In my soft sci fi/science fantasy world, humanity lives in a hollow planet. A long, long time ago, an alien species put them there and created a field that prevents anything from entering the planet's orbit. Life in this hollow planet is not too different from Earth. The inside of this hollow planet has its own atmosphere and biosphere. An artificial star provides heat and life. Until ~200 years back, humanity didn't know that they lived inside of a planet. Despite being a sophisticated society approximately 500 years ahead of ours technologically - for instance, they've developed artificial wombs, gyrojet guns as the predominant form of firearm, and advanced prosthetic limbs - they've never been able to put anything manmade into space, since, before it manages to stabilize its orbit, it ceases functioning and crashes into the surface.

With all this in mind, how would wars change without the ability to use GPS and other satellite-based technologies?.

Rockets are shot into the sky from the surface, not from inside the planet.

To the human eye, the field is invisible. They can see the stars and the sun, but not the field.

For the past 200 years, humanity has known that they are living inside of a planet, rather than its surface. Before that, they had no clue.

  • $\begingroup$ Couple problems here... First, "How would X differ..." kinds of questions are really very broad. SE likes more narrowly focused questions. Like focus on communications or perhaps on warfare. Second, it's not entirely clear: are they trying to shoot rockets "inward", i.e. their "up", towards the inner world's sky? Or do they know they live inside a dyson sphere but also have access to the outside surface? Can they see stars, but not the mysterious field? Why don't they live on the outside as well? Is there no atmosphere? This is really a good start for a worldbuilding query! $\endgroup$
    – elemtilas
    Sep 8, 2021 at 20:35
  • 1
    $\begingroup$ @elemtilas Thank you for the suggestions! I edited my post for some clarity. $\endgroup$
    – forgotenm
    Sep 8, 2021 at 20:44
  • $\begingroup$ People live on the inner surface? Then they will target the inner surface in their warfare. There is no need for satellites (communication, GPS etc) inside the planet. $\endgroup$
    – Alexander
    Sep 8, 2021 at 21:43
  • $\begingroup$ Excellent. Thanks for editing and clarifying! As far as my objections were concerned, they've been answered and I'll uncast my VTC as it is now sufficiently focused. $\endgroup$
    – elemtilas
    Sep 9, 2021 at 0:36
  • $\begingroup$ so are they generally doing the battle on the outer surface or inside? the inside are habitable like earth right? and the desert and frozen ocean mean the outer surface right? $\endgroup$
    – Li Jun
    Sep 9, 2021 at 2:45

2 Answers 2


They would have GPS using radio towers.

It would be easier than in our world! Hoisting all those finicky satellites was a trick. But up top both the curve of the earth, topography and the ionosphere make radio unpredictable.

Inside your hollow world there is effectively line of sight to the other side. Just like GPS orients on several "visible" satellites and triangulates position, your people could orient on multiple radio sources on the far side of their hollow world and use those signals to triangulate position. It is easier because the radio stations don't move and so their positions are always known.

I like the idea that these same radio stations play a variety of music for your hollow earth people to listen to.

If you are dead set that Pellucidar does not have GPS, and we are overlooking the fact that they are technologically 500 years ahead of us, then they would probably make war like the US did in the 1970s before GPS.

  • $\begingroup$ and get vietnam flashback? shouldnt it be the otherway around? $\endgroup$
    – Li Jun
    Sep 9, 2021 at 2:51
  • $\begingroup$ /otherway around./ you are going to have to unpack that idea. US make war in 1970s like they are futuristic people living inside a planet? That would be trickier for a couple of reasons.. $\endgroup$
    – Willk
    Sep 9, 2021 at 11:10
  • $\begingroup$ uhmm..... i mean... since if GPS not exist, i was thinking they likely depend more in gorila warfare than how US conduct their conventional warfare during that time, otherwise...... $\endgroup$
    – Li Jun
    Sep 11, 2021 at 0:59
  • $\begingroup$ Differential GPS combines the 2 types of GPS and can be used for very high accuracy positioning. $\endgroup$ Oct 12, 2021 at 21:16

In addition to Radio navigation beacons referred to previously DARPA and others organizations are working on and producing advanced laser inertial navigation chips (laser gyros on a chip) that have extremely high degrees of accuracy.

The idea is that once a start point on a digital map is logged into the system any changes in acceleration and orientation in 3D space (recorded by the gyros) together with an accurate time check (from a clock also included on the chip) allows the device to calculate its current location on the map. In theory the chips could be fitted to any device from a watch, to vehicles, aircraft or missiles etc.

Inertial navigation micro chip

EDIT: I just remembered a 3rd (old tech solution). Digitized global mapping systems. Something like this was used in first gen cruise missiles. Basically highly accurate maps of the 'globe' are digitized and stored on broad an aircraft (or low flying missile). The more accurate and detailed the map the better.

When traveling from point (A) to point (B) a wide 'ribbon' of the map along the per-selected course is loaded into a computer connected to a surface scanning radar. Then once the ship etc takes off:

  1. the radar unit scans the terrain its flying over at timed intervals looking for pre-selected way points along its flight path (again an accurate clock signal is required)
  2. gets a 'picture' of the ground beneath it.
  3. compares that 'picture' to the digitized map stored on board and adjusts its course as necessary to ensure it reaches the next way point on its flight path.

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