Battle of the architectures- BFR v Mars Cycler

[SteveKelsey]

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. 

 

[Russel]

Can it be BFR/BFS v Mars Cycler v Something Altogether More Pragmatic and Sensible

?

[SteveKelsey]

Help yourself Russel 

[TripleSeven]

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. 

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 order

1.  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. 

[Lampyridae]

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.

[TripleSeven]

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.

What you need in my view is redundancy in the Cycler to allow maintenance on it if something breaks or is disabled.  I dont have the exact number of years ISS has been crewed, but for all the talk about assurred return since it was perm crewed there has never been any real talk toward abandoning it for a technical problem...and it's unclear to me that there ever will.  The vehicle has enough (and it should have more but ...) redundancy to allow damaged sections to be closed off and "fixes worked".  A Cycler would certainly have more of all that...and all you really need is a vehicle which can ""jump on" and off...the jump off would mostly be aero braking...and the jump on is just solid propulsion...

But the key points for me at least is that you have gravity to push back the ill effects of no g...a lot of radiation shielding and a lot of power.  At worst in my view you would need two Cyclers...

[hkultala]

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. 

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 order

1.  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

Even when doing to these moons, atmospheric-capable ship can aerobrake on mars atmosphere while pure vacuum ship cannot.

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.

Two atmospheric-capable ships can be tethered together for artificial gravity.

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.

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

[su27k]

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.

[TripleSeven]

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. 

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 order

1.  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

Even when doing to these moons, atmospheric-capable ship can aerobrake on mars atmosphere while pure vacuum ship cannot.

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.

Two atmospheric-capable ships can be tethered together for artificial gravity.

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.

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

Sorry I am on my I pad so its harder to just do the quote answer thing

I would just say this.  What you said about atmospheric ships is accurate...but in the long run they are far from optimium for sustained inter planetary travel in terms of space, interconnectivity, power etc.  its my view based on the dynamics that I think are likely for "Mars operation" (and this would be true for Venus ops as well ie the sky cloud concepts) that 1) there will be repeated traffic between EArth and X during the launch windows, 2) there will be as many people coming and going and 3) the travel time will prove more limiting in terms of health and "sanity" than the stay time (2-4 years) on the planet or in its atmosphere.  The Cycler system can be "larger" and in my view more functional for that specific task. 

And as I noted I think that the two moons are going to play a large role in the planets (at least Mars) exploration and trying to figure out where to put the first perm base on the planet...ie robots are going to visit a lot of places before the choice is made, and people will visit a lot (but less than the robots) places as well ...all in short duration stays

As for space construction.  ISS has proved that works really well..and robots will in the future make it even easier. 

There is no right or wrong answer to this, its all opinion. 

The Moon in my view is kind of different...travel times are very short...what is going to be interesting there is to see what system evolves for exploring it...both for humans and robots.  A Cycler would not be needed because of the travel time issue.  The question is however in my view...issomekind of station needed as an initial point?  My guess is no.

[TripleSeven]

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.

I might quibble with the number but no doubt it is more expensive.  It is also more robuts inmy view

[SteveKelsey]

https://engineering.purdue.edu/AAECourses/aae450/2017/spring/docs/AAE%20450-Project%20Destiny.pdf

[Lampyridae]

https://engineering.purdue.edu/AAECourses/aae450/2017/spring/docs/AAE%20450-Project%20Destiny.pdf

Ah thank you, I had forgotten the link for this. An informative study.

Also, the study found the need for Mars direct flights in order to bring ticket prices down to $200 000pp. This was for the old 12m ITS though, and required huge numbers of flights. But I don't think this is necessarily the right conclusion. For a start, they are assuming one-per-ITS cyclers built with BA-330 and XL modules. Fair enough. But they were using 3 nuclear reactors each, at a cost of $4 billion out of the $18 billion per cycler.

At some point it simply becomes easier to keep your interplanetary habitats interplanetary and just using the BFR's enormous lift capacity to lift people instead of the same habitat space again and again. With 10 000 people per synod, you would wind up with small space-going resort cities.

Heck you could use the return capacity of the BFRs to make a cycler out of Martian resources, seeing as you've also got capacity to make habitats. Cyclers are also literally moveable assets. Brake one into cislunar space to serve as a gateway station / tourist trap, have some regularly visiting Venus (a good candidate), send them to the asteroid belt, Jupiter and so on.

[spacenut]

Mars cycler will be like a trans-Atlantic cruise ship.  BFS (Starship) will be the 747.  Which one won out over time.  Cyclers will take what?, about 9 months every time.  Starship will transit during the synods when Mars is closest to earth cutting time in transit.  Cycler will require a transport to and from the cycler adding a little more time and complexity. 

Cyclers will be great if they are built large enough to provide artificial gravity in route.  However two starships could dock and spin on the way to Mars and creating some partial gravity. 

[SteveKelsey]

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.

[TripleSeven]

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.

The only propulsive burns a Cycler would do would be to maintain its "cycle" orbit...there would be some but the fuel use would be "small"

The "shuttles" would have to expend energy to accelerate to rendezvous and dock with the Cycler but the mass that they would have to accelerate would be much much less than a BFR sized vehicle...and most if not all of the cargo transfer could and would be easily automated.  On arrival when it was time to "jump off" most plans use the atmosphere of the destination world to aerobrake into orbit.    Most of that could be done with expandable type heat shields.

If there was propellent on both the EArth and destination planet end...the job gets a lot easier...and then you use specialized entry/take off vehicles to get down to the planet...

The big deal with the cyclers is that you get gravity, lots of power, and mass to protect people...at least in my view

[SteveKelsey]

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.pdf

On 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.

[SteveKelsey]

I am sorry that last link leads to a very poor pdf copy of the original Aldrin proposal. Here is a better link to a latter paper that looks at a more efficient variation on the concept.

https://www.researchgate.net/publication/267241987_A_Low-Thrust_Version_of_the_Aldrin_Cycler

[TripleSeven]

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.pdf

On 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.

I suspect we are looking at differences of scale in the effort...I am "considering" 10-20 people at a cycle.

[SteveKelsey]

Good point. I am contrasting the BFR approach with an alternative Cycler architecture and therefore had assumed a much larger passenger manifest. Didn't make that clear, sorry.

[Zed_Noir]

My thinking is that the Starship BFS is for moving people between Earth and Mars as rapidly as possible. A jetliner analog.

While the Mars cycler will be much bigger than anyone is thinking right now capable of transporting cargo in the mega tons. A variant of the Starship BFS will be the cargo lighters/shipping containers. Since the Mars Cycler will have limited time to loaded and discharged cargo. It will be much easier to just docked the variant Starship BFS to the Mars Cycler. A large LASH (Lighters Aboard Ship) cargo ship analog. Cargo will be mainly bulk commodities like gases, fluids & raw materials.

There might be a caretaker crew aboard the Mars Cycler. Which would require some sort of artificial gravity.