Author Topic: Lots of little Raptors  (Read 62709 times)

Offline GORDAP

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Re: Lots of little Raptors
« Reply #140 on: 02/01/2015 03:20 pm »
I'll never understand the fascination with 'cyclers'. They really only give you ONE thing. More living space during the transit. That's all. You still have to bring ALL the supplies with you (no mass savings), you still have to accelerate to TMI (no propellant savings), and for what? To save on habitable volume? Remember that this is living space volume AND cargo volume that will be needed on Mars when you get there.

And as a cherry on top, you have a very narrow launch window, and add another failure more if you fail to rendezvous.

Cyclers are just a bad idea, and Aldrin arguing for them doesn't make it any better.

Lars-J, don't cyclers potentially give quite a bit more than the "One thing" (extended living space) than you say? 

I think you can more easily design them to give variable artificial gravity by spinning opposing habitat modules, and architect those habs to more easily provide a 'storm shelter' against solar flares.  But the big thing they give you is the ability to use low thrust, high ISP propulsion (ion, nuclear thermal, VASIMR, etc.).  This gives you either faster transit times or greater mass ratios (or a combination of these two).

Of course there's no question that the MCT will not be a cycler - Musk has been very clear about that.  But I just think there are too many advantages in the long run for having crafts that are optimized for their jobs:  Launchers/Landers for moving people and cargo to/from orbit (needing high thrust, streamlined form factor, TPS and landing gear, and very little life support) and planet-to-planet craft (high ISP, high degree of life support including spin gravity and radiation mitigation, unconstrained form factor, and no TPS/landing legs).  I suspect that if we do enter an era in the next few decades where multiple hundreds of folks are going to Mars each synod, I'd bet it'll be on some craft that'll never touch dirt or regolith. 

Note:  Your comment re restricted launch windows gives me pause.  Hmm, maybe I'm misunderstanding 'cyclers'?  I envision a craft that's constructed in LEO, and transits to Mars orbit where it offloads cargo and people to a lander that came up from the surface, then it transits back to Earth orbit where it gets it's next batch of cargo and people.  Repeat ad infinitum.  Guess I'll read up on Aldrin's version.

Edit: O.K., now I understand 'Cyclers' - should have done that before posting. ::)  I see your point about no fuel savings.  So let me call what I'm thinking about something else.  Hmm, 'vacuum ships' or something.  Anyway, still think there would be an advantage to high ISP, unconstrained form factor craft going just from orbit to orbit (never touch the surface).
« Last Edit: 02/01/2015 03:49 pm by GORDAP »

Offline guckyfan

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Re: Lots of little Raptors
« Reply #141 on: 02/01/2015 03:46 pm »
Note:  Your comment re restricted launch windows gives me pause.  Hmm, maybe I'm misunderstanding 'cyclers'?  I envision a craft that's constructed in LEO, and transits to Mars orbit where it offloads cargo and people to a lander that came up from the surface, then it transits back to Earth orbit where it gets it's next batch of cargo and people.  Repeat ad infinitum.  Guess I'll read up on Aldrin's version.

Yes, you do. A cycler is something that cycles between Earth and Mars on a free trajectory. Or almost free, it will need occasional course corrections.

Unless you have a whole ecosphere that can provide food and air to breathe, it indeed offers only better living space plus better radiation protection because it can be massive.

It requires more delta-v than direct flight because its trajectory is not an energy saving one. So it saves only if your vehicle can be substantially lighter. That may be the case for crew. Not with cargo. The cargo does not become lighter because you use the cycler for transport. So a cycler is worse than useless for cargo.


Offline GORDAP

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Re: Lots of little Raptors
« Reply #142 on: 02/01/2015 03:52 pm »
Yup, now I see.  See my edit above.

But wouldn't there still be other advantages for using high ISP, unconstrained form factor craft to transit from orbit to orbit only.  I think this would go for cargo as well.  (Sorry - I shouldn't have confused this with 'Cyclers'.)

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