Could the SuperHeavy booster be SSTO?

[tater]

8 minutes ago, Exoscientist said:

 Actually, SpaceX has not given the dry mass for the tanker version of the Starship, only for the passenger version meant to carry 50 to 100 colonists of a 6 month flight to Mars.

There's no way tanker SS masses much less than 85t. The current non-crew version is heavier than that. Even so, any mass savings buys little. Drop it to 65t? it gets ~18t to LEO. Still not enough to return.

If we can get it to 55t, it can get 28t to LEO, of which 20t is for EDL, so we have an 8t payload. Seems plausible—except there is no way SS masses 55t fitted for reuse, the 4mm steel alone is ~50t, and it has ~9t of engines. At 60t it can take ~3t to LEO and return.

All the above is predicated on an ave Isp of 363.

 

 

I'm not sure I understand the obsession with SSTOs.

The 3t use case is literally the only rationale that might make sense—taking 3t of humans to meet another vehicle.

[Exoscientist]

1 hour ago, tater said:

There's no way tanker SS masses much less than 85t. The current non-crew version is heavier than that. Even so, any mass savings buys little. Drop it to 65t? it gets ~18t to LEO. Still not enough to return.

If we can get it to 55t, it can get 28t to LEO, of which 20t is for EDL, so we have an 8t payload. Seems plausible—except there is no way SS masses 55t fitted for reuse, the 4mm steel alone is ~50t, and it has ~9t of engines. At 60t it can take ~3t to LEO and return.

All the above is predicated on an ave Isp of 363.

I'm not sure I understand the obsession with SSTOs.

The 3t use case is literally the only rationale that might make sense—taking 3t of humans to meet another vehicle.

 The  importance of SSTO’s is their operational simplicity for point-to-point human transport. That would be a major market for radically increasing the market for spaceflight.

 In this interview with the Everyday Astronaut at about 10 mins in, Elon gives the tank mass of the SuperHeavy as 80 tons:

The Starship at 1/3rd the propellant load can be estimated as 1/3rd that, so to ~27 tons. And SpaceX has suggested they could bring the tank wall thickness down from 4mm to 3mm. This would be a reduction in tank mass by 25%, bringing it down to ~20 tons.

Elon has not said what the dry mass would be specifically for the tanker version of the current incarnation of the BFR. The closest he came was in his article “Making Life Multi-Planetary”:

BFR ship overview

The ship is 48 meters in length. Dry mass is expected to be about 85 tons. Technically, our design says 75 tons but inevitably there will be mass growth. The ship will contain 1,100 tons of propellant with an ascent design of 150 tons and return mass of 50 tons. You can think of this as essentially combining the upper stage of the rocket with Dragon—it is as if the Falcon 9 upper stage and Dragon were combined.

 

 He talks both about the passenger version and tanker of the Starship in this article. It should be noted though in this passage he mentions it’s analogous to having the Dragon capsule combined with the Falcon 9 upper stage which suggests he’s talking here about the passenger version.  

 I said of the current version of the BFR Elon hasn’t said what the tanker dry mass would be. It should be noted he did make the distinction in dry mass about the prior incarnation the ITS, and the proportional size of the tanker version dry mass was much less than the passenger version:

 

 Based on this proportional size difference we might estimate the dry mass of the tanker version of the current Starship as ~50 tons.

  Bob Clark

Edited September 5, 2022 by Exoscientist

[SunlitZelkova]

49 minutes ago, Exoscientist said:

The  importance of SSTO’s is their operational simplicity for point-to-point human transport. That would be a major market for radically increasing the market for spaceflight.

This makes no sense. For all average routes, only a suborbital flight path is required for point-to-point flights.

I doubt point-to-point would be profitable for the foreseeable future. It requires a very high level of reliability, and lowering cost so average people fly on it. SpaceX is cheap within the context of launch costs, but it isn’t airliner ticket cheap, and it won’t become so for a very long time, if ever.

At this moment in time P2P passenger transport may very well end up like the Concorde, and that’s only after you pass the hurdle of getting approval to fly spacecraft over population centers to land at a spaceport.

The number of flights that would be required for this level of reliability to be achieved would be so high that SpaceX would likely already be making enough money from those launches in the first place and not need P2P from a financial point of view.

[KSK]

1 hour ago, Exoscientist said:

Apologies for the messed up formatting - this site isn’t the easiest on mobile devices.

Serious question though - assuming that a market for point-to-point human transport by rocket does open up - why bother going orbital?
 

I’d have thought that a series of sub-orbital hops be easier?  At first sight it would be a lot less operationally challenging in terms of vehicle design, be a lot more forgiving in terms of vehicle dry mass, and probably be safer because your vehicle (and passengers) don’t have to re-enter from orbital speeds on every journey.

The decline (and failure to rebuild) of supersonic air travel is a pretty good indicator that there’s not a big enough market for ‘need to be there right this hour’ passengers to justify the costs.  By analogy, I’m not convinced that there would be enough demand for true ‘anywhere to anywhere in one hop’ travel to justify an orbital point-to-point service.

Edited September 5, 2022 by KSK

[Exoscientist]

4 hours ago, SunlitZelkova said:

This makes no sense. For all average routes, only a suborbital flight path is required for point-to-point flights.

I doubt point-to-point would be profitable for the foreseeable future. It requires a very high level of reliability, and lowering cost so average people fly on it. SpaceX is cheap within the context of launch costs, but it isn’t airliner ticket cheap, and it won’t become so for a very long time, if ever.

At this moment in time P2P passenger transport may very well end up like the Concorde, and that’s only after you pass the hurdle of getting approval to fly spacecraft over population centers to land at a spaceport.

The number of flights that would be required for this level of reliability to be achieved would be so high that SpaceX would likely already be making enough money from those launches in the first place and not need P2P from a financial point of view.

 

 Transpacific flights from North America to Asia or Australia are so long to do it ballistically you might as well go to orbital speeds. Now, because of the distance they  commonly take a day. That could be cut to 45 minutes with orbital flights. This is a significant market at over 100,000 flights per year.

 The advantage of SSTO’s are described in the book:

https://www.amazon.com/Halfway-Anywhere-Achieving-Americas-Destiny/dp/0871318059

 Aside from the advantage for P2P travel, another intriguing fact  is the delta-v for round trip flights to the Moon from LEO is about that to Earth orbit. So if you have orbital propellant depots in place, then you could have tourism flights to the Moon as common as flights to LEO. But with SSTO flights to LEO happening at high volume we could have those orbital propellant depots in place.

   Bob Clark

 

Edited September 5, 2022 by Exoscientist

[Hannu2]

30 minutes ago, Exoscientist said:

 

 Transpacific flights from North America to Asia or Australia are so long to do it ballistically you might as well go to orbital speeds. Now, because of the distance they  commonly take a day. That could be cut to 45 minutes with orbital flights. This is a significant market at over 100,000 flights per year.

At what price level? If passenger capacity is few people and trip takes thousands of tonnes of propellants and need special rocketports it need pretty scifi-ish assumptions about economy to be profitable. Environmental issues are also very severe and probably many companies avoid such trips due to reputational damage.

 

[SunlitZelkova]

1 hour ago, Exoscientist said:

This is a significant market at over 100,000 flights per year.

There is no market if the costs are so high no one can afford it.

1 hour ago, Exoscientist said:

Transpacific flights from North America to Asia or Australia are so long to do it ballistically you might as well go to orbital speeds.

I don’t think this is correct.

If a craft is launched from say, Baikonur, and crosses the South Pole to reach Alaska, it then needs to reach orbital speed, as the FOBS did when targeting American early warning radars from the rear where they could not see.

Baikonur to Alaska is roughly 32,000 kilometers across the South Pole. Even to reach the more southerly Beale AFB in California it would still be roughly 27,000 kilometers.

But in contrast, Los Angeles to Tokyo is only 9,000 kilometers, Los Angeles to Beijing is 10,000 kilometers, and Los Angeles to Sydney is 12,000 kilometers.

Minot, North Dakota to Moscow, Moscow Oblast is roughly 8,000 kilometers, Minot to Orenburg is roughly 9,000 kilometers. ICBMs launching from Minot would utilize a suborbital flight profile, therefore orbital speeds should not be required for these sorts of distances.

In fact utilizing orbital velocities would put more stress on the vehicle during reentry, requiring more maintenance and thus increasing an already astronomical ticket price.

[tater]

P2P is fine to consider, and yes, single stage would IMO be preferable for obvious operational issues. That's a different thread, however (cause we'd need to get deep in the weeds on safety, etc).

We were talking about SH as an SSTO.

9 hours ago, Exoscientist said:

 In this interview with the Everyday Astronaut at about 10 mins in, Elon gives the tank mass of the SuperHeavy as 80 tons:

Cool. Also 2t per engine, and I used 1.5t. Note my tanker mass was for SS, not SH, the booster doesn't change.

https://www.twmetals.com/resources/calculators.html

1 ring is 1.67t of 304 stainless (9m dia, 1.84m per ring, 4mm thick). at 3mm it's 1.25t per ring.

9 hours ago, Exoscientist said:

The Starship at 1/3rd the propellant load can be estimated as 1/3rd that, so to ~27 tons. And SpaceX has suggested they could bring the tank wall thickness down from 4mm to 3mm. This would be a reduction in tank mass by 25%, bringing it down to ~20 tons.

 

9 hours ago, Exoscientist said:

 Based on this proportional size difference we might estimate the dry mass of the tanker version of the current Starship as ~50 tons.

No. Count the rings.

Starship is ~25 rings, then there are a few rings worth of tank dome. The taper lowers that, but then there are also stringers/structure. I guess the mass at ~28 rings worth of mass, YMMV.

That's just shy of 47t at 4mm, or 35t at 3mm. You now need to guestimate TPS mass, flaps, actuators, batteries, etc. 10 tons? More? Less? Call it 10. We're now at 57t at 4mm, 45t at 3mm. 6 engines is another 12 tons per Elon in the vid. 69t at 4mm (so that's what Elon chooses ) vs 57t at 3mm. Course 6 engines is not enough, that's barely above 1:1 TWR and they want closer to 1.5 for SSTO, so we need 9 engines.

Final SSTO SS mass range is on the order of 75t at 4mm thickness vs 69t at 3mm (guess Elon goes to 3mm for sure )

At 75t it SSTOs 18.5t to LEO, at 69t it gets ~24t to LEO. The heavier one doesn't have the propellant for reuse, the lighter one can land, while still delivering ~4t to LEO.

I would say those numbers are overly optimistic by a lot, since that is 5.75% payload to LEO—better than F9 or Saturn V. That doesn't pass the sniff test, SSTO should have a lower, not higher payload mass ratio (and that was with full reuse!).

 

Edited September 5, 2022 by tater

[Exoscientist]

 Perhaps our difference in estimates for the tank mass is coming from the fact the tank does not reach all the way to the top of the Starship. The tank length is a little more than half the length of the vehicle. Above it, would only be the empty, lighter fairing.

 

https://www.humanmars.net/2021/01/cutaway-schematic-of-spacex-starship.html

 

     Robert Clark

Edited September 5, 2022 by Exoscientist

[tater]

12 minutes ago, Exoscientist said:

 Perhaps our difference in estimates for the tank mass is coming from the fact the tank does not reach all the way to the top of the Starship. The tank length is a little more than half the length of the vehicle. Above it, would only be the empty lighter fairing.

Still 4mm steel. It has to survive orbital EDL. Maybe 3mm if that steel has enough strength, and can absorb heat the same way. Part of the point of steel is that the TPS can let some heath through that it could not with other materials.

It also needs actuators, etc to open, close, and latch whatever the final form of a real payload bay is.

There's no way that a SSTO rocket (and not even an air-breather that can use the atmosphere as propellant mass!) can be 100% reusable and also manage to get more payload to orbit than existing expendable or partially expendable rockets. I count the vehicle as payload here since it is reused. Alternately I suppose we could count the 4 tons of delivered payload, plus the reserved EDL props—but for the 3mm thick version guestimate that is still 1.9% to LEO! I have to be overly optimistic, than just can't be true, or all rockets would have been expendable SSTOs since forever, since they would all be better than everything we have now.

Edited September 5, 2022 by tater

[magnemoe]

18 hours ago, tater said:

Still 4mm steel. It has to survive orbital EDL. Maybe 3mm if that steel has enough strength, and can absorb heat the same way. Part of the point of steel is that the TPS can let some heath through that it could not with other materials.

It also needs actuators, etc to open, close, and latch whatever the final form of a real payload bay is.

There's no way that a SSTO rocket (and not even an air-breather that can use the atmosphere as propellant mass!) can be 100% reusable and also manage to get more payload to orbit than existing expendable or partially expendable rockets. I count the vehicle as payload here since it is reused. Alternately I suppose we could count the 4 tons of delivered payload, plus the reserved EDL props—but for the 3mm thick version guestimate that is still 1.9% to LEO! I have to be overly optimistic, than just can't be true, or all rockets would have been expendable SSTOs since forever, since they would all be better than everything we have now.

Yes, the fairing don't have the benefit of being under 6 bar pressure, 
And an SSTO will loose to even an fully reusable two stage rocket as it does not have to bring the second stage to orbit and protect it during reentry, Yes the first stage need to do an burn back and land but this require far less fuel than bringing it into orbit. 
 

[tater]

1 hour ago, magnemoe said:

Yes, the fairing don't have the benefit of being under 6 bar pressure, 

True, so the fairing is if anything heavier.

I think an SSTO with a large payload is plausible, but the payload mass % will be small—and it must be smaller than it is for TSTO—so as the desired payload increases, so does the mass on the pad.

[tater]

Got me thinking about other SSTO concepts—none actually flown—and what their estimated payload mass fraction was.

Venture Star was hoped to deliver 20 tons to LEO for 1000t on the pad—2%

Krafft Ehricke's NEXUS was to get 450t to LEO with a pad mass of 21,820t—2%

Chrysler SERV was to deliver ~50t to LEO with a gross mass of 2721t—1.8%

Boeing LEO was hoped to do 228t with a mass of 10,423t—2.2%

 

Phil Bono's ideas used drop tanks, not really SSTO:

ROMBUS hoped for 5% to LEO.

Pegasus was to deliver 90t with a pad mass of 1520t—6%

 

So the ~2% to LEO of the ballparks I did above are in line with previous estimates—of rockets that no one ever bothered to build. I have to assume that mass creep for actually building the concept SSTOs of the 60s-90s would have resulted in a meaningful drop in payload, doesn't take much to cut into a 2% margin.

 

[Exoscientist]

21 hours ago, tater said:

Still 4mm steel. It has to survive orbital EDL. Maybe 3mm if that steel has enough strength, and can absorb heat the same way. Part of the point of steel is that the TPS can let some heath through that it could not with other materials.

It also needs actuators, etc to open, close, and latch whatever the final form of a real payload bay is.

There's no way that a SSTO rocket (and not even an air-breather that can use the atmosphere as propellant mass!) can be 100% reusable and also manage to get more payload to orbit than existing expendable or partially expendable rockets. I count the vehicle as payload here since it is reused. Alternately I suppose we could count the 4 tons of delivered payload, plus the reserved EDL props—but for the 3mm thick version guestimate that is still 1.9% to LEO! I have to be overly optimistic, than just can't be true, or all rockets would have been expendable SSTOs since forever, since they would all be better than everything we have now.

 

 It is certainly not the case that every orbital rocket could be SSTO and carry significant payload. However, what I am arguing is that SSTO is possible with significant payload with currently existing chemical propulsion engines. In fact, they have been possible since the 70’s with the advent of the staged-combustion, high performance hydrogen SSME’s in the U.S., and the staged-combustion, high performance kerosene RD-170 in Russia. Now with the advent of the staged-combustion, high performance methane Raptor, we have another engine that could power SSTO’s and with significant payload.

About the weight of the structure of the Starship above the propellant tank, the scenario we’re really concerned with is using this space for cargo, so it doesn’t need the strength, and required mass, of propellant tanks. We can therefore make comparisons to the weight of payload fairings of various sizes. For example of the Atlas V:

Space Launch Report:  Atlas 5 Data Sheet.

Vehicle Components, Cont'd

	400 Large Fairing	400 Extended Fairing	5 m Short Fairing	5 m Long Fairing
Diameter (meters)	4.2 m	4.2 m	5.4 m	5.4 m
Length (meters)	12.2 m	13.1 m	20.7 m	23.4 m
Mass (tons)	2.09 t	2.26 t	4.09 t	4.65 t

https://web.archive.org/web/20220406013818/http://www.spacelaunchreport.com/atlas5.html#components    Using the simplifying approximation of the fairings being cylindrical, the volume of the smallest one listed is approx. 169 m^3 at a mass of 2.09 tons, and the largest at approx.  535 m^3 at 4.65 tons. For the cargo use  of the Starship, you probably also want to use fairings of various sizes like other orbital rockets do, as the Atlas V.  The empty space volume above the propellant tank of the Starship is about 800 m^3 so we can estimate the mass of a fairing of that size as about 50% higher than the largest Atlas V fairing so to about 7 tons.     Robert Clark  

[wumpus]

50 minutes ago, Exoscientist said:

with the advent of the staged-combustion, high performance hydrogen SSME’s in the U.S.,

The SSMEs provided 1,180,000lbs of thrust for ship weighing  4,480,000 lbs (the SRBs provided most of the thrust).  I'd recommend the RD-170s instead (or a new methane engine).  Sure, the SSMEs are refurbishable, but that really isn't going to happen with SSTOs.

On 9/5/2022 at 2:52 AM, Exoscientist said:

 The  importance of SSTO’s is their operational simplicity for point-to-point human transport. That would be a major market for radically increasing the market for spaceflight.

SSTO with reuse is significantly less in reach (so much I keep telling Spacescifi that he needs "magic" Isp to do it).  Getting the SSTO to orbit requires significant rocket science.  Getting it down so it can fly again requires much, much more.  Neither the means of surviving re-entry nor the means of landing can be done without adding mass.  And the current state of the art requires a lot of mass, especially for the landing.  You're arguing that just getting to orbit (with some payload) is possible but hardly showing any way to land the SSTO.

Without reuse, SSTO makes no sense.  If you are throwing away the rocket, what good is it to throw it all away at once as opposed to in pieces?  You'll always have more payload and less rocket required with TSTO.  And with reuse it is currently impossible.

[tater]

1 hour ago, wumpus said:

Without reuse, SSTO makes no sense.  If you are throwing away the rocket, what good is it to throw it all away at once as opposed to in pieces?  You'll always have more payload and less rocket required with TSTO.  And with reuse it is currently impossible.

Indeed, and stage 1 reuse is now routine, we watch it in real time about once every 6 days this year. That's 50-66% of the cost of the rocket, and should now be the benchmark.

2 hours ago, Exoscientist said:

However, what I am arguing is that SSTO is possible with significant payload with currently existing chemical propulsion engines.

Yes, but the part that matters is reuse. That was the point of the 60s and on SSTO designs. Starship/Super Heavy is being talked about for 100-150t to LEO. That is 2-3% of the mass on the pad as a TSTO. They are actually building it, unlike every other fully reusable launch vehicle proposed, ever. if TSTO can only get 2-3%, there is no way SSTO gets 2%, it must get less. What the useful % to LEO actually is for some proposed SSTO, I don't know. So we'd be trading something probably on the order of half the TSTO payload for some operational simplification.

There's certainly an argument to be made for that for particular use cases, but it's not what SpaceX wants, so someone else will have to do it (or convince SpaceX that it furthers their goals).

[wumpus]

23 hours ago, tater said:

Indeed, and stage 1 reuse is now routine, we watch it in real time about once every 6 days this year. That's 50-66% of the cost of the rocket, and should now be the benchmark.

Sustainer stage reuse was routine from 1981-2011, albeit with extreme refurbishing costs.  And the 50-66% almost certainly isn't just the rocket, the upper stage has a single engine (10% of the engine costs) and far less mass (not to mention fairing reuse).  30-40% of those costs have to be in the launch, with the army of highly trained professionals launching the thing, not to mention all the costs bringing the booster back and various tests needed.

Much of the key to the success of Falcon 9 reuse is that the booster doesn't get anywhere near orbital velocity.  So it doesn't need a heat shield (although it does need a back-burn) and all the issues the shuttle had with tiles (as far as I know, Starship is using tiles as well.  Different tiles, but they couldn't find a better solution even with the warning of Shuttle experience.

[magnemoe]

1 hour ago, wumpus said:

Sustainer stage reuse was routine from 1981-2011, albeit with extreme refurbishing costs.  And the 50-66% almost certainly isn't just the rocket, the upper stage has a single engine (10% of the engine costs) and far less mass (not to mention fairing reuse).  30-40% of those costs have to be in the launch, with the army of highly trained professionals launching the thing, not to mention all the costs bringing the booster back and various tests needed.

Much of the key to the success of Falcon 9 reuse is that the booster doesn't get anywhere near orbital velocity.  So it doesn't need a heat shield (although it does need a back-burn) and all the issues the shuttle had with tiles (as far as I know, Starship is using tiles as well.  Different tiles, but they couldn't find a better solution even with the warning of Shuttle experience.

Yes the shuttle SRB was reused, but it was an steel tube who was the part who was reused. Nozzle and avionic needed to be replaced. 

And I agree the second stage would be much cheaper than stage 1, with just one engine and shorter.  50-66% might be the entire cost of running the falcon 9 program. Yes you need to do recovery and restoring but they also test new first stages so not much change here. You also need to keep the pads running, now this is pretty fixed costs so with the high numbers of starlink launches you could see launch costs go down. The starship program should eat up lots of money and I don't think starlink makes serious money yet, but it might be to hide revenue in the future?  

[Exoscientist]

On 9/6/2022 at 1:11 PM, tater said:

…Yes, but the part that matters is reuse. That was the point of the 60s and on SSTO designs. Starship/Super Heavy is being talked about for 100-150t to LEO. That is 2-3% of the mass on the pad as a TSTO. They are actually building it, unlike every other fully reusable launch vehicle proposed, ever. if TSTO can only get 2-3%, there is no way SSTO gets 2%, it must get less. What the useful % to LEO actually is for some proposed SSTO, I don't know. So we'd be trading something probably on the order of half the TSTO payload for some operational simplification.…

 You’re not considering that 2 -3% for the SH/SS is coming from making it fully reusable. So those ~2% payload reusable SSTO’s are comparable to the reusable TSTO’s.

  Robert Clark

Edited September 7, 2022 by Exoscientist

[tater]

28 minutes ago, Exoscientist said:

 You’re not considering that 2 -3% for the SH/SS is coming from making it fully reusable. So those ~2% payload reusable SSTO’s are comparable to the reusable TSTO’s.

TSTO is always better from a mass standpoint.

If TSTO full operational reuse can be done with 2-3% payload delivered any SSTO will certainly be some fraction of that. So the upper limit for an SSTO is something under 2% (assuming SS/SH actually works and delivers 100t). Well under 2% I would imagine.

[Exoscientist]

On 9/5/2022 at 3:47 AM, SunlitZelkova said:

This makes no sense. For all average routes, only a suborbital flight path is required for point-to-point flights.

I doubt point-to-point would be profitable for the foreseeable future. It requires a very high level of reliability, and lowering cost so average people fly on it. SpaceX is cheap within the context of launch costs, but it isn’t airliner ticket cheap, and it won’t become so for a very long time, if ever.

At this moment in time P2P passenger transport may very well end up like the Concorde, and that’s only after you pass the hurdle of getting approval to fly spacecraft over population centers to land at a spaceport.

The number of flights that would be required for this level of reliability to be achieved would be so high that SpaceX would likely already be making enough money from those launches in the first place and not need P2P from a financial point of view.

Single Stage Point to Point Up To 6000 Miles With Mach 20 Starship

May 31, 2019 by Brian Wang

https://www.nextbigfuture.com/2019/05/single-stage-point-to-point-up-to-6000-miles-with-mach-20-starship.html

  To go 6,000 miles would take Mach 20, about 6,800 m/s. But 6,000 miles is only half the longest distance of 12,500 miles, half the Earth's circumference. 

 But orbital velocity is 7,800 m/s. When you launch eastward you get 400 m/s for free from Earth's rotation so an orbital rocket only needs 7,400 m/s. This is just 10% more than the 6,800 m/s suborbital velocity proposed. So just a 10% higher speed gets you full coverage to anywhere on Earth as well as orbit.

  Robert Clark

Edited September 8, 2022 by Exoscientist
Typo.

[Terwin]

22 hours ago, Exoscientist said:

 You’re not considering that 2 -3% for the SH/SS is coming from making it fully reusable. So those ~2% payload reusable SSTO’s are comparable to the reusable TSTO’s.

It looked to me like the ~2% SSTO payloads involved 0% reuse.

If I remember correctly, getting to orbit with 2% payload on the SH would actually have a negative payload fraction if you subtracted enough fuel for SS to deorbit and land(ie not enough for SH, just the much smaller SS), not even including things like structural reinforcement and heat shielding.

So the current comparison is:

~2% payload fraction for a single use SSTO (which is then space-trash)

OR

~2% payload fraction for a fully reusable TSTO that might have a marginal cost to launch in the low tens of millions for > 100T of cargo.  (perhaps $200/kg to orbit?)

 

[tater]

1 hour ago, Exoscientist said:

 But orbital velocity is 7,800 m/s. When you launch eastward you get 400 m/s for free from Earth's rotation so an orbital rocket only needs 7,400 m/s. This is just 10% more than the 6,800 m/s suborbital velocity proposed. So just a 10% higher speed gets you full coverage to anywhere on Earth as well as orbit.

Not counting gravity and drag losses. People usually ballpark something closer to 9300 m/s for orbital.

[Exoscientist]

3 hours ago, tater said:

Not counting gravity and drag losses. People usually ballpark something closer to 9300 m/s for orbital.

 Yes. But the phrasing there leads me to believe the Mach 20 mentioned is the actual speed that needs to be reached for the 6,000 mile range. So the comparison should be to the actual speed of orbital velocity.

   Robert Clark

Edited September 8, 2022 by Exoscientist

[tater]

Regardless, P2P is a different animal than SSTO from a use case POV. I'm fine with P2P being a thing (if it could actually work, pass regulatory hurdles, actually be safe, etc), but what is the use case for SSTOs for SpaceX, exactly?

They must certainly put less payload in LEO—which would largely be propellant—than with SS/SH, so what they gain in simplicity of launch, they lose in phasing. Twice as many launches, but SSTO doesn't really buy you anything.