Aldrin Cycler Ships

[kerbiloid]

1 hour ago, sevenperforce said:

And if you must have gravity, just make your shuttle/taxi a tumbling pigeon and call it a day.

Yes. But shuttle is not scalable. While a cycler can be as big as required.
Cycler can transport a whole crowd of prisoners slaves cultists colonists at once, providing all of them with gravity and rad-protection.

So, for me cyclers look enough reasonable in such particular scenario:

0.
Say, we are going to found a Martian colony.
Real colony, not all that... nonsense... about low-grav dystrophic mutants hating the Earthlings and degenerating due to inbreeding and lack of sun, gravity and vitamines, beltalowda and other artificial racism.
So, by definition orbital. Say, a rotating bunch of living cylinders.
I.e. like O'Neil's but less bucolic, without lambs jumping between the fruits under huge glass windows. Just living quarters, labs, workshops and command center.
_{Though, with halls for basketball and curling because it would be very funny to look at their gameplay under Coriolis.}

With semi-automatic industrial facilities on Mars (for fluids) and Phobos or Deimos (for metals).  Including greenhouses - just for fun, not for main food.
From time to time getting visited by shift engineers. Nobody stays there for more than a week. Landed, performed the task, returned to the orbital colony.

We don't hate the personnel, so as the colony lives under normal gravity, we just send there specialists from the Earth under 5-year contracts.
So, 2x5 or 1x10 = honorable pension on the Earth. No drama, no beltalowdas. That's why the colony is less bucolic than O'Neil's. They don't live there forever, they just work for several years.

This means, we have to send there thousands of next door people, and we must provide them with normal gravity on their way there and back.

1.
We prepare orbital modules of the future colony and send them to Mars orbit, maybe assemble.
We prepare several cyclers on LEO and put them on their Earth-Mars route.

2.
Then we begin sending hundreds by hundreds of colonists to fill the colony with initial population.
So, to avoid creating mega-ship by mega-ship, we deliver them to the nearest (by schedule) cycler and send to Mars.
This phase lasts for several tens flights, and after that we have a populated Martian orbital colony with several thousand peasants colonists.

3.
Cyclers get old and decommissioned, so we can no more send crowds at once.
We still keep (building new ones, if required) several cyclers to rotate the population, say, once per year, returning those whose 5-year contract is over, sending new employees.

4.
50 years later fast ships with high ISP can get to Mars as fast as the shuttles deliver the colonists to/from the cyclers.
No more cyclers. Direct flights.

So, probably cyclers can find some temporary purpose it this particular scenario.

Edited September 23, 2017 by kerbiloid

[Codraroll]

Uh... just a silly question: could Aldrin Cyclers be a way to get a decent-ish Internet/communications connection to Mars? You'd need a few hundred of them, working as relay stations, sending the signal in a chain back and forth between Mars and Earth. Evenly spaced, there would only be a few gigameters between each one, and with every one having a fixed transmitter and receiver pointing at both of its neighbours, you could get a decent bandwidth throughout the entire chain. Signal delay would be atrocious, of course, even more so than a direct connection, but bandwidth and signal loss should be good enough.

Or would a direct Mars-to-Earth connection be sufficient on its own?

Edited September 24, 2017 by Codraroll

[wumpus]

On 9/24/2017 at 6:12 AM, Codraroll said:

Uh... just a silly question: could Aldrin Cyclers be a way to get a decent-ish Internet/communications connection to Mars? You'd need a few hundred of them, working as relay stations, sending the signal in a chain back and forth between Mars and Earth. Evenly spaced, there would only be a few gigameters between each one, and with every one having a fixed transmitter and receiver pointing at both of its neighbours, you could get a decent bandwidth throughout the entire chain. Signal delay would be atrocious, of course, even more so than a direct connection, but bandwidth and signal loss should be good enough.

Or would a direct Mars-to-Earth connection be sufficient on its own?

This sounds like it is taking the "unlimited bandwidth of a UPS truck full of hard drives [tapes/flash]" to an extreme.  The catches:

• You have enough Aldrin Cyclers that you can always have much more bandwidth to your cycler than Mars
• Your replacement schedule (communications/storage) is in [many] decades (the old Ma Bell rule was all gear had to last 20 years)

In practice, I'd expect that you would never see anything quite like this.  People coming on/off the cycler would simply bring whatever storage devices along as cargo and never bother sending to/from the cyclers.  I could see a "library of Earth (and Mars)" that would keep expanding, but most of the works would be of so little interest that nobody bothered with interplanetary downloading, so the works would be added to cargo and added to the mirror.

[sevenperforce]

1 hour ago, wumpus said:

This sounds like it is taking the "unlimited bandwidth of a UPS truck full of hard drives [tapes/flash]" to an extreme.  The catches:

• You have enough Aldrin Cyclers that you can always have much more bandwidth to your cycler than Mars
• Your replacement schedule (communications/storage) is in [many] decades (the old Ma Bell rule was all gear had to last 20 years)

In practice, I'd expect that you would never see anything quite like this.  People coming on/off the cycler would simply bring whatever storage devices along as cargo and never bother sending to/from the cyclers.  I could see a "library of Earth (and Mars)" that would keep expanding, but most of the works would be of so little interest that nobody bothered with interplanetary downloading, so the works would be added to cargo and added to the mirror.

I think Codraroll was saying to use the Cyclers as relay stations to improve bandwidth. No physical storage.

Still couldn't avoid the lightspeed delay problem, though.

[kerbiloid]

The lightspeed delay is unavoidable, of course, but relay station would receive signal from a closer distance, so more clear, with less data loss.
So, any data package would be transmitted not, say, 10 times to receive it once without errors, but just 3 times.
This would increase bandwidth, because you can send several times more packages per time.

But as typical distance between cyclers would be tenths of AU, this relay network probably needs not cyclers, but just relay stations in round heliocentric orbit(s) between Earth and Mars.

[wumpus]

2 hours ago, kerbiloid said:

The lightspeed delay is unavoidable, of course, but relay station would receive signal from a closer distance, so more clear, with less data loss.
So, any data package would be transmitted not, say, 10 times to receive it once without errors, but just 3 times.

You don't need to use multiple transmissions to ensure complete reliability (although I'd expect it to be needed occasionally for optimal efficiency).  This is the ideal case:

C=Blog₂(1+S/N)

Where C is your channel capacity (your "bandwidth" as it is typically known).  B is literally bandwidth (i.e. how many frequencies you are using).  S/N is your signal/noise ratio.

This equation has been known as the absolute limit to reconstructable communications since the 1940s, and have been possible (especially when dealing with Earth/Mars latency) since the mid 1990s.  The point here is that you should be able to get a higher S/N when communicating to repeater stations than directly to Mars.  You should only need to repeat when the S/N drops below the design point (it will vary a lot with background noise and there will always be spikes where it simply disappears).  It is technically possible to figure out how much data was lost (assuming that noise the transmitter received was similar to noise the receiver received) and simply send more error correction, but I suspect that simple repetition would typically be used.  While most communication isn't quite up to Shannon-level (i.e. the equation above) thanks to the time it takes to code/decode, you can expect that all binary communication (including digitized voice) uses at least some error-correcting system.

I still suspect that plenty of SDHC cards are brought up to the ISS each mission even though communications to there doesn't have these issues.

Edited September 25, 2017 by wumpus
yet another close parens. Obviously I need to lean LISP so I remember to close them all.

[kerbiloid]

1 hour ago, wumpus said:

absolute limit to reconstructable communications

 

1 hour ago, wumpus said:

You should only need to repeat when the S/N drops below the design point

This is interplanetary signal.
And this is a typical DSN antenna used to communicate with Mars

Spoiler

They are 37 and 70 m, according to this.
So, I guess, it drops. And the shorter are distances between stations, the less data get lost and need to be repeated.
Also, don't forget that the formula doesn't take into account that network nodes send not just continuous data flow, but data packages of fixed size (say, several thousand bytes). And if a package is received with errors,  you have to send full package again.
Mars can be at 0.5 or 2.5 AU (and with Sun between) from the Earth, so S/N looks very uneven. Relay network allows to not use 2.5-AU-and-behind-the-Sun transmitter, just 0.5-AU one.

[tater]

Mars comms right now can be a few megabits/s (MRO is 2 Mbit/s average, 6 max). NASA has proposed improvements to DSN that would push this closer to 600 Mbit/s or even higher with laser comms. 

Remember that a lot of limitation is transmission power at the probe end, and larger power sources can help quite a bit WRT S/N as that's an issue with data coming FROM the probe, not the high-power signals sent TO the probe.

Edited September 25, 2017 by tater

[Tullius]

1 hour ago, kerbiloid said:

Also, don't forget that the formula doesn't take into account that network nodes send not just continuous data flow, but data packages of fixed size (say, several thousand bytes). And if a package is received with errors,  you have to send full package again.

Usually, you use error correction algorithms to account for errors so that, despite some errors, the correct data can be reestablished. For example, you can use an algorithm that encodes each 8 bit piece of data in 10 bits in such a way that even two transmission errors in 10 bits don't affect data integrity, and therefore won't cause data retransmission.

wumpus's formula now tells you how high the theoretical limit for the useful data rate is, given the channel bandwith and the signal-to-noise ratio. For our communication with Mars, we know exactly the channel bandwidth (as it is determined by our antenna setup) and we have a pretty good estimate of the worst possible expected signal-to-noise ratio. We can then use nice mathematical tricks to add additional bits to our data bits so that no data is lost in transmission (except in exceptional and extremely rare cases), and therefore we don't need to retransmit data.

I just looked up how data is encoded on a CD as an example: Each 8 bit block of data is encoded as 14 bits on the CD. This might seem extremely wasteful at first, as we are losing nearly half the capacity of the CD to error correction. However, since we added error correction to our CD, we can actually save three times as much data on our CD, as we could write without error correction, giving us 50% more usable capacity. And this is without needing to go back to reread a faulty byte (by the way, how do you detect that the data contains errors?).

So, there is no need for relay satellites to improve the time between transmission attempts, as error correction algorithms can already cover all errors. The only useful role of relay satellites is to improve signal-to-noise ratio, which could potentially increase transmission speeds, as one could use higher frequencies and less error correction. However, the question that remains is: How many satellites do you need until you beat a 70m dish?

[tater]

Why add relays when what you really need is transmission power, and a bigger dish? 

Slap more solar on your relay, and a decent radio.

what is voyager's radio? 8 watts?

The MRO has 2 100 watt radios (1 is a backup). Best S/N boost might be a bette radio and more solar panels to support it.

[wumpus]

3 hours ago, Tullius said:

How many satellites do you need until you beat a 70m dish?

 I'd have to assume a Aldrin cycler wouldn't be all that limited for size (and presumably the dish would be mostly mylar film anyway).  The power would be an issue (both solar and cooling), but in the end it would presumably be worth doing it that way for any tech level building Aldrin cyclers.

[tater]

The 70m dish is here on Earth, talking to a 3m dish, broadcasting at only 100 watts. Put a bigger dish on your base, or its orbital relay(s), and a more powerful radio.

While power (and hence cooling) is an issue with a more powerful radio, it's an engineering problem with mature solutions.

Optical is something they are also looking at.

https://scienceandtechnology.jpl.nasa.gov/research/research-topics-list/communications-computing-software/deep-space-communications

 

[PakledHostage]

6 hours ago, tater said:

Remember that a lot of limitation is transmission power at the probe end, and larger power sources can help quite a bit WRT S/N as that's an issue with data coming FROM the probe, not the high-power signals sent TO the probe.

I will have to look for references but maybe someone here remembers as well:

IIRC, Huygens was designed to use Cassini as a relay for its communication with Earth during its descent to Titan's surface, but the DSN was able to continue to receive telemetry directly from Huygens after Cassini went over the horizon (from Huygens' perapective) and Cassini could no longer relay data.

What blows me away about that is that Huygens' transmitter was about as powerful as a cell phone and we were picking it up through Titan's atmosphere and then from a further billion plus km away.

Kinda puts the DSN's receiver capabilities into perspective...

[kerbiloid]

Of course, I may be wrong here, but this is how I currently understand the situation.

8 hours ago, tater said:

Mars comms right now can be a few megabits/s (MRO is 2 Mbit/s average, 6 max). NASA has proposed improvements to DSN that would push this closer to 600 Mbit/s or even higher with laser comms. 

So, 600 Mbit/s per several thousands colonists with industry - max. Average - 200. Minimum - ... ?
(Btw, if 6 is when Mars is close, to the Earth, 2 - on average, what is minimum, when Mars is in opposition, "behind the Sun"?)

8 hours ago, Tullius said:

Usually, you use error correction algorithms to account for errors so that, despite some errors, the correct data can be reestablished. For example, you can use an algorithm that encodes each 8 bit piece of data in 10 bits in such a way that even two transmission errors in 10 bits don't affect data integrity, and therefore won't cause data retransmission.

And usually we use TCP (with guaranteed delivery, when packages get re-sent when received with errors) instead of UDP (with unguaranteed delivery) to deliver data.
Correction algorithms are fine, but you can't repair more than 1 (ok, 2) bit with 2 / 8 redundancy.

8 hours ago, Tullius said:

wumpus's formula now tells you how high the theoretical limit for the useful data rate is, given the channel bandwith and the signal-to-noise ratio.

Yes, it's theoretical limit. But we talk about reaching a practical ceiling , figuratively speaking, at 10% vs 30% of this limit.
So, the formula is just an optimistic case, a value which the data channel can't ever surpass despite of any efforts.

8 hours ago, Tullius said:

So, there is no need for relay satellites to improve the time between transmission attempts, as error correction algorithms can already cover all errors.

If we don't have to send every package, say, 3 times instead of 10.
We would have to share the 70 m antenna between thousands users, not use it to connect with one rover through one orbter.
So, put less energy in every channel, get lesser S/N, greater invalid packages percentage.

To keep S/N appropriate we have to receive the signal from a distance where S/N is still fine, then correct errors and send the signal to the next node.
If the received package is uncorrectable, requery it again (from a closer distance, not from Mars).
I.e. not just repeat the signal, but to repeat/restore the correct signal. Not just wi-fi repeater.

7 hours ago, tater said:

what is voyager's radio? 8 watts?

What's Voyager bandwidth near Mars? And per every colonist?

4 hours ago, tater said:

Put a bigger dish on your base, or its orbital relay(s), and a more powerful radio.

Share Curiosity's channel between whole colony or use 500 m dish?

Edited September 26, 2017 by kerbiloid

[Tullius]

5 hours ago, kerbiloid said:

If we don't have to send every package, say, 3 times instead of 10.
We would have to share the 70 m antenna between thousands users, not use it to connect with one rover through one orbter.
So, put less energy in every channel, get lesser S/N, greater invalid packages percentage.

To keep S/N appropriate we have to receive the signal from a distance where S/N is still fine, then correct errors and send the signal to the next node.
If the received package is uncorrectable, requery it again (from a closer distance, not from Mars).
I.e. not just repeat the signal, but to repeat/restore the correct signal. Not just wi-fi repeater.

Transmitting the data 3 to 10 times is probably the worst possible error correction algorithm, as it adds a lot of additional data for a very small gain in transmission reliability.

If there is a 2% chance of a transmitted bit being received wrong, the system I described above with 2 additional error correction bits for 8 bits of data has a 99.9% chance of correctly transmitting the 8 bits of data, i.e. there won't be much errors. Without error correction, the chance of correctly reestablishing the data would only be 85.1%, i.e. a rather high chance of error. And, if you somehow could tell that the 8 bits of data were badly received, you would need an average of 1.175 retransmissions to get a correct transmission, i.e. you need to send an average of 9.4 bits.

So 9.4 bits with no error risk vs. 10 bits with small risk doesn't sound that bad? But we haven't yet established how many bits are needed to decide if the received data is correct, and we won't need to add an additional 10 or 40 minutes to get our data through.

With CD grade error correction, even a 10% chance of flipping each bit can be recovered with 99.98% probability.

Retransmissions can still be useful for very precious data, if you notice through a basic error check that, despite a very low chance, an error still crept in. But in practice, you don't want to rely too much on them, as retransmitting costs a lot.

If you improve the signal-to-noise ratio, you can either reduce the amount of error correction you do or switch to faster connection speed (which increases the errors in the signal). The task is now to find the right compromise. In that respect, both your wifi and Curiosity use the same tricks to optimise the speed, while retaining the least tolerable amount of errors.

The only case, where it actually becomes useful to retransmit the data, is when the signal-to-noise ratio is affected by something like solar wind: Instead of always using the more secure transmission method, which won't drop out even when a solar flare occurs, you use the faster method and just accept that during solar flares nothing useful is transmitted and you have to retry later on. Since solar flares are rare, you might actually gain bandwidth with this technique, which is good, as long as there is no time-critical data.

And in the above example of non-time-critical data with occasional solar flares, your idea of relay satellites might actually become useful, provided that the transmission through the relays is actually of higher bandwidth than the one through the 70m antennas of the DSN. And having the relays buffer the data in case some of the data needs to be retransmitted is then obviously a nice bonus (By the way, NASA already tested an alternative internet protocol with the nodes buffering the data for retransmissions during an experiment on the ISS).

7 hours ago, kerbiloid said:

Share Curiosity's channel between whole colony or use 500 m dish?

Curiosity, as well as Opportunity, is only rarely communicating directly with the Earth, but rather through the Mars orbiters, as they have the more powerful transmitters as well as being able to share their time on the DSN. Sharing capacities has obvious advantages, but doesn't need interplanetary relays, but relays on the surface or in the orbit of Mars.

Also the advantage of a large and powerful dish on Mars or in Mars orbit is that it can communicate directly with Earth, which beats the transmission through multiple relays in orbit between Earth and Mars in signal round-trip time, as during opposition between Earth and Mars it can communicate in direct line instead of a half-circle.

[tater]

@kerbiloid, I see your point regarding bandwidth for colonists vs a single mission. Obviously a different animal altogether---of course I don't think of a Mars colony as a thing, I'm more in the O'Neil/Bezos camp there, and the bandwidth from Earth orbit to the surface would be great  .

[kerbiloid]

(Strikes the interplanetary relay network off the list. Anyway it doesn't relate to cyclers.)

Edited September 26, 2017 by kerbiloid

[Northstar1989]

Came back to this thread after a long hiatus, and man do you guys love completely derailing threads...

Putting aside the silly Groupthink that they can't possibly be worthwhile, Cyclers make sense at a basic level because you only have to launch them ONCE at a high cost, but can re-use them many times.  Stop comparing them to one-off missions, that never was a Cycler's intended purpose.

 

If an Aldrin Cycler gets re-used, say, 10 times, and it masses twice as much as a "conventional" Orbit-to-Orbit spacecraft you transfer to Mars, capture, and transfer back (that is, a dedicated orbital habitat that doesn't land on Mars, but rather remains in orbit, and gets re-used many times), here's what the propellant budget looks like for the main vehicles:

2 Cyclers (1 each way):

Year 0: 2A+2A (2A per cycler)

Years 2-18: minor course corrections

Conventional Orbit-to-Orbit Habitat:

Year 0: A+B

Years 2-18: A+B (9A and 9B in all)

Where A is the amount of fuel for a "conventional" Orbit-to-Orbit habitat to make an Earth to Mars transfer (with a transfer-time equal to a Cycler's short leg), and B is the fuel for a Mars to Earth transfer.  Aerocapture is assumed, but like the course-corrections is not considered to require enough fuel consumption to bother counting.

 

If B is 60% the value of A, then your fuel-consumption is 16A- exactly 4x greater over the course of 20 years of Mars missions (during the last 2 years you're just bringing the final crew home) using a conventional habitat vs. accelerating the Cyclers itself (which is twice as massive- and can include mass-saving devices like a greenhouse to grow food for mass-savings, mental health and recreation).

Of course, the Interceptor Ship needs to make two burns each trip.  We can reasonably assume it would need space and life-support capacity for about 4-5 days (not "weeks"- although the fuel consumption is higher, shorter ferry trips save you on mass for habitation space and extended life support systems).  So it might reasonably be expected to mass in about 20% as much as a habitat that sustains crews for 5 or more months (people can reasonably be expected to tolerate very cramped conditions for 120 hours they'd go nuts in over 150 days...)

So, the new fuel budget:

2 Cyclers:

Year 0: 2A + 2A + 0.2A + 0.2B

Years 2-18: 0.2A + O.2B (1.8 A and 1.8 B in all)

 

This bumps the fuel consumption to the Cyclers to exactly 43% that of the conventional architecture over 20 years, with the break-even point in year 8 of the mission (prior to the 5th misdion, fuel-consumption for the Cycler architecture is higher).

It's worth noting that a separate lander is needed with both the Cycler and "Conventional" architecture to get from Mars Orbit to Mars, but that lander either travels the same trajectory as the Interceptor Ship or the Orbit-to-Orbit Habitat (or, alternatively, "lives" on Mars with the surface base and only launches to meet with the orbital vessels a couple days every 2 years, receiving refueling and repairs the rest of the year...) and adds exactly the same amount to the fuel consumption of both architectures (though it does make the ratio between them more even).

 

In order to get a 4-5 day ferry flight and extraplanetary docking, you might need more than 20% the fuel-consumption of a dedicated Orbit-to-Orbit Habitat making an interplanetary transfer, but there's a LOT of room for error with the Cycler architecture still requiring a lot less fuel-consumption than a "Conventional" architecture.  And the 2-Cycler architecture puts a lot less wear-and-tear on the Cyclers than the dedicated Orbit-to-Orbit "conventional" vessel receives, as each Cycler only has to make the equivalent of a high-speed Mars-transfer once in its lifetime, and then spends the rest of its lifetime essentially in microgravity (course-corrections would likely be carried out with ion thrusters to save fuel, under insignificant acceleration).

By contrast, a "conventional" ship makes a 5-month Mars transfer (almost *exactly* the same Delta-V as entering a Cycler Orbit) and a return-journey to Earth under significant thrust both ways every 2 years, and might not last 20, or even 10 years of active service... (since you could build at least two for the cost of 2 Cycler ships, a shorter service-life would be acceptable)

 

I do agree with the point others have made that Cycler architectures require a larger upfront cost for a smaller marginal cost- but that's the case with literally ANY plan to get to Mars cheaper.  Even technology-driven approaches (new propulsion methods, new materials etc.) require an upfront R&D cost in exchange for a lower marginal cost for future missions...

That's the nature of any type of affordable access to space- you have to be willing to INVEST lots of money upfront in order to get an acceptable marginal amd lower long term cost- there are no free lunches, any low-hanging fruit that reduces both marginal and upfront cost for lottle effort has already been picked...  It's not something to be cynical about- investing money now to save more money later is the very cornrstone of good economic stewardship...

For not quite 3 times the initial fuel consumption in year 0, you more than cut in half your long-term fuel requirements with the Cycler architecture.  And while it's R&D costs that actually dominate the costs for a Mars mission, the Cycler need not be anything more than just a larger version of the Orbit-to-Orbit Habitat with extra radiation-shielding and better docking capabilities- its required capabilities (including the ability to sustain crew for a minimum of 5 months between resupply) are otherwise essentially the same... (note the Orbit-to-Orbit Habitat could resupply at Mars before making the return to Earth- otherwise it needs to be able to support crew for at least *10* months)  Anything else, like greenhouses, more crew space, or heavier comm-systems, is just added gravy for the Cycler architecture...

The Interceptor Ship could quite literally be an Orion Capsule with the proposed Cygnus Exploration Augmentation Module and a heavier transfer stage- capabilities we'd already want to have before going to Mars anyways.  In fact, an Orion+Cygnus EAM would be overkill- able to support a crew of 4 for 60 days (whereas a ferry-orbit shouldn't take more than a week) for a bit less than 30 (29.3) tons of launch mass (including the 15.5 metric ton Orion Service Module, 10.4 metric ton Orion Capsule, and 3.4 ton 4-segment Cygnus EAM) plus also a transfer-stage (or simply an extended Service Module with extra fuel onboard)

http://www.spaceflightinsider.com/missions/commercial/orbital-proposes-future-deep-space-applications-cygnus/

https://en.m.wikipedia.org/wiki/Orion_(spacecraft)

29.3 metric tons for an Interceptor Ship may sound like a lot, but any Mars vessel calable of sustaining 4 crew on both a 5-month journey to Mars and a 5-month journey back (let's forget resupply at Mars for a moment) could easily end up massing 160 metric tons or more, assuming plenty of radiation-shielding...

A Cycler ship would be about twice the size- so about 320 tons going by this estimate... (A lot of that in heavy radiation-shielding to protect the crew and onboard electronics from as much cosmic radiation as possible)  It would literally mass more than 10 times the Interceptor Ship- which is why any argument that having a Cycler isn't worthwhile just because the Interceptor would need to have life-support for a week or two is utterly hollow...

An Orion+Cygnus Exploration Augmentation Module might not be light, at 30 tons (you'd definitely need a dedicated Falcon Heavy launch to lift it and its transfer-stage in one launch) but it's certainly a lot lighter than a 320-ton Cycler Ship or a 160-ton "conventional" Orbit-to-Orbit transfer ship/habitat (either one of which would need to be launched in segments, as even a Falcon Heavy couldn't lift either in one go...) and would require a lot less fuel for a ferry-orbit to a Cycler ship (a considerable bit more expensive in Delta-V than a 5-month Mars transfer)

 

All my masses assume very generous allowances for radiation-shielding, thermal insulation, and redundancy systems.  I might be way off on how much/little space I assume the crew can get by on for a Mars transfer however- but nobody will really know the limits of human tolerance for overcrowding on an interplanetary mission until they try it with trained astronauts (civilian experiences with overcrowding don't cut it, as astronauts are specifically selected for their psychological resilience, and civvies are not.  Russian experiences with Mir, however, seem to indicate highly-trained, psychologically-screened humans are much more capable of withstanding cramped conditions than most people assume...)

Edited February 25, 2018 by Northstar1989