Since momentum is conserved, why not just have a 2 of the 1 g probes strapped to...

vjvjvjvjghv · 2025-10-24T16:15:40 1761322540

Isn’t that basically how a rocket works? Throw stuff out one side to get the thing on the other side moving. Not sure how this would compare to a rocket engine with hyperbolic fuel.

hinkley · 2025-10-24T18:34:08 1761330848

Only in the sense that throwing a knife at someone is the same as shooting a howitzer at them.

Specific impulse.

vjvjvjvjghv · 2025-10-24T19:18:51 1761333531

As far as impulse goes, the spring will probably be pretty inefficient relative to mass.

sandworm101 · 2025-10-24T20:47:39 1761338859

No. Very much no. The spring system would literally throw away half the mass of the craft for, maybe, a 10m/s delta. Fireworks would be more efficient. A pitching machine attached to a huge pile of baseballs would be more efficient (ie the baseballs could be thrown faster).

celticninja · 2025-10-25T12:02:44 1761393764

They all weigh a lot more than 1g though.

hinkley · 2025-10-25T15:38:30 1761406710

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

Please read.

hinkley · 2025-10-24T19:42:48 1761334968

The point we are trying to make is that there hardly anything that would be less efficient relative to mass.

floxy · 2025-10-24T16:52:39 1761324759

dylan604 · 2025-10-24T17:14:34 1761326074

It compares in that it doesn't require said hyperbolic fuel. That fuel is heavy and finite.

mlsu · 2025-10-25T06:26:26 1761373586

You can think of the hypergolic fuel as a type of spring. The chemical energy stored in the bonds of the fuel is what pushes the fuel products apart when it reacts. This is what pressure is, it's nothing more than KE of molecules.

The 'spring action' of fuel is very good because there's a lot more energy (per unit mass) stored in the bonds. Orders of magnitude more than a mechanical spring.

dylan604 · 2025-10-25T15:57:14 1761407834

But a mechanical spring will reset itself to its natural position once tension is released

lazide · 2025-10-24T17:29:38 1761326978

Uh, it does - the ‘fuel’ is the other probe.

Notably, this also has a particularly bad ISP?

Also, probes are presumably also heavier and rarer?

Alex-Programs · 2025-10-24T18:49:46 1761331786

That's just a really, really ineffective rocket. A spring has nowhere near the energy density of chemical fuel.

hinkley · 2025-10-24T18:38:35 1761331115

Because the specific impulse of the spring is negligible when you’re moving at 1/10c and why would they send a 1g probe if they could accelerate 100kg to that speed? Why do you suppose doubling the weight would be free instead of making the system infeasible?

sheepscreek · 2025-10-25T04:14:03 1761365643

Can a gyro work in space? Probably not or all the satellites would be using it instead of gas/ionized gas based propulsion.

nandomrumber · 2025-10-25T09:06:14 1761383174

Gyroscopes are used in spacecraft / satellites in the same manner they are in aircraft, to measure changes in orientation.

Reaction wheels are used to make adjustments to orientation. See https://en.wikipedia.org/wiki/Reaction_wheel

Thrusters of all sorts can also be used, generally to maintain altitude in satellites, and more generally to provide thrust for space probes.

Cthulhu_ · 2025-10-24T18:54:49 1761332089

What would the "screw" push off of? That rotational force would need to go somewhere or be corrected, else the probes would just rotate. I guess a gyroscope could do that, but what you're describing just sounds... very roundabout, and in terms of force, a few kilos of propellant would have the same effect.

floxy · 2025-10-24T19:52:16 1761335536

This is infeasible for the reason other have mentioned about specific impulse. But surely you can imagine a set of parallel boards with a coil spring between them and a set of cylindrical guide rods to prevent relative rotation between the boards. A motor fixed to one board turns a screw that engages with threaded nut on the other board, mounted on a thrust bearing, and guide bushing that allows a linear movement, but disallows the rotation degree of freedom. Think of the lead screw on a milling machine or lathe.