New Mars Forums

phobos: Yes, I have indeed taken fairly extreme measures to ensure the vehicle is safe.

The launch weight is 6 million pounds.  The thrusters produce 80 gigawatts of thermal output each, which translates to 1,200,000 pounds of thrust at an Isp of 3060. 

First: Since the engines produce 1.2 million pounds of thrust each, we could launch it with only 5 engines.  Since we have the POWER OF THE ATOM on our side, the first precaution I take is to add two extra thrusters!  What this means is that even if you lose an engine at launch, or two, you can still safely launch the vehicle to orbit.  Heck, after the first 60 seconds of flight, when the vehicle is high enough to lay over above the atmosphere, you can lose every engine but one and still make orbit just fine.

Second: The fissile fuel is in the form of a gas.  When the fuel is not actually being used, it is stored in an aluminum/boron fuel vault, completely sealed, and that vault is sturdy enough to survive any conceivable re-entry stress.

Third: The actual thruster itself has multiple scram systems, including one that is completely passive.  If anything goes wrong, the nuclear reaction is killed/poisoned and the fuel mass is placed into the fuel vault for safekeeping.

Fourth: Once in orbit, the spent radioactive fuel is fired into space, combining an orbital circularization burn with a waste disposal manuever.  Given the 30 km/sec velocity of the exhaust gases, the spent fuel can either be shot into interstellar space, or dropped into the Sun.

Fifth: The launch site is a semi-submersible tender ship, and that ship is placed in the US territorial waters of Baker Island.  Looking east from Baker Island, there is no land for over 6000 kilometers.  The Liberty Ship spends its entire powered flight regime over the deep Pacific.  Even if there is a total loss of the entire vehicle, the release of radiation is only equal to twice the inventory released from Chernobyl.  Now, that sounds bad, but you have to recall that US nuclear tests in the Pacific in the 50's released inventory equal to hundreds upon hundreds of times the radiation that Chernobyl did, and the mighty Pacific absorbed and diluted it all to undetectability.

So, I think it is plenty safe. 

If you have more questions, I ask you humbly to go read the thread I have linked above, and please, nitpick away!  The more hostile review the design gets, the better it becomes. 

Frankly, I am astonished at how easily the design is coming together, materials problems that I would have sworn were impossible prove to be quite do-able with todays technology.

We are more advanced than we know, folks! 

Let's get off this rock!

I completely agree with the topic starter on one thing: You can imagine all of the wonderful deep-space drives for getting to Mars you want, but until we can get off the Earth, they are simply fantasies.

So, how do we do that?  As has been written in this thread, normal chemical fuels have reached just about the end of their development.  Metastable and/or high energy chemicals are WAY out, if ever.  The only likely near-term candidate left for a heavy lift booster is the Nuclear Thermal Rocket (NTR).

Now, the NTR is a potent beast indeed.  As has been mentioned in this thread, the Isp of an NTR is dependent on the exhaust speed.  To get sufficient speed, extremely high temperatures are required, such that even a reactor core of uranium tri-carbide would melt.  To get those temperatures with high thrust takes huge power outputs, which is also difficult for a solid core to do.

The solution is to go with a reactor core that is already melted and extract the energy from the core using a radiative process, not a conductive one.   That is how a Gas Core Nuclear Reactor (GCNR) works.  The huge problem with the GCNR is that the uranium fuel is unconfined, and will leak out the exhaust.

Luckily, some very smart people back in the 60's figured out a way to stop that, by using a fused silica bulb to enclose the fission core. 

I have taken the liberty of designing (crudely) a SSTO heavy lift booster, using 7 very powerful GCNR thrusters with LH2 as reaction mass.  This launcher design, which I have christened the Liberty Ship, is fully reusable, has the same takeoff mass as a Saturn V, and can deliver 2,000,000 pounds of cargo to LEO per launch. 

I have been working on it on the forums at  www.nuclearspace.com , and would be pleased if any or all of the smart folks here would come and take a look at it.  All nitpicks happily accepted, criticisms carefully considered, and suggestions gleefully incorporated. 

The url for the main thread where the folks at Nuclearspace have been chewing on the Liberty Ship is : 

http://pub97.ezboard.com/fnuclea....3.topic

See what you think of it!