Now, every seeded asteroid would not only be a known resource base, it would have a basic solar storm shelter facility, and be part of a planned transit system, whether or not a colony ended up developing there. I personally think any colony at an asteroid would more likely be an orbiting station designed to produce spin G (rather than trying to build the whole colony inside the asteroid in microgravity, or trying to spin rubble-pile asteroids), but a critical piece of infrastructure would be to have a buried storm shelter that crew could retreat to, when they get the 8-24 hour warning of an incoming solar storm.
Here's an example of a separation-distance graph. Only, this is for the distance between our sun and nearby stars:It's quite trivial to imagine such a graph for asteroids - any given asteroid, looking at distances to nearby asteroids. Actually, I think this graph of stellar distances here is boring. Stars in our stellar neighborhood are mostly randomly distributed. Asteroids are lumped into all kinds of groups based on orbital parameters. Graphs like these might reflect some structure in the asteroid belt.Quote from: mikelepage on 11/15/2015 04:53 amNow, every seeded asteroid would not only be a known resource base, it would have a basic solar storm shelter facility, and be part of a planned transit system, whether or not a colony ended up developing there. I personally think any colony at an asteroid would more likely be an orbiting station designed to produce spin G (rather than trying to build the whole colony inside the asteroid in microgravity, or trying to spin rubble-pile asteroids), but a critical piece of infrastructure would be to have a buried storm shelter that crew could retreat to, when they get the 8-24 hour warning of an incoming solar storm.Even if you built a spinning space station, it doesn't necessarily have to be orbiting. For a 1 km asteroid, for example, you might just connect it to the asteroid with a truss. Orbits will have poor stability around such a body anyway since its gravity is so weak. Also, if it's a rubble pile, that implies that it will have voids inside it, and one of these voids is possibly large enough to fit your entire rotating space station into, so you can get gravity and radiation protection at the same time. No excavation required.In fact, this option might be only 1 or 2 realistic locations to get Earth gravity with low radiation. The other one I have in mind is the magnetically shielded equatorial orbit.
Oh, hey Al I wondered if it was you (we met at ISDC 2011). Australia is a bit too far for me to make it to more conferences unfortunately.A graph I've been imagining for a long time would essentially be a this graph (for asteroids) combined with elements from figure 2 of the link in Proponent's post: i.e. x axis = time, y axis = separation distance, z axis = dV. In the dV axis you have envelopes for each approaching asteroid, colour coded by forms of propulsion that could achieve a transfer (hotter colours for chemical thrusters, cooler colours for SEP and the like).As far as ELEO goes, I'm in full agreement with regards to all practical aspects, I'm just wondering how geopolitics of launch sites will play into that? You should probably set up a new topic in the forums here to discuss it if you haven't already: I'm curious about the mass penalty for launching from Cape Canaveral/Brownsville etc.
Distance is of little interest in space travel except how it impacts time and delta-V to make the trip. Of more use would be a graph of if I leave at a given time on a minimum delta-V trajectory for the target, what are the flight time and delta-V. Or if you can display a 3D graph properly, what is the trip time vs. delta-V vs. departure time. Or various cross sections of trip time for a given delta-V or delta-V for a given max trip time.
Quote from: mikelepage on 11/16/2015 03:52 amOh, hey Al I wondered if it was you (we met at ISDC 2011). Australia is a bit too far for me to make it to more conferences unfortunately.Extremely unexpected misunderstanding - I am not Al, the NASA contractor who wrote the paper on equatorial orbits. I was connecting that idea to the idea of colonies in asteroid pores based on a purely technical similarity. They are both low-radiation micro-gravity environments under consideration for long-term habitation. I have had no communication with him, and only know of him as the author of such papers.
Oh, hey Al I wondered if it was you (we met at ISDC 2011). Australia is a bit too far for me to make it to more conferences unfortunately.
when you titled this thread as an "Asteroid Transit Map", I suddenly envisioned a sort of subway system between asteroids in the Asteroid Belt!
If nothing else, it makes clear the unfortunate inverse relationship between accessibility (low eccentricity and similar semi-major axis) and frequency of launch windows (synodic period).
Quote from: Proponent on 11/14/2015 08:51 amIf nothing else, it makes clear the unfortunate inverse relationship between accessibility (low eccentricity and similar semi-major axis) and frequency of launch windows (synodic period).Yes, the closer asteroid semi-major axis is to 1 A.U., the longer the synodic period.And it gets worse. As you say, a launch window opens each synodic period. A launch window to a bitangential transfer orbit. However the low delta Vs often cited assume a bitangential orbit that reaches the asteroid at aphelion. See Shoemaker and Helin's paper.For bitangential orbits, departure Vinf and arrival Vinf sum to nearly the same quantity regardless of where the transfer orbit touches the asteroid orbit. Asterioid aphelion rendezvous usually means a smaller arrival Vinf but a larger departure Vinf. But a larger departure Vinf is mitigated by the Oberth benefit since the ship is departing from a deep gravity well. So an aphelion rendezvous means a lower delta V budget.The sort of transfer orbits Shoemaker and Helin imagine occur much less frequently than each synod.
Quote from: Hop_David on 11/18/2015 03:10 pmQuote from: Proponent on 11/14/2015 08:51 amIf nothing else, it makes clear the unfortunate inverse relationship between accessibility (low eccentricity and similar semi-major axis) and frequency of launch windows (synodic period).Yes, the closer asteroid semi-major axis is to 1 A.U., the longer the synodic period.And it gets worse. As you say, a launch window opens each synodic period. A launch window to a bitangential transfer orbit. However the low delta Vs often cited assume a bitangential orbit that reaches the asteroid at aphelion. See Shoemaker and Helin's paper.For bitangential orbits, departure Vinf and arrival Vinf sum to nearly the same quantity regardless of where the transfer orbit touches the asteroid orbit. Asterioid aphelion rendezvous usually means a smaller arrival Vinf but a larger departure Vinf. But a larger departure Vinf is mitigated by the Oberth benefit since the ship is departing from a deep gravity well. So an aphelion rendezvous means a lower delta V budget.The sort of transfer orbits Shoemaker and Helin imagine occur much less frequently than each synod.Excellent post David. Sorry it took me so long to respond but there's a lot in there and I wanted to give myself time to absorb it Would it be correct to say that if we limit ourselves to using bitangential transfer orbits, it's likely we're looking at average transfer times of months (or years)?
in which case a human-rated space craft would need the required facilities to support life for that long, which in turn will increase the mass of the transfer craft substantially, and also increase the risk of being exposed to potentially fatal solar radiation storms, etc etc. I can't see how it wouldn't only be cargo that is moved this way...If instead, we assume a network of asteroids as resource centres with radiation protection and agricultural facilities (i.e. colonies which are largely self-sufficient for basic necessities), then for human space flight it becomes economic to build low mass transfer vehicles which have the capability of high g-force departure and and arrival burns (probably with SEP in-between). Humans are incredibly valuable assets in space, so in pure $$ terms the optimisation becomes less to minimise for dV and more to minimise the amount of time people are kept cooped up in small tin cans. What I'm more curious about is what those trajectories look like? and what the most important characteristics of the orbits of those asteroids are? Imagine the transfer craft are Orion-sized or slightly bigger, designed for an average transfer time of a week or two, with emergency capacities of 100 days or so.Obviously, you still want to minimise dV, but the question I'm asking is not how to optimise trajectories for two given asteroids or a specific Earth/asteroid combination, but how you pick the groups of asteroids that make regular, short-duration asteroid hopping possible? (In my original post I explained why I think this kind of plan is worth having early on)
Let's say we have 26 communities named A thru Z (let's call earth E). A will have launch windows to B, C, D, etc. Every body will have launch opportunities to 25 other bodies. Obviously there is much more opportuntiy of trade, isolation would be less severe.And as you say, airless worlds might have the option to launch without using reaction mass. Rail guns, slings, in some cases Clarke Style elevators (Ceres and Vesta are well stuied for Clarke style beanstalks).My PDF I pointed to only works for coplanar circular to elliptical orbits. But transfers between asteroids would usually be between two non-coplanar ellipses. Software for making porkchop plots could work for finding low delta V routes between rocks. These rely on Lambert Space Triangles. This works well for most bitangential transfers except if the two tangent points are nearly 180 degrees apart. But in the case of two ellipses, the 180 degree separation between tangent points will be rare.
