Navigation in Local Spacetime For Engineers

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When Vice President Pence ordered NASA to return humans to the moon by 2024 during an announcement last month, he indicated that the Lunar South Pole, an area rich in water, is also rich in science.  Landing near that site might help astronauts’ long-term survival on the moon and could possibly lay the groundwork for future exploration farther out into the solar system.  However, as plans stand, certain navigation hurtles exist, mainly in the mindset of the administrative staff at NASA, apparently.  An example is this cartoonish DEEP SPACE ATOMIC CLOCK video…


If they have a signal from the reliable GPS constellation, why not use that “until it busts”?  NASA-Goddard, for example, believes this: that GPS signals from the constellations of GNSS and GLONASS in orbit around Earth are the ticket.

Other administrators (JPL-NASA) have thought about that, as well, and rejected it.  Knowing that the timing signals of the GPS systems orbiting Earth are pre-corrected in both General and Special Relativity for points on Earth’s surface, they argue for a “Deep Space” timing scheme, independent of any massive object.  They believe an independent deep-space based mercury-ion (Hg+) atomic clock is the way to go cartooned for us, above.

What both administrative groups fail to understand is that spacetime is less rich, more clear, when it is local. Like on the lunar surface.  We may not have deciphered all the perturbations of spacetime in our galaxy; or even our solar system, but if it is local, whether curved spacetime or flat, we can understand it as straight-line motion of objects.

IMG_0243The cover of GRAVITATION shows the authors’ inspiration as Newton’s famous apple. The magnifying glass highlights the local, focused approach we will use when paths are straight lines, whether in curved or flat spacetime.

In fact, a “good clock” allows objects to travel in straight lines.  A “good clock” must be local.  Hold on, what did we say?  “A good clock MUST be local.”

What does that mean?  It means that to proceed from accurate, precise time we must be close to the events we wish to time.

IMG_0244Maybe why Buzz wears two watches, a silver-colored one on the right arm and a gold one on the left, so he is never far from the one he loves 😉  photo credit: Buzz Aldrin Ventures, LLC;

In two separate cases of Lunar and Martian Navigation, that means the best timepiece and positioning system is a locally-based one.

For Lunar Navigation, two or more cubesat-type LPS constellations of satellites in orbit around the Moon sending time signals and relays to the Astronauts and spacecraft on the Lunar surface and in near-orbit.  The cubesat technology exists already at JPL.  Now that we know there are huge mass anomalies under the surface near the South Pole, this is the only sure way of safeguarding our crews and our ships.

For Martian Navigation, we need the same and more.  We even had Martian Orbiters photographing the terrain around the Rovers and sending those digitized positional charts to the Rovers so there Inertial Measurement Unit (IMU) can  – through dead reckoning – figure out where they are.

The Rovers were not independent, but dogs on a leash. Thus, the name “Rover.”  Without Martian Orbiters photographing them, they would be navigationally sightless.

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