Space enthusiasts have talked about space stations for decades, even before the launch of the first satellite.  In the 1950’s Colliers ran a series of articles about space exploration, with discussions about space stations and space shuttles.  Wernher von Braun, himself, was a champion of space stations.  However, no one proposed space stations as a goal for themselves.  Space stations, instead, were a means to a goal.  They were way stations, ports, and stepping stones to something bigger and better.  A fleet of shuttles would supply the stations and provide passenger transport.  This was the goal.

Now, many of the early goals of space stations faded.  Von Braun envisioned orbital communication centers, with switchboards and operators to handle long distance calls.  Electronics and satellite technologies made such mundane space station duties obsolete before the first station was even built.  But, he still thought of space stations as being important way stations to the Moon and beyond.  Shuttlecraft would ferry passengers and supplies to the stations, where lunar and interplanetary craft would dock and then fly onward.  Such craft would be optimized for their missions, and would have no need to enter Earth’s atmosphere.

Since people would be living and working in space stations, then it would be natural for science to be done there, as well.  Laboratories would be set up to conduct experiments best suited for low gravity conditions.  However, these sort of experiments were secondary to the mission of the space stations, as envisioned by the early space station proponents. 

During the golden years of NASA, the Apollo years, it looked as if these dreams would become reality.  Alas, budget cuts killed such auspicious plans.  NASA was faced with a choice:   a space station or a shuttle.  They picked a shuttle, feeling that a space station might follow for the shuttle to which the shuttle could eventually shuttle from Earth. 

The Soviet Union and the United States both began work on space stations in the early 1970’s.  The Soviets placed several Salyut modules into orbit.  These were self contained space vehicles that were manned by crew delivered in separately launched Soyuz spacecraft.  They could be operated for extended periods and later variants could be resupplied by unmanned supply craft.  The Salyut program culminated in Mir, whose first module was basically a souped up Salyut.  Addition modules were added, and Mir was operated for many years, being served by Progress Modules, Soyuz craft, and even the American Space Shuttle.  It was truly a space station.  However, NASA also put a space station into orbit:  Skylab.  The Skylab station was basically a modified Saturn-V third stage, fitted as a living and working unit rather than as a rocket.  Three missions to Skylab arrived via Apollo capsules launched on Saturn-1b rockets.  As the name implies, Skylab was mainly a scientific station, with experiments conducted in microgravity.

By the 1980’s, NASA wanted another space station.  We couldn’t let the Soviets have all the fun, right?  However, NASA was never really funded sufficiently to build a station.  Sure, there were plans, and studies, and some work done on the Space Station Freedom, which never was constructed.  But, it was apparent that the space station would be very expensive.  But, did we really need it?  With no space station to send a shuttle to, SpaceLab modules were constructed to fly aboard the Space Shuttle.  Extended missions of the shuttle could go for over two weeks performing studies aboard the SpaceLab.  Essentially, this made the Space Shuttle a temporary space station.  So, did we really need a space station?  In a sense, NASA sort of shot themselves in the foot by coming up with an alternative to a space station, since it was harder to justify to the government bean counters why we needed a space station to do what the Shuttle could already do.  Besides, we eventually even had our own astronauts and experiments being performed on Mir, for the science experiments that needed longer times in microgravity.  But, Mir could only last so long.

Eventually, someone came to an idea of a joint space station.  Already, both Russia and the United States were working on Mir, so perhaps they could work together to fund and operate a bigger and better space station.  And, for that matter, other nations could join in and support the endeavor, with money, equipment, etc.  We could share the costs.  The International Space Station (ISS) was born.  The thing was supposed to be much larger than Mir, able to house at least double the astronauts.  The problem is that a space station is a sort of autonomous spacecraft, and spacecraft are complicated to operate.  It takes about two crewmembers to operate the station, and the rest to do science.  Naturally, if you have more than two crewmembers, then they can trade off duties, but two will always be on duty running the station.  So, four crew members could do twice the work of three, and five crewmembers could do three times the work of just three.  However, the Soyuz craft that served as the primary transport and escape craft for both Mir and the ISS could accommodate only three.  That was fine, though, since NASA was going to develop a new crew vehicle that could handle more, allowing for a larger station crew.  Then, things went really bad with the Russian economy.  NASA wound up footing basically the entire bill for the station.  The whole point with having the Russians onboard as partners was supposed to be so that we could get a space station, and neither nation would have to foot the whole bill.  Well, Russia could not come up with the money to build their components.  So, we gave them the money to build their contribution.  We provided the money to put it up there, and we provide financial support to help the Russian space agency to keep running to keep supplying the station and to operate the backup mission control.  So, instead of sharing costs, we’ve footed most of the bill.  But, that cuts into NASA’s budget.  Something has to give.  Some science was lost, and so were plans for a larger crew vehicle.  So, that meant that the station crew would have to remain at three.

Constructing the space station involves a major expense, not only on the ground, but in space.  A lot of time is needed to build the station, and many components are designed to be delivered or assembled with the aid of the Space Shuttle, or with the additional personnel that fly with the Shuttle to dock with the ISS.  In fact, since 2000, only two shuttle flights have not been to the ISS.  Then, the Columbia accident happened (one of only two flights not ISS related in three years).  With the Shuttle fleet grounded, a new problem arose.  Russian Progress modules are not able to keep the ISS supplied for three people.  So, the crew had to be reduced to two until the Shuttle could fly again.  That means that about all the crew has time to do is keep the station operating.  There is very little time left for science.  The ISS isn’t finished yet, but there should be far more science coming out of it.  There has been precious little since the Columbia accident.  It has mainly been a budget black hole for NASA.  The ISS was supposed to be done by 2005.  Even by 2003, it was years behind schedule and vastly over budget.  It will take dozens more shuttle flights to really finish the thing as planned.  There won’t be dozens more shuttle flights to it, though.  We’ll be lucky if the ISS is mostly finished by the time the Shuttle fleet is retired from service.  But, then what?  Once the shuttles are gone, the crew goes back to just two crewmembers:  just enough to keep the station operating?  So, why bother?  Unless we have a new vehicle capable of allowing us to properly staff and supply the ISS, why should we actually spend the money to finish it? 

OK, backing out of the deal now makes us look bad.  But, we already look bad.  Already, there is little that can be done aboard the station unless we have more crewmembers.  There is talk of keeping two Soyuz craft there, allowing more crewmembers to be there, but that costs money, which Russia does not have.  We’d have to foot the bill for that.  And besides, that still does not solve the supply problem.  We’d have to devise a new supply craft.  But, wouldn’t that be like making a new crew vehicle?   It seems that we’ve got ourselves into a fine mess.  It would be silly to back out now after so much time and effort, and at the cost of so much else that has been put aside to fund this program.  On the other hand, it is stupid to continue if we can not afford to do it right.  And besides, we don’t seem to have any idea what we want to do with the thing once it is built!

Now, don’t get me wrong.  I think that having a space station is a good idea.  Also, an international cooperative venture is a very good idea.  However, a space station done wrong is worse than none at all.  It is a waste of money.  That’s just my opinion. 

-Astroprof

A few days ago, one of my students was asking me about the North Korean Taepodong-2 Missile that has been in the news so much lately. So, that makes them think that I know anything about missiles? Well, I guess that I do know a bit, but still …

Anyway, I thought that I might do another break with my normal posts and say a few things about the Taepodong missile. After all, I’ve done Atlas rockets and Delta rockets here, and I have plans to do Redstone and Titan rockets sometime in the future. However, those rockets are used in space exploration, so they sort of fit with my blog. But, rockets are rockets. When they launch, it makes no difference whether they are putting something into orbit or placing a payload into a suborbital trajectory. What makes the difference between a missile and a rocket is whether or not the payload is a warhead. The vehicle works the same way.

So, on to the North Korean missile. The Taepodong-2 missile strikes me as rather inferior technology to the missiles deployed by most nations. Of course, if the warhead is falling on you, then you don’t really care how sophisticated the missile that put it there might be. The Taepodong-2 seems to be basically two missiles stacked on top of each other. The first stage appears to be heavily based upon China’s CSS-2 missile (a very old, not very efficient, but sturdy design). Stacked on top of the first stage is what appears to be a North Korean No-Dong missile, or something that is merely a modification of one. As with many Russian or Chinese designs, the upper stage is supported by a truss type structure above the lower stage. Most American missiles at least cover such support structures with farings or cowlings. This is supposed to improve aerodynamics, and gives a much more aesthetic look to the rocket. Also, enclosing the structure keeps wildlife from trying to nest in the rocket prior to launch (a problem when launching from Florida). Simply stacking rockets, though the basic idea behind staging, is not as efficient as designing specific stages to fit seamlessly with the booster. This inefficiency could significantly reduce the performance and range of the Taepodong-2 below the figures often bandied about. A solid fueled third stage is believed to be capable of being fitted on top of the second stage. This would give either greater range or greater payload capability. The maximum anticipated range is in the neighborhood of 9000 km. This permits a warhead delivery nearly 3/4 way around the world from North Korea (Oops.  As a reader pointed out, this should be halfway around the world, not 3/4.  Sorry about that.). Both first and second stages are believed fitted with inertial guidance. Earlier versions steered using four steering vanes in the rocket’s exhaust gasses. Later versions are believed to possibly have gimbaled vernier rocket nozzles which can be used to steer. This is a more reliable technique if it works, but far more difficult to implement. Accuracy of the Taepodong-2 rocket is believed to be poor, particularly as the target range increases. At extreme range, it would probably be lucky if the rocket landed close enough to its designated target to do any damage at all, even with a nuclear warhead.

Both the first and second stages of the Taepodong-2 rocket use liquid storable propellants. The fuel is TM-185, a mixture of 80% kerosene and 20% gasoline. The oxidizer is AK-271, a mixture of 73% nitric acid (HNO₃) and 27% dinitrogen textroxide (N₂O₄). These are considered storable propellants because they can sit in the tanks for a while between fueling and launching the rocket, unlike cryogenic fluids such as liquid hydrogen or liquid oxygen. However, these fluids, particularly the oxidizer, are very corrosive and dangerous to handle. Rocket tanks are designed to be as light as possible in order to maximize payload capability (what good is a rocket if all it can do is lift itself off the ground but not carry anything else?). These lightweight tanks, though, are more susceptible to corrosion than heavier storage tanks. According to some reports, the tanks begin to corrode within 24 hours of fueling. So, fueling, removing fuel, and refueling runs a significant risk of increasing the possibility of a launch failure. That means that once fueled, the rocket is generally committed to fly. The corrosive nature of the fuel also means that firing the engines basically wears them out. They need to be rebuilt after firing. Thus, the engines aboard the rocket have never actually been tested. Engines just like them have been tested, but not those particular engines. So, there will always be a question as to how they will actually function in real usage. Thus, though the propellant is “storable”, that merely means that the rocket can be fueled and then held for up to a month or so before firing. The launch facility for the Taepodong rockets is a typical launch pad. This is a surface facility, with gantry and the like. This makes the entire assembly and fueling procedure visible to surveillance. Furthermore, such a facility limits the launches to one missile at a time, and even then only in fair weather. The Taepodong missiles probably can not be launched in the winter months due to poor weather. A surface launch facility is also subject to air raid, and even a very limited air raid would render the launch facility useless for future launches. Such limitations severely restrict the strategic military capabilities of the missile. This is clearly not a first strike weapon, nor is it a particularly good deterrent type missile. At best, though classified as an ICBM (Intercontinental Ballistic Missile), it is really a terrorist weapon.

The warhead payload of the Taepodong-2 is believed to be in the 500kg to 750kg range. Such a payload could allow the missile to carry a fairly large conventional warhead, but the poor accuracy of the missile would make such a warhead totally ineffective. While a nuclear warhead can be fabricated to that mass specification, it is difficult. Nuclear weapons, particularly fission weapons, are not difficult to make. Any second year physics student knows the basic theory. However, getting the raw material is much more difficult. This is where the bottleneck comes in. North Korea may have overcome this problem, and sufficiently enriched fissionable material is likely to be in their hands. However, while making a fission device that will explode isn’t so tough, making a small and high efficiency one is difficult. While it may be possible for North Korea to make nuclear weapons, it is much harder to make them light enough and small enough to fit on top of a Taepodong missile. I would think it unlikely that they have that technology at this time. Without a nuclear warhead, though, the Taepodong missile is very little threat other than to peace of mind. At best, they could fire one missile, which would likely miss the target and simply blow a hole if some farmer’s field somewhere. The international response would be immediate and decisive. North Korea would then be unable to launch any more missiles from its sole launch facility.

The Taepodong-2 missile limitations reminds me a bit of the Soviet R-7 missile. This rocket was also billed as an ICBM, but it could not be fueled and left to sit around, it took nearly a day to prepare, could only be launched from select locations, and could not be housed in silos. The R-7 missile, though, became the basis for almost all Soviet and Russian space launches, evolving into the Soyuz rocket. The Taepodong-2 is a very poor missile for military purposes. However, with a third stage fitted, the Taepodong-2 may be capable of lifting a satellite of 100kg to 500kg mass into orbit. Personally, I’d consider this a far better use for the rocket, anyway.

-Astroprof

I was bored this afternoon, so I decided to blow up the Earth.  OK, so I didn’t really blow up the Earth.  I only did it on paper and with a calculator.  But, with the mood that I’ve been in today, it sure felt good.

In Star Wars, the Death Star blows up Alderaan.  In The Hitchhiker’s Guide to the Galaxy, the Vorgon destructor fleet blows up Earth. Now, I can really understand blowing up Earth.  But, just what would it take to blow up a planet like Earth?  I wanted to know the energy needed to do that, so I pulled out some paper and started calculating.

Basically, the biggest problem with blowing up a planet is gravity.  If you only break the planet apart, then the gravitational attraction of all the pieces will pull them back together.  Something very much like this appears to have happened Uranus’ moon Miranda.  It appears that something pretty large slammed into it and blasted it apart.  Gravity, however reassembled the moon, but not the way that it originally was.  It is blocky and has a tortured surface.  It was reassembled, but part of the moon that used to be on the inside is now on the outside, and part that was on the outside is now buried deep in its interior.  Miranda is totally scrambled up!

Now for the purposes of the Death Star, whose primary function is to kill everyone on the planet, this would be most sufficient.  If we were to blast the Earth into a bunch of smaller chunks that remained in the general area and eventually reassembled, then everyone would die.  Each little chunk would have too little gravity to hold onto an atmosphere, and any air in the asteroid field would pick up enough solar energy to achieve escape velocity and leave.  Water can not exist as a liquid in a vacuum, so all the Earth’s water would evaporate and go the way of the air.  So, when the Earth reassembled, all mixed up, then it would have no air or water.  And, of course, everyone would be dead anyway.

However, in The Hitchhiker’s Guide to the Galaxy, Earth is being obliterated to make room for a cosmic bypass.  You wouldn’t want any pesky asteroid field left behind, and you wouldn’t want it reassembling itself, either.  So, you need more energy.  The Vorgons would have to atomize the Earth, blowing it to tiny bits, and each bit must have enough energy to get away from the swarm of other bits without being pulled back by gravity.  So, the minimum energy needed to do the job would have to equal the gravitational potential energy of the Earth itself.  So, how much energy is this?

Well, what I did was to figure out how much gravitational energy is released in assembling Earth in the first place.  To do this, I needed some data on the Earth.  Our planet is not a single solid rock.  It has several significant layers:  the inner core, the outer core, the mantle, and the crust.  The mantle can be further subdivided, but for the sake of my calculations I didn’t bother with that.  Each layer has a different density, and this changes the calculations of gravitational potential energy.  Really, the density varies with depth, but for the sake of simplicity, I assumed each layer to have constant density.  The inner core has a density of about 13 g/cm³.  A assumed an average density of about 11g/cm³ for the outer core.  The mantle actually varies quite a bit in density, with the higher density part lower in the Earth, but I assumed an average value of about 4.5g/cm³.  The crust is ordinary rock of density about 3.5g/cm³.  I also looked up how thick each layer was.  I then computed the potential energy by integrating over each layer of the Earth.  I can’t figure out how to make the calculus equations appear in MSN Spaces (Now why don’t they have an equation editor, I wonder?).  So, I won’t give the equations.  I suppose that if you really want, I can make a jpg of them equations and post that, but I figure that most of you don’t care.  Integrating for the solid inner core was pretty easy.  However, the equations got a bit tougher when integrating over the outer layers.

The end result of four and a half pages worth of calculating (of course, I wrote big) I came up with an answer.  Now, I made lots of assumptions and approximations, so the answer won’t be exact, but it should be in the ballpark.  What I came up with was 3.75x10¹⁴ joules of energy to blow up the Earth.  That is a lot of energy to come up with.  In fact, it is completely unreasonable to get this amount of energy in any conventional means.  About the only way of getting that much energy on site to use to blow up a planet is to carry a sufficiently large hunk of antimatter.  For those of my readers who don’t know about antimatter, every particle of matter has an antiparticle.  The antiparticle is essentially just like the particle, except that it has opposite charge.  That isn’t really what makes it an antiparticle, but it is the easiest way to think of it.  Clearly, that isn’t what makes an antiparticle, because neutral particles such as neutrons can also have antineutrons.  One interesting thing about a particle and its antiparticle is that if a particle and antiparticle come together, they annihilate each other, converting both particles completely, 100%, into energy.  The amount of energy released is given by Einstein’s famous equation:  E=mc².  Here, the mass is the combined mass of both the particle and antiparticle.  What will generally happen is that the particle and antiparticle will annihilate each other to produce two gamma rays moving in opposite directions.  However, one can imagine that a sufficiently advanced technology might be able to harness this energy to do something with it.  In Star Trek, this energy is used to warp space so that starships can move between the stars faster than light.  Presumably, the Vorgons could use this energy to blow up Earth.  So, how much antimatter is needed?

Once again, we can use Einstein’s E=mc² equation.  We know that E is the energy needed to blow up Earth, 3.75x10¹⁴ joules.  The term c is the speed of light, given by 3x10⁸ m/s. So, all we need to do is solve for m.  Doing so, we find that we need at least 4.16x10¹⁴ kilograms of antimatter.   Wow.  No wonder it takes a whole Vorgon fleet to do the job!  How big would such a hunk of antimatter be?  Well that depends upon what type of antimatter.  The easiest thing to get would be antiprotons and positrons (antielectrons).  Together, these would make antihydrogen.  Assuming that liquid antihydrogen has the same density as liquid hydrogen, this means that you’d need a spherical tank 22.5 kilometers in diameter to hold all of the liquid antihydrogen!  OK, so that’s not practical.  Hmm.  Well, you could try something else.  Antiprotons and positrons are not the only antiparticles.  You can also make antineutrons.  Again, assuming that fusion of antimatter works like fusion of matter, you can fuse the antihydrogen into antihelium, and fuse that into anticarbon, etc, just like what happens inside a star.  By the time that you reach iron, though, it takes more energy to fuse that you get out.  So, lets assume that you eventually make a large chunk of antiiron.  A number of years ago, the author Bertram Chandler wrote a series of science fiction stories about a fellow named John Grimes.  In some of the later stories, he used antiiron in spaceships.  So, how much antiiron would it take to blow up Earth?  Again, assuming that antiiron has the same density as ordinary iron, we find that you’d need a cube of antiiron 3.75 kilometers on each side to do the job.  Break that into manageable chunks, and you see why the Vorgons needed the fleet just to carry each, still quite large, piece of antiiron.

Anyway, that would be how you’d blow up the Earth.

-Astroprof