Daedalus Component Masses… part 1

Daedalus Starprobe Component Data…

(all masses in kg)

Starship Component  Masses (kg)
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
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

Mountains of Titan, not so Titanic…

Titan, as suspected, has some peaks, though Australian scale – i.e. about 2 km altitude. That’s a fair climb here in Australia, where our highest peak, Mount Kosciuszko, is only 2,228 metres high. Miniscule compared to other continents. Of course because Titan’s gravity is so low the peak is “only” 305 metres in Earth-gravity scale.

Mountains Discovered On Titan, Saturn’s Largest Moon

Brigham Young University release on the discovery…

BYU scientist leads discovery of mountains on Saturn’s largest moon

…and the abstract describing the work in Icarus

DOI link

…can you imagine free-climbing such a peak? Should be fairly “easy” in a suitably light-weight cryo-suit. With a rebreather system – just freeze CO2 out at ambient temperatures and rewarm with a small methane-oxygen flame – the breathing gear would be lightweight.

Science News Highlights

Neanderthals started making clothes a bit too late…

Neanderthals sewed too little, too late

…thus the bad weather turn 30,000 years ago got them, after enduring 200,000 years prior to that.

Dark Energy, cosmic mystery, might really be just an illusion caused by the uneven distribution of mass-energy in the Universe, according to general relativity work by David Wiltshire – an Aussie physicist who moved to New Zealand because Australia’s physics funding sucks…

Dark energy a furphy, says new paper

…thus bits of the Universe have been around longer or shorter times than others, due to the different clock speeds caused by general relativity – Galaxy time is about 14.7 billion years since the Big Bang, but out in the voids between clusters that time is more like 18 billion years or more. Doesn’t solve the “young Earth” problem of Recent Creationists, though.

Speaking of Creation here’s another found “Missing Link” – the earliest species of the Cetacean lineage…

Deer put toe in water, turned into whale

…and behaviour-wise Indohyus was probably similar to the living mouse-deer, which dives into the water when predators threaten.

Genesis – parallels with geology

The first book of the Hebrew Bible is “Genesis” and it has been hotly contested because of its apparent very short chronology of our current Creation. People have tried to reconcile the +6000 years of the genealogies with the multi-billions of years of geological and astronomical time for over two centuries, with no agreed way of correctly reading the text. Now I’m not about to solve the dilemma (for believers, as unbelievers just think the Bible is old, irrelevant fiction) in a single post, but I note with interest some curious parallels with geophysical theories and the sequence of events in “Genesis”. My focus today is two particular days in the sequence, the third and fourth.

The Third Day…

9 And God said, “Let the water under the sky be gathered to one place, and let dry ground appear.” And it was so. 10 God called the dry ground “land,” and the gathered waters he called “seas.” And God saw that it was good.

Now compare…

When the Earth Dried Out

…which discusses Eldridge Moores work concluding that the formation of the ancient super-continent Rodinia actually forced it above the waves for the first time about a billion years ago.

11 Then God said, “Let the land produce vegetation: seed-bearing plants and trees on the land that bear fruit with seed in it, according to their various kinds.” And it was so. 12 The land produced vegetation: plants bearing seed according to their kinds and trees bearing fruit with seed in it according to their kinds. And God saw that it was good. 13 And there was evening, and there was morning—the third day.


First Land Plants and Fungi Changed Earth’s Climate, Paving the Way for Explosive Evolution of Land Animals, New Gene Study Suggests

…in which Blair Hedges and colleagues discover that landplants got started 800 million years ago, once Rodinia had sprung up from below the waves. Of course the next event was the explosive emergence of animal life after about 600 mya.

Now what of day four?

14 And God said, “Let there be lights in the expanse of the sky to separate the day from the night, and let them serve as signs to mark seasons and days and years, 15 and let them be lights in the expanse of the sky to give light on the earth.” And it was so. 16 God made two great lights—the greater light to govern the day and the lesser light to govern the night. He also made the stars. 17 God set them in the expanse of the sky to give light on the earth, 18 to govern the day and the night, and to separate light from darkness. And God saw that it was good. 19 And there was evening, and there was morning—the fourth day.

…well the emergence of the continent and the rise of plants meant oxygen levels rose dramatically, thus ending the methane-dominated greenhouse effect of the Neoproterozoic Era…

Earth’s Hazy Past

…thus ending the multi-billion year haze of short chain organic aerosols. Such a haze utterly blurs away the objects in the sky, and because it forms a distinct stratum in the sky it could count as the “firmament” of Day Two.

There’s a bit of dating uncertainty about all these events and some researchers push the oxygen transition even further back in time to the end of the Archean, but the parallels are inescapable – if the “days” are really separated in time by billennia. This would fit with the “Days of Proclamation” model, in which the commands of God define each “day” – thus God made the world in six days separated by millions of years.

Of course the “firmament” was a hard sheet (even though that’s what the word means) nor were seed-bearing plants actually present when photosynthetic organisms first arose, nor were the “Greater” and “Lesser” lights of the Sun & Moon actually the largest things in the sky – these are all terms that are meaningful to primitive human cultures that God was communicating with. Aerosol hazes, microbial and lichenous photosynthesisers and the visual dominance of Sun & Moon were superfluous to the message – that God made the world with a purpose.

Problem is, aside from these few controversial parallels, there’s no apparent advanced knowledge in the Bible – God’s Word is written using words and ideas of the Bronze Age.

Dreams of Space I

Back in the late 1960s Wernher von Braun developed an architecture for colonising the Red Planet and the Moon, as a by-product, using Apollo-style boosters and NERVA-style nuclear rockets. Basically the Interplanetary vehicles were composed of three independent components – the Primary Propulsion Modules, the Planetary Mission Modules and the Mars Excursion Modules/Vehicles. A single Interplanetary Vehicle was composed, usually, of 3 PPMs, 1 PMM and 1 MEM, but an extra-PPM would be needed for some mission configurations. This was quite different to an earlier mission architecture which favoured using 4 PPMs, minimum, and an EEV (Earth Entry Vehicle) for direct returns, Apollo-style, to Earth. Von Braun believed that an Orbital Receiving Laboratory, at a 50 person Orbital Operations Centre (“Space Base”), was needed to isolate possible biological samples from Mars – von Braun had discussed the possibility of intelligent Martian life in his literature on Mars from the early 1960s, so he was being consistent.

The heaviest components were the PPMs, as fully fuelled they massed nearly 246 tons each. Each PPM was shrouded in a heavy meteoroid shield and staging components until they fired. They would be launched into orbit via a modified Saturn V, the Saturn V-25 (S)U Earth Launch Vehicle, designed to lift a maximum of 249 tons when the basic core was wrapped in 4 large Solid Rocket Boosters.

Stephen Baxter’s fictional account of a 1986 Mars Expedition, “Voyage”, explodes one such booster configuration in a launch accident in 1981 – due to a flaw in the SRBs, just like the real “Challenger” disaster of 1986. In “Voyage” that launch disaster and a core explosion in the Apollo-N nuclear test causes NASA to adopt chemical propulsion. While that was an option for a single-shot mission, von Braun’s long-term plan was to colonise Mars. Each vehicle was to carry 6 personnel, and two vehicles would carry 12 people to Mars. In one option two MEMs would depart for the surface and place 6 people on the surface, but another option was for a single lander and orbital operations amongst the Martian moons using a Space-Tug, itself capable of missions to both moons.

But eventually more people would need to be based on Mars and to do so specially designed freighters were required. These would carry Base Modules – the surface equivalent of a PMM – and Descent Modules, essentially the lander-half of an MEM. A single freighter could carry four of either at a time, and they would be combined in Mars orbit for delivery to the surface. A single Base Module could accommodate 12 personnel, just like the PMM and the core Space Station module that the PMM was to have evolved from.

On that issue, the Space Station, the original was to have launched in c.1975, to carry the “Skylab” experiment even further, and provide training in long-duration in-space activities for 12 astronauts, male and female. “Apollo” itself was to have finished with Apollo XX in 1975, to be succeeded by the much more powerful Space-Tug. The Space-Tug was to have been launched via a single Saturn-V for 14-day missions to the Lunar Surface with a crew of 3. Eventually a Space Station module was to have been landed using a Space-Tug Propulsion Module and to form the nucleus of a Moon Base. To sustainably operate a Base the Nuclear Shuttle was to have been introduced in 1978 to service the Base, carrying multiple loads of Base Modules, Propulsion Stages and freight modules. Eventually the Base was to be powered via nuclear reactors and/or solar power, depending on the applications.

You can see how the Moon Base was to be a practice run for Mars – power reactors, Nuclear Shuttles and PMM/Base Modules. A very crowded schedule with a first Mars Mission launching in 1981…

Did a Comet Cause the Great Flood?

Bruce Masse, an environmental scientist turned mythographer, has tentatively identified a candidate impact event for the historical nucleus behind the Flood of Noah, and countless imitators…

Did a Comet Cause the Great Flood? (from the November ‘Discover’ magazine)

Mabul is Real After All!! Skeptics Around the World Get frum again (Hebrew Bible literalism… defended or incomprehensible)

…Masse also dates the Flood to 2807 BC based on the reporting of a Solar Eclipse by some of the Flood tales. The concept was also splashed onto the Blogosphere via the New York Times reporting on Masse’s work in November 2006…

Ancient Crash, Epic Wave

…which was, inevitably commented upon – with varying degrees of ignorance, scepticism and slavish regurgitation – by pundits across the blogs…

May 10, 2807 BC

Ancient myth and asteroid impact

Little Asteroid Impacts and Mega-Tusamis[sic]

600′ Mega-Tsunami

Ancient Crash… etc

This one was interesting because he mentioned the Google Earth research behind the crater find… Flood Evidence Found Using Google Earth

‘Loose Wire’ wrote a similar Google Earth prefaced piece… Google Earth as Harbinger of Doom …which is doubtless a case of “great minds thinking alike” and not bloggo-cannibalism. Or so I hope…

Abnormal Interests is a blog by a biblical literature scholar of a skeptical bent:

Gigantic Tsunami 4800 Years Ago …as his comments clarify. His problem with Masse is Masse’s reliance on legend literature to infer natural events. But the blogger finds this dubious because the legends are full of ‘theological language’. Now Masse has successfully extracted real history from other tribal legends – notably in Hawaii and South America – so I dare say ‘god talk’ isn’t a big impediment to gleaning meaningful data from either “Genesis” or “Atrahasis” (Sumerian Flood Epic).

Speaking of Masse’s earlier work here’s a few annotated links to earlier news pieces…

University of Waterloo Student newsletter, Imprint … from 2006, discusses Masse’s ideas and his work with the Holocene Working Group, who are actively sifting the data to improve estimates on catastrophic impacts during the last 10,000 years. They might yet convince governments to take impact mitigation seriously.

Alan Boyle is science editor at MSNBC and always does his homework. His report, from 2000, on the Holocene Working Group is still relevant… Adding up the risks of cosmic impact …the punchline being that many lethal “impacts” don’t actually have to hit the ground and dig a crater. Some explode in the atmosphere and cause more damage via a shock-wave, while others strike the oceans and cause tsunamis.

Finally I have to say what I actually think. Personally I think there was a Noah, Ark and so forth, more or less as the Sumerians, via the Hebrews, tell us. Unlike the later Hebrew version the Sumerian accounts were quite specific – ‘noah’ was a king in Shurrupak who loaded a barge with his family and animals in accordance with words from a god. He ended up being washed into the Persian Gulf, floating around the ocean, and probably crash-landing in modern-day Bahrain. Maybe. That’s one reconstruction, borrowed slightly from Robert Best’s Noah’s Ark book. A few details would change in the new model – date slightly lower, impact wave as well as storm caused the Flood, and so on – but otherwise I think it was a real event in history.

But, as the universal nature of the legend tells us, Noah/Ziusudra/Atrahasis was not alone. People from every affected tribe and tongue had a survivor, someone who was lucky enough to either read the signs or, more mystically, listen to god. Now some of my fellow believers might take exception to the idea of there being many ‘Noahs’ around the world, but God is God for all people, not just some mythically pure bloodline through one man. Which is really what wanting ‘one Noah’ boils down to – racism.

Getting around Sol Space

Interplanetary travel is pretty arduous based on current technology – chemical rockets and solar-powered ion-drives. Back in the late 1960s NASA was seriously developing a nuclear rocket called NERVA, but it wasn’t really much of an improvement on chemical rockets for anything other than trips to the Moon. NERVA’s exhaust velocity was about 8,500 m/s to about 9,500 m/s, while advanced chemical rockets get about 4,700 m/s – sounds like a big improvement, but getting to Mars in a decent time requires a lot of delta-vee.

The minimum energy Mars mission with a transfer time of 250 days – a Hohmann transfer – meant a Mars ship with six crew and a 50 ton lander needed an initial Earth-orbit mass of 727 tons. The vehicle had several major sections – Planetary Mission Module (crew habitat, life support & power), Primary Propulsion Modules (3 modified nuclear Moon shuttles), and the Mars Excursion Module – each of which would be launched via up-graded Saturn V Heavy-Lift Vehicles. Thus we’re talking over 15,000 tons of on-Earth mass to land a single lander with 3 crew on Mars for a 30-60 day stay. Some missions required another PPM thrown in, but the total trip-time didn’t improve even with that extra power. Plus the expedition had to do a Venus fly-by to reduce the total propellant mass required and the total stay-time on Mars – pure Hohmann missions need over two years lay-over on Mars.

Mission designs since then involve trickier orbits which expend a bit more propellant to cut down the trip-times by almost half. When Mars is at perihelion, on arrival, the trip-time can be as low as 130 days, but when it is at aphelion it’s more like 180 days. That’s a long time travelling even so.

What if we want to go further out? Robert Heinlein’s “Farmer in the Sky” (1950) is set on a terraformed Ganymede which has been slowly colonised via fleets of small ships carrying 500 people at a time. These fly on Hohmann transfer orbits that take almost 1,000 days (two-and-a-half years). The Earth Government wants to speed the process up, so a high-speed torch-ship is launched carrying 6,000 people on a 60 day flight. You can imagine the chaos on Ganymede of handling so many people at once – it makes up a significant part of the story.

What’s the difference in flight-plans? Well the previous ships were all nuclear powered, but the new ship – the Mayflower, of course – uses a Total Conversion reactor to accelerator reaction mass to high speed. Kind of what an antimatter reactor would do, without the messy magnets to channel pions. With a relativistic exhaust velocity the Mayflower accelerates to 93 miles per second (150 km/s) using only a tiny bit of mass-energy. On a Hohmann transfer the ship maxes a mere 24 miles per second (38.6 km/s) – why then does such a trajectory take 1,000 days if you’re only travelling about 4 times slower than the Mayflower?

Earth itself travels around the Sun at 18.5 miles per second (29.8 km/s), so 24 mi/s isn’t much faster and the orbit the ship follows is more like a circle and less like a straight line path. Plus it is slowed down mightily by the Sun – by the time it reaches Jupiter a Hohmann orbit ship is doing just 4.6 mi/s. The Mayflower doing 93 mi/s follows an almost straight line to Jupiter and slows to 89.5 mi/s (144 km/s) – virtually no slowing by the Sun at all. Thus the Mayflower takes a mere 60 days.

To travel via Hohmann transfer to Jupiter a ship needs to increase its speed around the Sun from 18.5 mi/s to 24 mi/s, and to also escape the Earth’s gravity. Say it takes off from the ground – the speed needed is 14.2 km/s, neglecting gravity losses. Once it has escaped Earth’s Hill Sphere it’s in the Sun’s gravitational dominance and is moving 8.8 km/s faster than Earth. It arrives in Jupiter’s Hill Sphere doing about 7.42 km/s relative to the Sun and 5.64 km/s relative to Jupiter. It falls towards Ganymede’s orbit, about 1,080,000 km from Jupiter’s centre, and is doing 16.4 km/s relative to Jupiter when it arrives – needing to slow by 5.52 km/s to match speed with Ganymede. Thus to arrive in Ganymede orbit from Earth’s surface takes about 19.7 km/s. More than any rocket ever built and pretty heavy going for a nuclear rocket, but doable. Might need to refuel in Earth orbit.

To match the Mayflower we’d have to increase in speed by 120 km/s relative to Earth initially, then deccelerate at Jupiter by about 144 km/s. Total velocity change: 264 km/s… which is over 13 times the velocity change needed for a Hohmann trip. No chemical or nuclear rocket – short of actual nuclear detonations – could achieve the exhaust velocity needed to make such a trip practical. The most efficient energy use would need an exhaust velocity of 165 km/s and about 4 times the empty mass of the ship in propellant – there’s a theorem that the mass-ratio using the least amount of energy for a given velocity change is 4.92, and an exhaust velocity of 1/1.6 the total velocity change (mission velocity.) Such a jet would be like riding a nuclear detonation – say your ship masses 1,000 tons and is accelerating at 1 gee. The power output is 0.4 trillion Watts – the equivalent of 100 tons of TNT exploding every second.

And, of course, there is a rocket which could get such performance – the Orion Nuclear Pulse Rocket – which really would have been propelled by nuclear explosions. Some of its developers (between 1958-1964) were hoping to visit moons of Saturn by 1970, and it could have quite easily made the trip. Small nuclear “pulse units” equivalent to 1 kiloton of TNT energy would have exploded just behind the ship’s massive “pusher plate” – the explosion could be shaped into a jet of hot plasma that would have splashed around the plate, barely heating it at all. The bigger the plate, the more efficient the energy transfer – thus the highest performance would have been achieved by multi-million ton “Orions” using megaton pulse units. That system could land a ship the size of a city on any object with a solid surface in our Solar System in a matter of weeks.

Of course, in the process, all the Earth’s fission explosives stocks would be burnt up… so what’s the problem?

When did Humanity arise?

According to work by Aaron Miller bipedalism in primates began with our lineage some 20 million years ago, producing the apes as we know them today – gibbons, siamangs, orang utans, gorillas, chimps, bonobos and us – plus dozens of extinct species. So while bipedalism is important to our lineage, it isn’t a key to what makes humans human. Then sometime between 6 and 4 million years ago we became genetically distinct from our closest relatives, the chimp/bonobos (who split 2 million years ago), but at that time we were probably identical in morphology and remained so for millions of years. The two probably parted company thanks to the African Rift Valley’s geographic barriers and eventually the chimp/bonobos moved into the rainforests of West Africa, while we adapted to the more open forest around the lakes of East Africa.

Some 2.6 million years ago the first evidence of intentional modifications to stones can be found – our ancestors began breaking up stones to make crude sharp-edges for tools. No chimp/bonobo has ever done so, even though they do use stones to hammer at hard nuts. While this seems like a uniquely human thing to do the Oldowan stone technology (as it’s called) lasted a million years more or less unchanged – a very non-human approach to tool-making. Humans are too restless to let things remain unmodified, but the Oldowan people were happy with their stone flakes for millennia.

Around 2 million years ago humans under went a lot of changes producing Homo erectus and Homo habilis – the former being like us in body proportions, the latter being an odd hybrid of old ape and new human body forms. Homo habilis spread into Eurasia and seemingly became Homo erectus there – the hominids at Dmanisi, Georgia seem to be intermediate between the two. In a very short span the proto-humans filled Eurasia, though they avoided going too far northwards perhaps because their use of fire was haphazard and unable to provide sufficient protection against the seasonal cold. A new stone tool technology arose, the Acheulean, centred on the making of “hand axes” which are more like a multipurpose blade used for all sorts of things, from display (some were artistic) to wood-work.

Sometime around half a million years ago the Acheulean people became more like us, now known as Homo heidelbergensis or Homo antecessor. Their brains were bigger than Homo erectus and they seemed to have built shelters, used fire-hardened wooden tools, and eventually they birthed our own species, in Africa, and Homo neanderthalensis, in Europe. Homo erectus, in its later forms, survived until about 40,000 years ago in the Far East. An even earlier form, maybe Homo habilis, was survived by its diminutive off-shoot Homo floresiensis, the Hobbit, up until their (possible) extinction some 12,000 years ago.

In the last 300-200 thousand years the pace of technological change increased, producing a new tool set amongst the Africans and the Europeans, known as the Mousterian. Big things were happening in South Africa after 200,000 years ago – cave sites near the old sea-shore are revealing traces of modern behaviour, dating back to 164,000 years ago, perhaps further back. Further to the north in Herto, Ethiopia, anatomically modern humans appear 195,000 years ago. Even further north true Neanderthals appear in Europe along with Mousterian technology. Many of the diagnostic features of modern humans appeared piece-meal – use of ochre, symbolic engravings, micro-blades, bone tools, and so forth – over about 150,000 years between the Herto hominids and the explosion out of Africa.

And that explosion seemingly signaled a qualitative change in human beings. In all respects, bar that change, the humans between 200,000 and about 60,000 years ago were identical to us. Between 150,000 to 70,000 years ago Africa went through a series of massive droughts due to a glacial advance during the Ice Age, which might have driven humanity very close to extinction. There is evidence for some kind of genetic bottleneck that cut down our species to just a few thousand people. That we survived needs some kind of explanation, and would perhaps simultaneously explain what propelled those survivors out of Africa.

Between 60-40 thousand years ago the species burst forth into Eurasia and Austronesia, Australia itself by 50,000 years ago, and eventually into the Americas by 15,000 years ago. An unstoppable tidal wave of technological and culture change meant that humans developed projectile weapons (eg.boomerangs, bow-and-arrow, spear-throwers), sailing vessels, sewn clothing, thread and fabric, and a multitude of other advances that we take for granted. By developing all these things humans were able to adapt to an ever wider environment with wider extremes of weather – thus eventually allowing the long trek to America past the glaciers, either via the near-shore sea-route or via inland corridors.

After such a slow pace of change what came together some 60,000 years ago to propel our species forward? Did that mark our arrival as modern humans? Certainly genetically we’re all related by the groups that left Africa and I would argue that we all share the same basic cognitive tools, the same propensity that allows adaptive change via technology, perhaps producing the same belief in unseen “spirits” and “gods”. Even the most ancient human groups believe in invisible people like ‘gods’ – the !Kung Bushmen, for example, believe in a Father Creator, whose two wives produced the Sun and the Moon. Just how such beliefs arose and, more importantly, why they arose will give us untold insights into the human mind.

But will that knowledge tell us anything about those invisible people?

Self-Replicating Probe… REPRO

Robert Freitas designed a self-replicating probe, REPRO, designed to fly to another star-system and self-replicate. He based the design estimate on the “Daedalus” star-probe study by the BIS, but being a stellar orbital mission instead of a fly-by the mass of fuel was immensely more than “Daedalus”, a flyby probe. Roughly 10.1 million tons of fuel, and 600,000 tons of probe structure divided into 3 stages, launches and delivers REPRO to a nearby star.

The mass is dependent on the size of the payload – in this case REPRO’s business end masses 1000 tons. Freitas has become an expert on nanotech, especially nano-medicine, since then and believes smaller needle probes can be used instead massing a few grams. I’m not entirely convinced, but he might be right. Certainly nanoprobes have a lot of advantages, but they’re more fragile too, especially vulnerable to the cosmic radiation they’ll be bathed in en route. Perhaps the mid-range REPRO probes, massing a ton, might be the best approach.

Let’s stick with the 10,700,000 ton monster and see what that tells us. The fuel can be mined from a gas giant, and the solids from their moons. If we assume aliens are launching REPRO-style probes in order to cover the Galaxy in a network of monitoring stations then we can estimate just how much mass they’ve used in our solar system. Say a new REPRO arrives every decade – unlikely as we’d have noticed the fusion flames by now – and they take a decade to reproduce a new REPRO to launch off to other stars. Thus the solid mass can computed as:

M = 0.5*(T^2/(R1*R2))*Mp

T is the solar system’s age; R1, R2 the time between arrivals and reproduction, and Mp the finished probe mass.

Thus for 4.5 billion years of 600,000 ton REPROs arriving and breeding every decade there will be about 6 x 10^25 kgs consumed, or about 10 Earth masses. Sounds like a lot, but the Kuiper Belt was about 100 times heavier in the past – where did it all go? Perhaps we have an answer. About 171 Earth masses of fusion fuel would be needed from the gas giants, which would be a noticeable loss, changing the orbits of their moons. But it could also be star-lifted from the Sun without being missed.

Of course the 1 ton REPROs would’ve needed roughly 1000 times less and we’d be none the wiser. Or if we make the arrival rate somewhat lower to account for no telescope spotting a braking starprobe, then we get a similar result. One problem with there being 1 ton REPROs in such numbers (10^17) is why don’t we see their infra-red glow? If they mass 1 ton, roughly 50kg/m^3 density then they’d be about 3.36 metres across, with about 9 square metres of cross-sectional area, their collective area is 6,970 times Earth’s cross-sectional area. That should be pretty visible in infra-red I’d think.

But consider: there’s about 10^16 kg of zodiacal dust interior to Earth’s orbit composed of specks about 100 microns across, thus about 5 x 10^24 specks and about 391 Earth areas of reflective surface – and we barely notice it. If the “cloud” of alien REPROs is out past Pluto we’d never notice their collective IR reflection as there’s quite a lot of plain old dust out there. And if Freitas’s nanotech needle probes are possible then there would be no way of noticing even a million times the number.


After I wrote this I noticed that Freitas assumes a 1,000 year reproduction time, which means the masses quoted above drop into near invisibility, especially if the arrival time averages about 1,000 years too. A 1,000 ton REPRO would be about 34 metres across and a fully loaded daughter probe (10,000,000 tons) would be several hundred metres at least. How many would be under construction at the present time? Assuming the REPROs are ‘immortal’ we’d have about 4.5 million original parent probes in the system and roughly as many under-construction.

If they’re not immortal and last maybe 10,000 – 100,000 years then REPROs might actively cannibalize inactive REPROs as there would be many more dead than alive. An ecology of scavenging machines might have evolved in the Outer Solar System and we’d never know about it. They might also use different fusion cycles – proton-Boron or proton-Lithium are other options – and not need to mine the Jovians at all, finding all their fusion fuels in the multitude of comets in the Oort cloud. I don’t think anything can be said dogmatically at this stage of our ignorance about such possibilities…

…but I think They’re here and They know about us.

Ultra-sized Constructions II

Here’s a piece from ye Olde days of ye Webbe…


…which catalogues mega-structures – what I’ve dubbed Ultra-Sized Constructions. One of my comment writers, sweetcement, noted an idea of a ring around the Sun that wasn’t a ribbon like Ring-World. A hollow, rotating habitat is another option…

Topopolis: A long, cylindrical object, rotating for gravity, and wrapped
around a star in a spaghetti-like mass (or mess). The concept was invented
by Pat Gunkel and mentioned by Larry Niven in “Bigger than Worlds”, but as
far as I know nobody has yet had the audacity to write a story about it
(unless you count Greg Bear’s _Eon_ and _Eternity_, which describe a
vaguely related concept).

Imagine walking around such a gargantuan construct – 1 billion kilometres around. At 40 km a day it’s a journey of almost 70,000 years, and it takes our Earth 1 year at 108,000 km/h.