Perhaps a mass estimate based on adding up the parts of the MCT would be more reasonable.You'll need, # of Raptors and mass of Raptor (lets assume 100:1 thrust:weight which would make them 2.3 mT each. Thrust structure mass, probably proportional to thrust, few good examples to base a comparison onTank volume and tankage fraction, F9 tanks are reasonable basis for comparisonSurface Area and mass per unit area of Thermal protectionStructural mass, probably proportional to internal volume and peak g-forces.Landing legs, I've read that these are generally 10% of touch down mass.Auxiliary systems, solar panels, radiators, batteries, avionics etc etc, again hard to estimate.
Why would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?I would guess more like 30-35 tons.
L2 MCT Rending Effort (ongoing, large collection):http://forum.nasaspaceflight.com/index.php?topic=35307.0
Musk has said 80,000 people per year (and ten times as many cargo shipments), which is 1000 Passenger MCTs at once, plus 10,000 cargo MCTs (or actually, there ways around this, but it remains to be seen if they're worth it). So yeah, at any one time, there would need to be thousands of MCTs.
No, he has suggested a mature colony developed over decades would reach a population of 80k, not that eighty thousand settlers would be sent every year....
Incorrect.https://twitter.com/elonmusk/status/273483420468932608
Did this figure initially take you aback??
I like this method for estimation better than just scaling up Dragon (or just random guessing .)Was that 10% of touch down mass or touchdown weight? On Mars, it will have 100 tons of cargo but at a fraction of the gravity. Earth landing should be less 0-20 tons of cargo.The structural mass depends a lot on design details. For example if the crew/cargo section is below the propellant tanks, the walls have to be beefed up to support the full propellant load (~1000 tons) through max Q. Also, having the TPS somewhere other than the bottom (top or side), requires it to be beefed up further to handle load in multiple directions.I think that there will only be a pressurized version (as opposed to an un-pressurised cargo version) for reasons of the cargo/crew pressure vessel doing double duty as the support structure, just like the propellant tanks.
Quote from: Oceanbluesky on 06/20/2015 11:05 pmDid this figure initially take you aback?? Honestly it still does.But see it that way: combine 80000 people a year, 10 cargo flights for each colonist flight and 50 Million $ per flight the total cost of 440 Billion $
So .. uh .. the cargo is free?
Quote from: R7 on 06/21/2015 09:09 amSo .. uh .. the cargo is free?You are right, I miscalculated by one order of magnitude, sorry. Yes it is much higher than the US defense budget. Corrected my post.
Your original flight cost was calculated correctly (800 passenger flights, 8000 cargo flight, 8800 total at $50M a pop yields the $440B.The cost of the cargo is presently unknown. My gut feeling is that the answer to question "what do you have to pack in order to live on Mars" is quite lengthy, complex and thus expensive.
I would think once the flight rate of 80, 000 colonists per year is reached, the cargo requirements per colonist fight will be much less than 10:1.By that time, the mars industrial base should be able to produce anything they need short of integrated circuits.
Quote from: CyclerPilot on 06/21/2015 04:19 pmI would think once the flight rate of 80, 000 colonists per year is reached, the cargo requirements per colonist fight will be much less than 10:1.By that time, the mars industrial base should be able to produce anything they need short of integrated circuits.You may well be right. A colony needs to be well advanced to be able to absorb that many people per year. I really don't see that mass exodus happen, ever. It is just that it is not completely impossible with available ressources.
Quote from: Robotbeat on 06/20/2015 08:45 pmWhy would MCT weigh that much dry, particularly in a cargo config (because you mentioned 100mt payload, and Musk keeps talking about cargo flights as separate from passenger flights) and without yet counting the heat shield?I would guess more like 30-35 tons.Just the propellant tank portion, 5 Raptor engines and possibly landing legs too would weight ~40mt. Now add the reentry shield and the cargo bay structure. Of course the cargo variant will not have as high a dry weight as the crew variant but where is the tradeoff in crew payload size and crew vehicle dry weight increase. If you could get the cargo variant to have a dry weight as low as 60mt then reduce the payload size of the crew variant (crew + supplies) to only 60mt on a crew variant that dry weight 100mt things will work out better in that the overall system becomes smaller. You shrink the size and maybe some savings on the propellant tank dry weight due to smaller tanks.My only problem with the estimates is that the more detail we go the heavier the MCT gets.