Torchship SSTO's... Why and How?

[Spacescifi]

While I am aware why 2 staging is superior, if we actually did have rocket engines powerful enough to enable SSTO's, would they not be huge?

Which is ironic since smaller nozzles are preferred for launch, but a heavy SSTO would likely need a big nozzle to diffuse the torchship heat from melting it.

I suppose with torchship energies, launching with a giant vacuum nozzle into orbit is your only option, since smaller nozzles may melt.

Why make heavy torchship SSTO's?

 

Seems to me SSTO's are basically best for ferrying or shuttling payloads to or from planets.

 

SSTO' torchships should NOT be designed for long distance cruising in space.

 

Rather actual long distance space cruisers should be 2nd stage vehicles.

While SSTO's should be shuttle ships, but huge, unlike the tiny van-size ones Star Trek uses.

 

Likely real future spaceships will be stacks or racks of spaceships linked together, detaching at will for whatever mission is required.

 

There won't be jack of all trades vessels, rather, spaceships will be like a combo pizza or swiss army knife with various tools... in this case ships of various kinds will link as a supership.

 

No mothership, just a bunch of ships stacked or linked together, because in space you can link stuff on indefinitely... so long the inertia load is not greater than engine thrust.
 

You have endless amounts of free space... may as will use it efficiently.

You do not need a big cargo hold in space since you can literally just link up with anything you want.

 

The only ship that needs a large cargo hold IS an SSTO.

 

Scifi miseducates the public in so many ways it's not funny. Everyship needs a cargo hold in pop scifi... when in reality it pays to optimize space only ships and then shuttle only ships.

 

Huge Shuttle SSTO freighters will be a thing.

 

Millennium Falcon? No. Since making a full on optimized war vessel would do better than an SSTO optimized for doing SSTO with weapons added on as an after thought.

Edited September 17, 2021 by Spacescifi

[SOXBLOX]

You'll need a lot more than a big nozzle to dissipate torchdrive level waste heat.

[Spacescifi]

6 minutes ago, SOXBLOX said:

You'll need a lot more than a big nozzle to dissipate torchdrive level waste heat.

I know... I an just saying how a torchship will actually look... using known physics.

 

Regnerative cooling and a high propellant flow rate are known ways of keeping the nozzle from melting.

 

Alternately... the irony is that torchships begin to have a lot in common with project Orion. They scale up great, but they don't scale down well without melting or ablating.

Edited September 17, 2021 by Spacescifi

[kerbiloid]

A torchboat.

Spoiler

No oars, no motor. Only torches.

 

[magnemoe]

I say it depend a lot of the technology you are using.  Lots of fusion designs will not work at all in the atmosphere or they would create lots of radioactivity. 
You also has other demands for an SSTO like the ability to reenter and land safely  
While on an long distance spaceships you might want an living area who works both under trust and spin and you want to be far away from the engine. 

[kerbiloid]

A clear definition of a torchship is first required at all, as this is just a colloquial term.

[Codraroll]

Handwavium engines. Work every time.

[Spacescifi]

9 hours ago, magnemoe said:

I say it depend a lot of the technology you are using.  Lots of fusion designs will not work at all in the atmosphere or they would create lots of radioactivity. 
You also has other demands for an SSTO like the ability to reenter and land safely  
While on an long distance spaceships you might want an living area who works both under trust and spin and you want to be far away from the engine. 

 

Metalkic hydrogen or some similar future uber non radioactive propellant would work.

 

Just be huge ship is all.

Edited September 17, 2021 by Spacescifi

[KSK]

While I am aware why 2 staging is superior, if we actually did have rocket engines powerful enough to enable SSTO's, would they not be huge?

No reason why they would be. As far as I'm aware - and the actual engineers around here will correct me if I'm wrong -  choice  of nozzle size is much more to do with  a) having an appropriate expansion ratio and b)  strength and weight considerations.  An ideal vacuum nozzle would be infinitely long so that the pressure at the nozzle exit is zero. In practice, an infinitely long nozzle is obviously impossible, so compromises are made.  Heat dissipation by radiative cooling is nice to have because it makes nozzle construction much simpler but I don't think you'd ever pick a bigger nozzle purely for the sake of a bit more radiative cooling.

Seems to me SSTO's are basically best for ferrying or shuttling payloads to or from planets.

Only if you have no other choice, as in, there's no infrastructure on that planet for recovering and restacking a reusable TSTO. Otherwise - as has been discussed ad nauseum on a separate thread, if you have the technology to build an SSTO, you have the technology to build a better TSTO.

Likely real future spaceships will be stacks or racks of spaceships linked together, detaching at will for whatever mission is required.

Maybe.  That rack of spaceships still needs to hold together under thrust, have appropriate propellant/power/life support connections between it's various parts and have appropriately placed thrusters for maneuvering. A more practical design might be to have a general purpose 'mothership' consisting of engines at one end, a crew module at the other and a long truss in between them for propellant tanks and other ship systems, plus berths for shuttlecraft, cargo cannisters or whatever else you want to stick on.  All the optional bits are berthed so as to keep the centre of mass of the overall ship in the right place.

No mothership, just a bunch of ships stacked or linked together, because in space you can link stuff on indefinitely... so long the inertia load is not greater than engine thrust.

I'm not sure what you're trying to get at here.

You do not need a big cargo hold in space since you can literally just link up with anything you want.

I'd have thought that depends on the cargo. If you're talking about a dedicated freighter which loads up at one planet, flies to another planet and unloads without the crew ever having to touch the freight, then you could probably do without a cargo hold. On the other hand, it might be convenient to have all the cargo in the same place for ease of loading and unloading, rather than having it dotted around all over the ship.

Edit:  Having all the cargo in one place might be also be useful for safety reasons since it would allow you to keep all cargo moving operations well away from more breakable bits of the ship such as antennas, radiators, crew compartments etc.

Edit 2:  If the freighter is using nuclear thermal engines, then keeping the cargo - and any shuttles coming to load or unload it - away from the radioactive death machines is probably a good idea too.

It might also be useful to have some thermal and/or micrometeoroid protection for the cargo. Sure, you could have it all in individual containers, each with their own shielding - or you could use simpler containers and have a dedicated shielded area on the freighter for holding them all.  I can see advantages and disadvantages either way.

If you're talking about cargo that the crew will need to access in flight for any reason, then a proper cargo bay where the crew can work in a shirtsleeves environment could make more sense than the alternatives.

Scifi miseducates the public in so many ways it's not funny. Everyship needs a cargo hold in pop scifi... when in reality it pays to optimize space only ships and then shuttle only ships.

Since when was educating the public the purpose of science fiction?  You may as well declare the purpose of James Bond movies to be educating the public about espionage.  Also, that's the nice thing about optimization, You can end up with very different - but still optimal - designs, depending on what you're optimizing for.  

Edited September 17, 2021 by KSK

[wumpus]

 

Just to put these volumes of questions in perspective, does anybody know the percentage of space science fiction readers that have/haven't played KSP?  I'd think that a significant percentage of them have, and it teaches the rocket equation even more thoroughly than orbital mechanics.  For those who have played enough to get into orbit, you would be better off having the characters teleport to Mars (or wherever) than a SSTO.  Replacing SF with magic somehow is a lot easier to get away with than amazingly bad science.

The most critical thing about space travel is always mass.  This is the decree of our most tyrannical overlord, the rocket equation: V_delta=Isp*ln(M_f/M_e)

So the big heavy engines increase the dry mass of the rocket.  And don't forget that if you are lifting civilian passengers, you probably don't want excessive g forces, so maybe 2 gees top (don't forget to add gravity, and do you really want to experience weighing three times your current body weight)?  So you'll waste 33% of the thrust and 33% of the fuel until you start going sideways.  Expect to require even more "magic Isp fuels" than the typical "magic fuel" needed for SSTO.  And don't neglect where all those neutrons are going if you are using fusion or something.

Not to mention that I, as a regular on this forum and vastly more interested in the internals of jet engines than the general public, recently flew commercially and my only thoughts about the engine on said plane was to be glad it was a turbofan instead of a turboprop (a commuter flight between two fairly small cities).  A "as you know, Bob" infodump would be completely unnecessary to describe my flight.  I'd suggest describing space flight in terms of liftoff, a boring wait to get there, and finally reentry and landing.  Or teleports.  If you have to describe the staging  at all, you better finally break down and learn how the rocket equation works, and playing KSP is probably the easiest way to *get* it in a way most of your potential readers already have.  Otherwise they will know you can't be bothered to learn basic facts about science and any "hard sci-fi" cred goes out the window (far worse that if you had merely used a 15th level wizard to cast the teleport spell...).

This isn't to say that SSTO will never replace TSTO.  Maybe we will one day have enough ISP and enough thrust in a single engine to make staging appear as quaint as the steam engine is now.  But expect enough R&D work to go into making staging as easy as joining freight train cars is today long before we ever get these magic fuels.  At that point the inertia of staged design becomes hard to replace, although if the powerful engines are cheap enough to make than eventually they should replace the TSTO.  Perhaps your character can discuss the politics of why the "rocket catcher" companies  lobbying effectively makes SSTO illegal, even though the rockets could easily make orbit on their own.

15 hours ago, Spacescifi said:

Scifi miseducates the public in so many ways it's not funny. Everyship needs a cargo hold in pop scifi... when in reality it pays to optimize space only ships and then shuttle only ships.

And until you learn the rocket equation, you will be miseducating even worse than most (and yes, learning orbital mechanics in the process might help as well.  But far more of your questions are out  of ignorance of the rocket equation rather than orbital mechanics).  So if you don't pick up KSP, see if you can find the demo.  Or just use the teleporter (having it transport at the speed of light would be a scientific improvement on nearly all space fantasy science fiction).

[KSK]

Agree with @wumpus

If you're writing any sort of hard sci-fi involving space travel or just shooting the breeze about ideas for spaceflight, I would say that the rocket equation is about the single most useful thing to know about.  I couldn't derive it from scratch if you pointed a phaser at my head but luckily it's pretty straightforward to plug the relevant numbers into it and see what falls out.  If you have a bit of basic algebra, enough maths to know that e^x is the inverse of ln x (this is where I embarrass myself by getting the terminology wrong) and can find both functions on a scientific calculator (or suitable calculator app) then you can rearrange it to make some calculations a bit easier.

Being able to link the mass ratio of your fictional spacecraft design (difference in mass between an empty spacecraft and a fully fueled one), the ISP of its engines, and the total velocity change it'll be capable off, is invaluable for a quick back-of-the-envelope calculation that will tell you if your design is at least somewhat plausible for the situations you have in mind.    That calculation will inevitably involve a substantial amount of guesswork (which can be reduced to a greater or lesser extent depending on how much research you're inclined to do ) but it'll be good enough for a sanity check.

Example: 

I was writing a story in which the finale involved setting off on a trip to Mars (well Duna (this was a KSP story but with a solar system rescaled to match our own)). My Big Ship was assembled in orbit and I needed it to be able to carry out a trans-Mars injection burn, then burn into Mars orbit at the other end of the journey (no aerobraking here). Getting home required refueling at Mars but luckily the logistics of that weren't important to the story. It was to be powered by solid core nuclear-thermal engines running on ammonia (more storable than hydrogen whilst still giving a better ISP than a hydrolox motor).

I had a design in mind for the ship but I wanted to figure out if that design was at least somewhat plausible. Not that I planned to be getting that far into the details in the story (I wholeheartedly agree with @wumpus's air travel analogy) but I was describing the look of the spacecraft in some detail and wanted to satisfy myself that I wasn't describing something that was completely bogus.

Long story short, I did a bit of Googling to figure out what kind of delta-V, I'd need, did some digging on Atomic Rockets to get an idea of how capable my proposed engines could be, plugged the numbers into the rocket equation and figured out what mass fraction I'd need. My dry mass was a bit of a guess (I'm not going to dignify it by calling it an estimate  ) but hopefully a somewhat educated one. For example, my ship was partially built from inflatable modules, so I took a look at the numbers for BEAM  and used them to refine my guess. From there, I could figure out how what my wet mass was and therefore what kind of thrust-to-weight ratio I could expect. If I remember rightly, I had to rework the number of engines I was using to give me a sensible value for that. Knowing how much propellant I needed was also helpful for figuring out what sort of propellant tank volume I needed and whether that size of tank could be launched to orbit in one piece using the rockets available to my protagonists.

Most of that detail was completely glossed over in the story. I think the one thing that I did go into in a bit of depth was choosing ammonia as the propellant but that was pretty key to working out an overall mission profile and therefore something that I was comfortable having my characters discuss.

Edit:   For the avoidance of doubt, the point of all that verbiage above wasn't meant to be showing off what an awesome writer I was but just to demonstrate how the rocket equation plus a little bit of reading around on the internet, can go a long way when you're writing a hard sci-fi space story.

 

Edited September 19, 2021 by KSK

[magnemoe]

On 9/17/2021 at 8:09 PM, KSK said:

While I am aware why 2 staging is superior, if we actually did have rocket engines powerful enough to enable SSTO's, would they not be huge?

No reason why they would be. As far as I'm aware - and the actual engineers around here will correct me if I'm wrong -  choice  of nozzle size is much more to do with  a) having an appropriate expansion ratio and b)  strength and weight considerations.  An ideal vacuum nozzle would be infinitely long so that the pressure at the nozzle exit is zero. In practice, an infinitely long nozzle is obviously impossible, so compromises are made.  Heat dissipation by radiative cooling is nice to have because it makes nozzle construction much simpler but I don't think you'd ever pick a bigger nozzle purely for the sake of a bit more radiative cooling.

Seems to me SSTO's are basically best for ferrying or shuttling payloads to or from planets.

Only if you have no other choice, as in, there's no infrastructure on that planet for recovering and restacking a reusable TSTO. Otherwise - as has been discussed ad nauseum on a separate thread, if you have the technology to build an SSTO, you have the technology to build a better TSTO.

Likely real future spaceships will be stacks or racks of spaceships linked together, detaching at will for whatever mission is required.

Maybe.  That rack of spaceships still needs to hold together under thrust, have appropriate propellant/power/life support connections between it's various parts and have appropriately placed thrusters for maneuvering. A more practical design might be to have a general purpose 'mothership' consisting of engines at one end, a crew module at the other and a long truss in between them for propellant tanks and other ship systems, plus berths for shuttlecraft, cargo cannisters or whatever else you want to stick on.  All the optional bits are berthed so as to keep the centre of mass of the overall ship in the right place.

No mothership, just a bunch of ships stacked or linked together, because in space you can link stuff on indefinitely... so long the inertia load is not greater than engine thrust.

I'm not sure what you're trying to get at here.

You do not need a big cargo hold in space since you can literally just link up with anything you want.

I'd have thought that depends on the cargo. If you're talking about a dedicated freighter which loads up at one planet, flies to another planet and unloads without the crew ever having to touch the freight, then you could probably do without a cargo hold. On the other hand, it might be convenient to have all the cargo in the same place for ease of loading and unloading, rather than having it dotted around all over the ship.

Edit:  Having all the cargo in one place might be also be useful for safety reasons since it would allow you to keep all cargo moving operations well away from more breakable bits of the ship such as antennas, radiators, crew compartments etc.

Edit 2:  If the freighter is using nuclear thermal engines, then keeping the cargo - and any shuttles coming to load or unload it - away from the radioactive death machines is probably a good idea too.

It might also be useful to have some thermal and/or micrometeoroid protection for the cargo. Sure, you could have it all in individual containers, each with their own shielding - or you could use simpler containers and have a dedicated shielded area on the freighter for holding them all.  I can see advantages and disadvantages either way.

If you're talking about cargo that the crew will need to access in flight for any reason, then a proper cargo bay where the crew can work in a shirtsleeves environment could make more sense than the alternatives.

Scifi miseducates the public in so many ways it's not funny. Everyship needs a cargo hold in pop scifi... when in reality it pays to optimize space only ships and then shuttle only ships.

Since when was educating the public the purpose of science fiction?  You may as well declare the purpose of James Bond movies to be educating the public about espionage.  Also, that's the nice thing about optimization, You can end up with very different - but still optimal - designs, depending on what you're optimizing for.  

Nozzles is part of it but the real important part is that an rocket or spaceplane has two conflicting requirements, Its need to carry lots of fuel and engines to get to orbital velocity, less fuel but wings and different engine types for the plane. 
It then need to be able to handle reentry and land. 
It makes much more sense to have two stages for this. and the first stage don't get hot and the upper stage is small and light. 

Now if your ISP on your engine is much higher than chemical rockets the two stage benefit don't go away unless you say have an engine who is heavy but can give you high ISP and trust. 
You could easy have an setting with something like Skylon SSTO is used for passengers and light cargo or launches  while having something like an scaled up SS /SH for the bulk cargo. 

Still an orbital shuttle is not an good craft for using in space as it need to carry heat shields and landing systems. As you will dock in LEO after say 6 hours its sett up like an aircraft but with vacuum toilets. 
You then transfer to you interplanetary spaceship with cabins and variable spin gravity. 
And yes spaceX starship challenges this by brute force, probably work for Mars, not for the belt or outward. 

[Corona688]

On 9/17/2021 at 4:16 AM, kerbiloid said:

A clear definition of a torchship is first required at all, as this is just a colloquial term.

Quite a few useful and specific definitions here:  http://www.projectrho.com/public_html/rocket/torchships.php

But generally means output power in the gigawatts to terawatts range (space shuttle launch is double-digit gigawatts), 1+G acceleration sustained for days to weeks on end, and ISP in the high thousands.

Edited September 22, 2021 by Corona688

[kerbiloid]

7 hours ago, Corona688 said:

Quite a few useful and specific definitions here:  http://www.projectrho.com/public_html/rocket/torchships.php

But generally means output power in the gigawatts to terawatts range (space shuttle launch is double-digit gigawatts), 1+G acceleration sustained for days to weeks on end, and ISP in the high thousands.

That's desired parameters, not a physical principle.

[Corona688]

On 9/22/2021 at 10:01 PM, kerbiloid said:

That's desired parameters, not a physical principle.

Well...

Torchships aren't real.

[wumpus]

6 hours ago, Corona688 said:

Well...

Torchships aren't real.

Nuclear Thermal Propulsion has a TRL (tech readiness level) of 6, making it far easier to get through NASA paperwork than almost any competing tech.  Getting past the public is another issue.  Granted, either the amount or length of thrust on a NTR would probably be far too low to call it a "torchship", but it is a start.

Best definition of a "torchship" is something that accelerates at 1g until midpoint and then flips around and deccelerates at one g all the way back (the "1g" chosen to maintain gravity, possibly you'd do some sort of gradual change when going between planets with different gravities).

[mikegarrison]

47 minutes ago, wumpus said:

Best definition of a "torchship" is something that accelerates at 1g until midpoint and then flips around and deccelerates at one g all the way back (the "1g" chosen to maintain gravity, possibly you'd do some sort of gradual change when going between planets with different gravities).

Right, but unless you are in a real hurry, something less than 1-g is probably just fine. 0.5g would have a lot of advantages over 1g, unless you have magic engines.

(Sustained 0.5g accel needs also needs magic engines, so I guess I mean "magicker" engines. But point is, 0.5g engines probably about half the mass of 1g engines.)

[wumpus]

18 hours ago, mikegarrison said:

Right, but unless you are in a real hurry, something less than 1-g is probably just fine. 0.5g would have a lot of advantages over 1g, unless you have magic engines.

(Sustained 0.5g accel needs also needs magic engines, so I guess I mean "magicker" engines. But point is, 0.5g engines probably about half the mass of 1g engines.)

Pretty sure .5g accel needs "magic" engines as well.  And if you were trying to conserve delta-v, you'd simply push the amount you'd be running at 1g towards the start/end and coast (or run with low thrust for minimal gravity) in the middle.  1g was listed for crew/passenger comfort than anything else, if you are in a hurry you might have 3g for the first/last day...

I still think that with maximum magic (but not teleportation), you'd leave Earth at 1g, arrive at Mars deccelerating at .38g (Mars gravity) and gradually lower your  thrust all the way there to be an even change.  And vice-versa for the return trip.  Constant 1g would be for going to/from places with artificial gravity (presumably via  rotation) or Earth.

 

[magnemoe]

20 hours ago, wumpus said:

Nuclear Thermal Propulsion has a TRL (tech readiness level) of 6, making it far easier to get through NASA paperwork than almost any competing tech.  Getting past the public is another issue.  Granted, either the amount or length of thrust on a NTR would probably be far too low to call it a "torchship", but it is a start.

Best definition of a "torchship" is something that accelerates at 1g until midpoint and then flips around and deccelerates at one g all the way back (the "1g" chosen to maintain gravity, possibly you'd do some sort of gradual change when going between planets with different gravities).

Burn to turnover and then brake is kind of definition of an touch ship, but its also an stupid idea if you use reaction mass and reaction mass is most of your ship mass.  
The reaction mass used for the 5-10% last part of trust save you very little time as you will cancel it out almost at once, at the same time ship is heavier and will accelerate slower. At some point you will save time dumping fuel  
Even better to use heavier and stronger engines carry less fuel, get up to cruise speed faster and stay there. 
Two exceptions, you have an ship with lots of dV and you need to do an short burn to do an intercept or rescue mission, other to use trust for gravity, but here you might want to keep trust much lower after you got up speed. 

If you can reach Mars in a week or tow I say you have an touch ship. 

[mikegarrison]

3 minutes ago, magnemoe said:

 use trust for gravity, but here you might want to keep trust much lower after you got up speed. 

Thus my comment about 0.5g instead of 1g. Still gravity, but not as much wasted thrust.