Ideal SSTO's Versus Two Staging...Settled?

[Spacescifi]

20 minutes ago, sevenperforce said:

Like I said, this set of requirements is completely within the range of near-future scifi. 700 seconds of isp is not that much. It can land on Raptors on any prepared concrete surface, and with these kinds of energy budgets you can have as beefy of landing legs as you want. It's all very simple and straightforward if you just get a nice powerful LANTR bundled in between your Raptors.

You're starting with the wrong problem. If you have a world where you're flying an LANTR-based SSTO multiple times per day, material engineering is not going to be a problem for you. Materials can survive all this easily.

 

What if you try to make an emergency landing on the ground?

 

Raptors you suggest?

 

What if you...or should you not use the LANTR....because craters?

 

So LANTR won't make lava eh? We not there yet with the torch rocket?

 

Unless...LOL NSWR.

Edited July 4, 2021 by Spacescifi

[Codraroll]

33 minutes ago, Spacescifi said:

What if you try to make an emergency landing on the ground?

That scenario is pretty unlikely to occur in routine spaceflight. If you're at the point where you need to make an emergency landing on an unprepared surface, your rocket is borked anyway. Just like most airliners are today. The contingency plans depend on a certain level of preparedness and certain procedures in case of emergency, and if those can't be followed or aren't available, you will make a crater.

Besides, this whole "landing on unprepared surfaces" things weren't a part of the conditions you initially described. Your threads have a serious tendency to rely on wild assumptions, insane conditions, and flat-out wrong guesses, and when those are picked apart you try to mend them by throwing in even more wild assumptions and insane conditions. It usually never works to support the original conclusion, and yet you keep making more of the same type of threads almost every day with the same mistakes in them. Have you ever considered making an umbrella thread to put all your questions in, rather than flooding the forums with ... whatever this is?

But hey, at least I learn a lot from the serious answers from other members with more patience than I have. Kudos to them, I suppose.

Edited July 4, 2021 by Codraroll

[Spacescifi]

4 minutes ago, Codraroll said:

That scenario is pretty unlikely to occur in routine spaceflight. If you're at the point where you need to make an emergency landing on an unprepared surface, your rocket is borked anyway. Just like most airliners are today. The contingency plans depend on a certain level of preparedness and certain procedures in case of emergency, and if those can't be followed or aren't available, you will make a crater.

Besides, this whole "landing on unprepared surfaces" things weren't a part of the conditions you initially described. Your threads have a serious tendency to rely on wild assumptions and flat-out wrong guesses, and when those are picked apart you try to mend them by throwing in even more wild assumptions, and it usually never works and yet you keep making more of the same type of threads almost every day. Have you ever considered making an umbrella thread to put all your questions in, rather than flooding the forums with ... whatever this is?

But hey, at least I learn a lot from the serious answers from other members with more patience than I have. Kudos to them, I suppose.

 

 

If that is so then the scifi trope of landing large spacecraft on the ground is nonesense...for Earth worlds.

 

They would land them on the ocean only.

[Terwin]

1 minute ago, Spacescifi said:

If that is so then the scifi trope of landing large spacecraft on the ground is nonesense...for Earth worlds.

I have difficulty thinking of a single sci-fi trope that is not at least 50% nonsense, and the vast majority of them are 100% nonsense.

So, yes, that specific trope is also nonsense.

(most of the sci-fi tropes that are less than 75% nonsense have already been made into reality in some form or fashion, such as flip-phones being a real-live alternative to Start Trek TOS flip-open communicators, or submarines and the Nautilus; and thus not really a sci-fi trope anymore)

 

[Spacescifi]

12 minutes ago, Terwin said:

I have difficulty thinking of a single sci-fi trope that is not at least 50% nonsense, and the vast majority of them are 100% nonsense.

So, yes, that specific trope is also nonsense.

(most of the sci-fi tropes that are less than 75% nonsense have already been made into reality in some form or fashion, such as flip-phones being a real-live alternative to Start Trek TOS flip-open communicators, or submarines and the Nautilus; and thus not really a sci-fi trope anymore)

 

 

Good to know. The more your scifi rocket is like a torch drive the less places you can land the thing.

 

Good to know.

 

Same could be said forthe heavier an SSTO is, the more likely it can only land without wrecking ocean.

[Codraroll]

3 minutes ago, Spacescifi said:

Good to know. The more your scifi rocket is like a torch drive the less places you can land the thing.

But that's not what he said. What he said was that all sci-fi has elements of nonsense. That's yet another variant of the response you get to almost all the threads you're making, and yet you never seem to get it.

[magnemoe]

An two stage rocket will always be more efficient. Mass, reentry requirements and more so because you want to use different engines, this can go so far as first stage uses air breathing. However at some performance you just use one stage. This way you don't have to get them together and mate them before next flight. 

Planes only use stages after all and they run into the rocket equation problem on long flights, an plane going from Europe to US can not land with the amount of fuel it need and +12 hour flights needs so much fuel to carry the extra fuel they are more expensive than landing underway.  Obviously planes can land underway.

Now you can easy have an setting there you have passenger and light cargo SSTO while heavy lift is TSTO.

Or something like done in the Freefall comic, the fusion powered ship is capable of atmospheric flight even an vtol, but to reach orbit it need an electromagnetic launcher. 
Now this is pretty short so I assume its just to give them enough velocity for flight while fully loaded the same way the catapult on an carrier does. 
 

[RCgothic]

15 hours ago, GoSlash27 said:

I'm not aware of any chemical bipropellant that can achieve 700s specific impulse even theoretically, let alone with enough thrust to lift anything. I'd say that unless you invoke some kind of unobtainium propulsion system, 700s *is* a bit much.

Best,

-Slashy

The engine sevenperforce  suggested - LANTR - is a nuclear engine, not a chemical engine.

The methalox engines/raptors were suggested as landing engines, not the main stage propulsion.

Edited July 5, 2021 by RCgothic

[sevenperforce]

16 hours ago, Spacescifi said:

What if you try to make an emergency landing on the ground?

If you want a ship that is designed to land on unprepared surfaces, then design a ship with a set of landing legs capable of landing on unprepared surfaces.

If you do not want a ship that is designed to land on unprepared surfaces, then do not design a ship with a set of landing legs capable of landing on unprepared surfaces. 

16 hours ago, Spacescifi said:

Raptors you suggest?

What if you...or should you not use the LANTR....because craters?

You would want to run the LANTR in pure NTR mode, and downthrottled as well, which doesn't really make sense in the context of a very short landing burn. Methalox engines would do more aggressive surface excavation than a downthrottled nuclear thermal rocket, anyway. Again, if we are talking about nuclear engines, 700 seconds is really not that much.

16 hours ago, Spacescifi said:

So LANTR won't make lava eh? We not there yet with the torch rocket?

Of course it will make lava. Any modern rocket engine will make lava. The combustion temperature of the RS-25 is greater than the boiling point of iron. Exhaust from rocket engines is much, much higher than the melting point of rock.

But no one leaves rocket engines firing at rock long enough to make lava because that would be a big waste of time.

16 hours ago, Codraroll said:

Have you ever considered making an umbrella thread to put all your questions in, rather than flooding the forums with ... whatever this is?

You would not be the first person to have asked this.

16 hours ago, Spacescifi said:

If that is so then the scifi trope of landing large spacecraft on the ground is nonesense...for Earth worlds.

No, you can land pretty much anywhere you want, if that's how you design it. Again, it's a design question. Start with what you want and design around that, and then figure out what kind of engines you'll need. Otherwise you're just spinning in circles endlessly.

[sevenperforce]

On 7/3/2021 at 4:10 PM, Spacescifi said:

Unless the super SSTO can throttle it's heat waaay down to lose some of it's high thrust/efficiency in the process, it will nuke the launch/landing site every time.

Note that the larger your vehicle becomes, the higher T/W ratio you can squeeze out of a nuclear thermal rocket, because bigger reactors mean more surface area to transfer heat to the propellant.

There's really no risk of "nuking" the launch site; just use a water deluge on the pad. Use separate thrusters for landing. No big deal.

On 7/3/2021 at 4:10 PM, Spacescifi said:

Question: Anyone want to calculate the energy cost of sending the equivalent of Spacex mass (super heavy and starship second stage) as a complete SSTO, by sending it to orbit, and then stopping it's orbit to hover over the landing site in space before dropping straight down (linear reentry rather than ballistic)?

I will also note that this has already been done. 

This is the Nuclear DC-X, proposed back in 2004. About the same size as Starship+Superheavy, but fatter to hold the lower-density hydrogen. A single aerospike nozzle fed by five large NTRs and LOX injection at launch to add thrust. It used the same forward stabilator design as Starship to effect a biconic re-entry with a metallic heatshield. Notionally used steam thrusters for RCS and landing. 100 tonnes to LEO, fully reusable.

You could probably make it more efficient by adding Raptor engines for added liftoff thrust and the landing burn and using three different propellants: methane, hydrogen, and LOX.  Max thrust would involve running methane through the NTRs with full LOX afterburning alongside all the Raptors. As weight dropped during the climb, you'd shut down the LOX afterburn flow, then shut down the Raptors, then finally transition from methane to hydrogen in the NTRs. Use methgox hot gas thrusters for RCS on orbit and use the NTR in hydrogen mode for the deorbit burn. Raptors for the landing burn. 

Here's a cross-section of the engine cluster so you can get a better idea of what it looks like:

No reason why this wouldn't work. The fixed control surfaces even act as passive radiators on orbit so you can use the reactors to produce electricity via the Brayton cycle. 

And while the Nuclear DC-X would have used a heat shield, you're not the first person to propose going without one. If you want to go even bigger, you can ask nicely for the nuclear lightbulb design and do a 1000-tonne-to-LEO Liberty Ship with 15 km/s of dV, enough to go up and come back down.

You **would** want to launch that from water or from a Pacific atoll somewhere, not necessarily because you'd torch the launch pad, but because you want a wider berth for abort modes if something goes wrong on launch or landing.

[Spacescifi]

8 hours ago, sevenperforce said:

Note that the larger your vehicle becomes, the higher T/W ratio you can squeeze out of a nuclear thermal rocket, because bigger reactors mean more surface area to transfer heat to the propellant.

There's really no risk of "nuking" the launch site; just use a water deluge on the pad. Use separate thrusters for landing. No big deal.

I will also note that this has already been done. 

This is the Nuclear DC-X, proposed back in 2004. About the same size as Starship+Superheavy, but fatter to hold the lower-density hydrogen. A single aerospike nozzle fed by five large NTRs and LOX injection at launch to add thrust. It used the same forward stabilator design as Starship to effect a biconic re-entry with a metallic heatshield. Notionally used steam thrusters for RCS and landing. 100 tonnes to LEO, fully reusable.

You could probably make it more efficient by adding Raptor engines for added liftoff thrust and the landing burn and using three different propellants: methane, hydrogen, and LOX.  Max thrust would involve running methane through the NTRs with full LOX afterburning alongside all the Raptors. As weight dropped during the climb, you'd shut down the LOX afterburn flow, then shut down the Raptors, then finally transition from methane to hydrogen in the NTRs. Use methgox hot gas thrusters for RCS on orbit and use the NTR in hydrogen mode for the deorbit burn. Raptors for the landing burn. 

Here's a cross-section of the engine cluster so you can get a better idea of what it looks like:

No reason why this wouldn't work. The fixed control surfaces even act as passive radiators on orbit so you can use the reactors to produce electricity via the Brayton cycle. 

And while the Nuclear DC-X would have used a heat shield, you're not the first person to propose going without one. If you want to go even bigger, you can ask nicely for the nuclear lightbulb design and do a 1000-tonne-to-LEO Liberty Ship with 15 km/s of dV, enough to go up and come back down.

You **would** want to launch that from water or from a Pacific atoll somewhere, not necessarily because you'd torch the launch pad, but because you want a wider berth for abort modes if something goes wrong on launch or landing.

 

Interesting.

When I said turn to lava, I was referring an engine so powerful that it turns the ground to lava in the few seconds it takes to land.

No engines in use today I know of do that. That is the kind of engine power/heat I meant.

 

Overall I think ocean launch/landing/refueling is the best way to go for the heaviest reusuables with fast reusability.

 

You don't see land-ships do you?

The ocean is fairly easy to put massive weight accross and float it...or even crash it, with more room for error than ground shall forgive.

[sevenperforce]

3 hours ago, Spacescifi said:

When I said turn to lava, I was referring an engine so powerful that it turns the ground to lava in the few seconds it takes to land.

No engines in use today I know of do that. That is the kind of engine power/heat I meant.

And that would never be an issue because you would downthrottle or use separate landing engines. 

3 hours ago, Spacescifi said:

Overall I think ocean launch/landing/refueling is the best way to go for the heaviest reusuables with fast reusability.

Does your fiction need ocean launch and landing for a plot point? If so, make it so. If not, don’t.

3 hours ago, Spacescifi said:

You don't see land-ships do you?

I’ve never seen an ocean freighter two miles long, but I’ve seen a “land-ship“ that long or longer. 

3 hours ago, Spacescifi said:

The ocean is fairly easy to put massive weight accross and float it...or even crash it, with more room for error than ground shall forgive.

If you’re landing at sea on a platform, the platform will be moving, which makes it waaaaay harder. If your plot requires a vehicle that launches and lands on water, make it so. Otherwise don’t. 

[Codraroll]

6 hours ago, Spacescifi said:

Interesting.

When I said turn to lava, I was referring an engine so powerful that it turns the ground to lava in the few seconds it takes to land.

I assume you're talking about a spaceship so big and heavy that it needs engines so powerful that they would melt the ground upon landing. But such a ship landing on ground not prepared for it, is like a cargo freighter making land on an unprepared beach. It's not a situation a ship like that will encounter in the first place.

Your argument is like saying cargo freighters are unfeasible and should not be built, because you can't just beach them anywhere and sail away undeterred afterwards like you can with a canoe. But thing is, the ship is designed around its required infrastructure. You can have cargo freighters if you have harbours for them. You can have superheavy spaceships landing if you have pads for them. And if you need your ship to land on unprepared ground, you design a ship to land on unprepared ground. It probably will require certain design modifications, unless you just skip all that, do like 95% of all sci-fi, and just handwave it. That's a valid approach to. It's science fiction for a reason.

Overall, @sevenperforcegot it. Here's the general answer to all your threads: 

3 hours ago, sevenperforce said:

If your plot requires a (noun) that (does a thing), make it so. Otherwise don’t. 

 

Edited July 6, 2021 by Codraroll

[Spacescifi]

9 hours ago, sevenperforce said:

And that would never be an issue because you would downthrottle or use separate landing engines. 

Does your fiction need ocean launch and landing for a plot point? If so, make it so. If not, don’t.

I’ve never seen an ocean freighter two miles long, but I’ve seen a “land-ship“ that long or longer. 

If you’re landing at sea on a platform, the platform will be moving, which makes it waaaaay harder. If your plot requires a vehicle that launches and lands on water, make it so. Otherwise don’t. 

 

6 hours ago, Codraroll said:

I assume you're talking about a spaceship so big and heavy that it needs engines so powerful that they would melt the ground upon landing. But such a ship landing on ground not prepared for it, is like a cargo freighter making land on an unprepared beach. It's not a situation a ship like that will encounter in the first place.

Your argument is like saying cargo freighters are unfeasible and should not be built, because you can't just beach them anywhere and sail away undeterred afterwards like you can with a canoe. But thing is, the ship is designed around its required infrastructure. You can have cargo freighters if you have harbours for them. You can have superheavy spaceships landing if you have pads for them. And if you need your ship to land on unprepared ground, you design a ship to land on unprepared ground. It probably will require certain design modifications, unless you just skip all that, do like 95% of all sci-fi, and just handwave it. That's a valid approach to. It's science fiction for a reason.

Overall, @sevenperforcegot it. Here's the general answer to all your threads: 

 

 

Space freighters as large and heavy as sea freighters, likely more so due to propellant with equivalent cargo.

https://www.telegraph.co.uk/finance/newsbysector/transport/10496977/Worlds-largest-ship-bigger-than-Empire-State-Building-launches.html

You launch or land this kind of heavy and I wonder if you can even afford to throttle down to avoid glassing the ground without crashing hard.

Two stage has no weight limit since you lose weight on the way uo.

SSTO has a definite max weight limit though I think, at least with regard to cargo/propellant ratios

 

Sure you can send a massive propellant tank into orbit but that is pointless without meaningful amounts of payload or cargo.