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One compromise solution is to combine the benefits of the BDB with the SSTO in a way that reduces the limitations of both. Truax considered something similar in the early 1960s, if memory serves. Produce a two-stage to orbit, sea-launch vehicle with a take-off mass perhaps 10 times that of a Saturn V.
The lower stage would be constructed from alloy steels similar to those used for submarine pressure hulls and would have a fuelled mass of perhaps 20,000 tonnes. This would make it suitable for submarine-yard engineering techniques and construction cycles would fit in between sub-build programmes.
The fuel would be LoX/Heavy Oil with tanks pressurised with nitrogen and helium. The single pressure fed engine would include a fibreglass ablative lining that would be replaced after each use. The lower stage would achieve a delta-V of about 3km/s and would be used in pure booster mode - i.e. high acceleration, intermediate ISP, no transverse velocity increment. Following use, it would seperate and fall into the ocean, where it would be collected for reuse. The advantage of using steel tanks and engine bells is a good repeatable stress-cycle, so minor refurbishment would be needed between launches, i.e. engine liner replacement.
The upper stage would be constructed primarily from fibreglass composites and fuelled with LoX & liquified natural gas. Its delta-V would be 6km/s and its engine bell optimised for building up orbital velcocity in vacuum. This would be expendable in the traditional sense, but will be engineered to allow canibalisation upon reaching orbit. Its material construction would principally be polymers, which contain chemically valuable carbon and hydrogen for high-orbital manufacturing industries. Electrical components will be designed as modular units that can be slotted out and reused for other applications. Other components such as s-glass fibres, would be ground and used as mass-driver propellants.
In orbit, the the upper stage would be intercepted by a mass driver vehicle, which would carry it to the L5 manufacturing centres where it would be deconstructed. The upper stage will therefore be 'sold' upon reaching orbit. So in fact we have a completely reusable vehicle.
Hydrogen burns in a CO2 atmosphere, so the concept is in fact airbreathing. The question is whether it would be easier, cheaper, etc, to use a small gas turbine to burn the silane or an adapted fuel cell. Would a molten carbonate fuel cell work at all with silane as the fuel and compressed CO2 as the oxidiser?
This website went down for ages and I lost track of it. It is good to see it up and running again and that the same people have kept their enthusiasm!
On the subject of terraforming, I have come to realise that the most effective material will not be flourocarbon gases, heavy noble gases or CO2 but...carbon steel. Think about it: An inch of carbon steel weighing 200kg/m2 can contain an atmosphere as effectively as a 100 mile thickness of flourocarbon gas weighing 100's of tonnes per square metre.
My guess is that by the time people living on Ceres have enough resources to consider terraforming, the world will already be paraterraformed with tens of thousands of glass & carbon steel structures, each containing a small ecosystem. These people probably will not have any incentive or motivation to build a fully terraformed world. It simply would not offer value for money.
Compressed or liquified air vehicles would have poor energy efficiency across the full thermodynamic cycle. Additionally the energy density would be poor, making for a short range.
Compressed CO2 might however be a useful energy supply for stationary energy storage where power density is far less important. One could imagine excess nuclear or solar energy being used to power a compressor, which would store CO2 within a reinforced concrete tank. On release, the CO2 could power machine tools directly. An air driven tool would be easier to manufacture than a direct electric powered tool, so this technology would favour insitu manufacturing technologies.
For a ground vehicle, I would suggest decomposing the silane in a small chemical reactor, to yield silicon and hydrogen gas.
The H2 can then be burned in a fuel cell or small IC engine and the silicon collected as a solid for reuse. Some fuel cell vehicle concepts use a similar principle with gasolene or methanol.
A molten carbonate fuel cell might be used to burn the silane directly.
I based one of my nuclear engineering MSc projects on an SSTO vehicle. The conclusion was that a H2/O2 propelled SSTO was unlikely to be economic.
The basic problem is that with hydrogen/oxygen propellant (Isp = 440s), some 90% of the vehicle weight needs to be fuel. This requires a lightweight structure, very high performance engines, lightweight heat shield, etc. When all is added up, the payload fraction ends up no greater than 1-2%. When one considers the engineering cost of such an optimised vehicle, between-flight refurbishment costs and site related launch costs, it is difficult to see how such a vehicle would achieve much cost saving over a conventional rocket. Like the shuttle, it could easily end up being more expensive.
Using some seriously unpleasant chemical fuels (H2/F2, or H2/F2/Li) improved its physical performance, but introduced other hazard related costs and pollution difficulties.
The best solution would appear to be to use a nuclear thermal rocket engine for ground launch. Payload fraction then increases to about 30% and all costs are spread over much larger orbital payloads. A sea launch avoids the need for a ground based launch site and cuts costs further. The problem of crash related accident risks is mitigated by using element fuels that drain fission products into a carbon bottle that can be removed after each use. The vehicle can then be used dozens of times without the need for a core change.
A Lunar SSTO could potentially use pure oxygen as a propellant, derived from lunar ilmenite as modest energy cost using a carbon monoxide cycle.
The engine housing could be contructed from sintered fibreglass or glass-glass composite. The fuel itself would be in the form of uranium dioxide fibres. Nothing would oxidise as all components are oxides already.
I blieve an atmosphere 80% xenon, 20 % oxygen would be anaestetic.
would that lower the metabolism of the passengers?
Like putting them into a deep sleep could avoid some of the problems of 'cabin fever' in a six month + journey through mostly featureless space but we're trying to lower their food consumption to an absolute minmal - like hibernating animals do on Earth.
Another idea I have been toying a round with is a Large Modular Vehicle that does regular trips between Mars and Earth Orbit, but doesn't land on either planet.
Smaller craft launched of Ares type rockets would bring people up to it over a period of a few days from the surface of either planet.
These small people carrying craft would not need to bring many supplies up, just the people.
A seperate supplies craft would stock up the ship for a six month journey.
The smaller craft would serve would be used to depart and land on the surface of either planet (like Soyuz capsule)
The smaller craft would also be used to extend the living space of the over all vehicle.
This ship
How about a dedicated Big Dumb Booster Rocket to get them into space in the first place? Let me see: for a 1000tonne-to-LEO rocket:
Mass of person = 100kg, mass of cabin structure = 100kg/person, mass of life support = 50kg/person:
A BDB with 1000tonne to LEO lift capacity could life 4000 people in space. Lift cost = $500/kg x 250kg = $125,000.
Average wages in Solar Satellite Construction Industry are $250,000/year, so the transport to orbit could be payed off by a mortage of $150,000 spread over 3 years.
A closed cycle molten salt reactor may turn out to be the most practical SSTO propulsion system. Water or air could be used as the reaction mass and radioactive fission products could be separated from the molten salt before the vehicle reenters the Earths atmosphere. The waste would be stashed in orbit. A small rocket propulsion system could be used to jettison accumulated waste into a stable solar orbit.
The craft would probably be sea-launched from the Pacific, so any accident during takeoff would not contaminate a populated area.
Maybe just a pure oxygen atmosphere and a good sized global magnetic field to contain the ions that would otherwise escape from the upper atmosphere?
Giving the moon a xenon atmosphere would take a lot more xenon that is practically available in the solar system. I know that this thread is speculative, but I wish that people would try to think with just an ounce of practicality.
Could we liquidise Negative Hydrogen Ions? Such Ions could be prevented from slipping through the tank walls by an electrostatic barrier.
That's containment though. Ho would a rocket utilise them?
If you get diatomic hydrogen hot enough, it will dissociate into monatomic hydrogen. This means that very hot nuclear rockets using a hydrogen propellant have an added specific impulse advantage as the molecular mass of the propellant is effectively much lower.
The demonstrated possibility of producing blended hydrogen and oxygen gas from seawater by exposing it to photons of electromagnetic radiation at radio frequencies can be observed in several convincing video clips by searching eg. Google under "salltwater combustion". There's a lot of discussion regarding the topic, but nothing about the possibility of "burning" water (to which NaCl has been added) in vacuum. With a flame temperature of 3,000 F, surely some practical use can be made of this reaction in space?
Thermo-chemical production of hydrogen is likely to be more economic, as it does not need to start with a refined electricity source and for temperatures of 900C it can be up to 50% efficient. The heat can come from a solar heliostat or high temperature nuclear reactor.
The hot hydrogen gas produced can then be reacted with nitrogen to produce ammonia, or better still, carbon dioxide released from calcium or magnesium carbonate to produce methane, methanol, dimethyl-ether or best of all, dimethyl-ether carbonate, a dense fuel which requires no refrigeration and has properties similar to heating oil - a good rocket propellant.
Some of the calendar ideas are interesting. I think it makes more sense to stick with SI units for seconds and simply redefine a Martian hour or Martian minute (or both). The day-length is what it is, so is fairly inflexible and it would be daft trying to engineer an odd-hour into the clock.
I don't like the idea of abolishing the Christian calendar and have never liked any of this 'CE - Common Era' nonsense. The whole thing has a Marxian, multicultural, anti-Christian, anti-western and anti-white smell to it.
Basically, this idea is to use common U-238 as a reactor. I don't think it will start fission by itself, but a neutron source could start it. What do you think?
You need fast neutrons to fission U-238. Fission neutrons will not do. One idea that I saw reviewed a few years ago, was a hybrid Fission/Fusion reactor. A deuterium/tritium reaction could provide the fast neutrons needed to fission a U-238 blanket (80% of the energy from this reaction is carried away by the neutron). The fission reaction would improve the energy balance of the reactor over that of a pure fusion system. But the benefits are marginal. Adding fission material to a fusion system introduces a severe radiological hazard and the improvement to the energy balance is fairly marginal. The idea also proved unpopular in the fusion community, who did not want to see any psychological links between dirty fission technology and clean fusion technology.
Far better to breed the U-238 into Pu-239, which is fissionable.
I'm disappointed that the idea of mars cars powered by compressed CO2 is so quickly dismissed. Powering cars with a compressed version of the local atmosphere would be a simple and elegant method of propulsion; if it could be made to work. Is there anyone here that could look into the physics a little further?
This might work better as a stationary energy storage application, where power density and weight are not a problem. The energy required to boil the CO2 would be stored solar energy.
Why not use the Dark Sky Station to launch conventional chemical rockets? That high up Air resistence is minimal, meaning less fuel is neede to attain orbit, right?
Another design I've thought of would be similar to JPAs current design, although intsead of Helium it would use Hydrogen, the envelope would be made of steel, and it would carry onboard O2 (or H2O2 or some other Oxidiser). It would burn the Hydrogen for thrust (maybe after using an Ion drive/Vasimr to attain max. speed possible with that sort of propulsion). On orbit the crew would be able to gain access to the envelope, which would be converted into living space. On re-entry the high-drag design would help, meaning it could use steel heat shielding (like the X-33). Once in the atmosphere it would generate lift initially, and then craft would meet it (if that's feasible) and refill it with Hydrogen (unless it was possible to do that before re-entry). After docking with the DSS it would be checked over and readied for another flight.
So, any comments? I know the last parts probably aren't feasible, but the others?
Didn't we discuss this before? The logistical difficulty of launching from a balloon, greatly outweighs any advantage you get from launching 10-20km off the ground. It would be cheaper just to build a slightly bigger booster.
There is very little reason to do anything like this. Most of the energy released from the explosion wouldn't be possible to capture and use. It would require digging deep with expensive drills. People will be pissed at transporting Nuclears Weapons across space etc etc
There are much more practical means of obtaining energy on the Martian surface. Its not as if
By the time settleing Mars becomes possible, Fusion Power will have been cracked. Maybe ITER will do it or NIF or the even Dr Bussard's Polywell Fusor. Somebody will achieve it. Besides that in the future, Solar Cells will be way way more energy efficient. Some of them can reach 40% efficiency. With Quantum Dot and Nano Tech even higher efficiencies can be achieved.
It will be much easier to drag those across space and unfold them on the surface.Thermonuclear Weapons might have an interesting use for quickly removing/deforming terrain but thats just my personal speculation
False. The only energy that could not be captured as heat or focused plasma would be the part that emerges as neutrinos. There is no reason why a pulse unit fission/fusion reactor could not be made to work.
I agree that the Polywell would be a much easier way of harnessing fusion, if it can be made to work.
This 'Devil's Pot' idea has been discussed before.
You would be better off exploding the nukes within an evacuated, lithium/U-238 lined steel vessel, inside a powerful magnetic field. The fission fragments and ionised material could then be directed onto a graphite element at each end of the vessel, which would contain cooling tubes. The graphite would also act as a heat store, allowing the pulsed nature of the reactor to be smoothed, giving a continuous steam supply.
I'm not so sure about the economics of using mini H-bombs in this way though. If the things could be mass-produced cheaply enough, I suppose it could work.
It should be reasonably achievable to construct a containment vessel capable of containing kiloton level blasts in a virtual vacuum. Whether it would work politically is another matter.
NTRs rely upon heat transfer out of the core material into the coolant gas. To operate an NTR efficiently (ie, with high specific impulse and high power) it needs to operate at very high temperatures. This tends to degrade or partially melt the core material. Basically, engineering an NTR for reuse would mean accepting a lower ISP and a lower thrust-weight ratio. NTR cores will also generate significant decay heat following use and will tend to 'melt-down' when the propellant runs out, so it is a good idea to eject the things into space with all due expedience following use.
Spread of contamination from a used NTR cores would be a real headache if there were an accident over a populated area. They could spread contamination over hundreds of square miles of land. An accident would certainly be expensive and politically damaging.
What about mini mag orion? does it do ok?
On another, note, Orion is practical, but not allowable. I don't want that many radioisotopes in my solar system. And imagine what happens if a ship equipped for .1c goes supercritical- I'd say that it would outshine the sun.
Why is radioactivity a problem at all? Our own bodies are radioactive! So is everything that we touch and the very air that we breath.
Don't know about a mini-mag Orion. Even early versions of Orion depended upon focused nuclear charges, so the efficiency of the pusher plate will not increase linearly with increasing plate surface area. But as the ship increases in size, bigger bombs are used which are naturally more efficient with higher power to weight ratio which increases effective ISP. Very small designs need to rely upon very small pure fission bombs which are inefficient and dirty. Even if it were possible to magnetically extend the pusher plate, bigger bombs would produce unacceptable acceleration in a smaller Orion.
As for the possibility of all the bombs on the ship being triggered by a spontaneous detonation, that is simply not how A-bombs work. The frequency of a spontaneous detonation of even a single bomb is minute. If one goes off it will vaporise the others, but will not trigger fission.
Space is such a vast and radiation filled environment that the few tonnes of radioactivity produced by an Orion isn't going to be a problem to anyone.
Oh no, certainly not, the nuclear bomb is dropped behind the ship and detonates well clear of it. Containing a blast of that size is simply out of the question.
The bombs contain shaped lenses of propellant and a few milliseconds after detonation they squirt around 50% of the explosive energy of the blast into a narrow jet, that transfers its momentum onto the pusher plate. This is analogous to the shaped charges used in conventional explosives.
Another way of increasing the efficiency of the blast would be to fit a superconducting magnetic ring into the pusher plate. This would effectively contain the hot ions in much the same way as a rocket nozzle.
Well, that's from Wikipedia, the most unreliable source on the net. Whan planning a mission, do you really think people would rely on Wikipedia?
I should have pointed out people can get acclimatized to it. It's actually 5% that people start to get uncomfortable. Check out this post. 5%=50 mb. If we're aiming for a 650 mb atmosphere, that's 1/13 of the atmosphere. Half of the atmosphere would be 325 mb, below the combustion limit of 350 mb.
Human beings can survive quite well in a pure oxygen atmosphere, for indefinite periods. A partial pressure of 300mbar O2 will produce the same O2 concentration in our blood as sea-level pressure air. You do not need to flood the atmosphere with excessive CO2 or Xenon or anything else. The partial pressure of water vapour will generally be higher in an a lower pressure atmosphere and it will provide some buffer gas effects.
Again, I have to question the logic behind this discussion. We do not need pure fusion explosives.
If it is OK to use gasolene powered road transport, which causes untold numbers of lung cancers each year and similar numbers of heart attacks (not to mention the people killed in direct collisions) why is it so unacceptable to use a fission propulsion system which will provide similar levels of benefit at a much lower cost?
We wouldn't refuse to use our cars for the fact that the exhaust might expose someone to a 10(-9) chance of cancer. Nor would we be willing to invest in very expensive hydrogen powered vehicles for that reason alone. The reason is that we consider the risk to be tollerable and the cost of reducing it further is disproportionate. That is the mature way of looking at these things.
The thing to work on isn't really the technology (nuclear fission), which is already good enough for the job, but people's perception of risk. Lets say that using BDBs to lift 10,000 tonnes into orbit costs $5billion. Using Orion to do the same thing costs $1billion, but statistically will cause 1 fatal cancer world-wide. I'm sure we can spend a lot less than 4 billion saving 1 human life somewhere in the world? We could save many more with anti-malaria measures in places like Africa and those people would appreciate it.
Could we build a rocket system based on using lasers to beam energy to a spacecraft? It would work like an NTR, 'cept without the Nuclear bit. The Atmosphere could be used for the propellent. It would be forced in by the takeoff, compressed, and piped to the heating area where the lasers would be hitting. It would be heated up and forced out the back as in a conventional NTR. When it reaches it's Apogee, it would use Hydrogen as it's propellen to place it on an Orbital tragectory.
If it does work, how much would it cost?
This would actually be very difficult to achieve, at least for ground launch. You are effectively trying to hit a bulls eye on a not just moving, but accelerating target, with perfect accuracy. That target would be as little as 1m in diameter and the beam could not wander by more than a few inches without the vehicle suffering catastrophic power loss. The distance between the laser and target may be over 100km by the time you reach burnout. Any whiff of cloud or stray puff of propellant that comes between the target and the laser would obscure the laser light and cut off power.
Actually, I think a combination of the two would be best. Dig a 10-20 km hole, at the bottom if you're more than 10 or 20 km n/s of the equator, you NEVER get hit w/direct sunlight. Have it 1 km on, 1 km off, then you're golden (like this)
But this is going too far. Why not go down 1km? Why build shafts at all? Why not mine mercury w/ automated machines, and get the stuff from orbit? Venus, once you get it to a more-or-less earthlike state is somewhat stable. But mercury? Mercury will never be. Mercury should be the metal mine of the system. Instead of using insanely long shafts to build overheated and vulnerable habs, let's experiment w/ solar powered core mining.
A terraformed Mercury would require active methods for blocking out/reflecting unwanted sunlight. This might include a combination of orbital sunshade(s), relective high-atmospheric microballoons, high atmosphere sulphur dioxide injection and the placement of high albedo material in equatorial regions.
None the less, I like the idea of a sinkhole world. Getting sunlight into the sinkholes would be easy enough to achieve using mirrors. The long day length would be problematic for some crops but would not effect deciduous trees, as they lose their leaves in winter time anyway.
Mercury has a shallow axial tilt, so above a certain lattitude the bottom of a sinkhole will never recieve direct sunlight. With holes 20km deep, the atmospheric pressure at the bottom of the sinkholes would be roughly 10 times greater than the pressure at the top.