Highport for a Tide-Locked World

[AnotherDilbert]

ITTR having read somwhere (sorry, Icannot tell you where) that something like 0.05G will sufice, and that is not so expensive, I guess.

That will, I believe, suffice to stay in a stable orbit (like geosync) but not in any forced orbit.

 

[sudnadja]

To keep a station stationary above a point on Earths surface takes a force of:

F = mrω²

where r is the radius of the forced orbit, say 1000 km plus the Earth radius of 6400 km = 7400 km, and ω is the angular velocity 2π/86164s ≈ 0.000073 s⁻¹.

So F = mrω² ≈ m × 7400000 × 0.000073² ≈ m × 0.039 m/s² which is next to nothing. The problem is that gravity provides GM/r² ≈ 7.279 m/s² at that height.

So to stay in that forced orbit we need to accelerate at 7.279 - 0.039 ≈ 7.240 m/s² ≈ 0.74 g.

(Please check my calculations, I'm doing this with the help of wiki.)

To stay wherever we want over the planet we need a large fraction of 1 g, so almost a 1 g drive. 0.1 g will not make many forced orbits possible.

yes just solve r ω² == G M r ⁻² for r and that will give where the forces balance out in a two body system.

In Traveller 5 there are at least three drives that could support stationkeeping or forced orbits), the M-drive, the G-drive and Z-drive (lifter). I believe the implication of the lifter is that it simply cancels local gravitation. I'm not sure how it can cancel planet gravity without canceling star gravity (thus flinging it off into a stellar escape) but I don't see any limitation on the operating period of the lifter, it does work out to 1 diameter, and seems to be very inexpensive.

 

[AnotherDilbert]

yes just solve r ω² == G M r ⁻² for r and that will give where the forces balance out in a two body system.

Thanks.

In Traveller 5 there are at least three drives that could support stationkeeping or forced orbits), the M-drive, the G-drive and Z-drive (lifter). I believe the implication of the lifter is that it simply cancels local gravitation. I'm not sure how it can cancel planet gravity without canceling star gravity (thus flinging it off into a stellar escape) but I don't see any limitation on the operating period of the lifter, it does work out to 1 diameter, and seems to be very inexpensive.

I believe agrav simply provides thrust, not fiddles with the local gravity field. That was explicit in CT and MT, and is the only way to keep physics relatively intact.

 

[whartung]

Why would a high port be in geosynchronous orbit in the first place? Why would that matter? Are they lowering goods down on a rope?

 

[sudnadja]

I believe agrav simply provides thrust, not fiddles with the local gravity field. That was explicit in CT and MT, and is the only way to keep physics relatively intact.

Even then, they're going to provide at least 1G, in T5 the power system for the G-drive is integral and it doesn't need any extra power, and there's no word that I see about needed heat dissipation (which is probably not a problem at the higher TLs anyway- I don't remember where I saw heat destruction refrigeration in the tech chain though and can't find it, so might be misremembering an IMTU item as general canon. ).

Gravity manipulation is a TL-10 technology in T5, though I'm not really sure what "gravity manipulation" means in this context.

 

[AnotherDilbert]

Why would a high port be in geosynchronous orbit in the first place? Why would that matter? Are they lowering goods down on a rope?

Is was suggested by McPerth:

I'd say with the advent of the gravitics (when you can have thrust just from power, that can be obtained with solar pannels, so not needing reacion mass), station keeping thrusters make quite easier a geosynchronous placement of any orbital object, as it will no longer depend on orbital mevchanics, but may correct its positions as needed.

 

[AnotherDilbert]

Even then, they're going to provide at least 1G, in T5 the power system for the G-drive is integral and it doesn't need any extra power, and there's no word that I see about needed heat dissipation (which is probably not a problem at the higher TLs anyway- I don't remember where I saw heat destruction refrigeration in the tech chain though and can't find it, so might be misremembering an IMTU item as general canon. ).

As far as I understand Lifters are the same technology as G-drive, but just a weaker drive that can just achieve as much thrust as the local gravity field, but not more, so no horizontal or lateral acceleration. Hence it could not be used to accelerate upwards or accelerate to change orbital velocity.

To achieve and keep a forced orbit close to a planet we would need at least a G-drive, and outside 1 diameter an M-drive.

 

[sudnadja]

As far as I understand Lifters are the same technology as G-drive, but just a weaker drive that can just achieve as much thrust as the local gravity field, but not more, so no horizontal or lateral acceleration. Hence it could not be used to accelerate upwards or accelerate to change orbital velocity.

To achieve and keep a forced orbit close to a planet we would need at least a G-drive, and outside 1 diameter an M-drive.

So say an Air/Raft starts lifting and reaches orbital altitude - by what drive system did it do that, and what prevents it from just perpetually staying there? The traveller wiki states, "Cruising speed is usually 100 kph, with unlimited range and endurance."

 

[nobby-w]

If it can generate heat, it can also generate power (via thermocouple at very oleast). Presumably it consumes more power than it can theoretically produce?

If the system has any inefficiency at all it will generate a lot of waste heat.

 

[AnotherDilbert]

So say an Air/Raft starts lifting and reaches orbital altitude - by what drive system did it do that, and what prevents it from just perpetually staying there? The traveller wiki states, "Cruising speed is usually 100 kph, with unlimited range and endurance."

Liftcraft. Aircraft with lifters create a cancelled or coun- teracted gravity effect which lifts them above a world surface.
Lifters do not require atmosphere.
Lifters provide very small horizontal or vectored thrust. Additional thrust can be provided through the High Powered Option.

Still requires power, so no infinite duration.

Lifters are anti-gravity modules which effectively negate the force of gravity. Lifters are a hull component; they draw minimal levels of energy from a power source.

An air/raft can slowly ascend to great height, but not accelerate to orbital speeds, as far as I understand.

 

[sudnadja]

Still requires power, so no infinite duration.

Does it require power by the rules? I don't think I actually have a copy of the LBBs anymore.

 

[kilemall]

Hmm, I would think a space elevator is easier on a tidally locked world.


As to the issue with where the Highport, I would say that's a function of distance and busyness of the starport.


You could have one or more space elevator ports if the beanstalk has enough capacity for the port- I would think that would be an optimal small world/starport B option.


A single highport in orbit would probably do for small to medium B/C starports.


However, for busy highpop/medium to large/A starports, I have to think the way to go is multiple highports in low orbit-

• fast transit whether grav or M-drive craft,
• you have multiple facilities for optimal launches both to highport or outsystem,
• the highports have velocity to help with initial launch and having set vee for easier matching for incoming from either planet or 100D,
• the highports can orbit around until they match the optimal downport and drop straight down if the shuttle leaves out the 'IN' side (the trailing side), and
• you can just add more for greater capacity.

Flip side, low orbit would involve having M-drive, but having more utilized and effecient 'aerospace' lanes for very busy ports may be worth it.

 

[AnotherDilbert]

Does it require power by the rules? I don't think I actually have a copy of the LBBs anymore.

From CT:

Range in time or distance on a world is effectively unlimited, requiring refueling from a ship's power plant every ten weeks or so.

 

[tjoneslo]

Hmm, I would think a space elevator is easier on a tidally locked world.

It's actually harder. Like the previous discussion, you will need to put the highport in the L1 or L2 points, which is much further out. The slower the rotation of the planet, the further out the high point / anchor point needs to be, and hence longer the cable.

There are dynamic lift systems. The high port is in orbit and the lower point swings down and lifts off again. Rather than be anchored to a single point on the surface.

As to the issue with where the Highport, I would say that's a function of distance and busyness of the starport.

I recommend GT: Starports. It has rules to calculate the size of the port, number of people who work there and a starport construction system, including one or more High Ports.

 

[agorski]

I guess station keeping thrusters are quite smaller than M-1...

ITTR having read somwhere (sorry, Icannot tell you where) that something like 0.05G will sufice, and that is not so expensive, I guess.

The only thing I could find is an interdiction satellite design in IISS Ship Files. Solar panels, battery storage, and "attitude thrusters". No power plant or maneuver drive. This could be designed using T5 rules.

 

[McPerth]

The only thing I could find is an interdiction satellite design in IISS Ship Files. Solar panels, battery storage, and "attitude thrusters". No power plant or maneuver drive. This could be designed using T5 rules.

Well, solar pannels are a kind of power plant, and the thrusters, despite being under M1, are mini maneuver drive (that is defined as being thrusters, isn't it?).

 

[agorski]

Well, solar pannels are a kind of power plant, and the thrusters, despite being under M1, are mini maneuver drive (that is defined as being thrusters, isn't it?).

Sure. In a Traveller context, however, power plant in ship design implies a fusion plant, and maneuver drive implies an M-drive. So that's what I meant to say.

 

[McPerth]

Sure. In a Traveller context, however, power plant in ship design implies a fusion plant, and maneuver drive implies an M-drive. So that's what I meant to say.

Well, that depends on the power needs...

In fact, in MT and MgT (AFAIK, there are some systems I don't know about) there are provisions for a solar power plant. While it will not be useful for a jump ship (off course, as it spends about a wek out of the sunlight), it is for satellites and likely crafts.

Also in MT the drive may be M-drive or, in some cases, grav plantes, again for the same kind of ships (and of course, for smaller vehicles).

 

[AnotherDilbert]

In fact, in MT and MgT (AFAIK, there ares ome systems I don't know about) there are provisions for a solar power plant. While it will not be useful for a jump ship (off course, as it spends about a wek out of the sunlight), it is for satellites and likely crafts.

It is useful for satellites and stations in orbit, not for objects kept aloft by M-drive.

Extendible solar panels provide backup power for a ship’s power plant.
...
A ship equipped with solar panels consumes power plant fuel at one–quarter the normal rate so long as it is only engaged in minimal manoeuvring and does not fire any weapons. Minimal manoeuvring does not include long periods at full thrust, so solar power alone is useless for most commercial and military vessels.
No power plant fuel is consumed, and endurance is considered infinite, if the ship is not manoeuvring or refining fuel.

To rely on them you can't be manoeuvring.


In MT solar cells are limited by the surface of the vessel, and of course completely unable to power even life support.

 

[Grav_Moped]

Still requires power, so no infinite duration.



An air/raft can slowly ascend to great height, but not accelerate to orbital speeds, as far as I understand.

With near-indefinite duration hover and sufficient altitude, orbital speeds are easily (albeit tediously) achievable. Rise to orbital altitude, accelerate laterally with whatever little thrust is available, and wait. As velocity increases (remember, no air so drag-limited airspeed is irrelevant), reduce antigravity to keep from gaining altitude. Eventually, the grav lifters will be at zero lifting force and the Air/Raft will have achieved orbit.

I did the math a while back, and on a Size 8 world with standard atmosphere it takes about 2.75 hours to establish Low Earth Orbit (assuming an equatorial launch). This assumes 0.1G vertical acceleration and 0.1G horizontal acceleration capability, and minimal lateral acceleration while still in the denser lower atmosphere.

Getting to a specific orbit and orbital position (say, to meet an orbiting satellite or station) from an arbitrary point on a world's surface could take somewhat longer.