Tractor beams in Startrek

[Roondar]

From the Construction of ships thread, where the discussion also touched on tractoring large objects using starships:

The ability for small starships to tractor starbase does pose an interesting question about tractorbeams tho: how do starbases then use them to hold ships in place (as in stop them escaping)?

DS9 does not fire it's engines to compensate when it does so and the implication is they manage to stop ships dead in their tracks, even though a starship like the Enterprise-D was already able to move moon at 92 m/sec.

That is fast enough to be visible to the naked eye, yet no movement is ever observed.

[Mike DiCenso]

Curiously enough, tractor beams do exert pressure and stress on whatever it is they are being used to hold. The most notable, and one of the earliest examples is from "Tormorrow is Yesterday" [TOS, Season 1], where it is described that Capt. Christopher's F-104 was "caught and crushed" by the tractor beam, also that it had "broken up" in the tractor beam's influence.

Later in TNG's "Mind's Eye", for example, a Romulan D'Deridex warbird's tractor beam caused sub-microscopic deformations in a shuttlepod's hull.

So a tractor beam at least causes some sort of compression effect on the target object.
-Mike

[Cocytus]

There was also the 300 year old freighter in "Final Mission." The E-D's tractors were placing shear stresses on the freighter's hull.

And this was touched on in the other thread, but the Enterprise-D shifted the course of a stellar core fragment in "The Masterpiece Society." As per the episode's dialogue, the fragment had a density of 100,000,000,000 kilograms per cubic centimeter. To be fair, the tractor beam was a special model developed by Georgi and Hannah Bates, a scientist from the colony. Rather than exerting a continuous force, the multiphase tractor beam fired a rapid series of compressed pulses, allowing the tractor emitters to avoid overloading.

[Who is like God arbour]

We don't know, how a tractor beam does work.

Fact is, that, if it would work accordingly to classic physical rules (actio est reactio), a force, equal high, as the force with which the tractor beam pushes against an object, would push against the tractor beam emitter and would compel it to move in the opposite direction of the pushed away object, if the tractor beam emitter wouldn't be affixed to the ships frame. The ship can counter that motion with its own propulsion.

But that would mean, that, if the force, with which an object is pushed (or hold) is too high, the opposite force, that is applied to the tractor beam emitter and compel it to move in the opposite direction would be also too high and the ships propulsion could be to weak to counter that motion or the tractor beam emmiter could breack free of its fixture.

But as we have seen in the episode »The Naked Now«, Wesley could hold a self-made tractor beam emitter without any effort althoug at the same time, the tracto emitter was holding up a chair.

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That wouldn't be possible, if the actio est reactio principle would apply - or Wesley is very far stronger than he looks.

In the same episode, he adjusts his tractor emitter to create a kind of force field over the entrance to an important part of Engineering, that prevents, that other persons are able to enter it.

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The emitter has only stand on the table without any visible fixtures.

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Jim Shimoda, an assistant chief engineer aboard the USS Enterprise, a not exactly lightweighted fellow, walks into the force field and is knocked back without upsetting the emitter on the table.

That also wouldn't be possible, if the actio est reactio principle would apply.

Granted, later in the epsidoe, Wesley modifies the tractor beam of the Enterprise to push the Tsiolkovsky against the nearing stellar core fragmet to win some time. But I'm not sure, if he has won that time by accelerating the Enterprise in the opposite direction (away of the fragment) in the same time or if he has won the time because the impact of the Tsiolkovsky in the stellar core fragment has reduced its speed. But even if the Enterprise was accelerated away from the fragment, that does not confute the first examples. The plausible conclusion would have to be, that the modifications, he has done to the tractor beam emitter of the Enterprise have allowed for that instance, that the counter force of the push against the Tsiolkovsky is transmitted to the emitter and with it to the Enterprise itself - something, that usually does not occur (in that way).

We can only speculate, how the tractor beam prevents, that counter forces are aplied to it. Or maybe it does not prevent it, but does apply somehow a counter force to the counter force. Or maybe the point of origin of a tractor beam is somehow anchored in space and space can not be ruptured.

But the fact still stands, that several events were shown, where the tractor beam (and its ship or space station) emitter should have been destroyed, if the actio est reactio principle would apply normaly.

[Roondar]

Well, there is also a rather simple energy problem.

The E-D managed to change the velocity of a moon-sized asteroid by 92 m/sec. It took about 10 seconds to do so. Granted, it nearly burned out the tractorbeam in the process, but this was before they tried lightening the asteroid via <failed technobabble>.

Just consider that for a while. If that moon was made of rock and had a 10 KM radius (which is an absurdly low estimate), it would have a mass of 1,089 *10^16 kg*.

Per E=1/2mv2 that would be 4,61 *10^19 J, spread over 10 seconds that becomes 4,61 *10^18 w, or the equivalent of 1,097 GT of explosive force per second. A little excessive, considering it's pumped through a tiny non-weapon emitter, no?

If their tractor beams are that strong they don't need other weapons - they'd just rip everything they came across to shreds using this monster instead.

*) density of granite: 2600 kg/m3. Volume: 4,189 * 10^12 m3.

[Mike DiCenso]

The E-D managed to change the velocity of a moon-sized asteroid by 92 m/sec. It took about 10 seconds to do so. Granted, it nearly burned out the tractorbeam in the process, but this was before they tried lightening the asteroid via <failed technobabble>.

Actually the mass-lightening technobabble did work, but the Calamarain in their attempt to get at Q interfered with the operation before it could be completed, and restore the moon's orbit.
-Mike

[Roondar]

The E-D managed to change the velocity of a moon-sized asteroid by 92 m/sec. It took about 10 seconds to do so. Granted, it nearly burned out the tractorbeam in the process, but this was before they tried lightening the asteroid via <failed technobabble>.

Actually the mass-lightening technobabble did work, but the Calamarain in their attempt to get at Q interfered with the operation before it could be completed, and restore the moon's orbit.
-Mike

I didn't rewatch the entire episode, but in my memory the plan did not work nearly as well as they where hoping for. I freely admit this could be wrong though.

[Mike DiCenso]

Here's dialog from that scene where the Calmarain attack the E-D during the second attempt:

LAFORGE: Extending warp field forward.
PICARD [OC]: Engineering, is that the forward limit?
DATA: Yes, Captain. We are unable to encompass the entire moon.
PICARD [OC]: Do you recommend that we proceed?
Q: The two parts of the moon will have different inertial densities.
LAFORGE: Stand by, Captain. I can adjust the field symmetry to compensate.
Q: I doubt it.
LAFORGE: You don't know what this ship can do, Mister. Yes, Captain, I still believe it'll work. Increasing power and warp field and tractor beam.
Q: And if you're wrong, the moon will crumble due to subspace compression. Don't say I didn't warn you.
LAFORGE: Shut up, Q.
Q: I will not be spoken to in this manner!
LAFORGE: Data.
DATA: Q, I strongly suggest that you cooperate.
DATA: Inertial mass of the moon is decreasing to approximately two point five million metric tonnes.
LAFORGE: It's working. We can move it. Firing impulse engines.

[Bridge]

DATA [OC]: Captain, the moon's trajectory has moved point three percent. Point-four percent.
WORF: Emergency! Shields up.
RIKER: Disengage tractor beam.
WORF: Calamarain attacking. (big jolt) Shields holding. Tachyon field repelled.
LAFORGE [OC]: Captain, the impact of the blast is pushing us into the upper atmosphere.


As you can see, the only reason they had to stop was because of the Calamarain attack, not because of a problem with the mass lightening procedure.
-Mike

[Roondar]

Here's dialog from that scene where the Calmarain attack the E-D during the second attempt:

LAFORGE: Extending warp field forward.
PICARD [OC]: Engineering, is that the forward limit?
DATA: Yes, Captain. We are unable to encompass the entire moon.
PICARD [OC]: Do you recommend that we proceed?
Q: The two parts of the moon will have different inertial densities.
LAFORGE: Stand by, Captain. I can adjust the field symmetry to compensate.
Q: I doubt it.
LAFORGE: You don't know what this ship can do, Mister. Yes, Captain, I still believe it'll work. Increasing power and warp field and tractor beam.
Q: And if you're wrong, the moon will crumble due to subspace compression. Don't say I didn't warn you.
LAFORGE: Shut up, Q.
Q: I will not be spoken to in this manner!
LAFORGE: Data.
DATA: Q, I strongly suggest that you cooperate.
DATA: Inertial mass of the moon is decreasing to approximately two point five million metric tonnes.
LAFORGE: It's working. We can move it. Firing impulse engines.

[Bridge]

DATA [OC]: Captain, the moon's trajectory has moved point three percent. Point-four percent.
WORF: Emergency! Shields up.
RIKER: Disengage tractor beam.
WORF: Calamarain attacking. (big jolt) Shields holding. Tachyon field repelled.
LAFORGE [OC]: Captain, the impact of the blast is pushing us into the upper atmosphere.


As you can see, the only reason they had to stop was because of the Calamarain attack, not because of a problem with the mass lightening procedure.
-Mike

Fascinating stuff, they lower the mass to 2,5 * 10^9 KG.

Subspace is a very, very interesting thing - think of it: they have a moon, they put a subspace field around part of it and manage to lower the mass of the entire object by (at the lowest end estimate we've made for the moon) by seven orders of magnitude. Merely by putting a warpfield around parts of the moon.

[Mike DiCenso]

Well, yes. One of the reasons behind my creating the moon estimation thread is because if we can come up with a reasonable probable size for the Bre'el moon, then maybe we can get an idea of what percentage of the it's mass it was reduced by, which in turn we can apply that percentage to a starship's (or a space station's like DS9's was) apparent inertial mass, and what it is reduced down to.
-Mike

[Mike DiCenso]

Fascinating stuff, they lower the mass to 2,5 * 10^9 KG.

Subspace is a very, very interesting thing - think of it: they have a moon, they put a subspace field around part of it and manage to lower the mass of the entire object by (at the lowest end estimate we've made for the moon) by seven orders of magnitude. Merely by putting a warpfield around parts of the moon.

Near as I can tell with the latest mass estimates from the Bre'eel moon size thread, that object's mass was reduced by 4 million times! Now applying that to the E-D herself, that means that every time she puts up a warp field, she reduces her apparent inerital mass from 6.5 million metric tons down to a mere 1.625 tons! That certainly explains many of the incredible high-speed maneuvers and accelerations we have seen over the course of all 5 Trek series.
-Mike

[Roondar]

From our thread on the Bre'eel moon we have come to the following figures on the E-D's tractorbeam:

Secondly, since we now know the moons most likely mass, we can finalize the E-D's maximum tractorbeam output.

To make an object weighing 1 * 10^16 KG move by 92 m/sec requires 4,23 * 10^19 J, or in the ten seconds they took, 4,2 * 10^18 watt - aka ~1 GT/sec.

An impressive number to be sure. Suffice to say that tractoring starbases around is not going to be any problem. It also helps me understand why tiny ships such as runabouts get to tractor along massive objects like Galor class warships without any apperant strain.