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Sunday, 29 March 2020

Space news this week: In-space servicing for satellites, OneWeb and Bigelow fold thanks to Corona, Space Force launches its first mission, balloons to space, and loads more... ,


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First: A message from The Doctor:

Pick o' the podcasts
From the video store

NASAspaceflight.com, a new space news channel:

Atlas rocket launches its first satellite for U. S. SpaceForce


Sea Dragon: The largest rocket that never flew:

Starship SN3 nears completion

How much do rockets pollute? 


Thursday, 26 March 2020

Answers for Authors: Where can my characters stay as they travel the galaxy?





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Part 1: Stations, bases and habitats....
At least the ISS has toilets and Internet... 

It's hard to imagine Darth Vader couch surfing his way across the galaxy, although I can see Kylo Ren doing that. But everyone needs to get their head down somewhere and, while some spaceships are flying cities with accommodation for thousands, even the La Sirena from Star Trek Picard is bit cramped to live in for months or years of a long interstellar journey.
So what are the options for a weary Starfury or X-wing pilot to put their head down?


Space stations - the kind that are being designed and built for real today:

We’ve had a pretty few of these over the years – Skylab, Almiraz, Salut, Mir, Chenzou, and the ISS. Generally they're classed as 1st, 2nd, or 3rd generation: Originally these were just a habitat module with a single docking port for a capsule to return the crew to Earth, and were abandoned when their supplies ran out (generation 1 stations) . Later models had two reusable docking ports and air locks, allowing multiple crews to stay over time, and conduct spacewalks (generation 2). Since the 1980's bigger space stations have been made of semi independent modules, each with a separate purpose, that are flown into orbit and assembled there (generation 3). Recently people are trying to make staying in a space station more affordable, widen access, and get more people living and working out there. 

It looks like there could be three main types of space station for the 21st century: Hard hulled (like the ISS), inflatables (like the BA330 module Bigelow Aerospace is working on), or a combination of both types. To date they have no kind of artificial gravity, although some experiments on them have centrifuges to supply variable 'gravity'. That means the crew spend a lot of time exercising to stave off the wasting effects of microgravity, and ensure they sleep in an air current to avoid a bubble of CO2 building up around them. They also have at least enough capsules to carry the whole crew back to Earth docked at all times, and each of these will have a survival kit, including a hand gun, aboard (so, yes, there are guns in space right now - and they belong to the Russian crew) .
The basic construction methods are...

Hard hulled space stations:
Above: Mir, the original hard hulled modular space station

Until recently all space stations have been of this type – Mir, Chenzou, ISS - basically a big can in space*. OK, a very strong can designed to survive for years in space and support a continuous crew, run experiments, house space telescopes, launch mini satellites etc etc. But, on some level, a can filled with air. It's a reliable approach to building an orbital home: The ISS, for example, has served as a launch site for miniature space satellites, a destination for space tourists, boasts its own gym, internet connections, viewing cupola, and masses of experiments going on. Spacecraft from across the world dock regularly to bring fresh crew, supplies, and experiments. And it's set to leave more than just a legacy: Private company Axiom Space plan to built an extension to the ISS that will become an Independent station when the ISS is eventually retired.

Inflatable space stations:
These are a new development, but based on an old NASA design called Transhab: They’re bouncy castles in space, albeit bouncy castles made of unbelievably tough material. The support structure of one is filled with gas under pressure to make it rigid, and it’s launched folded up, saving a lot of launch volume. Using inflatable structures this way also saves on the weight of a traditional support structure.
Bigelow Aerospace has launched two prototype inflatable stations – Genesis 1 and Genesis 2, as well as its BEAM module on the ISS. Genesis 1 and 2 performed very well – in fact both are still in orbit and pressurised today. This looks like a real possibility for the next few decades or space exploration.

A combined design:
In theory a prototype of this, using both hard shelled and inflatable modules, already exists in the form of the ISS with BEAM attached – and until the inflatable designs have really proven themselves this is probably how they will be used...


Planetary bases:

Moonbase:
ESA is currently trumpeting the idea of a 3D printed Moonbase, made at least partly from the lunar soil. Habitat modules – and you could use the exact same types of module used to build space stations - would be buried beneath meters of lunar dirt to provide radiation protection. The prime site for such a base would be at the lunar poles: That would put it close to places of scientific interest (like the valleys of eternal shadow), and close to mountain tops that get almost nonstop sunlight. That would give the base an abundant power supply, and the ices frozen in the dark valleys would allow the base to experiment with producing their own water, oxygen, and fuel.

Above: An artists impression of ESA's proposed 'Moon Village'. Courtesy of ESA. 

Martian Base:
On Mars ice is abundant near the surface in many areas, but the thin atmosphere is a pain: It’s thick enough to produce global dust storms that can block out the Sun for months (and plummet the surface temperatures waaay below freezing), making solar power unreliable – but it’s too thin to provide much radiation protection, or any real help in landing a spacecraft big enough to carry people. And, because the launch windows to and from Mars are so far apart, a Mars base will have to be built as apart of any attempt to and people there: They will be there for months at least.

Above: Artists impression of a Martian outpost, courtesy of NASA

For a larger base on the Moon or Mars you could look to their networks of tunnel like lava tubes. These tunnels, carved out by ancient lava flows, can be nearly a mile across, and would provide protection for a small city, even from the fiercest solar storms….

Venus Base:

An artist's impression of a Venusian base, courtesy of Xmadedx

This idea was floated*** decades ago: Although the surface of Venus is much like one of the less salubrious suburbs of hell, there is a layer in the atmosphere, about seventy kilometers up, where the temperature and air pressure are compatible with liquid water and human life. Radiation levels there are tolerable, and the gravity is 90% of Earth-normal.
In the Venusian atmosphere breathable air is a lifting gas, so a light weight dwelling full of Earth-normal air will simply… hang there. In fact, this layer of Venus atmosphere is actually the friendliest spot for humans in the whole solar system: It holds fewer challenges to overcome than even Mars.
If this sounds a little like something from Star Wars that’s because it’s exactly like Bespin city from Empire Strikes Back – but it could really be built, no sci-fi antigravity needed.
There would still be the teensy problem of all the acid clouds to overcome, but humankind has been protecting our structures from corrosion for centuries. And probes sent to hover on balloons through the Venusian clouds have held up pretty well.
The inhabitants of such a place would probably be scientists studying the planet below – from an aerostat home they could remote control robots on the surface, trying to unlock Venus’s mysteries. There’re also plenty of unusual chemical phenomena in the acid rain clouds. So, if you’d like to drift off to the sound of (battery acid strength) rain on you window, head for Venus.

Space habitats:


But all those are small fry. There are designs for much more impressive living spaces that, although we probably won't be building them anytime in the future, might be built by future generations. These are true space habitats, not stations, in that they provide a fairly Earth-like environment - including gravity, or a reasonable imitation of it. To keep thing manageable I’ve divided them into three broad category's:

Space bases we could build today - if we had the money:
In many ways this is the most interesting category, because the engineering and maths for these ideas checks out… it's just the maths associated with construction costs that don't close. And by ‘don’t close’ I mean you'd probably have to mortgage Earth itself to pay for just one.

I'm not sure who you'd mortgage it to, either... 

As such they make a cool look at the kind of in-space megastructures we might build if we really do expand into our solar system in a big way - to make them work monetarily we’d have to have a thriving off world economy, and the means to transport many thousands of residents off Earth and onto the new colony. As we’d need to get tons of building material, and power from in-space sources, to make these ideas work some of the concepts that companies like Planetary Resources and SpaceX are working on (asteroid mining, space based solar power, and mass space transportation) may one day feed into these concepts...

Bernal Sphere:
A steel and concrete globe about a third of a mile in diameter, floating in space, the Bernal sphere wold be a teeny, inside out, planet. Residents would live inside and it would rotate once every thirty seconds to provide Earth like gravity along its equator. Since this artificial gravity would peter out near the poles, and the poleward surfaces would appear to be sloped, it would be like living near the bottom of a really weird valley, wrapped around itself. A valley with one added bonus: If you climbed the walls high enough you could fly!
10,000 people could live in one, their buildings lining the curve and appearing overhead. Although it’s a perfectly good design, I like to look at the stars at night, so the Bernal Sphere’s not my personal favourite – although I could always just dig ‘down’ until I found them…

Stanford Torus:

Above: The Stanford Torus from the movie Elysium. 

Have you seen the movie ‘Elysium’? That space station is a Stanford Torus: A donut-shaped tube 130 meters thick with a diameter just over a mile. It also spins to produce its gravity, but unlike the Bernal Sphere the inner portion of the tube is open – the artificial gravity alone holds the atmosphere in place.
The torus would house a similar number of residents to the sphere. I prefer the torus as, looking up, you’d see both the far side of the torus, and the stars beyond. Spokes could connect the habitat ring to a central hub where spacecraft can dock, so when you visit your first sight will be the whole ring stretching around you. Weighing in at 10 million tons, you’d need an asteroid mining industry already in place to build this beast, but it could certainly done using materials like steel and concrete.

The O'Neill Cylinder:

Above: The Babylon 5 space station, the adventures of which crew I watched on a Sunday as a kid.

If you’re old like me**** you probably remember a Sci Fi show called Babylon 5. If you don’t: The show was about the crew of an O'Neill cylinder, christened Babylon 5. As the name suggests, it’s a cylinder the main body of which is about 5 miles wide and 20 miles long. Once again, a gentle spin of one revolution every minute and a half would be enough for terrestrial gravity. O'Neill’s original design had two cylinders built in counter-rotating pairs to offset destabilising, gyroscopic effects that would cause the cylinders to stray from their intended, Sun-facing angles.

While any of these space colonies would be far more vast than the International Space Station, their engineering challenges could be met. "From an engineering standpoint, the structure is very easy—the engineering calculations are totally valid," says Anders Sandberg, a research fellow at Oxford University who has studied megastructure concepts.

Ideas that might be built using the strongest conceivable materials:

These are space habitat concepts where the engineering numbers close... just barely, and only if you use things like carbon nanotubes, or mass manufactured diamond. To build these structures you’d need massive amounts of such super-strong building materials – and, since these materials are usually only available in tiny quantities, these ideas will almost certainly stay fictional for a long time. But, that said, the numbers do close in theory...

Bishop ring:

Above: An artists impression of a Bishop ring 

A Bishop Ring, originally proposed in 1997 by Forrest Bishop, is the Staford Torus’s big brother. Like Stanford's design, the Bishop Ring would spin to produce artificial gravity, but differs that it would use carbon nanotubes instead of steel. That would allow it to be approximately 1,000 km in radius and 500 km in width, containing 3 million square kilometers of living space – about the same size as India.
The habitat could either have an arrangement of mirrors to reflect sunlight onto the inner rim or an artificial light source in the middle, powered by a combination of solar panels on the outer rim and solar power satellites.

Mckendree cylinder:

Above: Artists impression of the inside of a McKendree cylinder, courtesy of Eburacum 45. 

The Stanford Torus has a big brother, and the O’neill cylinder has one too: A McKendree cylinder is a space habitat originally proposed at 'NASA's Turning Goals into Reality' conference by NASA engineer Tom McKendree. As with other space habitat designs, the cylinder would spin to produce artificial gravity by way of centrifugal force. It differs from the classical designs by using carbon nanotubes instead of steel, allowing the habitat to be built much, much, larger. In the original proposal, the habitat would be 460 km in radius and 4600 km in length, containing 13 million square kilometers of living space… nearly as much land area as Russia.
McKendree proposed dedicating half of the surface of the colony to windows, allowing direct illumination of the interior. The habitat would be composed of a pair of counter-rotating cylinders which would function like momentum wheels to control the habitat's orientation.
Complete flights of sci-fi gibberish? But then, what would the people of the Roman empire thought of the geostationary satellite ring that encircles our planet, 36,000 km wide? Or the Three Gorges dam?

Those are the building methods available – what about the all important location?

Possible Locations:

Orbit of Earth (or the local habitable planet):
Being sited near Earth has it’s advantage… and it’s perils. On the pro side:

  • A station in Earth orbit can be powered by solar panels.
  • Should anything bad happen it’s short journey back to the safety of Earth – the ISS and most other stations have at least one man rated space craft docked at all times, to act as a life boat should aliens attack, someone crash into the station**, or a storm of space debris threaten to tear the place to splinters.
  • Being close to Earth also means that the station can take advantage of the Earth’s magnetic field. Cosmic radiation can seriously increase a persons risk of cancer. Earth’s magnetic bubble diverts the worst of this, so staying within it makes sense.
On the con side…
  • Have you seen that movie about the storm of space debris that chews up everything in orbit? Well, that’s not the far fetched nightmare scenario you might hope it is, although such a chain reaction wouldn’t happen that fast: Near Earth space is pretty crowded these days, and what it’s crowded with dead satellites and pieces of satellites, whizzing along at 7 or 8km/sec. Satellites have been blown apart by it, the ISS has had it’s reinforced windows damaged.
  • Space agencies track the larger pieces, and space stations often have to manoeuvre to avoid anything that’s going to come too close
  • Above: The cracked ISS window that probably caused Tim Peake to change his space underwear
Between the Earth and Moon:
Above: A Cygnus freight ship, the proposed base unit for Orbital ATK's space station

An idea that is being seriously looked at, and might well get built. The most often proposed site is at a Lagrange point between Earth and the Moon, and in orbit about the Moon. A Lagrange point is a place where the gravitational pull of two objects cancel out, creating a zone where objects can sit without needing to orbit anything. That makes navigating and docking to a station there a lot simpler, and also makes the station a convenient point to store fuel and other supplies for missions deeper into space. Orbital ATK is proposing to build such a station from two of it’s Cygnus freighters, which would be loaded with goods as they left Earth. Such a space station could also be used to conduct better microgravity experiments, and as a safe refuge if a Lunar mission ran into trouble a-la Apollo 13.

A graphic of Orbitals proposed lunar station. Courtesy of Orbital ATK

But the big question mark over a Lagrange point or lunar orbit space station is the cosmic radiation problem we mentioned earlier. Protecting such a station has never been tried before, and while there are a few potential technologies that could do it – from simply lining the walls with water tanks to a magnetic field around the station that would imitate Earth's - none of them has ever been tested against background space radiation, never mind the type of radiation storms our Sun can put out.

Orbits around non-Earth-like planets:
If we look a bit further ahead, at space stations around Mars, Venus or other worlds, we need to deal with all of the above and new kinds of challenges: A station orbiting Venus or Mercury would need a beefed up thermal regulation system, to shed the heat from the intensified sunlight. Go much further out than Mars and your station can no longer collect enough sunlight without an unrealistically huge set of solar panels, so you’ll need a nuclear generator, or other more complex power source... but it will probably be a very long time before we have manned stations that far out.


*Let me be clear: It is definitely lot more complicated than that – lest some ESA engineer come to my house tonight and slap me
.

** This has happened- link here:

*** I couldn’t resist, sorry.


**** I saw my first home computer at age 10. My 3 year old son has to have his tablet time rationed.



Saturday, 21 March 2020

This week in space news: RIP lunar gateway, iron rain, SpaceX and OneWeb launch huge batches of satellites and lots, lots more...






From the video store

OneWeb launch 34 internet satellites on one ArianeSpace Soyuz rocket:

The Sun is home to gigantic 'plasma cannonballs' that race about at huge speeds

SpaceX launches 60 Starlink satellites on a 5 times re-used booster, but misses landing.


Friday, 13 March 2020

In space news this week: SpaceX and Axiom, Iceland aurora, Falcon 9's 50th landing, planet where it rains molten iron and lots, lots more...



Pick o' the podcasts:

From the video store:

Take a tour of the Moon:






Watch SpaceX's Falcon 9 rocket land for the 50th time:



Reading material:







Tuesday, 10 March 2020

Answers for Authors: Are there any realistic stardrive ideas?



I just like this picture.
Interstellar travel is a sci-fi staple, but writing about it in a realistic way always hits the same problem: The distances involved, and speeds required, are mind numbing. Worse is the universal speed limit - lightspeed - which seems to dictate that interstellar journeys must take years or decades. Overcoming that isn't just a question of better power sources and engine design: As you approach lightspeed all sorts of weirdness breaks loose to slow an object down, and time itself slows, then virtually stops. Time running incredibly slowly prevents any engine or power source from operating (this is a huge oversimplification, but for a better explanation you'll have to follow the link), so on the face of it lightspeed can never be reached.

If you didn't follow the link, here's the video explanation.

Even so, for a writer looking for a touch of realism there are resources to draw upon: There have been a lot of interstellar drive ideas seriously proposed1, going back to designs from the 1950's. 2016 even saw the announcement of the privately funded 'Breakthrough Starshot' research project, which is an effort to solve the problems of sending a probe to the nearest star. So here are some of the ways it's been suggested we might tackle the problem of interstellar travel, from the 'with unlimited money we could actually build this today' type to the 'hey, someone's been feeding this physicist LSD2' type.
Let's start with sub-lightspeed drives, which are usually based on more realistic, near term, technology. For spacecraft that don't mind spending decades travelling the void, e.g. robot probes, sleeper ships or generation arks they're a perfectly serviceable option:

  
Orion drive:
Yes, nukes can be used for better things than genocide.

In the 1950's a bunch of the engineers who'd worked on America's nuclear program developed 'project Orion'. This was a plan for spaceships that would be propelled by throwing nukes out of a hatch in the back (with what was basically a huge air rifle) and setting them off.
Because... well, er... why not, I guess?
The interesting thing is that, according to modern computer modelling, with the right combination of low yield nukes and massive construction it probably would have worked. The ship would have consisted of a massively armoured pusher plate, topped with equally massive shock absorbers, topped in turn with a habitation module built like a nuclear submarine. For additional protection the pusher plater would have been enveloped in a magnetic shield to prevent plasma from the nuke actually contacting it. The nukes would have ranged from a little bigger than those developed for the 'Davey Crockett' nuclear grenade launcher to about 20 kilotons, and would have been surrounded by carefully shaped casings filled with beryllum oxide reaction mass, to direct the majority of the force towards the ship's pusher plate.



Above: The design for one of the Orion drive nukes.
The enormous amounts of energy available from riding nuclear explosions would allow an Orion ship to be both very long range, very fast (able to reach Mars in about a month), and absolutely huge by today's standards: The smallest complete designs were 40 meters in diameters and 80 meters from nosecone to pusher plate - that's nearly as long as the International Space Station.

Above: The design for the interplanetary Orion ship.
Two things closed the project down, and neither was engineering feasibility: The nuclear test ban treaty and one important piece of technology never happening - a fallout free nuke. Without that even starting an Orion drive up in orbit would have increased cancers worldwide. There're still people interested in the general idea today - as I said, it's very possible it could have been made to work. The original engineers even built a miniature Orion that used high explosive instead of nukes:


Above: The high explosive propelled Orion model. 

The biggest version of the Orion engine would have been a monstrous, 100,000 ton, nuke spitting behemoth capable of reaching 3% of lightspeed. It would have a long trip to the stars (around 150 years to the nearest), and a fairly radioactive one... but the obstacles are ones of engineering, political will, and money, not engineering plausibility.
 
Above: A video on Daedelus. From courtesy of Times Infinity, via youtube. 

The British Interplanetary Society developed this idea in the 1970s, as a cleaner update of the Orion concept. Their engine would use deuterium fusion explosions, heating coin sized pellets of deuterium fuel with an electron beam until they triggered fusion in the pellet's core - a process called 'inertial confinement fusion'.
The Daedelus design differed from Orion in other ways: The explosions would happen in a reaction chamber rather than against a pusher plate, and the plasma produced would get directed by powerful magnetic fields, generated by superconducting coils, out of a huge nozzle to produce thrust.



A breakdown of the two stages of the Daedelus design. Courtesy of the British Interplanetary Society.
Daedelus would use a much higher rate of detonations than Orion - 250 per second - to boost the ship to 12% of lightspeed. It would also be even bigger than most Orion designs, at 190 meters total lengths, and be divided into two sections: A 1700 ton 'boost' stage that would run for 24 months before being dropped, and a 1000 ton science stage, that would accelerate for another 21 months and carry the science and communications equipment (the reference design was unmanned) up to full speed.

A Daedelus ship compared to a Saturn 5 rocket. The Saturn 5 is about 100 meters tall. 

Daedelus would have been mother ship to a number of sub-probes, and a team of robotic 'wardens' that would maintain the ship during it's decades long mission - the reference plan called for a 50 year long cruise to Barnard's star, 6 light years away.
The Daedalus team weren't ever aiming to build a working starship, it was simply a theoretical exercise. But it established ICF engines as a potential interstellar drive.
Interestingly, ground based inertial confinement fusion reactors have continued to be tested and developed, becoming the first fusion reactor design to generate more energy than they used in 2015 - so this is another idea that's already gone beyond the theory stage.


Bussard Ramscoop:
Above: The starship Red Dwarf, probably the smeggiest ramscoop starship ever, and the best known. Courtesy of the BBC.
In a previous post I mentioned how, although it seems empty, the space between the stars is actually filled with a very thin soup of ionised gas and dust. That gas is mostly hydrogen, the main fuel for a fusion reactor, and in the 1960's an engineer called Robert Bussard came up with a remarkably simple idea: Build a ship that could collect and concentrate that diffuse fuel source - a ramscoop. It would have a huge electromagnetic scoop, which would funnel the interstellar hydrogen into the front of he ship, concentrate it, and use it as fuel.
It's a brilliant thought, but when engineers actually ran the maths they found problems: First, the interstellar medium is too thin in our part of the galaxy for the idea to work - though in other regions of the galaxy it might be more feasible. Second, collecting the gas in the magnetic scoop creates a huge amount of drag - in fact the scoop makes a more effective sail or brake than it does engine. Several variations seeking to overcome the originals problems have been proposed since:

This variation uses a fusion reactor with it's own fuel supply to generate power, and instead of collecting the hydrogen as fuel the scoop just redirects down the vessel's throat and accelerates it out the back. In effect the vessel is pulling and pushing against the gas without absorbing it, a little like a squid's jets propulsion. Because the scoop never has to bring the hydrogen up to the same speed as the ship the drag is greatly reduced.


Squid, doing their water-jet propulsion thing.

This design would use the same 'squid jet' idea as the RAIR engine, but instead of an onboard reactor energy would be beamed to it as laser light, from a beaming station on Earth. That would mean that, like the original ramjet design, the LAIR engine wouldn't need to carry fuel or propellant.

The original Bussard Ramscoop isn't an inherently flawed idea - it's just that the local interstellar hydrogen won't provide enough power to overcome it's own drag. But there's a way around that: Create a 'runway' of deuterium gas (a much more potent fuel than interstellar hydrogen) for the scoop to collect and use. That could be done by using something like a particle accelerator to fire ionised deuterium gas into space, creating a long 'tongue' of fuel. The speed at which the gas in the tongue was moving could be adjusted to match the expected speed of the vehicle as it reached it, eliminating drag from fuel collection. The idea could also be made to work using pellets of fuel, fired at such a speed that the ship would catch and collect each pellet just as it reached the right speed to overtake it.

Artists impression of a Ramjet starship, courtesy of Nick Stevens.

Laser boosted lightsail:
This is the idea being (tentatively) put forward by the Breakthrough Starshot initiative. Sunlight driven lightsails are a technology that is fairly well understood, and have already been flown in space. Both JAXA's IKAROS space craft and the Planetary Society's Lightsail satellite are propelled this way.

Above: JAXA's lightsail, the IKAROS.

The idea is very simple (to be fair the execution is fairly tricky): Although it's to subtle to influence much here on Earth, light produces a very tiny push on things it reflects from. In space, where there's no air friction, a lightweight mirror surfaced sail can collect enough of this push to slowly accelerate a spacecraft. Because it's 'wind' is travelling at lightspeed the sail can (in theory) keep accelerating up to just below lightspeed itself - it's the ultimate victory of fuel efficiency over raw thrust.


Above: The Planetary society give a run-down on their (now launched and successful) lightsail mission.

The downside is that light spreads out as you get further from its source, loosing intensity and reducing the push on a sail. So, to get a lightsail up to interstellar speeds, you'd need to replace the Sun with a laser beam - laser's don't spread out nearly as much. The approach of Breakthrough Starshot would be to have a square kilometer of Earth-based lasers, that focused their combined beams onto the sail, pushing up to between 5% and 20% of lightspeed.


Above: An animation showing the Breakthrough Starshot laser sail proposal. 

Like any idea it has it's own problems: An interstellar sail would need to be far higher quality reflector, not to mention more heatproof, than any sail flown to date. And the best sails we might build (in the near future at least) could only carry a few tens of grams at most. We can build micro-electronic sensors that small, but sending a signal back to Earth will be very difficult with so little room for a power source. But, all that said, this is probably the best developed potential starship engine.
For a manned mission, needing a ship massing many tons, the sail would need to be huge - at least a hundred of kilometers across. It would need to be driven by an equally huge array of lasers, which would probably be stationed near the orbit of Earth and powered by vast arrays of solar panels. The lasers would be focussed onto the sail by a gigantic Fresnel lens, floating in space in front of the lasers.


An alternative approach is to have the sail do a very close flyby of the Sun, and pick up enough speed from the intense light before it gets too far away. That eliminates the need for a laser beaming station, but has two drawbacks: The sail and probe need to be even more heatproof, and the maximum speed is limited to about 0.5% of lightspeed - which would get you to the nearest star in around a thousand years.

Above: An infographic on lightsails, from space.com.

Antimatter rocket:
Above: The rings of Saturn, the most abundant source of natural antimatter in our solar system. Courtesy of NASA/JPL.


Antimatter, made famous by Star Trek as the fuel of choice for starships, is very powerful stuff: Inert by itself, it reacts with regular matter to release astounding amounts of energy. A piece weighing only grams could produce a bigger explosion than the Hiroshima bomb. Various stardrive proposals over the years have been designed around various ways of harnessing the power of antimatter. Some are essentially a supercharged project Orion, others use the heat from an ongoing antimatter reaction to vaporize propellant, producing a continuous thrust like a regular rocket.

Four different types of continuous thrust antimatter engines. For more details see sections 6.2 and 6.3 of this paper from the University of Paris-Saclay plasma and gas laboratory.

They all run up against the same basic problem: Antimatter is fantastically rare in nature, and so hard to make that it's market price is 63 trillion dollars per gram. 
But...
...that may not be as much of a showstopper as once thought, for two reasons:
1: There are a whole class of antimatter engines that use antimatter to enhance conventional fusion or fission reactions, and so need much smaller amounts.
2: There are small but significant sources of naturally occurring antimatter in our solar system, which it would be perfectly possible to mine. The biggest lies in the rings of the planet Saturn, but there are very small sources in near-Earth space too. An 'antimatter mine' could conceivable collect enough to make some of the lower end antimatter drives reality. 
A schematic of the ICAN 2 antimatter powered spacecraft, a sort of antimatter supercharged project Orion.

But even antimatter propulsion runs up against the lightspeed limit - so if we want to look beyond the very nearest stars we'll have to start investigating the more exotic options sooner or later.... 

Faster Than Light travel: Up to now we've been looking at engines we could build, or at least realistically research, today. They're great... for unmanned probes, generation ships, or sleeper ships to the nearest star systems.
 

Above: The nearest other solar systems to our own - it's lonely out here! Space.com

But they're limited by the 'speed of light' rule: Basically, anything approaching lightspeed begins to experience seriously weird effects: Time slowing down, mass increasing, and distances distorting - all stopping any further attempts to increase forward speed.

How quckly time moves, compared to how fast you travel- and if time slows down, so does whatever mechanism is running your engine, so your engines stop working.
Here's the thing: When you get into their details, Einstein's theories point to certain... loopholes. These point to ways a ship might reach it's destination sooner than the lightspeed limit strictly allows, without actually breaking the limit: Yes, we're into the realm of engines that warp space itself - although 'engines' might not be the right word. 'Bizzare theoretical phenomena that haven't yet been conclusively proven to be totally impossible' is a better way of describing them.
None of these are anywhere near even a laboratory demonstration3, but the theories are at least sound enough to be worth understanding better.


Wormholes:


Above: The basic concept of a wormhole: If space is the sheet, and normally you'd need to travel all along the sheet to the destination, a wormhole lets you jump straight from one side to the other.

In many ways these are the grandaddy of FTL ideas, coming straight out of the equations of general relativity: Two distant points in the universe can be connected by a bridge made of space-time itself (called a wormhole) which stretches through a higher dimension than our usual three, along which the distance is much shorter. 
If the two points are very far apart then a wormhole can simply provide a shortcut, like in the picture above. The trick works because that light rays moving along the wormhole with you will still be moving faster than you - so the speed of light rule stays in one piece. But being a shortcut isn't the only way such a bridge can be used: The ends of the bridge could be made to connect to different times. Connect the other end of the wormhole to last Thursday and you could actually arrive before you set out. A wormhole sounds like just the ticket for reaching distant planets, but there are all sorts of problems with actually building and maintaining one:
  • It would be hugely unstable, prone to slamming shut and crushing travellers - in fact the vibrations of just one photon could cause it to collapse, making it useless even for communication. To counteract this it would need immense amounts of 'exotic matter', (matter with negative mass) pushing into it.
  • Bringing the mouths of the wormhole close to each other, if it could be kept open, would cause an endless loop of regurgitated photons to build up between them, resulting in a gigantic radiation pulse.
  • Building it in the first place would mean tailoring black holes to have specific properties, no small feat considering we don't even understand what goes on inside one.

All that said, there is some hope: A recent study found that, while a truly stable wormhole might be impossible, very small wormholes might be persuaded to collapse very slowly - slowly enough for communications at FTL rates through it, at least. 

Alcubierre (warp) drive:

Yes, warp drive inspired by Star Trek.
This is a (very slightly) less outlandish take on the trick wormholes pull. The Alcubierre 'engine' is inspired by the observation that the expansion of our universe is not simply due to galaxies flying apart through space; the space between them is actually expanding, like the skin of an inflating balloon. And, if space can expand, then in theory it can also  contract. 




Above: Space itself is expanding - courtesy of minutephysics, who do a lot of interesting videos!


So, in principle, if you could apply huge amounts energy to the space behind a ship, making it rapidly expand, and huge amounts of negative energy to the space in front of the ship, forcing it to rapidly contract. The ship itself is caught in a calm bubble in between these two zones, and that bubble is dragged across the universe at FTL speeds by the expansion behind and contraction in front, along with anything inside it.
A bit like the wormhole it works (or at least the equations don't totally rule out it working) because a ray of light, in the calm bubble with the ship, would still be moving quicker than the ship. So again the ship is not, technically, breaking the speed limit. It's like being in an airbus flying inside a fast wind: It's ground speed might actually exceed the speed of sound, but it's airspeed is always slower than sound because the air is flowing in the same direction as it - hence it encounters none of the shockwaves or extreme airframe stresses that would normally stop an airbus going so fast.


Above: The high speed jet stream created by storm Ciara, which allowed jets flying from New York to London to exceed the speed of sound with their groundspeed, without exceeding it with their airspeed, and make the trip in record time. Going the other way it made all the jets super slow. Courtesy of the New York Times.

To work the drive needs negative energy, which we can only make in minute amounts, and it would build up a gigantic 'radiation shockwave' as it travelled, probably vaporising the destination world. Even so NASA has seriously looked at what would be needed to apply the theory, albeit as a simulation only.
Do these seemingly impossible design problems mean we should give up on FTL? If you ask me... no. We may never succeed, but every time we've tried to look for a work around for lightspeed we've learnt new things about the laws of physics. And, who knows, maybe, one day, we'll learn enough...


Out-of-the-box ideas:


Let's say we'll always be limited to below lightspeed: It would take us decades just to reach the very nearest stars. That's no good for building an interstellar empire. There are, however, ways around the problem...

Make yourself immortal:

Tick tock, tick tock...
The longest lived humans make it to maybe 120 years. But there are creatures, like tortoises, that can easily clock up two centuries. There are simpler organisms, like jellyfish, that can live much longer: One species in particular can return to a larval state and regenerate, effectively living forever.

Above: Jonathan the 184 year old tortoise gets his first ever wash.

What if that's the real key to a species establishing itself in the galaxy - not high power stardrives but just having a long lifespan? Does that make us permanently excluded from the club?
Maybe not.
It shouldn't come as much of a surprise that life extending technologies are being investigated, with some promising results. We've only got lab only experiments so far, but fruit flies, mice, and other creatures have had their lifespans extended. Some insects have had their lifespan doubled by deliberate genetic mutation.


Above: Turritopsis dohrnii the tiny, immortal, jellyfish.

If we could count on a hale and hearty existence into our 230th year, would a wait of 100 years for a slow-boat mission to reach a nearby star system really seem so terrible?
And, if enough life extension to cross the galaxy seems too much to hope for, there're other ways of living to the end of a long mission...

Freeze yourself:

Space travel: A great excuse to get nude with everyone. Until the aliens star jumping out of people's chests...

People have been falling (and getting pushed) into freezing water since forever, and once in a while they would be found and revived - sometimes after hours. So what about freezing a person in a controlled way, and reviving them at a distant future date? It's a sci-fi staple and, although in the real word we're still a long way off, simple organisms have been revived and born after over ten years on ice.
Although freezing people for space travel is still impossible (don't believe people who claim they can freeze your body to be revived in the future - think about that promise for a second), research into it actually has more immediate life-and death applications. In hospitals suspended animation has been used to prevent gunshot and stabbing victims from deteriorating until they can be operated on.

 

Become an A.I.
Yup, we're into Matrix territory.



This is probably the most extreme of the 'live longer' options: Take the human mind, download it into a computer, and you can crew your ship without having actual bodies. The computerised minds won't age, and can run the spacecraft for centuries if needs be.
As bizarre and terrifying as this sounds, it's being investigated. 'Uploading' a human is a real goal for Ray Kurzweil, director of engineering at Google, who claims people will be able to "upload" their entire brains to computers by 2045. IF that were to happen then worries about lifespans on a space mission would be irrelevant: The uploaded people would be effectively immortal.
Although that immortality does have a weak spot.


Although uploading a full human mind is still far away (if it should be done at all) there are glimmers that it could eventually be done: The 'Openworm project' succeeded in copying the nerve patterns of a nematode worm (it's 'mind' as far as it has one) into an artificial body.  
Move Earth:
Earth. Ta-daa!

Yep, this has seriously been looked at and found, if not practical today, not impossible either. And, if you want to commute from Earth to another planet quickly, why not 'just' move Earth closer?
Well, OK, the obvious answer is because that's freaking insane. Except that the idea's obvious insanity haven't stopped astrophysicists making serious suggestions on how it might be possible to move the Earth. These include building a huge light sail (which we mentioned above), and towing Earth with it, using the planet's own gravity as a tether. Another involves slingshotting asteroids around Earth, gradually altering its orbit with the reverse of a spacecraft's gravitational slingshot manouvre.
Although these ideas show that moving a planet isn't as impossible as it sounds, it would take a huge amount of time to move Earth far. Even if you waited for a close pass by another star - as happened 70,000 years ago - you'd need a far more efficient method of propulsion to transplant Earth into another solar system. That said... it might be possible to engineer such a close encounter - and it might be desirable to do so, since one day our Sun will die.
Extreme as it is, in many way's it's more plausible than things like warp drives or wormholes - they need large amounts of negative energy, and precise control of black holes to be made to work - this would just need patience and precision.
And it's not the most audacious plan to improve interstellar commuting. Not by a long shot....
  
Move the solar system
If you're looking for an insane idea that would make any James Bond villain wet themselves in awe, look no further than the Shkadov thruster: A plan to turn the Sun into a gigantic engine and steer this entire solar system through the galaxy like... well I can't think of anything it'd be like. Well done Leonid Shkadov, you've broken my ability to metaphor.
To do this you'd have to take the planet Mercury, dismantle it and spin it out into thin, reflective sheets. Then wrap half the Sun in a gigantic structure called a Shkadov sail, made from those sheets. The pressure of sunlight would hold the sail up against gravity, much like today's solar sails, and the Sun's light and particle emissions would be diverted in one direction, generating a thrust.
Although such a drive would take millions of years to work, it would eventually allow a patient race to park their star system in easy commuting distance of any other star they liked the looks of - or several races together could park their stars into a miniature, artificial, cluster. In combination with the planet moving ideas mentioned above, that might allow them to make their homeworld immortal, hopping from solar system to solar system for ever.

Move to a star cluster...
Above: A globular cluster.

If a civilisation has the patience to consider Skadov's ultimate engine then they'd know there's a natural alternative: Around the edges of our galaxy lie collections of stars called 'globular clusters'. Although they sound like something you spit up when you've got a bad cold, they're actually huge complexes of long lived stars, all living within fractions of a light year of each other. Havard scientist Rosanne DiStefano has pointed out that, for the advanced alien who likes company, worlds inside such a cluster would be a prime location - species could live within easy travelling distance of each other, making something like Star Trek's Federation (Or Star Wars' Galactic Empire) practical, even with sublight drives.

Conclusion:
Before anyone points out that at least three of those ideas are, well, insane.... yes I realise they are. But they make a great leaping off point for thinking and talking about our place in the universe, and just how big and grandiose engineering might get for an advanced star faring race. It's worth remembering too: There's a difference between an idea that's currently (utterly) impractical and one that's physically impossible.
If there's anything history on Earth has teaches it's that as long as something is possible it's not question of if it will be done, just when...



1: I use the word 'seriously' in the context of discussions with theoretical physicists here, so don't get too hopeful.

2: That sounds like hyperbole, but it's hard not to suspect that either the minds behind some of these ideas were either on something illegal, or should be put on something medicinal.

3:That would be a pretty astounding and terrifying lab, as it would need tame black holes and huge amounts of negative energy. Ever try house training a black hole?