Great article. I had a question about this though "Note, the number of Tanker Starships (used to refill these depots) could be relatively low because they are designed to be rapidly reusable."
I am not sure I understand how the rapid reuse pertains to the number of tankers required to refill a depot.
I am also curious of the relative merits of using a refilling a depot vs refilling a Starship (all concept videos from SpaceX show direct refilling of the Starship en-route to Mars.)
Some valid points, worth discussing. In the past it has been suggested Starship could launch once every 4 hours. If so, ia single Tanker Starship could fully replenish a orbital fuel depot in a day. Which implies 3 Tanker Starships could refill 2,000 depots in less than 26 months, i.e. the interval between Mars launch windows. Of course they will likely operate 10+ Tankers to allow for downtime and account for any losses due to wear and tear etc.
For Artemis Program NASA insist SpaceX use a propellant depot for sound operational reasons. They want all the necessary propellant to be available at a depot before HLS launches to orbit. This should reduce the number of automated docking maneuvers required to one, at least between the HLS and propellant depot. Automated docking is fraught with danger, the Progress M-34 nearly totalled Russia's Mir station in 1997, In 2021 the Nauka module caused the ISS extreme problems after docking.
Hence for safety's sake, the Tankers will only dock with the depot, limiting the risk to this one disposable vehicle. Propellant depots can be replaced relatively easily, Human Landing Systems are priceless, and need to be maintained in pristine operating condition.
You can also do some spin gravity moves, which can be more efficient. I am sort of waiting (probably til 2025) to see a real test. One item that I still find interesting is that the notional SX depot depiction shows a larger ship, despite that it is main tank to main tank direct, so you could have a shorter depot ship. It seems to point to 2 specialized tanks with some pumps and they won't use the depot main tanks for shuffling fuel. As with most SX renders I think they are place holders and the final systems won't look so sleek.
I fully agree that Mars (MethLOX) and Lunar surface (LOX) fuel depots will need to be part of the long term vision (2040+) for regular, lower risk, lower cost ops. You continue to be much more optimistic (10x) about the number of Starships that will be created.
Thanks for your valued comment and insightful links. I agree, SpaceX will find it difficult to achieve 1,000 Starships in simultaneous operation, although that appears the plan at present. I have written a post titled: "Next Gen Starship" which I intend to publish soon. It details SpaceX's transport problem and through analysis suggests how their vehicles will likely evolve. Likely Starship will still play a role, but subordinate to a a much larger transport vehicle.
Very good. Not sure I agree about ship 26 (not enough information), but I largely agree with you on the rest of it.
The configuration of multiple depot craft at a fuel depot needs consideration as does how fuel load balancing and different fuel types is managed (especially hydrogen which is notoriously tricky), but apart from that I'm in general agreement.
Great article. I had a question about this though "Note, the number of Tanker Starships (used to refill these depots) could be relatively low because they are designed to be rapidly reusable."
I am not sure I understand how the rapid reuse pertains to the number of tankers required to refill a depot.
I am also curious of the relative merits of using a refilling a depot vs refilling a Starship (all concept videos from SpaceX show direct refilling of the Starship en-route to Mars.)
Some valid points, worth discussing. In the past it has been suggested Starship could launch once every 4 hours. If so, ia single Tanker Starship could fully replenish a orbital fuel depot in a day. Which implies 3 Tanker Starships could refill 2,000 depots in less than 26 months, i.e. the interval between Mars launch windows. Of course they will likely operate 10+ Tankers to allow for downtime and account for any losses due to wear and tear etc.
For Artemis Program NASA insist SpaceX use a propellant depot for sound operational reasons. They want all the necessary propellant to be available at a depot before HLS launches to orbit. This should reduce the number of automated docking maneuvers required to one, at least between the HLS and propellant depot. Automated docking is fraught with danger, the Progress M-34 nearly totalled Russia's Mir station in 1997, In 2021 the Nauka module caused the ISS extreme problems after docking.
https://chrisprophet.substack.com/p/spacex-transition-to-starship
Even Space Shuttle caused significant oscillation when it docked to the ISS on the STS-133 mission.
https://appel.nasa.gov/2011/08/04/taking-a-risk-to-avoid-risk/
Hence for safety's sake, the Tankers will only dock with the depot, limiting the risk to this one disposable vehicle. Propellant depots can be replaced relatively easily, Human Landing Systems are priceless, and need to be maintained in pristine operating condition.
Makes sense. I cannot imagine such a launch frequency given the constant bureaucratic headaches we are seeing.
I am still wondering the mode of fuel transfer and what % can can be moved from A to B. Every mode will have some fuel loss.
I posted an idea at https://www.reddit.com/r/space2030/comments/135s9hg/some_thoughts_and_spreadsheet_analysis_about/
You can also do some spin gravity moves, which can be more efficient. I am sort of waiting (probably til 2025) to see a real test. One item that I still find interesting is that the notional SX depot depiction shows a larger ship, despite that it is main tank to main tank direct, so you could have a shorter depot ship. It seems to point to 2 specialized tanks with some pumps and they won't use the depot main tanks for shuffling fuel. As with most SX renders I think they are place holders and the final systems won't look so sleek.
I also suggest another use of an expendable fuel depot ship will be on the move, as part of a Venus flyby to Mars LLO mission with a small lander option (removes the need for Mars produced MethLOX): https://www.reddit.com/r/space2030/comments/trjoov/notion_to_eliminate_the_need_for_mars_surface/
I fully agree that Mars (MethLOX) and Lunar surface (LOX) fuel depots will need to be part of the long term vision (2040+) for regular, lower risk, lower cost ops. You continue to be much more optimistic (10x) about the number of Starships that will be created.
Thanks for your valued comment and insightful links. I agree, SpaceX will find it difficult to achieve 1,000 Starships in simultaneous operation, although that appears the plan at present. I have written a post titled: "Next Gen Starship" which I intend to publish soon. It details SpaceX's transport problem and through analysis suggests how their vehicles will likely evolve. Likely Starship will still play a role, but subordinate to a a much larger transport vehicle.
Very good. Not sure I agree about ship 26 (not enough information), but I largely agree with you on the rest of it.
The configuration of multiple depot craft at a fuel depot needs consideration as does how fuel load balancing and different fuel types is managed (especially hydrogen which is notoriously tricky), but apart from that I'm in general agreement.
1000 starships at starbase. That will be a sight to see!
I wonder if they will ever come up with bigger depots. Like building in space and sending components separately.