Author Topic: Three-stage Starship proposal  (Read 20266 times)

Offline steveleach

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Re: Three-stage Starship proposal
« Reply #140 on: 10/30/2024 12:48 pm »


Quote from: lamontagne
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.
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
I don't think it was lack of precision, tbh.

RJMAZ is constructing a scenario in which the only viable option is a disposable upper stage, and it is going to be next to impossible for us to refute that. In this case, he's assuming that aerobraking even from Low Mars Orbit is not viable.

Offline Brigantine

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Re: Three-stage Starship proposal
« Reply #141 on: 10/30/2024 01:05 pm »
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
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)

You've been making the rules up as you go along this whole thread, and now you're at the point where they're not just pessimistic but empirically wrong.

Mars atmosphere is nominally 6.75 HPa, on Earth that pressure is reached at ~27.2 km. S30 at 27.2 km was going a hair under 600 m/s (interpolating from IFT-5) - that's only [EDIT] 500 m/s more than at the start of the actual landing burn on Earth. In Martian gravity, terminal velocity at the same atmospheric pressure will be even slower.

You don't have a leg to stand on, this time. You should learn to choose your battles.

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. 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)
« Last Edit: 10/30/2024 01:11 pm by Brigantine »

Offline lamontagne

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Re: Three-stage Starship proposal
« Reply #142 on: 10/30/2024 02:00 pm »
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 450 years.
« Last Edit: 10/30/2024 02:13 pm by lamontagne »

Offline steveleach

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Re: Three-stage Starship proposal
« Reply #143 on: 10/30/2024 02:27 pm »
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.
The OP already assumes that neither full reusability nor orbital refueling are viable, and this isn't really any different tbh.

Offline lamontagne

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Re: Three-stage Starship proposal
« Reply #144 on: 10/30/2024 03:15 pm »
Well, I'll just wait for RJMAZ's confirmation of that, and if it is so, I guess I'll just go on to other more useful things then.

Offline cabeese

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Re: Three-stage Starship proposal
« Reply #145 on: 10/30/2024 04:52 pm »
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.
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.

Offline meekGee

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Re: Three-stage Starship proposal
« Reply #146 on: 10/30/2024 06:33 pm »
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.
The OP already assumes that neither full reusability nor orbital refueling are viable, and this isn't really any different tbh.
I'm only half following this, but wasn't his argument that you can manufacture ships with less resources than refurbing them (times 4)?

He's basically assuming that it's for all practical purposes easier to make Starships fresh than it is to reuse them.

IIUC.
« Last Edit: 10/30/2024 10:26 pm by meekGee »
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Offline RJMAZ

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Re: Three-stage Starship proposal
« Reply #147 on: 10/30/2024 06:52 pm »
Quote from: steveleach
In 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.

Quote from: steveleach
The OP already assumes that neither full reusability nor orbital refueling are viable, and this isn't really any different tbh.
My system still uses orbital refueling. It simply reduces the number of launches to a single digit percentage.

Quote from: cabeese
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.
And that is the core of the problem.

I never said the Starship upper stage will have refurbishment hours similar to the Shuttle. I base all my analysis that Starship upper stage refurbishment will be around 1% of the cost of the Shuttle. This would be an amazing achievement. Unfortunately even at 1% it is still far greater than the fuel cost.

Some members think the refurbishment will be 0.0001% of the Shuttle. I think these members are crazy.


Quote from: Brigantine
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)
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: Brigantine
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?
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: Brigantine
P.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.

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.

The Mars atmosphere is extremely thin. The entry speeds involved will not provide enough duration to slow down. This is why I estimate 2 km/s of aerobraking. The level of aerobraking achieved will determine how much fuel a tanker can place into Mars orbit from the Mars surface. It also determines if ships leaving from Earth will need to depart from HEEO.

With 2 km/s of aerobraking a Mars tanker launched from the Mars surface will be able to send approx 200 ton of fuel to Mars orbit. Approximately 5 Mars launches are then needed to refuel a ship returning to Earth LEO instead of direct entry. Mars booster solves this and provides a massive fuel saving.

Quote from: meekGee
I'm only half following this, but wasn't his argument that you can manufacture ships with less resources than refurbing them (times 4)
Spot on. The disposable ship would also be half of the cost of a reusable ship. So now the disposable ship can cost 8 times of the refurbishment cost to reach parity. 4x2.

Plus when the Mars launch window opens all the cheaper disposable Starships can be prebuilt and ready to launch. No need for a sudden surge of refurbishment manpower.
« Last Edit: 10/30/2024 06:54 pm by RJMAZ »

Offline Twark_Main

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Re: Three-stage Starship proposal
« Reply #148 on: 10/30/2024 07:34 pm »
My system still uses orbital refueling. It simply reduces the number of launches to a single digit percentage.

For the benefit of everyone, 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%. It's hard to piece it together across eight pages.

Thanks.


PS: if you hit "quote" the forum auto-populates a  [​quote]  tag complete with hyperlink, making the whole discussion a lot easier to follow. This is why everyone else's quotes have the full post info with link, and your quotes just have a name.
« Last Edit: 10/30/2024 07:49 pm by Twark_Main »

Offline lamontagne

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Re: Three-stage Starship proposal
« Reply #149 on: 10/30/2024 08:49 pm »
Quote from: steveleach
In 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.

Where does the 2 km/s figure come from? Did SpaceX get this (relatively old) simulation completely wrong?
https://www.spacex.com/humanspaceflight/mars/

Offline steveleach

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Re: Three-stage Starship proposal
« Reply #150 on: 10/30/2024 09:05 pm »
Some members think...

Members are betting/wishing/hoping...
Actually, I think you'll find that they are simply accepting that there's a good chance that Starship will deliver on its design goals; at least enough that SpaceX won't have to abandon the core principles on which it is based.

So in effect, you're not really arguing with the forum members here, you're (indirectly) arguing with the SpaceX engineering team.

Offline Twark_Main

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Re: Three-stage Starship proposal
« Reply #151 on: 10/30/2024 10:00 pm »
Valiantly trying to piece together RJMAZ's posts into a cohesive thesis, I unearthed this passage:

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.

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!
« Last Edit: 10/30/2024 10:04 pm by Twark_Main »

Offline RJMAZ

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Re: Three-stage Starship proposal
« Reply #152 on: 10/30/2024 10:02 pm »
Quote from: lamontagne
Where 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.
« Last Edit: 10/30/2024 10:04 pm by RJMAZ »

Offline RJMAZ

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Re: Three-stage Starship proposal
« Reply #153 on: 10/30/2024 10:18 pm »
Valiantly trying to piece together RJMAZ's posts into a cohesive thesis, I unearthed this passage:

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.

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.

The 16 ton left for payload could include a roll of stainless steel in the nose. On the way to Mars they offload their remaining fuel to the crewed ship and then crash land into Mars a short distance from the Mars colony. The steel from the ship and the 16 ton of payload is then recovered at a later date. I mentioned this on previous pages. Repurposing is just as good as reusability. This unearthed post was from an earlier page where fuel production has not started on Mars. They will need to send plenty of one way disposable tankers.

I have always admitted from the very start that my three stage system with disposable upper stage is only for the short to medium term. I have admitted that after decades of service and technology improvements humans will have a better system with lower cost per kilo to Mars. My three stage system is simply better and more conservative than the current proposed high risk two stage system. It might takes decades for the current proposed system to achieve airline reusability and safe direct entry. SpaceX can continue to work on that in the background using test flights. For now they should to a conservative system that 100% will work.
« Last Edit: 10/30/2024 10:26 pm by RJMAZ »

Offline Brigantine

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Re: Three-stage Starship proposal
« Reply #154 on: 10/30/2024 10:28 pm »
Quote from: Brigantine
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)
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: Brigantine
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?
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: Brigantine
P.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.

1) It's a fact that the landing was a soft touchdown. Also you're getting confused - "airline level of refurbishment" has only ever been discussed about Earth-LEO workhorses, not Mars spaceships, and even then it's nobody's stated requirement. Red herring

2) Unsupported claim which is also wrong, that would also imply 9,256 m/s from Earth to LEO also requires the whole launch to happen in 1 second. You're just assuming & wishing for those extra '00m/s. Two things you didn't consider: about 200 m/s gained from Mars' axial rotation (depending on latitude), and that gravity drag is basically cosine losses, which mainly only apply in the troposphere, whereas Mars' atmosphere is very thin and gravity is low so you can pitch over very far very early.

3) Which members? Quote them. I've never seen that claim. Including the section above Mars orbital velocity of course you will aerobrake more than 3 km/s, but the number I've always seen on the forum is 1 km/s of delta-V for direct-descent EDL from Earth-Mars transfer. [EDIT: Well I agree that a landing burn under 500 m/s isn't physically impossible, I'll look at the simulation some time]

4) Earth's upper atmosphere above 27.2 km is also equally thin, and when you start from orbital velocity and have even a small amount of lift, you have plenty of time to slow down. More to the point, S30 has already demonstrated the EDL flight profile in that thin part of the atmosphere, and in fact did slow down (to 600 m/s) - covering all the speeds involved in a low Mars orbit EDL or even an Earth-Mars transfer EDL. Other than the last 600 m/s (or a bit more depending on landing site elevation), Mars' thin atmosphere is not a point of difference.
« Last Edit: 10/30/2024 10:49 pm by Brigantine »

Offline lamontagne

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Re: Three-stage Starship proposal
« Reply #155 on: 10/30/2024 11:52 pm »
Quote from: lamontagne
Where 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.
You may have missed the reference I posted here a few pages back?  SpaceX had done re-enty on Mars, in Earth higher atmosphere.  And proven to NASA and themselves the concept of supersonic retropropulsion works.  They have the necessary information to feed fluid dynamics models that can replicate the landing burn on MArs.  Mars' s atmosphere is well known by now.  They had all the required information 7 years ago when they did that model.  I know spaceX likes to try things in real, but the also do simulations before hand. 

You're joking when you say quadrupling the landing burn is a reasonable assumption, right?  You're also joking wheen you say that pulling 5gs for a brief period is not acceptable?
Can you at least concede that a tanker form Mars is much more likely than a tanker from Earth, or making Starship on Mars into a two stage system? 
Using 1200 m/s landing burn, rather than 2000 m/s, can return a Starship to Earth with no aerobraking at Earth (except for landing) and a single Mars tanker.
If I go to your 2000 m/s landing burn, then I need an extra 100+ tonnes, so a fraction of an extra tanker. 
And going for a 600 m/s landing burn, I don't need a tanker at all, because I can also do aerobraking on Earth.

By the way, 600 m/s is more than 500 m/s so it's a wee bit conservative.  So we're not hoping for less, we're planning for more.  I'll certainly admit it's all pretty tight.  But tankers do away with much of the risk, if need be.
« Last Edit: 10/30/2024 11:55 pm by lamontagne »

Offline Twark_Main

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Re: Three-stage Starship proposal
« Reply #156 on: 10/31/2024 12:25 am »
Valiantly trying to piece together RJMAZ's posts into a cohesive thesis, I unearthed this passage:

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.

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.

No problem, happy to help.   8)

Hopefully you can now keep up with the conversation.

It may improve things going forward, but it doesn't help me keep up (catch up?) with the past eight pages. The thing that will really help is what I (politely) asked for:

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%

Thanks again.
« Last Edit: 10/31/2024 12:49 am by Twark_Main »

Offline TomH

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Re: Three-stage Starship proposal
« Reply #157 on: 10/31/2024 07:07 am »
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)

Agreed, your idea would be much better if you took the original 3 stage New Glenn, but expanded it to New Armstrong proportions. If you intend to throw away everything, then make the S1 Kerolox for the greater energy density and place numerous AR-1 engines on it. You'd have something like Von Braun's Nova. If you want to reuse the S1, you could think about refurbishing like F9 or stick with Methalox.
« Last Edit: 10/31/2024 07:11 am by TomH »

Offline Brigantine

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Re: Three-stage Starship proposal
« Reply #158 on: 10/31/2024 08:38 am »
Regarding the old SpaceX Mars landing simulation:

I get Mars speed of sound = 240 m/s
Landing burn starts at 434 s at Mach 2.3 = 550 m/s, 2.5 km
Landing burn duration 39 s, gravity acting at an average cosine of maybe 0.75 (eyeballed), Mars gravity = 3.72 m/sē
→ total gravity drag during the burn about 110 m/s for a total non-gravitational acceleration of 660 m/s

alternatively, landing burn starts at flight path angle approx -40⁰ (eyeballed, with bad perspective), horizontal velocity 420 m/s,
vertical velocity ⁻355 m/s plus gravity drag 39*⁻3.72 = ⁻145 m/s for a total ⁻500 m/s
→ by pythagoras, total non-gravitational acceleration of 650 m/s (plus modest cosine losses)

Aerodynamic drag will contribute to that non-gravitational acceleration, I'm got ~6 m/sē at first, averaging 2 m/sē over 17 s so only about 34 m/s. So I get the delta-V for the landing burn for that profile at roughly 630 m/s.

Am I missing something? Do these numbers seem reasonable?
« Last Edit: 10/31/2024 09:18 am by Brigantine »

Offline drzerg

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Re: Three-stage Starship proposal
« Reply #159 on: 11/03/2024 04:56 pm »
After rereading whole thread once more time again i have a thought that the only benefit to add 3d stage is to get 1st stage really slow and close to the pad, which should produce only 1 km/s dV. To make it cheaper to bring it back and reuse faster. Second stage as result could have smoller amount of engines and operate falcon 9 way-ish with 1.5 km/s dV and total 2.5 km/s at engine shut down. Which is current margin for reentry without proper heat shield.

This whould work regardless of what could be the 3rd stage.

Whole idea is useless if it cost too much to develop and operate. Benefit of 500 m/s is to small.

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