Sloped Ramps, Long Runways, and Heavy SSTO's

[kerbiloid]

4 hours ago, Terwin said:

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.

They are not nozzles, they are smoke pipes. Just they smoke with photon gas.

They are calmly lighting, but don't produce thrust or damage anything behind.

 

59 minutes ago, Gargamel said:

Then when this rolling death trap to tarmac reaches a few Mach, it runs into a ramp.

Monorail.

We need a monorail.

Spoiler

 

[KSK]

1 hour ago, kerbiloid said:

They are not nozzles, they are smoke pipes. Just they smoke with photon gas.

They are calmly lighting, but don't produce thrust or damage anything behind.

Mood lighting. It's a little known fact that the main engines on the Executor can be set to rhythmically flash in 'Disco' mode when Lord Vader is feeling particularly funky.  The reason that you don't see this in the films is because Lord Vader rarely feels funky.

Edit. Another little known fact is that the Executor's engines are absolutely based on de Laval nozzles. Lord Vader took a keen interest in their design and personally ensured that the nozzles were properly choked. Scuttlebutt at Kuat Drive Yards says that "he found their lack of Isp disturbing."

Edited July 18, 2022 by KSK

[jimmymcgoochie]

Why bother with a slope at all? Just make the ramp perfectly flat, ignore the curvature of the planet and just drive up it into space.

Space elevators are SSTO when you think about it, plus they don’t need propulsion systems powered by little children’s birthday cake candle wishes or bulldozing a straight line across an entire continent to make them happen.

A shipping container going from A to B might need a truck to take it from A to a train to take it to a ship to take it to another train to take it to another truck to take it to B; the container ship doesn’t do the whole journey, so why should space cargo be any different? Specialisation brings efficiency: the deep space vessel can be optimised for that role, the means of transporting cargo to/from the surface of a planet can be optimised for that role (cough space elevator cough) and there’s no need for a spaceship, probably built in space, to ever not be in space.

[kerbiloid]

1 hour ago, KSK said:

Another little known fact is that the Executor's engines are absolutely based on de Laval nozzles. Lord Vader took a keen interest in their design and personally ensured that the nozzles were properly choked.

This was done intentionally, in hope that de Laval reflectors make the rays parallel.

[sevenperforce]

8 hours ago, kerbiloid said:

10 hours ago, KSK said:

Another little known fact is that the Executor's engines are absolutely based on de Laval nozzles. Lord Vader took a keen interest in their design and personally ensured that the nozzles were properly choked.

This was done intentionally, in hope that de Laval reflectors make the rays parallel.

Lord Vader needed to fake a moon landing and had to come up with a parallel light source to do it.

[KSK]

1 hour ago, sevenperforce said:

Lord Vader needed to fake a moon landing and had to come up with a parallel light source to do it.

That wasn't a moon...

"It's an older meme, sir, but it checks out."

[Vanamonde]

Stick to the topic, please. 

[Codraroll]

4 hours ago, Vanamonde said:

Stick to the topic, please. 

Not sure how much more could be brought to the topic, but perhaps I can try a summary?

@jimmymcgoochie said it, but I think it bears repeating: 

17 hours ago, jimmymcgoochie said:

Specialisation brings efficiency: the deep space vessel can be optimised for that role, the means of transporting cargo to/from the surface of a planet can be optimised for that role (cough space elevator cough)

 I think this is a really important crux of the whole matter. Moving stuff to/from surface to orbit is a specialized task, moving stuff between planets is another specialized task, and trying to make the same craft do both makes it kinda bad at either job. Barring magic technology, of course, but ... nah, possibly even then. SSTOP (Single stage to Other Planets) is like building a container ship that takes cargo between two inland cities without navigable waterways. It would be a quite crappy land craft, and the modifications required for it to even work on land would make it a bad seafaring ship as well. And for the sake of the analogy, the shipbuilder insists on staying within the realm of surface travel even when everybody shouts "just use aircraft!" at the top of their lungs.

That is not saying SSTO isn't necessarily useful, it could definitely be as long as it only hauls as much mass as it has to. It must be specialized to go to orbit, nothing more. Of course, SSTO shouldn't be an end goal in itself, efficient transport to orbit should. As far as current engineering limitations are concerned, that means multiple reusable stages à la Starship or a space elevator, but if you can handwave a good reason why the ship can haul its entire first stage to space without losing performance, go for it. Cargo and passengers should then be transferred to another craft that is specialized for transport to other planets, but that doesn't need all the complicated stuff required to navigate an atmosphere, land on a surface, and take off afterwards. 

Of course, if you want Star Wars-level craft that can take off from one planet carrying hundreds of tons of cargo and fly it to another planet, then exchange its load and fly home with a different set of cargo, possibly without refueling on its way ... then you can of course do so, but you have to accept that it's as much of a stretch of reality as the Force is.

[snip] The answer is always "Yes, in sci-fi you can pretend it works, but in real life this and this and this and this and this and this would make it a terrible idea", and the only form of acknowledgement seems to be "Oh, so it's a good idea if we just ____", with "____" being something that was never brought up among the counterpoints at all. The insistence on discussing these topics in the context of real life physics, but constantly failing to acknowledge the limitations of real life physics, gets a bit exhausting over time.  Especially when the threads usually revolve around the same few topics too.

Edited July 19, 2022 by Vanamonde

[sevenperforce]

On 7/17/2022 at 4:57 PM, Spacescifi said:

On 7/17/2022 at 4:34 PM, 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?

You are correct that in order to get single-stage interplanetary spaceships, you're going to need a very high-energy propulsion system. And you are correct that the kind of high-energy propulsion system you will need to make it to another world and back without staging or refueling is going to tend to produce rather spectacular damage to anything close to the exhaust flow.

However, there are a number of solutions to this, most of which are much simpler than the solutions you have suggested. As I've said in this thread and others, if you want the solutions you've suggested simply because you like their aesthetic, that's great, but they are by no means the inevitable outcome.

If you want to avoid melting your launchpad, then you can always use an afterburner. Afterburners sound like something that would cause more damage, not less, but afterburners on rockets do the opposite. If you have an extremely high-energy engine and you dump extra propellant into the nozzle downstream of the throat, you increase thrust dramatically but decrease the velocity of your exhaust. Then, as your vehicle climbs, you can maintain the main throttle while throttling down your afterburner injection to increase specific impulse when you no longer need quite as much thrust.

The easiest way to throttle down for landing is to simply use clustered engines. Each engine in the cluster can have its own afterburner for launch, after all, and so using fewer engines to land will give you whatever throttle setting you want.

The only situation where it would make sense to use completely separate engines for landing is if your super-high-energy main engine cannot be throttled and needs to be huge in order to work at all. Then sure, use separate landing engines. You can use these same landing engines to provide added liftoff thrust, too -- the gravity drag savings will make up for the lower specific impulse.

Launch ramps make sense exactly never, unless the ramp itself is providing the impulse.

[snip]

Edited July 19, 2022 by Vanamonde

[Vanamonde]

Some comments removed. 

Firstly, please stick to the subject of the thread rather than talk about the other people in the thread.

Secondly, if someone's posts really bother you, don't read them, or even simply set that person to ignore. Don't waste your time writing out why that person's posts bother you. Just go do something fun instead.

Thirdly, nobody is born knowing everything and asking questions is how we learn. Nobody benefits from shaming the person who asks. 

[Spacescifi]

 

The magnetic hoverboard uses liquid nitrogen and superconducting magnets to allow it to hover over magnetic surfaces.

 

In theory, an SSTO could launch this way using a ramp.

To return it could just land by using a powered thrust landing via ship chemical rockets.

 

My whole point was to rationalize the classic scifi belly lander spaceship with the engines in rear...but IRL you would need belly engines as well to survive a powered thrust landing. Rear overpowered pulse engines would mean that keeping them in the rear rather than landing with them (in lava) is the safe choice... thus the need for landing rocket engines and the more efficient and powerful rear pulsed fusion rockets for reaching space.

Wings would allow you to glide to land but are otherwise useless for reentry and space travel in general.

 

In practice for a spacecraft I think what Lexus did would have to be inverted.

 

In other words, make a superconducting chilled runway and ramp, then use a spacecraft with a magnetized belly to boost it's rear engines and half-loop launch into the sky.

 

I suppose one could land using wings to glide over a superconducting surface as well.

 

So if you want to land an 8000 ton space freighter in one go without rocketry, you need a lot of wing and a lot of superconducting runway and a magnetic underbelly on the spaceship.

Otherwise it would have to trade cargo space for propellant for a powered thrust landing.

As for shape, I think a blunt edged disc would be best, either winged or without. If winged the wings must be able to sweep all the way backward to avoid reentry damage. If un-winged it will be a clumsly flyer but will be able to land or launch so long it has propellant.

 

Pulsed fusion being more efficient would not take nearly as much fuel, since it would rely on meter wide snowballs enriched with fusion fuel per pulse.

Edited July 20, 2022 by Spacescifi

[Terwin]

6 minutes ago, Spacescifi said:

In theory, an SSTO could launch this way using a ramp.

This does not in any way reduce the force that the ramp would need to apply to the space ship, nor the forces that the ramp would need to undergo during a launch.

If anything, this makes the problem harder as you no longer have anything keeping your vessel from sliding off to the side of the ramp and greatly limits the strength of the materials you can use for the surface of the ramp.

You would also need a magnetic field strong enough to hold up that 8 kiloton vehicle, and I have serious doubts that a fixed magnet can manage that much force in the area available.(and if it can, it may be a bigger hazard than the engines.  Such a strong magnet right next to the engines would also likely cause problems with your magnetic nozzle.

This also does not in any way address the issue of losses due to high speeds low in the atmosphere nor the need to make a 90 degree turn so to change the rocket from horizonal to vertical(Rear engines with no wings = falling with a high horizontal velocity unless you are vertical)

[Codraroll]

1 hour ago, Spacescifi said:

In other words, make a superconducting chilled runway and ramp

If you have the funds and the technology to make this thing (remember the necessary size of the ramp), you're long past the stage where SSTOs could net you any savings whatsoever. You could possibly launch the ship in chunks carried by the freakin' SLS, and assemble it in orbit, and throw the entire ship away at the end of every mission, and still come out with lower operations costs. 

1 hour ago, Spacescifi said:

Wings would allow you to glide to land but are otherwise useless for reentry and space travel in general.

But they are pretty much essential if you want to get out of or into the atmosphere in any other way than a conventional rocket, which you keep on insisting.

1 hour ago, Spacescifi said:

So if you want to land an 8000 ton space freighter in one go without rocketry, you need a lot of wing and a lot of superconducting runway and a magnetic underbelly on the spaceship.

Otherwise it would have to trade cargo space for propellant for a powered thrust landing.

That "a lot of wing and the magnetic underbelly" would require a lot more concessions to cargo space (and importantly, mass) than the propellant required for a powered thrust landing. Never mind the runway.

Edited July 20, 2022 by Codraroll

[Spacescifi]

1 hour ago, Terwin said:

This does not in any way reduce the force that the ramp would need to apply to the space ship, nor the forces that the ramp would need to undergo during a launch.

If anything, this makes the problem harder as you no longer have anything keeping your vessel from sliding off to the side of the ramp and greatly limits the strength of the materials you can use for the surface of the ramp.

You would also need a magnetic field strong enough to hold up that 8 kiloton vehicle, and I have serious doubts that a fixed magnet can manage that much force in the area available.(and if it can, it may be a bigger hazard than the engines.  Such a strong magnet right next to the engines would also likely cause problems with your magnetic nozzle.

This also does not in any way address the issue of losses due to high speeds low in the atmosphere nor the need to make a 90 degree turn so to change the rocket from horizonal to vertical(Rear engines with no wings = falling with a high horizontal velocity unless you are vertical)

 

The rocket nozzle won't be magnetized. The reaction chamber uses magnetic fields for compression and redirection of fusion blasts out the vacuum chamber into and out of the throat of the rocket nozzle.

 

It seems this is less a no go and more a matter of finding a mass sweet spot for an SSTO.

100 ton SSTO is a lot more doable.

Perhaps 1000 tons is pushing it but may be possible.

And yes... even I agree 8000 tons is extreme for an SSTO. But it is relevant to know what is the heaviest an SSTO should practically be in this setting.

 

I think lifting on par with Starship (SpaceX) but with my SSTO design would be totalky possible... at the very least. With the difference that unlike Starship it would carry less liquid propellant since it would use it's super thrusty and efficient fusion pulse main engines to slow it's descent before flipping belly first to use it's belly chemical engines for a powered descent.

 

Starship stats are only a rough estimate.

How many tons can a Starship carry?

 

The Starship has a dry mass of 85 tons and has a propellant capacity of 1200 tons. The ascent payload capacity is 150 t to low earth orbit and it has a return capacity of 50 t. The Starship is to reenter belly-first with two aft fins and two canards provide skydiver-like

32 minutes ago, Codraroll said:

If you have the funds and the technology to make this thing (remember the necessary size of the ramp), you're long past the stage where SSTOs could net you any savings whatsoever. You could possibly launch the ship in chunks carried by the freakin' SLS, and assemble it in orbit, and throw the entire ship away at the end of every mission, and still come out with lower operations costs. 

But they are pretty much essential if you want to get out of or into the atmosphere in any other way than a conventional rocket, which you keep on insisting.

That "a lot of wing and the magnetic underbelly" would require a lot more concessions to cargo space (and importantly, mass) than the propellant required for a powered thrust landing. Never mind the runway.

 

I do not care so much that it is difficult... only that it CAN be done. At any rate the lightest weight one can go with still a reasonable payload ought to be interesting.

 

And the magnetic hover tech is just too cool anyway not to use!

Edited July 20, 2022 by Spacescifi

[Terwin]

2 hours ago, Spacescifi said:

I do not care so much that it is difficult... only that it CAN be done. At any rate the lightest weight one can go with still a reasonable payload ought to be interesting.

 

And the magnetic hover tech is just too cool anyway not to use!

The 'difficulty' is more expense and mass fraction than anything else.

If you want a realistic vehicle using all of these wiz-bang ideas without ignoring realism, you should expect your 8kiloton STO to have a useable payload of perhaps 50 tons, and costs that might bankrupt a level 3 civilization with each launch.

[Spacescifi]

29 minutes ago, Terwin said:

The 'difficulty' is more expense and mass fraction than anything else.

If you want a realistic vehicle using all of these wiz-bang ideas without ignoring realism, you should expect your 8kiloton STO to have a useable payload of perhaps 50 tons, and costs that might bankrupt a level 3 civilization with each launch.

 

I am willing to make lighter weight SSTOs that are 100 tons.

I am not married to the idea of SSTOs being the end-all... I recognize the value of two stage orbital cruisers.

 

But without SSTOs orbital cruisers are just that... forever stuck in orbit.

 

Ultimately I see orbital cruisers carrying one or two large SSTOs sitting outside the hull.

 

Even SSTOs could be optimized... wingless for non-air moons, winged for anywhere with atmosphere.

Having a pair helps.

Edited July 21, 2022 by Spacescifi

[kerbiloid]

5 hours ago, Spacescifi said:

To return it could just land by using a powered thrust landing via ship chemical rockets.

Why bother with powered landing?

Spoiler

Just attach the landing sleds.

 

 

5 hours ago, Spacescifi said:

make a superconducting chilled runway and ramp

Some call it maglev.

[Codraroll]

8 hours ago, Spacescifi said:

I do not care so much that it is difficult... only that it CAN be done.

OK, let me put it this way: Has any responses to this thread in any way indicated that it can be done?

[Terwin]

14 hours ago, Spacescifi said:

I am not married to the idea of SSTOs being the end-all... I recognize the value of two stage orbital cruisers.

 

But without SSTOs orbital cruisers are just that... forever stuck in orbit.

Why?

Starship is designed to land on earth after launching SSTO from mars(where SSTO is much more reasonable).

Launching from earth requires a SH first stage, but Starship is fine making orbit from mars or the moon, and even has dv left for going somewhere.

14 hours ago, Spacescifi said:

Ultimately I see orbital cruisers carrying one or two large SSTOs sitting outside the hull.

If you want Star Trek type adventures, your engines(and shuttle craft/transporters) will need to be fantasy, not hard sci-fi. 

Nothing realistic can manage Star Trek, even in a size-constrained multi-system like the 'verse from Firefly.

[Spacescifi]

8 hours ago, Terwin said:

Why?

Starship is designed to land on earth after launching SSTO from mars(where SSTO is much more reasonable).

Launching from earth requires a SH first stage, but Starship is fine making orbit from mars or the moon, and even has dv left for going somewhere.

If you want Star Trek type adventures, your engines(and shuttle craft/transporters) will need to be fantasy, not hard sci-fi. 

Nothing realistic can manage Star Trek, even in a size-constrained multi-system like the 'verse from Firefly.

 

I do not plan on mimicking Star Trek totally.

You can indeed design SSTO's like starship that can land on their own and SSTO off low gravity worlds.

To mimic star trek IRL, you need large SSTO's period, since as I already stated..  landing in lava because of an overpowered pulse fusion rocket is bad... which is why I recommend less efficient chemical rocket engines for landing/lift off... and of course flipping upward to use the more powerful and efficient fusion pulse engines to reach space.

 

Can we do it now?

 

Doubt it. Yet pulsed fusion is something we KNOW how to do... containing it is what's hard.

Naturally enough in a scifi setting with hyperspace/warp FTL, fusion tech should be old and established as the automobile.

 

To be sure you do not even need the magnetic surfaces or hover tech... that is just a cool technology that has manifold applications.

 

As for engines... yes I see the folly in one big nozzle.

 

I am thinking a wiser design is a cluster ring of chemical rocket nozzles surrounding a somewhat larger one in the middle that is the fusion pulse nozzle.

 

That way the ship can throttle easier and only use the overpowered engine when it desires to. Which is very important for any orbital rendezvous.

Edited July 22, 2022 by Spacescifi

[kerbiloid]

3 hours ago, Spacescifi said:

To mimic star trek IRL

Countless is the devastation caused by Star Trek in the Western sci-fi...

3 hours ago, Spacescifi said:

Naturally enough in a scifi setting with hyperspace/warp FTL, fusion tech should be old and established as the automobile.

If they have a portable fusion reactor, it would be some kind of low-power cold fusion, and the spaceship doesn't need a 100 hoarse powers engine.

(Unless it's a lifeboat in orbit).

3 hours ago, Spacescifi said:

magnetic surfaces or hover tech...

on launch are required only to probide the difference between the ship lifting force and weight while the horizontal speed is to low.
For a wingless rocket, the T/W doen't depend on speed and thus a slope isn't needed.

***

Also the single large nozzle can't be scaled down.

Does anybody use the 7 MN F-1?

While the 4x2 MN RD-170 is in profuction for the last forty years. Because splitted into the 2x2 MN RD-180 and 1x2 MN RD-191.