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# mass shifting drive

variable length "piston" rods
 (+1, -3) [vote for, against]

The only way to achieve + or near light speed from my understanding will be a drive that uses mass as a means of propelling the craft. would creating a variable length piston rod (extending in the direction you want to go and shortening in the direction you don't) shift the center of gravity of your craft. I wanted to test this, but have not yet been able to.
 — Zimmy, May 03 2003

reactionless propulsion model http://jnaudin.free.fr/html/hbimp35.htm
Mechanical means of achieving reactionless propulsion [Anarch, Oct 21 2004]

Gravity Waves Idea Gravity_20Waves
Mentioned in an annotation, I suppose I should have added this link years ago. [Vernon, Mar 15 2007]

 Rockets already work by changing the centre of mass. The mass that this thrown backwards to propel the craft forwards is called fuel.

Putting an eccentric piston in the centre of a spacecraft will make it wobble, nothing more.
 — st3f, May 03 2003

 // would creating a variable length piston rod (extending in the direction you want to go and shortening in the direction you don't) shift the center of gravity of your craft //

no.
 — ato_de, May 03 2003

anyone know where I can read up on why there is only a wobble? The "piston" is a simplification of my concept which would envolve a circular mass accelerator which allowed mass to escape on a tangent and then be re-captured w/ electromag pulling the escaped mass back into the circular accelerator creating what I thought would be a mass-drive. (what is Yr 5 science?)
 — Zimmy, May 03 2003

Whatever thrust you acheived by throwing mass away would be lost in trying to retrieve it..
 — phoenix, May 03 2003

Baked. I had a friend who had a car with Mass shifting drive. At times, we got out and pushed his car. That's a design that works.
 — sartep, May 03 2003

 phoenix, the association of mass with momentum has caused lots of physicists to pooh-pooh notions such as this. The interesting truth is that momentum is not necessarily ALWAYS associated with mass in motion. For example, photons have no mass but do possess some (rather small) amount of momentum. Thus a flashlight qualifies as a reaction drive that doesn't throw out exhorbitant amounts of mass (just exhorbitant amounts of energy, if you really want a decent drive from a beam of photons).

 Then there is that expected/unknown-for-sure subatomic thingy known as the graviton, which is also some sort of pure energy, and may also carry some momentum. We don't know enough about gravitons to say how much or how little momentum they can carry. Photons have a straightforward fixed ratio of energy-to-momentum content, and thus they make for a very expensive reaction drive.

 Gravitons, though, might offer us the chance to throw out lots of momentum along with relatively little energy. IF SO, then they would make for an ideal reaction drive -- with an invisible exhaust! A gravity-wave reaction drive would LOOK LIKE a reactionless drive...and what little data we have so far SUGGESTS that impacting masses may be able to produce gravitons/gravity-waves. Not very much, of course, or the leaking energy/momentum would have been noticed many decades ago (hmmm...1935?), in various experiments. But as Zimmy indicated here, if we can get any such reactionless-seeming effect, and apply it long enough, then eventually we can go anywhere.

As you probably know, I've written more about this elsewhere on the HalfBakery, under the titles of "Gravity Waves" and Gravity Waves 2". This was a nice chance to remind people that there are STILL "more things in Heaven and Earth, [place skeptic's name here], than are dreamt of in your philosophy".
 — Vernon, Jun 27 2003

You've written more somewhere? ;-)
 — bristolz, Jun 27 2003

I just want to point out that rockets do NOT shift the center of mass. When a rocket and propellent go flying apart, the center of mass in the system stays constant. Both elements (rocket and propellent) are moving away from the center of mass in opposite directions, but the centroid does not move. (unless acted upon by an outside force, such as air resistance or gravity)
 — netmanakre, Jul 16 2003

The Lums, who drove my great-grandmother-in-law to mass say they have an automatic transmission and not a shifter and don't go that fast.
 — cloudface, Sep 28 2003

Baked but not common knowledge. See: www.USPTO.gov Quick search by patent #'s: 3,968,700 and 4,631,971
 — thrival, Jan 08 2004

I've seen a few things about this sort of reactionless drive. Most websites that claim it works include links to Nicolo Tesla, and perpetual motion machines. Most websites that bother to claim it does not work talk a lot about pendulums, and fluid dynamics, and a "shuffle," or "laundry machine" effect, which requires a gravity well to work.
 — ye_river_xiv, Mar 15 2007

 If force is equal in both directions, using a mass drive means that the force on a small object is the same as the force on a heavy object. But force makes acceleration (f=m.a), so the lighter object is accelerated quickly. As 'm' tends to zero, then 'a' tends to infinity.

So you could accelerate vacuum up to infinite speed.
 — Ling, Mar 15 2007

 Theoretically, the center of mass of a rocket in an isolated system will never move. What I mean is that.... the fuel in the rocket, once it has left the exhaust nozzle will have an equal and opposite force on it (and hence momentum) than the rocket does.

Since the momentum of the rocket and the rocket's exhaust are equivalent, this means that the center of mass does not ever accelerate or move from where it originally started out at (in an isolated system). Actually, that's true for any isolated system, even for the entire universe....since every action in the universe has an equal and opposite reaction, the center of mass of the universe always stays in 1 place.
 — quantum_flux, Mar 15 2007

The centre of the mass of the universe always stays in one place??? hehehe overextending understanding to the nth aren't we, young master Flux?
 — the dog's breakfast, Mar 15 2007

//the center of mass of the universe always stays in 1 place.//
...but the Universe could be whizzing along at some undefined velocity. Similar problems occur when trying to measure the velocity of a magnetic field.
 — Ling, Mar 15 2007

... probably the restraunt at the end of the universe.
 — Custardguts, Mar 15 2007

Oh? Are particles supposedly going FTL?
 — Zimmy, Sep 27 2011

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