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#1 2026-06-04 16:59:24
ZRVTO (Zero Relative Velocity Transfer Orbit) between Phobos & Deimos
The left panel shows a Phobos anchored elevator with the orbits payloads would follow if released at various points on the tether.
The right panel shows a Deimos anchored elevator with the orbits payloads would follow if released at various points on the tether.
The two family of orbits share an orbit, the one pictured in the center.
If you release a payload from the top of a 1000 km tether ascending from Phobos it can reach the foot a 3000 km tether descending from Deimos. On arrival it is moving at the the same velocity as the tether foot.
And vice versa.
This orbit is the Zero Relative Velocity Transfer Orbit (ZRVTO).
The two moons could exchange payloads with virtually no rocket propellant.
Hop's [url=http://www.amazon.com/Conic-Sections-Celestial-Mechanics-Coloring/dp/1936037106]Orbital Mechanics Coloring Book[/url] - For kids from kindergarten to college.
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#2 2026-06-04 17:19:06
- tahanson43206
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- Registered: 2018-04-27
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Re: ZRVTO (Zero Relative Velocity Transfer Orbit) between Phobos & Deimos
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#3 2026-06-05 11:19:48
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 6,234
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Re: ZRVTO (Zero Relative Velocity Transfer Orbit) between Phobos & Deimos
Neither moon is geosynchronous with the planet. You cannot build a proper space elevator to either of them, stretching to the surface. The lower ends would drag around the surface of the planet, Phobos very rapidly indeed. All you could do is build partial elevators bottoming out above the atmosphere, meaning well above the entry interface altitude of 135 km at Mars.
GW
Last edited by GW Johnson (2026-06-05 11:20:53)
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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#4 2026-06-05 17:34:33
- Void
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- Registered: 2011-12-29
- Posts: 9,546
Re: ZRVTO (Zero Relative Velocity Transfer Orbit) between Phobos & Deimos
I have not originated any better thinking than either of you guys, but I thought I would search for what other have provided.
Query: "Tethers for Phobos and Deimos"
https://www.bing.com/search?q=Tethers+f … pc=EDGEXST
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Tethers for Phobos and Deimos
Tether systems for Mars’ moons Phobos and Deimos are proposed concepts for enabling mass transfer, power generation, and even orbital infrastructure without expending propellant.NASA’s Tether-Mediated Transport System
A 1985 NASA study proposed a tether-mediated transport system that could move mass between the Martian surface, Mars orbit, and open space by leveraging the orbital momentum of Phobos and Deimos NASA Technical Reports Server (NTRS). The design considered:Tether dynamics during different operational phases.
Micrometeoroid impact effects and segment replacement.
Contingency methods for tether failure.
A schematic for a prototype system linking Mars, its moons, and space.
This approach could use the moons’ orbital velocities to “boost” payloads into higher orbits or out of the Martian system, reducing reliance on chemical propulsion.
Phobos Tether Concepts
Phobos, with a diameter of ~22 km and a low orbital period (~7.66 hours), is a prime candidate for tether-based infrastructure:Lagrange Points L1 and L2 are only ~2.5 km above Phobos’ surface due to its irregular shape NASASpaceFlight.com.
Tethers anchored at L1/L2 could allow spacecraft to dock without disturbing Phobos’ regolith.
Solar arrays at these points could provide continuous power, though they still experience ~50-minute Mars eclipses every 7.5 hours.
Tethers could also serve as space elevators or orbital rings, enabling cargo transfer between Phobos, Mars, and Deimos without reaction mass NASASpaceFlight.com+1.
Deimos Tether Considerations
Deimos, smaller (~12.6 km diameter) and farther from Mars (~23,460 km), has a longer orbital period (~30.35 hours). While less practical for direct Mars surface access, Deimos tethers could:Support inter-moon transport if combined with Phobos tethers.
Provide low-gravity habitats or resource depots.
Serve as backup or alternative orbital stations.
Engineering and Material Challenges
Strength requirements: Tethers must withstand tensile loads from orbital momentum transfer and micrometeoroid impacts NASA Technical Reports Server (NTRS).Materials: Steel or aluminum are common candidates; composite or corrugated designs could reduce mass NASASpaceFlight.com+1.
Maintenance: Irregular moons like Phobos may require frequent stationkeeping; micrometeoroid shielding is essential.
Dynamic effects: Orbital velocity differences between Phobos and Deimos mean tethers must be designed for variable loads and potential resonance issues.
Potential Applications
Propellant depot networks for Mars missions.Orbital transfer stations between Mars, Phobos, and Deimos.
Habitat modules in low-gravity environments for radiation shielding.
Power generation via solar arrays at Lagrange points.
In summary, tethers for Phobos and Deimos offer a way to create a low-cost, high-capacity orbital infrastructure for Mars exploration, leveraging the moons’ orbital mechanics to enable efficient mass and energy transfer without traditional propulsion NASA Technical Reports Server (NTRS)+2.
So, maybe that is a brain enema.
I think Hop may have been a member here at one time: https://www.bing.com/images/search?view … ajaxserp=0
https://hopsblog-hop.blogspot.com/2016/ … ether.html
Image Quote: 
I don't think I have the ability to be sure or unsure about these things. But better people have worked on them, it seems.
I had recalled Hops work.
Ending Pending 
Last edited by Void (2026-06-05 17:45:10)
Is it possible that the root of political science claims is to produce white collar jobs for people who paid for an education and do not want a real job?
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#5 Yesterday 11:01:19
- GW Johnson
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- From: McGregor, Texas USA
- Registered: 2011-12-04
- Posts: 6,234
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Re: ZRVTO (Zero Relative Velocity Transfer Orbit) between Phobos & Deimos
Well, I understand better what is being proposed here. The velocity difference between the apoapsis or periapsis of an elliptical orbit and the tangentially-touching circular orbit will never be zero, but it can be small, depending upon distances and masses of the celestial bodies.
That difference can be reduced further by the tethers as shown, yes. But bear in mind that as an object moves radially along the tether, its circumferential momentum is conserved. It will push sideways on your tether. The tether must be strong in bending, and much more massive than the object, to resist the deformations induced by "pushing on the string". Further, the tether must be radially symmetric above and below the moon, to balance its inertias as the moon moves in its orbit.
Why deal with all these complications? The moons have very low escape speeds. Why not just simply fly from moon to moon? That set of dV's is still rather small, even without tethers. The big one is Phobos-to-surface. Why build a bunch of infrastructure when all it takes is a little propellant in a dead-simple vehicle?
Of course, I have no idea what it is you think you want to transport from moon to moon at Mars. (No one else yet does either, because no one has been there yet.) Of what use are carbon-bearing silicate minerals? These moons are spectrally Type C carbonaceous chondrites. Those bodies are too small and too close to the sun for there to be any significant volatiles still inside after 4+ billions of years' exposure to vacuum. The odds of finding something useful, other than relatively useless rocks and dusts, are quite low.
My question is this: after the initial visits to confirm what these things are, and what they might offer, then if they really are what we think they are, why bother to even continuing to go there? Seems like very long odds to me.
GW
Last edited by GW Johnson (Yesterday 11:08:06)
GW Johnson
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"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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