I am sure this has been debated a lot on this site but the topic keeps coming up in replies to another thread so I thought I should start a specific thread on the debate- which architecture is better for mass colonisation- the BFR architecture being built by SpaceX or the Mars cycler approach.In the Crimson corner is the BFR- reusable spacecraft that launch from Earth and return to Earth repeatedly with an Earth booster stage to cope with the Earths gravity well.In the Scarlet corner the Mars Cycler, a big zero-G ship assembled in orbit served by shuttles.My belief, to be challenged and corrected, is that the complexity of the Mars cycler architecture will always lose out to the simplicity of the BFR approach on economic grounds, but that just me.
Basically to make a cycler passenger service work, you need something that can quickly convey passengers and have some kind of way to get to Mars if something goes wrong. In other words a BFR.I can see a cycler that's basically a flying hotel resort that merely provides legroom, artificial gravity and radiation shielding for BFR passengers.But you can get these things with multiple BFRs flying together.
Quote from: SteveKelsey on 11/28/2018 09:32 amI am sure this has been debated a lot on this site but the topic keeps coming up in replies to another thread so I thought I should start a specific thread on the debate- which architecture is better for mass colonisation- the BFR architecture being built by SpaceX or the Mars cycler approach.In the Crimson corner is the BFR- reusable spacecraft that launch from Earth and return to Earth repeatedly with an Earth booster stage to cope with the Earths gravity well.In the Scarlet corner the Mars Cycler, a big zero-G ship assembled in orbit served by shuttles.My belief, to be challenged and corrected, is that the complexity of the Mars cycler architecture will always lose out to the simplicity of the BFR approach on economic grounds, but that just me. Since we are speculating here...in my view the Mars Cycler is the system that eventually in a lot of years that humanity (or the US and western powers) will settle on to do a Mars science program. Three reasons in no particular order1. Its unclear to me that a Mars science program has or will be based on Mars. Mars has two natural space stations which have enormous advantages in terms of exploring Mars with both Robots and humans. Its not clear to me that a base on Mars in the early (first twenty years) stages is a good thing in terms of exploring the entire planet. Particularly if either or both of the moons end up having water on them
2. Cycler ships will probably have some sort of artificial gravity ...and my belief is that this will be essential for keeping the folks who are going to Mars in usable shape.
3. Ships that can take off from earth, refuel, go to Mars, land, take off go back to EArth are going to be very complicated...and not have shapes ideal for interplanetary travel...the configs will mostly be governed by the entry phases.Ones mileage may vary.
Quote from: TripleSeven on 11/28/2018 10:27 amQuote from: SteveKelsey on 11/28/2018 09:32 amI am sure this has been debated a lot on this site but the topic keeps coming up in replies to another thread so I thought I should start a specific thread on the debate- which architecture is better for mass colonisation- the BFR architecture being built by SpaceX or the Mars cycler approach.In the Crimson corner is the BFR- reusable spacecraft that launch from Earth and return to Earth repeatedly with an Earth booster stage to cope with the Earths gravity well.In the Scarlet corner the Mars Cycler, a big zero-G ship assembled in orbit served by shuttles.My belief, to be challenged and corrected, is that the complexity of the Mars cycler architecture will always lose out to the simplicity of the BFR approach on economic grounds, but that just me. Since we are speculating here...in my view the Mars Cycler is the system that eventually in a lot of years that humanity (or the US and western powers) will settle on to do a Mars science program. Three reasons in no particular order1. Its unclear to me that a Mars science program has or will be based on Mars. Mars has two natural space stations which have enormous advantages in terms of exploring Mars with both Robots and humans. Its not clear to me that a base on Mars in the early (first twenty years) stages is a good thing in terms of exploring the entire planet. Particularly if either or both of the moons end up having water on themEven when doing to these moons, atmospheric-capable ship can aerobrake on mars atmosphere while pure vacuum ship cannot.Quote2. Cycler ships will probably have some sort of artificial gravity ...and my belief is that this will be essential for keeping the folks who are going to Mars in usable shape.Two atmospheric-capable ships can be tethered together for artificial gravity.Quote3. Ships that can take off from earth, refuel, go to Mars, land, take off go back to EArth are going to be very complicated...and not have shapes ideal for interplanetary travel...the configs will mostly be governed by the entry phases.Ones mileage may vary. Building a ship from parts in orbit is much more complicated. Look at the "project troy" plans of reaction engines. They first need to build an orbital factory until they can even start building the craft itself.http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.679.3415&rep=rep1&type=pdf
Purdue University AAE 450 Project Destiny basically did this: A comparison of Mars colonization using ITS direct vs cycler (built using Bigelow modules, launched and assembled by cargo ITS, transport to/from cycler is also using specialized ITS ship). The conclusion is cycler is about 3.5x the cost of ITS direct.
https://engineering.purdue.edu/AAECourses/aae450/2017/spring/docs/AAE%20450-Project%20Destiny.pdf
I have a number of questions regarding the study as well but must caveat those heavily in that the degree of expertise that went into the study far outstrips mine. However, we are in the final analysis considering a mass transportation system. It may be a challenging one, but those challenges do not remove the learns from mass transportation where scale and simplicity of operation reduce costs. My concerns regarding the cycler architecture are.The cycler must maintain a high velocity to avoid the burden of deceleration and acceleration at Earth or Mars orbit. A shuttle therefore has to match this velocity at both ends of the trip not just attain LEO. It seems an extravagant use of fuel and demands a high performance from the shuttle, in fact it demands a BFR like performance and fuel expenditure just to catch up with the cycler and return to Earth or Mars. If the Cycler solves this problem by decelerating, it needs constant replenishing at both ends of the trip. As we are talking about a very large vehicle it will be expending a large amount of fuel. Refuelling can be sequenced with loading/offloading passengers and cargo but it is an unnecessary additional task.Accelerating and decelerating the Cycler also puts significant limitations on its design which makes this an even less attractive option.So we need BFR like performance form our shuttles, which the study acknowledges. That means we still need an Earth booster stage and we still need in orbit refuelling in order to deliver that performance. It seems odd to me to propose a system that demands an interplanetary capability from its shuttles, but then limit their use to supplying another interplanetary craft.Assuming the Cycler is bigger than a BFR we then need to handle the in orbit transfer of cargo, passengers and fuel in multiple operations. If you limit the scale of your Cycler to reduce this task your reduce the Cyclers carrying capacity and therefore its earning capacity. If you max out its carrying capacity you increase the complexity and risks involved in multiple docking and loading operations. Remember it's not as 'simple' as docking. Cargo and passengers have to be transferred.My final point of concern is that with a Cycler architecture you are significantly increasing the development and production cost of the system. With the BFR architecture you need the ship and the booster and you are done. With the Cycler you need Interplanetary ship and the means of launching the components and assembling the modules in orbit. You still need a BFR style and scale of shuttle at both ends of the trip to intercept the Interplanetary Cycler ship. Thats three times the number of vehicles to achieve the same goal per passenger head. I don't see how that can ever be more cost effective.
I agree that the shuttles should deal with the velocity transfer. Based on the Aldrin cycler model that means you need a shuttle capable of reaching circa 24,000kph for Earth and 35,000kph for Mars. That is a non-trivial performance, you still need a BFR performance level for the shuttle.http://buzzaldrin.com/files/pdf/1985.10.28.ALDRIN_SAIC_PAPER.Cyclic_Trajectory_Concepts_0.pdfOn shuttle size you can't just scale down the ship size without addressing the efficiency issue. Sure it's easier to build a smaller ship, but you need more of them or more launches to transport the same passenger and cargo load adding operational complexity, risk and therefore cost. You might be be able to automate cargo transfer using cargo modules - a bit like containers for shipping, but you still have to deal with multiple passenger transfers.
Cyclers will always have two crippling disadvantages:1. No delta-V savings at all. All ships docking with the Cycler need to accelerate to TMI to reach it. (I get the feeling that many subconsciously forget that and think that it will just pick up crafts in LEO)2. A single cycler could not cover every launch window, you would need several. And it would also severely limit Mars windows. A standalone ship going to Mars can tweak the launch window up to a few weeks in either direction. No such thing with a cycler - you have a pretty instant launch window from LEO.Cyclers will never make sense, IMO. Not for *any* Mars architecture.
A bit off topic, but I see a potential future use for cyclers (non-mars) that only need to match one object. One case is if we have an asteroid civilisation. We could have say twelve cycler trajectories, named for the month or constellation when they encounter earth, that pass through the asteroid belt a year or so later, and needs practically no delta-v to remain on target. They could be very large. They could be towns and universities as well. The craft that accelerates to meet them could be a flimsy tin can, but you only spend a week or so in that.
Quote from: KelvinZero on 11/30/2018 12:50 amA bit off topic, but I see a potential future use for cyclers (non-mars) that only need to match one object. One case is if we have an asteroid civilisation. We could have say twelve cycler trajectories, named for the month or constellation when they encounter earth, that pass through the asteroid belt a year or so later, and needs practically no delta-v to remain on target. They could be very large. They could be towns and universities as well. The craft that accelerates to meet them could be a flimsy tin can, but you only spend a week or so in that.But that's the problem... It can't be just that. If your engine shuts down before necessary delta-v to meet the cycler, you are in deep s**t. You need to have a much larger ship to be a safe haven until rescue can be mounted.
On that note I'll simply point out that my ideal architecture involves transport to and from Earth orbit and Mars orbit and then a specialised lander/ascent vehicle on the Mars end. One can then consider which Mars orbit.
The original problem that Cyclers were meant to solve was avoiding the costs involved in escaping the Earth and Mars gravity wells. But as has been pointed out, the "taxi" needed for a Cycler has to be a fairly capable craft and then you have to consider what can go wrong.
Since then we've proven reusable boosters and this is game changing since we can now afford to use chemical fuel and high energy transits. That partly deals with the radiation issue.
Secondly, I'm not bothered by the idea of going from LEO to LMO and back again using entirely chemical thrust. Provided you can deliver fuel cheaply enough to LEO you can effectively brute force it. And this is exactly where we are headed with reusable boosters - and possibly a reusable upper stage.
Triple Seven said the nice part about cyclers is(lots of interesting stuff and...)2. the fuel needed to "meet" the cycler and load on crews (from Mars, the Earth and Venus) is less than having to boost the entire space ship carrying all these people into a transfer orbit(followed by more interesting stuff)
Quote from: Russel on 11/30/2018 12:03 pmSecondly, I'm not bothered by the idea of going from LEO to LMO and back again using entirely chemical thrust. Provided you can deliver fuel cheaply enough to LEO you can effectively brute force it. And this is exactly where we are headed with reusable boosters - and possibly a reusable upper stage. Thats the idea because I separate High Orbit from Transfer Orbit.Ion is efficient, but acceleration is slow, so leave Earth Orbit takes too much time. Time that means mass for manned in another way. Life support.So chemical to high orbit is faster. And later, Between Earth and Mars, we could use ion, because we have plenty of time to use the engine.From mars high orbit to mars low orbit, chemical is better again.Time mean more mass too on manned missions.
Quote from: TripleSeven on 11/30/2018 03:10 pmTriple Seven said the nice part about cyclers is(lots of interesting stuff and...)2. the fuel needed to "meet" the cycler and load on crews (from Mars, the Earth and Venus) is less than having to boost the entire space ship carrying all these people into a transfer orbit(followed by more interesting stuff)This is the bit that this numpty doesn't get Tripple7. To meet a cycler you have to match velocities. Unless you decelerate the cycler at each end then your shuttle has to match transfer velocities. Wherever you expend the energy, you have to match velocities so I am so dumb I am not seeing the reduction in fuel. Can you expand on why a cycler means less fuel/energy to help the mentally challenged?
I have a feeling (and that is all it is really) based on ISS stuff that three things are going to be an issue with TRAVEL in the solar system given our present technologies in propulsion. the first is solar radiation. I know everyone talks "safe places" but I suspect that is not going to be good enough to stop large affects from it.
the second is no gravity. after X months in Zero g...I suspect adaption back to gravity is going to be time consuming...
the third is isolation and space. lack of it I think is going to be very difficult mentally
Quote from: TripleSeven on 12/02/2018 01:45 pmI have a feeling (and that is all it is really) based on ISS stuff that three things are going to be an issue with TRAVEL in the solar system given our present technologies in propulsion. the first is solar radiation. I know everyone talks "safe places" but I suspect that is not going to be good enough to stop large affects from it.Not a significant problem in my opinion. With a storm shelter solar radiation is not significant even during solar storms. Cosmic rays are significant, but only add a few % to the risk of getting cancer (not necessarily the risk of dying from it), confounding effects like better healthcare for crew make average days of life lost difficult to estimate. Cosmic rays for a 3 month journey are likely to have less effect than things like diet, exercise and pollution all of which will be different for Mars crew and settlers. Cosmic rays for Mars missions are much less dangerous than smoking. The mortality from other dangers during Mars settlement (accidents, etc.) are much higher than cosmic rays.For longer journeys, say to the moons of Jupiter then cosmic rays start to become a major issue.Quote from: TripleSeven on 12/02/2018 01:45 pmthe second is no gravity. after X months in Zero g...I suspect adaption back to gravity is going to be time consuming...Definitely a major problem. Probably acceptable for 3 month transits and 2 years at Mars gravity, especially with gradual improvements in mitigation methods. Longer missions to Mars and settlement are unknown at present as there has been little research on partial-g living.Missions to the main belt asteroids and moons of Jupiter almost certainly need artificial gravity.Quote from: TripleSeven on 12/02/2018 01:45 pmthe third is isolation and space. lack of it I think is going to be very difficult mentallyA real problem with small crews. Up until BFS crew sizes on Mars missions were small (DRM 1,3,4, Mars Direct, etc.) usually had crews of 4 or 6. Sometimes the crew would be split for a month or so, say to investigate the moons of Mars or for a long duration rover traverse. These missions had relatively small amounts of space per crew member. The current plan for Starship seems to be to send two crews of 12 on the first mission and then build up to larger sizes over subsequent synods. Between the crew and cargo Starships there will be relatively large amount volume per person, which will grow as surface structures are constructed.Isolation from family and society in general will be an issue, and perhaps a problem for some. However most people are pretty strong mentally, even more so those selected for Mars crews; they will also benefit from stimulating work, a diverse intelligent Mars community and free communication with Earth (not real-time because of speed of light delays).
I doubt very much that the first Mars crew will be 12 strong. Each person carried adds a large overhead of oxygen, water, food, clothes and assorted other items. I would be very surprised if the first mission carried more than 6 people and probably only 4. The first Mars missions will be very difficult mass wise as it is unlikely that ISRU can be used for oxygen and methane production. Oxygen may be produced direct from the atmosphere but finding sufficient water is unlikely to be reliable at first so methane will need to be brought from Earth with subsequent mass penalty.
For ‘battle’ in the title read competition . If we apply mass transportation economics the Cycler architecture will never compete with the SS/SH architecture. The Cycler system will always be more complex to operate and expanding the Cycler system capacity will never be as simple as just rolling more SS/SH units off the production line. The cruise ship v airline analogy holds. Today, after decades of competitive development, Cruise ships are for pleasure, to move people en-mass you use aircraft because it’s the cheaper architecture. Don’t get me wrong, I love the idea of an interplanetary cruise liner, I just can’t see it being competitive.P.S. Typo city using my phone- now corrected
I'm curious why this needs to be a battle?It's like having Columbus hold off his voyages of exploration while he waits for the development of the Clipper Ships. The Clippers couldn't be developed until the technology and the economic demand were both in place. Similarly, Cycler Ships are geared toward high volume, strong economic demand.An interesting note is that the great liners were often served off-shore from some ports by launches carrying as many (or more) passengers as the early colonization ships.Personally, I see BFR and Cyclers as having a sequential, followed by symbiotic relationship. Early on, BFR with 100 passengers flies the route to establish the initial colony. Later, BFRs are modified to carry 2 or 3 hundred passengers out to meet a cycler and several are sent at once. (Look at how the airlines have fitted out the demo models of the 747 and A380 compared to how the actual operators have them outfitted.)They would dock with the cycler which would house the passengers for the trip. They'd then re-board the Hi-Cap BFR for the descent to Mars.
Propose we need both, competitively, to determine the statistical cost/benefit of using one vs other vs both in cooperation.Question is who will actually field either, both, or neither.Gut feeling is cyclers lose in the "responsiveness" category but win in the "economy" category. Refueling should become routine, and the economics of refueling events vs mass vs ISP vs capability would *hopefully prove out on a near-even playing field. In a sci-fi future, of course.
One major economic benefit of a cycler is freeing up resources. Say a cycler can handle 10 BFS' worth of passengers. That's 10 BFS that now immediately fly back to Earth and can be used for revenue generation for the rest of the synod, rather than spending that time coasting to Mars earning zip.
maybe use cyclers for bulk cargo (little or no crew) with no pressing time limit? something you don't care if it takes an extra year or so to get to its destination?
<snip> If 6 tankers are needed to fill up a Starship in LEO, then that is a lot of docking operations needed quickly to keep people from waiting several days in LEO before proceeding to Mars. Why not use Starship cargo or tankers to fill a fuel depot constantly year round so during the synod when Starships go to Mars, they could refuel much more quickly.
Quote from: edzieba on 01/14/2019 03:49 pmOne major economic benefit of a cycler is freeing up resources. Say a cycler can handle 10 BFS' worth of passengers. That's 10 BFS that now immediately fly back to Earth and can be used for revenue generation for the rest of the synod, rather than spending that time coasting to Mars earning zip.That's not how orbital mechanics work! Whatever craft are used to send stuff to the cycler will need to stay with it.A cycler would swing by Earth at the same speed as a mars injection burn. To rendezvous with a cycler a craft needs to put itself on a Mars intersecting transfer orbit. ZERO propellant is saved.With a BFS/BFR architecture available, Cyclers make NO sense. Maybe some decades later they could work. But then a bigger and better BFS could be available. And so on.
Quote from: Lars-J on 01/14/2019 09:45 pmQuote from: edzieba on 01/14/2019 03:49 pmOne major economic benefit of a cycler is freeing up resources. Say a cycler can handle 10 BFS' worth of passengers. That's 10 BFS that now immediately fly back to Earth and can be used for revenue generation for the rest of the synod, rather than spending that time coasting to Mars earning zip.That's not how orbital mechanics work! Whatever craft are used to send stuff to the cycler will need to stay with it.A cycler would swing by Earth at the same speed as a mars injection burn. To rendezvous with a cycler a craft needs to put itself on a Mars intersecting transfer orbit. ZERO propellant is saved.With a BFS/BFR architecture available, Cyclers make NO sense. Maybe some decades later they could work. But then a bigger and better BFS could be available. And so on.- 'Chomper' holding a crew transfer module launches- Tanker fully loads chomper with propellant- Chomper burns to catch cycler (which has slowed on approach using high-ISP-low-thrust engine such as SEP or NEP)- Chomper offloads CTM to cycler- Now empty chomper burns to return to Earth- Meets tanker in Earth orbit (or prior if needed) to reload propellant for landingIf insufficient propellant remains for the chomper to return to Earth after meeting the cycler, a full tanker can be dispatched along with one or more chompers to re-fill prop at the cycler. The CTM acts as a convenient way to avoid dwell time at the cycler, containerise all life-support systems and avoid trucking them back with the chomper (with said life support acting as distributed backup - or even primary - when attached to the cycler) and acting as a useful hold for personal goods and supplies while attached to the cycler. The CTMs still end up idling during transit, but those have minimal revenue generating potential and would still need to do so even with direct transit integrated into a Starship.Overall propellant use is rather higher than direct transit, but avoids leaving revenue-generating vehicles to coast in idle. Direct transit would still occur for many years beforehand as it makes so sense for lower flight rates, and allows a collection of vehicles to accumulate at the Mars end for offloading (a mirror of the onloading process).
I am sure this has been debated a lot on this site but the topic keeps coming up in replies to another thread so I thought I should start a specific thread on the debate- which architecture is better for mass colonisation- the BFR architecture being built by SpaceX or the Mars cycler approach.
At present, cycler isn't practical.
Quote from: Lar on 01/28/2019 04:37 pmAt present, cycler isn't practical.Neither is BFR. We aren't going to start colonizing Mars any time soon.
What I'd like to see is an interplanetary vehicle parked in planetary orbit between trips. Like in Andy Weir's The Martian.
My issue with cyclers is where does the propellant come from?(Simplified) With BFS you only need sufficient propellant for a one-way trip. Aerocapture is used at the other end.Cycler shuttles (even if they use aerocapture) need to either ride the whole way on the cycler and deposit passengers on the other end or enough propellant both to enter the initial transfer orbit and then boost back to the launch planet.The first eliminates the savings from specialized vehicles for Earth and Mars and the second greatly increases the shuttle propellant and delta-v requirements. Moreover, if the shuttle tanks from the cycler, where does it get that propellant mass from?
The other is orders of magnitude closer to realization since it's under active development. And thus a lot closer to practical.
However the notion of an interplanetary vehicle berthed in planetary orbits is not. An interplanetary vehicle that descends and descends all the way to/from the bottom of planetary gravity well is impractical. If that's what Musk has in mind I'd say he's being optimistic.
I am encouraged to see Musk talking more about propellent depots. If the BFR is refueled, we're no longer talking about 20 km/s delta V budgets.
About 9 years ago, Buzz Aldrin and I went to meet with @ElonMusk at SpaceX HQ in El Segundo, CA. Buzz had hoped to share his plans of perpetual cycling orbits between Earth and Mars with Elon. (a thread) 📷@RGVAirealphotos
Buzz’s Cycler is a spacecraft and system using the trajectory he devised similar to the spacecraft in the movie “The Martian” even though author Andy Weir didn’t give Buzz credit.
Buzz wanted Elon to support his concept and maybe work together on Mars missions. However, during the meeting Elon said he didn’t want to see Buzz’s plans. Buzz was flabbergasted. He said, “I thought you wanted to get to Mars!”
Elon replied that he did and Buzz asked how he was going to do it. Buzz was convinced his Cycler was the only logical and sustainable way.Elon said “I’m going to build a big f*cking rocket. It’ll be able land vertically.”
Buzz was extremely skeptical. I asked about the timeline and Elon said between 10-12 years. Lo and behold - here’s that big f-ing rocket. @elonmusk did it!
Lo and behold - here’s that big f-ing rocket. @elonmusk did it!
Quote from: FutureSpaceTourist on 08/08/2021 11:52 pmLo and behold - here’s that big f-ing rocket. @elonmusk did it!Don't count your rockets before they are operational.
Elon said “I’m going to build a big f*cking rocket. It’ll be able land vertically.”
Can it be BFR/BFS v Mars Cycler v Something Altogether More Pragmatic and Sensible?
How about this there are a number of earth orbit crossing asteroids, Apophis in 2026 is a good starting point. Send a Starship loaded with tools and machinery that digs a large hole and builds several thrusters on the surface. Most of these thrusters can literally be at the throwing rocks level of sophistication...