I have read many sources and understand that impulse drive can be very fast. A quarter of impulse can be way faster than the escape velocity on Earth (11 km/s) or on the Sun (600 km/s).

Does this mean that the impulse drive is used by ships that can land on planets, like Voyager, to get the ship back into space?

If so, is it therefore true that thrusters, struts, and dampers are what make starships have planetary landing capability? (All relate to helping the ship land, not propelling the ship to space.)

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    I have no idea what this question is asking.
    – Tango
    Feb 1, 2015 at 20:07
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    Why is my question hard to understand? I gave the scenario and asked questions.
    – dh16
    Feb 1, 2015 at 20:10
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    This question is have to understand because the question is not clearly stated. It seems to be asking how starships that land on planets can achieve escape velocity. That's how I read it, at least. That said, the 2nd paragraph in particular is hard to understand, and the grammar in the first makes it difficult to isolate meaning.
    – Jeff
    Feb 1, 2015 at 20:16
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    First, you need to understand what escape velocity is. If you don't know or know very little about it, everything I said is non-sense to you. I read StarTrek wiki for planetary, and my words struts, dampers, and thrusters are from there. en.memory-alpha.org/wiki/Planetary_landing A few sources also mentions impulse drive can't be used in a planet's atmosphere. That's why I gave the scenario. This is the first time I provided too much details, and you guys said it's too ambiguous.
    – dh16
    Feb 1, 2015 at 20:35
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    I'm not 100% sure you understand escape velocity, either, since 11km/sec is the escape velocity of an object with no means of propulsion. If you could manage a sustained 1 cm/hour upward velocity you would eventually leave the Earth; it's the amount of thrust required that really matters.
    – KutuluMike
    Feb 1, 2015 at 20:46

5 Answers 5


Your question kind goes all over the place, but you seem to be asking, essentially:

Why does a ship like Voyager need special equipment to take off from a planets surface when the impulse drive is more than sufficient.

The answer is that the impulse drive is way overkill for lifting a vessel out of a planet's gravitational field into space. The impulse drive operates at something like 0.5 warp (150kish km/sec); you can escape from an Earth-sized planet for less than 5% of that. (The space shuttle, for example, only travels about 4km/sec while on solid booster). So, clearly the impulse engines are capable of pushing a ship out of even the biggest planet's gravity.

However, the impulse engines are not designed to operate in an environment with an atmosphere. The drive runs on an impulse reactor, a kind of nuclear reactor that, in order to produce its thrust, churns out the same kind of plasma, as the warp engines do. The plasma is so high energy, in fact, that the warp reactor output is one of the power sources used to run the ship; any excess is simply dumped into space via the "plasma exhaust".

In space, the plasma will simply radiate away as it cools, probably getting pulled along behind the ship. In a gaseous atmosphere, it could easily ignite the surrounding gas or cause extreme damage to any nearby structures or vegetation.

Instead, the ships use the much smaller kinds of gravitational nullifiers that smaller vehicles did in that time (e.g. anti-grav cars) to move the ship into a safe range to start up the real engines.

The other two things you mentioned have nothing to do with creating thrust:

  • The inertial dampeners were used to prevent sudden changes in the ships velocity from causing everything inside the ship to fly around. They basically counter-act the normal inertial behavior in the face of acceleration or deceleration of the ships hull. Inertial dampeners were always operating while the ship was in motion, they just need to be properly adjusted for the deceleration of a landing.
  • The landing struts are just landing gear for ships. You don't want to set the ship's actual hull down on a solid object, as it could cause damage and would probably not balance very well, so they put out struts for the ship to rest on while immobile.
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    Can you provide the source(s) where this information comes from? The ST:TNG technical manual does suggest the impulse engines create high-energy plasma, but not "using the same technology as the warp engines", i.e. matter/antimatter reactions creating plasma which supplies energy to the warp nacelles, but rather by nuclear fusion reactions which expel plasma as exhaust (a fusion rocket). Also, the part about using gravitational nullifiers in the atmosphere seems plausible (provided there is a limit on what they can do to account for the eps with black holes I mentioned), but where's that from?
    – Hypnosifl
    Feb 1, 2015 at 21:08
  • @Hypnosifl to be honest, I oversimplified a lot on the "same technology" bit because it wasn't all that relevant to this question. I just meant that both used high-energy reactors that produced similar "electro-plasma" as a by-product. The anti-gravs bit I pulled from memory alpha while looking up episode references, and it seemed like the only logical alternative, but I will see if I can find a reference in the ST:VOY tech manual.
    – KutuluMike
    Feb 1, 2015 at 21:13
  • and of course, the ST:VOY tech manual only says that planetary landing is "theoretically possible"
    – KutuluMike
    Feb 1, 2015 at 21:19
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    Thanks, I searched chakoteya.net and the references to anti-grav thrusters are from two Voyager episodes, The 37's and Coda. In The 37's Voyager had landed on a planet, and at the end of the episode there was this dialogue before they took off: "JANEWAY: All stations prepare for departure. Condition blue, Mister Tuvok. Miss Torres, anti-grav thrusters online. TORRES: Thrusters enabled. JANEWAY: Mister Paris, inertial dampers to flight configuration. Impulse drive to stand by."
    – Hypnosifl
    Feb 1, 2015 at 23:14
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    "They churn out a huge volume of plasma, using the same technology as the warp engines do to produce thrust." Wait, what? I don't think so... For starters the warp engines don't produce thrust... Feb 2, 2015 at 0:43

If you accept any of the books as canon, then impulse drive is indeed used to to get ships from ground to orbit. In the book A Flag Full of Stars, which takes place shortly before the first movie, the Federation had taken the Enterprise saucer section down to the Earth's surface for its part of the refit. When it was time to take it back to orbit to join the newly refit secondary hull, they used "1/10th impulse power" for forward thrust and thrusters for the initial vertical thrust off of the to ground.

Also, in the movie Star Trek III, when Kirk and crew steal the Enterprise in spacedock, they use 1/4 impulse power while still inside the space dock. If impulse, as the technical manual states, were indeed .5 warp, then 1/4 of that would still be fast enough for the Enterprise to have smashed into the side of that enclosed space and ripped both the Enterprise and space dock into little bits.

That's the problem with Star Trek. Much of it is very inconsistent from one show to another and between the shows and the novels. It's hard to come up with consistently valid answers to questions.

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    That's why it's a fiction.
    – dh16
    Feb 2, 2015 at 20:47

It's important to understand that, in addition to thrusters and impulse drive, Star Trek ships have the ability to manipulate gravity. If a ship is able to control gravity sufficiently to provide normal gravity within the ship in the depths of space, the same technology can be used to make the ship effectively immune to standard gravity while on a planet.

Essentially, for a ship which has anti-gravity capabilities (like all ST ships from TOS onwards), there is no such thing as escape velocity as they do not have to escape a gravity well.

Finally, in answer to another question you seem to be asking, impulse drive is what all Federation ships use when not at warp speed. There's no indication that it is unsafe to use within atmosphere, so it is also what ships like Voyager use to take off after a landing.

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    This seems like speculation, can you point to any canon source that says they use gravity control to move on and off planets? It could be that they can locally increase gravity but not cancel external gravity, for example. Also, I think there have been various episodes showing them in danger of being pulled in or trapped by some strong source of gravity like a black hole, like the TOS episode "Tomorrow is Yesterday" or the Voyager episode "Parallax".
    – Hypnosifl
    Feb 1, 2015 at 20:24
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    @Hypnosifl: They have gravity in space. That indicates that they can manipulate gravity to the point of generating at least 1G. If they can generate 1G, they can negate 1G by pointing their generation field the other way, thus negating a planet's gravity. Being able to create 1 G does not mean they can't be put in danger by black holes (which have thousands of G's of force).
    – Jeff
    Feb 1, 2015 at 20:32
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    Gravity can only be manipulated WITHIN the ship. It can be called artificial gravity, which it doable somewhat with nowadays technology.
    – dh16
    Feb 1, 2015 at 20:38
  • As Michael said earlier, a ship under power does not have to reach escape velocity to escape a planet's gravity well. As long as it keeps thrusting upwards, it will eventually get into space. The concept of escape velocity only applies to unpowered objects.
    – rojomoke
    Feb 1, 2015 at 20:53
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    "If they can generate 1G, they can negate 1G by pointing their generation field the other way, thus negating a planet's gravity." -- Not necessarily, p. 144 of the TNG technical manual says the gravity generators use a "controlled stream of gravitons", and in real physics gravitons would hypothetically only be able to exert a pull on mass, never a push--if there are no such thing as "antigravitons" that push mass away from the direction they're coming from, I don't see how they could negate gravity by turning a graviton-generator around.
    – Hypnosifl
    Feb 1, 2015 at 22:13

Imo the answer is Yes. Depends on source. Impulse can be over 150,000 mph. I'm thinking a Defiant Class Ship, so Voyager could easily achieve escape velocity, as it did get back into space in those episode, as evidence. Your question was clear to me.

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    – fez
    Mar 28 at 6:08

In the pilot episode of Enterprise, young Archer builds and flies a model. The model's "engine" doesn't look like anything that could produce thrust in any conventional sense, especially considering the nature of its installation. That would suggest it is some sort of reactionless drive - not an "impulse" drive, and a scaled down version of what would be fitted to full-size craft.

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