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.

Addendum

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…

Megastructures

…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.

Amazing Killifish… but which one?

The Daily Mail had this little snippet news item for no apparent reason except oddness…

The fish that can survive for months in a tree

…discussing the ‘killifish’, as if that said enough. Not so. As Wikipedia explains a killifish can be anyone of over 1200 species of fish – the name is from Dutch and means ‘puddle fish’. However only one ‘killifish’ is able to self-fertilise – the only known vertebrate that does so – and that’s the Mangrove Rivulus. Oddly they are either male or hermaphroditic – there are no females.

Kind of reminds me of Cordwainer Smith‘s tale in which a human colony on a far-flung world suffers a horrible death that only targets women. By injecting male hormones to keep alive the last woman, a doctor, allows the colony to survive by enabling men to become pregnant. Thus all the couples on that world are homosexual, give birth via caesarean, and fight sword-fights for their lovers. But their psychology suffers and they become something not quite human anymore. Yet if we were fish we could change sex depending on our size and age, or even our birth temperature.

What we find un-natural, Nature has a way of giving us even more extreme examples.

A real Flying Saucer from the 1960s

“Star Trek” (1968), “2001:A Space Odyssey” and “The Time Machine” (1960) mentioned orbiting nuclear weapons, but few details have arisen of how advanced such plans were. Mark Wade’s Encyclopedia Astronautica discusses one US design which, oddly enough, is a flying saucer…

NAA Manned Bombardment and Control Vehicle

…armed with four H-bombs and controlling potentially dozens of orbiting nuke platforms. A rather scary prospect which, as Mark discusses, was possibly developed to the point of drop testing via balloon in outback Australia in the 1960s.

Sorry for the Inconvenience

Whoah! What a scare! I thought the whole of this blog had been trashed by a bad back-up plug-in. No. Instead I needed to upgrade WordPress and then let Fantastico put it all back together… whew!

So I’m back-up and backed-up :-)

Print your own organs | COSMOS magazine

Body prints! Imagine reduplicating your own body from a high-resolution scan… well it’s not that unlikely given the advances happening in tissue engineering. According to this article: Print your own organs | COSMOS magazine it may be a reality 10-30 years from now.

May be.

Our understanding of the genetics of cell differentiation is advancing rapidly and may well allow our own stem cells to be arranged and activated into whole organs, including blood vessels and nerves. Eventually I think we’ll be able to “print” whole functioning bodies – with sufficient resolution, even reconstituting brains.

However what will the legal/ethical status be of people who are dead and yet still existing as records of their bodies/brains? Alive? Half-life? Or legally dead? Will a “reprint” be legally a person? Or merely a “meat puppet” of a dead-person?

I mean that as pejoratively as the word “sock puppet” is meant on the Web. What rights will reprinted dead people have? If any?

Carbon 14 Dating On Shroud of Turin Were Botched 2005

In 1988 the enigmatic Shroud of Turin was carbon-14 dated to the 13-14th Centuries, roughly its age if it was a fake. However in 2005 chemical evidence arose that suggested the sample area was in fact Medieval, but the rest of the Shroud wasn’t. The samples had come from a patch invisibly rewoven into the Shroud – over the centuries the Shroud has been nearly destroyed several times, with successful repairs masked as the real thing…

Carbon 14 Dating On Shroud of Turin Were Botched 2005

…as Dan Porter explains in this article the Shroud doesn’t show any of the breakdown products that’d be expected from a 700 year old artefact, but plenty that’d be expected from a cloth 2,000 years old.

I believe the Shroud captures the in-situ image of Jesus’s corpse – it may, or may not, tell us something about his putative resurrection too. And more probably it may explain just what the disciples viewed and handled in the wake of that event.

Bipedal Apes before Man

Some 20 odd million years ago a species of African ape became bipedal by a homeotic mutation being selectively advantageous enough to let the species succeed and to spawn many more species, including our own a few “species generations” down the line. What’s more most of those apes remained significantly bipedal, only occasionally reverting to all-fours, like the gorillas, bonobos and chimps. Aaron Filler published his conclusions along these lines in the open access journal family, Public Library of Science…

ScienceDaily: Early Apes Walked Upright 15 Million Years Earlier Than Previously Thought, Evolutionary Biologist Argues

…and it’s an interesting finding. I wonder why bipedalism succeeded for our ape ancestor and why we didn’t end up knuckle-walking (itself an odd locomotive system, unique to the African apes) too. Gibbons and Orang utans remained bipedal because it works in the trees, but our ancestors left the rainforests and ventured into more open terrain around lakes.

An interesting thought, in a SETI context, is why did it take 20 million years for the freedom of the hands allowed by bipedalism to produce an intelligent tool-wielding species? To me that indicates that intelligence wasn’t a given even once bipedalism appeared. Sure apes are smart animals, but none ever got to the level of smashing rocks to make cutting edges and making fire – the two earliest “technologies” unique to humans.

What happened to trigger that?