Let's take a simple example. Let's say I have 50W_Mars/kg solar panels and 50W/kg of electrolysis and sabatier equipment. And let's say I have 200 tonnes of payload to the surface of Mars per cargo ship, half solar and half propellant production, whose dry mass will be 100 tonnes. That means I get 5MW of solar per trip. With a 20% capacity factor, that's about 1MW on average.To send 100 tonnes dry mass back costs 70 tonnes of methane. With 100MJ/kg to make methane and 1MW, that means I can produce enough propellant to send that ship back in just 81 days out of the 26 months it takes to do a synod.Mars has no reason to be energy-starved.
... Even if you could use each ship 10 times, you save less than half the cost,...
Quote from: meekGee on 08/01/2023 06:17 am... Even if you could use each ship 10 times, you save less than half the cost,...Nah, I don't think that's true. The ships, if one-way, will end up being most of the cost, just like I think the upper stage for Falcon 9 (which is very simple by comparison...) is most of the marginal cost of a F9 mission at this point.Especially for crewed Starships, those things will not be extremely cheap. They'll probably not be any cheaper per unit dry mass than an airliner and probably more in the early days. They'll probably be most of the marginal cost of a ticket. So getting it back 7-10 times could more than halve the marginal cost of a ticket.*Plus* you'll need to get a lot of people back anyway.
This talk of hundreds of Starships per synod makes me cringe 😖.The infrastructure required to handle that amount of traffic on Mars would dwarf LAX. C’mon guys. It ain’t going to happen. Starship will morph into something bigger, faster and more versatile long before we’d see 100 ships travelling together.
Quote from: Robotbeat on 08/01/2023 05:49 amLet's take a simple example. Let's say I have 50W_Mars/kg solar panels and 50W/kg of electrolysis and sabatier equipment. And let's say I have 200 tonnes of payload to the surface of Mars per cargo ship, half solar and half propellant production, whose dry mass will be 100 tonnes. That means I get 5MW of solar per trip. With a 20% capacity factor, that's about 1MW on average.To send 100 tonnes dry mass back costs 70 tonnes of methane. With 100MJ/kg to make methane and 1MW, that means I can produce enough propellant to send that ship back in just 81 days out of the 26 months it takes to do a synod.Mars has no reason to be energy-starved.If you want the ship back in one synod, you don't have 26 months, you only have about 3 months to do all that.And suppose you did. What did you save? Even if you could use each ship 10 times, you save less than half the cost, and you need to ship forward additional payload comparable to those ships you sent back.It makes absolutely no sense to send them back.Reusability is great and a key to a lot of things, but in this narrow case it is simply counter-productive.
Sometimes I think some of you are insistent in keeping the costs at more than $1 million per ticket.
Does anybody have a good feel for the cost of Starship avionics?
Musk wanted the bulk of a rocket’s computing systems to cost no more than $10,000. It was an insane figure by aerospace industry standards, where the avionics systems for a rocket typically cost well over $10 million. “In traditional aerospace, it would cost you more than ten thousand dollars just for the food at a meeting to discuss the cost of the avionics,” Watson said. During the job interview, Watson promised Musk that he could do the improbable and deliver the $10,000 avionics system....Watson and other engineers built out the complete computing systems for Dragon and then adapted the technology for Falcon 9. The result was a fully redundant avionics platform that used a mix of off-the-shelf computing gear and products built in-house by SpaceX. It cost a bit more than $10,000 but came close to meeting Musk’s goal.
One of the advantages of large rockets is that your avionics don't really get any heavier/costlier, so you achieve better amortization.
Quote from: meekGee on 08/01/2023 06:20 pmQuote from: Robotbeat on 08/01/2023 08:39 amSometimes I think some of you are insistent in keeping the costs at more than $1 million per ticket. Now this cuts deep. Take it back! We share the goal, you're just wrong in your math.I'll explain in more detail.Imagine there were two Mars colonization architects.One designed a ship that's reusable, can fly 10 times, and can do it so fast it's available for reuse on the next synod. Let's call him Reusable Robert.The other designed a ship that flies once, and once landed it becomes storage tanks, batteries, pumps, etc. Lets call her Non-reusable Nelly.Both Robert and Nelly want to launch double as many ships each synod, starting with 1 ship at synod 0, until they reach 1024 ships.So: 1,2,4....512, 1024 for a total of 2047 outbound trips.Nelly has to build 2047 ships.Robert thought he can save 10x, but even though he always has every ship ever launched available for reuse on each synod, his progression looks like:1,1,2,4...512 for a total of 1024 ships.He didn't save 90%.. he saved only 50%!!!But wait. Common practice is that when you make twice as many ships, your cost per ship drops by 20%.The cheaper ships lie towards the end, so when you average it out, the savings are not 50% but only 37% (says excel)But wait - Nelly has a lot of assets on the surface - thousands of tanks for all the ISRU fluids for 100,000 people, batteries, pumps, etc.Robert meanwhile had to build a much more capable spaceport - he has to turn around hundreds of ships per synod, not just let them land. That's a tough task even on Earth, not to mention on a colony that's still growing.On the flip side, Robert has a fleet remaining at the end, but after 20 years - is it really relevant? Because the ships of the first decade are not the ships of the second decade, or the third..So in fact Nelly might hit a lower cost to Mars than Robert. It doesn’t cost nothing to double how many ships you send every year. By reusing ships, you halve the factory size necessary at each step even if you DO double every synod, so there’s a pretty good case to be made for doing it.
Quote from: Robotbeat on 08/01/2023 08:39 amSometimes I think some of you are insistent in keeping the costs at more than $1 million per ticket. Now this cuts deep. Take it back! We share the goal, you're just wrong in your math.I'll explain in more detail.Imagine there were two Mars colonization architects.One designed a ship that's reusable, can fly 10 times, and can do it so fast it's available for reuse on the next synod. Let's call him Reusable Robert.The other designed a ship that flies once, and once landed it becomes storage tanks, batteries, pumps, etc. Lets call her Non-reusable Nelly.Both Robert and Nelly want to launch double as many ships each synod, starting with 1 ship at synod 0, until they reach 1024 ships.So: 1,2,4....512, 1024 for a total of 2047 outbound trips.Nelly has to build 2047 ships.Robert thought he can save 10x, but even though he always has every ship ever launched available for reuse on each synod, his progression looks like:1,1,2,4...512 for a total of 1024 ships.He didn't save 90%.. he saved only 50%!!!But wait. Common practice is that when you make twice as many ships, your cost per ship drops by 20%.The cheaper ships lie towards the end, so when you average it out, the savings are not 50% but only 37% (says excel)But wait - Nelly has a lot of assets on the surface - thousands of tanks for all the ISRU fluids for 100,000 people, batteries, pumps, etc.Robert meanwhile had to build a much more capable spaceport - he has to turn around hundreds of ships per synod, not just let them land. That's a tough task even on Earth, not to mention on a colony that's still growing.On the flip side, Robert has a fleet remaining at the end, but after 20 years - is it really relevant? Because the ships of the first decade are not the ships of the second decade, or the third..So in fact Nelly might hit a lower cost to Mars than Robert.
