Last weekend’s space school featured a talk from a very nice Ph.D contemporary of mine about what goes into astronaut training and the qualities needed to become an astronaut. This talk did exactly what it was supposed to — got the kids in attendance fired up the prospect of becoming involved with the space program – and was far more interactive than my talk, which was basically a dreary narrative on where in the solar system we might end up colonising if we could ever be bothered¹. However, there were a couple of points where I had to physically restrain myself from heckling her since it was a rather saccharine view of astronaut training and you’re basically not allowed to be cynical when your job is to inspire kids to do science. So I’ll just talk about it here instead: these are some of the other things you need to be an astronaut, but which they don’t usually publicise because they have an image to maintain, dammit.

 You need to be a citizen of a country which has a manned spaceflight program. This means the USA, or Russia, or China. The USA in particular told ESA to sod off when they asked to be involved in the Ares program, so now that the space shuttle is done ESA is going to be in a very awkward position once the ISS is decommissioned because they’ll have an astronaut corps with nowhere to go and no way to get there (unless they pay the Russians). If you look at this comedy list of British astronauts you’ll notice that nearly everyone on it was born to US parents or otherwise acquired citizenship there. The sole exceptions on that list are space tourists with a lot of money who paid the Russians to take them up (hi, Richard Garriott) and Helen Sharman. Sharman’s interesting because she wasn’t even government-funded; a private initiative paid the Soviets to send her up in a Soyuz launch so that we could say we’d launched a British person into space. While I don’t want to diminish Sharman’s achievement in any way – if anything the competition for that single seat into space was more cutthroat than for a regular astronaut berth, and getting the first Briton into space was a genuine landmark – the fact that there hasn’t been another British astronaut in the intervening 26 years basically confirms it as a pure PR exercise. So if you don’t have citizenship, you can’t get citizenship and you can’t pay the Russians to take you, I’m sorry to say you’re out of luck.

You need to have a complete lack of personal dignity. Everyone heard the story about the crazy astronaut who drove 900 miles cross country to confront a romantic rival, right? Every single newspaper and website that wrote about it also mentioned the little titbit that she’d worn adult diapers the whole way so that she wouldn’t have to make rest stops, and that astronauts do this regularly during takeoff and landing and EVAs. The part about her wearing a nappy during the drive turned out to have been made up/repeated verbatim by news sites more interested in salacious gossip than in actually reporting the story accurately (i.e. all of them), but astronauts wearing nappies in space is perfectly true. After all, it’s not like space suits have zippers and while it might take just five minutes to wriggle out of the suit in an emergency that’s not much help if you’re caught short during your delicate repair job on the Hubble space telescope. The high-tech nappies – called Maximum Absorption Garments –  are unpleasant, but necessary. And this isn’t even getting into the gruesome detail of how space toilets work.

You don’t need to be able to fly an aeroplane. The pilots of spacecraft like the space shuttle are invariably really, really good fighter pilots, and this is amusing to be because as far as actually flying the damn thing is concerned their presence is almost totally unnecessary. Spacecraft are flown by computers, and basically always have been; you hear about astronauts like John Glenn who had to do re-entry manually because something went horribly wrong but those days are long gone. If the pilots have a function at all it’s as an absolute last-ditch backup in case the layers of redundancies on redundancies on redundancies in the computer system fail, and — as the Columbia/Challenger disasters proved – if something on board your spacecraft suffers catastrophic failure you’re likely not going to be coming back no matter how good a fighter pilot you are.

Of course the pilots do other things and play a crucial and necessary role in the command structure of the mission, but they don’t need to be pilots to do that (although the military training and experience with command hierarchies is handy). I particularly like the story — which is probably apocryphal, but eh — that the pilots of the first space shuttle missions felt so helpless during takeoff and re-entry that the engineers who actually took care of flying the spacecraft gave them something to do so that they’d feel wanted: pushing the button that lowered the landing gear.

You need to not end up on this thing (or your national equivalent). Actually looking up the stats it turns out that being an astronaut is safer than you might expect. Of the 528 people launched into space only twenty-two have died during missions, giving manned space flight of all kinds a mortality rate of just 4.1 percent. If you go into space the overwhelming probability is that you will come back alive! Of course 4.1% still isn’t that great when compared to certain Earthbound professions that are considered particularly lethal (fishing is the number one most dangerous job in the US, and that only kills 0.1% of the people who do it annually), and it rises further when you consider astronaut/cosmonaut deaths in training/testing, as well as anyone who was unfortunate enough to be standing next to the Soviet space program.

1. Although the three hour activity they did afterwards where they had to convince me to fund their space colony kind of made up for that.

The post What You Need To Be An Astronaut. appeared first on The Scientific Gamer.

Rockets suck. This is a thing that we have established here; they’re terrifically awful ways of getting into space that are only used because nobody has really come up with anything better. There’s all sorts of ideas for wacky drive systems once your spacecraft is actually in space – ion drives, solar sails, Bussard ramjets – but these all sidestep the real problem facing future space travel, which is that you have to get out of the Earth’s gravity well first. This is not easy; even though the Earth is pretty small for a planet it’s still the heaviest of the four terrestrials and has what is to us a very hefty gravitational pull.

In order to exit Earth’s gravity well, an object being launched on a ballistic trajectory from the Earth’s surface must attain escape velocity. Escape velocity is calculated by

where G is the gravitational constant, M is the mass of the Earth and R is the radius of the Earth. For “ballistic” you can read “in freefall” – i.e. an object moving without any other forces acting on it. Rockets do have external forces acting on them thanks to their propulsion systems, so a rocket doesn’t necessarily have to reach escape velocity of 11.2 kilometres per second in order to escape the Earth’s gravity so long as it’s under constant power. However, the amount of energy it will have to expend will be the same as this hypothetical ballistic object, and that can be worked out by using the equation for kinetic energy.

where m is the mass of the spacecraft. With Earth’s escape velocity being 11.2 km s^-1, we can rearrange this equation to find out how much energy per kilo of mass a launch vehicle will need to have to escape Earth’s gravitational pull, and this turns out to be about 63 megajoules per kilogram. I always get a little lost when trying to visualise what a joule is in everyday terms, but Wikipedia tells me that 63 megajoules is roughly the amount of energy you’d release if you detonated fifteen kilograms of TNT. So for a crude method of visualising this, go and look at a picture of a rocket. Imagine a pile of TNT fifteen times as big. Blowing up this pile of TNT would release the same amount of energy as would be needed to get that rocket out of the Earth’s gravity well.

(One significant caveat here: rockets going into orbit don’t need to expend this much energy. They just need to go fast enough that they never hit the ground.)

This amount of energy is fixed. There is no way of getting around it; if you want to go into space, you have to expend at least 63 MJ per kilo of spacecraft mass and this energy has to come from somewhere. For rockets, it comes from rocket fuel; unfortunately rocket fuel increases the mass of the rocket, which requires more rocket fuel, which increases the mass of the- actually I think I’ve done this already, haven’t I. Anyway, rockets suck, but we still use them because the alternative solutions are, to put it mildly, just a little bit far-fetched.

Solution 1: Build better rockets.

Ahaha. Ahahaha. Ahaha. No. Rocket science isn’t necessarily all that complicated – I can understand it, after all – and one of the things that struck me when I was studying space science in the second year of my undergraduate degree was that rockets are a dead end. Well, that’s a bit harsh. Better to say that they’ve been refined as much as they can be.

Two things affect the amount of thrust you can get out of a rocket: the expansion velocity of the exhaust gas you’re creating by burning the fuel, and the size of the rocket nozzle. Rapidly expanding rocket fuels tend to be rather unstable – again, see the Nedelin catastrophe – and so there’s an upper limit on just how volatile you want to make that. What about the rocket nozzle? How wide/narrow this is determines the pressure at which the exhaust gases exit the rocket. For reasons I won’t go into, rockets produce the maximum amount of thrust when the pressure of the exhaust gas equals the pressure of the ambient atmosphere through which the rocket is flying. Atmospheric pressure decreases as you ascend into space, so ideally you want a rocket nozzle that automatically adjusts in size with altitude to keep the rocket working as efficiently as possible. This has been done. After that, there’s no real way to further improve a chemical rocket. We’ve taken them just about as far as we’re going to.

Solution 2: Don’t launch them from Earth.

One of the attractive things about a Moon colony – aside from the whaling opportunities – is that the Moon has a gravitational pull less than one-sixth that of Earth’s. It has an escape velocity of 2.38 km s^-1, and consequently it would only take 2.83 MJ to get one kilogram of mass out of the Moon’s gravity – under a twentieth the energy you’d need to get the same kilo off of Earth! Probably the best way to illustrate this is the ascent module on the Apollo lunar landers; that little capsule was able to create enough thrust to return to orbit to rendezvous with the command module.

It would be far easier, therefore, if we could somehow launch rockets from the Moon instead. Unfortunately this idea merely replaces the problem of getting out of the Earth’s gravity well with the even larger problem of building the necessary industrial base on the Moon to build and launch rockets. I’m not saying it couldn’t be done, and if somebody did manage to do it there’s every chance we’d see the commonplace spaceflight depicted in movies like 2001 (if you were lucky enough not to live on Earth, anyway), but the level of commitment and resources it would require would be staggering.

Solution 3: Mass drivers.

This one is simple, and operates on the principle that while achieving 63 MJ per kilo is a tall order for a chemical rocket, if we could somehow use electricity instead it’d be far easier to generate the energy required. The idea is you have a long, long, long, long launch track, kind of like a very high-tech version of Japan’s bullet train network (see maglevs for further information), and you accelerate the thing you want to launch down this track using superconducting electromagnetism. The track slopes upwards towards the end, and so once it reaches the end of the line your launch vehicle is shot into the stratosphere. At this point some small rocket boosters would take over and move the launch vehicle to the desired orbital trajectory. Building this thing would be a bit more feasible than the Moon colony, but there’s just one tiny snag: room temperature superconductors capable of carrying the currents required haven’t been invented yet.

Solution 4: Project Orion.

In which the Orion spacecraft is supposed to fart out shaped nuclear explosions, the brunt of which is directed against an impact plate on the ass of the spacecraft which makes the nukes “push” the spacecraft along. Utterly, utterly mad.

Solution 5: A space elevator. Also unicorns.

A very old concept that’s rather in vogue in 4X games, for some reason. As mentioned here geostationary satellites orbit the earth with a period of one day – that is, they remain above the same point relative to the Earth’s surface throughout their orbit. In theory, if you had access to a material strong enough as well as the combined and focused resources of the largest superpowers on Earth over a half-century or more, you could lower a cable from geostationary orbit all the way down to the surface of the Earth and simply have vehicles ride up and down the cable just like an elevator car. This is attractive because the energy costs are similar to those of a mass driver launch with the added bonus that you get most of it back as elevator cars come back down from orbit. If we then wanted to launch stuff further out into the solar system we could take advantage of the fact that the space elevator would kind of act like a giant sling to any payload launched from the far end.

Sounds fun, right? Perhaps so, but space elevators have several minor niggles past the huge advances in space technology, robotic manufacturing, materials science and megastructure construction (I just made that last one up, but someone’s going to have to invent it before they can build the elevator) that would be required, not to mention the totalitarian world government that’d have to be in place to keep everyone pointed in the right direction long enough to finish the bloody thing.

• In order to make it work you need a big counterweight of some kind to produce the necessary centrifugal force to keep the elevator cable taut. These days space elevator designs merely pay out the cable a little further past geostationary orbit to provide a counterweight mass rather than the previous idea of moving an asteroid to GEO to act as counterweight, but even if you do this you still need the asteroid because a) you need to build the elevator from both ends at once and so you’re going to need a base of operations in space from which to do it, and b) an asteroid would provide necessary raw materials for cable construction. So first you need to move several million tonnes of rock into geostationary orbit. This is just a little bit tricky to do, and I imagine it might make people down on the surface a little bit nervous as well what with the potential consequences if something goes wrong.

• There is no material which can currently be mass-produced in the quantities required which has the necessary tensile strength to support thousands of kilometres worth of its own weight. People always point to carbon nanotubes as the catch-all solution, but while they have the theoretical capacity to support the quantity of mass required, it would require the cable to be structurally flawless over its entire 40,000 km-odd length. Even one flaw would introduce a weakness which could be potentially fatal to the whole shebang.

• Transmitting power to the elevator cars is also going to be a bit of a bugger, since you still need that 63 MJ/kg to get into orbit. A nuclear power source would do it, but that’d probably make passengers a bit uncomfortable. Solar panels would increase the weight of the car, while using the cable itself to transmit power is going to run into the very inefficiency problems the space elevator is supposed to avoid. The current favoured proposal is wireless energy transfer via lasers or something, which has the tiny drawback that it is literally space magic.

• Elevator cars would travel fairly slowly, with an ascent to GEO taking anywhere from 6-12 hours to a full day. This brings the Van Allen radiation belts into play; the cars would travel through them slowly enough that anyone inside would end up taking lethal doses of radiation. It would be necessary to shield the cars in some way, which again would add to the weight.

Personally I think the space elevator is the ultimate manifestation of Archimedes and his lever; something that is theoretically possible but practically stupid. We can’t even agree on the best way to fly three people up to LEO; we abandoned the moon after sending barely two dozen guys up there. We are nowhere near being ready to take on the incredible engineering challenges of building something like this, and so anyone who thinks the space elevator is going to be built in the next half-millenia needs their head examined.

Where do I think the likely future of spaceflight lies? Well, assuming the world doesn’t enter a period of terminal dystopian senescence in the next couple of decades I think the mass driver concept is probably the most feasible solution as long as somebody comes along to solve the superconductor problem. It’s the smallest engineering project, it has the very great advantage of the thing being built on Earth rather than in space or on another planet, and it has the fewest question marks over necessary technology advances. Plus, if aliens ever try to invade we can use it to shoot rocks at them. Welcome to Earth.

The post The Future Of Spaceflight. appeared first on The Scientific Gamer.

On Monday there were words about the various types of manned spacecraft we’ve flung into orbit (and beyond). Particularly discerning readers will have noticed that the vast majority of them — Vostok, Voskhod, Soyuz, Mercury, Gemini and Apollo – were designed and launched within a single decade between 1960-1970. Since then we’ve had exactly one new manned space vehicle: the Space Shuttle. Manned spaceflight has been more or less left to stagnate by national governments, but there are promising signs that the next decade may be as groundbreaking as 1960-1970. Are governments becoming interested in spaceflight again? Hardly. The US government is still dragging its feet over the design and development of the MPCV, while I’ve heard very, very little about the proposed replacement for Soyuz (on the other hand that doesn’t really need replacing since it does what it’s supposed to extremely well). No, what’s going to be exciting about the next ten years is the opening up of human spaceflight to a variety of commercial efforts.

If you know me you’d probably expect me to hate the idea of private companies going into space, but to be honest governments have ignored it for the last fifty years and there’s at least a chance that profit will provide the driving force that simple discovery could not, so I’m broadly in favour of it. Regardless: not only has development of private “spaceflight” been in progress for a decade or so what with Virgin Galactic and all, but the US government recently initiated something called the Commercial Crew and Cargo program (CCC, or C3) whereby they subsidise the development of several different private spaceflight efforts with the view to buying or leasing the most suitable vehicle once development is complete.

It probably sounds inefficient to pay private companies to develop spacecraft that you then have to pay to use, and that’s because it is. It’s very inefficient. However, going up to LEO is relatively routine these days and by subsidising private efforts NASA ensures that the private sector has the technology base to take up any slack created by them abandoning LEO. And they are abandoning it; the MPCV mentioned in the last post theoretically has the capability to do LEO, but the ultimate intention of the program is to return astronauts first to the Moon or a suitable nearby asteroid, and then eventually in a few decades to possibly put a man on Mars (I nearly said person, but you know it’s going to be a guy). As it is they have to pay the Russians to make flights up to the ISS, so why shouldn’t they give some of that money to their own commercial efforts? It makes a twisted sort of sense, if you think about it.

Anyway, there’s several different competitors vying for a slice of the C3 pie. Excluding the Mickey Mouse effort of Virgin Galactic (which is literally a plane that goes really high rather than a true spacecraft), these private spacecraft are:

Boeing’s CST-100 – This catchily-named capsule is basically a space bus with a very simple design brief: deliver anywhere from between two to seven astronauts to LEO and then return them to Earth. It’s not going to go any further than that because it doesn’t have the capacity to do so.

Sierra Nevada’s Dream Chaser – Like Boeing’s effort, designed to take up to seven astronauts to LEO and back. You may notice that it looks like a miniature space shuttle, but the Dream Chaser launches on top of a rocket booster just like a capsule does. The wings and whatnot are just to allow it to land on a runway instead of splashing down in the ocean.

SpaceX’s Dragon – The interesting one. Like CST-100 and Dream Chaser, Dragon can do LEO with no problems, but it also has the theoretical capacity to go further – perhaps even to the Moon. It’s also the only one of the three private efforts to have actually made an unmanned test flight into orbit, so it actually does work. This got them noticed by NASA and they’ve been awarded a contract to resupply the ISS, so this is the one you’ll most likely see flying in the next decade or so.

In theory, then, that’s LEO taken care of. What about going further afield? You may or may not remember some hullaballoo about five or six years ago when President Bush announced the Constellation program. This was supposed to set NASA’s manned spaceflight goals for the next quarter-century, and those goals were lofty: to return to the Moon, to establish a permanent base there, and to put a man on Mars by 2030. Even the most insufferably optimistic space scientists thought that achieving all this on such a short timescale was a little unrealistic (it could be done with enough money and political will, but NASA doesn’t have anywhere near that much in their manned spaceflight budget), and sure enough when Obama was elected one of the first things he did was cancel the Constellation program. This meant that the proposed Ares heavy rocket booster and the Altair lunar lander were both cancelled, but what didn’t get cancelled was the Orion space vehicle (similar to the Apollo command and service modules). They couldn’t cancel that because despite the shifting political winds they still needed a replacement for the shuttle – which had been pushed far beyond its projected operational lifetime – and Orion was the best they had.

So Orion morphed into the Multi-Purpose Crew Vehicle. This is a four-man spacecraft designed to be launched on refurbished shuttle rocket boosters, and it’s multi-purpose because it can, theoretically, do pretty much any manned mission we can think of. Want to make a trip up to LEO? No problem, just launch the capsule. How about a near earth object? Stick a service module on it to extend its flight time and send it out there. Mars? Even that’s doable if you daisy-chain several service modules together to increase power, life-support and fuel capacity. This is the great advantage of a modular capsule design: it is hella adaptable in comparison to a fixed-mass spacecraft like the shuttle. It’s a great design if they can pull it off; an unmanned test flight of the Orion is scheduled for 2014, although I really wouldn’t expect to see it flying with people inside until the 2020’s at the very earliest.

Other countries are also looking at getting into space; Japan and India both have nascent manned spaceflight programs, while the European Space Agency was somewhat put out when NASA announced they wouldn’t be accepting international participation in Orion like they did with the shuttle, thus forcing ESA to start developing their own solution pretty damn quickly; it currently consists of a jury-rigged version of the unmanned Automated Transfer Vehicle that carries supplies up and down from the ISS. All of these plans are still very much on the drawing board though, and it usually takes a spacecraft design at least a decade to actually make it off the drawing board and into space – and as the Chinese have proved, even then it can be a slow, arduous process developing the technology. No, I think that in the future LEO will belong to Soyuz and the commercial spacecraft, with the MPCV providing a longer-range option should we ever want one.

The post A Brief History Of Spaceflight, Part Two. appeared first on The Scientific Gamer.

Following on from why the Space Shuttle sucked, I’m going to do a little summary of manned spaceflight – both where it’s been, and where it’s going.

You’d have to look pretty hard to find someone who didn’t know that Yuri Gagarin was the first man in space in 1961. However, finding someone who doesn’t have a clue what the hell he was flying would be significantly easier. Gagarin made Earth orbit in what was essentially a tin can strapped to a converted ICBM. The tin can was called Vostok, and it was incredibly basic; it was a metal capsule containing the cosmonaut attached to an equipment module with RCS¹ thrusters and a small rocket engine to make the re-entry burn. Vostok amuses me because once the re-entry capsule had separated from the equipment module the cosmonaut had no way of controlling his re-entry – no thrusters, no parachutes, no nothing. Well, I suppose they did have parachutes, but only in the sense that the cosmonaut would physically have to eject from the capsule and parachute down before the capsule smashed into the ground. Still, it proves that you can do spaceflight in an incredibly basic way if you’re willing to economise.

The American Mercury program was next; this is slightly better known thanks to Freedom and Hollywood and whatnot. Alan Shepard was beaten by Gagarin’s flight by a mere month, but what the films and documentaries tend not to emphasise was that Shepard’s flight was sub-orbital – i.e. there wasn’t a huge amount separating it from a regular aeroplane flight except the altitude. It wasn’t until 1962 and the third Mercury flight that NASA finally achieved a stable orbit. On the other hand the problem lay more in the Redstone rocket boosters they were using than the Mercury spacecraft themselves; compared to Vostok it was a model of sophistication, with a conical shape for controlled re-entry (this is important because you only have to plaster your heat shield along the flat bottom of the capsule rather than shielding the whole thing as they had to do with Vostok), limited fly-by-wire maneuvering capability and a parachute for a “soft” splashdown into the ocean². Most of this was down to the direct participation of the Mercury Seven astronauts in the design process – they were aviators³ used to being in control of whatever they were flying, and so they demanded features like a bigger window and a manual re-entry control system.

Mercury and Vostok were essentially proofs of concept. We knew spaceflight could be achieved, and now it was time to do something with it. That something was the space race for the Moon. Pretty much every single thing the Americans did post-Mercury had the final goal of supporting the Apollo program and the Moon landings. By contrast, while the Soviets had the same general objective they were more concerned with space “firsts” – first EVA, first space station, first probe around another planet and so on. This is one of the reasons they went running up the blind alley of the Voskhod programme.

Voskhod wasn’t even a second generation spacecraft – not really. It was simply a Vostok capsule modified to take two cosmonauts instead of one, and it retained most of the limitations of the Vostok capsule. Improvements in the boosters used to carry them into space meant that Voskhod had a braking rocket added which allowed for a “soft” descent on land with the cosmonauts still inside, but otherwise it was basically the same spacecraft. Jury-rigging Vostok in this way meant the Soviets got two of their firsts – first multi-person spacecraft, and the first spacewalk⁴ – but since Voskhod was a technological dead end it turned out to be mostly wasted effort, with only two flights being made.

Gemini on the other hand was a pure technological testbed for Apollo. There were ten manned Gemini flights over a two year period in 1965 and 1966; not only were these testing the systems and procedures required for multi-person spaceflights, they were also testing the maneuvers that would be necessary for a Moon shot – docking two Geminis in orbit, endurance spaceflights, that sort of thing – and giving the Gemini astronauts valuable experience in these manuevers that they would later find useful on Apollo missions. Design-wise Gemini superficially resembled a larger brother of Mercury, but the internal mechanisms were very, very different. In particular where the Mercury spacecraft combined its critical systems like power and life support into the Mercury capsule itself, Gemini hived these off into a separate equipment module similar to Vostok. This laid the groundwork for the modular construction of Apollo.

Not that the Soviets were sitting around all dejected after the relative failure of the Voskhod programme. They started design work on the Soyuz capsule in 1963, with the first generation Soyuz flying in 1967. Soyuz was intended to be part of the Soviet Moonshot⁵; the idea was that it’d make up part of a modular spacecraft attached to a lunar lander in the same way as Apollo’s command/service module. Soyuz has the same sort of construction, with orbital and service modules that contain all the stuff the spacecraft needs while it’s actually in space which is then jettisoned before landing to make the re-entry module’s job easier. An unmanned Soyuz capsule even made a test flight around the Moon in 1969. You can essentially think of it as the Russian equivalent to Apollo – and while you’re thinking about that, consider that while it’s undergone several generations of redesigning the Soyuz spacecraft is still flying today ferrying astronauts up to the ISS and back, albeit in a heavily modified form. Imagine what NASA could have done had they stuck with Apollo instead of putting all their hopes in the space shuttle.

Speaking of Apollo, there’s a decent argument to be made that it represents the peak achievement in manned spacecraft design. The modular construction meant that it could be tailored to a specific mission – there’s no reason an Apollo capsule couldn’t make routine flights to LEO just as well as it flew to the Moon – and considering it had to keep astronauts alive during the most insanely ambitious and dangerous missions in the history of manned spaceflight it speaks volumes about how well it was designed that it did an astonishingly good job, with only three astronaut fatalities when Apollo 1 caught fire on the launch pad.

This is why I think Apollo is so amazing (and indirectly, why I think the space shuttle was so terrible). Here is a picture of an Apollo spacecraft.

The big cylinder with the rocket is the service module with life support, power and propulsion systems⁶. The small cone on top is the command module which contains the astronauts during flight and re-entry. The service and command modules would be launched into space together on top of a Saturn V, and then they’d dock with the lunar module in Earth orbit before switching to a trans-lunar orbit.

Everyone got that? Right. That was spacecraft design in 1969. This on the other hand is spacecraft design in 2012. It’s the proposed design for what used to be the Orion spacecraft, part of the Multi-Purpose Crew Vehicle system that’s supposed to replace the space shuttle. Note the way it looks exactly the goddamn same as Apollo. That’s how good Apollo is: when today’s NASA engineers were asked to design a next-generation spacecraft, they used Apollo as the blueprint.

Aaaaanyway. After the Moon landing everyone kind of lost interest in space flight as a national pursuit, and the design of new spacecraft stagnated. The US launched the last Apollo in 1972 and haven’t made a manned spaceflight that didn’t involve the space shuttle since.  The Soviets – and then the Russians – continually refined the design of Soyuz and made great advances for the long-term human habitation of space with their Mir space station, but they too are somewhat stuck in the past as far as manned spaceflight is concerned. China is the only other nation with an operational manned spaceflight program; while people sneer at their Shenzhou capsules as barely being at the Gemini level of technology, you have to remember what I said about the MPCV – NASA is still using the Apollo design after running down the blind alley of the shuttle for the last thirty-five years. It’s the launch rate that concerns me, with the Chinese managing just three manned missions in nine years. They’re not going to make any progress if they don’t physically launch the things into space with taikonauts inside.

So spaceflight has been rather static for the last forty years. It’s only now starting to take off again (har) and the major driving force behind that has come from a rather surprising source: the private sector. More on that on Thursday.

1. RCS stands for reaction control system; if you want to make a small adjustment to the trajectory of something flying through space the best way to do it is to squirt a small amount of pressurised gas in the opposite direction and let Newton’s third law do the rest. That bit in WALL-E with the fire extinguisher? That was scientifically accurate.
2. American capsules all splashed down into the ocean. Soviet capsules all landed in Siberia or the deserts of Kazakhstan. Why is this? It’s a more a divergence in the cultural design philosophy than anything else — both methods are equally valid in their fulfilment of the main requirement for a spacecraft landing site: that it be really, really, really hard to miss.
3. Flying ability wasn’t really necessary for astronauts, except in so far as it demonstrated their ability to handle very complex machines. However what was useful was their complete self-confidence and conviction that they could handle anything, which was a trait common to combat pilots.
4. Which nearly went comically awry when Alexei Leonov realised his air-filled spacesuit — which he’d clambered into in the pressurised cabin of the spacecraft — had inflated in the vacuum of space to the point where he could no longer bend his joints to get back inside the airlock. His problems didn’t end there, either; Voskhod 2 overshot its landing site by some 400km and the two cosmonauts ended up spending a very chilly night in the Ural mountains before they could be recovered.
5. The Soviet moonshot didn’t fail because their spacecraft were bad. It failed because they couldn’t get their heavy lift rocket launch vehicles working properly before the Americans landed, thus cementing my opinion that Rockets Suck.

6. Putting all the critical systems in one place does have a drawback, as the Apollo 13 disaster demonstrated. An exploding oxygen tank damaged the service module, and because the astronauts didn’t know how bad the damage was they couldn’t trust any of the systems contained on board – including, critically, the large propulsion engine that they’d normally be using to adjust their orbital trajectory. If they hadn’t had a convenient set of backups in the form of the lunar module life support systems and descent engine, the Apollo 13 astronauts would have been screwed.

The post A Brief History Of Spaceflight, Part One. appeared first on The Scientific Gamer.

Warning: post contains moderately difficult algebra along with hints of calculus. But don’t worry, it’s not that bad.

Rockets are kind of sucky for getting into space. Right now, though, they’re all we’ve got.

Rockets work by the classic principle of Newton’s Third Law: every action has an equal and opposite reaction. Push against a wall, and the wall also pushes against you with the same force. Friction between your feet and the ground stops you from moving backwards in response to this force, but if there wasn’t any friction – if you were standing on a big sheet of ice or something – then if you thumped the wall hard enough you would start to slide away from it. In a true Newtonian environment like space, even a simple action such as throwing a wrench away from you can nevertheless produce an appreciable impulse on you in the opposite direction to which you threw it, and that’s where you’d end up drifting.

This is basically how rockets work, except instead of a wrench they’re using thousands of kilograms of rocket fuel shot out of the back of the rocket at several kilometres per second. This creates an equal and opposite force which pushes the rocket upwards – thrust, in other words. When they’re considering how much fuel to put in a rocket, rocket scientists don’t think “Well, we want the rocket to reach such and such an altitude so we need this much fuel,” because that would be needlessly complex. Instead they think in terms of something called delta-V, or ΔV, which is the change in the velocity of the spacecraft that will be caused by burning X amount of rocket fuel. If your rocket’s delta-V is roughly equal to the Earth’s escape velocity, then congratulations! You’re on your way out of Earth orbit.

The amount of fuel you need to accelerate a given payload to a certain delta-V is dependent on how heavy that payload is. A bigger payload means more fuel. And as mentioned in the post on satellite orbits, it’s not enough just to add more fuel to the rocket, because now you’ve just added a whole bunch of extra kilograms that also needed to be lifted into orbit. So you need more fuel to lift the fuel, and then more fuel to lift the fuel to lift the fuel, and the whole thing would get dreadfully complicated if it weren’t for something called the Tsiolkovsky rocket equation. Because I’m trying to re-teach myself some basic physics I’m going to derive it from first principles. Don’t worry if you can’t or don’t want to follow what I’m doing, just skip to the end.

WARNING. WARNING. AWFUL CALCULUS STARTS HERE. SKIP FORWARD IF YOU’RE ALLERGIC TO MATHS.

Start with the principle of conservation of momentum.  Momentum is mass times velocity. Consider the state of the rocket at two different times: t, which for our purposes is the rocket sitting on the launch pad just before blast off, and t + dt, which is a time dt after that when the rocket has burned off all of its fuel.

(Note: dt is part of the Leibniz notation of calculus. The d doesn’t stand for a specific quantity, but instead basically means “change in”. So dt is the change in time, dm is the change in mass, and so on. They can be combined, too, so dm/dt would be the rate of change in mass over time. For a real world example, dV/dt is the rate of change in velocity over time, which is equivalent to acceleration a. Here, t + dt is similar to saying something like “D-Day +17”, where the +17 is equivalent to + dt.)

The rocket will start with a mass M(t), and will eject a quantity of exhaust gas as it burns its fuel which will have a total mass dm (because the mass of the rocket will change by this much). Due to conversation of momentum, the momentum of the payload after the fuel burn  — which for our purposes we will treat as everything on the rocket that isn’t the fuel (i.e. M(t) – dm) – will be equal and opposite to the momentum of the exhaust gas dm. We can model these separately to find out their respective momentums at the times t and t + dt, but to do this we need to make some assumptions about the velocity of the payload and the fuel.

At time t, the fuel is unburnt and flying along with the payload, so it and the payload have the same velocity V(t). At time t + dt, the fuel will have been converted into exhaust gas travelling at a constant velocity U (since for the purposes of simplicity we’ll say a single fuel type will burn at a constant rate). The payload will be travelling at the same velocity V(t) plus some positive change in velocity dV provided by burning the fuel, making its total velocity V(t) + dV. The fuel will be travelling in the opposite direction with velocity U, but it had a velocity of V(t) to start with, so its true velocity with respect to the payload will be V(t) – U. (The U is negative because the fuel is travelling in the opposite direction to V(t)).

Right, now we can get on with the interesting stuff. The momentum of the payload and the fuel can be expressed as:

To find out the change in momentum over time dt, we have to subtract the intial momentum at time t from the final momentum at time t + dt.

Because we’re treating the rocket as a closed system with no external forces, conservation of momentum means the sum of the change in momentum of the rocket and the payload will be zero. In other words, adding together the terms we’ve derived for ΔP_payload and ΔP_fuel should equal zero.

We’re trying to find the rocket’s change in velocity – its delta-V, or dV – so we rearrange this in terms of dV.

And now comes the part where I’ll probably lose even the more dedicated amongst you. The mass of the burned fuel dm will be equivalent to the change in mass of the rocket M(t), or -dM(t), so we can substitute that in for dm.

Then we do a wonderful, magical thing called integration. Say you have a line on a graph which is described by the equation y = x. Integrating that equation will give you the area underneath the line y = x. This is bloody complicated and there’s a whole bunch of different rules for doing it. For our simple example, the integral of y = x will be x²/2. Don’t understand? Don’t worry, I don’t either. The one thing you should grasp about integrals is that since most lines described by set equations will be technically infinite, we need to identify the bit we actually want to find the area under and integrate between upper and lower limits that define that part of the line.

We integrate the left hand side of the equation with respect to V between the limits V_o and V_final, the initial velocity of the rocket and the final velocity of the rocket respectively. This gives

Simple, right? Unfortunately we then have to integrate the right hand side with respect to M between the limits of M_payload and M_o, the mass of the payload and the original mass of the payload plus the fuel.

That’s substantially gnarlier. Fortunately there’s a neat way to simplify logarithms by smooshing them together, so

Since the final velocity minus the original velocity is the change in velocity, or delta-V, then

IF YOU ARE SKIPPING ALL THE HORRIBLE CALCULUS START READING AGAIN HERE.

It’s a lot of effort to go through for such a little thing, but the final product of all that work is Tsiolkovsky’s rocket equation. From it you can easily see that the delta-V you’ll get out of a given rocket will depend on the velocity of the exhaust U and the logarithm of the ratio of the total mass of the rocket divided by the payload mass. However, since I said rocket scientists usually think in terms of “How much fuel do I need to reach a given delta-V?” rather than “What delta-V do I want to reach today?”, a more useful form of the equation is

Everything on the right side of the equation is stuff the rocket scientist should know in advance – the exhaust velocity U, the desired delta-V and the mass of the payload. And if you subtract the mass of the payload from the total mass of the rocket M_o, what you have is the mass of the fuel. This can therefore be used to quickly and easily calculate what amount of fuel you’ll need to boost a given payload to a given delta-V. Just for the lols we can make a graph of how the fuel-to-payload ratio changes for that given delta-V depending on what sort of fuel you use. For a desired delta-V of 9.4 km s^-1 (the lower limit required for low Earth orbit)

Obviously there’s a law of diminishing returns in effect here, but we can see from the graph that in order for your rocket to even be feasible you need a fuel with an exhaust velocity of at least 4-5 km s^-1. Happily there are fuel mixtures which exist which are capable of this, and some go even higher, but there’s a limit to how big you can make U. Remember the Nedelin catastrophe I referenced last week? That neatly demonstrates that high-power rocket fuels are very, very volatile and prone to exploding, and so you don’t really want a U that’s too big. It’s essentially fixed at 4-6 km s-1. Assuming that you’re not willing to reduce the mass of your payload at all, is there any way we can further increase the efficiency of a rocket?

Well, I wouldn’t have asked the question if there wasn’t an answer. There is. It’s called rocket staging. The idea is that once you have burned X amount of fuel, whatever you were using to keep that X amount of fuel in is useless dead weight. Lifting it along with the rest of the spacecraft is inefficient; it’s better to just cut it loose entirely if you can. Rocket staging is basically a matter of perching a small rocket on top of a larger, more beefy rocket. The beefy rocket fires first and uses all of its fuel, and then a series of explosive bolts cut it loose from the small rocket which then starts burning its engines. We can work out how efficient this is by using the rocket equation for each successive stage.

Assume that your rocket requires 1% of storage mass for every 8% of fuel mass. For a one stage-rocket with a payload that is 1% of the total mass, this allows for a fuel mass of 88%. Your achievable delta-V will therefore be

Compare this with two rockets stacked on top of each other, using the same fuel/storage ratios. The first rocket has a fuel mass of 80% and a storage mass of 10%, with the second rocket making up the last 10% of the mass. The first stage will boost the second stage to a delta-V of

So this first stage has less delta-V than our big one-stage rocket. However, once it’s finished burning it’s cut loose and the second rocket fires as a standalone entity with

i.e. exactly the same as the first rocket since the fuel/storage mass ratio is identical. This is added to the delta-V from the first stage to give a total delta-V of 3.22 U – half as much again as a one-stage rocket carrying the same payload with the same total mass. Depending on how far you want to go and how complex you want to make your rocket you can add even more stages; the Saturn V which sent the Apollo astronauts to the Moon was a five-stage monster.

So! Hopefully this has at least been useful for crystallising in your minds the reason why we use multi-stage rockets. It’s certainly been helpful for me; I learned this stuff back in 2004 so it was good to spend an afternoon deriving the Tsiolkovsky rocket equation from first principles. Good. Yes.

*eye twitches*

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The space shuttle flew its last mission in July 2011, signalling a temporary end to America’s manned spaceflight capability. NASA has been working on the Shuttle’s replacement, Project Orion (no, not that Project Orion) for seven years now but it’s yet to get off the drawing board in any serious way and projections that it’s going to make the first unmanned test flights in 2014 are extremely optimistic, so this is a state of affairs that’s likely to continue for at least half a decade or so. You won’t have been able to hear it amongst all the dewy-eyed wall-to-wall coverage about the last space shuttle flight heralding the end of an era, but a significant portion of the space scientist community could be seen muttering “Well thank god that’s over with” after Atlantis touched down on the runway at Kennedy Space Centre.

You see, despite what people might think about the space shuttle, despite its value as a symbol of NASA’s technological superiority, as an actual space vehicle the Space Shuttle sucked. It sucked like nothing else in space flight before or since. It sucked more than the Soviet rocket that blew up on the launch pad, incinerating 120 of Russia’s best rocket engineers. It sucked more than the flight of Soyuz 11, which inconveniently vented the spacecraft’s entire atmosphere into space on re-entry killing the three cosmonauts on board. It sucked more than Voskhod 2’s crash-landing, which dumped the crew in the middle of the Siberian taiga where they had to spend a very uncomfortable night fending off wolves and bears. And the reason it sucks more than all of these things is because Voskhod, Soyuz and all the rest were successful space vehicles that did what they were designed to do and only killed hundreds of people when there was an unfortunate glitch in the system. The space shuttle, by contrast, was very, very bad at what it did, which was delivering both manned and unmanned payloads to low earth orbit (LEO). This wasn’t because it couldn’t lift very much. It could lift quite a lot. It  wasn’t because it was particularly bad at carrying crew, either; the space shuttle is probably the most comfortable manned space vehicle in existence. The problem was that it combined both of these functions into a single highly complex vehicle (it’s been called the most complicated machine made my humans, which isn’t too far off the truth) where two different vehicles specifically designed to do only one of them would have been far, far cheaper.

Cheaper, I hear you say? Isn’t the whole point in a reuseable space vehicle that it’s supposed to be cheaper than fire-and-forget one-shot launchers that can’t be reused? Well, that’s what the designers of the space shuttle thought back in the 60s. The main Orbiter? That’s completely reusable; just build one and use it again and again and again. Those two little boosters on the side of the big orange external tank? Those splash down into the ocean after they separate from the main vehicle, are recovered by surface ships and hauled back to land to be refurbished. Those are reusable too. The only part of the space shuttle that isn’t reusable is the external tank itself, and how expensive can those be?

 The answer is: pretty expensive. But the price tag attached to the components wasn’t the problem with the shuttle program. The problem was that when the shuttle was being designed, it was anticipated that it would make 24 flights per year. This was lowered to 12 flights a year after the designers realised they could only make 12 external fuel tanks (the only non-reusable component) in that time. The actual record for most shuttle flights in a year was 9 flights in 1985, and now that the shuttle program is over we can see that they averaged out to just over four flights per year. Four. Six times less than the original estimate. And remember, all the time the shuttles are sitting around on the tarmac it costs money for maintenance to keep them in good working order. Every time a shuttle comes back from a mission it basically has to be torn apart and rebuilt to make sure it still functions and won’t kill the astronauts next time it flies, and that costs a staggering amount of money. The shuttle spend over a year grounded after both the Columbia and Challenger disasters; it was eating up money then as well. The up-front cost of a single shuttle launch is $450 million. When you factor in what the entire shuttle program has cost and average it out over the total number of launches, it actually works out to just over $1.5 billion per launch. And this is compared with the launch of a non-reusable Russian Soyuz rocket, which can carry either a satellite payload or the Soyuz manned capsule, and which costs approximately $250 million dollars up-front.

So the space shuttle was a fantastically expensive and complicated way of doing something that the Russians (and now other countries) were doing cheaper and more efficiently with the traditional one-shot orbital capsules. Unfortunately by the time the Americans figured this out; it was far too late, the Shuttle was already flying, and it had a lot of national prestige attached to it as a symbol of America’s obvious technological superiority over those perfidious commie Russians. They couldn’t cancel the Shuttle program at that point; it would have been like cancelling Apollo. They were stuck with it. Bizarrely they also dragged their feet when the time came to design a shuttle replacement, keeping the shuttle flying for nearly a decade past the date it was originally supposed to retire and only doing so when there was a significant chance the next orbiter launched would drop out of the sky because it was so old. Orion was nowhere near ready when the shuttles stopped flying. Now theUS has to pay the Russians to use Russian launch facilities to launch American astronauts in Russian Soyuz capsules mounted on Russian rockets, and it’s all because of the space shuttle. Nice one, guys.

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