assuming that all that's been said, that Elon want's to send 80,000 people to Mars per year, the logistics of it is staggering.Stying with the MCT craft hauling 100 people each, that's going to take 800 craft, per year to Mars, or 2000 MCT's per 2.5 year cycle!The MCT's wouldn't be sufficent to sustain this kind of work load, and accidents would happen. I think I have a handle on how this could be done, but it would take at least 5 to 10 years of ramp up time to make possible.
Quote from: Robotbeat on 11/14/2014 06:47 pmMusk isn't looking for those types for his colony. He's openly skeptical, scoffing at Mars One's plans. No doubt many of those 80k would be people who don't intend to stay their entire lives on Mars. But once you have a thousand, ten thousand, hundred thousand people there, it's more like deciding to live in Minneapolis in January (you really can't go outside for more than a minute except after spending 15 minutes bundling up, but all the buildings are interconnected in the downtown with tunnels and skyways and people have climate-controlled garages so that's not a show stopper) than it is anything at all like a one-way suicide mission. You'll need a few thousand incredibly driven and bright people at first no doubt, but you don't need and don't want anti-social "suicide geeks."No, Mars is more like winterover on the South Pole, only for 3 years instead of 9 months, and the conditions outside are much worse.You know what, let's say someone built us a perfect underground base on Mars, with greenhouses, gyms and swimming pools. Still, what's the attraction? Why would you want to spend your life there?
Musk isn't looking for those types for his colony. He's openly skeptical, scoffing at Mars One's plans. No doubt many of those 80k would be people who don't intend to stay their entire lives on Mars. But once you have a thousand, ten thousand, hundred thousand people there, it's more like deciding to live in Minneapolis in January (you really can't go outside for more than a minute except after spending 15 minutes bundling up, but all the buildings are interconnected in the downtown with tunnels and skyways and people have climate-controlled garages so that's not a show stopper) than it is anything at all like a one-way suicide mission. You'll need a few thousand incredibly driven and bright people at first no doubt, but you don't need and don't want anti-social "suicide geeks."
Sounds sweet. An entire virgin planet. With lots of other smart and driven people doing something that has lasting, historical, existential significance. That's all anyone can ask for.
Quote from: RanulfC on 11/14/2014 06:15 pmQuote from: CyclerPilot on 11/14/2014 08:29 amBelow is my speculative MCT design.I constrained the design by following as many Elon and SpaceX statements as possible. I tried to optimize for both development and operational costs. I got most of my inspiration from the other excellent designs in this thread, but tried to make something unique.Nice design but... Lord-n-Lady how do you get to the surface from that thing? Jump? Rope ladder or cable lift. Do you even treehouse?
Quote from: CyclerPilot on 11/14/2014 08:29 amBelow is my speculative MCT design.I constrained the design by following as many Elon and SpaceX statements as possible. I tried to optimize for both development and operational costs. I got most of my inspiration from the other excellent designs in this thread, but tried to make something unique.Nice design but... Lord-n-Lady how do you get to the surface from that thing? Jump?
Below is my speculative MCT design.I constrained the design by following as many Elon and SpaceX statements as possible. I tried to optimize for both development and operational costs. I got most of my inspiration from the other excellent designs in this thread, but tried to make something unique.
Quote from: Robotbeat on 11/14/2014 07:36 pmSounds sweet. An entire virgin planet. With lots of other smart and driven people doing something that has lasting, historical, existential significance. That's all anyone can ask for.What's the significance of spending your life in a box, unless you are an anchorite? There are many people who do research on the South Pole, but I don't recall any of them wishing to actually live there indefinitely. The same will be true about Mars. A research base - sure. A colony - bloody unlikely.And I don't think you need 80k people per year for a research base. 80k people in total on Mars will probably be more than enough to research the crap out of it. :-)
I mean sheesh, am I the only one that is motivated by something other than just living a life of comfort??Significance is a powerful motivator.
I made a thread about would-be colonist motivations since it's quite off-topic here
How fast do you hit the ground after jumping from 30 meters on 0.3g? Really, very nice design.It resembles a possible dragon2 + stage2 glued together which I think is a very interesting option for near term stage reuse.
Quote from: Robotbeat on 11/14/2014 07:36 pmSounds sweet. An entire virgin planet. With lots of other smart and driven people doing something that has lasting, historical, existential significance. That's all anyone can ask for.What's the significance of spending your life in a box, unless you are an anchorite? There are many people who do research on the South Pole, but I don't recall any of them wishing to actually live there indefinitely. The same will be true about Mars. A research base - sure. A colony - bloody unlikely.
Quote from: guckyfan on 11/18/2014 03:08 pmQuote from: Nilof on 11/18/2014 12:16 pmOn the Mars side, I'd expect a dedicated BFR upper stage doing work as a reusable Mars SSTO. That makes the return leg a lot easier, since the MCT does not have to perform both the ascent to Mars orbit and the full transfer burn by itself, which would require a lot of delta-v for a fast return.But that would require capability of doing maintenance for MCT on Mars incl. the heatshield. I don't believe that capability will be available any time soon.Now if there was fuel production in Mars orbit (say they find water and CO2 on Phobos) then the idea suddenly becomes much more feasible. They would not need refueling flights from the Mars surface in that scenario. And a lot less fuel ISRU on the surface as they no longer need to lift all the fuel for the return flight out of the Mars gravity well.A BFR upper stage only really needs a heat shield if it is required to be capable of bringing payloads down with it. Otherwise, it does not need to be built for reentry. Just do propulsive braking like with the Mars transfer, there's no need to use the atmosphere for that. The payload mass to dry mass ratio would be so large that the penalty for propulsive braking ends up being small, much like for Earth first stage RTLS which has roughly similar delta-v requirements for boostback.
Quote from: Nilof on 11/18/2014 12:16 pmOn the Mars side, I'd expect a dedicated BFR upper stage doing work as a reusable Mars SSTO. That makes the return leg a lot easier, since the MCT does not have to perform both the ascent to Mars orbit and the full transfer burn by itself, which would require a lot of delta-v for a fast return.But that would require capability of doing maintenance for MCT on Mars incl. the heatshield. I don't believe that capability will be available any time soon.Now if there was fuel production in Mars orbit (say they find water and CO2 on Phobos) then the idea suddenly becomes much more feasible. They would not need refueling flights from the Mars surface in that scenario. And a lot less fuel ISRU on the surface as they no longer need to lift all the fuel for the return flight out of the Mars gravity well.
On the Mars side, I'd expect a dedicated BFR upper stage doing work as a reusable Mars SSTO. That makes the return leg a lot easier, since the MCT does not have to perform both the ascent to Mars orbit and the full transfer burn by itself, which would require a lot of delta-v for a fast return.
The amount of maintenance needed would depend on how reliable and serviceable the Raptor turns out to be, and on how bad the cyclic stresses on the cryogenic tanks are. If they are planning to eventually refly first stages within days on Earth, launching a Mars SSTO a few times a year would probably not be a huge deal.
There is no need for multiple refueling trips either. Just launch the damn thing whole. There's just no need for it to lug something the size of a Falcon 9 first stage all the way back to Earth. This thing called "staging" improves payload a lot.
Phobos or Deimos ISRU (or more general asteroid ISRU around Martian space) would be a nice thing to have, and is very viable for a Mars roadmap that involves asteroids or visiting the moons of Mars before Mars itself.
It is heavy enough by itself. Braking from orbital speed down to a speed where reentry is possible without heatshield would require a prohibtively high delta-v of at least 6-7km/s. No way of doing that propulsively with appreciable payload.
Quote from: guckyfan on 11/20/2014 06:22 amIt is heavy enough by itself. Braking from orbital speed down to a speed where reentry is possible without heatshield would require a prohibtively high delta-v of at least 6-7km/s. No way of doing that propulsively with appreciable payload.Actually, that is quite possible, with significant margins, as long as you don't bring the payload down with you.At 3600Ns Isp, the mass ratio for launching to orbit is exp(3.8/3.6) = ~2.9. For landing, you have another factor of 2.9, which gives a minimum required mass ratio of ~8.4 for the stage. For comparison, the Falcon 9 first stage has a mass ratio of 22.To keep our numbers round, assume our Mars SSTO has a dry mass of 10 tonnes and can carry 200 tons of fuel, and let's round up 2.9 to 3. The US needs to save 20 tons of fuel for landing. But at a mass ratio of 3, 200 tons of fuel is enough to put 100 tons into orbit. So you're left with a 100 - 30 = ~70 ton payload to low Mars orbit, vs a 90 ton payload to orbit if it were fully expendable. The payload hit for fully propulsive landing is so small that a heat shield probably isn't the best option.
I am not suggesting the MCT to lift fuel. I am talking about repurposing a BFR upper stage as a Martian SSTO separate from the MCT. And that the MCT could be lifted by it so it doesn't have to do the full trip back to Earth with a single stage.As I said in my original post, I envision the MCT as a vehicle with 2-3 km/s delta-v and optimized for areocapture/areobraking and landing with heavy payloads, while using a BFR upper stage for any delta-v intensive burns such as transfers and Mars liftoff.
Quote from: Nilof on 11/20/2014 08:55 amI am not suggesting the MCT to lift fuel. I am talking about repurposing a BFR upper stage as a Martian SSTO separate from the MCT. And that the MCT could be lifted by it so it doesn't have to do the full trip back to Earth with a single stage.As I said in my original post, I envision the MCT as a vehicle with 2-3 km/s delta-v and optimized for areocapture/areobraking and landing with heavy payloads, while using a BFR upper stage for any delta-v intensive burns such as transfers and Mars liftoff.And I gave the reasons why I see a problem with that approach.