Well as Quora User says in her answer, SpaceX's main motive is that they want a spacecraft that can land on other places in the solar system without runways, especially Mars. So he is trying to do two things at once - optimize for launch from and landing back on Earth and simultaneously optimize for landing on Mars.
If you talk about what can be done in theory, rather than what can be done practically right now - I don't think this is necessarily optimal for Earth launch to orbit. In terms of reusability especially, the single stage to orbit seems far preferable if you can do it. And an air breathing spacecraft even better - why power through the dense lower atmosphere and carry all your fuel with you when you can pick up the atmosphere as you go through it and use it as reaction mass? And particularly, to land vertically from orbit instead of gliding down - it just seems rather surprising if that ends up being the optimal future solution for all time.
And even using the atmosphere as fuel seems sub-optimal compared with using a lifting gas like hydrogen or helium to lift your spacecraft up to the very edge of the upper atmosphere first, then launch from there, if you can find a way to accelerate it to the desired speed efficiently in the high upper atmosphere as an airship rather than having to use the fuel to support its weight. If you can support it in the upper atmosphere, surely that's going to be a huge fuel saving? In principle anyway.
So, as you say, I think it is more that it may happen to be a pretty good solution at present stage of technology. Plus it happens to dovetail well with his Mars ambitions.
And - it is work in progress. They seem very confident that it is going to work. But have not yet recovered a stage successfully. And haven't re-used it. So I think until it becomes a regular thing for them to re-use their stages - and until you have some idea of turn around time, how much refurbishment is needed, and whether it is as reliable after it is used several times - well there's a lot to be done yet before they demonstrate that this idea works conclusively. For everyone else I think a case of "watch this spot".
I hope they succeed with this approach. If so though, they may not be the only company launching to LEO and the competition may be beneficial.
To give an idea of other approaches under development, here are a couple of other possibilities - I'm copying this over from my Science20 article on the same topic:
There have been several ideas for single stage to orbit. Including the Delta Clipper, which got quite advanced, before it eventually was scrapped. This achieved a vertical take off then vertical landing ready for reuse long before SpaceX, in the 1990s. They hoped eventually to be able to do single stage to orbit with passengers.
This is a UK project, called Skylon, a design for a jet that can fly directly to orbit. It would launch from an ordinary runway - like an airplane - the runway needs to be strengthened but is otherwise normal. And it doesn't need booster rockets at all, it carries all its fuel on board.
Artist's concept of it taking off into orbit
It burns a mixture of hydrogen and oxygen, but in the early stages it gets the oxygen from the atmosphere. It does that by a remarkable system that cools down the incoming air by 140C in a hundredth of a second, so can take in the air and still use lightweight materials.
It has a massive reduction of fuel needs because it is air breathing in the early stages of its flight.
This is under active development right now, they are working slowly but steadily towards their goals. So one day it might happen. Possibly as soon as the 2020s. If this works out, it seems likely to cost much less than the SpaceX approach for the same payload.
Then there is the idea of airships:
A balloon filled with hydrogen or helium could rise almost indefinitely - if the skin is light enough, even close to the boundaries of low Earth orbit. This is a very low cost method because no fuel needs to be expended to do the lifting itself.
JP Aerospace plan to make airships that would rise to orbital platforms at 200,000 feet - so that's 60 km, in the mesosphere - above the stratosphere, near vacuum conditions.
They have the current altitude record for an airship for an unmanned but manoeuvrable airship of 95,085 feet, or 29 km
JP Aerospace Airship Flies to the Edge of Space, Smashing the Existing World Altitude Record
The maximum height achieved with any ground launched balloon so far is 56 km with a NASA experiment Bu60-1
These would be truly orbital airships - slowly accelerating to Mach 20 and greater.
When they set off from their base station at 200,000 feet (60 kms), they would be just floating. It's almost a vacuum inside the ship, yet still, because it is filled with hydrogen or helium, contained by the skin, then the lighter atoms of hydrogen or helium will float on the denser almost vacuum of oxygen / nitrogen outside it.
LEO starts at around 160 km Low Earth orbit
They would accelerate to orbit slowly over several days, by using ion thrusters. First they use a combination of lift and velocity - and eventually travel at orbital velocity at levels too high to get noticeable lift.
This idea of Mach 20+ airships accelerating to reach orbital velocity may seem absurd at first, it did to me when I first read it. But the more you think about it, the more it begins to make sense.
We launched several balloons to LEO in the Echo program, so there is no problem with balloons once they reach LEO. The problem is the transition between high altitude and LEO. For that, we want to find out about suborbital balloon flights. Those are rare.
An early experiment sent one of these balloons into a sub orbital hop which it survived for most of the hop and disintegrated eventually. When it did explode, this was mainly because they made a mistake and left too much gas in it.
That isn't much by way of experimental data, as this seems to be the only example of a suborbital balloon flight to date. Also that's with a small balloon not the huge kilometer scale airships of JP Aerospace.
Still, what data there is, is reasonably promising that the high speeds of the balloons won't be a problem so long as they are well above most of the atmosphere in close to LEO vacuum conditions by the time they approach orbital velocities. At any rate, JP Aerospace don't consider this to be their main challenge.
You can hear John Powell, the man himself talk about it in a recent Spaceshow talk, and decide for yourself. They have a very interesting philosophy also, it's a company that does its development in the slow lane. They've been working towards this for decades and finance their development by the discoveries they make along the way.
Find out more here: Guest: John Powell. Topics: Updates on JP Aerospace and the Airship To Orbit program.
So if this ever worked out - it would be a huge cost saving relative to SpaceX and even relative to Skylon. With the downside that it would take several days to get into orbit, but then, passengers might enjoy that, and it is no issue at all for fuel and water etc.
Again JP Aerospace seem quietly confident that they will succeed eventually. And the Skylon engineers are confident in their approach also.
SpaceX are obviously way ahead of the game right now compared to these ideas, but they could easily catch up over timescales of a decade or two, and if so the far lower prices to orbit would give them the edge.
Also, they aren't the only game in town either for low cost launch to orbit, with reusability. They get most of the publicity, but you get other news stories from time to time about the other developments.
Another company that is working on this in a more low key way, indeed rather secretive at times, with fewer public announcements is Blue Origin and there are several other Reusable launch systems that may or may not get developed in the future.
Then, China also is exploring re-usable launchers, see China Looks to Recover Booster Stages
And India is working on Avatar (spacecraft) - an unmanned reusable space plane which will be launched from a rocket, but eventually they hope it can launch horizontally.
And then there's Dream chaser reusable spacecraft under development
Dream Chaser
Several of these hope to be able to fly passengers to LEO eventually.
And of course the mini shuttle Boeing X-37 - not for passengers - used only for military flights at present, with some civilian "add ons".
For many more ideas that have been explored, some of them under active development - this answer consists mainly of an edited extract from a longer article, by me from my Science20 blog - see my Projects To Get To Space As Easily As We Cross Oceans - A Million Flights A Year Perhaps - Will We Be Ready?
If you talk about what can be done in theory, rather than what can be done practically right now - I don't think this is necessarily optimal for Earth launch to orbit. In terms of reusability especially, the single stage to orbit seems far preferable if you can do it. And an air breathing spacecraft even better - why power through the dense lower atmosphere and carry all your fuel with you when you can pick up the atmosphere as you go through it and use it as reaction mass? And particularly, to land vertically from orbit instead of gliding down - it just seems rather surprising if that ends up being the optimal future solution for all time.
And even using the atmosphere as fuel seems sub-optimal compared with using a lifting gas like hydrogen or helium to lift your spacecraft up to the very edge of the upper atmosphere first, then launch from there, if you can find a way to accelerate it to the desired speed efficiently in the high upper atmosphere as an airship rather than having to use the fuel to support its weight. If you can support it in the upper atmosphere, surely that's going to be a huge fuel saving? In principle anyway.
So, as you say, I think it is more that it may happen to be a pretty good solution at present stage of technology. Plus it happens to dovetail well with his Mars ambitions.
And - it is work in progress. They seem very confident that it is going to work. But have not yet recovered a stage successfully. And haven't re-used it. So I think until it becomes a regular thing for them to re-use their stages - and until you have some idea of turn around time, how much refurbishment is needed, and whether it is as reliable after it is used several times - well there's a lot to be done yet before they demonstrate that this idea works conclusively. For everyone else I think a case of "watch this spot".
I hope they succeed with this approach. If so though, they may not be the only company launching to LEO and the competition may be beneficial.
To give an idea of other approaches under development, here are a couple of other possibilities - I'm copying this over from my Science20 article on the same topic:
SINGLE STAGE TO ORBIT
There have been several ideas for single stage to orbit. Including the Delta Clipper, which got quite advanced, before it eventually was scrapped. This achieved a vertical take off then vertical landing ready for reuse long before SpaceX, in the 1990s. They hoped eventually to be able to do single stage to orbit with passengers.
FLYING DIRECTLY TO ORBIT
This is a UK project, called Skylon, a design for a jet that can fly directly to orbit. It would launch from an ordinary runway - like an airplane - the runway needs to be strengthened but is otherwise normal. And it doesn't need booster rockets at all, it carries all its fuel on board.
Artist's concept of it taking off into orbit
It burns a mixture of hydrogen and oxygen, but in the early stages it gets the oxygen from the atmosphere. It does that by a remarkable system that cools down the incoming air by 140C in a hundredth of a second, so can take in the air and still use lightweight materials.
It has a massive reduction of fuel needs because it is air breathing in the early stages of its flight.
Then there is the idea of airships:
AIRSHIPS TO ORBIT
A balloon filled with hydrogen or helium could rise almost indefinitely - if the skin is light enough, even close to the boundaries of low Earth orbit. This is a very low cost method because no fuel needs to be expended to do the lifting itself.
JP Aerospace plan to make airships that would rise to orbital platforms at 200,000 feet - so that's 60 km, in the mesosphere - above the stratosphere, near vacuum conditions.
They have the current altitude record for an airship for an unmanned but manoeuvrable airship of 95,085 feet, or 29 km
The maximum height achieved with any ground launched balloon so far is 56 km with a NASA experiment Bu60-1
JP Aerospace plan to build airships that set off at a level higher than the highest flying balloon ever - huge airships made of such light materials that they couldn't be inflated at ground level.
This is the highest flying balloon ever at 56 km, on the edge of space
ISAS | BALLOONS:Research on Balloons to Float Over 50km Altitude / Special Feature
These would be truly orbital airships - slowly accelerating to Mach 20 and greater.
When they set off from their base station at 200,000 feet (60 kms), they would be just floating. It's almost a vacuum inside the ship, yet still, because it is filled with hydrogen or helium, contained by the skin, then the lighter atoms of hydrogen or helium will float on the denser almost vacuum of oxygen / nitrogen outside it.
LEO starts at around 160 km Low Earth orbit
They would accelerate to orbit slowly over several days, by using ion thrusters. First they use a combination of lift and velocity - and eventually travel at orbital velocity at levels too high to get noticeable lift.
This idea of Mach 20+ airships accelerating to reach orbital velocity may seem absurd at first, it did to me when I first read it. But the more you think about it, the more it begins to make sense.
We launched several balloons to LEO in the Echo program, so there is no problem with balloons once they reach LEO. The problem is the transition between high altitude and LEO. For that, we want to find out about suborbital balloon flights. Those are rare.
An early experiment sent one of these balloons into a sub orbital hop which it survived for most of the hop and disintegrated eventually. When it did explode, this was mainly because they made a mistake and left too much gas in it.
That isn't much by way of experimental data, as this seems to be the only example of a suborbital balloon flight to date. Also that's with a small balloon not the huge kilometer scale airships of JP Aerospace.
Still, what data there is, is reasonably promising that the high speeds of the balloons won't be a problem so long as they are well above most of the atmosphere in close to LEO vacuum conditions by the time they approach orbital velocities. At any rate, JP Aerospace don't consider this to be their main challenge.
You can hear John Powell, the man himself talk about it in a recent Spaceshow talk, and decide for yourself. They have a very interesting philosophy also, it's a company that does its development in the slow lane. They've been working towards this for decades and finance their development by the discoveries they make along the way.
Find out more here: Guest: John Powell. Topics: Updates on JP Aerospace and the Airship To Orbit program.
So if this ever worked out - it would be a huge cost saving relative to SpaceX and even relative to Skylon. With the downside that it would take several days to get into orbit, but then, passengers might enjoy that, and it is no issue at all for fuel and water etc.
Again JP Aerospace seem quietly confident that they will succeed eventually. And the Skylon engineers are confident in their approach also.
SpaceX are obviously way ahead of the game right now compared to these ideas, but they could easily catch up over timescales of a decade or two, and if so the far lower prices to orbit would give them the edge.
OTHER COMPETITORS FOR SPACE-X RIGHT NOW
Also, they aren't the only game in town either for low cost launch to orbit, with reusability. They get most of the publicity, but you get other news stories from time to time about the other developments.
Another company that is working on this in a more low key way, indeed rather secretive at times, with fewer public announcements is Blue Origin and there are several other Reusable launch systems that may or may not get developed in the future.
Then, China also is exploring re-usable launchers, see China Looks to Recover Booster Stages
And India is working on Avatar (spacecraft) - an unmanned reusable space plane which will be launched from a rocket, but eventually they hope it can launch horizontally.
And then there's Dream chaser reusable spacecraft under development
Several of these hope to be able to fly passengers to LEO eventually.
And of course the mini shuttle Boeing X-37 - not for passengers - used only for military flights at present, with some civilian "add ons".
For many more ideas that have been explored, some of them under active development - this answer consists mainly of an edited extract from a longer article, by me from my Science20 blog - see my Projects To Get To Space As Easily As We Cross Oceans - A Million Flights A Year Perhaps - Will We Be Ready?
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
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