How would one navigate on Larry Niven's "Ringworld"?

Question

A long,long time ago I read Larry Niven's "Ringworld" and "The Ringworld Engineers".

It recently occurred to me that trips on the Ringworld have a problem: The Ringworld is so vast that finding out where one exactly is at any moment is fraught with difficulties. Meeting places are hard to find ("We will meet exactly 1650'000 km spinward and 244'000 km to port, next to a small forest"). Of course, there are some distinctive places one can easily identify, like Mons Olympus on the Map of Mars, but these are far and few between.

So how would one determine one's position on the ring? I thought about the following:

• Firstly, there is no practical way to navigate by the stars (or is there?) ;
• There is no GPS (as no satellites) ;
• I suppose one could use extremely exact inertial navigation (but won't the integrator be mightily confused by being on a rapidly rotating ring?) ;
• The Engineers might have thought about embedding radio-emitting marker beacons into scrith in a regularly spaced, tight network, each one emitting its position, every 1000km or so ;
• Or they could have given the Ringwall a distinctive, irregular, zigzag rim, like mountain peaks, so that one could do basic navigation by measuring the angles to distinctive Ringwall peaks (as is done in coastal navigation); this would only work near the Ringwall though; not a chance of seeing it through 100'000 km of atmosphere.

Are there any other possibilites?

Answer 1

Note: This answer is written in the form of a fictional, in-universe briefing document. I've done my best to keep the "facts" correct and sourced from the Ringworld novels, but this "document" is my own invention. The format of this answer is currently under discussion in meta.

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Navigating the Ringworld

NOTE: THIS DOCUMENT IS CONFIDENTIAL, AND THE PROPERTY OF THE UNITED NATIONS AMALGAMATED REGIONAL MILITIA. DISTRIBUTION IS PROHIBITED AND PUNISHABLE BY LAW.

Purpose and context

This document assumes the reader is familiar with the Ringworld, a megastructure located outside of Known Space; but in brief:

The "Ringworld" is an artificial ring about one million miles wide and approximately the diameter of Earth's orbit (which makes it about 600 million miles in circumference), encircling a Sol-type star. It rotates, providing an artificial gravity equivalent to 99.2% of Earth's gravity by way of centrifugal force. Ringworld has a habitable flat inner surface equivalent in area to approximately three million Earth-sized planets.

(Source of summary text, including Ringworld parameters)

There are many possibilities for an ARM agent to navigate the Ringworld. After the ARM's interaction with the Ringworld during the Fringe War, it became clear that any future exploratory forces that need to prepare to navigate on the Ringworld surface (should its location become known again) would need guidance in this regard. This article, assembled by the United Nations ARM police force, is an extrapolation based on the Ringworld's known features.

While conventional spacecraft autopilots suffice for navigating in space and around planets, the Ringworld presents special challenges, including the presence of an extremely potent defense system. You will not be able to easily use your ship for travel on the Ringworld without risking being shot down by the meteor defense system. Small craft like flycycles and landing boats can travel on the Ringworld safely, as long as their altitude is no higher than that of the ring walls (approximately 1,600km).

(Landing on the Ringworld is possible. Approved landing procedures are discussed in detail in the ARM document "Ringworld landing procedures", and difficulties are laid out in the summary of the 2855 expedition to the Ringworld.)

Electronic satellite navigation

The Ringworld's shadow squares are large panels of an unknown material, whose main purpose is to shade parts of the Ringworld from the sun and create a day/night cycle. They are connected by a monofilament thread that, unlike Sinclair Molecule Chain, retains its cutting ability even when not at tension. The shadow squares are part of an extremely sophisticated system that was designed to expand and contract as needed, not only providing night and day but also being part of a correctional and defensive system.

The squares are linked electronically to the Ringworld repair center, and the ring surface is plainly visible from their location hugging the Ringworld's star. It has been confirmed that observation and tracking equipment is present and functional.

Assuming that the so-called "Ringworld engineers" kept and maintained accurate maps of the surface, a GPS-like system would have been be a relatively simple matter for them to implement on top of existing detecting equipment. However, such a system would likely not be available to an ARM agent. Early probes of the Ringworld showed that the shadow square system is now in some disrepair, but its defensive capabilities are confirmed as operational. These defensive measures, X-ray lasers powered with energy from the star's photosphere, are also most effective in the plane of the Ringworld itself. They can and do strike against targets on the surface of the ring. (See document "Ringworld defense system capabilities and avoidance" for critical information about this deterrent.)

Even if any shadow square navigation system is still functioning, it is almost certainly a complex and sensitive system with sophisticated firewalls. (See document: "Ringworld Engineer: Probable identity and protective nature".) If an agent were able to get past the software defenses, the risk of using this potential resource is very high.

Recommendation: Avoid

Scrith-based electronic navigation

There is a network of superconducting cable embedded in the ring floor. It has been shown that signals can travel through scrith (the Ringworld floor material), so it may be possible to use this network as a sort of location system.

Even if there are no active signals in the network, a sort of magnetic echolocation may be useful using deep radar.

Recommendation: Promising

Stellar navigation

When one is on the Ringworld the night sky is never fully dark - the arc of the ring overhead drowns out the dimmer stars. But one can see stars at night, so navigating by the stars is quite possible.

The visible constellations change with each rotation of the ring, just over nine days. Knowledge of the entire cycle of constellations is necessary, but could be combined with accurate timekeeping to produce usable coordinates.

Recommendation: Almost certainly useful, although tedious without computer support. Bring star charts and navigational components as a backup system to Scrith-based navigation

Navigation via physical landmarks

The Ringworld keeps its atmosphere contained with a wall along the edge. There are mountains against the rim walls, called the "spill mountains". Using these features as points of reference is possible, but difficult. The spill mountains are composed of sea-bottom muck, dredged and piped to the ring walls, and they change over time. Careful sighting of the ring wall would be required, difficult unless one is close to the rim and atmospheric conditions are good.

The modern traveler will almost certainly be equipped with a recording inertial navigation compass, and is advised to leave it in recording mode. At the very least, this will allow for backtracking and finding the reference points of spinward and antispinward.

Recommendation: Workable, but difficult. Necessary to supplement other systems

Answer 2

Or they could have given the Ringwall a distinctive, irregular, zigzag rim, like mountain peaks, […]

Well … they did, in fact. Have you forgotten the spill mountains?

Lots of mountains, a lot higher than the Map of Mars (at least in Ringworld — They magically shrink in the later books.), with no indentations on the outside of the rimwalls, conveninently placed for infrastructure work, with the rim transport system at their peaks and elevators running down them. One could ask (and people have asked) some fairly interesting questions about the spill mountains.

If, as Speaker said in Ringworld, the rim transport system is "a major transport system", and if the spill mountains are the "stops" on that system; then it's pretty much a given that there's a system of identifying which "stop" is which.

The Engineers might have thought about embedding radio-emitting marker beacons into scrith in a regularly spaced, tight network, […]

There is, indeed, something embedded into the scrith. And we know that it emits a fairly powerful magnetic field. ☺

Answer 3

The shadow squares produce maps (This was speculated by louis wu in the first book while in the map room) so in a way this acts as a navigation system if you had a portable device.

Answer 4

There are two main oceans on Ringworld, each on opposite sides of the ring (separated by 180 degrees of arc). One ocean contains world maps from Known Space, the other one contains maps of the Pak home world. Either one of these oceans could be taken as a reference point for large-scale navigation.

Seeing Protectors made Ringworld, it's only fitting to take the "other" Map Ocean as reference. So Fist-of-God, being spinward of the Worlds Ocean, would be almost 180 degrees anti-spinward of our reference point.

If I recall correctly spill mountains are located at regular intervals. They could be used in combination with the Map Ocean reference, eg. "175 degrees anti-spinward from the centre of the Map Ocean, between the Xth and X+1th spill mountain, P kilometers anti-spinward from the centre of the Xth spill mountain, Q kilometers from port".

Of course, there are some distinctive places one can easily identify, like Mons Olympus on the Map of Mars, but these are far and few between.

Would you be able to identify Olympus Mons from the opposite side of Ringworld? Remember, you would see OM from directly above in a map that is a polar projection of Mars. With a sun that is always at high noon: no shadows. From a distance of a little over 300 million kilometers (190 million miles). But the Map of Mars itself would make a good reference: a perfectly circular map in the Great Ocean that has the world maps (not the Pak world maps). Take the middle of that map/land mass as the starting point. Define all other locations by rotation along the arc spinward/anti-spinward and distance between port and starboard walls.

If you have the technology to be able to travel a significant distance along Ringworld, you'll also have the technology to make your coordinates precise enough. And to be able to locate a reference point in either of the Oceans.

Oh, one small problem. You would have to correct for time lag though. If Mars were on the opposite side of Ringworld it takes light 1000 seconds to cross that distance. Ringworld makes a full rotation in 225 hours. So in those 1000 seconds Ringworld will have rotated by 1/810th of its circumference. Which is 1.18 million kilometers (737,000 miles).

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Given enough resources it would be better to place beacons along both rim walls at regular intervals. Each beacon emits a continuous unique signal. Using the inverse square law it would be fairly easy to determine where you were. The problem with that one is the inverse square law. You wouldn't want to be near one of those beacons. Not unless you needed to open-air microwave a bandersnatch.

Answer 5

One factor that would help people identify their position on the Ring is the fact that the Ring's inner surface is curved two ways - it's curved to make a Ring around the Sun, obviously, but it's curved across the width of the Ring as well - if it wasn't the gravity of the Sun would draw water and soil towards the centerline of the Ring. Therefore, the direction of the vertical on the surface of the Ring changes as you move from the Spill mountains to the centerline. Using a sectant and a plumb bob, you can measure (and Chmeee could have measured, when he was uncertain about which Spill mountains were closer) the angular distance of the Sun from the vertical to determine how far from the centerline you are at any time.