Ok...Originally Posted by JonClarke
And this approach is right around the corner?
Come on!
Banned
Ok...
And this approach is right around the corner?
Come on!
Order of Kilopi
I don't think it is round the corner.
Order of Kilopi
I still have to read those links. The first one I've read a couple times in the past, but the other ones I will get to soon.
I do see this proposal of mine to be a long-term plan predicated on developing a grand plan for a system-wide space infrastructure that includes bases on many worlds and in interplanetary space, including mining and manufacturing. However, I think it needs looking at now in order to get information on what is really needed. Unfortunately, space planning right now seems to be like building a highways by following rivers and contourlines to see if they lead anywhere. I think we need to look at it like they Interstate System was planned before it started. Plot the paths and the businesses will pop up along the side of the road to serve it. I don't mean that we should necessarily drop everything and do it, but instead of having a small plan for this and then a new idea for that, we should have a multi-decadal strategy and stick to it. Let government subsidize it like they do with highways and let businesses lease space from them on the bases to sell to personnel and to pay fares and to lease mineral claims and to high construction teams to build new facilities, and expand on the smaller end stuff until they are large enough to fund their own major projects.
I'd like to see all four of those points happen. Heck, I'd love to forget about cyclers and have fast and cheap constant boost ships that can get to Mars in less than a week. I think we might add space-based laser propulsion to the mix in #1 where a taxi might be techer released and then use laser ablation for additional Dv and use chemical rockets for reserve. I think the highspeed mini-cycler idea might also expand on this, where a larger "mothership" type of vehicle carries the passengers, cargo and taxi for several hours or several days in a high orbit (I'm not sure of the period or apoapsis of such an orbit) that reaches close to escape speed at periapsis for a high speed pass that coincides with the passage of the interplanetary cycler.
BTW, the cycler I suggest would be fairly robust and over-engineered. We have battleships nearing 70 years old that are still in good shape and could be recommissioned. If we over-engineer it, one of these cyclers could last centuries with routine maintenance. Keep the mass shielding off the rotating section to reduce material stresses, use multiple layers of defense against pressure breaches, and spin the pressurized rotating habitat inside a non-rotating pressure vessel so that you don't have to worry about spinning seals. Keeping it simple might mean making it massier, but if Dv isn't a huge issue then we can make it massive. I'll whip up some drawings to show what I'm thinking, in case that helps.
I think of it as less of an airliner and more of an ocean liner. It will be big. It can have luxury class and science/business class, but it can also have steerage class and even worker class. Some people may be paid to work aboad ship to pay for passage or stay on the vessel as employees of earth corporations that have storefronts there. Scientists may stay there long term (beyond planetary transit segments) to explore the space beyond mars where the cyclers tread at apoapsis. Maybe there will be solar-orbiting stations in the asteroid belt that will send vehicles that will pickup supplies and drop off certain materials.
You're right that it has strong competition as a means of travel, but it can be so much more.
Et tu BAUT? Quantum mutatus ab illo.
Banned
Oh.
Well, it sounded like you were saying a tethered approach was a long ways off, then contrasted that with your non-tethered transfer system.
Order of Kilopi
An analogy might be the cruise ships in SE Asia that nominally take people on cruises from (say) Singapore to Pguket and back, but are really floating casinos operating in international waters. They are not economic as a means of transport for either freight or passengers, but provide an profitable income in areas the others do not. One can only hope that cylers would provide a more productive source on income.
Jon
Order of Kilopi
I don't think an Earth-Mars cycler offers any compelling advantages over a simple space liner which parks in highly elliptical orbits. Assuming you park in 10 day orbits, the delta-v cost to go from Earth to Mars is only 450m/s and the delta-v cost to go from Mars to Earth is only 700m/s (Mars has weaker gravity then Earth, so the Oberth effect is less potent).
Local shuttles can transfer people/cargo to/from these 10 day orbits at a leisurely pace, as the space liner waits for the next transfer window.
Order of Kilopi
I still think the mass advantages make a cycler more affordable if the amount of mass required for safety limits is high. If we discover that mass shielding for cosmic rays and solar radiation isn't as massy as we think it need be and discover that free-fall isn't seriously detrimental to health, and discover that engines and propellant aren't as massy and problematic as we think it could be then smaller and lighter MTVs will win out. It will really depend on where the break-even point is for mass, Dv and propellant mass and cost. If the propellant is cheap enough and plentiful enough, we can always slap a big engine and turn one of those cyclers I designed into an MTV. Mission will dictate design and if we're going to be moving large numbers of people then large, massy vessels may become the norm.
Et tu BAUT? Quantum mutatus ab illo.
Order of Kilopi
What safety limits might those be? If yopu mean radiation then a better option might be to send on shorter trips. But If we are so worried about radiation that we want people to hide behind metres of shielding then we might as forget about going to Mars or anywhere else.
Jon
Order of Kilopi
Meters of shielding isn't necessarily so bad, in the long run. Shielding mass scales with the square of the ship's radius, while the available volume scales with the cube of the volume. Make the ship big enough, and the proportion going into even "meters" of shielding is small.
Order of Kilopi
If you are going to provide Earth level shielding ( 500 g/cm2) then the masses required are going to be in the thousands of tonnes even for a comparatively small spacecraft. Almost 8,000 tonnes for a volume of 6,000 cubic m (enough for 100 people). Almost 170,000 tonnes for a spacecraft large enough for 1000 people. This might be feasible for an O'Neill-sized station, but it is then no longer a means of transportation, except incidently. It is a space settlement in an orbit that happens to pass close to two planets allowing short transit flights (but not cheap ones) to and from the settlement.
If you are avocating thousands of tonnes on shielding alone I still think it would a better investment to use that mass for shorter treansit flights, these are just as effective at reducing radiation exposure, and making sure that people on Mars live habitats which can be heavily shielded at a fraction the cost.
Jon
Order of Kilopi
IsaacKuo's got my point. Make it massive and worryfree. Fast transit times can help with GCR, but a solar radiation event can happen unexpectedly and trying to cram everyone into a small, well shielded radiation bunker can be troublesome, especially once we have lots of non-military/non-science civilians taking trips.
I've been saying all along that my cyclers would be full-on space stations that happen to make transit possible and that they would merely be an alternate route. The real issue will be taxi propulsion technology and cost. If we use rockets alone, then the cost analysis swings in favor of direct transits. Howeover, this could vary depending on refueling infrastructure and costs, as based on ideas like IsaacKuo's about the Jupiter and Saturn systems. If we use momentum transfer systems in whole or in part, then the costs might be calculated much lower, depending on how you amortize the capital construction costs.
We might also want to consider other, unrelated costs. If the risk of CME during a particular opposition is high, insurance rates may make people choose a cycler over a direct transit in a cheaper but less well-shielded vehicle.
My position on space infrastructure in general is that once we start mining and manufacturing in space and on moons, we'll end up with more raw and refined material than we know what to do with. A space facility that can roll plate and sheet aluminum in usable timeframes for making one ship can keep making it and would probably outpace demand rather quickly. Thus, the formerly astronomical costs of space exploration will drop dramatically (with the major difficulties still being ascent to orbit from Earth). A lot of the material for a cycler mass shield might be bricks made of sintered moondust. Mass shielding on Mars shouldn't be affected by this because they can make their own mass shielding in situ.
Et tu BAUT? Quantum mutatus ab illo.
Order of Kilopi
I agree that you can make "it" massive and worryfree. I disagree that "it" needs to be in a cycler orbit. Just put rocket thrusters on the thing and operate it like any other spacecraft. The delta-v requirements to go from one elliptical parking orbit to another planet's elliptical parking orbit are not high.
The proportion of mass devoted to even Earth level shielding (which is massive overkill) would not be so great, and it can be in the form of cargo and life support hardware which you already need anyway.
Order of Kilopi
Solar radiation is a very different issue to GCR. You only need 20-30 g/cm2 of shielding to protect against it. In fact, too much is bad, because you start generating secondary cosmic rays. Even in in a small spacecraft, much of this will be provided passively by the spacecraft structure. On a large passenger spacecraft I don't see why all of it could . Since solar radiation events have many hours warning and last only a few hours the worse case would be that passengers would be confined to their cabins (or the dining area, or wherever).
Agreed, that is the most likely option.I've been saying all along that my cyclers would be full-on space stations that happen to make transit possible and that they would merely be an alternate route.
In a solar system scale economy we would expect fast transits to be routine. Why would cycler transits have any attaction for transport except as a novelty, like freighter travel today?The real issue will be taxi propulsion technology and cost. If we use rockets alone, then the cost analysis swings in favor of direct transits. Howeover, this could vary depending on refueling infrastructure and costs, as based on ideas like IsaacKuo's about the Jupiter and Saturn systems. If we use momentum transfer systems in whole or in part, then the costs might be calculated much lower, depending on how you amortize the capital construction costs.
As I said, protection against CMEs is not very difficult with large spacecraft. I find it hard to imagine a passenger spacecraft of any type getting insurance unless it offered protection against common hazards like CMEs. I would be like expectinga passenger liner getting registered if it was not proof against likely storms.We might also want to consider other, unrelated costs. If the risk of CME during a particular opposition is high, insurance rates may make people choose a cycler over a direct transit in a cheaper but less well-shielded vehicle.
Again, all pointers to the possibility of some settlements being put into cycler orbits. But why? What scientific or commerical justification there for such an orbit? Especially when it is more costly than putting such a facility into Earthj or Mars orbit? Just because something is possible does not make it desirable or even practical.My position on space infrastructure in general is that once we start mining and manufacturing in space and on moons, we'll end up with more raw and refined material than we know what to do with. A space facility that can roll plate and sheet aluminum in usable timeframes for making one ship can keep making it and would probably outpace demand rather quickly. Thus, the formerly astronomical costs of space exploration will drop dramatically (with the major difficulties still being ascent to orbit from Earth). A lot of the material for a cycler mass shield might be bricks made of sintered moondust. Mass shielding on Mars shouldn't be affected by this because they can make their own mass shielding in situ.
Jon
Order of Kilopi
If you do use such life-support equipment and material, it will need to be easily accessible by the inhabitants. This suggests that it would be attached to a rotating section, if there is one, or that the entire vehicle would be rotated, which introduces a different set of pros and cons. The entire mass of a spinning section would be increased, requiring more mass for stronger bracing. Also, if you're talking about life-support consumables, they may decrease over time, reducing the effectiveness of them as radiation shielding, unless the location is used as a sewer later on.
Et tu BAUT? Quantum mutatus ab illo.
Order of Kilopi
Yes, it was the concern about bremsstrahlung and current unknowns that led me to decide to separate mass shielding from rotating sections. I don't know as much about it as I should, and articles I've read don't give a good estimation of shield depth. That and secondary considerations for external systems that would operate better without spinning, such as solar panels, radiators, communications and astronomical equipment. But if we are to use rotating sections at all, then that mass for shielding, whether passive or specifically for shielding, will add strain to the rotating section and require additional mass for stronger bracing.
There will be warning of solar events if someone's watching. This might require additional infrastructure in solar observatories. SOHO can't be of such use if you're on the other side of the sun. It might be a case of better-safe-than-sorry to have a detector on board the craft itself, which might be benefitted by not rotating it along with everything else. Even if you use a radiation bunker, it could provide balance problems in a rotating section or, in located near the axis to reduce mass, be problematic for people used to higher acceleration. Is that orb of vomit floating around the low-g bunker from someone who's suffering motion sickness or radiation sickness?
Routine may not equate to cheap. I hope I don't sound like a broken record, but this will be determined by money cost, which should not be confused with Delta-v "cost". Both a small vehicle and a big vehicle need the same Dv to get from Earth to Mars, but that requires different amounts of propellant, which means one is more expensive. Also tied into this is capability and capacity. If we have a bottleneck in the propellant supply chain, then the mission that requires the lesser amount of propellant is more feasible (capability). This may argue against the initial setup of a cycler, but it may argue in favor of cyclers later, when measured on a per-mission basis. Capacity will depend on the amount of traffic that the vehicle systems can handle, basically which ones can carry more people and other mass. Cyclers could be designed with excess capacity and expandability in mind from the beginning and made larger because there is less concern about mass after it's initial launching. Direct transit vehicles are more flexible and can be as small or as large as needed, but this could mean building lots more of them over time which may increase the cost of that system's assets.
True, but my point was that achieving a comparable level of protection would probably mean achieving a comparable level of mass, making propellant costs more of a factor. For the same amount of money/propellant, you can be either fast or massy, but you can't be both. Of course, that's true with any transit system. The cycler initially spends propellant on mass, then during operation it spends it on fast (taxis). Yes, I know, it's a hurry up and wait strategy, hurry up in the taxi, and then wait longer in the cycler than you might for a direct shot (if in an Aldrin trajectory). It will depend on how things are setup, but a combinations of factors could make cycler transport cheaper.
It will depend on what trajectories the cyclers are on. If a cycler travels far enough beyond Mars into the asteroid belt, it could serve as a transportation link to those locations. They could duplicate other observatories, such as solar observatories, watching from different angles than SOHO or other satellites that may be placed in orbit, increasing the net amount of data and its quality, serving as backups as well. They could act as astronomical observatories for general baseline interferometry. Not only would they routinely reach large distances from Earth, extending the baseline, their trajectories move them around enough to generate many additional baselines in useful timeframes. Also, any observatory on a cycler would be more easily serviced by a scientist or technician on station, perhaps new parts could be made on site from emailed instructions instead of waiting years for a servicing mission or a replacement satellite. If large enough, a cycler could become a net food producer because it routinely moves closer to the sun than Mars and could use the additional energy (or sunlight directly) to have rapid growing seasons using bulk plant nutrients picked up from Mars or elsewhere. This could be useful if agriculture is problematic on Mars or in its vicinity due to sunlight, gravity, radiation or other factors.
I'm not married to the Aldrin cycler trajectory, nor would I require a strictly ballistic or low-Dv semi-ballistic trajectory. Perhaps there is a set of semi-powered trajectories that would achieve cyclical operation with low cost in money and propellant. IsaacKuo knows more about the Oberth Effect than I, so maybe he could say if a highly elliptical solar orbit could be devised that passes by Earth and Mars near opposition that would make a fast transit, and then be precessed or otherwise altered using the Oberth Effect near the sun to get more Dv bang for the propellant buck. I wonder if it could service Venus too. Or maybe a low-propellant/high-power system would make more sense using some sort of electric drive in more constant operation, used for both accelerating and decelerating when appropriate for a cyclical trajectory.
Et tu BAUT? Quantum mutatus ab illo.
Order of Kilopi
The increase in mass for the support structure is not much, considering air pressure force dominates over artificial gravity force. Because of this, the entire vehicle should be rotating, or the entire vehicle should be non-rotating. (If necessary for health, you can have a rotating ring on a circular track within the cabin.)
I favor an all-rotating design. It simplifies many things, and is more tolerant of failures. With a rotating ship, you can get away with fixed thrusters and you really only need one fixed thruster to perform all maneuvering. (Imagine a cylindrical spacecraft with a ring of parallel thrusters along the bottom edge--now imagine just one of them is operational, but the spacecraft is spinning. That one thruster can mimic the entire ring just by varying the throttle while spinning.)
I tend to favor recycling for life support, which may mean a significant amount of mass for algae vats (mainly to provide oxygen and scrub CO2, but possibly also to provide food). You'd likely have dehydrated food stores which are consumable, but what goes in must come out...as you break out storage containers of dehydrated food, you'll be replacing them with storage containers of dehydrated waste.Also, if you're talking about life-support consumables, they may decrease over time, reducing the effectiveness of them as radiation shielding, unless the location is used as a sewer later on.
Order of Kilopi
A highly elliptical solar orbit will have an excessively large delta-v compared to either Earth or Mars. Roughly, it will be on the same order of difficulty as Hohmann transfers to/from Mercury, which I'm familiar with since I had calculated them. Basically, after I did these calculations I realized why we've sent so few missions to Mercury--it is HARD. Even Mars-Venus is relatively expensive.
Order of Kilopi
Are you referring to initiating such a cyclical orbit, adjusting such an orbit for more frequent use at opposition, or Delta-v for taxicraft that would rendezvous with a cycler in this orbit?
Et tu BAUT? Quantum mutatus ab illo.
Order of Kilopi
The delta-v for taxicraft for rendezvous. The initiation of a cycler could, depending on the exact details, be just a one-time cost. And maybe you can arrange things so there's no adjustment necessary. But the taxicraft need to get to/from the cycler each time.
Matching velocities with a cycler in a highly elliptical solar orbit will be similar in cost to getting to an Earth-Mercury transfer orbit.
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