Real SSTO challenge.

[Exoscientist]

 We’ve been discussing in this thread the feasibility of creating this as a real SSTO:

 

 My argument that it is doable is just by using the rocket equation. Who wants to take up the challenge of doing a Real Solar System mod simulation showing it is possible?

 

  Robert Clark

 

[Rakaydos]

Noone is arguing it isnt POSSIBLE. We are all saying it's stupid, and that all the technologies you would use for it would make a better TSTO.

[Exoscientist]

 A key issue is it continues to be said SSTO’s aren’t technically feasible. Whenever they are spoken about it is like you need nuclear engines or some “unobtainium” materials. That it has been feasible since the 70’s is an important fact. Doing an accurate trajectory simulation is therefore important to establish that fact.

  When you did the accurate trajectory simulations you would find an optimized rocket that uses both  maximally efficient engines and maximally lightweighted tanks would as an SSTO have better payload than current rockets which are not optimized. Moreover such an optimized rocket when used in a TSTO version would double the payload of a current TSTO which is not optimized.

 So even if you don’t want to use SSTO’s, it is important to confirm this using accurate trajectory simulations to prove you can double the payload of a current TSTO using simple methods already known about for decades.

  Robert Clark

[camacju]

The problem with KSP is that the aero model isn't super realistic. With fairing and heat shield glitches you can get some crazy payload fractions on a RSS SSTO plane. Ferram Aerospace will help with that but it's still not completely accurate since that would take up way too much processor power.

Anyway, your calculation says that an optimized two stage to orbit rocket with first stage recovery will always be way better than a single stage rocket. This is true for carrier spaceplanes also - something like the Sänger (jet powered carrier plane, rocket powered shuttle) will have a higher payload fraction, just because you won't need to lug all those fuel tanks all the way to orbit.

[Exoscientist]

 Thanks for that. But what I want first  is an estimate of the payload as a simple expendable rocket of the Delta IV Medium equipped with SSME's. Then you can try various landing modes such vertical propulsive or winged horizontal. 

 Not having wings for the expendable version should simplify the aerodynamics.

 

  Robert Clark

[GoSlash27]

On 7/10/2021 at 2:53 AM, Exoscientist said:

When you did the accurate trajectory simulations you would find an optimized rocket that uses both  maximally efficient engines and maximally lightweighted tanks would as an SSTO have better payload than current rockets which are not optimized. Moreover such an optimized rocket when used in a TSTO version would double the payload of a current TSTO which is not optimized.

 I find this difficult to accept at face value. Has someone actually done this simulation, and if so could you please provide a link?

 I'd be willing to bet that a TSTO will beat the pants off an SSTO, even with these handicaps.

Thanks,

-Slashy

[Dr. Kerbal]

Hm. Instresting. A real SSTO? Has there ever been a concept? 

[Rakaydos]

1 hour ago, GoSlash27 said:

 I find this difficult to accept at face value. Has someone actually done this simulation, and if so could you please provide a link?

 I'd be willing to bet that a TSTO will beat the pants off an SSTO, even with these handicaps.

Thanks,

-Slashy

I consider it more of an inditment of pre-spaceX launchers. 

[GoSlash27]

Just now, Rakaydos said:

I consider it more of an inditment of pre-spaceX launchers. 

You would.

 I just consider it the tyranny of the rocket equation.

Best,

-Slashy

[OHara]

Often, the challenge maker will submit his own attempt at the challenge, and that often helps the rest of us understand the intention.

I use only the simpler SMURFF with RSS (not the full Realism Overhaul). SMURFF adjusts the mass of KSP's engines and tanks to more realistic values, but does not change their Isp, nor the types of fuel, so I am using KSP's generic 'liquid fuel' and 'oxidizer'.

The US Space Shuttle's Main Engine (SSME) is the RS-25, which inspired the KS-25 in KSP, so I used the 'Mammoth' engine which groups 4× KS-25 'Vector' engines and sized my rocket around that to see how much I could get into orbit.  To my surprise, I could get the 2-tonne 3-kerbal MK3 pod into a 1180-km circular orbit.

Isp = 3090 m/s = 315 s·g   (same as in stock KSP)

SMURFFed tanks which when full are 97% fuel by mass

dV = 3090 m/s log( 395 t / 20 t ) = 9218m/s (in vacuum)

Payload fraction (Mk3 pod and heat-shield) 2.9 t / 395 t =  0.7%
In hindsight, given that this is a SSTO so the engines come all the way to orbit, I should have balanced payload mass closer to that of the engines and empty tanks.

I had to throttle rather deeply to avoid excessive g-forces, which drives home the fact that the single-stage design has me carrying heavy powerful engines beyond where they are needed.

(I did not expect to reach such a high orbit, so had not enough monopropellant to de-orbit the pod, so now I'm making a rescue mission.)

[OHara]

It probably makes more sense to do this using Realism Overhaul.

I cannot use the same parts as above, because Realism Overhaul replaces the 'Mammoth' with 4 SSMEs on a larger 8.4-m tank, and replaces the S3-1440 with an 8.4-m fuel tank, but I see no parts to taper to the 4-m Mk3 pod.

I could make a similar rocket using Making History fuel tanks. Realism Overhaul has not yet made configurations for MH parts, so I made the patch below to set fuel capacity following the pattern of Real Fuels.

Spoiler

// Save tank capacity before RealFuels deletes the info
@PART[*]:HAS[@RESOURCE[MonoPropellant]]:BEFORE[RealFuels] {
   RealFuelsNeedsTankVolume   = #$/RESOURCE[MonoPropellant]/maxAmount$
   @RealFuelsNeedsTankVolume *= 3.6 // 3.6 litres per unit monopropellant
}
@PART[*]:HAS[@RESOURCE[Oxidizer],@RESOURCE[LiquidFuel]]:BEFORE[RealFuels] {
    RealFuelsNeedsTankVolume   = #$/RESOURCE[Oxidizer]/maxAmount$
    @RealFuelsNeedsTankVolume += #$/RESOURCE[LiquidFuel]/maxAmount$
    @RealFuelsNeedsTankVolume *= 5 // 5.0 litres per unit LFO
}
@PART[*]:HAS[@RESOURCE[LiquidFuel]]:BEFORE[RealFuels] {
    RealFuelsNeedsTankVolume   = #$/RESOURCE[LiquidFuel]/maxAmount$
    @RealFuelsNeedsTankVolume *= 5 // 5.0 litres per unit LiquidFuel
}
// If neither RealFuels nor RealismOverhaul has made a RO tank, make one.
@PART[*]:HAS[#RealFuelsNeedsTankVolume,!MODULE[ModuleFuelTanks]]:AFTER[RealismOverhaul] {
    MODULE {
        name = ModuleFuelTanks
        volume = #$/RealFuelsNeedsTankVolume$
        type = Default
}}
@PART[*]:HAS[#RealFuelsNeedsTankVolume]:AFTER[RealismOverhaul] {
    !RealFuelsNeedsTankVolume = delete
}

 

4× SSME engines with Isp = 4440 m/s = 453 s·g 
With Realism Overhaul, engines throttle down only slightly, so I shut down 2 of the 4 to avoid excessive g-forces.

The Mk3 3-kerbal pod and heat shield weighs 5.24t
Payload fraction 5.24 / 347.27 = 1.5%

dV = 4440 m/s log (346t / 41t) = 9460m/s (in vacuum)

Engines do not re-ignite, so it takes some skill to steer so as to make a circular orbit, which skill I have not yet practised.

It might be interesting to see who can get the highest  payload fraction from a SSTO in RSS/RO.  People use many different part mods with Realism Overhaul, though, so their engines will be configured by designers with varying degrees of optimism.

[Exoscientist]

 I would love to do my own Realism Overhaul simulation, but I have never learned Kerbal. 

(What would be the suggested approach to take to first learn Kerbal, and then proceed to Realism Overhaul?)

 Rather than your digging  into the details of my proposed Delta IV Medium's first stage modified with two SSME's and lightweighted tanks, you could just assume some hydrolox stage with a 10 to 1 mass ratio, since the existing Centaurs get that, and then give the stage SSME engines.

 I think you'll be surprised at how high the payload you could get as an expendable. Given the high payload fraction, you could then estimate how much mass is needed for thermal protection, landing legs, and propellant needed to be kept on reserve for a vertical, powered landing for the reusable case.

 Alternatively, you could estimate the thermal protection, landing legs and wing mass needed for the horizontal landing method of reusability. In this regard, if you're using a non-lifting ascent to orbit, the wings only have to be sized to support the dry mass of the craft on return. This will significantly reduce their mass. I also advise using short, stubby wings, not the oversized, heavy wings used on the shuttle. As in these examples:

 

 

[GoSlash27]

7 hours ago, Exoscientist said:

 I think you'll be surprised at how high the payload you could get as an expendable.

I think you'll be surprised at how high the payload isn't. Your best bet is to just get KSP, figure it out, then move on to the RE mod.

Best,

-Slashy

 

 

[Exoscientist]

On 7/15/2021 at 7:10 PM, OHara said:

4× SSME engines with Isp = 4440 m/s = 453 s·g 
With Realism Overhaul, engines throttle down only slightly, so I shut down 2 of the 4 to avoid excessive g-forces.

The Mk3 3-kerbal pod and heat shield weighs 5.24t
Payload fraction 5.24 / 347.27 = 1.5%

dV = 4440 m/s log (346t / 41t) = 9460m/s (in vacuum)

Engines do not re-ignite, so it takes some skill to steer so as to make a circular orbit, which skill I have not

 Can you say what is the bare dry mass and propellant load is for the expendable rocket (no heat shield or landing legs)? Then what is the expendable payload to a 200 km basic orbit. Then there are various materials we can use to get light weight heat shield and landing legs.

 Robert Clark

[CFYL]

I would like to take the challenge with smurff. It may take a bit long to get it done.

IMO the only benefit of a fully reusable SSTO is that it can be used as a private car. TSTO is believed to excel at payload percentage but clearly harder to manage for an individual. IF the price of space travel can be afforded by average families then TSTO can be like public transport and SSTO is a private vehicle. Of course this is all based on the practicality of relatively small lightweight SSTOs.

[OHara]

On 7/17/2021 at 5:09 PM, Exoscientist said:

Can you say what is the bare dry mass and propellant load is for the expendable rocket (no heat shield or landing legs)? 

For the Realism Overhaul rocket that I posted above, 
propellant would be 347.6 − 41.4 = 306.2 tonnes,
dry mass of the lifter 41.4 − 5.2 = 36.2 tonnes,
and payload 5.2 tonnes.

8 hours ago, AllenLi said:

I would like to take the challenge with smurff.

That sounds like a good idea.  This challenge was a nice idea, because an SSTO rocket is moderately difficult in RSS with the mods that give realistic performance to parts.

Previous similar challenges (link link link link) had not much response. 
I think SMURFF is the best choice of part-mod for a challenge that invites players who are new to RSS, because it does the minimum change: gives realistic mass to the familiar KSP parts.

I put the rocket that I posted above on KerbalX.  It leaves plenty of room for improvement.  It has a decoupler to separate the payload from lifter, because I thought the challenge might use payload fraction as the score. 

If you make a rocket that gets to orbit, de-orbits, and is recovered it all as one piece, then I will try that style myself.

[Exoscientist]

1 hour ago, OHara said:

For the Realism Overhaul rocket that I posted above, 
propellant would be 347.6 − 41.4 = 306.2 tonnes,
dry mass of the lifter 41.4 − 5.2 = 36.2 tonnes,
and payload 5.2 tonnes.

That sounds like a good idea.  This challenge was a nice idea, because an SSTO rocket is moderately difficult in RSS with the mods that give realistic performance to parts.

Previous similar challenges (link link link link) had not much response. 
I think SMURFF is the best choice of part-mod for a challenge that invites players who are new to RSS, because it does the minimum change: gives realistic mass to the familiar KSP parts.

I put the rocket that I posted above on KerbalX.  It leaves plenty of room for improvement.  It has a decoupler to separate the payload from lifter, because I thought the challenge might use payload fraction as the score. 

If you make a rocket that gets to orbit, de-orbits, and is recovered it all as one piece, then I will try that style myself.

 

 Thanks for the response. I think we can get a  better payload as an expendable considering the high average Isp of the  SSME’s, approx. 4,400 m/s. This page takes the delta-v to orbit as only 9,000 m/s , about right for a base 200 km orbit and launching eastward to take advantage of the Earths 400+ m/s rotation speed near the equator: 

Towards Reusable Launchers - A Widening Perspective.

https://www.esa.int/esapub/bulletin/bullet87/pfeffe87.htm

 Then using your numbers:

4400Ln(1 +306/(36 + 9.4)) =  9,000 m/s, for a 9.4 ton payload as expendable.

 

  Robert Clark

 

[CFYL]

On 7/24/2021 at 12:55 AM, OHara said:

That sounds like a good idea.

Yes that was a good idea but I failed after several trials with either smurff or RO. I cannot meet my own requirement of relatively lightweight, so Ive decided that I would leave the challenge instead. Good luck to everyone!

[GoSlash27]

On 7/23/2021 at 1:56 PM, Exoscientist said:

9.4 ton payload as expendable.

Reminder: The Falcon 9 does 20 tonnes to LEO. 22, if I remember correctly.

Best,

-Slashy

[Pds314]

So one thing here is rapid turnaround. At some point, you reach a tipping point in reuseability where making the thing be able to relaunch quickly becomes more important than making it able to launch efficiently. If an SSTO has twice the initial cost and size for the same payload, but the relaunch process is something that can be done in an afternoon, not multiple days, it might be worth being fuel inefficient to be able to just land at some nothing space port already under your flight path. Because the SSTO, while twice the price, pays for itself faster by launching multiple payloads a day vs multiple payloads a week and only from areas that have a spaceport that can mate the lower stage to the upper one.

 

All of this of course assumes that this demand actually exists. Which could be a bit of an issue. People have a way of growing their appetite for something when it gets cheaper but I don't know how quickly people would think of, say, enough payload for a fleet of 100 launchers with 100 tonne capacity, going up and down 100 or even 1000 times a year. How many megatonnes a year of space launch capacity will we actually want in the reasonably foreseeable future? Anyone's guess. Even the lower end of that is pretty enormous by modern standards though. Basically a Saturn V launch an hour or to put it another way, 5 ISS's a day.

 

 

 

Edited July 26, 2021 by Pds314

[Exoscientist]

On 7/26/2021 at 4:25 AM, Pds314 said:

All of this of course assumes that this demand actually exists. Which could be a bit of an issue. People have a way of growing their appetite for something when it gets cheaper but I don't know how quickly people would think of, say, enough payload for a fleet of 100 launchers with 100 tonne capacity, going up and down 100 or even 1000 times a year. How many megatonnes a year of space launch capacity will we actually want in the reasonably foreseeable future? Anyone's guess. Even the lower end of that is pretty enormous by modern standards though. Basically a Saturn V launch an hour or to put it another way, 5 ISS's a day.

 Peter Diamandis, progenitor of the X-prize has proposed an answer:

 

Spoiler

The payload is people with the SSTO’s forming point-to-point transports.

 

[Pds314]

3 hours ago, Exoscientist said:

 Peter Diamandis, progenitor of the X-prize has proposed an answer:

 

  Hide contents

The payload is people with the SSTO’s forming point-to-point transports.

 

point to point transport on Earth ends up competing with subsonic airlines. Fuel economy wise, that's a losing battle. It's not as bad as some people seem to suggest but pretty much you'll struggle to get better fuel economy per passenger km than the Concorde (I'm not counting oxidizer either, but it is pretty cheap). Also I think there's a safety issue. A launcher with a life expectancy of 10000 flights and a 0.005% catastrophic failure rate would still be far behind commercial aviation in safety and cost, and the rigors of near-orbital flight are quite a bit more violent (>2.5 G vs <1.5 G) and inherently less safe than an airline flight (cabin depressurization on a spaceship is harder to deal with, you can't just pump pure oxygen into an unpressurized mask and call it good, and indeed, can't safely expose even the skin to the outside pressure, let alone the lungs, ballistic landing requires engine power and fuel while aerodynamic landing doesn't, rockets have a 20-50% margin of safety while airliner aircraft often have >100%, loss of attitude control during reentry is significantly more dangerous than in subsonic cruise flight over land with adequate fuel to recover).

So even if we had a rocket with only a 1 in 20000 fatality rate, so 1 fatality per ~200,000,000 passenger km or so, that's a bit safer than car travel but only a bit.

From the passenger point of view, we can think of there being three sources of "cost."

1. The time the flight and surrounding activities take, including getting through security, secondary transportation, boarding, booking the trip, launch delays, etc. There would be a novelty factor of incidental space tourism but this would likely wear off pretty fast.

2. The average quality adjusted life year of injuries or deaths from a flight.

3. The ticket price of the flight in time spent doing work at low quality of life, or opportunity cost of what they could spend that money on and get higher quality of life.

 

So:

1. Fairly short flight times (less than an hour for sure) would come with considerable transit and security time. Especially if you don't live near a spaceport or are not going to one. Land requirements for a space port may be even higher than those of an airport because of noise pollution. I would say at least an hour of overall security, and depending on safety features, maybe even an hour of boarding and deboarding. Probably a couple hours of secondary transportation. We're probably talking 5 hours minimum trip time.

2. Even with our 2 order of magnitude hypothetical improvement in safety, losing on average 1/20000th of your remaining life is not an insignificant safety concern. If the average person has 40 years of remaining life expectancy, that's about 17.5 hours. Obviously if it's more in line with modern risk levels, the expectation would be closer to 1750 hours.

3. Ticket price. This one varies considerably by country and income level but you had to spend time to Earn money buy the ticket. Fuel alone would probably be like ~2000 liters per person per trip, each of which is around $1 or maybe $2-3 if it's expensive fuel. Right, that works out to 100 people burning ~200 tonnes of fuel or 600 people burning 1200 tonnes. I think you'd be hard-pressed to fit many more than that many people on a ship that size. We also mentioned that ships are retired after 10000 flights. So if each ship costs about $500000 per seat, in line with subsonic airliner costs which is probably very optimistic, that's $50 extra per ticket for the cost of the ship itself. If the ship is 10x the price, that would be $500 a seat. ROI is another factor to consider. If a ship can average 6 flights a day, that will be retired in about 5 years. If it can only make 8 flights a month, then that's gonna take about a century to retire meaning it's actually overly reuseable. If we assume the spaceline wants a 10 year ROI, then anything under 3 flights a day and we start having to add a very large markup to the ticket cost. If you can only do 1 flight a day, then you're only reusing it 3652 times in that 10 year period. So more like $150-1500 per flight. Finally, we have maintainance costs. These things operate with thin margins of safety so presumeably a lot of things will need to be maintained. Current estimates are 0.4-10% total relaunch costs for boosters. If we take the optimistic side of that, assume half is maintainance, then cut it by a factor of 10, that's still twice the cost of the vehicle in maintainance over it's lifetime. So that's around $100-1000 per ticket going to maintainance. Add in a healthy margin to further development, subsidize other projects, buy more  and/or make the person owning this operation richer than god, and I think we can see a scenario where even an "ultra-reuseable" vehicle could have a $10000 price tag on one flight, but I could also see as low as $3000 if we're very optimistic. Either of those is hundreds of hours of first world median wage, suggesting that perhaps fuel costs would be the primary determinant of mass adoption.

That being said, the same does not apply to weakly or moderately reuseable craft. If you have 500 launches per ship, 0.1% mortality, and 50 launches a year, and 0.4% maintainance costs, your fuel cost will still be $2000-6000/head, but your fixed capital cost will be $1000-10000/head, and your maintainance cost $2000-20000/head. Add in a few thousand for the company and you have maybe $8000-50000 ticket price. Reasonably economical space tourism but not competitive with any kind of airline.

 

Overall, I think we're still kind of in the range where 50 flight reuseability, 20 flights a year,  0.5% maintainance costs per flight would be considered very good. And thus, spaceliners are not yet viable for mass market.

 

Edited July 27, 2021 by Pds314

[GoSlash27]

27 minutes ago, Pds314 said:

point to point transport on Earth ends up competing with subsonic airlines. Fuel economy wise, that's a losing battle. It's not as bad as some people seem to suggest but pretty much you'll struggle to get better fuel economy per passenger km than the Concorde (I'm not counting oxidizer either, but it is pretty cheap). Also I think there's a safety issue. A launcher with a life expectancy of 10000 flights and a 0.005% catastrophic failure rate would still be far behind commercial aviation in safety and cost, and the rigors of near-orbital flight are quite a bit more violent (>2.5 G vs <1.5 G) and inherently less safe than an airline flight (cabin depressurization on a spaceship is harder to deal with, you can't just pump pure oxygen into an unpressurized mask and call it good, and indeed, can't safely expose even the skin to the outside pressure, let alone the lungs, ballistic landing requires engine power and fuel while aerodynamic landing doesn't, rockets have a 20-50% margin of safety while airliner aircraft often have >100%, loss of attitude control during reentry is significantly more dangerous than in subsonic cruise flight over land with adequate fuel to recover).

So even if we had a rocket with only a 1 in 20000 fatality rate, so 1 fatality per ~200,000,000 passenger km or so, that's a bit safer than car travel but only a bit.

From the passenger point of view, we can think of there being three sources of "cost."

1. The time the flight and surrounding activities take, including getting through security, secondary transportation, boarding, booking the trip, launch delays, etc. There would be a novelty factor of incidental space tourism but this would likely wear off pretty fast.

2. The average quality adjusted life year of injuries or deaths from a flight.

3. The ticket price of the flight in time spent doing work at low quality of life, or opportunity cost of what they could spend that money on and get higher quality of life.

 

So:

1. Fairly short flight times (less than an hour for sure) would come with considerable transit and security time. Especially if you don't live near a spaceport or are not going to one. Land requirements for a space port may be even higher than those of an airport because of noise pollution. I would say at least an hour of overall security, and depending on safety features, maybe even an hour of boarding and deboarding. Probably a couple hours of secondary transportation. We're probably talking 5 hours minimum trip time.

2. Even with our 2 order of magnitude hypothetical improvement in safety, losing on average 1/20000th of your remaining life is not an insignificant safety concern. If the average person has 40 years of remaining life expectancy, that's about 17.5 hours. Obviously if it's more in line with modern risk levels, the expectation would be closer to 1750 hours.

3. Ticket price. This one varies considerably by country and income level but you had to spend time to Earn money buy the ticket. Fuel alone would probably be like ~2000 liters per person per trip, each of which is around $1 or maybe $2-3 if it's expensive fuel. Right, that works out to 100 people burning ~200 tonnes of fuel or 600 people burning 1200 tonnes. I think you'd be hard-pressed to fit many more than that many people on a ship that size. We also mentioned that ships are retired after 10000 flights. So if each ship costs about $500000 per seat, in line with subsonic airliner costs which is probably very optimistic, that's $50 extra per ticket for the cost of the ship itself. If the ship is 10x the price, that would be $500 a seat. ROI is another factor to consider. If a ship can average 6 flights a day, that will be retired in about 5 years. If it can only make 8 flights a month, then that's gonna take about a century to retire meaning it's actually overly reuseable. If we assume the spaceline wants a 10 year ROI, then anything under 3 flights a day and we start having to add a very large markup to the ticket cost. If you can only do 1 flight a day, then you're only reusing it 3652 times in that 10 year period. So more like $150-1500 per flight. Finally, we have maintainance costs. These things operate with thin margins of safety so presumeably a lot of things will need to be maintained. Current estimates are 0.4-10% total relaunch costs for boosters. If we take the optimistic side of that, assume half is maintainance, then cut it by a factor of 10, that's still twice the cost of the vehicle in maintainance over it's lifetime. So that's around $100-1000 per ticket going to maintainance. Add in a healthy margin to further development, subsidize other projects, buy more  and/or make the person owning this operation richer than god, and I think we can see a scenario where even an "ultra-reuseable" vehicle could have a $10000 price tag on one flight, but I could also see as low as $3000 if we're very optimistic. Either of those is hundreds of hours of first world median wage, suggesting that perhaps fuel costs would be the primary determinant of mass adoption.

That being said, the same does not apply to weakly or moderately reuseable craft. If you have 500 launches per ship, 0.1% mortality, and 50 launches a year, and 0.4% maintainance costs, your fuel cost will still be $2000-6000/head, but your fixed capital cost will be $1000-10000/head, and your maintainance cost $2000-20000/head. Add in a few thousand for the company and you have maybe $8000-50000 ticket price. Reasonably economical space tourism but not competitive with any kind of airline.

 

Overall, I think we're still kind of in the range where 50 flight reuseability, 20 flights a year,  0.5% maintainance costs per flight would be considered very good. And thus, spaceliners are not yet viable for mass market.

 

Yeah, I agree with all of this. More importantly, an SSTO point to point launcher cannot attain the schedules and ease of use of commercial air travel. It's got to wait for range clearance, needs special checkouts, facilities and procedures that limit not only the points of departure/ arrival, but also hugely increases the time from passenger arrival at one spaceport to departure from another.

 Paradoxically, this means that it can't match the travel time of mundane airliners from point A to point B, let alone the corporate jets that people who can afford the ticket already have access to. Couple that with the high ticket cost, and you have very low demand. Low demand means that you have a hard time filling your ships with paying passengers, which makes it impossible to operate at a profit.

 All this put together is why I've always said that point to point rocket travel was never a viable business model.

Best,

-Slashy

[Exoscientist]

 Keep in mind the main market would be trans Pacific flights that now take a day to make.
Making the flight to space could do it in 30 minutes.

 

  Robert Clark

Edited July 28, 2021 by Exoscientist

[GoSlash27]

6 hours ago, Exoscientist said:

 Keep in mind the main market would be trans Pacific flights that now take a day to make.
Making the flight to space could do it in 30 minutes.

 

  Robert Clark

Exoscientist,

 The fact that it would only serve a small percentage of the market is not a point in its favor, and unfortunately it wouldn't take half an hour. Gate-to-gate time would have to include fueling, range delays, weather delays, and scrubbed launches.

If there was any money in faster air travel across the Pacific, the airlines would already be running supersonic flights on those routes.

Best,

-Slashy