How is M-Drive Thrust applied?

[Stainless Steel Fox]

M-Drive is your basic reactionless drive system, fair enough and the visible 'engine nacelles' are actually exhausts for ionisation produced by the thruster plates, from what I've read here. The question I have is, is the thrust applied to the hull of the vessel as a whole, or is it applied to the drive plates of the M-drive and the force is transmitted to the hull by a bracing structure, as with a reaction drive engine?

In either case, can the vector of thrust be changed without changing the orientation of the M-drive?

In the second case, could you change the vector of thrust by either mechanically gimballing the drive plate assembly, or use multiple drive plates running at different thrust levels to produce differential thrust?

 

[JustEastOfTheEdge]

I would assume multiple plates, and activating only the required ones to get the vector change needed. But since the whole thing is science-fantasy anyway...

 

[Condottiere]

1. That depends, I would guess, on the author.

2. Gimbals are so technological level seven.

3. Vectoring is most likely through the use of magnetic/gravitic field manipulation.

4. I'd say the High Guard manoeuvre drive is directed push.

5. Exception is likely factor zero, the larger size and lack of substantial thrust implies it's distributed throughout a significant part of the hull.

 

[paltrysum]

M-Drive is your basic reactionless drive system, fair enough and the visible 'engine nacelles' are actually exhausts for ionisation produced by the thruster plates, from what I've read here. The question I have is, is the thrust applied to the hull of the vessel as a whole, or is it applied to the drive plates of the M-drive and the force is transmitted to the hull by a bracing structure, as with a reaction drive engine?

Not sure about this one. Perhaps Adrian will cover that in his Starship Operator's Manual.

In either case, can the vector of thrust be changed without changing the orientation of the M-drive?

Yes, it can. See p. 15 of High Guard 2022.

In the second case, could you change the vector of thrust by either mechanically gimballing the drive plate assembly, or use multiple drive plates running at different thrust levels to produce differential thrust?

In HG2022, we imply that they remain stationary, but that Thrust can be applied in other directions, albeit at reduced efficiency. A manoeuvre drive on gimbals, now that sounds pretty cool. Haven't really wrapped my head around the applications yet. Slightly improved time-to-destination maybe, since your gimballed thruster plates could be optimizing Thrust while the ship turns around at the halfway point for slowdown.

 

[Stainless Steel Fox]

Interesting. If the thrust vector can be altered without reorienting the drive plate, it may be similar to how a phase array radar can change the direction of the radar beam without moving the radar. Though I'd have to assume it had a limited range of vectoring.

One reason I was looking at a gimballing or thrust vectoring M-Drive was for first generation M-drive spaceplanes, without the niceties such as artificial gravity or contra-gravity (Z drives). One G of thrust along their horizontal direction could provide atmospheric flight, while vectoring it downwards then allows you to fly with the floor under you in space. The thrust plate would oriented at 45 degrees down and backwards with a 45 degree vector angle either way.

Of course a Thrust 1 spaceplane without Z drives would need a higher thrust booster to boost it to several kilometres per second on an arc out of the atmosphere which would give the M-Drive to boost it to orbital speed. The booster could be reusable, returning to land like the Falcon 9 first stage. I don't think simply dropping it from a sub-sonic plane like the X15 or SpaceShip Two would give it enough momentum, even if it could fly upwards using it's wings for hypersonic lift.

A capsule design using this system, such as a Dragon or Orion capsule with the M-drive replacing the regular engines respectively wouldn't need vectoring.

I did some maths. a 10 ton vehicle with a Thrust 1 M-Drive uses 1 power. I know we should be putting aside another 2 power for ships systems, but this is primitive, so we're assuming other power usage is negligible.

I suspect a vehicle that small wouldn't be able to fit a first generation fusion/fission powwer plant, so it might well use a more primitive High Efficiency accumulator (TL-10 gives 40 power/ton for a round and TL-12 gives 60 power/ton for a round so a TL8 version would logically be 20 power/ton). A round is 6 minutes in space ship scale operations, so 1 ton gives us 120 minutes or 2 hours of operation.

4 tons, or in general 40% mass of the vehicle as accumulators woiuld give ample power for a constant boost round trip to the moon, and even 1 ton or 10% vehicle mass would easily achieve extended orbital operations, including slowing down enough for a low speed re-entry, removing the need for a heat shield.

 

[Technetium 98]

The Starship Operator's Manual for MGT2 has yet to come out, but there's still its MegaTraveller equivalent! Any of this might be superceded, though.

Is the thrust applied to the hull of the vessel as a whole, or is it applied to the drive plates of the M-drive and the force is transmitted to the hull by a bracing structure, as with a reaction drive engine?

The latter, though there are a couple of earlier sources I don't quite recall implying the former. Not sure how inertial compensation works in this context, maybe it's tied into the artificial gravity systems?

In either case, can the vector of thrust be changed without changing the orientation of the M-drive?

Yes, but you can only achieve 100% thrust in a narrow cone behind the drive. That drops to 25% laterally, and 10% when it's vectored directly to fore. The book describes taking off with a nose-up attitude, which... I hate, honestly, and runs counter to a lot of other Traveller art. Maybe it's got lifters in the ventral hull to hover?

Interestingly, you could use this for attitude control - refer to contemporary jet boats for an idea of what 360 degree control authority can look like - but this book instead chooses to reference a fuckoff massive flywheel at the centre of mass, instead.

 

[Condottiere]

Manoeuvre drives, whose function is described in Ship Design on page 15, use thruster plates to move a ship without the need for propellant. Manoeuvre drive thruster plates are typically located on the outer surface of a ship (facing aft is standard) where they can perform best. While acceleration to their facing is optimised, a ship may accelerate in other directions at reduced thrust without turning the ship to a new facing. For example, thruster plates can accelerate a ship at up to 25% of their maximum thrust to port or starboard and 10% to fore. Therefore, a ship with Thrust 4 could exert one G of thrust to left or right and 0.4G to fore without the need to turn the ship on its axis.

 

[Stainless Steel Fox]

Interestingly, you could use this for attitude control - refer to contemporary jet boats for an idea of what 360 degree control authority can look like - but this book instead chooses to reference a fuckoff massive flywheel at the centre of mass, instead.

This is exactly the sort of thing I was looking for. If the thrust plates are at the back and along the centre line, forward/aft acceleration is in a straight line, and that 25% sideways vector would act as roll/yaw attitude control, spinning the vehicle to face a new heading.

Manoeuvre drives, whose function is described in Ship Design on page 15, use thruster plates to move a ship without the need for propellant. Manoeuvre drive thruster plates are typically located on the outer surface of a ship (facing aft is standard) where they can perform best. While acceleration to their facing is optimised, a ship may accelerate in other directions at reduced thrust without turning the ship to a new facing. For example, thruster plates can accelerate a ship at up to 25% of their maximum thrust to port or starboard and 10% to fore. Therefore, a ship with Thrust 4 could exert one G of thrust to left or right and 0.4G to fore without the need to turn the ship on its axis.

However, this suggests that the sideways vector moves the entire vessel laterally, translating or strafing rather than turning. That would only work if the thrust was applied to either the centre of gravity of the ship, or the entire surface of the ship, meaning that the thrust plate is on the surface to make solid contact with the hull and transmit the thrust effect across it.

 

[Condottiere]

Possibly one reason for the drop off in actual thrust tonnes is compensating for the off centre placement of the thrust plates.

It's up in the air if you're looking at a field effect, or directional thrust.

 

[Stainless Steel Fox]

Though the vectoring idea gives me a thought about Z-drives, contra-gravity. They are a TL-7/TL-8 tech whereas full blown M-Drives are TL-9. What if Z-drives work by altering the acceleration vector of the natural gravity field while TL-9 is where you learn to generate your own acceleration vector as well as vectoring it.

To hover you divert the downwards vector out to the sides in a horizontal circle. Varying the effect on different sides gives you a horizontal flight vector, admittedly only 25% of the downwards acceleration. Likewise, you can even accelarate upwards at 40% of the downwards acceleration.

Of course, since you're only manipulating an existing acceleration vector, and only getting a partial acceleration you only get low speeds, and can only operate in relation to a significant body of mass, like a planet.

 

[Condottiere]

Can't remember which edition lifters are integrated as part of the manoeuvre drive.

 

[phavoc]

If I recall correctly, the guide said that a ship could go to 400% power for short periods to accommodate the 25% lateral thrust. Unless a ship had a 4G drive, that was what was required for a 1G ship to hover on a 1G world. This is unnecessary and design-wise rather silly since anti-gravity is available at TL-9. I thought the SOM was great, but the M-drive explanation was off-putting and made no logical sense to me. Since TNE came out after, and wasn't repeated in other versions, it's kind of been dormant since.

 

[paltrysum]

Can't remember which edition lifters are integrated as part of the manoeuvre drive.

TNE incorporated heplar.

 

[Lurking Grue]

Yes, TNE had HEPlaR drives (which are not reactionless drives) and had contra-gravity which is different from the grav drives of other Traveller editions. Contra-Grav produces no thrust, only lift (well, pseudo-lift), while the grav drives of other editions did produce thrust. With HEPlaR, you've basically got yourself a high tech (very high efficiency) rocket and you do have nozzles at the back of the ship for the rocket exhaust. Any thrust vectoring needs to be done the old fashioned way and any landing site is going to be torched if you take-off/land with a HEPlaR drive not aided by CG (or runways, wheeled landing gear etc.).

 

[Condottiere]

It's one reason I'm interested in orbital range with five disadvantages.

Those become lifters, at minimum volume and/or energy input.

 

[phavoc]

I have to look at my TNE, but contragravity in gurps is equivalent to anti-gravity. And in most sci-fi generally equates them. Pipers Space Vikings talked about contragravity, but they were written in the 50s and that was the norm for the label.

 

[Annatar Giftbringer]

An excellent question, Stainless Steel Fox, and something I've wondered about as well.

With the High Guard update confirming that M-drives lose effect when vectoring output (25% for lateral thrust, which presumably includes up/down) it's clear that something else is needed for ships to be able to takeoff and land without runways or external aid.

Solomani Front introduces momentary overthrust, and doesn't go into details regarding how much extra thrust can be gained, or for how long. It might well be able to provide a 4x temporary boost, likely just for seconds or a minute or so, after which the process cannot be repeated without a cooldown period. The ship in question would then likely travel slowly towards the landing spot, using vertical thrust to slowdown the fall before applying a short boost burst for the actual landing.

Element Class Cruisers mentions secondary lifting/maneouvre units, capable of maintaing hover against 0.177G.
Perhaps streamlined ships have more powerful lifters?

I was also thinking about grav compensation, mentioned in High Guard Update on p.15. What if they could negate not just the ship's acceleration, but external acceleration as well? Meaning that a ship with 1G M-drives could counteract up to 1G local gravity and float, while using its M-drive at 25% capacity to move up and down for takeoff and landing?

Or simply assume that whatever system grav vehicles use is included in space ships as well.

Either explaination could work imho. Momentary overthrust and its cooldown period would mean that any ship with M-drives less than 4x local gravity would be unable to quickly land to pick up or drop off people or goods, unless it's done quickly enough for landing and takeoff within a single overthrust cycle.

 

[phavoc]

Engineering-wise, the explanations provided in SOM and the passage in HG. Safe operations is the number 1 priority for carrying passengers and for merchants.

The issue here, as I see it, is that they are just unwilling to answer the question simply and logically. Anti-gravity is a MASSIVE boon for designers and for safe operations. If you have a personal grav belt, you are gonna have anti-grav in these ships. Also, the designs/illustrations imply that these ships have the ability to negate gravity and land/take off using it.

From an engineering point of view, regularly stressing your plant beyond its normal operations is hard on the equipment and leads to more costly maintenance. While there is some modern designs that do this, most are military and not civilian. A Boeing or Airbus aircraft engines ramp up to maximum power for takeoff, and then throttles back for cruise. That's 100% power and then settling back to about 90% for cruise. They do that for fuel consumption and costs.

It just makes too much sense for tl9 ships and above to come with antigrav by default.

 

[Condottiere]

Technological level ten gives us access to factor three manoeuvre drives, so in the big picture, it's not an issue.

But if we're min maxing technological level nine, then it does bear examination.

 

[Annatar Giftbringer]

Engineering-wise, the explanations provided in SOM and the passage in HG. Safe operations is the number 1 priority for carrying passengers and for merchants.

The issue here, as I see it, is that they are just unwilling to answer the question simply and logically. Anti-gravity is a MASSIVE boon for designers and for safe operations. If you have a personal grav belt, you are gonna have anti-grav in these ships. Also, the designs/illustrations imply that these ships have the ability to negate gravity and land/take off using it.

From an engineering point of view, regularly stressing your plant beyond its normal operations is hard on the equipment and leads to more costly maintenance. While there is some modern designs that do this, most are military and not civilian. A Boeing or Airbus aircraft engines ramp up to maximum power for takeoff, and then throttles back for cruise. That's 100% power and then settling back to about 90% for cruise. They do that for fuel consumption and costs.

It just makes too much sense for tl9 ships and above to come with antigrav by default.

Agreed. There needs to be a safe and reliable system to facilitate takeoff and landing, or every ship intended for planetary landings would/should have M-drives strong enough to support it.

The momentary overcharge might be a builtin design feature, with M-drives capable of short over locked bursts without additional wear and tear thanks to (technobabble), or simply grav lifters.

I’ve never given it any thoughts until recently, just assumed that “they can” since so many ships have a 1G M-drive yet are designed for planetary interaction.