Northstar1989

I just want to recap here. A trend is starting to emerge that ideas that I initially thought were great, like cargo-only MCT's or Cycler Ships will, individually, only yield very small cost-savings (between 8 and 11%) and require, substantial additional R&D investment... This does *not* mean that these are not good ideas (and some of them are synergistic- providing greater savings when used together: like implementation of cargo/crew seperation and landers/Cyclers). Only that they are small optimizations to Musk's mission architecture that aren't really worth the R&D investment with the smaller scale of launch volume ("only" a handful of MCT's every two years) that Musk and any sane person would initially anticipate. SpaceX has probably looked at these ideas as well, and came to similar conclusions. That these are optimizations best saved for the day when we are launching thousands of MCT's a year (if we ever get to that point), and even tiny improvements to cost-effectiveness are worthwhile. For the meantime, SpaceX has quite enough on its plate already... The only advice I could give to SpaceX, if they were somehow listening, is to keep these possible future optimizations in mind when designing the MCT now, to make them easier to later implement... For instance, placing a small docking-port on the MCT capable of crew-transfers will provide the capabilites that are useful today, like being able to make last-minute adjustments to the crew compliment of an MCT, or perform emergency evacuations if the MCT somehow lost its ability to land and were stranded in LEO... But it would *also* pave the way for later implementation of lander or Cycler infrastructures, when the cost-savings these provide someday become worth the extra R&D due to the numbers of MCT's flying each year... Finally, I would also like to note that I believe that 100 passengers every two years and 1 ton of cargo per passenger to survive on Mars are both WILDLY over-optimistic figures in the beginning. I think that SpaceX should slash that crew capacity to roughly a fifth its current amount, and cram as much cargo as humanely possible into the mass-budget that frees up. People aren't going to be able to survive on Mars with just 1000 kg of equipment each, they're just not. Regards, Northstar

That's not how rockets work. The payloads of rockets like the Falcon 9 and Falcoln Heavy are limited by what can fit inside the fairings because they were *designed* with fairings of theur current sizes. If they had been designed with larger fairings, they could transport less dense cargoes. And the MCT is still in the design stage- NOW is when SpaceX is deciding how much volume to make available for cargo... The MCT currently is designed with a payload capacity of 450 tons. 350 of those tons (and a certain volume) are dedicated to crew accommodations for 100 people. 100 remaining tons are for cargo. Those are the numbers they are currently intending to design around. However it's easily within limits to expand the design volume of the MCT so that you can have a full 450 tons dedicated to crew accommodations, and enough volume within the aeroshell to allow for that. Just the same, you can easily fill an alternate version of that expanded aeroshell with nothing but cargo until you run out of space or run out of mass-budget. Guess which limit you'll bump up against first? Mass is the limiting factor by a longshot. In the current design, 100 tons of cargo takes up maybe 10% of the space of 350 tons of crew accomodations. That's of course with the cargo flat-packed to minimize the mass expended on cargo bay (there's nothing to say they couldn't design in a more spacious cargo bay- but all that extra volume incurs extra structural mass from a larger aeroshell), but the fact still stands that cargo is much denser than crew quarters... With a cargo-only MCT, you could easily fit 450, even 1200 or more tons of cargo inside the expanded aeroshell (roughly 24% larger than the current preliminary design to allow for a 28% increase in crew capacity- remember that the cargo still occupies volume, even in the current reference design). The true limiting factor would be that you really can't load much more than the current mass of the tanker on the booster stage and still reach orbit... Beyond that point, you need to load any additional cargo in orbit, or change the distribution of fuel tanks between the upper and booster stages of the MCT so that the upper stage needs pack less Delta-V to reach orbit (this would, however, increase the length of the manned journey to Mars *unless* you made use of a Cycler Ship mission architecture...) Fully-fueled, it appears the MCT will need to pack between 6.4 and 8 km/s of Delta-V to reach Mars and land on it within 90-150 days, depending on how aggressive of an aerobrake Musk plans to make use of at Mars capture. But you *can* reach Mars with as little as 3-4 km/s on a slower trajectory. Roughly cutting your Delta-V requirements in half means you could shrink the fuel tanks on the cargo-only MCT and load on extra cargo at launch until you reach the point where, fully-fueled, the cargo MCT packs just enough Delta-V to reach orbit (5.4 km/s with current booster cut-off speeds) and weighs about the same as the fuel tanker (about 50 tons more than the crewed MCT), which seems to be about the upper limit of what the booster can boost towards orbit. That extra capacity only used for the tanker is probably to provide the crew with better safety margins and engine-out capability, but you *might* be able to dip into it for cargo MCT's launched a full transfer window ahead of the crew (if cargo costs will be under $140k/ton, equipment probably won't be as over-engineered and expensive as current space equipment is, meaning it might be affordable to just build equipment in duplicate in case of a launch-failure...) The bottom-line is this: a crewed/cargo MCT specialization will only save you money in two situations. The first is if you are willing to give up some safety-margin on cargo launches so it is only about as reliable as the fuel tanker launches. This will net you a roughly 8-11% increase in the amount of cargo you can deliver to Mars for the same number of MCT launches and crew members sent to Mars, more if you build a seperate (smaller) aeroshell for the cargo MCT due to its lower volume requirements than crew. But it will cost you in launch failures- so it remains to be seen whether this would actually be economical. The SECOND is if you are willing to load additional cargo onto cargo-only MCT's in orbit the same way you currently would fuel in the plan Musk presented on. In this case, you actually could more than double, perhaps triple the amount of cargo you send to Mars with a given number of MCT launches (remember, it takes more than 2x the fuel to obtain 2x the Delta-V, and you could *expand* the fuel tanks on a cargo MCT in this situation as cargo needs less,volume than crew), but of course you would have to engage in orbital cargo-loading operations, and that could get expensive as well... In the end, I am forced to conclude that Musk's solution of sending crew and cargo together may actually be the optimum balance of R&D costs and long term cost-effectiveness. An increase in launch failures or the need to load cargo in orbit both eat up most of the cost-savings of sending cargo seperately. Meanwhile there are other, lower-hanging fruit for saving money on long-term operations at the expense of higher initial R&D: like making use of a lander to ferry crew and cargo down to the Martian surface instead of landing the MCT there... Regards, Northstar

It's quite simple. In order to send people, you have to send cargo to support them. And the limiting factor on getting things to space is mass, not volume anyways, you should know that. Let's say each MCT can carry 100 people and 100 tons of cargo to Mars. If you seperate the cargo into a seperate craft, you might be able to transport 500 tons of cargo in a single MCT and increase the crew capacity of each MCT by a third. So in 4 MCT's you get the same amount of crew and 25% more cargo to Mars fir the samw cost. The differences are that drastic. It has nothing to do with volume and all to do with Delta-V. Regards, Northstar

Well, that's interesting- since the helium system was *precisely* what failed. Anyways, industrial sabotage rarely gets caught. So I wouldn't count on it. And besides, better drop it. Wouldn't want to have somebody censor our conversation, would we? So, where were we? Ahh yes- can anybody think of a good reason why SpaceX *shouldn't* send their cargo on a slower, lower Delta-V trajectory to save money? Regards, Northstar

They said the explosion involved a breach of the second stage's helium pressurant system (which they have no clue why occurred). That actually *could* have caused an explosion, although I don't know whether it could have been caused by a bullet... Regards, Northstar

Well, there's a bit more than that. Apparently they've eliminated all the "obvious" possible causes and thus are left investigating all sorts of oddball ones. There's also the fact that they saw a flash and some kind of shadow up there just *before* the accident. And that audio shows a softer bang right before the explosion. Oh, and did I mention that ULA actually denied SpaceX access to the rooftop? (it's not like it's a space crammed full of company secrets- or at least, it shouldn't be- they could've let them up there...) And then called in Air Force officials to go up there for them (the Air Force, of course, ULA has been building close friendships and allies with basically since the ULA was created. So I would hardly call those unbiased investigators likely to notice if there actually was something up there implicating ULA involvement, or even helping explain the explosion- remember, ULA wants this investigation to drag on without results as long as possible because it's bad PR for SpaceX...) I've watched enough documentaries about historical scandals and cases of industrial theft or sabotage to know something isn't quite right with this whole situation. I wouldn't rule out that ULA had something to do with the explosion, especially given their proven penchant for underhanded tactics that really ought to be, or actualy were, illegal (like trying to bar SpaceX from defense launch contracts in the first place- that violated soooo many antitrust laws, and should have gotten the ULA seriously fined...) Maybe I'm biased. Something about this explosion has seemed fishy to me from day one. But SpaceX has previously been very good about figuring out the reasons for launch failures exceptionally quickly in the past. If they have literally no clue what went wrong this time and have crossed off all the obvious possible technical causes, then there's a reasonable chance this actually was sabotage of some kind. I really wouldn't put it beyond ULA... Regards, Northstar

Which is exactly why SpaceX needs to plan on sending their cargo seperately. It can cost little over 3 km/s to get to Mars according to the chart posted earlier, and less with aerocapture (I thought the 3 km/s figure included aerocapture in its assumptions???) and lunar gravity-assists. Plus, if the tankers really do end up being completely reusable and as cheap as Musk seems to antocipate, you could actually cost-effectively bring the Delta-V gap even further down by refueling cargo shipments in an elliptical or lunar orbit (or an elliptical lunar orbit!) before proceeding to Mars... Since it takes 5.4 km/s just to get the upper stage in orbit, though, they will either need to re-design the booster to reduce the Delta-V requirements on the upper stage, or launch the cargo ships empty and only load them once they are in Low Earth Orbit to really get the most out of them with a slower trajectory... (the idea is to cram as much cargo into a single shipment as possible- until you bring the cargo-only ICT's Delta-V down to 4 or 5 km/s or less...) Regards, Northstar

The South Pole has the same problem as the Republic of Minerva- it's on Earth, so SOMEONE will try and enforce a claim on it if you seriously begin an effort to settle it... Additionally, as I pointed out, it's actually a lot harder to keep warm on the South Pole than on Mars. And huge drifts of snow and ice can cover solar panels and crush greenhouses. I don't know why people keep insisting it would be easier to survive in the Antartic than on Mars- that's simply NOT true. You require more heating, more insulation, and a lot more and more dangerous ourside maintenance just to keep the electricity running in the Antartic. Just like Mars, unprotected exposure will very quickly kill you, but unlike Mars the atmosphere is dense enough for winds to pose a serious hazard (The Martian is unrealistic in this manner- the strongest winds on Mars hold less momentum than a light breeze on Earth...) and to covect all your heat away very quickly. Compared to all that, the availability of free O2 is a relatively small boon. Life on Mars would be more easily sustainable than life on Antartica. Regards, Northstar

There actually is a test-plot for growing crops underground in, of all places, Idaho. But that's not actually about growing crops on Mars- it's about growing cheaper food here on Earth (turns out the superior control over light, humidity, and temperature, and the ability to exclude pests or weeds from an underground farm actually make it CHEAPER than growing crops aboveground in places where electricity is cheap, and suitable tunnels such as abandoned mining tunnels are already available... Note that you can light the xrops during the night, and let them rest by day, in order to cut down on your electricity costs- as electricity is actually cheaper at night in many parts of the USA...) There are also secret military installations under mountains and such, designed to survive a nuclear bomb blast. That's basically an underground colony, for many purposes...

You actually CAN grow crops in enclosed, heated spaces on Antartoca, and some of the research stations there actually do precisely that- growing a small amount of produce beneath growth-lamps for "research purposes" (although the scientists probably don't hesitate to eat it at the end of the experiment- fresh vegetables are hard to come by at the South Pole between supply shipments...) Lighting really isn't a problem in either case, because you can provide plenty of supplementary light with growth-lamp... As for water, there ate actually many areas outside of the poles with abundant subsurface ice deposits. You have to dig a few meters down, but in some areas the soil is actually more ice by volume and weight than silica or other materials... (in other areas, it's very dry. You have to know where to land and establish a colony, which is why water prospecting is one of the single best things we could do with the SpaceX payloads they'll be sending from 2018 on if Musk is at all serious about this whole permanent colony thing...) Regards, Northstar P.S. FYI, before you raise the accusation of this going off-topic again Nibb: know that several SpaceX-related threads were actually merged into this topic, and basically any others about the company's surface plans will be as well. So this is really a thread for discussing all things SpaceX, despite what the title might say...

The insolation (sunlight exposure) of the Martian equator is actually much higher than that of Antartica because there's very little atmosphere to interfere with sunlight reaching the surface. Additionally, the CO2-rich atmosphere and the tendency of colonists to convert O2 to CO2 through breathing virtually guarantees that crops will be grown in a CO2-enriched environment. This is actually a good thing, because, up to a certain point, plants actually grow much BETTER in a CO2 rich environment than one that is more Earth-like. I believe the ideal point was 1200-1600 ppm: I remember it was at least 3-4 times higher than current atmospheric CO2 levels on Earth (in fact, if not for its tendency to lead to severe weather and droughts through climate-change, our enriching our atmosphere with additional CO2 would actually HELP alleviate World Hunger...) Regards, Northstar

Backseat moderating generally isn't appreciated Nibb (trust me, I've gotten in trouble for it before...) As for the substrate, it's not even necessary to grow crops in the first place. Contrary to popular belief, all plants actually need for growth is light, water, air, and mineral nutrients in their water- thos is why many crops grow perfectly well using hydroponics. I don't know about where you live, but I can't go to the grocery without finding hydroponic lettuce for sale every day of the week. It's simply routine to grow crops without substeate these days... That being said, providing crops with substrate can only help their growth. Substrate can help to retain water and nutrients on the microscopic level, eliminating the need to keep the roots constantly submerged in nutrient solution- which is highly beneficial to certain species susceptible to root-rot. Nonetheless, sterile substrate is better than no substrate for a number of reasons, and provided it is cleaned of toxic substances first, it can't possibly do any harm. And if you really want, it's easy enough to seed substrate with organic matter and bacteria like is done in The Martian. Take it from a real life biologist- that part of the book (inoculating sterile soil with bacteria) is perfectly feasible. Regards, Northstar

That's a common, but terribly incorrect assumption. The Antartic actually is effectively "colder" than the surface of Mars is. Even though the average temperature is higher than certain parts of Mars (it actually gets surprisingly warm near the Martian equator- during the dayvit can exceed 70 F), the atmosphere is much thicker at Antarctica- which leads to MUCH greatet heat-losses due to conduction and (especially) convection. Mars' atmosphere may be cold, but it's basically a vacuum, so it doesn't actually wick that much heat away from heated structures such as a greenhouse... It's perfectly possible to keep a greenhouse warm with electric heating elements on Mars. As for light, you augment the natural light with growth-lamps anyways. So it's basically an artificial environment you grow these crops in... Regards, Northstar

Agreed. It shouldn't actually be that hard to clean the dirt anyways. The basic process would look like this- you spray the dirt with a bunch of water to leach out perchlorates (which are HIGHLY water-soluble). Then you collect the contaminated water from below the dirt, evaporate it all off by heating it to reclaim the water (alternatively, you could just dispose of it by exposing the contaminated water to surrounding Martian atmosphere- the low pressure will cause it to boil in a hurry), and then after condensing the water again spray it back on the soil until you have removed all the perchlorates... This will probably leach all the minerals out of the soil as well, but that's alright. There are plenty more minerals on Mars you can mine and use to re-enrich the soil... For this process to work, all you need is water and lots of energy. Of course, it might be simpler to grow most crops via hydro- or aeroponics, and only clean soil for those crops that prove intolerant of hydroponic cultivation methods... Regards, Northstar

You seperate the cargo into dedicated cargo-only ITS's that don't interact with the Cycler at all, and arrive ahead of the crew. This is worth it even without a Cycler architecture because it allows you to send your cargo on a slower, lower Delta-V trajectory, but with a Cycler it is an absolute necessity in order for the Interceptor to focus on only carrying crew (which is the only type of payload that benefits from a Cycler Ship) and make it worthwhile to use one... As for gettimg 2x the crew with 2x the ship space dedicated to crew, that is true, yes. But the main benefit of a Cycler, and what makes it worthwhile, is not somehow needing to launch less mass in crew accomodations in order to carry people to Mars, it's the fuel-savings. With a Cycler architecture, you can pack roughly 2x as many people into the Interceptor as into an ITS dedicated solely to crew, but you only need to conduct the same number of Tanker missions to refuel the Interceptor as you would a standard ITS. The result is substantial fuel and cost-savings over a number of missions. It's no coincidence I said you could save $110 million over the course of a number of ITS missions where you relied on a Cycler and an Interceptor where two crew-only standard ITS's could have held the same number of people- that's precisely equal to what I estimated the refurbishment and refueling cost of an ITS to be over 11 missions. Basically, you still have to refurbish and refuel the Interceptor between missions like you would a normal ITS, but you don't have to do the same for the Cycler, since it requires very little fuel or maneuver to maintain its orbit and make necessary plane-changes (and what little fuel it DOES need is provided by surplus from the Interceptor each trip- this is also why I said the Interceptor and Cycler together could accomodate 800 people instead of 900- I assumed you'd replace the crew accomodations and life suppory of roughly 100 people on the Interceptor with extra fuel tanks for this purpose- which would start out fully-fueled to get the same launch mass as an ITS that could carry 450 people instead of 350...) If you're only sending 800 people to Mars every two years (not that many when our planet has a population of over 7 billion, and at least 800 million of those are wealthy enough their families could probably afford to travel to Mars at $140,000 a person if they really wanted...) then you only save about $5 million a year in refueling and refurbishment costs this way. But if you're sending 80,000 then that number jumps to $500 million a year, and designing a Cycler Ship becomes much more worthwhile... Musk was right. Cycler Ships are a thing for when you've really scaled up your transit system to Mars and are spending a lot of money on refueling ITS's each year. They don't make sense when your cost of mass to LEO and the number of people you're sending to Mars each year are both low... (not coincidentally Cycler Ships make GREAT sense in the "classical" scenario we have right now where ever kg of mass you send to LEO is incredibly expensive... Hence why they made sense to Buzz Aldrin back when he proposed them- he never foresaw anyone finding a way to get mass to orbit as cheaply as SpaceX will be able to if their launch-stage reusability works and the ITS booster ends up being as cheap as planned...) On the other hand, if the fuel tanker architecture Musk proposed turns out to be a lot MORE expensive than projected, then the fuel-savings of a Cycler Ship will really be worthwhile. And let's not forget that if you're really patient, you can accelerate a Cycler Ship to its Cycler Orbit with nothing hut ion engines, since you don't have to worry about crew waiting the excruciatingly long time this would take if you establish the Cycler in its orbit unmanned, and only send it crew the next time it swings by Earth... Regards, Northstar

The Cycler needs a propulsion system to get into its LEO and its Cycler Orbit, but it doesn't need a very large one to make orbital adjustments (in fact an ion engine would probably work for this purpose). So it starts to look A LOT more appealing if you developed a seperate reusable tug that could haul the Cycler into its Cycler Orbit and then detach and return to Earth orbit the next time its orbit swings back that way... With an Interceptor-Cycler system, you only need a fraction of the normal propulsive-capacity for each crew member you carry to Mars. For instance, if the Cycler and Interceptor were of roughly equal mass (because they were both designed to launch on the same booster), then you could have a single tug deliver the Cycler to its orbit unmanned, then seperate and perform a course-change to arrive back at Earth ahead of the Cycler, where it would refuel, pick up the Interceptor Ship, and bring the Interceptor to the Cycler when it made its Earth flyby. This would mean that if, between the two of them, the Cycler and Interceptor ships packed twice as much mass as a standard ITS normally could, then you would only need a single tug between the two of them, instead of two tugs for an equivalent number of standard ITS's. Of course, any proposal to utilize reusable tugs would probably work best if the Interceptor itself did not descend to the Martian surface, but instead relied on specialized landers to carry crew down to Mars. That way you wouldn't need to worry about performing re-entry and propulsive landing with two craft only attached together via docking- which would pose some structural integrity problems... It's worth noting that you would basically never have to dock or undock the tug with anything again after docking it with the Interceptor Ship. So you could basically weld those two craft together if you wanted, even design the RCS system to be self-contained and detachable to save on deadweight on future missions, as the tug could very well remain attached to the Interceptor for the rest of its usable lifespan... Regards, Northstar

Fair enough, let's run the numbers in greater detail, more explicitly, and this time with the assumption that you entirely remove the cargo capacity in order to provide the extra fuel tanks for the Cycler's plane-changes, but increase the crew complement a single Cycler ITS can sustain to 450 (each person requires about a ton of payload capacity) by greatly enlarging the crew quarters, removing the heatshield and landing legs from the Cycler variant, and the crew capacity of the Interceptor to 350 (you also remove all 350 tons of cargo from it), and can only re-use each Cycler and Interceptor 12 times. Let's also say the marginal cost of each new ITS is $640 million, roughly based on Musk's presented figure of $140,000 a ton with 12 re-uses of the 450-ton payload capacity, 100-man, 350 tons cargo ITS he proposed, and it costs $10 million to refuel and refurbish the ITS each time it lands back on Earth, and refuel it again in LEO before TMI (the actual costs are lower, due to accounting for capital costs in the $140,000/ton figure, but I'll ignore that for now). Ok, so launch-schedule with two ITS's, using one as a Cycler and the other as an Interceptor (and launching the Interceptor with double its sustainable crew-capacity) would look like this: Transfer Window #1: - Launch two ITS's, with 800 total people aboard (450 on Cycler, 350 on Interceptor). Cost = $1280 million. Payload = 800 people. Transfer Windows #2-12 - Refurbish and refuel Interceptor. Launch with 800 people (450 will be transferred to the Cycler after rendezvous with it) each launch. Cost = $110 million. Payload = 8800 people. So, the total cost ends up being $1390 million to transport 9600 people to Mars. Compare that to the baseline plan Musk recently proposed: Transfer Window #1: - Launch 8 ITS's, with 800 people aboard (100 on each ship), and 2800 total tons of cargo (350 on each ship). Cost = $5120 million, Payload = 800 people, 1400 tons cargo. Transfer Windows #2-12: -Refurbish and refuel BOTH spacecraft. Launch with 800 people, 2800 tons cargo each launch. Cost = $880 million, Payload = 8800 people, 30800 tons cargo. So, the total cost for the "traditional" plan ends up being $6000 million, to transport 9600 people and 33600 tons of cargo to Mars, vs. $1390 million for the Cycler design, which transports 9600 people and 0 tons of cargo to Mars. That means you cut $4610 million off the cost, but lose 33600 tons of cargo capacity. However you should be able to send cargo-only ITS's with a minimum of 450 tons of cargo each launch, and probably about 500 tons if you rely on a slower transfer-trajectory for cargo. So, let's say you conduct a series of launches of cargo-only ITS's. This should cost you about $750 million for each 12 launches ($640 million to build each ITS, $110 million to refuel and refurbish it each subsequent transfer-window), but place 6000 tons of cargo on the Martian surface over the 12-reuse lifetime of each ITS with a 500-ton capacity to Mars for each cargo-only mission. Meaning you need 6 of them to place 36000 tons if cargo on the surface, at an additional cost of $4500 million. So, you saved about $110 million (1.8%) on the cost of your mission, and sent 2400 (7.14% more) additional tons of cargo to the Martian surface. These aren't exactly enormous margins vs. the plan Musk proposed, but it's a small improvement. It does appear, however, that a Cycler ship design variant only makes sense if you strip ALL the cargo from the Interceptor and send it on slower cargo-only ITS's. This is because the Cycler Ship only benefits the crew you can bring to Mars with each ITS, the cargo doesn't benefit in any way. So, you will need to develop 3 closely-related variants of the ITS instead of one for a cost of under $110 million. That's not a lot of money to play with for extra R&D, and less when you consider that over 24 years (the lifetime of each ITS, and time period over which you save $110 million- at a rate of $10 million each transfer-window after the first) any money you spend up front essentially accrues capital costs of around 5% a year- meaning you only ACTUALLY have around $50 million to play around with in extra R&D (compare that to an estimated $10 billion R&D budget for the ITS), and whatever you don't spend constitutes your actual cost-savings for using a Cycler Ship... I'm starting to see why Musk wasn't interested in Cycler Ships- apparently the cost-savings are MUCH less than I expected, and you have the extra hassle of needing to develop 3 different closely-related variants of the ITS right at the beginning for the plan to work at all... Regards, Northstar

Fair enough. It looks like Musk HAS seriously considered the idea of Cyclers. Back in 2012 at least. And he is correct that you need to make small changes in the orbital plane each cycler, or have roughly 18 different Cyclers at different inclinations and positions relative to the sun (with each reusable only about once every 30 years). Obviously the plane-changes are the only feasible option early on... I still think he might not be adequately accounting for the fact that you can roughly halve the per-seat cost to Mars with Cyclers. A bit less if you need to reduce the capacity of the ITS design to add more fuel-tanks to provide Delta-V for plane-changes, but if you can re-use a Cycler even five times, and keep anything over 60% of the crew-capacity on the redesigned ITS, then you'll still end up with a lower cost-per-seat to Mars by the time you retire the Cycler... Regards, Northstar

The idea may never have been pitched to him as literally just "launch two ITS's and leave one in a Cycler Orbit for re-use the next time it swings by Earth" before. People aren't perfect. And *sometimes* (wink, wink) they dismiss perfectly good ideas when they really ought not to. It's likely Musk didn't receive a very good pitch of the idea at a press conference, and definitely didn't have much time to think about the version being presented to him then and there. I stand by use of a Cycler design being a good idea, and think somebody really ought to create a formal write-up of it and pitch it to SpaceX in writing... Regards, Northstar

For newcomers to conversation, the first 3 items of my running list of possible improvements to SpaceX's recently-proposed Mars mission architecture can be found above. And here is #4, which is currently being debated. Note that due to the ability to basically (or even literally) re-use the same ITS design as both a Cycler and Interceptor, I have suggested that somebody write up #4 and submit it to SpaceX as a serious idea proposal. Regards, Northstar

Getting twice the people to Mars for the same cost is a boon, no matter how you look at it. If you don't need 200 people, and 100 will do, you could always cut the baseline capacity of each Cycler to 50 people, and shrink the booster and tanker designs to match. If you only need 50, you could cut crew capacity to 25, and still do it cheaper with a Cycler Ship than without. There is literally no limit to how far you can cut crew capacity to reduce surplus capacity, up until the point where your target crew to Mars is two people and each ship only has space for one. Although, past a certain point you start to lose sharply in terms of cost-effectiveness because larger spacecraft are more cost-effective than smaller ones below a certain size, and over time, more people WILL want and be able to pay for a trip to Mars. You and I may disagree about where the demand will initially fall (I happen to believe that SpaceX would have no problem finding 200 people willing to pay for a seat to Mars on the first transfer-window, and surveys of the population about how many would be willing to go to Mars if they could afford it have backed me up for many, many years on this conclusion). Your criticism doesn't make logical sense Nibb. Then again, this isn't a personal attack, but you *never* do anything but spread doom and gloom and talk about how any given proposal to increase our space capabilities, no matter how well-designed, won't work, Nibb. You've been doing it on these forums for years, so you'll have to excuse me if I respectfully take your criticism with the appropriate grain of sand. Once again, that's not meant as a personal attack. Some of your criticisms are, at times, highly valid and very well thought-out. The problem is that your conclusions are always, I mean always, the same- that we'll never do anything in space greater than what we've done already, all facts about the march of human progress to the contrary. Respectful Regards, Northstar

So anyone, this? It could and probably should be pitched as the "launch two identical ITS's and use one as a Cycler" version of explaining this, and leave Elon Musk and the engineers at SpaceX to figure out what additional refinements to the design will or will not improve the cost-efficiency further than that. But it's obvious that it's a workable plan that will cut costs, and it's relatively simple and easy-to-understand. So, would anyone have an interest in writing up an idea proposal on this and mailing it to SpaceX? Regards, Northstar

The shorter launch-window is worth the hassle, and doesn't increase costs at all if you do it right. And did you not catch the point about cramming twice as many colonists into the Interceptor ITS since you will have twice the habitable space for most of the journey? For one transfer-window you get the crew complement of two ITS launches to Mars for the cost of launching two ITS's, so the costs are flat. The second transfer-window when you don't need to launch another Cycler ITS as one is already in orbit, you get the same number if colonists as FOUR launches, for the cost of just three. On the third window, it's 6 times the crew for 4 times the cost. And so on and so forth, approaching a limit of half the cost until you need to eventually replace the Cycler ITS due to its age. Regards, Northstar

All those things would not increase costs at all, since you could literally just build the exact same ITS twice, and use one as a Cycler and one as an interceptor. The Delta-V needed to establish a Cycler Orbit is almost exactly the same as the Delta-V needed to make a 5-month transfer to Mars, so it's actually a bit LESS than the ITS already uses for its TMI at some of the better transfer-windows. And the Delta-V needed for course-corrections is quite a lot less than the Delta-V an ITS already packs for a Mars capture and propulsive landing. So basically, there's no issue with just using an ITS as the Cycler and an ITA as an interceptor. Anything beyond that is just about improving the efficiency even further. The difference in Delta-V needed to actually rendezvous with the Ctcler Ship vs establishing basically the exact same orbit without rendezvous is not very significant- and definitely covered by the cost-savings of the Cycler mission architecture and the surplus Delta-V the ITS already has built into its budget- *especially* at those transfer windows where the ITS could already reach Mars in 3 months instead of 5. Regards, Northstar

Many hippies ALREADY grow their "crops" completely hydroponic. The project to grow food in the abandoned London air raid shelters also has no substrate already in-location to work with (they use a version of hydroponics adapted to use solid plastic mats, basically). The same goes for the ISS. We've already done this closed-loop growth thing (or close enough to it- note that on Mars you can bring in compressed outside atmosphere, mined mineral nutrients like Potassium and Magnesium, manufactured ones like Nitrates, AND regolith that has been processed to remove perchlorates, eventually) many times. It's a non-issue.