There's no such thing as a benevolent dictator. Not among humans, anyway. And if there was, they probably wouldn't have the intelligence to do it effectively. Everyone comes up short in some way. That's why you have combine our collective abilities, and average it all out without giving anyone exclusive control. In doing so, our collective self interest can sometimes manifest as intelligent and rational.
Refueling is shown as expected. For insertion burn, they need to transfer thrust loads which is easier with more contact area. They would also want to use up Starship's propellant to lighten it for Mars entry and landing. Tanker stays fuller and potentially refuels Starship for their return trip.
Agreed.
I don’t see how the ship-to-ship contact area changes if they are nose-to-tail vs nose-to-nose.
But if the ships are too unequal in mass when they are attached and rotating during Mars transit won’t that result in flight path deviations that will need to be corrected somehow?
Oh... yeah... I was picturing offset refueling connection, not mirror image...
Why wouldn't tanker and Starship separately accelerate during the insertion burn?
Good points
It's a scenario.
I’d never seen such a proposal either, but it appears that graphic is not from SpaceX. If it is not, then I don’t know if the objective of the stretched V2 Starship is to eliminate the need for a companion tanker on the transit to Mars. I thought it was to increase the payload, in combination with adding 3 RVacs.
Yes, and perhaps that is the real advantage of the mission design outlined in that graphic; the tanker ensures that even if ISRU fails to provide needed propellants for the Starship, the tanker will be available as a backup, assuming of course that the tanker propellants can be properly managed during it’s approximately 2 years in LMO (Low Martian Orbit ;-).
Thanks for clarifying.
Good point, that would make sense. But if the two vehicles are rotated nose-to-nose, won’t the lower distance of the crew compartment from the center of rotation — as compared to rotating end-to-end — reduce the level of artificial gravity that the crew experiences? Also, nose-to-nose coupling might be very hard to design without interfering with the TPMS at the nose.
Yes. Even worse, the difference in rotation between a person's head and feet is going to make them seriously nauseous, and coriolis effects would be a nightmare.
That would give more options for sure, but it's not something that is at all practical in the immediate future. A tether handling just 40% gravity needs to support something like 640 tons (a full tanker plus a cargo-loaded Starship at 0.4g). That's a pretty serious tether. I'd run them between the lift points on the Starships as that matches their design use - except that I doubt the lift points are currently designed to handle anywhere near 640 tons.
And unknown unknowns.
Dock the ships at each tether point to capture a tether end, then back away. Leave some mechanism on the connector to allow it to be released (when not under tension).
Saving folks a click: Karen R Pease. Not that the name means anything to me, even after hunting around for some kind of information.
The required tension would be far less than this. Starship's dry mass is ~100T, plus ~100T payload, plus (wild guess) ~50T fuel after trans-Mars injection. So even at a full 1g acceleration, the tether would only need to support ~250 tons tension. (It wouldn't matter if Starship is tethered to a heavier tanker; the tanker would be closer to the center of spin and thus experience less G-force, offsetting its higher mass.) With a 5x safety margin relative to nominal breaking strength, this setup would require e.g. a Dyneema tether about 6cm in diameter. This would mass about 1 metric ton for a 300m tether, spun at 2.5rpm for 1g, or at a more comfortable 1.6rpm for 0.4g. (Or with a 2-ton 600m tether, one could spin at 1.8rpm / 1.1rpm.) Dyneema is probably useful stuff to have on Mars, so it wouldn't even be wasted payload.
Thank you for pointing that out. I was being completely simpleminded and was focusing on balancing propellant between vehicles so that they'd rotate around the middle of the tethers.
Yeah, I think tankers got mixed in here as a result of somebody putting a graphic together that says that. The graphic from a SpaceX guy back in 2018 shows a fueled Starship going to Mars. With those beautiful solar wings.
Do you have any applications in mind? Dyneema is polymer-impregnated so I assume it cannot easily be broken down to individual strands. How many applications are there for lifting hundreds of tons on Mars over hundreds of meters? Having a cable that can be turned back into individual strands would probably allow it to be used in more applications, despite the lower tensile strength and greater mass.
It was suggested as an emergency backup in the event that ISPP fails in any way. I wouldn't send a crew to Mars without the propellants already in place, but that's me.
