Much as I love to cheer for British engineering, I don't understand the logic here. A rocket would require an expensive inspection before reuse but a spaceplane wouldn't? Why?
Also not one SABRE engine has even been built yet, whereas SpaceX has got very close to landing their rockets.
I'm no rocket scientist but I could imagine rockets having a place in regular space travel. Lets assume that we can harness solar power efficiently and safely store the extra energy in hydrogen and oxygen gas. Then let's say that we could construct sturdy and modular components that can be disassembled and re-assembled at some kind of orbital station, so that the boosters that take people into orbit for whatever reason could be rebuilt in orbit to carry a load of asteroid-mined metals back to the surface.
Again, I don't know any of the mechanics or physics, but if energy was abundant and parts could be reused, would rockets really be all that bad?
Fuel is a small part of the cost of a rocket, most of the cost is in the engines and structures. Cheap production of hydrogen or oxygen is unlikely to make things much cheaper.
Also, any mass left over at engine cut-off requires a large quantity of fuel at lift-off and possibly necessitating a larger more expensive rocket. This would make re-purposing of boosters in orbit less likely.
I was hoping the article would talk about space elevators, and not space planes. I'm eagerly awaiting materials science and geo-politics to mature enough to allow the construction of space elevators.
I think the problem with space elevators are not as much with the materials but with the logistics of deploying that. How do you get the cable up there? You can't just shoot up a rocket with a cable attached and expect the cable to stay upright: it would fall down unless you give it horizontal speed. But if you do that, you'd probably end up orbiting the Earth and tying it up with the cable.
The other option would be dropping the cable down, but you'd probably end up with a similar problem. I'm no physicist, but I'm pretty sure that dropping that amount of mass would shift the center of mass of the satellite-cable system and mess with the orbit.
Even if you manage to deploy the cable, you'd still have the problem of the counterweight. I've read that proposed solutions include a captured asteroid (we've just been able to land - or crash, depending on how you see it - in one), a space station/spaceport (that's definitely not cheap), an extended cable (which probably would require even more complex materials) or junk from the construction (still the same problem).
And we still haven't got to the point of security. How do you keep things (space junk, satellites, meteors) from hitting the cable? What would we do if several kilometers of ultra-strong cable fell down into the earth?
I think that space elevators are a nice fantasy, and just that. When we have mature enough materials and geopolitics, we'd probably be better off using them on other methods that seem to be far more viable.
> You can't just shoot up a rocket with a cable attached and expect the cable to stay upright...
Well, actually...
Package your cable up, launch it, move to geosynchronous orbit. Start deploying your cable. Once it gets long enough, say a few kilometres long, tides hold it rigidly pointing towards Earth. You solve the counterweight problem by also extending a cable outwards from your launch vehicle, so keeping the centre of gravity still. Eventually the bottom of the cable reaches ground level and you're done. On the plus side, you now also have a 36,000km long cable extending past geostationary orbit, ideal for interplanetary launches.
> What would we do if several kilometers of ultra-strong cable fell down into the earth?
Not much. If the point at which it's severed is low, the lower part will just fall down and you pick it up and weld it back on. If it's a bit higher, the lower part falls down and burns it. If it's a bit higher still, it goes into orbit.
People have been thinking about the engineering and geometry of space elevators for a long, long time...
The first issue would be touchy, I think. You'd have to find a way to deploy gradually the cable, or else each end would gain really high speeds that could break the cable when it stops deploying.
Regarding the second part... If the cable is severed, the lower part goes down and the upper part goews away as it does not have an anchor on Earth anymore (I think). Either way, you lose the cable. If it's a bit higher, maybe it doesn't burn up completely (for example, in Spain we've recently found space junk landing almost unharmed in a field [1]). And if it's several kilometres long (just a few hundreds) it could cause considerable damage.
>You solve the counterweight problem by also extending a cable outwards from your launch vehicle, so keeping the centre of gravity still
I don't follow. If you didn't do this, wouldn't your centre of gravity still remain still? Just start at geostationary and make sure you have enough mass to act as a counterweight already on-ship (doesn't have to be in the shape of a cable). The center of gravity will remain in geostationary, the cable will reach the ground, and the ship/counterweight will end up at just the right height to balance it.
No, it wouldn't. As you extend the not inconsiderable mass of the cable towards the earth, your centre of gravity will move inward with it. Assuming your ship massed nothing compared to the cable, then the centre of gravity will be at the midpoint of the cable.
For the space elevator to work, the centre of gravity must be precisely in geostationary orbit (otherwise the entire elevator will drift relative to the ground).
You could achieve this by having a massy ship, and then carefully moving the ship outwards as you unreel the cable. But it's easier to have two cables. It also solves some other engineering problems, such as reaction effects as you control the speed at which the cable unreels.
> As you extend the not inconsiderable mass of the cable towards the earth, your centre of gravity will move inward with it
What I'm saying is that without firing rockets, there's nothing you can do to change the trajectory of your centre of mass. When you "extend" the cable towards earth, presumably you are pushing on it in some way, and there will be an equal and opposite reaction. You don't have to "carefully move the ship outwards" - the ship (which is inherently "massy", as it has the rest of the cable as cargo) will move outwards by itself, exactly the right amount for the centre of gravity of the ship-cable system to remain in geostationary.
So I still don't see what two cables gets you apart from keeping the ship itself exactly at geostationary, which strikes me as unimportant.
FYI for all the readers here: Carbon nanotubes won't work, the phonon effects (lattice interactions) in that very large crystal usually add up to break them after a few cm. Think of it like like a very narrow and very long tube half filled with water. There are vibrations along the length of it, some big and some small in amplitude. When those random waves in the water tube interact, they can add up, sometimes so much so that they break the tube. I know that is now totally correct, but that's the gist.
Is it not possible to dampen phonons before they will break the thread? You probably don't need to have vary long monomolecular threads, you can have many shorter ones weaved in a thicker rope.
Good question. I am not an expert in this in any way. I'd think that you have to have dampners in the lattice of the crystal. The only way that works is to dope the lattice with either another 4 valence element, like silicon, or to dope the carbon itself with something. The only think I can think of is to modify the isotopes to be VERY heavy which is obviously therefore radioactive and would need to be replaced a lot. If you used silicon dope then you'd reduce the interatomic strength and therefore make the rope possibly too weak to be used.
I thought that the whole point of carbon nanotubes was that they are the only thing with the 'pull strength' (forgetting the term here) that could withstand the tension. If you weaved them, then you would rely on the Van Der Waal forces to keep the tubes together which is much weaker. Also you have to contend with the phonon interactions, anything tangential to that 'plane' has no effect on the strength, you have to be a part of the lattice to effect things.
I used to think space elevators are practically impossible because of interactions with lower flying space objects. Now I'm less sure; perhaps we can have a technology of active avoidance.
Other problems - like an extremely capable cable material, ways to climb up and down etc - are getting gradually solved over last years, so I'm cautiously more optimistic than before.
I don't really see the benefits of space elevators, to be honest. At an altitude of 100km the gravity is still virtually the same. And you still need a huge amount of fuel in order to put your rocket/plane into orbit. Unless you build an elevator with a height of 42'164km (geostationary orbit) - but that seems unrealistic to me.
> Unless you build an elevator with a height of 42'164km (geostationary orbit) - but that seems unrealistic to me.
Actually, much of the point is to build one that is significantly taller than that. The idea is that, if the center of mass sits at geostationary orbit, the elevator doesn't actually have to hold itself up. Centripetal forces do the heavy lifting. Try the wikipedia link posted by gp - the first thing you'll see is a very clear diagram.
I think it's just prohibitively expensive at the moment. 100km (I think it would have to be a lot more anyway) is not much in terms of space exploration. And even then you will always use the majority of your fuel for acceleration towards and deceleration at your destination (however fuel needs for deceleration might be much lower if you can do some sort of atmospheric braking).
It's a slick looking video, but what about reentry? It's not that hard to get a ship up there (the X-15 was flying to the edge of space 50 years ago), and launching like a jet plane obviously has many advantages over rockets, but when it comes back down it's going to hit the atmosphere at a pretty high velocity, unless it's carrying enough fuel to gradually lower itself back into airspace where the jets can kick in. The craft in the video does not appear to have VTOL capability.
But, if they can solve such problems, great. I'm thinking that eventually we'll have some kind of electrical or hybrid mass driver (catapult) system for getting non-human cargo into low orbit[1], much cheaper (and quieter) and obviously could accomplish many launches a day for one-way missions.
You could get a large space station or interplanetary craft up there rather affordably using this approach. Specialized reentry vehicles as well. Launch the parts cheaply, robots assemble the parts in orbit, then launch the humans expensively.
Space planes should absolutely be part of our strategy, but their effectiveness diminishes once you get past LEO. An effective program would have different vehicles for different purposes, using the right tool for each job.
Taking mass to low earth orbit (LEO) is the gating item to increased space travel and exploration; Skylon, SpaceX, Blue Origin, and Orbital Sciences are all focused on reducing this cost. It is quite well understood that outside of plans like Mars Direct and Semi-direct, interplanetary and interstellar travel will require other technologies such as novel electric and nuclear drives, but we are simply not at a point where that is an issue yet.[1][2]
20 years ago, I remember dreaming up a train pulling a cable with a glider at the far end. I'm sure there are many technical issues with this approach, possibly including the cable needing to be incredibly strong, light and flexible. Please tell me it would work, though, as I still enjoy the mental image.
Reaching orbit is mostly an issue of velocity, not altitude. This is why balloons can get very high, above of almost all earth's atmosphere, while being far from orbit. Rockets spend most of their ascent traveling nearly horizontal to the ground (they only go straight up at the beginning to get out of the densest part of the atmosphere).
Exactly. The most expensive part of getting to orbit is circularization. It takes a delta-vee of ~9.4km/s to reach LEO from earth. If you could lift yourself into LEO altitude without any thrust, you'd still have to circularize to the orbital velocity of ~8km/s [!]. That's still the majority of your delta-vee!
[!] I am not a rocket scientist, so I haven't taken into account the orbital velocity you'd get from being rooted on the earth at takeoff, but it should be at most ~500m/s.
The train would glide the aircraft to the mesosphere (50 km or 31 miles) and than rocket to orbit? So you would need 62+ miles of track going hundreds of miles an hour at 45 degree angle with the tow rope?
What about geostationary orbit wrt balloons? Do the balloons slow down horizontally a lot during the ascent? If not, what if we floated a rocket up most of the way and let the rocket do the rest?
Balloons float because dense air in the lower parts of atmosphere pushes them up with buoyant force. They lose the ability to float way before they would reach LEO, let alone GEO.
You've just described a ballocket. You launch a rocket from a very high altitude balloon.
You gain nothing from the height, because you still need to spend ~10km/s getting up to orbital velocity, but you don't have to push your way through the thick lower atmosphere any more. Rockets don't work very well in atmosphere, so you do get fuel savings due to more efficient engines.
I don't know if this has ever been tried for real.
So is infertility in astronauts still a problem? I could be totally wrong, but I was under the impression we haven't solved the problem of increased radiation negatively affecting fertility in both male and female astronauts.
So, with Saturn-5 only 15% was dry mass - and with Skylon 20%? That's 33% increase. Moreover, Saturn-5 was staged - and Skylon is single-stage, and have single stage to orbit with 20% dry mass looks somewhat like a miracle.
www.et3.com gradually leading up to the top of everest, jettisoning the capsule (6,500 km/h (4,000 mph)) to break out of the atmosphere.
I have not done the math, physics, etc on this, but it's an interesting idea worth exploring.
But that said, do we really belong in space when we cannot care for our own? Wouldn't that be akin to giving sugar to ants? only multiplying suffering and cruelty exponentially in space? Perhaps a refactoring of our culture and our methods of using/allocating/expending resources should be our first priority.
If people had waited to leave Europe until the 1970s the culture had been "refactored" enough for the masses, I doubt the world would have advanced as far as it had and the pressure of the population growth from industrialization would have caused some real issues. Actually I think it might be refactored even worse for the masses. Letting the average person go out and build new things helped a lot.
Also, do you really think we can only fix one problem at a time? Did the birth of the transistor stop the civil rights movement?
Perhaps technology has advanced too fast for the "culture".
Perhaps we should design our intentions before we build the tech, and not the other way around. Look at NASA for inspiration on design and forethought.
I don't know why you're being downvoted, those ideas make perfect sense to me. Thoughts about how we want to structure our society should drive decisions on technology, we shouldn't have to adapt society to new technology if the society decides against using it.
The problem with this is you're designing based on your current world view and assumptions. When does this type of planning ever work and actually stand up to 20 years of history? 40? 100? In the 50's the us was DESIGNED around the car and suburbs. That worked well.
> "The problem with this is you're designing based on your current world view and assumptions. When does this type of planning ever work and actually stand up to 20 years of history?"
My logic is based on numbers. Earth Population, Imaginary lines in the sand, War over money. These are not signs of intelligence, especially when they have only 1 planet to survive on that gets more populated every day with little regard to long-term resource management, although I am proud of the Svalbard Global Seed Vault. :)
This type of planning worked for Voyager (NASA/JPL).
fyi: cars suck. Dirty, inefficient, and it follows the same logic of giving every person in a 200 person hotel an individual elevator. It makes no sense, when you can instead design cities and transportation to be like the site I linked above (www.et3.com).
It's their choice though, if they want faster horses instead of cars, so be it.
If they want faster cars instead of et3, so be it.
I disagree but still upvoted this to get it to 0. I find the tought interesting but wrong. It seems more suffering is caused by various misguided attempts at refactoring culture etc and less by technology.
National socialism and communism are two widely known attempts at refactoring culture that has created more misery than all technological advances combined so far.
I prefer a Resource-based Economy (rather than the failed money-strived attempts) that has a central hub for resource-distribution to all humans based on global reserves to raise the standard of living for all instead of a select few which every monetary system has ultimately created.
This would make an interesting topic to discuss how to design this system with our current tech, but that's another thread altogether.
Pushing boundaries technologically has a tendency to pull others along with it, accessing space cheaply would have the potential to create entire new markets and access to new resources all of which would help in the long term everyone else.
Interesting, let's say it should be our first priority, how does that translate into action?
Please remember that mobilizing large amounts of people towards a goal is hard problem, specially when the goal involves copious amounts of research and experiment.
I personally believe people do not deserve to go to space yet.
They haven't mastered the ability to house, clothe, and feed the human family yet, despite having the technical ability to do so. As a result of this, you see the derivatives that exist today. Walk among Miami at night and you see homeless crackheads muttering to themselves while sipping on beer. The conditions that cause a person to do this would be probabilistically lower with a society that cares about one another more [designed-in] instead of fighting amongst each-other for paper slips.
If we absolutely need to go to space, we require research to determine the amount of materials needed to build this track length, and the renewability of those materials in reference to the earth. If this request for the materials meets a certain threshold, it will be dispensed, otherwise, the remaining materials can be reserved for further research to create synthetic alternatives. It helps to have a global database of known resources and their reserves, in fact, it might be a crucial requirement.
Imagine culling redis for this information, it sends a request to the global cybernetic hub, and it permits or denies the request, along with the terminal node you requested it to be sent to...
example: I request 13 Ounces of Gold (AU) at terminal #324-214-495-2341 to perform an experiment. (Since gold is currently in enough abundance for my request it is sent to my terminal as soon as technically possible, and any of the resource I do not use or can scrap back to the global hub, is done so)
So all resources are to be distributed from a central organization. Pray, who will be decide this? How will disputes will be solved when, inevitably, an armed group decides to use resources some other way?
Also, the whole point of leaving earth is leaving scarcity.
There are meteorites with gold, we can and we should mine them as we see fit.
By creating abundance, it lessens the need and purpose for armies to take resources from others. There are no armies I am aware of that invade and conquer for Oranges, but they do for Oil.
To complete your second statement, why do you believe we should mine them for gold when we cannot efficiently manage them here on Earth to begin with?
Also keep in mind that Elon Musk is trying this, but as a bastardization of its potential. What do I mean by this? The shortest distance between two points is a straight line (currently). Look at a map. The cities that were cultivated where they are geographically located are influenced by (Water + Politics + Monetary incentives to build roads closer to smaller cities to draw business (corruption) ) So if this hyperloop does pick up, it will be a horrible expenditure of resources.
The hyperloop could be related to space if they decide to experiment with slightly altering the trajectory to lead into space, giving it an edge energy-wise to break out of the atmosphere.
It would be a horrible expenditure of resources because when you look at a map of where humans designed and placed their cities, they are inefficient for travel and resource distribution.
Example: Manufacturing parts are created in Tennessee, shipped to Michigan, Manufactured in Michigan, and shipped to Florida to sell/distribute.
Instead, why not ship the raw materials to a equidistant manufacturing node/plant, create the material there, then distribute it. It's not done this way (most efficient) because money/corruption incentivizes backwards thinking of keeping "jobs" in sectors that are a waste of energy to complete and continue. Interesting times we live in.
Surprisingly, I actually did a fair bit of research into this field.
Both rail guns and light gas guns cap out at around 6km/s, and you really want 8km/s (more actually, for hypersonic drag loss) for this to be economical. Otherwise you need to launch a large enough rocket to make up the 2km/s difference, and you stuck solving the rocket equation again. Except you've subjected your rocket to 1000g, and the odds of it being reusable are really small.
For rail guns, the plasma discharge on the rails limits your speed. Around 6km/s.
For light gas guns, the working temperature of the gas cannot exceed the melting point of the barrel (or get close), otherwise tungsten/steel will get into the working gas and slow down the speed of sound. With hydrogen+tungsten, also around 6km/s.
The difficulty here is more technical/scientific than engineering. Synchronizing microwave beams is hard, and if you don't you get destructive interference. I don't know if they have solved that problem yet (there have been a few proposed solutions, we'll see if any work).
Edit:
Yes, rail would work great on the moon/mars. Actually there was a movie (Moon, with Sam Rockwell) where fuel is harvested on the moon and shot into orbit. Fun, crazy movie.
Still, g-hardening may not be a showstopper. Artillery shells routinely have electronics in them nowadays. It doesn't have to be reusable, but needing only 2km/s from outside the atmosphere basically.
I think the oil derrick idea was a bit crazy (why make the problem harder than it has to be?), but the concept is sound provided that the rockets are fairly inexpensive.
I think the idea of launching to an arbitrary orbit appeals to engineers, but economically it would be more efficient to launch to a common orbit, and use cheap fuel to change orbits later if necessary. Of course, in-space refueling is only in the concept stage (but getting solved!).
To get above 6km/s, the only way I know of would be to use induction tracks (see Lawrence Livermore patent in doc). The original problem with the EM methods was getting high power switches to work repeatably. They used to cost a fortune, and last only for 10s of cycles. However this problem was solved by a completely different industry in the last couple of years (connecting wind power to the grid), and now you can get them cheap on Alibaba.
The major difficulty, actually, would be:
1) Sound pollution (not many places have high mountains, easy industrial access, and no local population).
2) Hypersonic drag (which is quadratic with velocity at that reynolds number). This is half as hard at 6km/s than 8km/s.
Squished human beings, but good for some cargo. Would be cool if we could shoot fuel and metal into space, but the heat would be through the roof through the first layer of atmosphere.
Also not one SABRE engine has even been built yet, whereas SpaceX has got very close to landing their rockets.