I am sure it is not a new idea, I was wondering if there had been any consideration of what mass object we could slowly alter course to where we want, how long it would take and what size comet (or asteroid?) we would want. Are what we want and what we could do completely incompatible or might there be a rough size range that might make it just about plausible? Hoped it might prompt interesting discussion even if it is completely impractical for centuries.
Quote from: crandles57 on 11/28/2025 07:30 pmI am sure it is not a new idea, I was wondering if there had been any consideration of what mass object we could slowly alter course to where we want, how long it would take and what size comet (or asteroid?) we would want. Are what we want and what we could do completely incompatible or might there be a rough size range that might make it just about plausible? Hoped it might prompt interesting discussion even if it is completely impractical for centuries.I strongly suggest an intense scrutiny of the links provided by Interested Engineer. Only having time to skim them I believe they will help your cause. There are many games that can be played with gravity capture that I hadn't previously noticed. I have been more interested in means of moving them. Solar thermal. Enhanced gravity tractor. Small body beanstalk for rapidly rotating objects. And so on. That a hundred meter object can be over a million tons of material makes for an interesting thought experiment.Strongest objection that I am aware of is the danger of making a mistake that causes a planetary impact. There are various entities that might get a bit nervous at the idea of megatons of material impacting at escape+ velocities. Impact energies of towards a gigaton deserve a bit of attention.
As for what we might be able to steer, QuoteTechnology LevelMax Asteroid Size/MassMax Comet Size/MassDelta-V ExamplePropulsion/MethodNotes/SourcesCurrent (2020s tech, e.g., ARM/KISS baselines)7-10m diameter500-1,300 tons5m diameter100-500 tons (theoretical; no missions)0.1-1 km/s (rendezvous + return)SEP (40-150 kW, xenon ion thrusters, Isp ~3,000-5,000 s); robotic capture (e.g., inflatable bag)Focus on near-Earth objects (NEOs) with Earth-like orbits (low delta-v ~170 m/s for return). ~28:1 mass amplification (spacecraft returns 28x its mass). Comets harder due to ~10-20 km/s excess velocity. Feasible launch: Single Falcon Heavy/Atlas V. Near-Future (2030s-2040s, advanced SEP/ISRU)20-50m diameter10,000-200,000 tons10-20m diameter1,000-10,000 tons (speculative)0.2-1 km/s per cycle (cycler maintenance)VASIMR/SEP (high-thrust plasma, Isp ~10,000 s); gravity tractor for fine adjustments; ISRU for on-object propellantProposals for cycler insertion (e.g., 1,000-ton asteroid). For 15,000-ton object, ~35 tons propellant per 230 m/s correction. Larger sizes via multi-stage missions or nuclear electric propulsion. Comets possible if intercepted early. Far-Future/Speculative (2050+, e.g., fusion/nuclear)100-500m diameter1-100 million tons50-200m diameter100,000-10 million tons1-5 km/s (major orbit changes)Nuclear thermal/electric (Isp >10,000 s); mass drivers (eject material for thrust); swarm roboticsTheoretical for massive shielding (e.g., 370m NEO for natural path-crossing). Full cycler networks possible, but upfront costs immense (trillions). Comets viable for outer-system sourcing. Risks: Political/ethical (e.g., Earth intercept fears). Yes it is looking like beyond the top end of "Far-Future/Speculative" !
Technology LevelMax Asteroid Size/MassMax Comet Size/MassDelta-V ExamplePropulsion/MethodNotes/SourcesCurrent (2020s tech, e.g., ARM/KISS baselines)7-10m diameter500-1,300 tons5m diameter100-500 tons (theoretical; no missions)0.1-1 km/s (rendezvous + return)SEP (40-150 kW, xenon ion thrusters, Isp ~3,000-5,000 s); robotic capture (e.g., inflatable bag)Focus on near-Earth objects (NEOs) with Earth-like orbits (low delta-v ~170 m/s for return). ~28:1 mass amplification (spacecraft returns 28x its mass). Comets harder due to ~10-20 km/s excess velocity. Feasible launch: Single Falcon Heavy/Atlas V. Near-Future (2030s-2040s, advanced SEP/ISRU)20-50m diameter10,000-200,000 tons10-20m diameter1,000-10,000 tons (speculative)0.2-1 km/s per cycle (cycler maintenance)VASIMR/SEP (high-thrust plasma, Isp ~10,000 s); gravity tractor for fine adjustments; ISRU for on-object propellantProposals for cycler insertion (e.g., 1,000-ton asteroid). For 15,000-ton object, ~35 tons propellant per 230 m/s correction. Larger sizes via multi-stage missions or nuclear electric propulsion. Comets possible if intercepted early. Far-Future/Speculative (2050+, e.g., fusion/nuclear)100-500m diameter1-100 million tons50-200m diameter100,000-10 million tons1-5 km/s (major orbit changes)Nuclear thermal/electric (Isp >10,000 s); mass drivers (eject material for thrust); swarm roboticsTheoretical for massive shielding (e.g., 370m NEO for natural path-crossing). Full cycler networks possible, but upfront costs immense (trillions). Comets viable for outer-system sourcing. Risks: Political/ethical (e.g., Earth intercept fears).
I don't know where those numbers for moving asteroids come from, but I'd strongly disagree with some of the assumptions, especially on propulsion. Xenon propellant? Starlink has already gone to cheaper propellants, xenon is just too expensive at scale. I don't see the advantage of VASIMR for this application either. QuoteNuclear thermal/electric (Isp >10,000 s); electric, fine, but no way nuclear thermal is getting 10,000s Isp! Solid core is probably limited to 800-900ish; a nuclear lightbulb might give you 1500 or so?; an open cycle gas core (insanely expensive) maybe 3000?
Nuclear thermal/electric (Isp >10,000 s);
Quote from: Vultur on 12/16/2025 11:32 pmI don't know where those numbers for moving asteroids come from, but I'd strongly disagree with some of the assumptions, especially on propulsion.Just another ludicrous question I had previously asked grok for a different thread. Not at all sure it should be believed.Probably more sensible than what I imagine:Set up huge solar sails on the asteroids. Not sure whether the solar sail should have solar panels or focus light onto solar panels. Besides controlling the solar sails, use the electric generated for a rail gun that fires off tiny pieces of the asteroid. Maybe you can also generate some gasses from the asteroid materials for ion engines propellants.I am not expecting this to be fast/create much delta-v and I expect you need to select your asteroids carefully to be ones that are going to have a close approach with a planet in a few years anyway so you can fine tune that encounter to send the asteroid off in an appropriate direction that then gets slowly adjusted to a course that gets captured by Venus.It is probably slow but it is a rather long term project anyway. Perhaps this doesn't need huge leaps in technology nor huge masses to be launched from Earth?
I don't know where those numbers for moving asteroids come from, but I'd strongly disagree with some of the assumptions, especially on propulsion.
Could comets be made to crash into Mars for more water and possible eventual terraforming? This was done on Startrek as mentioned in the show "Enterprise".
