Dirty Propellant For High Thermal Rocketry?

[Spacescifi]

Just curious....cannot common dirt from barren airless moons and worlds be melted down to fluids and be turned wholly into rocket propellant and burned off with high thermal energy out a rocket nozzle?

 

The idea is to land and quickly refuel propellant without having to extract, separate, or purify or refine it. Off low gravity moons or asteroids without atmosphere, likely using an auxilliary tank other than the one used for launch to orbit.

I know the ISP will be not great....but I also know the higher the thermal energy the higher the ISP becomes.

So if energy portals connected to the National Igniton Facility were connected to a rocket engine using liquified moon regolith...what kind of thrust and ISP are we looking at?

And I do mean ALL the powerful lasers of the NIF are focused down a portal to fire into rocket engine on the other side to ignite the regolith propellant.

 

NIF's 192 powerful laser beams, housed in a 10-story building the size of 3 football fields, can deliver nearly 2 million joules of ultraviolet laser energy in billionth-of-a- second pulses to the target chamber center.

 

EDIT: With this kind of power, will this allow for torch ships of any kind?

Minus all the usual radioactive death?

Edited April 28, 2021 by Spacescifi

[kerbiloid]

If use the dirt from Chernobyl, you could build a Molten Salt Rocket. Probably.

[KerikBalm]

35 minutes ago, Spacescifi said:

Just curious....cannot common dirt from barren airless moons and worlds be melted down to fluids and be turned wholly into rocket propellant and burned off with high thermal energy out a rocket nozzle?

One, its not dirt, its gravel, rock, dust... etc. Dirt has a high content of biologically derived organics.

Two, no, it would not work as a melted fluid passing through a hot reactor

Three: What you can do is use a powerful laser to vaporize/ablate the materal, and produce thrust that way. This would work fairly well with beamed power propulsion.

Your ship scoops up regolith, compresses it into a block, and ofcuses a laser beam on the block that procedes to vaporize the regolith of the block, producing an exhaust jet as it bores into the block. You don't even need a hole for a crude nozzle. A flat plane uniformly ablating will already produce highly directional thrust (with just inefficiencies along the edges). This would take a lot of power, so having beamed power would be great, as your ship doesn't need to supply the power. You could have an orbiting mothership, and your lander just uses regolith and the motherships laser to ascend and descend.

Also, you could use it to augment thrust from a nuke. The orion drive envisions using shaped charge nuclear blasts, but if you are low on nukes, you could pakc in some regolith to increase the propellent mass at the expense of reduced Isp. Within certain bounds, this can dramatically increase youd remaining dV.

[Shpaget]

44 minutes ago, Spacescifi said:

NIF's 192 powerful laser beams, housed in a 10-story building the size of 3 football fields, can deliver nearly 2 million joules of ultraviolet laser energy in billionth-of-a- second pulses to the target chamber center.

 

EDIT: With this kind of power, will this allow for torch ships of any kind?

No, because NIF can't fire those lasers continuously. It takes a while to recharge. Average power would be much much lower then the instantaneous power they achieved for that tiny fraction of a second.

Just for comparison, total energy they produce in these laser firings is about the same as released from burning about 60 ml of petrol.

[YNM]

10 minutes ago, KerikBalm said:

Dirt has a high content of biologically derived organics.

^^ this. If anything, dirt is a major contaminant for aggregates in concrete - which are usually sand and crushed rock. There are test that checks for this.

AFAIK there has been some idea to use the aluminum in regolith to be used as chemical rocket fuel, but I think that ablative propulsion is a pretty sound idea too. (sound as in it works on paper, don't ask me how much power do you need for it)

Edited April 28, 2021 by YNM

[kerbiloid]

Dirt means a thin mess, doesn't matter if biological or no.

[wumpus]

First, what you want is light elements.  Hydrogen is ideal, water is ok.  Note that using water means your Isp won't be any better than hydrolox.  Lunar regolith is inferior to water, but I can't tell how much (and perhaps you can at least process it down with your reactor before launch, so at least you have just oxygen).  If you can get enough carbon dioxide from Mars, maybe you can simply feed graphite into your reactor.

One thing I can't stress enough is that this makes SSTO off Earth-sized planets next to impossible (unless you are cracking water or hydrocarbons for the hydrogen).  Getting high thrust out of nuclear thermal rockets would require tremendous cooling, and you'd have to try to stop the reaction immediately after liftoff (and hope that by the time you stop needing propellant, your reactors are cool enough for closed loop cooling).  Trying to do this while lifting a nuclear reactor and having an Isp less than hydrolox (efficient hydrolox is fuel-rich) just isn't going to happen when you need a delta-v of over 9000 (m/s).

 

[DDE]

11 hours ago, Spacescifi said:

Just curious....cannot common dirt from barren airless moons and worlds be melted down to fluids and be turned wholly into rocket propellant and burned off with high thermal energy out a rocket nozzle?

Molten down? Not with much efficiency. But much of it are oxides of iron and silicon, so they can be broken down into the two contituents to produce low-performance chemical rocket fuel.

[kerbiloid]

Leaving a road of sand behind.