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Although I haven't followed GCFR development and implementation very closely, the only accidents with this technology that I'm aware of come from nuclear weapons production and the 1967 Chapelcross incident, which was admittedly pretty bad but also resulted in no loss of containment. Can you provide any documentation on the dangerous failures you noted?
The failure at Chapel cross was of 2 out of 4 reactors. As I recall there was dimensional change in the graphite. In one there was damage to one or more fuel rods resulting in leakage of radioactive material. In reactor 4 no such leakage was reported, but the reactor was never restarted although it was supposed to have been repaired.
Other Magnox failures involved quite rapid corrosion by hot CO2. The reactors were derated by reducing operating temperature to avoid severe shortening of their lives.
I also recall reported failures of coolant circulators. This didn't cause reactor problems because of redundancy. On Mars there would be a problem of stand by power to these. If you have to shut down the reactor, how do you run the circulators to get rid of residual heat in the core?
On the positive side, these reactors could run with very low enrichment fuel.
Musk's recent presentation showed no consideration for artificial gravity, either. I don't see this as realistic. There is no point in shipping people to Mars if they are seriously incapacitated when they get there. Even with 38% g objects still have the same inertia as they would on earth.
We need to keep away from steep slopes. There are plenty of landslips on Mars and we need to do a lot of work on Martian slope stability before we can identify a good spot to burrow into. You will need to put your initial habs in the flatlands well away from hills. Conveniently, this is likely to be where the ice has collected, but we haven't got proof of that.
If there are remnant ice masses protected by layers of volcanic and Aeolian dust, how can we locate them without sending people? Most manned mission proposals need water for fuel and oxidant manufacture so we have to find suitable resources before we send humans. I still like my idea of dropping iron balls from orbit and observing the ejecta on impact.
You need to carry dilution gas (Argon/Nitrogen mixture would be a by product of the fuel manufacturing process if it uses atmospheric CO2). Pure oxygen comes with most severe fire risks.
Strikes me that none of the big agencies have any intention of sending people to Mars then returning them to Earth. If they had they would have an orbital experiment to check the effects of long term exposure to Mars gravity, and to discover whether low gravity diseases can be reversed by gradually spinning up a vehicle over the six month return period. So either they don't intend to go, or they don't intend to bring the people back if they do go.
Also the issue of fuel and/or oxidiser manufacture in situ has been bypassed, and landers are not going to the probably icy areas, where the best resources may be found for this production.
More power to Musk.
My opinion is that nuclear power would be best as a static installation at a main base and rovers/hoppers should be powered with tanks of chemicals which can be prepared there, just as earth rovers are, except that oxidants will have to be taken along as well.
As to graphite moderated, CO2 cooled reactors, some of these have failed dangerously. You don't want that if you only have two situated close to your major infrastructure.
Partial static testing of the engine, I think. I don't suppose they can effectively test the air breathing coolers yet as they probably don't have the means to accelerate it to hypersonic velocities. They will have to build a special test vehicle.
For single stage to orbit, take a look at Reaction Engines' Skylon proposal.
Well, you might be able to capture a few thousand tons of metallic asteroid, using a nuclear rocket to alter its orbit until it was captured and circularised. Then how would you convert it to alloy steel sheets. I just can't see a rolling mill in earth orbit as realistic. It has to go on either the moon or Mars.
A lot of reactors use carbon as a moderator. I suspect that CO2 would contribute to this and might give problems of reactor control.
Also there are big heat lags in fission reactors so you have to give them a lot of notice of a shutdown. You cant just cut off the coolant when you want the thrust to stop. For this reason nuclear thermal devices are really only suitable for interplanetary or interstellar operations.
for the same thermal output, dissociation absorbs some of the available heat and restricts the temperature of the exhaust so reducing exhaust velocity.
It probably would be easier and make for a more simple vehicle to put the reactor near the base generating power(which will be needed in quantity) and manufacture propellant locally, either using imported hydrogen, or by using hydrogen extracted from local ice resources.
Was it loading LOX? I recall a couple of cases where distillation columns for LOX have taken off and devastated large areas due to contamination with organics.
Wouldn't an updated nuclear thermal design be more realistic? Nuclear explosions are very unpopular. Hence the restrictions on testing of nuclear weapons.
If a thruster can be designed for the Dragon that uses propellants which can be manufactured on Mars, it could also serve as a hopper for exploration. Peroxide and methanol, or peroxide monopropellant may be the best choice as they don't require much in the way of refrigeration or heating on the Martian surface. Current NTO and MMH have similar storage properties, but are likely to need to be imported from Earth.
First find a good landing area, then place a beacon. Check position of beacon is good, then land the first load, with another beacon, near it. You could have, say eight loads landed in a circle around the first beacon, each in its own sector and none landing on top of one another. This only works with power landing, but not Skycranes as you don't want an exhausted one of those landing on your cargo, or your beacon.
GW
I think a source of fresh water is the real enabling element here. No point going to a site without a known-to-be-buried glacier there. That is a deceptively-simple requirement: just how do you really know the buried glacier is really there?
It would help if we knew how to make concrete out of Martian regolith. We're going to need it.
GW
You can find buried ice by using penetrators and observing the ejected material. I proposed iron balls dropped from orbit.
Provided you can protect against water loss and excess water ingress, you may be able to use gypsum plaster to bind rocks or bricks. The presence of Calcium Sulfate has been reported.
Alternatively, you may be able to locate volcanic deposits like pozzolana, which was used so successfully across the Roman Empire.
I would think about a multi use device. A rocket powered hopper for use as local transport. Add a second stage (disposable or reuseable) to get into orbit and rendezvous with a larger ship for earth return. Leave the hopper in Mars orbit for use by the next group.
Ian M.
In an electro magnet, the field is perpendicular to the axis of the coil. Your arrangement would give a four pole field with poles around the equator. The current can be split between cables but they must form a single coil to create a two pole field like that of the earth.
Void said
"An example would be Mars, and I think Earth, in opposite ways. Mars has its highlands at the south pole, and the Earth by my reckoning has it's highlands at the north pole. That is there seems to be more continental mass in the northern hemisphere of Earth than the southern."
I don't know enough about Mars to comment on that planet's crust, but on Earth the continents are in approximate isostatic equilibrium, so no mass imbalance. The continents float on the more dense mantle rocks. There are lags such as adjustments following removal of the Northern ice sheets, but over a few thousand years these resolve themselves.
There may be some effect on rotational inertia due to the fact that the continental masses are carried higher than the ocean floors by reason of their lighter rocks, so moving some mass away from the axis of rotation. This would be reduced by the uplift of dense rocks at seafloor spreading axes and increased at subduction zones so there may be a residual effect from the continents.
The main point of exploration of Mars, as opposed to some other location, is that Mars may be habitable, or may be so rendered. If this were not the case we would be wasting too much money on it. If it is habitable that money would provide for a refuge from global disaster on Earth. If not we would do better spending money on Callisto, or not on space exploration at all.
I think we should do the exploration and I think the result will give a second home for humans.
We do need to find a means of growing grapes on Mars, and yeast. So we must find some water and devise means of cleaning it up. Membrane technology is one route, but membranes are prone to fouling, so don't last very long. Other methods involve phase changes, and freezing uses a much smaller enthalpy change than does evaporation.
To deorbit a cannon ball you could attach a small rocket assembly using an electromagnet. When it reaches the desired re-entry velocity just open the circuit. Cannon ball and rocket will separate. Track the right object!
Range depends mainly on power available. If it is truly abundant an aircraft of some type, or maybe a rocket powered hopper, becomes possible. Then you could go hundreds of kilometres.
If you are confined to surface vehicles a fuel cell, or heat engine would probably give you a range of a few days, but then you need to carry supplies for the crews for longer duration trips. Use of moderately high concentration peroxide as power source would give usable oxygen and water in the engine exhaust so could reduce tankage for these. Batteries need a huge step up in capacity to compete with a tank full of chemicals.
Ground rovers might achieve maybe 20 km per hour going out and a bit more returning if following the same track ( so less need to recce before the vehicles) so a three day trip is about 200 km with a limited amount of science included, if the rovers are the accommodation. If crews need to make camp the range is reduced because of restricted time. Depots, as used in polar exploration on earth, could extend this range.
Supplies for both crews would be needed in each rover, but only for the return trip to base, and the emergency part would only get used in the event of inability to transfer supplies from a failed vehicle to a functional one. So the extra supplies don't need to meet the full requirements of an active crew.
Given a supply of peroxide or other suitable rocket fuel a pair of hoppers seems very attractive, to me. It gives much better mobility and range than a pair of ground rovers. Drawback is that it can't pull a trailer full of rocks or ice.
How many Ampere Turns of superconducting cable would we need to put around the Martian equator to create a global field?