Escaping a gravity well is never an easy proposition. Unlike other kinds of wells there are no walls, so your options are ilimited. Over the years we humans have experimented with a variety of ways of getting out – with varying levels of success.
Trying to build your way out was first attempted – at least allegorically – with the Tower of Babel which (again allegorically) did not go well. Even with today’s engineering, it remains a dubious prospect. The relatively new Burj Khalifa in Dubai has managed to scale only 830 metres. The official defintition of where ‘space’ starts is 100 kilometres (or 60 miles).
Firing yourself out of a cannon or strapping explosives to your throne in the case of Wàn Hù, generally described as a minor official of the Ming Dynasty circa 1500, is similarly fraught with problems. See the Mythbusters episode Ming Dynasty Astronaut to see how that worked out.
Even if you do survive the initial blast, the huge acceleration required to achieve a projectile escape velocity of 11.2 kilometers a second from sea level will kill you anyway. And there’s also an issue of atmospheric drag – since the air in front of you will be superheated, your already Gforce-demised self will get cremated on the way up.
It would all be so much easier if someone could just throw down a rope. Various people have been attributed with first thinking up the space elevator – but it was probably Konstantin Tsiolkovsky – involving getting a base station into geostationary orbit and then lowering down from it kilometre-lengths of a carbon nanotube cable that we’ll be inventing any day now.
- The last Saturn V launch (with Skylab 1) in May 1973
So for the moment at least, we are stuck with good old-fashioned rockets – for which we can also thank Mr Tsiolkovsky, amongst others. Although achieving a zero to 11.2 kilometers a second velocity at sea level will kill you – if you can get a bit of altitude at a lower acceleration rate, the escape velocity from that altitude will be lower. So as long as you can launch with enough fuel to keep gaining altitude, you can keep on applying this logic until you eventually escape the gravity well. We’ve done it with robotic spacecraft, but we’ve never done it with people.
Before I start sounding like a Moon landing denier, remember the Moon is still orbiting within Earth’s gravity well. Lagrange points 1 and 2, about 1.5 million kilometres away mark the edges of the Earth’s gravity well. L2 is perhaps the better target since you could use the Earth’s shadow to reduce your exposure to solar radiation. At 1.5 million kilometers, it’s about four times the distance to the Moon, so a one month round trip maybe. It’s still challenging and you’ll still collect a hit from cosmic rays – but nothing like the potentially suicidal two year round trip to Mars. So, if we can get past this obsession with landing on things, wouldn’t it be a wothwhile goal to try and finally get someone out of the well?
23 Replies to “Astronomy Without A Telescope – The Only Way Is Up”
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Admittedly reaching altitudes of near space is not the same as placing an object in orbit.
However access to those regions, and beyond, is of grate interest for many applications beside a space elevator.
A super tall building providing infrastructural support for large industrial atmospheric activities like a super tall antenna or the facilities for CO2 sequestration are just a couple of important examples. Other interesting applications are those of a launching platform for long distance aircraft gliders or for chemically powered space shuttles or perhaps real-estate in the shape of space utility barges, perhaps to accommodate photovoltaic panels.
Such examples could fit within elevations of a few kilometers, to the Karman line, and further. If reaching altitudes comparable to those proposed by the CNT tether based space elevator, our proposed system would provide the same functionality of giving enough impetus, to undocked satellites, to stay aloft without major effects of Earth’s gravity.
Under the general name of SpaceShaft a new method of construction and simultaneous transportation is being proposed that can be tailored to the specific needs of a different space elevator. This method of construction makes use of buoyant building blocks, which by constantly cumulating upthrust within the planet’s dense atmosphere during their deployment, a chimney like building can be constructed, and simultaneously have it working as a high capacity transportation system. Once beyond the regions of significantly dense atmosphere, it shall behave as a spar-buoy and therefore its upper sections will emerge into space.
The upthrust of such a system would only be limited to either, the diameter of the structure at low altitudes, or the medium in which it is assembled, i.e. some sections could be also assembled under water and therefore increasing the buoyancy force by a factor of 1000 times.
One question we really need to ask ourselves when considering the current political climate in which less and less money is becoming available to many space agencies is; are we ever going to have a space elevator if for whatever reason the CNT tether becomes a non viable technology for the near future? Shouldn’t we have a plan B?
I have been musing on an alternative to rockets.
I would be interested in what others think of this.
Essentially Im thinking Hydrogen Balloons.
Hydrogen because you want to lift enough of it to space to use for further missions as propellant and because its relatively cheap and easy to obtain.
Current altitude records for Balloons are in the order of 30km. At this altitude the (membrane) typically bursts from the expanding gas.
But in a craft designed to break this barrier you would be (using the expanding gas) to power your rockets. Gradually switching from lift provided by the pressure differential to direct use of the propellant.
Hydrogen however is difficult as it leaks through everything, so containment becomes a technical challenge. One interesting approach might be to use a Aerogel layer filled with Xenon gas.
Aerogel being only slightly heavier then air is very lightweight so the Surface Volume required for containment (the membrane) can be quite large.
Lastly, using a magnetic field for containment and or lift has some merit as an idea.
The problems are material sciences, How to make a container strong and lightweight enough to withstand the Pressure difference as you ascend. Our advances in this field however have been tremendous. From Aerogels to nano-technology there should be a viable solution. The question is weather anyone thinks to be a viable idea worthy of funding and research.
As opposed to the metal firecracker idea. 🙂
The altitude record for an unmanned balloon is 53.0 kilometres. It was reached by a Fujikura balloon with a volume of 60 thousand cubic metres, launched in May 2002 from Sanriku, Iwate, Japan. (Wikipedia)
Halfway there.
There is of course the old idea of a (vacuum balloon) but I dont see the point as the purpose of this is to actually lift surplus hydrogen and oxygen as fuel into LEO. Or possibly even to recombine it back to Water to use as life support in a space habitat.
Just musing. 🙂
Damian
oops check out the proposed system at: http://spaceshaft.org
Damian, bravo to your suggestions you are not that far from what we are building
A balloon, or dirigible-drone, could loft a sizable telescope to the upper stratosphere. I am looking at the latest issues of AAAS “Science,” and there is a little short about a guy who is planning to sky dive from 36km up. I think you have to be crazy to want to do this, but… . If the purpose is getting above most of the atmosphere of the Earth I could well imagine putting some creative telescope systems on large dirigible-drones that might serve just as well as Hubble Space Telescope.
If your intention is to get into Earth orbit or beyond balloons do not help a whole lot. Balloons operate by buoyancy and they can’t reach altitudes higher than where the atmospheric density is less than the density of the lifting gas. However, Damian mentions the vacuum balloon, and this help a bit in getting into space. Of course the problem with that is there is nothing which maintains a pressure to hold it. Making it out of rigid metal defeats the purpose of the balloon. However, suppose the skin is made of a diamagnetic material. This is a material which repels magnetic field lines. You then provide a magnetic field, say with a Helmholz coil (a big one!) interior to the bag and the diamagnetic envelope expands out. This creates the vacuum and up you go. There is a rub with the idea, for the magnetic fields intensity has to be huge to provide the energy E = H^2/2 requires to provide the pressure p so that E = pV, for V = volume of expansion. So given the power source probably required, that it has to be lifted up, the lack of materials sufficiently diamagnetic and so forth, this idea is impractical.
So what next? That is another crazy idea. Instead of using hydrogen as the lifting gas, we use positronium. Now again this might not be that practical, but it is an entertaining idea I have. The idea is this. The anti-electron or positronium and the electron form a sort of hydrogen-like atom with a mass of 1MeV. A proton is 938MeV so the hydrogen atom is nearly a thousand times as massive. A buoyancy calculation reveals that a positronium balloon could be buoyant up to 1000km. The first rub with the idea is that the positron and electron tend to quantum transition into two gamma ray photons. That is not good. So one must then provide an electromagnetic field which keeps the electrons and positrons apart in quantum levels of high Rydberg numbers. The envelope of the balloon could be made of mylar or some similar metal surface which acts as an EM resonance cavity and the EM field is sustained. So there are some rubs with the idea: We need to generate a lot of positrons and stability of positronium.
Let me assume that we have these issues solved, or that we can get the diagmagnetic vacuum balloon working. This still does not get us into orbit of out of the Earth’s gravity well. This just permits a balloon to bob around at in the ionosphere. Suppose we have a high powered laser and a light sail or mirror on the balloon craft. Once the balloon has cleared about 75km up we turn it on and use the remaining 1000km or so of buoyant lift to accelerate the craft with photons. With an acceleration of a = 20m/s^2, in 450 seconds you have approached ~ 6.4km/sec and from there the laser system can continue to push the craft upwards to escape velocity. The lifting gas overcomes one-gee of gravity force long enough so that a two-gee force from a high powered laser could push the craft to escape velocity.
LC
@ Lawrence B. Crowell,
I would like very much to know what brand of coffee do you drink? I could do with some of that! 🙂
I think you guys missed the sarcasm there.
Look, I admit that at first burn a rocket sounds like a crazy concept too:
“- I wish we could get to orbit…
– But we can. Here, just take this stick and aim it away from me; light it up and it’s throwing away stuff to go forward.
– What?! That can never work!
– But it’s throwing massive things, (mumble) hot gas actually (mumble), really fast.
– Throwing … massive … hot gas???
– … oh, and by the way, did I mention you can’t do it all in one go? You also throw away the engines and start all over again with a smaller stick. In fact, you do that a number of times.
– It’s like a stacked Russian doll?
– It’s a Matryocket, baby!”
…, er, anyway, fact is that a rocket is an eminently practical thing. We already got climbing the gravity well licked.
New methods may be useful some day and eventually cheaper. But don’t bet on it. (In fact, very few does.)
They have to make out against the competition, which is observably getting cheaper by orders of magnitude as we are speaking. (Compare Space-X launching costs against NASAs.) While the alternatives have yet to materialize beyond feverish dreams.
Compared to flight, the technical development is all backwards. There they started with flimsy balloons and eventually developed reliable and dependable aircraft, because they had to.
Here we have reliable, dependable space craft which already has spun of a tourist industry. And now people wish to invent flimsy balloons for reasons that are still to be determined. [CO2 sequestration in the upper atmosphere, where it is at it’s scarcest? Why would anyone even imagine that?]
Good luck with the practicality and ROI of that.
I’ll agree with the post that visiting L2 would be a good thing. I’m raring to go! Who knows that may be collecting up there? Old Earth/Moon ejecta, interstellar stuff, PAHs on dust, …
Not space elevators and balloons, that’s for sure. 😀
To not douse the spirits of the willing:
There are many actual unlicked problems of space flight. Those concerns all the rest of it. 😀
First, we would like to have really fast rockets to travel the solar system fast enough, to avoid problems of sustained 0-g, sustained radiation and sustained boredom. People and money is working on that, but not nearly enough.
Second, we know how to ascend the gravity well good enough, but we have a really lousy handle on how to descend it. Air braking to orbit can be used in some places, but not everywhere. (The above engines would help, though.)
And no one knows how to land large masses on Mars. Here space elevators and balloons could help one day, provided they can be constructed out of local materials, say from Phobos minerals.
HIC SVNT PECUNIA
I just love the image!
Brian.
Positronium Balloon, I love it. 🙂
Great Post Lawrence.
Any technology where we can manipulate atomic level forces in elements like hydrogen is a step in the right direction. Ionized Argon or Xenon Gas could work as a container for hydrogen. If we could bottle a hot Plasma in a container that is another way to go up.
But back to whats possible now. Why think of the balloon as having to ascend lazily upwards? It can be accelerating from sea level with assisted lift from the beginning. Even with an air breathing engine to begin with.
IF your craft is accelerating all the way to 50km its probably halfway to escape velocity. Past a certain point (perhaps 80km) you can switch to Ion propulsion for better fuel efficiency. Possibly dropping mass in terms of a booster aircraft.
By this stage you will have burnt up most of the oxygen but there should still be enough Hydrogen in your tank to be used for other purposes in LEO.
This is the Purpose of my idea, Nasa’s new vision is for LEO re-fueling, this is me thinking about how to get Hydrogen fuel up there for that purpose. It does not have to be pretty or carry people.Nor indeed return to earth.
I would argue that the Framework supporting such craft have a dual purpose, as solar panels or habitats from the outset. It kills me that our present technology favors discarding most of what actually goes up.
High altitude orbital platforms for telescopes and research are also an interesting idea. Certainly not beyond our present technological capabilities.
If we are talking private industry, why not explore such notions? The chemical rocket is a concept born of dual purpose research, as a delivery system for bombs first and space exploration second.
Other ideas were never explored as they had no military advantage. Now is the time to actually consider such alternatives. Regardless of how (out there) they may seem. 🙂 The space shaft is one such idea, and I like it a lot, but it megalithic nature is one that becomes its biggest detractor. Its hard to imagine such a massive construction.
Damian
Here’s a question for the technical bods, has anybody actually done the maths (strength to weight ratio) for C60 nanotubes.
A space elevator needs a tether (rope) 23000 miles long, I worked out that a steel rope over 20 miles long would break under its own weight. Also any tower over 20 miles high would collapse under its own weight even if it was built on solid granit the rock beneath it would be crushed.
Yes I know these figures can be improved a bit (maybe doubled) if the tower or tether was shaped like a long cone instead of a cylinder but the fact remains we are still only a fraction of a percent there.
Now where’s that coffee
Alan
The idea of the positronium balloon is pretty off the wall. The other problem is that even if you can keep the electron-positron annihilations from happening with an EM field, the positrons will still annihilate with the electrons in the material of the outer envelope. So for a number of reasons I suspect the idea will never work. With a laser propulsion a more ordinary hydrogen balloon might serve. Once the balloon has cleared 30,000 m, the high powered laser would accelerate the craft from there with a force F so that F/m > g, and you then push the mirror-sail craft outwards from the ground after the balloon is detached. The main function the balloon would serve is to loft the craft far enough so air drag is not a competing factor with the laser acceleration.
There are reasons why one might consider something other than rockets. Using Newton’s third law of motion you can derive the so called rocket equation. Newton’s third law tells that
d(mv)/dt = 0.
Now if we break m as m = m – dm + dm where m for mass of the rocket and dm mass of an increment of ejected rocket plume and v –> v – dv for the rocket velocity and the velocity of the rocket plume gasses we get
Vdm = (M – dm)dv (set dmdv ~ 0)
or that
dv = V(dm/m)
so the velocity of the rocket ends up after integrating this as
v = V log(m_i/m_f)
for V the plume gas velocity and M_i the initial mass and m_f the final mass. The main point is that if m_i = 10m_f the velocity of the rocket is about 2.3 times the plume velocity. The logarithm is a “killer,” for it means the maximum velocity grows slowly with m_i/m_f increasing. Physically you are using most of your energy to carry the fuel up with you, which means a very small percentage of the energy you generate actually goes into the final kinetic energy of the payload. However, for considerable time in the future I suspect rockets will be the only way to send spacecraft up.
The space elevator idea is of course one of those ideas. The biggest problem is I fail to see how we can get Jack’s beanstalk to grow up from the ground without collapsing. So the best option is to build it top down. So suppose we are able to adjust the orbits of asteroids and we maneuver one into Earth orbit and gently lower it so as to park it at geosynchronous orbit. You then build down from there. If this is a carbonaceous asteroid the carbon nanotubes and fibers are fabricated and “woven or spun” downwards, while at the same time the anchoring mass at a radius greater than geosynchronous is constructed. Eventually the whole construction reaches close to Earth and the elevator is completed.
This is of course a huge project. This would require a considerable fabricating facility be placed on the asteroid you park in geo-synch, and manipulating the orbit of a hefty asteroid this completely a daunting task as well. So I don’t expect to see a space elevator in my lifetime, or probably not in this century.
LC
Giggle Snicker Chuckle I have to say the Positronium idea made my morning.
Naive questions re: space elevators, towers, carbon nanofibre cables etc.
I’ve been around a lot of St. Elmo’s Fire.
Given that the fairweather field causes a huge potential between say ionosphere or exosphere, let alone through troposphere, to ground is there an intrinsic problem with respect to conductivity of carbon when placing a structure completely through this field? Would it be vulnerable to thunderstorms or just be a giant lightning conductor – which is of course by definition unharmed by a lightning strike? Or if this is a potential problem is a technical solution already in hand?
Blad – the amount of current in the Space Elevator tether will likely be determined by carrier deprivation around it – the coupling between a small physical object and a sparse medium is not so good.
Otherwise, while some CNTs are good conductors, the spun aggregate cable will be much less so. It is also a very loooong resistor, so resistance is high. (the correct version of ohm’s law to use is local field gradient divided by the resistivity of the material, really)
So as far as reacting to the potential differences, no problem.
Lightning strikes are a different matter. There are two mitigations for that. First, the anchor ship will stay out of weather’s way. That’s not a difficulty today, since ship can travel faster than weather systems. (They only get into bad weather since they can, and since they have a delivery schedule to keep).
However, if a local weather cell is forming around the anchor point, it will have to be discharged. Electrostatically charged clouds can be detected and measured, and an ionizing nanoSecond laser pulse will ionize a seed path for lightning to occur – somewhere else. (Read about electrolasers for references on that)
Wow – interesting ideas here.
It’s not a show-stopper necessarily, but consideration needs to be given to the fundamental risk underlying the construction of either a space elevator or tower to enable access to very high altitudes.
That is – the catastrophic level of damage that could result if they break or fall over (e.g. I’m thinking of Kim Stanley Robinson’s Red Mars novel where the space elevator cable is cut).
The question I have is with the mechanical stability of the elevator. The object has its center of mass at geosynchronous, with a ballast mass further out and a long tapering mass pointing to the Earth. In principle every point on it should have the same circular frequency equal to the reciprocal of an Earth day period. Now the problem is that there are perturbations, such as lunar gravity. Now this object has for any length a frequency for vibrations given by f = sqrt{k/m}. Since the object tapers the frequency of vibration increases towards to end of in near Earth. So we might think of this as a set of harmonic oscillators with increasing frequency towards the tip near or at the Earth’s surface. There is a familiar object with this property called a bullwhip. This feature means that any small perturbation on the object gets amplified near the tip. Stability is a critical issue it seems to me, or else this object could start whipping around uncontrollably.
LC
ok, I have to bite. 🙂
Using a construction strength of 25 GPa-g/cc (the tether-to-payload ratio is about 250, so a tether that can lift 20 tons will weigh 5000 tons.
That’s very far from the mammoth SE that are often depicted in Sci Fi. If the entire SE falls down (I’ll get to that in a sec) then the 5000 tons are spread around the equator, for an average of 125 kg per km – hardly a calamity.
Even more so, only the portion under the cut point can fall down (the rest flies off) and likely the break point is low. Even if high, simulations show that the tether breaks up before it completely collapses, and only about a quarter of it ends up on the ground.
Finally, at that mass density, and since the tether is shaped like a ribbon, it won’t get through even the highest reaches of the atmosphere.
So seriously, no worries.
moving on the LC’s comment:
a) – the CM is not a GEO, but that’s just a technicality.
b) – the dynamic simulations of the tether in place, under various perturbing forces, were done numerous times. (Follow the SE conferences for more info, or contact me) The bottom line is that this is a very long regular pendulum, with a twist, (tied to the ground and falling INTO the sky), and whatever you do to it, it behaves like a very long pendulum, around the equilibrium point, which is straight up. Meanwhile, the ship-borne anchor I mentioned before does active damping (the main modes are many hours long) and takes energy out of the system.
c) – the dynamic simulations of two other sets of scenarios have also been done – during deployment, and during collapse. The collapsing one does the “bullwhip”, which is why it breaks up even if the initial cut-point is high up (say near the counterweight) During deployment, just before being attached, the SE is at its most unstable position, and actually has a total energy greater than zero, which means if you lose the local minimum, the whole thing can escape. 🙂
If the CM is above GEO then you would have some net tension which must be sustained by anchoring it to the ground. I would imagine it could not be to far out from GEO, or else that tension would be huge.
I think the idea of a laser propulsion is likely to work before a space elevator. If a sail craft is lofted above most of the atmosphere by a balloon, then a laser is turned on and directs photons to the mirror, which are then directed back to the laser. If done right the mirror on the craft and the mirror in the laser can act as a single laser cavity. So the coherent states of the laser produce a pressure. As energy is fed into the laser it produces photons which are a sort of gas filling a cylindrical volume between the two mirrors. The increase in energy will by basic thermodynamics result in pressure which then expands the volume by pushing the mirror craft outwards. It is a laser version of a piston and cylinder.
LC
@ CEB
Thank you.
This is wonderful stuff.
LC – for the CM argument, do an exercise yourself – take two point masses, connected by a tether with a midpoint at GEO. You’ll find out that even though the CM is at GEO, the structure is not geo-stationary, since the two half-tethers don’t contribute opposite forcesto the system if it is geo-stationary. No big deal though – the CM of the SE doesn’t have to be at GEO for this discussion.
The tension wouldn’t be huge – that’s also a pretty easy calculations. Actually, the tension is tuned to be just a bit higher than the load you want to climb up the tether.
The expanding-resonant-cavity you describe is an interesting system – I saw a presentation about it at a conference some years ago. Still, even if you do the balloon trick as “stage 1”, you’ll still need to pull a full 1 g to go further, and that’s a LOT of photons…. At that presentation, they were describing a milli-newton system. I don’t think it is applicable for a ground-to-space launcher.
Still – let’s weigh each system on its own merits rather than comparatively, since they don’t really compete.
I suppose for a very long tether there is set up a differential gravitational force on the two ends. I have not spent a lot of time really pondering these issues.
With the laser driven sail this might only potentially work if you build up a photon gas, if we think of it that way, as photons in a cavity between the mirror on the ground and on the craft. We might then think of a single photon as bouncing back and forth between the mirrors many times rather than reflecting just once. This still requires a very high powered laser system though, and alignment between the two mirrors is a critical issue. I agree the idea is not something I expect to see any day soon.
I suppose I could throw out the idea of anti-gravity. A spacetime curvature which defocuses spacetime paths (geodesics) in a hyperbolic curvature will result in anti-gravity, and can also be used to set up warp drives and worm holes. However, the source field for the curvature has negative energy conditions that violate the Hawking-Penrose conditions. These sources are ultimately quantum mechanical, and the quantum field theory for such sources has enormous pathologies. So anti-gravity is beyond the domain of practical difficulty and probably in the domain of impossibility.
LC