos – They’re too far away for us to meet up until a few trillion years from now. Else They would be here by now, if they were closer than about 13 billion light years. And in a few trillion years we, and They, will know how to get on better than we do now.

Or else we don’t have a future.

A simple choice:

Everything – real Infinity for all of us;

or Nothing.

Bussard Fusor papers online

Oil can be made PURE GREEN by fusion power

Robert Bussard’s Polywell Fusor design is incredibly exciting for any space enthusiast because it promises REAL atomic power for spaceflight. Sure fission rockets have been “atomic power” in our minds since the late 1940s, but any fission reactor is such a cranky system and only offers thermal power generation options. Aneutronic fusion – the burning of Lithium-6, Helium-3 or protium-Boron-11 – offers something utterly different: direct energy conversion. In the case of p+B11 => 3He4 fusion/fission reactions the energy of the produced alpha particles can be turned into electricity at ~ 95% efficiency. This is a real breakthrough – or will be when Bussard gets proper funding – as electrical power can be used to heat reaction mass via relativistic electron beam guns. Ionised exhaust and no thermal contact with the reaction mass means the exhaust velocity can be pushed a lot higher, thus the vehicle can use just plain water as reaction mass.

Thanks to Askmar (Emerging Technology Marketing) Bussard’s papers are available online for all to see…

IEC Fusion at Askmar

…have a quick browse, but for specific breakdowns of Bussard’s estimated costings of

  • A 4000 person colony on the Moon
  • A 1200 person colony on Mars
  • A 400 person colony on Titan

    • …all for less than the NASA budget over the same time period, then check out this one:

    System Technical and Economic Features of QED-Engine Drive Space Transportation

    …QED being “Quiet Electric Discharge” or Monster Electron Guns blasting stuff into plasma Engines.

    The transformation of the world’s power economy is a little bit harder to discern. Firstly, to minimise replacement costs and timelines Bussard proposes using D-D fusion for power extraction via the neutron flux. Neutrons would heat water, and that would directly hook-up with regular steam-plant at a pre-existing coal/fission power-plant. All new power-plant could then use aneutronic fuels and minimise thermal losses by direct power conversion.

    All sorts of liquid fuels could be made using a fusor at some point in the production cycle, without any greenhouse emissions being needed. Ethanol or methanol are good options, but eventually battery/ultra-capacitor technology might make liquid fuels an irrelevance. However hydrocarbon engines are so power dense it’s hard to see just how successful that transition will be. Fusion heating could make extracting oil from very marginal deposits highly practical and fusion-powered atmosphere processes could draw-down carbon dioxide directly from the atmosphere. In fact it’s perfectly feasible to re-form hydrocarbon fuels directly from water-and-carbon-dioxide exhausts via fusion energy. Thus oil, as a high-density energy-storage medium, might never have to be abandoned, even if it does have to be made PURE GREEN via fusion power. After all oil is essentially a natural product, used by virtually all living things to store energy – we know it as “fats and oils” as part of a healthy diet.

    A suitably high energy density storage system would make small electric aircraft perfectly feasible, and a large aircraft could have on-board fusors and essentially infinite range. By extracting deuterium from the atmosphere an aircraft could stay aloft without refuelling, resupplied by small shuttle planes. Such a system might allow larger luxury air-vehicles to fly continuous routes, loading and unloading via shuttles from airports along the way.

    Once Robert Bussard’s work is completed with a working power reactor then we’ll know if fusion power will yet save the world.

James Kasting Online

HabZone gets expanded

In 1964 there was Stephen Dole’s “Habitable Planets For Man” which was the first informed guesstimate of habitable planets in the Galaxy. Dole’s planets had optically thin atmospheres and no modeling of their climate’s temporal evolution. The HabZone was from about 0.75 AU to 1.25 AU.

In 1978 Michael Hart presented the first evolution models of habitable planet atmospheres and discovered they were incredibly unstable – a very narrow band around the star allowed a long term stable atmosphere – but even Earth’s was due to become uninhabitable within a 100 million years. The HabZone had narrowed to just 0.95-1.01 AU – any further out and Earth became locked in ice; any closer in and the Earth became a greenhouse.

Then in 1993 James Kasting and his posse shook things up by accounting for climate stabilisation via carbonate weathering – and the habitable zone widened to 0.95 AU – 1.4 AU, perhaps even further. The year before Kasting & Ken Caldeira had extended the use-by for Earth’s biosphere to c. 1 billion AD. The odds for life in the Galaxy went up, and the mystery of the Fermi Paradox became an even bigger mystery.

Much to my surprise and joy most of James Kasting’s classic papers are available online…

James Kasting’s papers

…spanning his early 1980s papers to the present. Thank you James!

Notable papers are “The Lifespan of the Biosphere Revisited” (1992) and “Habitable Zones Around Main-Sequence Stars” (1993), but lots of other meaty stuff for planetology nerds like myself.

Whedon’s ‘Verse

Joss Whedon’s “Firefly” reflects Joss’s disinterest in science in a subtle way. As a series it got so much right, like no noise in space, but it does have a few oddities from the point of view of Hard SF. Aside from that weird space-drive, I mean.

For example, the terraformed moons & planets of the ‘Verse are said to have had their atmospheres and gravity fixed by the terraforming process. Atmosphere is OK (in decades, mind), but gravity?

Here’s a speculative, but hopefully Hard SF take on fixing a planet/moon’s gravity. Question: without adding mass how do you increase a planet’s surface gravity?

Ans: Shrink the planet.

Consider: materials under compression increase in density. Intense gravitational and electromagnetic fields, perhaps even strong nuclear fields, cause materials to compress into denser forms. Some such are metastable, like diamond too, thus remain dense after the pressure subsides. Some fretful types still worry that particle accelerators might create bits of quark matter (strangelets) which can catalyse catastrophic collapse of the Earth to nuclear density. There’s several reasons why that’s unlikely, but what if there was a nuclear process that can collapse a planet’s metallic core and leave the silicate mantle?

The energetics are actually in favour of that occurring since shrinking a mass releases gravitational binding energy. If ‘Verse engineers found a way of shrinking a metallic core to 0.1% of its previous size then a planet would contract and its surface gravity would increase. At the core/mantle boundary the core’s gravity has increased 100-fold, thus enhancing compression of the silicates of the mantle.

How much would gravity increase? To double the surface gravity a spherical body would need to shrink to 70.7% of its previous size. Doesn’t sound like much, but it means the average density increases by sqrt(8)= 2.83. Escape velocity increases by just 19%, but that’s a second-order problem. Earth, so shrunk, would be just 9,010 km across.

One result I can’t parameterize is where the released gravitational energy would end up – some would become heat and probably melt much of the mantle, but that might be needed to create volcanism and revive a magnetic field. The rest would end up in the chemical bonds of the new high density phases of the compressed mantle.

Anyway there’s a new trick to add to fiction: compressed planets. I’m sure someone can imagine a way of limiting strong nuclear material, like quark matter, to just compacting a metallic core in the 500 years between Now and the ‘Verse.

Milky Way Census

Stars and life-homes estimated for you

I am rather puzzled by just how many stars there are in the Milky Way too. Different sources give different figures, but ask an astronomer and they usually say 100 billion, roughly. That figure comes from actually measuring the light put out by the Milky Way and doing the sums.

If you look at the mass of the Milky Way – for example by taking the orbital radius and velocity of the stars at the galactic periphery, then working backwards – you get hundreds of billions of solar masses. However a BIG fraction is dark-matter and dark gas etc. and we really don’t know how much there is of either. If you look at the Milky Way from M31 and measure its mass via its satellite galaxy orbits you get about 1.2 trillion solar masses.

The total luminosity gives a less theory laden measure. That works out at about 55 billion solar luminosities and a baryon mass of about 60 billion solar masses. For a recent study check out this link. Divide that mass-figure by the average stellar mass and multiply by the fraction that is stars, and you only get about 100 billion stars. About 20 billion of those are roughly Sun-like. Assuming a Galactic disk age of 10 Gyr, a random spread of ages, and an oxygenic biosphere life-time of 1 billion years, thus there’s about 2 billion stars that could have planets with oxygen.

I’ll put my head out and say that 50% have terrestrial planets (Geoff Marcy’s estimate) and 50% of those systems have a planet in the habitable zone (Kasting’s estimate.) Thus there’s 500 million planets as old as Earth and in the right place for life-as-we-know-it. Not a lot different from Stephen Dole’s estimate from 1964 of 640 million. What’s different is that we now KNOW there are planets out there. Dole only know of a few possible planets – none of which are correct, though 61 Cygni is still a maybe.

But how many actually have life? A new study by researchers from my Alma Mater has demonstrated actual microbial remains from 3.5 billion years ago which is a boost to prospects for figuring out just when Life got started here. But does it tell us about Out There? Many popularists for SETI – the Search for ExtraTerrestrial Intelligence – argue that because Life arose very soon after Earth became stable (any time after 3.9 billion years ago) then it must be ‘inevitable’ and arise wherever it can. However the mystery of Life’s origin is still a matter of debate and very few facts. We do know that DNA-RNA style life is incredibly complex compared to basic organic chemistry, but we also know that cells make themselves using relatively small amounts of information. Their constituent molecules assembly themselves into an ordered whole very easily. How?

Until we know that the numbers of planets with Life might just be one.

Engineer the Sun!

Trying to imagine Life billions of years from now seems kind of futile to me. But if there’s any trace of us left then I can imagine they’d be familiar and yet very strange too. Certainly no end of SF writers have tried – Stephen Baxter, Poul Anderson and Charles Sheffield have had the balls to take readers to the end of Time, and beyond. Let’s be a bit more prosaic and stick to our little Solar System. So what would billions of years of technological advancement let us do?

We all know the Sun will evolve into a bloated, overluminous giant about 5 billion years from now – a timeframe that depends on the amount of heavy elements in the Core. According to a fairly standard model, the Sun’s future is as follows (in gigayears of the Sun’s age. Subtract 4.6 Gyr to get the date from now)…

(A) Core burning ends, t = 9.4 Gyr
(B) Redwards Traverse, end of Main Sequence, t = 10.9 Gyr (Sun pretty stable, Mars’ temperature rather nice)
(C) First RedGiant ascent, t = 11.6 Gyr (Sun goes from about 3 times present luminosity to about 2,400)
(D) Sun’s Core explodes, Helium burning begins, t = 12.1 Gyr (Sun pretty stable, Jupiter’s rather nice)
(E) Asymptotic Giant Branch, t = 12.2 Gyr (Sun goes from about 45 to 6,000 times present)
(F) Planetary Nebulae shed off, Sun dies as White Dwarf, t = 12.25 Gyr

Of course Earth, left to Nature’s course, dies long before the Sun even finishes Core burning. In about a billion years photosynthesis will crash and/or the oceans will be ploughed into the mantle by plate tectonics. Bacteria might survive for another billion, but eventually it’s all desert and a slow warming towards a Venus-like greenhouse. For Earth’s biosphere – and our “descendents” – the usual options are:

(1) extinction
(2) Move the Earth
(3) Live in mobile space colonies
(4) Put up sunshades
(5) Move to another planet

Instead of migrating, moving the Earth, or moving into space permanently – and they’re all options that might be taken – I would suggest a more radical option: engineer the Sun.

A few facts suggest this might be worthwhile.

First, the Sun will go red giant after using a tiny fraction of its total energy potential. This seems rather wasteful to me.

Second, magnetic fields can potentially reach all the way down into the Sun’s core. Thus we might be able to control the Sun’s energy output and its chemical evolution by inducing convection.

So just how much energy is available? If all the Sun’s mass converted to energy at current output it would last 14.5 trillion years. But it’s a giant fusion reactor instead. Proton-proton fusion, and associated reactions, convert 0.7% of the mass into energy. As the Sun is currently 74% hydrogen, proton-proton fusion would last 75 billion years using all the hydrogen. If we ignited helium fusion after that we might get another 30 billion years.

That sounds pretty good, but could we go further?

Some of the energy involved in the Sun’s evolution is from gravitational collapse. About half the Sun’s mass will collapse into a white dwarf liberating a few billion years worth. If the Sun could be collapsed further then even more would be liberated. The absolute limit is, of course, when the Schwarzschild radius is reached and we’ve made a black hole. If we collapsed the Sun into a quark-star just 6 km in radius we might extra a few trillion years of energy out of it.

Via reverse baryogenesis we might then extract all the mass-energy out of the remaining quark mass, thus getting the full 14.5 trillion years. All up we might extract 20 trillion years out of the Sun. But what happens then?

Instead of burning the Sun’s mass up perhaps we could change power sources. There’s a lot of dark matter around and the evidence is good that it self-annihilates with a release of real energy. Perhaps the Sun could be converted into a dark matter reactor? This is believed to happen naturally in white dwarf stars – but the power level is low. We might clever enough to develop a means of funnelling dark matter in to improve the output.

After all the options of this universe are tried perhaps we’ll have to look into higher dimensions to extend the Sun’s life even longer. We have a long, long time to figure out what to do.

How Big is a Planet?

Stars are fundamentally different to planets and one surprising way in which they differ is just how big they can get. Heavy stars get hotter and they puff-up from very fast fusion rates – stars heavier than the Sun fuse hydrogen chiefly via the much faster carbon-nitrogen-oxygen cycle, which is a minor cycle in the present Sun. What faster fusion rates means is that the big, fat stars are BIG – some are much larger than the Sun. Some are so large and violently bright that they’re losing mass into space, forming gigantic nebula. One spectacular example is Eta Carina and its rather pretty nebula.

But what about planets? “Cold” matter – anything less than a 10,000 K – supports itself against the remorseless pressure of gravity by electrostatic forces, rather than the fusion heat of a star’s interior (which is over 3,000,000 K at a minimum.) As the pressure increases – and thus the planet’s mass – the electrons and nucleii of the planet’s core part company, becoming pressure ionised. Past this point the planet is supported by the mutual Pauli exclusion of electrons, which has some strange properties, one of which is increasing mass causes the planet’s size to shrink. When this happens the core is said to be composed of degenerate matter. Shrinking a planet releases energy and this causes the interior to become increasingly hot, puffing the planet up slightly. As a result planets heavier than Jupiter are roughly all the same size – roughly Jupiter size (about 10% of the Sun’s diameter.)

But that’s planets composed of so-called “cosmic abundancies” of matter – about 3/4 hydrogen, 1/4 helium and a bit of everything else. Planets can lose all their gaseous hydrogen/helium as they form and thus be composed of things like water, carbon, sulphur, “silicates” (chiefly metal oxides) and iron. Other elements are too rare to make bulk components of a planet, though they can be selectively concentrated in the outer crust (like uranium/thorium and potassium seem to be on Earth.) A new paper has come out discussing just how big a planet made of such things can get, with some interesting results…

Mass-Radius Relationships for Solid Exoplanets

…one of the co-authors is Marc Kuchner, who has previously enticed us with descriptions of carbon-rich planets, and planets made of ice. A few years ago one of the first exoplanets in a circular habitable zone orbit was discovered…

HD 28185

…and it masses about 5.7 Jupiter masses. Most exoplanet watchers assumed it might have habitable moons – if moon mass scales linearly with planet mass it should have about 4-5 moons as big as Mars – but one brave soul thought the planet itself might be a “super-Earth” made of Earth-like stuff. At that mass, if silicate/iron mixes didn’t get denser with pressure, the planet would be as big as Jupiter (about 12 Earth diameters) with about 12 gees gravity. But, as the new paper describes in detail, such materials get a LOT denser with pressure, and the MAXIMUM size a super-Earth can get to is 3 Earth radii. Thus HD 28185b would have a surface gravity of 200 gees – a most unsuitable home for life-as-we-know-it.

Hypothetically, though, what would such a planet be like? Firstly it would have 1800 times the radioactive material heating up only 9 times the surface area – thus a radioactive heat flow of 16 watts (cf. Earth’s mere 0.08 W.) Such a heat-flow would mean the planet would remain at 130 K even without a star – though that’s an average temperature, and in reality much of the surface would be lava. With so much tectonic activity and so much mantle heat flow gases and volatiles wouldn’t remain trapped in its mantle for long – it would probably be wrapped in a thick layer of superheated steam and carbon dioxide, the surface aglow at over 900 K before its heat could escape into space. Even in interstellar space the planet would glow a dull red and remain at hellish temperatures for billions of years.

Abiotic Production of Oxygen/Ozone

Planets with carbon dioxide rich atmospheres won’t produce oxygen or ozone is amounts large enough to look misleadingly like an Earth-like planet…

Abiotic formation of O2 and O3 in high-CO2 terrestrial atmospheres

…but only if they have oceans. If the planet is frozen or a desert then the geochemical sinks for O2/3 produced by photolysis of CO2 won’t be working and they can build up. Thus signs of water, mild temperatures and oxygen means an oxygenic biosphere, not funny chemistry.

Except… Venus during its runaway greenhouse phase probably lost an ocean of water and had a very thick oxygen atmosphere as a result – but did that show? Scalding oceans covered in cloud, to an astronomer looking at its very cold cloud-tops (250 K) it probably looked like an “icehouse” and not a nice “Pale Blue Dot”.