Quote from: RJMAZ on 10/30/2024 10:36 amQuote from: lamontagneSo Starship is designed for Aerobraking. If it turns out to be impossible, I expect plan B is refueling in Mars orbit, not a second stage.How do you get fuel to Mars orbit?1) Disposable tanker from Earth. That requires 20 extra launches from Earth to send one disposable tanker to Mars orbit. That tanker allows the one manned ship to Return.2) Reusable tanker from Earth. You need to send 4-5 tankers to Mars orbit to offload 100 ton if fuel each. That is 80- 100 launches from Earth to allow one manned ship to return.3) Send tankers from the Mars surface to Mars orbit using fuel created on Mars. With 4 km/s ascent and 4 km/s decent using propulsive landing means a Starship could not send fuel to Mars orbit and return. You assume best case scenario that the tanker can return to Mars surface with minimal fuel use? 4km/s up and 2km/s down? That is still 6 km/s and you will then need multiple tankers from the Mars surface to send one manned ship back to Earth. So instead of a 1,000 ton of propellant from a booster you now have thousands of tons of propellant using tankers. Add a couple square kilometres of extra solar panels to make that extra fuel for the inefficient Mars tanker system.Or just use a Mars booster.Sorry, I was imprecise: if 'full aerobraking at Earth' turn out to be impossible because the entry velocity is too high, then the Starship can refuel in Mars orbit. A Starship tanker from Mars surface should be able to carry 500 tonnes to Mars orbit. So a single tanker can make up the propellant required for a full burn back to Earth, since the transfer is 6,1 km/s of deltaV.Aerobraking from a stable LEO is obviously possible. Spreadsheet added. Added flight from Mars in a separate tab
Quote from: lamontagneSo Starship is designed for Aerobraking. If it turns out to be impossible, I expect plan B is refueling in Mars orbit, not a second stage.How do you get fuel to Mars orbit?1) Disposable tanker from Earth. That requires 20 extra launches from Earth to send one disposable tanker to Mars orbit. That tanker allows the one manned ship to Return.2) Reusable tanker from Earth. You need to send 4-5 tankers to Mars orbit to offload 100 ton if fuel each. That is 80- 100 launches from Earth to allow one manned ship to return.3) Send tankers from the Mars surface to Mars orbit using fuel created on Mars. With 4 km/s ascent and 4 km/s decent using propulsive landing means a Starship could not send fuel to Mars orbit and return. You assume best case scenario that the tanker can return to Mars surface with minimal fuel use? 4km/s up and 2km/s down? That is still 6 km/s and you will then need multiple tankers from the Mars surface to send one manned ship back to Earth. So instead of a 1,000 ton of propellant from a booster you now have thousands of tons of propellant using tankers. Add a couple square kilometres of extra solar panels to make that extra fuel for the inefficient Mars tanker system.Or just use a Mars booster.
So Starship is designed for Aerobraking. If it turns out to be impossible, I expect plan B is refueling in Mars orbit, not a second stage.
3) Send tankers from the Mars surface to Mars orbit using fuel created on Mars. With 4 km/s ascent and 4 km/s decent using propulsive landing means a Starship could not send fuel to Mars orbit
The defining point where SpaceX determined that the Mars plan was possible was when they confirmed supersonic retropropulsion as a landing process on Mars and got rid of parachutes, ballutes and entirely propulsive architectures. If you don't use that design element, you need to remove Starship from the name of the post, and change it to reaching Mars with a methane Saturn 5 and, probably, a nuclear thermal upper stage architecture. The architecture that failed to go anywhere for 40 years.
Now if each upper stage requires 1 week of refurbishment how do you intend to do 15,000 launches during the Mars launch window? During the launch window there will be huge bottleneck in the refurbishment process between launches. SpaceX will need 100,000 refurbishment workers trained and waiting to work on the reusable upper stages every time the Mars launch window opens. They will need a factory that is 10 times bigger than the biggest factory in the world to do this refurbishment. The heat shield work needs to be done under cover.Where the disposable upper stage system really shines is you require only 4,000 launches to get the same 1,000 ships to Mars. The biggest benefit is all of the disposable upper stages can be built and stored in the years before the the launch window opens. They can all be parked out in the open side by side with simple covers on the engines nozzles. So when the launch windows open SpaceX doesn't need a huge number of refurbishment workers or huge factory. I have never seen anyone on this forum ever post this as an issue.
Quote from: lamontagne on 10/30/2024 02:00 pmThe defining point where SpaceX determined that the Mars plan was possible was when they confirmed supersonic retropropulsion as a landing process on Mars and got rid of parachutes, ballutes and entirely propulsive architectures. If you don't use that design element, you need to remove Starship from the name of the post, and change it to reaching Mars with a methane Saturn 5 and, probably, a nuclear thermal upper stage architecture. The architecture that failed to go anywhere for 40 years.The OP already assumes that neither full reusability nor orbital refueling are viable, and this isn't really any different tbh.
In this case, he's assuming that aerobraking even from Low Mars Orbit is not viable.
The OP already assumes that neither full reusability nor orbital refueling are viable, and this isn't really any different tbh.
I imagine most people on this forum believe that through iteration, Starship TPS will achieve very low to zero (think airline level) refurbishment requirements. Just because Shuttle was stuck with its first design doesn't mean Starship has to be.
By that logic S30 can't go to LEO and then land softly in the Indian Ocean, even if B12 takes it all the way to orbit. (Ninja'd)
P.S. my source (Solar System delta-V map) says 9,256 m/s from Earth to LEO and 3,578 from Mars to low Mars orbit - so I dispute your "4 km/s" figure. Where did you get that from?
P.P.S. If you want to make a 100% propulsive architecture, forget about Starship-derived-ELVs and use hydrogen.
I'm only half following this, but wasn't his argument that you can manufacture ships with less resources than refurbing them (times 4)
My system still uses orbital refueling. It simply reduces the number of launches to a single digit percentage.
Quote from: steveleachIn this case, he's assuming that aerobraking even from Low Mars Orbit is not viable.I actually included 2 km/s of aerobraking on Mars. That has been my estimate for my analysis so far. Aerobraking will work fine. The only thing up for debate is how much aerobraking can be achieved with such a thin atmosphere.My 100% propulsive landing argument was simply to show how critical aerobraking will be. Without aerobraking Starship wouldn't even be able to make it from the Mars surface to orbit and back down to Mars surface.
Some members think...Members are betting/wishing/hoping...
The rocket sized in the first post using the Silverbird Astronautics launch calculator showed 254 ton of payload to LEO with expendable upper stage. This is totally realistic considering SpaceX lists 300 ton expendable. Propellant capacity of this lighter upper stage is 1,000 ton. The Starship that plans to go to Mars can take off from Earth and arrive in LEO with 238 ton of propellant remaining. It then receives three 254 ton loads of propellant to reach full capacity 1,000 ton capacity. Four launches from Earth then get one Starship to Mars.
Where does the 2 km/s figure come from? Did SpaceX get this (relatively old) simulation completely wrong?https://www.spacex.com/humanspaceflight/mars/
Valiantly trying to piece together RJMAZ's posts into a cohesive thesis, I unearthed this passage:Quote from: RJMAZ on 10/27/2024 09:26 pmThe rocket sized in the first post using the Silverbird Astronautics launch calculator showed 254 ton of payload to LEO with expendable upper stage. This is totally realistic considering SpaceX lists 300 ton expendable. Propellant capacity of this lighter upper stage is 1,000 ton. The Starship that plans to go to Mars can take off from Earth and arrive in LEO with 238 ton of propellant remaining. It then receives three 254 ton loads of propellant to reach full capacity 1,000 ton capacity. Four launches from Earth then get one Starship to Mars.Subtracting, that leaves me with only 16 tons to play with for both the payload headed to Mars and the difference in dry mass between the expendable upper stage and the Mars transit vehicle (if any). I'm trying, I'm really trying. Please help revise or clarify, because I want something good to come out of this thread!
Quote from: BrigantineBy that logic S30 can't go to LEO and then land softly in the Indian Ocean, even if B12 takes it all the way to orbit. (Ninja'd)1) The last flight still had a fin burn through. I wouldn't call that a soft land or airline level of refurbishment requirements. A very long way to go.Quote from: BrigantineP.S. my source (Solar System delta-V map) says 9,256 m/s from Earth to LEO and 3,578 from Mars to low Mars orbit - so I dispute your "4 km/s" figure. Where did you get that from?2) The figure of 3,578 m/s only applies if it takes 1 second to go from the surface to orbit The flight will take a couple minutes so you will need to add a couple hundred m/s to the delta-V requirement for gravity loss.Quote from: BrigantineP.P.S. If you want to make a 100% propulsive architecture, forget about Starship-derived-ELVs and use hydrogen.I assumed 2km/s of aerobraking on Mars entry.3) Members are betting/wishing/hoping that the Mars descent will be 3+ km/s of aerobraking and less than 0.5 km/s of propulsive landing. This would allow Mars launched tankers to comfortably send fuel to Mars orbit. It also allows Starships to go direct from LEO to the Mars surface.4) The Mars atmosphere is extremely thin. The entry speeds involved will not provide enough duration to slow down.
Quote from: lamontagneWhere does the 2 km/s figure come from? Did SpaceX get this (relatively old) simulation completely wrong?https://www.spacex.com/humanspaceflight/mars/I am aware of that old simulation. As you can see it has around 500 m/s of landing burn.That is why I said members are betting/wishing/hoping that the Mars descent will have less than 0.5 km/s of propulsive landing. My estimate of 2 km/s of landing burn is only 4 times longer than the landing burn proposed by the best case scenario of SpaceX.my estimate still has aerobraking used for 75% of the total Mars entry. The old simulation has the ship pulling over 5g knocking most passengers unconscious. I have never suggested a full propulsive landing like on the Moon. Super Heavy warped the outer engine nozzles while performing the best case simulation entry. So yes SpaceX can get their simulations completely wrong. It looks like SpaceX will need to dedicate more fuel to protect the engines or stage much earlier like with the planned V3 version.I will cross my fingers and toes that Mars entry only requires a 500 m/s landing burn. This would be a bigger achievement than landing the booster or upper stage on Earth in my opinion. Doing a test flight on Earth to test re-entry is very simple. To test the re-entry on Mars requires waiting a few years and doing a dozen tanker flights. I assume when the Mars window opens SpaceX will send multiple test vehicles to Mars say 1 week apart. So when they re-enter and crash they can tweak and upload a new flight profile for the ship arriving the following week. Hopefully by the last ship they have nailed the landing and it doesn't require a hardware upgrade or big landing burn. As these first ships won't have payload or a cabin fitout they should have enough fuel to increase the landing burn if required. SpaceX can then determine if the crewed ships have to launch from a HEEO.
Quote from: Twark_Main on 10/30/2024 10:00 pmValiantly trying to piece together RJMAZ's posts into a cohesive thesis, I unearthed this passage:Quote from: RJMAZ on 10/27/2024 09:26 pmThe rocket sized in the first post using the Silverbird Astronautics launch calculator showed 254 ton of payload to LEO with expendable upper stage. This is totally realistic considering SpaceX lists 300 ton expendable. Propellant capacity of this lighter upper stage is 1,000 ton. The Starship that plans to go to Mars can take off from Earth and arrive in LEO with 238 ton of propellant remaining. It then receives three 254 ton loads of propellant to reach full capacity 1,000 ton capacity. Four launches from Earth then get one Starship to Mars.Subtracting, that leaves me with only 16 tons to play with for both the payload headed to Mars and the difference in dry mass between the expendable upper stage and the Mars transit vehicle (if any). I'm trying, I'm really trying. Please help revise or clarify, because I want something good to come out of this thread!That was referring to the cheap disposable Mars tankers. No payload is required. Maybe my quotes not having the link is making it hard for you to keep track of the conversation. I didn't know that the forum had links to the original quotes. Thanks for pointing it out as the other forums I use do not have that feature.
Hopefully you can now keep up with the conversation.
can you lay out the math in one single post? I mean specifically the numbers that show the conventional plan (given your expected underperformance) requires X launches, and your plan needs Y launches, and Y/X is less than 10%
If you want to make a 100% propulsive architecture, forget about Starship-derived-ELVs and use hydrogen. The design choices for Starship are all poor choices for that. Low ISP, heavy tanks. Blue Origin is a better starting point. You can even justify sending hydrogen tankers from Earth. (though Oxygen can be ISRU, and hydrogen is a small fraction of prop mass)