Dr. Lades [...] You're not going to accuse an ISEC Director of being confused etc... are you?
...What are some other plausible methods for ice removal?
Fullerenes are hydrophobic. Is there reason to believe ice would collect?
Quote from: LMT on 11/25/2017 02:44 amDr. Lades [...] You're not going to accuse an ISEC Director of being confused etc... are you?Hard to say. The only Martin Lades I've seen involved in Space activities is an AI researcher in pattern recognition and neural networks; which doesn't seem related to to any special expertise in orbital mechanics.And the page on ISEC about their "Martin Lades" reads, in full:"Nemo enim ipsam voluptatem quia voluptas sit aspernatur aut odit aut fugit."...making it a little difficult to profile the guy.Your appeal-to-authority seems a little weak. If you've done the analysis, why not answer Meberbs questions instead hiding behind someone else?
Another strange post. Naturally we calculated the Omaha Trail, as I said. Rocket equation etc.
And of course ISEC Director and research physicist Dr. Lades knows orbital mechanics well enough to mark our rocket equations
is the difficulty of the Phobos/tether collision problem underappreciated?
Another strange post. Naturally we calculated the Omaha Trail, as I said. Rocket equation etc. That answered the question Meberbs didn't ask.
Quote from: LMT on 12/05/2017 05:55 amis the difficulty of the Phobos/tether collision problem underappreciated?Off-equator tethers is an old concept, Lades didn't come up with that. (And I'm not accusing him of taking credit for that.) His own calculations of the minimum off-equator angle necessary to avoid Phobos are just geometry, not orbital mechanics.
Quote from: LMT on 12/05/2017 05:55 amAnother strange post. Naturally we calculated the Omaha Trail, as I said. Rocket equation etc. That answered the question Meberbs didn't ask.You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta V
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Quote from: meberbs on 12/05/2017 04:37 pmQuote from: LMT on 12/05/2017 05:55 amAnother strange post. Naturally we calculated the Omaha Trail, as I said. Rocket equation etc. That answered the question Meberbs didn't ask.You have made the false statement that adding 130 tons of mass to a spacecraft does not affect its available delta VNever said any such thing, obviously. You should quote people fairly, and you really should apologize for the misunderstanding that fed your accusations here.
Quote from: meberbs on 11/12/2017 06:03 pmYou aren't particularly clear on how you cut proton flux by 90%, but that would basically involve heavy shielding everywhere, wasting much of the carrying capacity.It's a 130-ton water shield from Deimos. What's unclear? As for "carrying capacity", ascent cargo payload limit applies during ascent. It has no bearing in transit.
You aren't particularly clear on how you cut proton flux by 90%, but that would basically involve heavy shielding everywhere, wasting much of the carrying capacity.
Would you like to see estimates of the transit delta-v and mass possible for an ITS craft on the Omaha Trail?
Ah, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.
Quote from: Asteroza on 09/26/2017 08:21 amAh, firing the Deimos coilgun inward as a lead-in boost for a conventional oberth maneuver departure burn then, didn't catch that.Delta-v Example: DRL & Gravity AssistIf used efficiently, tethered systems at Mars, such as Deimos Dock, Deimos Rail Launcher (DRL) and Mars Lift could improve flight efficiency significantly. Example: M/E transit with the Omaha Trail's proposed DRL.Here 0.94 km/s DRL delta-v launches to Mars periapsis, and gravity assist. At periapsis a small burn of 1.55 km/s gives approximate transfer to Earth. This is a Mars perihelion transfer; near aphelion, the burn delta-v is less, ~0.8 km/s.Options: The Deimos Dock propellant load could be minimized for minimum periapsis delta-v, or else maximized for greater delta-v or greater payload.
GMAT OmahaTrailSpacecraft.DryMass = 850;...GMAT EarthTxfr.DecrementMass = false;GMAT EarthTxfr.Isp = 382;
Pedantry, because it's one of those things that always bugs me:Quote from: Dao Angkan on 08/12/2017 08:35 pmFor a tether, the part in circular orbit is not at the centre-of-mass. Because centripetal acceleration is linear to distance, but gravitational acceleration is to the square, the balance point of the forces on a tether (and hence its orbit) is below the centre-of-mass.
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 admire Isaac Arthur. But I am skeptical that the rings he describes would be stable. Even with an interior counter rotating ring, both parts feel the same GM/r^2. If Mars center coincides with rings' center of rotation, a decrease in r also means a decrease in ω^2 r, regardless if the inner ring is retrograde. So dipping closer to Mars means stronger gravity and weaker centrifugal force. The instability remains.The inner and outer component of a low Mars elevator would be moving at greater than orbital speed with regard to one another. That would be more than 3.4 km/s. How far apart are the inner and outer rings? Should they come in contact with one another, the failure mode would be spectacular. 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? Isaac Arthur has been talking about megastructures that might come to pass in the distant future.My focus has been elevator to payload mass ratios. The less ambitious Deimos and Phobos elevator scenarios described would take tonnes to tens of tonnes infrastructure. They could happen in the 21st century.
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.
You can tether an orbital ring to the surface to make it stable, since it can be built just above the atmosphere.
With that said, Mars is so much smaller than Earth that the advantages of an orbital ring don't make a lot of sense.
As for space tethers, several of the posts here seem to overstate the utility of a tidally locked tether. In an earlier space elevator thread, I made some computations for a climber and came to the conclusion that a space elevator with chemical energy is strictly less efficient than getting to orbit with a chemical rocket. So space elevators and tidally locked tethers in general require a dedicated remotely-powered climber vehicle with good performance to outperform chemical.
It would be more efficient to use a rotating tether in order to do the tethered equivalent of a gravity assist to steal orbital energy from Phobos.