How Dead Stars are Teaching Us What You Need to Build a Planet

What I actually do for living...

Repost alert! This first appeared as a guest post on Andrew Rushby's excellent II-I blog. I'm reposting it here as I'm off to a conference at Cambridge today, so will hopefully have quite a lot to write about soon. This post was written as an introduction to the research I'm doing for my PhD, so may be useful in providing some context for what I talk about next time. If you've already read it, feel free to stop here. If not, read on!

An asteroid plummets to its doom around the white dwarf GD 29-38. Studying the debris left from these asteroids can reveal the chemical composition of exoplanets. Image Credit: NASA

Twenty seven years ago astronomers noticed something strange about the white dwarf star GD29-38.

White dwarfs are dead stars, the burnt out carbon cores of stars like our Sun which have exhausted their hydrogen fuel; incredibly dense, incredibly hot balls of matter roughly the size of the Earth. Because of this high temperature, tens of thousands of degrees, all white dwarfs glow blue.

But the light from GD 29-38 wasn’t just blue. When it was split into a spectrum, separated into a rainbow of separate colours, there seemed to be something else there. Something shining with an infrared light, beyond the range of our eyesight.

Initially the discovers were excited, as the red light could have come from an orbiting brown dwarf, a mysterious object several times bigger than a planet but much smaller than a star. But both the white dwarf and the infrared source were pulsating slightly, periodically getting brighter and dimmer. If the red light was from a separate object, then it shouldn’t have pulsed in time with the white dwarf.

The spectrum also revealed metals in the white dwarf’s atmosphere, heavy elements like calcium, magnesium and iron. These were also out of place, as white dwarfs have such a strong gravity that anything heavier than hydrogen or helium should have sunk down into their cores long ago. The metals must be falling onto the white dwarf from the space around it- but how did they get there?

It took until 2003 for the origin of the mysterious infrared glow to be found, during which time many more white dwarfs with similar red spectra and metal polluted atmospheres were found. The explanation was that the infrared light is coming from a disc of dusty debris surrounding the white dwarf.

This debris was formed from the wreckage of an asteroid, leftover from when GD29-38 was a Sun-like star with its own system of planets. The dust in the disc rains down onto the white dwarf, explaining the metals we see in the atmosphere.    

The spectrum of GD 29-38. Along the bottom is its wavelength, or colour, going from blue on the left to invisible infrared on the right. The vertical axis shows how bright the white dwarf is at each wavelength. The difference between the blue white dwarf and red dust cloud can be clearly seen. Image Credit: NASA

The story of how the debris disc got there is a result of the turbulent formation of the white dwarf. As it runs out of fuel a star swells up to a huge red giant, then blows away roughly half of its mass in an immense stellar wind, leaving the tiny white dwarf core.

 With the gravitational force at its heart cut in two, the system of planets around the dying star is thrown into chaos. Planets begin to migrate outwards, trying to reach orbits twice as far away from the central star as before. As they do this, they risk coming into close contact with each other.

Some of the planets survive these encounters and carry on as they are. Others, especially when a big Jupiter sized planet is involved, are thrown out of the system into the depths of interstellar space. And some are scattered into the centre of the system towards the white dwarf. 

These unlucky asteroids and dwarf planets fall in towards the white dwarf until they reach a point known as the tidal disruption radius. There the tidal force, the difference in gravitational pull between the parts of the asteroid nearest the white dwarf and the areas further away, becomes so great that the asteroid is ripped apart, forming the dusty debris disc that we see as an infrared glow.

The discovery of this process lead to an important conclusion. As the dust rains down onto the white dwarf it becomes visible to our telescopes. If we can measure what metals there are, and how much of each there is, then we can reveal the chemical composition of the asteroid or planet that formed the disc. We can ask, and answer, the question: “What are planets made of?”

Two decades ago we only knew about the eight planets in our solar system (Pluto was never a planet, it was just mislabelled). Now we know of over a thousand planets, new worlds orbiting hundreds of stars. Through our telescopes we can measure the size of these planets, what their masses are, and even in some cases get a glimpse into their atmospheres.

But we can’t find out what they’re made of, what the geology of these newly discovered planets is like. This means that we don’t know for sure if the way that the rocky planets are built in our solar system, the particular mix of iron, oxygen, magnesium, silicon and other chemicals that make up the Earth and its neighbours, is the way all planets are built.

The metal polluted white dwarfs form a perfect laboratory, presenting us with rocky objects that have broken apart into their chemical components. By observing as many as we can, we can begin to explore the chemical diversity of planets and planetary systems. We can see if the way our planets are built is the normal way to construct a planet, or whether Earth is even more unique than we thought.

To date we’ve discovered around a dozen white dwarfs with enough chemicals to compare their systems in detail with our own. So far, they look fairly similar to the Earth, a hopeful sign. But we need many more to truly explore this area, and over the next few years myself and others will be scouring the sky, using the Hubble Space Telescope above us and an array of telescopes on the ground. We will find more metal polluted white dwarfs, measure the chemicals of the planetary debris around them, and begin to explore in detail what things you need to build a planet.

Nasa's Orbiting Carbon Observartory 2 Launches into Space in a Dramatic Liftoff

This morning NASA's Orbiting Carbon Observatory 2 (OCO2) launched into Earth orbit on a Delta 2 rocket. I've posted the video of the launch here, as it was one of the most dramatic rocket launches I've ever seen (and I watch most of them).

When the engines ignited there was a huge flash, which for a moment made me think the rocket had exploded.  Fortunately, a second later the Delta 2 soared into the sky, completing a flawless launch and orbital insertion within the hour.

Losing this rocket would have been incredibly sad, as the first Orbiting Carbon Observatory was lost during launch in 2009. The protective faring (the pointy bit on the front of the rocket) on its Taurus XL launcher failed to open, resulting in the rocket being too heavy to reach orbit.

NASA quickly ordered a replacement, OCO2 to be built, a process complicated by the fact that many components were no longer being produced. When a second Taurus XL rocket failed due to problems with the fairing, the OCO2 was switched to the ultra-reliable Delta 2. Today, five years later, that Delta 2 delivered OCO2 to it's place in the "A-train", a large formation of Earth-observing satellites.

Artist's impression of NASA's Orbiting Carbon Observatory 2 (OCO2), which launched this morning on a mission to precisely measure the amount of carbon dioxide in Earth's atmosphere. Image Credit: NASA.

The OCO2's mission is to precisely measure the amount of carbon dioxide in the atmosphere below it, It has a high enough resolution to distinguish both regional  variation, identifying areas which produce or remove CO2, and seasonal variation, investigating how the CO2 levels change with time.

OCO2's only instrument is a spectrometer, designed to split the light coming through the atmosphere to distinguish the particular colours emitted from CO2. It is so precise that it will be able to measure changes in CO2 levels of less than 2 parts in a million.

Hopefully over the next few years the OCO2 will provide a new and important insight into this vital component of the atmosphere. But for now, enjoy the video of its incredible launch!

New blogs will be poster on Twitter.

The Strangest Star: A Neutron Star Inside a Red Giant

Artist's impression of a neutron star, which may sit at the heart of a red supergiant in a newly discovered Thorne-Zytkow object.  Image Credit: NASA

Some of the stuff in space is truly weird. Last month a group of astronomers announced the discovery of what might be one of the strangest: A star inside another star.

The star, which has the exciting name HV 2112, is thought to be a Thorne-Zytkow Object (TZO). This type of star, the existence of which was first suggested in 1977, is made up of a red supergiant, a vast dying star many times the size of the Sun, with a neutron star sitting at its core.

Neutron stars are some of the most extreme objects in the universe. The remains of the explosive deaths of massive stars, neutron stars are the densest objects we know of (black holes excepted, because they're just odd).

Most matter, including you, me and everything we see around us, is made of atoms, comprised of a tiny nucleus surrounded by a cloud of electrons. While the common statement that atoms are mostly empty space isn't quite true (there's all sorts of fields and virtual particles flying around in there), the vast majority of the mass of an atom is concentrated into a tiny area relative to it's overall size.

Not so for neutron stars. They, as the name suggests, are made almost entirely out of neutrons, one of the particles found in atomic nuclei. The neutrons are packed in literally as tightly as it is possible to be, making the star ridiculously dense.

Though they have a mass of between one to two times the mass of the Sun, neutron stars never get bigger than about twenty kilometres across. This means that a sugar cube-sized lump of neutron star weighs around a billion tons.
 
(To use the accepted measurement standards of this blog, a 10km radius gives it a surface area of roughly 0.06 Wales)

The TZO would have started off as a binary, two massive stars closely orbiting each other. When the larger of the two stars ran out of hydrogen fuel in its core, it blew up in a supernova explosion, its core collapsing to form the neutron star.

From that point there are two ways by which the neutron star could have fallen into the core of its companion. The physics of supernovae  are still not fully understood, but it is thought that in many cases the explosion may not be symmetric. The explosion could have given the neutron star a "kick", slamming it into its nearby companion.

Alternatively the neutron star may have remained as it was until its companion also reached the end of its life and swelled up into a red giant. The forming red giant would have engulfed the neutron star, slowing it down until it spiralled down into the core of the red giant.

However once the neutron star reaches the core of the companion it begins to look just like every other red supergiant. Without being able to see the buried neutron star, how can we tell that HV2112 is a TZO and not just a (far more common) red supergiant?

There are two main ways to move heat around inside a star. Heat transfer in the Sun is dominated by radiation, where material that gets hot shines out light, heating up material around it and so on. In the Sun energy is transferred by radiation for about 70% of the distance from the core to the surface.

For the last 30% this changes, and energy is transferred by convection currents, where the material itself moves. Hot material expands and becomes less dense, so rises up through the cooler materiel around it until it reaches the surface. It then radiates its heat in to space, cooling down and sinking back into the Sun to be heated up again, and so on. This mix of rising hot material and sinking cooler stuff creates a granulated pattern of convection cells on the Sun's surface (a structure I studied as part of my Masters degree).

Granulation on the surface of the Sun, caused by convection cells formed of hot (light) and cool (dark) material. This phenomena can reveal the presence of a neutron star at the heart of a red supergiant. Image Credit: NASA

It's these convection currents that allow us to distinguish between a normal red supergiant and a neutron star-cored TZO. Unlike the Sun, in a red supergiant the convection zone extends all of the way to the core. This means that material is being regularly transferred from the core to the surface: material that in a TZO has recently been in contact with the neutron star core.

The interaction between the surface of the neutron star and the mass of hydrogen around it ignites a unique nuclear reaction, the rapid-proton process. This creates large amounts of otherwise uncommon elements, such as rubidium, strontium, yttrium, zirconium and molybdenum. The convection currents then carry these material up to the surface, where we can see them with out telescopes.     

By looking at the the spectrum of HV 2112 the discoverers were able to observe all of these elements and compare them with the material they expected to see in the atmosphere of the neutron star. They found much higher levels of rubidium, lithium and molybdenum than they expected, leading them to suggest that HV 2112 had a neutron star hidden at its core. The 37 year search for a TZO may well be over.

The team behind the discovery were careful to point out that, although the signs of HV 2112 being a TZO are all there, there were other signs in its atmosphere that didn't quite fit. Some of the ratios of different metals were different from what we'd expect, and the way the light from the star varied over time was unusual. However none of these anomalies are showstoppers, although they show us just how much more we have to lean about these giant stars.

If it is a TZO, HV 2112 is certainly one of the strangest, most interesting objects around. We'll just have to see what weird and wonderful things we'll find next...

The discovery paper is here. Follow me on Twitter for new blogs.

SpaceX reveal the Dragon V2 Manned Spacecraft.

SpaceX's new Dragon V2 Spacecraft, a seven person capsule that may soon be taking astronauts to the International Space Station. It was revealed to the public on the 29th of June. Photo Credit: SpaceX

On Thursday evening (well, Friday morning here)  SpaceX founder Elon Musk took to the stage to reveal the Dragon Version 2, SpaceX's entry to the race to build the next manned spacecraft for Nasa.

In my not so humble opinion, it looks amazing.

The design is very different from the current, cargo carrying version of the Dragon. Instead of the blunt-nosed capsule based on traditional spacecraft designs, the Dragon V2 is a sleek cone, flanked by pairs of SuperDraco rocket engines.

It's these (3D printed!) engines that are the Dragon V2's key innovation. They are powerful enough to act as a launch escape system, blasting the capsule away from an exploding rocket in the event of an accident. But their primary purpose is to allow the Dragon V2 to do what no space craft has done before: Land propulsively, coming down onto a landing pad using rockets, without the use of a parachute.

 This will hopefully allow it, along with its Falcon 9 launch rocket, to be rapidly reused, massively reducing the prohibitive cost of spaceflight. SpaceX have released an animation showing just how this would work:

The video shows my favourite bit of the new spacecraft: The trunk, the disposable rear section holding cargo and the Dragon's solar panels, has rocket fins! Combined with the propulsive landing, this makes the spacecraft remind me of old-school, 1930s Flash Gorden-esque sci-fi.

The interior of the Dragon V2, with seats for seven astronauts, is incredibly futuristic.Photo credit: SpaceX

The interior, however, is anything but old fashioned. With it's spacious, seven seat design and touch screen controls, the Dragon's insides are radically different from anything thats gone before. My first reaction to it was "that can't be real"- it's just nothing like the cluttered, button heavy Soyuz or Space Shuttle cockpits. But this is the first time we've seen a new manned spacecraft for decades, so we really should expect not to recognize it. It will be interesting to see what the interiors of spacecraft built by SpaceX's competetors look like. Indeed, the glimpses Boeing have released into their CST 100 craft look similarly futuristic.

The Dragon V2 certainly looks beautiful, but will it work? Only time will tell. Pending Nasa funding, SpaceX plan to start flying it into orbit next year, with its first manned flight penciled in for 2016. If all goes well, we could soon finally have a true twenty-first century spacecraft.

Rosetta's Destination Comet Grows a Tail

Comet 67P/Churyumov–Gerasimenko (centre), target for ESA's Rosetta space probe, begins to develop a tail.

Image credit: ESA

Just a short post today, as I'm writing a lot of other stuff at the moment (more on that to follow...).

Back in January I wrote about the European Space Agency's exciting Rosetta mission as it reactivated from a three year hibernation. Last week the mission reached another major milestone, although not one it had any control over.

Rosetta's target, the comet 67P/Churyumov–Gerasimenko, has begun to wake up.

The comet, seen as a fast moving white dot in this series of images taken with Rosetta's main camera, has suddenly exploded into life, beginning to form the huge tail that comets are famous for. As Rosetta closes into orbit with 67P/Churyumov–Gerasimenko in August, we will be able to see this fascinating process unfold up-close for the first time.

Comets actually spend most of their time without tails, orbiting for millions if not billions of years in the far reaches of the Solar System. Occasionally a chance encounter with another object will give them just enough of a gravitational nudge to send them tumbling into towards the Sun.

Once there, the increasing heat from the Sun begins to melt the ice that makes up most of the comet. The ice is embedded and mixed in with rock and dust, so as it sublimates (turns directly from solid to gas) it beings to blast that dust out in volcano-like eruptions. The escaping gas and dust flows out into a huge cloud, or coma, out of which forms the tail. And it really is big: Whilst the nucleus of a comet may only be few kilometers across, the tail can grow to lengths of hundreds of millions of kilometers. That's significantly larger than the Sun, although the coma is much less dense.

Comets actually have two tails, seen clearly in the image of comet Hale-Bopp below (One of my earliest memories is of being taken outside at night to watch this comet as it flew past Earth in 1997). The blue tail is formed of charged particles, or ions, individual charged particles released from the comet. These interact with the magnetic field carried in the solar wind, so stream out from the comet in a straight line directly away from the Sun.

The white tail is formed out of the dust liberated by the escaping water, pushed away from the comet by sunlight. As they fall back from the comet each dust particle moves into a separate orbit, slightly slower than the orbit of the comet thanks to the increased distance from the Sun. This causes the tail stretch out into a curve, as each successive particle out from the comet gets slightly further behind on its orbit.

Thanks to this behavior comet tails are a key tool in our attempts to understand the solar wind, which has a big affect on the satellites and other space technology that modern civilization depends on. One of Rosetta's targets as it closes in on 67P/Churyumov–Gerasimenko is to investigate this relationship between the comet and the solar wind from the inside.

Comet Hale-Bopp, which flew past Earth in 1997. The separate ion (blue) and dust (white) tails can be clearly seen.
Image credit: Nasa. 

Rosetta is closing in on its target, aiming to reach orbit in August. As I hope I've shown you, the show has only just begun...

New blogs and other stuff on Twitter. 

Spaceflight via Russian Trampolines

You can't get off Earth using a trampoline, but you might just be able to escape Mars biggest moon, Phobos. Image: NASA

Since the Space Shuttle was retired in 2011, NASA has had to rely on Russian Soyuz rockets to get its astronauts into space. This hasn't come cheap, costing $70million a seat. But they've had to grin and bear it, as the next American spacecraft capable of carrying humans (probably the SpaceX Dragon) wont be ready until at least 2017.

As you may have noticed in the news, US-Russian relationships are rather strained at the moment, and the Ukraine sanctions are beginning to affect the Russian space industry. Yesterday Dmitry Rogozin, the Russian deputy prime minister, tweeted that:

“After analysing the sanctions against our space industry, I suggest to the USA to bring their astronauts to the International Space Station using a trampoline,”

Now this could have lead to a very interesting long blog post about the politics of space exploration, but there's a far more important question the ask: Could you actually get into space using a trampoline?

The key factor in getting off a planet is the escape velocity, how fast you need to go to escape a given object's gravity. For Earth this value is about 11.2 kilometres per second, which is fairly fast.

How fast can you go using a trampoline?

The Guinness Book of World Records lists the highest height achieved by a team on a trampoline as 6.73 meters, using two people to provide the bounce for a third. With a bit of maths, that means that the speed they were going as they left the trampoline was about 11.5 meters per second.

Not fast enough for Earth, but the Solar System is full of smaller objects. Which is the largest with an escape velocity of less than 11.5 meters per second?

It turns out to be Phobos, one of the moons of Mars, which comes in with an escape velocity of 11.4 metres per second. Its a small world, a lumpy rock with an average diameter of eleven kilometres and a mass nearly two billion times smaller than that of the Earth.

This might be a practical question, as Phobos has been mentioned as a possible destination for Mars-bound astronauts. It takes much less fuel to get there than to land on Mars, and could be used as a base to remotely control Mars rovers without the annoying time delay caused by the signals having to go from Mars to Earth and back.  

So if in 20 years time you're an adventurer stranded on a desolate Martian moon, make sure you've got a trampoline.

Note: Discussions over lunch resulted in the decision that the speed you could jump on the trampoline wouldn't be affected by the lower gravity, as the key factor is the energy you're  producing in your legs. You'd jump higher, but accelerate less slowly down towards the trampoline, affects which would cancel out. If you can do some maths showing this is wrong, please let me know. 

New blogs will be posted on Twitter, as always.

Falcon 9, Skylon and the Future of Spaceflight

It costs over £1000 to send a single kilogram of anything into space. In that one figure lies the ruin of many predictions of the future.

In 1968 Arthur C Clarke and Stanley Kubrick presented the world with their vision of the future in 2001: A Space Odyssey. They imagined a future of mankind in space, complete with bases on the Moon, space planes, voyages to the gas giants and a vast circular space station.

A PanAm space plane approaches the huge Space Station V in 2001: A Space Odyssey...

As far as we've got: The International Space Station is much smaller than Space Station V. Although its still just about the most incredible thing we've ever built.

None of this has happened. Neither have countless other predictions of the future. Wernher Von Braun imagined a complex space infrastructure; Nasa planned to have humans on Mars in the 1980s; The Space Shuttle promised easy access to space for all.

Many factors contributed to this, not least the changing requirements of politics at the end of the Space Race, but the major one has been cost. No one predicted just how ridiculously expensive space flight would be.

One of the main reasons behind this expense is that every time a rocket is launched, at a cost of around $100 million, it is thrown away. These high launch costs lead to even more expensive spacecraft. Without the chance to launch repair missions or backups, satellites have to be built to never fail, with multiple redundant systems. Communications satellites cost hundreds of millions, and the price tags of science missions are often measured in billions.   

It can be argued then that the key to the future of space flight lies in reusability. And true reusability, not like that of the Space Shuttle which ended up costing over a billion dollars per launch.

However getting a rocket back to use again turns out to be rather tricky. Rockets are built in stages to save on fuel. Each part burns through its own stock of propellant before dropping off, leaving the next stage(s) to get the now much lighter rocket into space.

When the first stage detaches it is going very fast, travelling through very thin air. With no thrust remaining, the stage follows a parabolic arc downwards, at which point it smashes into the thicker air near the ground and turns into tiny pieces.

Even if it survives this, the next stop is the ocean or ground, both of which are rather bad for you at high speed. Amazon founder Jeff Bezos recently recovered parts of the Saturn V moon rockets from the Atlantic. There wasn't much left. The space shuttle boosters, which parachuted down into the ocean from relatively low heights, required months of refurbishment after being soaked in salty water.

That's just the first stage. Recovering the later parts of the rocket from space means surviving the extreme temperatures of reentry, impossible without a heavy heat shield. And every kilogram you use on reusability is one kilogram less put into space. 

With these challenges, it isn't much of a surprise that it's taken fifty years for someone to have a go.

With landing legs folded up around its base, the latest SpaceX Falcon 9 rocket blasts off from Cape Canaveral. The first stage would later be successfully landed  into the ocean. Photo Credit: SpaceX 

Last Friday a SpaceX Falcon 9 rocket blasted off on an otherwise routine mission to the International Space Station, (accidentally drenching itself in dirty water as it did so). What made this rocket unique was its choice of optional extras: Landing legs.

The Falcon 9 version 1.1 is deliberately more powerful than it needs to be. So when the first stage separated it had more than enough fuel left to fire up three of its nine engines, slowing it down enough to safely fall back down to Earth. As it reached the ocean with landing legs unfolded, one engine fired again to lower it gently down into the Atlantic. The first stage of a rocket has, for the first time, successfully landed in one piece. 

Stormy seas have meant that SpaceX have been unable (at time of writing) to recover the stage, but that doesn't matter too much. Just getting the rocket down has provided them with the knowledge they need for the next step: Flying the stage all the way back to the pad, ready to be used again.

Being able to reuse a rocket has huge advantages. Currently a Falcon 9, the most cost affective rocket available in the world at the moment, has a price of $56.6million. (I find it amusing that SpaceX list the prices of their rockets online- do they take Paypal?)

However, the fuel for a launch comes to about $200 thousand. Being able to reuse the first, largest stage of a rocket, turning it around with no more maintenance than an airliner gets between flights, could dramatically slash the cost of flying into space. SpaceX already has long term plans to bring back not just the first stage, but the whole rocket.

Using some of the rocket's fuel to retun it to Earth comes with a price, of course: A 30% hit to the amount of payload the Falcon 9 can carry to space. This is where, I think, reusable rockets will benefit all of us. If SpaceX start saying rockets capable of lifting 4 ton satellites cost half a million dollars each, but lifting 5 tons will cost fifty million, then there's going to be a huge pressure to miniaturise technology, much of which will probably end up in your pocket.

Concept art of the Reaction Engines Skylon, a huge space plane scheduled to being flying at the end of this decade

While SpaceX are trying make rockets work like aeroplanes,  across the Atlantic a plan is coming together to turn planes into rockets. The British company Reaction Engines is working on bringing to reality one of the staples of science fiction: The space plane

Known as Skylon, the 85 metre long behemoth will take what is both an old fashioned and radically different way into space. Taking off from a runway, its unique hybrid SABREs (Synergetic Air-Breathing Rocket Engine) will run like jet engines at first, taking in air from the atmosphere and burning it with on board hydrogen fuel.

Then, when the plane reaches five and a half times the speed of sound, the SABREs will switch to rocket mode to take the Skylon and fifteen tons of payload into low Earth orbit. Cargo delivered to space, the Skylon will then fly back to Earth, landing on a runway and ready to fly again in a couple of days.

Whilst space planes have been imagined for years (see the first image), Reaction Engines have only just managed to develop the key piece of technology needed to actually make one fly. At Mach 5.5 the air hitting the engines will be hugely and quickly compressed, causing it to heat up to temperatures of thousands of degrees. To avoid melting the engine, the air must be cooled to well below zero degrees Celsius in a fraction of a second.

The solution is to use a precooler, sending the air between a series of tiny pipes through which the plane's cold hydrogen fuel is being pumped, taking away the tremendous heat. Last year Reaction Engines successfully demonstrated this technology, securing funding to work towards a full scale prototype. If all goes to plan, the first Skylons could begin flying at the end of the decade.

Funding is Skylon's main challenge. Reaction Engines have raised only a small amount of the roughly $10 billion they need to bring the plane to life, mainly from private industries. This is a deliberate policy, as it will only be worth having space planes that can fly every day if there will be something to launch every day. If the space industry thinks not, they simply won't fund it. 

SpaceX's reusable Dragon spacecraft becomes the first privately-operated vehicle to dock with the International Space Station in 2012. Photo Credit: SpaceX

If SpaceX and Reaction Engines succeed in their aims to create reusable spacecraft, and it's a big if, then it could completely change the paradigm of space flight. SpaceX are talking about sending people to Mars for half a million each, whilst Reaction Engines plan to launch dozens of people ta a time in Skylon. Asteroid mining, space tourism, huge space telescopes and more would all become more affordable.

The challenges ahead are huge. SpaceX has yet to recover, let alone re-fly, a single rocket stage. Skylon's mighty SABREs are at this point no more than small prototypes in an Oxfordshire backyard. Both companies may yet fail in ther dreams of reusability, a subject so complex that I've only been able to touch on the basics here.

But if they succed, then we may just get 2001's dream of a future in space. Just a little bit later than pannned.

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