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Sloped Ramps, Long Runways, and Heavy SSTO's


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During my time here I have heard many times how impractical heavy SSTO's are. The reasoning has mainly to do with the fact that chemical rocketry is less efficient when you use a single stage... since it requires more propellant and therefore turns the ship into a giant fuel tank with very little practical room for much of anything else.

 

I think I may have had a breakthrough though... and it is grounded.... mostly... in stuff we can actually do with a single exception which is point number one.

 

1. SSTO that weighs 8,000 tons and uses a runway and a ramp to take off. Relies on a pulsed fusion rocket with a large and thick bodied nozzle. Thrust can be throttled by detonating and expelling smaller fusion fuel or increased by detonating and expelling larger fusion fuel out the nozzle as plasma. Uses a vacuum reaction chamber lined with uber magnetic field generators which are able to compress  and fuse and expel fusion fuel out the nozzle. A plasma window separates the vacuum chamber from air that would enter from the nozzle otherwise on planets. If you want to use smaller nozzles you will need more of them to get the same thrust... yet the good thing is that you can also throttle thust back for each nozzle by using less fusion fuel for each one... therefore the nozzle can handle the pressure without needing to be as big as it would need to be otherwise

2. To take off the ship uses a moderately lower thrust fusion pulse to allow it to drive on wheels down the runway and up the ramp and off into the sky.

3. Last of all the ship continues to detonate and expel fusion fuel to reach orbit.

Conclusion: No I do not think we can currently do this as it requires uber magnetic fields that I doubt we can generate at such a scale of energy.

 

Yet the ramp and runway seem sound enough. The way I see it, if the main engine is in the rear, why bother with VTOL at all... especially for an 8000 ton SSTO? Chemical rocketry is inefficient for heavy SSTO's anyway.

 

 

Space: Since 8000 tons is a bit much to try to land using chemical rocketry onboard the ship, instead the 8000 ton ship will be an orbital cruiser, cruising from orbit to orbit.

 

Reentry: At the end of the mission the 8000 ton SSTO will return to it's homeworld to land. How? By using a really long runway and landing with wheels. That's how. It will likely have to pulse fire the main engines to get some horizontal velocity before landing on the runway.

 

Massive jet fans flanking the runway can slow the 8000 ton ship down more than it's wheels on the runway would, and eventually it comes to a stop.

 

Thoughts?

Edited by Spacescifi
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19 minutes ago, Spacescifi said:

Thoughts?

Once again, I see this curious fixation on a really unrealistic/unreasonable solution, and trying to invent a problem it can solve. Like the modern revival of the Zeppelin, it's an answer on a futile search for the right question. The base concept has massive drawbacks, yet you keep inventing new complications to justify it, rather than doing something about the fundamental approach. Which, again, is fine for sci-fi if that's what you want, story first and all that, but you seem to want to evaluate the concept in terms of realism, in which case reality keeps throwing more hurdles in your way the more you try to walk around them. Every "but what if we do it like this?" will give several handfuls more problems on top of the ones you already have. And yet, here we are at "but what if we do it like this?" thread number countless +1, still seemingly without willingness to adjust the base concept. 

The big conceptual question is: "Why single-stage?" What is the benefit of bringing this thing in one piece to and from the surface if it already needs to be compatible with a shuttle for personnel and cargo? The technology required to launch this thing would be overwhelmingly more advanced than an orbital shipyard anyway. And if it's only going to be used as an orbit-to-orbit cruiser, why must it ever land? Just service the thing in orbit.

Second, you seem to have realized one drawback of SSTOs, which is that they demand a very low mass fraction of cargo for the rocket equation to be forgiving in any way. But you don't seem to have taken into account that they also need to carry everything required to withstand aerodynamic forces as they travel through the atmosphere, both when ascending and re-entering. In this case, you seem to base the concept on horizontal velocity at low altitudes, which means oodles of drag, and you need the design to provide aerodynamic lift to get airborne at TWR < 1, which means large control surfaces, which once again add mass like crazy. And as you know from making aircraft in KSP, achieving the right balance for stable flight is no easy task either. And it has to survive reentry, even.

Then there's the "fun" job of carrying something that weighs 8000 tons on wheels, at takeoff speed. Never mind landing. 

And making the runway capable of withstanding "fusion pulse detonations" strong enough to push 8000 tons of mass up to takeoff speed. 

41 minutes ago, Spacescifi said:

Reentry: At the end of the mission the 8000 ton SSTO will return to it's homeworld to land. How? By using a really long runway and landing with wheels. That's how. It will likely have to pulse fire the main engines to get some horizontal velocity before landing on the runway.

Lose some horizontal velocity, you mean. When re-entering the atmosphere at orbital speeds, your problem is excess horizontal velocity, in spades.  Unless you somehow make a vertical re-entry profile, of course, in which case other problems will present themselves (and barely get past "hello" before you get to the crater phase of the confrontation).

And these are just the problems I can think of off the top of my head. They are not small and trivial problems with easy workarounds. The base concept has enormous flaws if examined through the lens of realism (as you seem to insist on doing). To be blunt, I am honestly a bit flabbergasted that this idea could be thought through by someone with a basic (KSP-level) grasp of engineering without the problems being immediately apparent as deal-breakers. 

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Posted (edited)
1 hour ago, Codraroll said:

Once again, I see this curious fixation on a really unrealistic/unreasonable solution, and trying to invent a problem it can solve. Like the modern revival of the Zeppelin, it's an answer on a futile search for the right question. The base concept has massive drawbacks, yet you keep inventing new complications to justify it, rather than doing something about the fundamental approach. Which, again, is fine for sci-fi if that's what you want, story first and all that, but you seem to want to evaluate the concept in terms of realism, in which case reality keeps throwing more hurdles in your way the more you try to walk around them. Every "but what if we do it like this?" will give several handfuls more problems on top of the ones you already have. And yet, here we are at "but what if we do it like this?" thread number countless +1, still seemingly without willingness to adjust the base concept. 

The big conceptual question is: "Why single-stage?" What is the benefit of bringing this thing in one piece to and from the surface if it already needs to be compatible with a shuttle for personnel and cargo? The technology required to launch this thing would be overwhelmingly more advanced than an orbital shipyard anyway. And if it's only going to be used as an orbit-to-orbit cruiser, why must it ever land? Just service the thing in orbit.

Second, you seem to have realized one drawback of SSTOs, which is that they demand a very low mass fraction of cargo for the rocket equation to be forgiving in any way. But you don't seem to have taken into account that they also need to carry everything required to withstand aerodynamic forces as they travel through the atmosphere, both when ascending and re-entering. In this case, you seem to base the concept on horizontal velocity at low altitudes, which means oodles of drag, and you need the design to provide aerodynamic lift to get airborne at TWR < 1, which means large control surfaces, which once again add mass like crazy. And as you know from making aircraft in KSP, achieving the right balance for stable flight is no easy task either. And it has to survive reentry, even.

Then there's the "fun" job of carrying something that weighs 8000 tons on wheels, at takeoff speed. Never mind landing. 

And making the runway capable of withstanding "fusion pulse detonations" strong enough to push 8000 tons of mass up to takeoff speed. 

Lose some horizontal velocity, you mean. When re-entering the atmosphere at orbital speeds, your problem is excess horizontal velocity, in spades.  Unless you somehow make a vertical re-entry profile, of course, in which case other problems will present themselves (and barely get past "hello" before you get to the crater phase of the confrontation).

And these are just the problems I can think of off the top of my head. They are not small and trivial problems with easy workarounds. The base concept has enormous flaws if examined through the lens of realism (as you seem to insist on doing). To be blunt, I am honestly a bit flabbergasted that this idea could be thought through by someone with a basic (KSP-level) grasp of engineering without the problems being immediately apparent as deal-breakers. 

 

No wings. Maneuvers with rocket RCS and main engines are used for forward thrust.

 

No wings needed for takeoff as the ramp will send the SSTO up anyway  From there it only needs to pulse thrust into space.

8000 tons is relative anyway for reentry, as some mass my have been shed (cargo delivery).

To shed horizontal kinetic speed you just flip over and pulse fire main engines as needed.

As for the exhaust it is a rocket plume, and I reckon the runway could be actively cooled to handle the heat from the plume.

 

I agree the challenges are severe, but they are not impossible from a physics standpoint if you allow for the number one exception of a heavy SSTO and a pulsed fusion rocket.

 

Physics does not say no, it just says it's difficult.

Edited by Spacescifi
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2 hours ago, Spacescifi said:

No wings. Maneuvers with rocket RCS and main engines are used for forward thrust

Then what’s the point of runway??  If we don’t have wings, why the heck are you going sideways?     The only reason to go sideways is to generate lift using wings and slowly (relatively) gain speed as you gain altitude.  
 

You have a magical super heavy craft capable of vertical flight, just go up.    

2 hours ago, Spacescifi said:
Edited by Gargamel
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A waterfall.

We need a sloped waterfall.

Then the rocket/non-rocket will accelerate along the water slope and damage nothing.

To make a water slope we need either a huge rotating centrifugal chalice, or a gas generator, blowing at the water and making the water surface parabolic (like the launch pool in huge rocket projects of 1950s-1960s).

Spoiler

81LkcDjpaoL._AC_SX466_.jpg

 

But as we already have a huge rocket, let her exhaust generate a water crater, so the rocket will be sliding up along its slope.

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9 hours ago, Spacescifi said:

No wings needed for takeoff as the ramp will send the SSTO up anyway  From there it only needs to pulse thrust into space.

How big do you envision this ramp to be? And how steep? I guess the idea is something like the barrel of an artillery gun, where the vessel builds up speed along a straight portion and exits it fast enough that the ballistic trajectory takes it into space. However, this would require the ramp to be several kilometers tall and hundreds of kilometers long. And capable of withstanding a live load of 8000 tons ... needless to say, that is foolery.

Alternately, it could work like a skateboard ramp, where speed is built up horizontally, then the ramp curves to direct the trajectory upwards. This would run into the same effect as rollercoaster trains do in loops: G-forces perpendicular to the direction of travel, which again necessitates an absolutely colossal ramp. And of course, there's the whole thing with gaining speed while in the thickest part of the atmosphere. 

9 hours ago, Spacescifi said:

No wings. Maneuvers with rocket RCS and main engines are used for forward thrust.

How do you envision a runway landing without wings? No wings means you'll be on a ballistic trajectory. And that means gaining a vertical velocity component of 9.8 m/s2, courtesy of gravity. If you plan to use RCS thrusters to cancel out this, you need those thrusters to be powerful enough to lift the whole thing vertically, which means packing a VTOL engine on board anyway.

9 hours ago, Spacescifi said:

8000 tons is relative anyway for reentry, as some mass my have been shed (cargo delivery)

If cargo is brought to its destination planet using a shuttle, the ship can be stocked at its orbital shipyard of origin using a shuttle, and you will never need the whole thing to land in an atmosphere anyway. Again, I ask, what is the point of making the heavy ship an SSTO?

9 hours ago, Spacescifi said:

To shed horizontal kinetic speed you just flip over and pulse fire main engines as needed.

In atmosphere? Aerodynamic forces are not your friends in that situation. And engineering the ship to withstand them (and perform a flip in atmosphere) means adding lots of mass and a large amount of other design constraints you can easily be without. Again, just build the dang thing in orbit.

9 hours ago, Spacescifi said:

As for the exhaust it is a rocket plume, and I reckon the runway could be actively cooled to handle the heat from the plume.

Consider the necessary length of the runway and the ludicrous amount of infrastructure you're proposing for this ordeal. Any engineering assessment would conclude, in the first thirty seconds, "just ditch the SSTO concept to solve the problem instead".

9 hours ago, Spacescifi said:

I agree the challenges are severe, but they are not impossible from a physics standpoint if you allow for the number one exception of a heavy SSTO and a pulsed fusion rocket.

Why do you insist on examining the physics from a realism standpoint if you're going to make exceptions for something as ludicrous as a heavy SSTO in the first place? 

 

9 hours ago, Spacescifi said:

Physics does not say no, it just says it's difficult.

Physics says, in flaming letters a thousand feet high, that IT'S A BAD IDEA. And you seem intent on trying to find new ways to ask "But is it a good idea if we just ... ?". The answer will still be the same.

Again I would point out the similarity to trying to improve horseback riding as a means of transport, by making powered rollerskates for the horse. 

Edited by Codraroll
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9 hours ago, Spacescifi said:

 

No wings. Maneuvers with rocket RCS and main engines are used for forward thrust.

 

No wings needed for takeoff as the ramp will send the SSTO up anyway  From there it only needs to pulse thrust into space.

8000 tons is relative anyway for reentry, as some mass my have been shed (cargo delivery).

To shed horizontal kinetic speed you just flip over and pulse fire main engines as needed.

As for the exhaust it is a rocket plume, and I reckon the runway could be actively cooled to handle the heat from the plume.

 

I agree the challenges are severe, but they are not impossible from a physics standpoint if you allow for the number one exception of a heavy SSTO and a pulsed fusion rocket.

 

Physics does not say no, it just says it's difficult.

Why? It is difficult, expensive and dangerous to roll huge speeds on ground. What that gives over vertical takeoff? You can not have wings with reasonable assumptions so you need TWR of greater than 1 at launch. If we talk about completely fictive fusion engines, TWR can be anything. If you need visually stunning scene in scifi movie, feel free to use a ramp, but it is hard to see any use in realistic scenarios.

Have you heard a physicist joke? Rich gambler asked mathematician to make a model  for predict horse race winners. Mathematician thought a minute and said no, there is too much too complicated things. I can not do it. Disappointed gambler went to engineer. Same answer, there are too much unknowns. Then it was physicist's turn. Physicist said, yes, of course, it takes two days. After two days he came with a fancy program. Gambler asked why you could do what other specialists could not? Physicist said. It was not difficult. Let's assume first, that horses are perfect spheres which moves in vacuum...

Edited by Hannu2
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The An-225 is reported to have been the heaviest aircraft in the world with a maximum take off weight of 640 tonnes. 

So we’re discussing a runway launched vehicle which is an order of magnitude heavier than the heaviest aircraft ever flown.

Regardless of any other issues with this proposal, neither the runway, nor the landing gear are going to be straightforward problems to solve in this scenario.

As others have pointed out, the lack of lift is also going to place significant extra requirements on the landing gear, given that it’s going to have to deal with a vehicle that’s pancaking in at terminal velocity and bring it to a controlled stop without breaking any of the airframe, the runway, or the crew.

 

Edited by KSK
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29 minutes ago, KSK said:

The An-225 is reported to have been the heaviest aircraft in the world with a maximum take off weight of 640 tonnes. 

Abandoned (by considered viable in their time) projects of 2 500 .. 4 500 t.

https://en.wikipedia.org/wiki/Beriev_Be-2500

https://en.wikipedia.org/wiki/Boeing_Pelican

https://en.wikipedia.org/wiki/TTS-IS

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1 hour ago, kerbiloid said:

All of them notable for using the ground effect principle, though. That's a fine principle with lots of interesting applications, but I'd say it's a little optimistic to use it for travelling to space.

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10 minutes ago, Codraroll said:

All of them notable for using the ground effect principle, though.

Only on takeoff and landing, if you read the articles.

The flight is at airplane altitude and speed.

***

Of course we should mention the (ta-dam! TA-DAM!!!) Aldebaran project.

Spoiler

Space World, April 1965hrovz0pbbxe31.jpg

It's a pulse rocketship, just like OP likes.

P.S.
It's sitting surprisingly high in water.

Edited by kerbiloid
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18 hours ago, Spacescifi said:

During my time here I have heard many times how impractical heavy SSTO's are. The reasoning has mainly to do with the fact that chemical rocketry is less efficient when you use a single stage... since it requires more propellant and therefore turns the ship into a giant fuel tank with very little practical room for much of anything else.

I think I may have had a breakthrough though... and it is grounded.... mostly... in stuff we can actually do with a single exception which is point number one.

It is grounded in stuff we can actually do, with a single exception, which is all of it.

Your latest fixation seems to have drifted to "fusion pulse with large and thick bodied nozzle with uber magnetic fields". None of those things make sense in connection with each other. If you have the capacity to control nuclear fusion then just heat your propellant using nuclear fusion and use regenerative cooling on your nozzle; no need for magnetic fields or a "thick bodied nozzle" (whatever that is supposed to mean).

18 hours ago, Spacescifi said:

A plasma window separates the vacuum chamber from air that would enter from the nozzle otherwise on planets.

I'm not sure why you would imagine that a fusion rocket engine delivering over 8,000 tonnes of thrust would have problems with air ENTERING the chamber.

18 hours ago, Spacescifi said:

To take off the ship uses a moderately lower thrust fusion pulse to allow it to drive on wheels down the runway and up the ramp and off into the sky. Last of all the ship continues to detonate and expel fusion fuel to reach orbit.

If your wingless vehicle can accelerate into orbit after yeeting off the end of a ramp, then its TWR was already greater than 1 to begin with, so the ramp and wheels were all unnecessary to begin with.

18 hours ago, Spacescifi said:

At the end of the mission the 8000 ton SSTO will return to it's homeworld to land. How? By using a really long runway and landing with wheels. That's how. It will likely have to pulse fire the main engines to get some horizontal velocity before landing on the runway.

No part of this makes sense.

If it has no wings then it will fall vertically into the ground.

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From what I'm gathering, the only large SSTO that would work isn't going to have stages; it's going to be a craft fitted out with anti-grav repulsors and Star-Trek engines.  Is that the state of current understanding?

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21 hours ago, Spacescifi said:

Yet the ramp and runway seem sound enough. The way I see it, if the main engine is in the rear, why bother with VTOL at all... especially for an 8000 ton SSTO? Chemical rocketry is inefficient for heavy SSTO's anyway.

You are conflating two things:

1) SSTO is inefficient for anything*

2) Chemical rockets are the only thing that is currently useful for achieving orbit

*) But science fiction ignores this for the sake of the story

and you keep ignoring that Bigger is Better when it comes to chemical rockets, and huge** is the only way to get chemical rockets to SSTO.

**) While SH+SS is huge for a TSTO, it *might* be big enough for a reusable SSTO that can actually do something useful, even if it would be terribly inefficient compared to the existing TSTO.

 

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And to repeat myself again, go back to the rocket equation.

Ramps, slopes, and runways only make sense if your TWR<1.  If the slope is low enough (or flat), you'll need wings.

SSTO implies "magical" Isp.  On the other hand, air-breathing engines tend to use such launch methods and can have enormous Isp.  One possibility is a ramped rail system (something like a linear induction motor) to get a ramjet/scramjet up to speed.

Note that even with all the advantages of the Isp of air-breathing engines, it still only gets that high Isp while in the atmosphere (and all the drag/heating that comes with it).  I'd expect 21st century rockets like this to leave the atmosphere at a respectable speed (mach 6-mach 12)  and then switch to rocket engines.  Going SSTO would still involve using shear technical power to make such things happen anyway.

Not to mention the clunkiness of working the explanation into a sci-fi novel would be fairly contrived: "as you know Bob, the unobtanium widgets allow us to bleed the compressed heat of the scramjet air into the bypass ducts and get enough velocity to make orbit".  Contrast it to a "golden age" work having two passengers flying from NYC to Paris in 2000 discussing how the jet engines work.  Except as far as I know, 2000 "jet" engines didn't work that way and are high-bypass turbofans.  Closer to turboprops than "real" jets (which are mostly confined to military use).  I guess you could always play it up for laughs by having Dr. Alice Bechtel saying "as you know Roberta...".

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Posted (edited)
On 7/13/2022 at 6:49 PM, Gargamel said:

Then what’s the point of runway??  If we don’t have wings, why the heck are you going sideways?     The only reason to go sideways is to generate lift using wings and slowly (relatively) gain speed as you gain altitude.  
 

You have a magical super heavy craft capable of vertical flight, just go up.    

 

Imagine if your SSTO has both VTOL and runway takeoff ability via a ramp.

 

If you use the ramp to launch upward then you can save your VTOL engine propellant for later when you really need it... namely landing on another world or for landing someplace other than a runway when you return to the homeworld.

 

As you know.... outer space is drier than the driest desert for liquids... and you have cross vast 'oceans' of outer space before you even reach a place to refuel.

 

 

Edited by Spacescifi
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28 minutes ago, Spacescifi said:

Imagine if your SSTO has both VTOL and runway takeoff ability via a ramp.

If you use the ramp to launch upward then you can save your VTOL engine propellant for later when you really need it... namely landing on another world or for landing someplace other than a runway when you return to the homeworld.

Using a ramp doesn't save you any propellant costs.

Using a ramp requires more dV than merely launching VTOL.

So this makes no sense.

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57 minutes ago, sevenperforce said:

Using a ramp doesn't save you any propellant costs.

Using a ramp requires more dV than merely launching VTOL.

So this makes no sense.

Using fusion fueled pulsed high thrust rockets as in the OP should require considerably less fuel mass than if one used the equivalent in chemical propellant to drive off up/on the ramp.

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3 hours ago, Spacescifi said:

Imagine if your SSTO has both VTOL and runway takeoff ability via a ramp.

Like this.

Spoiler

 

***

Makes sense only for helicopters, who can start either vertically (with normal cargo) or after runway running by wheels (when overloaded).

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22 hours ago, Spacescifi said:

Using fusion fueled pulsed high thrust rockets as in the OP should require considerably less fuel mass than if one used the equivalent in chemical propellant to drive off up/on the ramp.

If you are using fantasy drives, why not just assume that you can use them for VTOL as well?

Star trek and star wars do not even bother to put engines other than the ones at the rear, yet they still more or less VTOL.

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Posted (edited)
21 minutes ago, Terwin said:

If you are using fantasy drives, why not just assume that you can use them for VTOL as well?

Star trek and star wars do not even bother to put engines other than the ones at the rear, yet they still more or less VTOL.

 

Because scifi drives based on the power it would actually take to pull of such feats  likely leave craters behind.

 

My idea is that at a planetary spaceport you don't want craters.

 

The ship still has chemical rockets though for VTOL because again... who wants to labd inside a smoking crater?

Edited by Spacescifi
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22 minutes ago, Spacescifi said:

 

Because scifi drives based on the power it would actually take to pull of such feats  likely leave craters behind.

 

My idea is that at a planetary spaceport you don't want craters.

 

The ship still has chemical rockets though for VTOL because again... who wants to labd inside a smoking crater?

The whole point of fusion over fission is that fusion scales down.

Fission requires critical mass, providing a minimum possible blast, while fusion scales down to levels that are insufficient to even melt an entire snow flake.

Also, you are using fantasy engines, so they have whatever properties you want them to have.

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On 7/16/2022 at 7:24 PM, Spacescifi said:

 

Imagine if your SSTO has both VTOL and runway takeoff ability via a ramp.

 

If you use the ramp to launch upward then you can save your VTOL engine propellant for later when you really need it... namely landing on another world or for landing someplace other than a runway when you return to the homeworld.

 

As you know.... outer space is drier than the driest desert for liquids... and you have cross vast 'oceans' of outer space before you even reach a place to refuel.

 

 

Wut?

Without wings, a ramp is 100% useless.   Your craft doesn’t fly, it hovers.    And if it can vtol from the ground, it can vtol straight into space.    Your craft is fueled by magical unicorn farts, so it’s not a problem there.  
 

But let’s say we do try this ramp idea.   The TL:DR of the scenario is that a heavy lift space elevator is a much simpler civil engineering project than your ramp and runway would be.  

Let’s say your launch speed will be a small yet not insignificant fraction of your eventual orbital velocity, so let’s say 3,000kph when you hit the ramp.  

Take a look at the wheels on the rocket cars vying for the land speed record today.    They are huge aluminum discs with a tiny, TINY, contact patch     And this is for a car that only weighs a few tons.  Your craft would require TENS of thousands of wheels to not sink into the ground, with the engines turned off.    Now let’s add exploding unicorn farts coming out the back of a craft the mass of  a World War II light cruiser sitting on ten thousand pizza cutters.     Then when this rolling death trap to tarmac reaches a few Mach, it runs into a ramp.    There isn’t a structure or material imaginable able to withstand this device.    Even if the craft did manage to survive yeeting itself airborne, the runway and ramp would be demolished and require a complete rebuild every launch.   
 

But all of that is still ignoring the fundamental problem with this idea:

There is zero, Zero, ZERO benefit to horizontal motion on the ground for a craft that doesn’t have wings.

 

 

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