Wiki Super Heavy/Starship - General Development Discussion

[FoverM]

Segmentation means no meaningful reusability. I think you're missing the whole point of Starship/Super Heavy.

Segmentation enables reusability, performs better, and results in smaller/simpler pieces. F9's booster is a prime example. A lunar lander designed to only handle the LLO-to-lunar surface roundtrip is reusable. Some sort of LEO-LLO roundtrip ferry is more difficult but less complex than SS.

Even a second stage segment that only goes from the booster to LEO and back is easier a universal second stage like SS. It only has to deal with the Earth's atmosphere, always lands on a prepared surface, and has a lower reentry velocity.

 

[mongo]

My mistake. There will be some sort of header tanks for RCS but I have to assume they'll be smaller/simpler if they aren't used for the big Raptors on landing. Here's a thread on NSF about potential RCS on SS:

Starship Methox RCS Thrusters

You can see the mess made by trying to create a jack-of-all-trades system like SS. Sometimes you need vacuum-optimized nozzles on the RCS and mains, sometimes sea-level. Aerodynamic shapes that are useless in a vacuum. I always favor a segmented approach where each part is optimized for its task. Apollo is a prime example. Even F9 is segmented: a booster that only serves one purpose and an in-space second stage to get Dragon to orbit.

Seal level thursters work just fine in a vacuum, only drawback is lower isp (unless you can throttle them)

Segmentation enables reusability, performs better, and results in smaller/simpler pieces. F9's booster is a prime example. A lunar lander designed to only handle the LLO-to-lunar surface roundtrip is reusable. Some sort of LEO-LLO roundtrip ferry is more difficult but less complex than SS.

Even a second stage segment that only goes from the booster to LEO and back is easier a universal second stage like SS. It only has to deal with the Earth's atmosphere, always lands on a prepared surface, and has a lower reentry velocity.

SpaceX is making a lunar lander version...

I'm not sure what the point is of "a second stage segment that only goes from the booster to LEO and back". What does going back to the booster accomplish?

 

[bxr140]

Segmentation enables reusability, performs better, and results in smaller/simpler pieces. F9's booster is a prime example. A lunar lander designed to only handle the LLO-to-lunar surface roundtrip is reusable. Some sort of LEO-LLO roundtrip ferry is more difficult but less complex than SS.

This is legacy logic that is clearly being challenged by the notion of Starship going from earth's atmosphere to moon/mars surface and back. The legacy logic is rooted in the relatively simple mission of getting there and back. The Starship logic is rooted in bringing a bunch of *sugar* along to enable a much broader and more comprehensive mission, combined with the economics and reliability of "less parts".

Its fair to challenge the Starship logic, but its a little premature to make definitive statements against its effectivity.

 

[e-FTW]

Have not seen it posted yet, but many, many answers are here:

 

[FoverM]

Seal level thursters work just fine in a vacuum, only drawback is lower isp (unless you can throttle them)

SpaceX is making a lunar lander version...

I'm not sure what the point is of "a second stage segment that only goes from the booster to LEO and back". What does going back to the booster accomplish?

Goes from booster to LEO and back to the Earth's surface.

 

[FoverM]

This is legacy logic that is clearly being challenged by the notion of Starship going from earth's atmosphere to moon/mars surface and back. The legacy logic is rooted in the relatively simple mission of getting there and back. The Starship logic is rooted in bringing a bunch of *sugar* along to enable a much broader and more comprehensive mission, combined with the economics and reliability of "less parts".

Its fair to challenge the Starship logic, but its a little premature to make definitive statements against its effectivity.

Actually, a "Direct Ascent" mode like SS is legacy (it was the original plan for Apollo):

Apollo program - Wikipedia

Right down to using an enormous booster and/or a large number of refueling missions to LEO (SS requires both).

 

[Grendal]

Goes from booster to LEO and back to the Earth's surface.

I believe the "moon lander" version of Starship will be LEO, refueled in LEO, boost to Artemis, dock at Artemis to pick up supplies and people, boost to the Moon and land there, launch from Moon back to Artemis after whatever mission is accomplished. I'm sure that the Starship lander will need some smaller engines as well as the Raptors. It might need to land on Earth at some point in its life but that might not be in the original plans. I can see them leaving the Moon lander Starship at Artemis or LEO for future mission to the Lunar surface. It's possible the plan is to never bring it back to Earth.

 

[mongo]

Goes from booster to LEO and back to the Earth's surface.

Sorry, I'm still not following:

Even a second stage segment that only goes from the booster to LEO and back is easier a universal second stage like SS.

What about Starship is more complicated than launch, LEO, land on Earth? The only additional feature for Mars is the refueling. Landing on Earth is the hard part.
Mongo confused

 

[bxr140]

Actually, a "Direct Ascent" mode like SS is legacy (it was the original plan for Apollo):

Apollo program - Wikipedia

Right down to using an enormous booster and/or a large number of refueling missions to LEO (SS requires both).

I appreciate the semantics nuance; it should be obvious that legacy logic is in reference to the multi-stage, multi-element configuration pretty much every space exploration mission has implemented, including launchers. This legacy configuration is a result of a number of things, such as:
--Practical limits of technology 'way back when' that required mission functions be served by something close to the exact tool for the job
--Additional safety/reliability from both physical separation of mission infrastructure across mission phases, as well as more discrete offramps enabled by multi element missions. (If the lunar module fails to come online, you just dump it and go back to earth)
--A *sugar* ton of scope that needed to be spread across a huge workforce
--Let's be honest, state run projects like to spread the love, regardless of efficiency/cost

 

[ItsNotAboutTheMoney]

Segmentation enables reusability, performs better, and results in smaller/simpler pieces. F9's booster is a prime example. A lunar lander designed to only handle the LLO-to-lunar surface roundtrip is reusable. Some sort of LEO-LLO roundtrip ferry is more difficult but less complex than SS.

Even a second stage segment that only goes from the booster to LEO and back is easier a universal second stage like SS. It only has to deal with the Earth's atmosphere, always lands on a prepared surface, and has a lower reentry velocity.

F9's first stage is reusable, but the 2nd stage is lost, which is part of the reason why the cost of a Falcon 9 launch is so high.

Starship is optimized for full and rapid reusability, for Starlink and with Superheavy for Mars. At the rate SpaceX wants to be able to launch it, some additional cost of manufacture won't matter.

 

[e-FTW]

SpaceX posted a couple of pics to their Flickr. Go and get your new backgrounds!
Official SpaceX Photos

 

[FoverM]

I appreciate the semantics nuance; it should be obvious that legacy logic is in reference to the multi-stage, multi-element configuration pretty much every space exploration mission has implemented, including launchers. This legacy configuration is a result of a number of things, such as:
--Practical limits of technology 'way back when' that required mission functions be served by something close to the exact tool for the job
--Additional safety/reliability from both physical separation of mission infrastructure across mission phases, as well as more discrete offramps enabled by multi element missions. (If the lunar module fails to come online, you just dump it and go back to earth)
--A *sugar* ton of scope that needed to be spread across a huge workforce
--Let's be honest, state run projects like to spread the love, regardless of efficiency/cost

No, your bullet items are almost the exact opposite of why things happened the way they did. Everyone was centered on landing the whole thing that left LEO on the Moon (like SS). Whether it was launched from the surface in one piece or assembled in LEO (aka EOR), the whole shebang was destined to land on the Moon. Fortunately, Houbolt realized this was horribly inefficient:

John Houbolt - Wikipedia
Lunar orbit rendezvous - Wikipedia

There were no practical limits on the technology. After all, they developed the gigantic F-1 main engines that still haven't been equaled.

I'm no rocket scientist ... but just a glance at the rocket equation shows you that mass-at-destination absolutely rules. That's basic physics and it never changes for chemical rockets. You can use Excel to get ballpark numbers. Take the rocket equation, a reasonable Isp, the delta-V required, and mass at the destination to calculate the starting mass (including propellant). It gets really ugly, really quickly:

Tsiolkovsky rocket equation - Wikipedia
Delta-v budget - Wikipedia

It's a fun Excel-exercise to do it for an Apollo mission. The numbers are available online. When you do this you see how "brittle" spaceflight really is ... everything is linked together. The only way to break that linkage is to segment the mission (and, preferably, have depots strategically placed that are serviced by big, dumb rockets). SS does the first segmentation by using itself as a temporary depot in LEO.

 

[Zaxxon]

Jeez...

https://twitter.com/SciGuySpace/status/1337187531717292034?s=19

 

[adiggs]

I'm no rocket scientist ... but just a glance at the rocket equation shows you that mass-at-destination absolutely rules

Maybe you can elaborate on this. I agree that this is true for very low volume and proof of concept type activities (have to solve for that to be successful the first time).

It looks to me like cost and turnaround / maintenance ease and time become (at minimum - probably more variables) the important criteria as long as an adequate mass at destination is achieved.


Seems to me like the variable you consider paramount in the optimization problem, is actually a constraint that becomes increasingly minimized as capability enables increasingly large and cost efficient levels of adequate mass at destination (made that term up just now).

 

[Grendal]

Moderator discussion about future SN attempts. Instead of focusing all the different launches in this "General Development" thread I will be creating individual threads for each of the testing SN's. You will see the first of these posted right after I finish writing this for SN-9.

 

[Grendal]

Elon's response to Everyday Astronaut:
https://twitter.com/elonmusk/status...-Q0Wuh8S33yyl2hTm0KqD-nU-bpdrfZElV9J8yibp7YsE

 

[Grendal]

 

[FoverM]

Maybe you can elaborate on this. I agree that this is true for very low volume and proof of concept type activities (have to solve for that to be successful the first time).

It looks to me like cost and turnaround / maintenance ease and time become (at minimum - probably more variables) the important criteria as long as an adequate mass at destination is achieved.

Seems to me like the variable you consider paramount in the optimization problem, is actually a constraint that becomes increasingly minimized as capability enables increasingly large and cost efficient levels of adequate mass at destination (made that term up just now).

The rocket equation applies at all times for chemical rockets. It was as applicable for Apollo then as much as for SpaceX, ULA, etc. now. The Isp for various engines are all comparable. There has been no technological breakthrough in chemical rockets since the 1960s and SpaceX's Raptor (methalox) is a little less efficient than the upper-stage engines (hydrolox) used in Apollo. To give you an idea of the magnitude of the problem, at launch the Saturn V was around 2970 metric tons (mT) and what returned to the Earth's surface was a 5.6 mT command module. This was using an optimized, segmented architecture that discarded mass along the way and we ended up with a 500:1 ratio. Almost all the launch mass was propellant.

SS has a dry mass of at least 100 mT and that's what returns to the Earth's surface. Calculate how much total mass (dry + propellant with an Isp of around 380) is required to go from the lunar surface to the Earth's surface. It's ugly and we're just beginning. That's the amount of mass you need to land successfully on the lunar surface to get an SS back. You have to get that total mass to the Moon, so that's your destination mass when calculating how much total mass you need to leave LEO with. Then you need to get that total mass to LEO from the Earth's surface (which is the largest delta-V of the entire mission).

These are requirements of the physics of chemical rockets. SpaceX can't finesse their way around them. There are no dilithium crystals or warp drives to shortcut them. What SpaceX is planning on is to shortcut the Earth-to-LEO portion by positioning a SS in LEO then sending a bunch of "tanker" SSs (5 to 12) to LEO to fill it with propellant for its BEO mission. Each tanker can net around 100 mT of propellant to LEO (which is comparable to the mass-to-LEO of a single Saturn-V), so it would take 12 tankers to fill up an empty SS in LEO (SS can hold around 1200 mT of propellant).

There are a few actual rocket scientists on the nasaspaceflight.com forums and they think that SpaceX would actually launch an SS tanker to LEO, fill it up with propellant with multiple tanker flights, then launch the mission SS to rendezvous with the filled tanker to get enough propellant to execute the BEO mission.

 

[mongo]

SS has a dry mass of at least 100 mT and that's what returns to the Earth's surface. Calculate how much total mass (dry + propellant with an Isp of around 380) is required to go from the lunar surface to the Earth's surface. It's ugly and we're just beginning. That's the amount of mass you need to land successfully on the lunar surface to get an SS back. You have to get that total mass to the Moon, so that's your destination mass when calculating how much total mass you need to leave LEO with. Then you need to get that total mass to LEO from the Earth's surface (which is the largest delta-V of the entire mission).

First off, SpaceX is working on a lunar version with neither fins nor heat shield, but including higher mounted engines for landing/ takeoff. So lunar surface to earth surface isn't a design constraint.

Why is required mass/ fuel load ugly? Fuel is the least expensive part of the entire endeavor (once all the other pieces are reusable). At two million dollars a launch (2019 Elon estinate) for a refueling run, even a dozen trips (if SS needed totally full tanks) is only $24 million. That is about the cost of four sets of F9 fairingsn about the cost of reused F9 launch ($50 million). Other than requiring more fuel, what's the problem?

Methalox can be generated from solar + water + CO2. Heck, it's carbon negative so we should launch as much outside Earth's influence as possible.

 

[HVM]

...There are a few actual rocket scientists on the nasaspaceflight.com forums and they think...

"Rocket scientists" -my a$$. Bunch of jokers I'd say. Somebody posted this to the NSF for the reason of low header tanks pressure: