Quote from: Hop_David on 07/01/2017 02:50 pmIn any case, I don't think the folks suggesting some of these scenarios grasp what 1.1 e16 kilograms is. A civilization capable of moving this mass around is in the distant future. Wikipedia says the Port of New Orleans handles 62 million short tons of cargo plus a million passengers. Ignoring passengers and barges they handle 5.6 x e10 kg. Gravity on phobos is 5.81 e-4 earth.
In any case, I don't think the folks suggesting some of these scenarios grasp what 1.1 e16 kilograms is. A civilization capable of moving this mass around is in the distant future.
So the lift capacity of similar cranes would be around 9.6 e14.
Quote from: Hop_David on 07/01/2017 02:50 pmSolid rings are not stable. [...] There would be a constant expense to keep the ring from crashing into Mars.As noted in Isaac Arthur's video, the advantage of orbital rings is that the ring's shell is stationary WRT to the surface, but vastly lower than geostationary (or areostationary) orbit (in theory even inside the atmosphere). That drastically lowers the strength requirements of the ground cables. And since you can use the ring for fast point-to-point ground transport, you end up with a lot of ground cables, stabilising the ring.
Solid rings are not stable. [...] There would be a constant expense to keep the ring from crashing into Mars.
and store in bags at the equivalent to Lagrange 4/5 points.
The station could be placed in GSO of Mars or at a L station. [...] and cargo and people could be sent directly to a fixed point on the Martian surface.
Quote from: Paul451 on 07/02/2017 10:06 amQuote from: Hop_David on 07/01/2017 02:50 pmSolid rings are not stable. [...] There would be a constant expense to keep the ring from crashing into Mars.As noted in Isaac Arthur's video, the advantage of orbital rings is that the ring's shell is stationary WRT to the surface, but vastly lower than geostationary (or areostationary) orbit (in theory even inside the atmosphere). That drastically lowers the strength requirements of the ground cables. And since you can use the ring for fast point-to-point ground transport, you end up with a lot of ground cables, stabilising the ring.I am skeptical that the rings he describes would be stable.
And we're talking very massive infrastructure. A low Mars orbital ring would be 23,000 kilometers in circumference.
What is the mass of this ring?
The less ambitious Deimos and Phobos elevator scenarios described would take tonnes to tens of tonnes infrastructure. They could happen in the 21st century.
However, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.
Read my comment again. I wasn't arguing that they would be stable, I'm saying that they can be low enough to reach the Earth with many short cables, and those cables provide stability.
Quote from: Hop_David on 07/17/2017 03:42 pmAnd we're talking very massive infrastructure. A low Mars orbital ring would be 23,000 kilometers in circumference.Much less than the length of a Mars space elevator. Or an Earth or lunar space elevator. And with much lower material requirements. (Which is what it is being compared to.)
Quote from: Hop_David on 07/17/2017 03:42 pmThe less ambitious Deimos and Phobos elevator scenarios described would take tonnes to tens of tonnes infrastructure. They could happen in the 21st century.I'm a fan of the Phobos elevator. And the Phobos/Deimos transit system. Obviously an orbital ring isn't going to compete against that. But orbital rings are intended to be a better planetary space elevator. It allows direct connection to the ground, at multiple locations, at short lengths (a few hundred km instead of tens of thousands of km, hence travel times of hours vs multiple days) and within the material strengths of realistic substances.
Around Phobos a minimum space elevator is so short there's no point building an orbital ring. Mars/Phobos L1 is lower than the radius of Phobos. Plus if you were going to build a ring around Phobos, you might as well just build it on the surface, or tunnel a linear accelerator through the centre. When you have a giant momentum bank, your options increase.However, by the time you've extended the Phobos tether to the edge of Mars' atmosphere, and you have the volume of traffic to justify it, you're are probably within the economic range of building an orbital ring.
Quote from: stefan r on 07/17/2017 01:24 pmand store in bags at the equivalent to Lagrange 4/5 points.There's no [useful] equivalent around Mars, assuming you mean a Mars-moon Lagrange. Phobos and Deimos are too small.
Quote from: stefan r on 07/17/2017 01:24 pmQuote from: Hop_David on 07/01/2017 02:50 pmIn any case, I don't think the folks suggesting some of these scenarios grasp what 1.1 e16 kilograms is. A civilization capable of moving this mass around is in the distant future. Wikipedia says the Port of New Orleans handles 62 million short tons of cargo plus a million passengers. Ignoring passengers and barges they handle 5.6 x e10 kg. Gravity on phobos is 5.81 e-4 earth.You're wanting to move Phobos? It is Mars' gravity you want to look at, not Phobos gravity.Quote from: stefan r on 07/17/2017 01:24 pmSo the lift capacity of similar cranes would be around 9.6 e14.And what distance do the cranes move the cargo? I would suppose From the deck of a ship to a dock. Not the same as moving Phobos thousands of kilometers. At any rate, the cranes of New Orleans are quite massive infrastructure. Even if your model was sound, your scenario isn't plausible.
Some of the containers get loaded in Shanghai and travel through the Panama canal before getting unloaded from container ships in New Orleans. Some of the containers have a thousand kilometer trips before and after shipping. Some of the components in the products already made ocean trips before assembly. Of course some containers could be Huston to New Orleans.
Quote from: Paul451 on 07/18/2017 02:29 amRead my comment again. I wasn't arguing that they would be stable, I'm saying that they can be low enough to reach the Earth with many short cables, and those cables provide stability.I believe that cables even to a low orbit would need to be tensile rather than compressive towers. So they would not prevent a ring from dipping and suffering regions where gravity exceeds centrifugal force.
Quote from: Paul451 on 07/18/2017 02:29 amHowever, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.Actively using energy to accelerate or decelerate discrete parts of an inner ring might be a way to keep the ring from spinning out of control.
Quote from: stefan r on 07/18/2017 10:53 pmSome of the containers get loaded in Shanghai and travel through the Panama canal before getting unloaded from container ships in New Orleans. Some of the containers have a thousand kilometer trips before and after shipping. Some of the components in the products already made ocean trips before assembly. Of course some containers could be Huston to New Orleans. So you're not just talking about the cranes at the New Orleans harbor. You are also talking about all the ships that move between New Orleans and points throughout the planet. You're also talking about the Panama Canal which is rather massive.Also a ship traveling on the Atlantic has different fuel requirements than a tug moving stuff to different orbits. Delta V to move a mass from Phobos to Low Mars Orbit is about 1.2 km/s. By my arithmetic it would take about 3.1e15 kilograms of hydrogen/oxygen bipropellent. The world's annual production of oil was about 77,500,000 barrels per years as of 2014. That comes to about 4.4e12 kg of oil.So the hydrogen/oxygen bipropellent to move Phobos would need to mass about 700 times as much as the world's annual oil production.What is the mass of the infrastructure you imagine?This is an important factor that people seem to want to ignore.
Quote from: Hop_David on 07/18/2017 01:57 pmQuote from: Paul451 on 07/18/2017 02:29 amRead my comment again. I wasn't arguing that they would be stable, I'm saying that they can be low enough to reach the Earth with many short cables, and those cables provide stability.I believe that cables even to a low orbit would need to be tensile rather than compressive towers. So they would not prevent a ring from dipping and suffering regions where gravity exceeds centrifugal force.For the ring to drift off-centre (so that one side brushes the planet), as one side lowers, the other side is lifted. If (tensile) ground-cables prevent that side from lifting, the ring itself prevents the other side from dipping.Quote from: Hop_David on 07/18/2017 01:57 pmQuote from: Paul451 on 07/18/2017 02:29 amHowever, AIUI, you can also dynamically stabilise a ring that isn't secured against the ground, provided the inner-ring is made up of discrete objects, not a continuous ribbon of cable. You can vary the energy applied at each magnetic station, hence you can transfer momentum around the ring, from the high-side to the low-side, letting you actively re-centre the ring.Actively using energy to accelerate or decelerate discrete parts of an inner ring might be a way to keep the ring from spinning out of control.The whole structure is active, that's the whole point. It only works because the mag-stations are guiding the inner-ring (even if you completely enclose the inner-ring(s), the mag system is still always on.) Actively changing the orientation of the ring would simply be a variation within that continuous process.[BTW I might be wrong about my interpretation of how a non-grounded ring is stabilised. I'm going from fragments of what I've read, but its always pop.science stuff, I haven't tried to dig up any genuine scientific papers.]
These guys are moving faster than something in a normal low earth or low Mars orbit. LEO orbital period is about an hour and a half. LMO is about two hours. In less than two hours after an impact all the rapidly moving elements will have reached the impact site.The elevators to the ring as well as much of the ring structure would fall to the planet surface. There would also be an impressive debris cloud that would remain in orbit for some time.
Aren't some active full ring systems predicated on very small projectiles (grain of sand or less) with a fairly generous vacuum tube area? Penetration events, if not very catastrophic, aren't going to make much of a tube debris cloud, and would basically sandblast any accident debris to dust while accelerating it down the tube right? Eventually debris dust would line the tube upper surface past the penetration site due to splatter because it can't be magnetically directed too right?
A sensor package that “floats” just above the surface of Phobos, suspended by a tether from a small spacecraft operating at the Mars/Phobos Lagrange 1 (L1) Point would offer exciting opportunities for science (SMD), for human exploration (HEOMD) and for advancements in space technology (STMD). Detailed information on the Martian moon Phobos is limited even though it is considered an important destination for near term human exploration. A PHLOTE spacecraft would perform fixed point station keeping at the Mars/Phobos L1 point to allow a tethered sensor package to “float” just above the moon’s surface and also park instruments on the surface for in situ science measurements. This can include ground penetrating radar for subsurface composition measurements to determine how thick the layer of fine grained regolith is for future landings. Other key instruments would be dosimeters for understanding the radiation environments for future human missions, cameras, and a spectrometer for surface mineral analysis. If deployed after a human landing, a PHLOTE spacecraft could provide a constant “eye in the sky” for ground controllers to monitor mission deployments and operational activities. The PHLOTE mission concept has only now become feasible due to recent technology advances, many of which have been supported by NASA’s STMD. Key technologies that make this mission concept feasible include: The Navigation Doppler Lidar (NDL) Sensor for the providing precise spacecraft position and rate knowledge relative to Phobos. This high precision is needed to maintain position at the L1 point; Carbon Nanotube (CNT) braided yarns for a structurally strong tether that doubles as a power and data conduit, Ultralightweight solar arrays, and highly efficient electrospray micro-propulsion thrusters for long term “hover mode” station keeping.The Martian Moon Phobos offers a key waypoint toward enabling human surface landings on Mars. In particular Stickney Crater, which always faces Mars due to Phobos’ synchronous rotation, provides an excellent stepping stone destination as a precursor to a human Mars landing. There is very limited information on the composition and the environments at Stickney Crater on Phobos. Since Phobos has a composition similar to carbonaceous chondrite meteorites, it is believed that it could provide minerals that can be used for In Situ Resource Utilization (ISRU) to recover key elements such as Oxygen for use as return trip propellant. The mission concept below would answer many of these questions as well as provide TRL advancement in key technology areas for human exploration.This mission concept is a synthesis of new technologies that would provide a unique platform for multiple sensors directed at Phobos as well as Mars. Since the Mars/Phobos L1 point is only ~3.1 km from the surface of Phobos, the PHLOTE tether length only needs to be a few kilometers long. A tether configuration with its Center of Gravity at the Mars/Phobos L1 point can place a sensor package on the moon’s surface or float it just above. Due to Phobos’ very low gravity, the tether will be under very low tensile loads.Using a longer tether, this concept can be similarly used for other missions such as Mars/Deimos or at the Pluto/Charon L1 point where both bodies are tidally locked which means a PHLOTE spacecraft with a much longer tether could descend into Pluto’s tenuous atmosphere and sample its chemistry at all elevations unlike a traditional probe.If selected, a feasibility study for the Phobos L1 Operational Tether Experiment (PHLOTE) mission would be performed that will define the PHLOTE mission, determine the technology needs and assess the technology readiness. The study would also model the system, identify risks, as well as explore new science opportunities that could be done with this unique sensor platform.
NASA’s Planetary Science Deep Space SmallSat Studies, or PSDS3, program recently selected a team at the Goddard Space Flight Center in Greenbelt, Maryland, to further develop a mission concept called the Bi-sat Observations of the Lunar Atmosphere above Swirls, or BOLAS. The study, led by Goddard Principal Investigator Timothy Stubbs, could lead to the first tethered planetary CubeSat mission, Stubbs said.“This is an exciting concept,” said Michael Collier, a BOLAS co-investigator who has studied tether-based missions for gathering difficult-to-obtain lunar measurements since 2015. “Candidly, I think it’s groundbreaking. Tethered satellites are a very natural approach for targeting lunar science.”As currently conceived, the mission would involve two 12-unit CubeSats, whose individual units would measure just four inches on a side. Once the pair reached a low-maintenance, quasi-stable orbit about 62 miles above the Moon’s surface, the two, connected by a 112-mile-long thin tether, would separate. The top satellite would climb 118 miles above the surface, while the lower, nearly identical twin would plunge to an altitude of about six miles above the surface.“The tension in the tether keeps the CubeSats in vertical alignment as they orbit,” Stubbs said. “The configuration, with the center-of-mass in a quasi-stable orbit, should enable the lower CubeSat to fly for long durations at low altitudes.”
That looks like the deployment method proposed for an Earth space elevator. For asteroids an alternative was to land the whole lot on the asteroid, dig in and fire the ribbon into space. Has this option been considered?A 2 stage launch may be needed for the L1 equipment.