I just finished watching the remastered version of "The Emissary" and thought the way that K'Ehleyr rendezvoused with the Enterprise was interesting. She was stuck inside a Class 8 probe, which looked like a photon torpedo and traveled at Warp 9 to meet the Enterprise. How could a probe travel at Warp 9 when there is no obvious signs of any type of equipment (Warp engine) that would allow the probe to travel at such speeds? She barely fit in the probe, had an oxygen mask and that pretty much took up all the space in the probe. Does Starfleet have some secret Warp-nano technology? Here are some pictures:
I liked her best there too, it's too bad they were wary of using Vulcans too much back then. Suzie also looks good as a tough Andorian amazon in ENT: Cease Fire.
To answer the question seriously, I believe it's the TNG tech manual which says that photon torpedos and such have warp sustainer engines...essentially a torpedo/probe fired at warp tends to remain at warp.
But apparently this contraption was not fired at warp, because it originated from a starbase that claimed it couldn't send the passenger aboard a ship because none were available... A starbase supposedly can't travel at warp! Also, there are several examples in TNG of these small probes being fired at crawling speed, and soon providing information from across interstellar distances (most notoriously "Inner Light"). They could well have the ability to accelerate to warp on their own, then. OTOH, the probes seen achieving such feats are of a special design that does not look like a photon torpedo. This design could also be somewhat larger than a photon torpedo (if we forget about some ambiguous "full scale" prop work in "The Enemy") - and it has two semicircular wings that curiously resemble Vulcan warp engines... Possibly the Class 8 Probe is a multistage affair: the Vulcan warp engine accelerates the larger whole to high speeds, at which point the instrumented, photorp-sized payload separates and continues at warp. Or then this particular Class 8 Probe was launched by a booster, available at the starbase, while those used by starships are not boosted that way; only the larger probes with the Vulcan-style drive (usually called Class 1) are capable of high warp when ship-launched. All this musing becomes irrelevant, though, if Starfleet indeed has miniature warp engines. And we must remember that photon torpedoes often travel at warp, despite leaving the launcher of the starship at very low speed (unless the launch is seen in slow motion, perhaps?). Timo Saloniemi
I don't see why Starfleet can't have mini-warp engines. Ship engines always scale with the ship. I imagine that, if we wanted to be methodical and mathematical about the matter, we could calculate the size of the engines for the probe given the relationship of engine size to ship size for everything from shuttle pods to starships.
We could also complain about the lack of warp glow around the probe - either in the form of the usual red lightning that surrounds a photorp, or in the form of blue glow from engine "grilles". We have never really seen "warp coasting", and supposedly shutting down the engines takes any ship out of warp, if not immediately (see "Force of Nature"), then pretty fast anyway. But various alien spacecraft manage to warp without the glowing bits, and arguably Kirk's old ship did that, too. Timo Saloniemi
Well, for a little while until the sustainer engine runs out of fuel and then it drops back to sublight (but the DS9 Tech Manual says that if a photon torpedo misses its intended target and flies out of range, it will self-destruct). Back to the TNG Manual, though, it does list that Class-8 probes are capable of accelerating to Warp 9, but it can only maintain that for 6.5 hours, which roughly matches the little over six hours the Enterprise had to rendezvous with K'Ehleyr's probe after it left Starbase 153. It could be argued that there are such things as mini-warp engines, but due to their small size, they can only maintain warp for an correspondingly short period of time.
We actually hear of exceptional probe feats fairly often. Indeed, the earliest probes mentioned, such as Friendship 1, seem to greatly outperform not only the starships of the era, but also starships of significantly later eras. We might argue that probes achieve great propulsive performance because they can do something crewed vessels cannot - say, maintain a more intense warp field or run on a more capable power source or other technology that will do serious harm to any humanoids nearby. Packing K'Ehleyr in one of those deathtraps might not be inconsistent with this; it would merely highlight her bravery and/or devotion to the mission... A bit like how the pilots of German rocket-powered interceptors agreed not just to operating aircraft that had high odds of blowing up on their own, but to sitting in cockpits whose poisonous rocket fuel fumes were certain to kill them after a relatively low number of missions regardless of mission success. Timo Saloniemi
This and the sun killer missile from Generations made me wonder about something. In the Cold War, we were used to being under the theat of missiles. So I figured that when growing up, the Feds and Klingons had warp capable drones that could accelerate very fast but would burn out. By the time TNG rolled out, we had merculite rockets. I assume Soren's drone would self-destruct from the strain after a few moments, but by then it had reached its target anyway. So I am going to say the probe was placed in front of a starbases free floating communications array (a starbase isn't just a spacedock, but ground facilities under it, space elevators on the bottom, etc.) This work scame before the soliton wave, but a modified torpedo drone type deal--was all that could be fired in this way--a one man subspace catapault of sorts. In the old GEC, there was a Klingon version called venom lance or something.
Maybe the Starbase doesn't travel at warp, but there may be some contraption that is capable of launching small ships into warp speeds - something like that catapult in a Voyager episode.
...Like said, we have seen probes capable of that: TNG features several shots of probes being flown out of the forward torpedo tube at crawling speed, but soon transmitting information from far, far away. And then there are the shuttlecraft: not that much smaller than a torpedo, but (seemingly) capable of going to distant stars and back. So we'd probably have to provide an explanation for why a torpedo-sized machine could not go to warp all on its own. The problem with "The Emissary" is that the probe is among the smallest we have ever seen; is shown to be mostly empty inside; reaches exceptionally high warp speed; and sustains that speed for a long time. We may limit the problems with that by saying that the probe we see is just the last stage in a multistage system, and that it uses the powerless coasting trick from "Force of Nature", and so forth, but the sum total of the problems is still rather overwhelming. Timo Saloniemi