How close are orbital starports?

[phavoc]

Anyone can build a spaceport, presumably, in the Imperium.

Starports are administered by the Imperium itself, and probably with a little bit of arm twisting, aren't limited to a single dirtside facility and one orbital satellite.

Though I wonder if that authority is systemwide, or only per planet.

The Imperium would build the Imperial starport (both ground and orbital) for a system. A planet with a large population, decent tech base and large amounts of shipping would have multiple orbital facilities as well as ground ports. And there would be additional ones spread throughout a system to support colonies and other remote facilities.

It's actually an interesting question. I've not seen much literature that talks about orbital facilities and what to expect.

 

[paltrysum]

In Mongoose's Trojan Reach setting, many of the starports of the Void were built by the General Development Company. Their motives (other than profit, which I would be dubious of in the Void) is shrouded in mystery and addressed in the Pirates of Drinax campaign. The Void starports exhibit a broader range of ownership/administration than in the Imperium where all (or most?) are said to be administered by the Imperial government.

 

[dragoner]

I'm sure this would vary a lot from system to system, but typically how close would you imagine an orbital starport to be to the system mainworld? Surely inside 100-diameters. Inside 10 diameters? Inside 1 diameter?

Using Earth as an example, from 30 to 60 thousand kilometers away, probably at the end of a tether/space elevator.

 

[Rikki Tikki Traveller]

Another option would be to use natural LaGrange points if the world has a moon. The L4 and L5 points (60-degrees ahead and behind a moon's orbit) are naturally stable and would not require thrusters or a drive to keep them in place.

 

[Condottiere]

Terra was under Solomani control during the Rim War, but I recall mention of three separate Starports, or at least, ground facilities.

 

[steve98052]

The only difference between a starport and a spaceport is the presence of administrative facilities to process visitors from other systems. So an "E" starport is a level patch of rock or concrete with a customs and immigration shack and a marked extraterritoriality line, while the corresponding spaceport is a level patch of rock or concrete without the customs and immigration shack and extraterritoriality line -- but maybe a similar shack and line equipped only for intra-system traffic.

There aren't many space elevators mentioned in canon, because in the Traveller technology scale gravitics arrive fairly early, and extreme tensile strength materials arrive fairly late.

The idea of multiple highports just inside the 100 diameter limit of the main world or star is somewhat appealing, but a more practical alternative would be high-G lighters or module tugs (and fuel tankers) stationed in anticipation of scheduled super-freighters or giant liners. Those would serve the goal of keeping the expensive jump ships operating with less time in normal space.

I would think that the range of planetary defenses would influence positioning of highports, since they're juicy targets in time of war.

 

[Condottiere]

Transport infrastructure can sort of be divided between most efficient, least resistance, and promoted, not necessarily the same thing.

If you have government subsidies and tax benefits for building space elevators, lobbied by vested interests, you'll get beanstalks.

But our manoeuvre drives that you get in an early prototype form by technological level seven tends to allow direct access to space from any point on the surface, with presumably the only requirement being a firm landing surface, or even just plopping on calm water.

 

[GypsyComet]

From a pure safety standpoint you'd want orbital warehouses and stations at the 99D limit rather than at the 100D or beyond. The reason for that is safety, and security. It means that a ship exiting jump space would not be an immediate hazard to a station.

...

While speed and efficiency are the wherewithal of any merchant line, safety and security trump them.

Which is why I think stations will be in lower orbits, to be honest. The difference between 99 diameters and 100 diameters is negligible in space combat. A station at 1 to 5 diameters is easier for the planet to defend, while 99 diameters is roughly twice as far out as Luna is from Earth.

The safe answer is, of course, "it depends". On system topography, political and traditional thought, aggressive vs passive stance toward the universe, the nature of the neighbors, and other things.

 

[Nobby-W]

I'm sure this would vary a lot from system to system, but typically how close would you imagine an orbital starport to be to the system mainworld? Surely inside 100-diameters. Inside 10 diameters? Inside 1 diameter?

Typically low orbit - a few hundred km up. This type of orbit will have a period of (say) 1.5-2 hours, meaning that it can service multiple downports with a launch window every orbit for shuttles between the highport and downports to make a time-efficient rendezvous (i.e. shortest flight time). This will be the cheapest and quickest orbit to get to/from ground-based downports.

 

[steve98052]

Short answer: highports are in fairly low orbits, by Traveller distance standards.

Long answer:

For Earth, a geosynchronous orbit -- 42,164 km (26,199 miles) from the center or 35,786 km (22,236 miles) from equatorial sea level -- is about 3.305 diameters from the center or 2.805 diameters from the surface, based on 6378.1 km (3963.2 miles) equatorial radius, or 12756.2 km (7926.2 miles) equatorial diameter.

Geosynchronous orbit is considered a high orbit, but in Traveller terms it's pretty close. One of the reasons (secondary to capacity today, though not at first) that undersea fiber optic cables have mostly replaced satellite relays for most data communication is distance. The round trip time for a phone conversation through a geosynchronous communication satellite is long enough that people notice the lag in a phone conversation. That's why the Iridium phone satellites were placed in low orbit.

Low orbit, such as the International Space Station, is just a few hundred km from the surface.

By contrast, 100 diameters is really far away, far enough that the highport and downport aren't just two sections of an integrated port system. For Earth, that's about four light seconds, so communications are conspicuously delayed (eight seconds round trip latency).

The in-universe rationale for the 100 diameter limit is the distance where planetary gravitational influence is weak enough the it doesn't disrupt jump. (By that rationale, it should depend on gravity, but out of game that's too much math for gaming purposes, so they simplified to diameters.) At 100 diameters out, the planet's gravitational influence is weak enough that stable orbits may not exist, due to perturbation by other planets.

 

[BigDogsRunning]

Most starports are going to be in geostationary (it orbits at the same speed as the planet does) geosynchronous (equitorial orbit around the planetary access). Since thrusters are relatively cheap, station keeping in LEO orbit would be easy. All of these orbits would be around 1 diameter or less.

But, to muddy the waters, busy star systems that are transit points would normally have orbital warehousing and stations at the 100D limit so that cargo ships could more quickly load/unload their cargoes without the delay of flying into the local gravity well. You could find some passenger ships doing the same, but most likely they would be offloaded at major stations around the planet while they wait on their connecting starship. Planets are much more interesting to layover on.

I agree with you on the first part, putting stations close to the planet creates numerous efficiencies.

It seems like putting facilities at the 100D point wouldn't solve that problem, unless you put a bunch of them out there. If you come in on the other side of the 100D orbit, you now have to travel twice as far to reach the facility. And now transferring cargo to the planet is significantly more expensive, as is bringing fuel up from the planet to sell to the docked ships. Obviously if you're harvesting from a gas giant for fuel to sell, there is no increase in cost, but no real decrease either.

Given that you don't necessarily know where in the 100D orbit ships will be coming in, it might be useful to put them at 80D or so, instead of right at 100D. For the earth that would work out to about 2.5 times the moon's orbit.

 

[Condottiere]

Fusion creates practically free energy, efficiency at this point is time based, which is hard capped at one week down the rabbit hole.

 

[baithammer]

Some food for thought.

Suns 100 diameter limit in our solar system is 139.14 million km.
Earth distance to the sun is 149.60 million km.
The moon's 100 diameter is 347,400 km.
The distance between the moon and the earth is 384,400 km.

 

[phavoc]

I agree with you on the first part, putting stations close to the planet creates numerous efficiencies.

It seems like putting facilities at the 100D point wouldn't solve that problem, unless you put a bunch of them out there. If you come in on the other side of the 100D orbit, you now have to travel twice as far to reach the facility. And now transferring cargo to the planet is significantly more expensive, as is bringing fuel up from the planet to sell to the docked ships. Obviously if you're harvesting from a gas giant for fuel to sell, there is no increase in cost, but no real decrease either.

Given that you don't necessarily know where in the 100D orbit ships will be coming in, it might be useful to put them at 80D or so, instead of right at 100D. For the earth that would work out to about 2.5 times the moon's orbit.

Shouldn't be difficult, as that's what your navigational charts are for. You would know where a planet and it's major hub stations where before you jumped to another system. Yod simply plot your arrivaluable accordingly.

Stations at the outer edge are there to speed transit times for the jump ships as that appears to be the higher cost. And if the system is part of a hub and spoke system then you are still saving money because some passengers and cargoes are just stopping over in the system on their way elsewhere.

 

[steve98052]

A system's primary port is the starport. All others are spaceports. If quick connections are economically justified, it makes sense to provide a few minimal service spaceports just inside the 100 diameter limit, in directions that optimize the most important connections. The only services those spaceports would provide are the ones that are necessary for quick turnaround:
- Slow robot fuel skimmers,
- Fuel tanks,
- High acceleration fuel tankers,
- Planetary cargo transit shuttles,
- Pass-through cargo module docks,
- High acceleration modular cargo lighters,
- Planetary passenger shuttles,
- Passenger connection services (short term hotels, restaurants, entertainment, etc.),
- High acceleration modular passenger shuttles, and
- Employee facilities.

One could call such a facility and express spaceport.

There would still be a regular starport, with highport and downport sections to handle customs and immigration, and traffic that hasn't been optimized for special fast turnaround traffic. There might also be other regular spaceports.

 

[BigDogsRunning]

I agree with you on the first part, putting stations close to the planet creates numerous efficiencies.

It seems like putting facilities at the 100D point wouldn't solve that problem, unless you put a bunch of them out there. If you come in on the other side of the 100D orbit, you now have to travel twice as far to reach the facility. And now transferring cargo to the planet is significantly more expensive, as is bringing fuel up from the planet to sell to the docked ships. Obviously if you're harvesting from a gas giant for fuel to sell, there is no increase in cost, but no real decrease either.

Given that you don't necessarily know where in the 100D orbit ships will be coming in, it might be useful to put them at 80D or so, instead of right at 100D. For the earth that would work out to about 2.5 times the moon's orbit.

Shouldn't be difficult, as that's what your navigational charts are for. You would know where a planet and it's major hub stations where before you jumped to another system. Yod simply plot your arrivaluable accordingly.

Stations at the outer edge are there to speed transit times for the jump ships as that appears to be the higher cost. And if the system is part of a hub and spoke system then you are still saving money because some passengers and cargoes are just stopping over in the system on their way elsewhere.

OK, but, if the charts are that detailed, and the calculations that simple, why don't ships regularly accelerate out to 100D, Jump into position such that they reserve their momentum and merely decelerate at the destination. This seems like it would shave time. Since you already have to account for changing vectors based on orbital position of your target world, differences in relative velocities of departure and destination systems. There is an assumption of super precise navigational data, exquisitely precise instruments to determine your departure position. Not to mention allowing for traffic at destination systems, especially busy ones. If everyone can jump in with pinpoint precision, why not just save the cost of maneuver drives and have tugs available to grab ships as they come out of jump right on target?

If everyone was operating at TL15, I can see it, but you've got shipping that is barely jump capable, really primitive systems to begin with, and no ability to control for sensor miscalibration. I just think they would build more tolerance into the system to reduce risk. I'm surprised that as a default, incoming jump points aren't located above or below the ecliptic, to reduce the chance of someone jumping in with a lot of delta-v, in front of, and moving toward an inhabited world. It doesn't take much in the way of relative velocity to make a very large crater with a 200dton freighter. That would also prevent things like interference from the gravity well of satellites, and give you a clear approach toward whichever orbital or surface destination that you choose.

I only point out the relative velocity issue because a big deal is made of it in the psionics rules for teleportation. I'm not suggesting that they are one and the same, just that some effort has been made somewhere to address velocity/energy issues.

Other related questions include things like, is the time variation of Jump objective, or subjective. If its objective, then you have a lot more slop in where you are emerging from Jumpspace. Our sun is moving at roughly 777313km/hr, or 18.6million km/day. At one end of the 10% variation in jump time, the Sun, and all of its bodies have moved about 13.6 million km, or, about 1100 diameters, which distance you'll have to make up.

Thoughts?

 

[BigDogsRunning]

A system's primary port is the starport. All others are spaceports. If quick connections are economically justified, it makes sense to provide a few minimal service spaceports just inside the 100 diameter limit, in directions that optimize the most important connections. The only services those spaceports would provide are the ones that are necessary for quick turnaround:
- Slow robot fuel skimmers,
- Fuel tanks,
- High acceleration fuel tankers,
- Planetary cargo transit shuttles,
- Pass-through cargo module docks,
- High acceleration modular cargo lighters,
- Planetary passenger shuttles,
- Passenger connection services (short term hotels, restaurants, entertainment, etc.),
- High acceleration modular passenger shuttles, and
- Employee facilities.

One could call such a facility and express spaceport.

There would still be a regular starport, with highport and downport sections to handle customs and immigration, and traffic that hasn't been optimized for special fast turnaround traffic. There might also be other regular spaceports.

Yeah Buddy! You are right on target, and those are great details! New components assimilated, now officially part of MTU.

 

[Condottiere]

You can pick your point of departure, and only guesstimate your point of arrival.

Regular routes would probably allocate, let's call them arrival lanes, large enough to compensate for most random drops out of hyperspace, so that traffic can avoid each other.

 

[baithammer]

Just need to remember that in the habitable zone, you wouldn't be able to jump on the star facing side of the planet as it would be in the stars 100d limit.

 

[BigDogsRunning]

Just need to remember that in the habitable zone, you wouldn't be able to jump on the star facing side of the planet as it would be in the stars 100d limit.

I think the habitable zone is larger than that, but the Sun's 100D limit in our system would be at 86.4 million miles from the sun, or about about 6.5 million miles closer than earth's orbit. doesn't mean you can't have a stars 100D completely encompass a habitable world's 100D limit. I've starting doing some things in MTU for gas giant refuelling. Gas Giants aren't always close to the main world, and their 100D limit can be sizeable. You may have to travel several days, or more, to reach a Gas Giant for refuelling.

Also, depending on the star class, its 100D may be way out there. take a Blue Giant, for instance, or even a Red Giant. You could have a Red Giant whose radius encompasses Earth's current orbit. If there is a habitable world in the outer system, that is going to be one mother of a commute. would make a good Naval, or Pirate base however.