So... if there is no firm ground at all - say "landing" on the surface of a lake, would the lifters disturb the surface of the lake? If above a sea, how high above the waves will the ship be (assuming calm weather)? This might make adventuring on a water world a bit more interesting.
This is partly covered in the 'Gravitics' chapter of the new
Starship Operator's Manual; I'll quote an edited, condensed version below:
Lifters have often been called ‘grav plates with their polarity reversed’, which, while not technical language, is an acceptable summation of how low power, early lifters work.
It is a common misconception among many lay sophonts that gravity drives such as lifters, g-drives, and m-drives are ‘inertia-less’ and instead they violate Agaashir’s Law of Reciprocal Motion or, among the Solomani, Newton’s Third Law of Motion. This is incorrect; they very much do obey conservation of momentum.
As solid-state machinery, lifters have no moving parts but there are noticeable cues that they are in operation. Lower-tech lifters make a characteristic low-volume, high-pitched, faintly perceptible whine as the individual grav modules flick on-and-off at a high frequency. An always-present sign of lifter operation is a soft but persistent breeze emanating from beneath the vehicle. This effect explains the strange sensation when putting a hand or equivalent under a lifter in operation, for as it enters the field, it suddenly feels slightly heavier, as if wearing a lightly weighted glove. That is because the hand is helping the lifter stay aloft.
(...)
As a lifter vehicle climbs in altitude, it needs to increase its operational envelope size so that it encompasses enough mass to keep it aloft. In doing so, it increases its power expenditure; the bigger the envelope, the more power it draws to keep operational. To deal with this increased draw, the lifter can decrease the strength of its generated gravity field but that generates less lifting power for a given field size.
Larger power supplies, lifters manufactured from higher-efficiency grav modules and optimised field geometries can all increase the altitude a lifter vehicle can attain but even an idealised, perfectly efficient lifter will inevitably reach a maximum operational altitude of roughly one planetary diameter. Worlds with dense atmospheres have more available mass to push against beyond the surface, so they allow for a slightly higher operational ceiling; worlds with thin atmospheres allow slightly lower. Beyond this point, a lifter simply cannot generate enough lift to keep itself aloft.
(Disclaimer: The above if quoted from an earlier manuscript of the SOM)
So strictly speaking, the answer is 'Yes, but...'; if the lake is small, its entirety is probably within the operation envelope of the lifters' field, and the acceleration the mass within said field is subjected to is very very small, so no ripples.
If the ship was hovering over a
huge lake though, there's a possibility – especially if it is hovering at a low altitude close to its surface and, therefore, is using a small envelope size with a slightly more perceptible acceleration – that the gravity gradient between the regions within the field and outside will create a kind of upside-down convective current, causing surface disturbances.
But these would be very small and would be hard to make out from the usual wavy-ness of large lakes.
If the ship were
moving though, now
that would create waves; but not because of the lifters, but due to the fact that any object (especially massive ones) moving inside an atmosphere will create a low-pressure zone behind them, and
that would create a noticeable effect on the surface of the water if flying low, doubly so for denser atmospheres.
I couldn't care less what Mongoose says maneuver drives are like in their version of the Third Imperium, but if they now have lifters built into every m-drive - which they do according to SOM but not mentioned in CRB or HG - then ship opperations in the setting change a lot. The law of unintended consequences strikes again.
When writing the SOM under the mandate of 'try to reconcile the two currently published Traveller versions', the way we tried to reconcile their absence from Mongoose's Highguard was saying:
On any modern starship designed for planetary landings, lifters are included in the hull, much like landing gear. Normally integrated into the ventral hull, they are sometimes co-located with the landing gear bays but more often spread among the ventral surface. These lifter plates provide redundancy and a degree of fine control to allow the vessel to take off and land vertically with minimal difficulty, as well as to hover at any desired altitude [within their operation range].
It's a bit weaselly in that it leaves the presence or absence of Lifters in any given ship design as something to be arbitrated by the Referee, but given they're not part of the design sequence itself and SOM was meant as a largely system-agnostic, Chaterd Space-specific book of fluff, that was what we were able to do.
If one needs a heuristic to decide whether a ship has or hasn't lifters, personally I'd use the following:
- If the ship it TL7 or lower, it automatically lacks lifers*.
- If the ship is a non-gravity hull, it lacks lifters†.
- If the ship is unstreamlined, it (probably) lacks lifters*.
*Subject to The Zeroth Rule: the referee can, at their table, simply say otherwise on a case-by-case basis
†This specific point is the only one I feel we should be a bit stricter on, because I rationalise the higher cost and power per-unit for the Gravity Hulls as being due to lifters, gravity generators, inertial compensators
et al.
So using the above heuristic, the Beowulf-class Type-A
would have Lifters, but a Type-L Lab Ship would not. The Azhanti High Lightning, despite being both partially streamlined
and a gravity hull probably wouldn't include lifters as it isn't really meant to land on planetary surfaces, but if the Referee
really wanted to have the AHL hovering ominously over a town in an adventure, they could rule that it does have them; so on and so forth.
Hopefully, if ever/when a new revision of the High Guard rules is made, it'll include lifters within its own design sequence, but for the moment this is what we have, such as things are.
