How To Dodge The Waste Heat Bullet As A Heavy Scifi Rocket SSTO....

[Spacescifi]

Some will say waste heat no matter the energy can be managed as long as you burn enough propellant to get rid of it. In practical terms what that means is more rocket nozzles/ engines, since there is a practical limit to how fast you can pump propellant into a reaction chamber, but there is theoretically no limit except practicality for how many nozzles or engines you put on an SSTO.

In scifi SSTO VTOL belly landers/taker offers are commonplace. Yet if you apply IRL science and math to them one quickly realizes that the energy required to fly to space without using up most or all of the propellant on a 300 ton SSTO would also melt the engine... unless you used disposable staging at lower efficiency but then it is no longer SSTO.

The secondary problem of using greater fuel flow to solve waste heat issues of heavy scifi SSTOs is the fact that it trades one problem for another. The whole point of a scifi SSTO is to try and take 10% propellant mass and get to space without using most or all of it up. So for a 300 ton SSTO that means 30 tons of propellant to get 270 tons of SSTO to space orbit without exhausting all or even most of it. Instead you would only use 10% of 30 tons to reach orbit, which is 3 tons.

If you increase your propellant flow you run out faster and you will need more than 10% propellant, which eventually means your spaceship is back to a large propellant tank with a tiny payload... which defies the entire point of a heavy scifi SSTO.

Scifi ways of dodging waste heat: If you don't want to waste more propellant just add extra energy to propelling it. Normally this is limited by how much heat an engine can tolerate... but what if the reaction happened OUTSIDE the engine?

Scifi Scenario: Scifi rocket nozzles are like super batteries that can store enough electrical energy to equal their mass/weight at maximum. They can convert the stored energy with 100% efficiency into tactile kinetic energy. In practical terms what this means is a liquid sprayer down the throat of each nozzle sprays propellant down the inner walls of the nozzle. Yet when the nozzles' tactile kinesis is activated the propellant squirted down them is moved so fast it ionizes and become a plasma plume as it exits the nozzles.

Main Question: It costs no waste heat to convert the stored electrical energy of the nozzles into tactile kinetic energy... because of scifi conceit. Yet I am also aware that moving propellant fast enough to heat it would ALSO heat the nozzle from the sheer heat the propellant is generating as it is accelerated out the nozzle. So have I dodged the waste heat bullet with my scifi conceit? Or have I just made the matter much worse? Meaning that the plasma plume is so hot it begins to melt the nozzles... which releases all their stored electrical energy at once with a blast that would wipe a small country off the face of the earth.

 

I dunno.. I would like to think that the heat on a rocket nozzle from a plasma plume thrusty and efficient enough to burn 3 tons of propellant to orbit carrying 297 tons of propellant/SSTO could be managed with regenerative cooling but I dunno. Granted if we use multiple nozzles... like 16 you divide that heat by 16 so it's not as much. Or maybe it requires a hundred... I dunno.

Or maybe 3 tons is just unrealistic and I would need to use more to reach orbit, like ten tons... and just refeuel in orbit with a fuel tanker.

 

Thoughts?

Edited April 13, 2023 by Spacescifi

[Shpaget]

In early 23rd century, with the discovery of I-Can't-Believe-It's-not-Paper (digital, cheaper, better alternative to paper), the world finally went almost completely paperless, effectively collapsing the inkjet cartrige market almost overnight. Luckily for HP, they've been diversifying for a while, and invested heavily into space propulsion tech.

Refuelling your SSTOs has never been easier and more convenient. Call your HP representative and schedule a refuelling appointment at the time of your choosing at any of the 73 space ports on Earth and 34 off world stations. Replacing your launch licence chip and HP Fuel Cartriges takes mere minutes. We would like to remind you that both HP Planetary Launch Drive Fuel Cartrige*, as well as HP Space Drive Fuel Cartrige are needed for launch and space travel. Both cartriges are integrated in one convenient unit and need to be replaced at the same time. It is not possible to transfer unused fuel to a new cartrige. Your HP representative will take care of your spent fuel cartriges and safely transport then for recycling. Your HP representative will also perform a diagnostics check of your HP Drives and inform you of the upcoming HP Drive Licence expiration dates.

 

*HP Planetary Drive Fuel Cartrige contains enough fuel for 17 launches OR landings at any rocky body in the solar system.

 

That's all your reader needs to know about fuel usage in fiction, unless you want to go hard SF, but then forget doing 10 orbital launches without refuelling.

[Terwin]

On 4/13/2023 at 8:35 AM, Shpaget said:

That's all your reader needs to know about fuel usage in fiction, unless you want to go hard SF, but then forget doing 10 orbital launches without refuelling.

Only if you want to SSTO from a large body.

Demios has an escape velocity of only 20kph, letting you both land and launch with only about 12m/s/s of thrust.  This would let a MMU land and liftoff twice before running out of fuel, and any 'real' rocket could probably do a lot more.

 

But for earth?  Any realistic rocket using less than 50%  of it's wet-mass as propellant to get to orbit is pure fantasy.  (the real number is probably above 80%, but I am willing to allow for new technologies like rotating detonation engines getting that number lower, just not *that* much lower)  

[magnemoe]

34 minutes ago, Terwin said:

Only if you want to SSTO from a large body.

Demios has an escape velocity of only 20kph, letting you both land and launch with only about 12m/s/s of thrust.  This would let a MMU land and liftoff twice before running out of fuel, and any 'real' rocket could probably do a lot more.

But for earth?  Any realistic rocket using less than 50%  of it's wet-mass as propellant to get to orbit is pure fantasy.  (the real number is probably above 80%, but I am willing to allow for new technologies like rotating detonation engines getting that number lower, just not *that* much lower)  

Agree, yes its systems  like antimatter or nuclear salt water but you don't want to irradiate the planet. Also lots of fusion engine concepts will not work in an atmosphere. 
One potential way to get high trust is to have the fusion happen outside the ship and control the plasma with magnetic fields. This way gamma rays and neutrons mostly escape. 
This will not work in an atmosphere. 

Now very good fusion reactors is probably your best bet, use the helium ions created to heat up air for the first part, then heat up reaction mass once out of atmosphere. In space you simply use the helium exhaust as an very high isp but much lower trust, still an touch ship  but far lower than 1 g trust. 

But  its not much of an issue refueling after each flight. Planes does. Yes you might use an long range plane for an pretty short trip, say Stockholm to Paris. In this case you don't top up the fuel tanks as you will just use more fuel carrying the extra fuel around.
For transatlantic flights planes carry so much fuel plane has to dump or burn fuel to land, for shorter flight they can just turn around and land. Experienced both. 
First was an national flight who could not retract the nose wheel. Second was an navigation system fail on a transatlantic one. 
 

[Codraroll]

The word "Scifi" is in there, which greatly lowers the difficulty of the question into a simple two-step process:

1) Pretend it's not an issue. It's fiction.

2) See 1.

 

[Spacescifi]

9 hours ago, magnemoe said:

Agree, yes its systems  like antimatter or nuclear salt water but you don't want to irradiate the planet. Also lots of fusion engine concepts will not work in an atmosphere. 
One potential way to get high trust is to have the fusion happen outside the ship and control the plasma with magnetic fields. This way gamma rays and neutrons mostly escape. 
This will not work in an atmosphere. 

Now very good fusion reactors is probably your best bet, use the helium ions created to heat up air for the first part, then heat up reaction mass once out of atmosphere. In space you simply use the helium exhaust as an very high isp but much lower trust, still an touch ship  but far lower than 1 g trust. 

But  its not much of an issue refueling after each flight. Planes does. Yes you might use an long range plane for an pretty short trip, say Stockholm to Paris. In this case you don't top up the fuel tanks as you will just use more fuel carrying the extra fuel around.
For transatlantic flights planes carry so much fuel plane has to dump or burn fuel to land, for shorter flight they can just turn around and land. Experienced both. 
First was an national flight who could not retract the nose wheel. Second was an navigation system fail on a transatlantic one. 
 

 

Unless you are doing the Star Trek thing where ISRU do it yourself is the only way to refuel your propellant.

Fortunately the drive is not my only scifi gimmick. Another propellant saver is a slower than light vacuum translation drive which translates or moves space past the ship at the same rate of it's current acceleration. So just do a  quick 3g burn, shut it off, and let the translation drive let you slow warp at 3g. Once dropped out of warp, speed and heading returns to normal... meaning you can get places a lot faster because you do not have to accelerate all the way there and retroburn to slow down nearly as much.

So use this to get close to ice. Mine it. And refuel. Vacuum translation drive only works in vacuum though.

[Terwin]

14 hours ago, Spacescifi said:

Vacuum translation drive only works in vacuum though.

Compared to what?

Interstellar space(1/10 particles per cc) is a vacuum compared to the solar wind, the solar wind(5 particles/cc) is a vacuum compared to the surface of the moon, the surface of the moon(10^4-10^5 particles/cc) is a vacuum compared to Mars, and Mars(0.02 kg/m^3) is a vacuum compared to earth, and earth(1.3kg/m^3) is a vacuum compared to Venus, and Venus(65kg/m^3) is a vacuum compared to Jupiter(25,000 mile deep ocean of liquid metallic hydrogen).

Can it enter the solar system?  Can it land on the moon? Can it land on Mars?  Can it land on Earth? etc.

If you are trying to write a story, spending all your time coming up with rules about the universe is a backwards way to do it.

First you come up with the story, then you identify interesting complications that can be added to the story.  

Only then are you in a position to do general world-building, and it must be constrained by your story.  (and every question you ask would need to include the relevant story-beat details so helpers know the constraints)

And frankly, anything that involves startrek-style shuttles is science-fantasy at best.

[magnemoe]

15 hours ago, Spacescifi said:

Unless you are doing the Star Trek thing where ISRU do it yourself is the only way to refuel your propellant.

Fortunately the drive is not my only scifi gimmick. Another propellant saver is a slower than light vacuum translation drive which translates or moves space past the ship at the same rate of it's current acceleration. So just do a  quick 3g burn, shut it off, and let the translation drive let you slow warp at 3g. Once dropped out of warp, speed and heading returns to normal... meaning you can get places a lot faster because you do not have to accelerate all the way there and retroburn to slow down nearly as much.

So use this to get close to ice. Mine it. And refuel. Vacuum translation drive only works in vacuum though.

I assumed shuttle launched from a mothership who would carry fuel for shuttles like an aircraft carrier carry jet fuel for the planes as an worst case, if you launch from an spaceport you would refuel at ground.
You could use an fusion powered shuttle for interplanetary missions a bit like how SpaceX plan to use Starship.  But shuttles tend to be better as you want ship comfort for month long flights but plane level comfort works for hours. 

[StrandedonEarth]

On 4/17/2023 at 10:35 AM, Codraroll said:

The word "Scifi" is in there, which greatly lowers the difficulty of the question into a simple two-step process:

1) Pretend it's not an issue. It's fiction.

2) See 1.

 

You forgot something…

1a) Add copious amounts of handwavium

[Codraroll]

24 minutes ago, StrandedonEarth said:

You forgot something…

1a) Add copious amounts of handwavium

I prefer to call it the "five-finger oscillating motion device". Solves every problem in sci-fi.

[Shpaget]

What happens if somebody starts moving about the ship just as this vacuum translation thing cones online? Do they continue to accelerate through ship walls?

What about moving parts of the ship itself, or even the structure of the ship that is certainly experiencing some vibration? Your ship would disintegrate as soon as you turn this on.

[KSK]

On 4/18/2023 at 5:46 PM, Terwin said:

If you are trying to write a story, spending all your time coming up with rules about the universe is a backwards way to do it.

First you come up with the story, then you identify interesting complications that can be added to the story.  

Only then are you in a position to do general world-building, and it must be constrained by your story.  (and every question you ask would need to include the relevant story-beat details so helpers know the constraints)

I’m always a bit wary when folks get all prescriptive about writing, since I doubt that any two writers have exactly the same process.

Your way is certainly one way of doing it but it’s not difficult to think of counterexamples.

Sometimes a widget that can do x, y, or z is central to the story - and might be the initial idea behind the story. In which case, figuring out some ground rules about how the widget works might be a sensible place to start (for consistency if nothing else) and might be a way of coming up with those interesting complications to add to the story.

Likewise (and here I have personal experience), general worldbuilding can be the framework that makes the story and holds it together. It’s not necessarily something that’s just painted on at the end.

I do agree that there’s a point at which it’s probably more useful to just present the reader with ‘a widget that does x’ rather than bombarding them with screeds of technobabble to justify it. Where that point is, is harder to define.

 

Edited April 19, 2023 by KSK