Feasibility of using 'rocks/boulders' as propellant?

[Heretic391]

As per the title, most asteroids are clumps of boulders, rocks, pebbles etc. So assuming you had 'infinite' energy or years to throw away could you literally collect boulders/rockets then to travel around space you 'shoot' them out to utilize newton's third law? Was thinking a slingshot would work but not sure now that i look at it 

p.s this is for fun so let your imagination go wild.

[HebaruSan]

This is the usual name for this idea:

https://en.wikipedia.org/wiki/Mass_driver

[Heretic391]

Wow its so cool, thanks for sharing  

[Nuke]

if you flash vaporize it, strip the electrons and run it through a charged grid or magnetic nozzel, you can use anything as propellant. you may not get the same isp as doing the same with hydrogen, but for a wilderness vessel that seldom finds itself near a point of interest, being able to use anything as propellant has quite a bit of utility. 

Edited September 29, 2023 by Nuke

[mikegarrison]

The big advantage to using rocket fuel instead of rocks is that rocket fuel contains its own potential energy. It is both reaction mass and energy source.

If you use rocks, that's fine for covering the "reaction mass" part, but you still need an energy source.

[darthgently]

5 hours ago, mikegarrison said:

The big advantage to using rocket fuel instead of rocks is that rocket fuel contains its own potential energy. It is both reaction mass and energy source.

If you use rocks, that's fine for covering the "reaction mass" part, but you still need an energy source.

We just need to handwave into existence a quantum method to "charge" rocks with potential energy from zero point energy using the correct balance of the merciful and severe properties of quarks

[magnemoe]

2 hours ago, darthgently said:

We just need to handwave into existence a quantum method to "charge" rocks with potential energy from zero point energy using the correct balance of the merciful and severe properties of quarks

Like power from solar panels or an nuclear reactor  
Rocks has the benefit that if you mine the asteroid while moving it you get the reaction mass for free. 
 

[farmerben]

This is one application where spin launch makes sense.  You would need reaction wheels roughly the same size as the launcher though.

[darthgently]

3 hours ago, magnemoe said:

Like power from solar panels or an nuclear reactor  
Rocks has the benefit that if you mine the asteroid while moving it you get the reaction mass for free. 
 

Ok, so zero point would be a luxury.  On a related note, one of the major KSP1 mods has thrusters that use mine tailings for reaction mass.  Might be one of Nertea's, can't remember for sure

[Vanamonde]

You'd expend more fuel of whatever kind going around to collect the asteroids than you'd gain by using the asteroids themselves as fuel. Remember that it's not really like movies and they are actually very far apart. 

[AckSed]

Pretty high. Note that SpinLaunch didn't invent the rotary mass driver; I saw a 1977 NASA paper on space settlements that, among other things, described a Rotary Pellet Launcher to launch ~200 10g regolith pellets a second. Granted, it had to have a TiNi wear liner that needed replacing regularly, but at an impressive 4 kilometres/sec with a thrust of 8.9 kN, there's no reason a counterrotating pair couldn't be used on an asteroid to provide thrust. Shame about the 16 megawatts of power it needed.

Here's the paper. A linear mass driver is also described: https://archive.org/details/SpaceSettlementsADesignStudy1977

[Nuke]

On 9/29/2023 at 6:39 AM, farmerben said:

This is one application where spin launch makes sense.  You would need reaction wheels roughly the same size as the launcher though.

just run two in opposite directions, you can either match your masses or tweak the release velocity so their ke matches. 

[StrandedonEarth]

The biggest problem I see with regular, common, widespread use of rubble-mass drivers is that now space is being filled with streams of fast-moving debris. Yes, space is mid-boggling huge, but keep hurling stuff around long enough and the odds of a catastrophic intersection will keep rising as space also becomes more populated.

E: We used to think Earth's oceans and atmosphere were "bottomless" too, as far as dumping waste, but the cumulative effects of long-term actions are rarely seriously or urgently considered until it's time to counter said effects.

Edited September 30, 2023 by StrandedonEarth

[darthgently]

6 hours ago, StrandedonEarth said:

The biggest problem I see with regular, common, widespread use of rubble-mass drivers is that now space is being filled with streams of fast-moving debris. Yes, space is mid-boggling huge, but keep hurling stuff around long enough and the odds of a catastrophic intersection will keep rising as space also becomes more populated.

E: We used to think Earth's oceans and atmosphere were "bottomless" too, as far as dumping waste, but the cumulative effects of long-term actions are rarely seriously or urgently considered until it's time to counter said effects.

And no matter what direction you release the mass, unless it is >= escape velocity, it is almost guaranteed to cross your current orbit later.  One could kick oneself in the butt down the road

Edited September 30, 2023 by darthgently

[magnemoe]

18 hours ago, Vanamonde said:

You'd expend more fuel of whatever kind going around to collect the asteroids than you'd gain by using the asteroids themselves as fuel. Remember that it's not really like movies and they are actually very far apart. 

Who is true, so its most relevant if you are returning from one or even moving it while mining it. 

[Jacke]

On 9/29/2023 at 11:43 AM, darthgently said:

We just need to handwave into existence a quantum method to "charge" rocks with potential energy from zero point energy using the correct balance of the merciful and severe properties of quarks

You may have wanted to just make a humorous comment.  However, to those who think this could be real, it ain't.  Zero Point Energy can't be used for anything beyond the Casimir Effect and AFAIK it can't be used to extract nothing.  As for the related concept of Dark Energy, it currently stands upon research that used Supernova ranging over a small area of the sky and could be a complete analysis artifact, ie. it ain't there.

You can't use quarks any more than you can use electrons, except by using the forces that influence them.  Which are well understood with no fancy-pants energy mojo.

[darthgently]

8 hours ago, Jacke said:

You may have wanted to just make a humorous comment. 

Was "handwave" a pretty good clue?  I'll try harder in the future

[Jacke]

18 hours ago, darthgently said:

Was "handwave" a pretty good clue?  I'll try harder in the future

Any sufficiently out-there woo-woo by a true-believer is almost indistinguishable from satire.

[darthgently]

6 hours ago, Jacke said:

Any sufficiently out-there woo-woo by a true-believer is almost indistinguishable from satire.

There was the addition of merciful and severe properties of quarks which I pulled from kabbalistic mysticism in a further attempt at humor.  I won't quit my day job based on your feedback, for which I am in your debt