--how many SS raptors are needed to launch an F9-equivalent payload?
--how many SS raptors are needed to launch an F9-equivalent payload?
That doesn't make any sense. Just better to continue F9.
There is no need to change much if Starship is used as expendable. Just delete flaps and maybe simplify plumbing. It just launches heavier payloads than FH. And the Starship can be used for escape missions.
RTLS is cheaper than a barge landing
RTLS is cheaper than a barge landingIs it? and by what measure?
A Falcon RTLS attempt requires the evacuation of several thousand personnel from the CCSFS industrial zone for from 75 minutes to six hours. There are reports that this has a cost in the high six figures. (There have also been reports that Space Force is working to reduce the evacuation area and possible to move the landing zone to somewhere more remote so this might be ameliorable.)
Any efforts to reduce cost should not just force the government to pay.
Consider a scenario where SpaceX gets the booster (SH) and its recovery system working well, but a rapidly reusable second stage is delayed.
Is it feasible to build a very inexpensive expendable second stage to use instead? SH is supposed to be very cheap to operate even compared to Falcon 9, so a super-cheap expendable SS would allow SpaceX to continue with the F9 economic approach. In particular for Starship to work at all, the SH is RTLS so the recovery fleet is not needed.
Consider a scenario where SpaceX gets the booster (SH) and its recovery system working well, but a rapidly reusable second stage is delayed.
Is it feasible to build a very inexpensive expendable second stage to use instead? SH is supposed to be very cheap to operate even compared to Falcon 9, so a super-cheap expendable SS would allow SpaceX to continue with the F9 economic approach. In particular for Starship to work at all, the SH is RTLS so the recovery fleet is not needed.
This might be a good approach if the recoverable Starship was found to be unfeasible but if it's only delayed, then the thing causing the delay is almost certainly the lack of sufficient opportunities to experiment with recovery.
Starship R&D takes what Starship R&D takes. Gathering recovery data on every launch is part of that R&D effort. SpaceX will need to price its launches accordingly.
To a first-order approximation, a Starship is a stainless steel tube, six Raptors, some funny aerosurfaces, and a heat shield. It's hard to imagine the Raptors being less than 25%-50% of the manufacturing cost. If they cost less than $1M each, that puts the maximum manufacturing cost of the Starship at less than $24M.
Similarly, it's hard to imagine Raptors being less than 50%-75% of the manufacturing cost of a SuperHeavy, and here we can reasonably expect recovery to work in fairly short order. Even if SH is only 10x reusable to begin with, that amortizes each launch at less than $7M.
Add in $5M/launch in ops costs, and you're at $36M in cost. Figure 50% gross margin during the R&D phase and you're at a retail price of $72M. That's almost at the F9 price point even without Starship reusability.
If the cheap expendable upper stage is only needed for a short period of time. It might be attractive to rework the sea level Merlins from retired Falcon 9s to a more vacuum optimized iteration as the stage engines. Think a trio of modified Merlins (about 2700 kN total) in a shorten expendable Starship variant should be adequate for most missions. Just need to adjust the tankage for a different propellants ratio and make bigger payload fairings that can landed in the Ocean.
The Merlin engine rework is mostly adding an exhaust nozzle extension to increase the expansion ratio. Probably with the ratio somewhere between the current sea level and vacuum variants of the Merlin.
Starship R&D takes what Starship R&D takes. Gathering recovery data on every launch is part of that R&D effort. SpaceX will need to price its launches accordingly.
To a first-order approximation, a Starship is a stainless steel tube, six Raptors, some funny aerosurfaces, and a heat shield. It's hard to imagine the Raptors being less than 25%-50% of the manufacturing cost. If they cost less than $1M each, that puts the maximum manufacturing cost of the Starship at less than $24M.
Starship R&D takes what Starship R&D takes. Gathering recovery data on every launch is part of that R&D effort. SpaceX will need to price its launches accordingly.
To a first-order approximation, a Starship is a stainless steel tube, six Raptors, some funny aerosurfaces, and a heat shield. It's hard to imagine the Raptors being less than 25%-50% of the manufacturing cost. If they cost less than $1M each, that puts the maximum manufacturing cost of the Starship at less than $24M.This is a crazy way to estimate costs. It's very easy to imagine the thermal protection system being 90% of the cost. At the very least there is no relationship between the cost of thermal protection and the cost of a motor. Figuring out how to build one cheaply does not help with the other.
Silica tiles may turn out to be a dead end and they have to use barelyobtainium or they may need unobtainium, which they can't have. As you say, the R&D effort costs what it cost, and, as I say, it gives you what it gives you, not always what you started looking for or need. Then SpaceX has to decide if they can live with it.
Expendable SS will only need VAC Raptors but how many?.
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Pretty much every proposal for a product variant that I've seen during my professional life that got into real trouble started with the word "just". <shudder>
Adjusting the tankage for a different propellant ratio (and propellant type, don't forget) changes centers, moments, resonances, plumbing, cabling, baffle placement and number, temperatures, pressures, control software, guidance software, GSE, processes, procedures and on and on and on. All this needs to be designed, reviewed, built, tested and certified. People need to perform these jobs so there will be transfers, relocations, hiring and other personnel issues. Then this whole thing will have to be managed, including being documented to various government agencies' satisfaction (IRS, FCC, FAA, etc.). To paraphrase Yoda, "There is no 'just'".
Adding all this to an engine type change, as well as a fairing change, makes me agree with those who question the real utility of this over using an alternate existing operational rocket while pushing through to find and fix the problem.
My initial question assumed a few variants, depending on payload mass. From 1 to three. beyond that, use an expendable version of a "real" Starship. So, my question now becomes what is the payload mass to LEO for each of these variants? can the single-Rvac variant get to LEO at all? It's basically a legless starhopper.
My initial question assumed a few variants, depending on payload mass. From 1 to three. beyond that, use an expendable version of a "real" Starship. So, my question now becomes what is the payload mass to LEO for each of these variants? can the single-Rvac variant get to LEO at all? It's basically a legless starhopper.
... every time you reduce the gross mass of the second stage on a SuperHeavy, you have to maintain the same approximate MECO speed for the SH. Otherwise, you have to redesign its TPS, which pretty much defeats the purpose of what you're trying to do here. You can do that by de-engining it and only partially filling the tanks, but then you're on the path to producing an F9 with a particularly terrible structural mass fraction.
My initial question assumed a few variants, depending on payload mass. From 1 to three. beyond that, use an expendable version of a "real" Starship. So, my question now becomes what is the payload mass to LEO for each of these variants? can the single-Rvac variant get to LEO at all? It's basically a legless starhopper.
... every time you reduce the gross mass of the second stage on a SuperHeavy, you have to maintain the same approximate MECO speed for the SH. Otherwise, you have to redesign its TPS, which pretty much defeats the purpose of what you're trying to do here. You can do that by de-engining it and only partially filling the tanks, but then you're on the path to producing an F9 with a particularly terrible structural mass fraction.Is SH already near its MECO speed limit?
OK, that means the "stubby Starship" is a waste of time and resources, so The "cheapest feasible expendable Starship" is a full-sized Starship carrying a full load. SpaceX can launch full loads of Starlink V2.0 on Starship prototypes that can also do EDL testing and if they don't have a new variant to test they can use a slightly cheaper expendable, but they cannot completely retire Falcon 9 until they really do have a reusable SS.