A new type of SSTO

[Spacescifi]

 

 

So I was thinking... rocket thrust is limited by thermodynamic material limits.

Another way to still get higher thrust without worrying as much about thermodynamics is to use pusher plate propulsion.

 

My idea: An SSTO belly lander shaped like the sausage shaped craft above. Instead of a rocket at the rear, put a pusher plate with shock absorbers.

The middle of the ship's belly has VTOL landing thrusters. So the ship will lift off with them, but flip over and use pusher plate propulsion to actually reach orbit. Likewise it could use the pusher plate as a heatshield on reentry and even to slow down some with bombs before flipping over to use landing thrusters to land on it's belly.

The bombs: I propose metallic hydrogen bombs. While we do not have them, I think if we did they would be an alternative for my belly lander non-nuclear Orion.

Granted, the ship may have to be lighter in weight, but I still think metallic hydrogen bombs could serve as a good radiation free substitute.

 

Modern tech version: I honestly believe we could build a nonnuclear pusher plate SSTO even now. Who knows how efficient it would be, but we wiuld have to use the lightest weight, most powerful non-nuclear bombs we have for propulsion, and the vehicle itself would have to be lightweight. It may or may not be cost effective though. Since the tried and true rocket is always more readily available.

 

 

What do you think about all this? Could metaloic hydrogen bombs really serve as a substitute for a belly lander pusher plate SSTO?

By the way it uses methane ice with a closed cycle fission reactor and heat exchangers for the VTOL thrusters at the middle of the belly.

Edited August 26, 2019 by Spacescifi
Build

[DDE]

4 hours ago, Spacescifi said:

Who knows how efficient it would be, but we wiuld have to use the lightest weight, most powerful non-nuclear bombs we have for propulsion

And that's where you lost the plot. Such a design was offered in the mid-XIXth century. Problem is, high explosives tend to have lower energy content than rocket propellants. You're looking at an SRB, minus the casing that makes the reaction products go in the direction you need them. I reckon two-digit ISP at best.

Why are you dodging a true Orion, anyway?

Edited August 26, 2019 by DDE

[Scotius]

31 minutes ago, DDE said:

Why are you dodging a true Orion, anyway?

Because pulsed propulsion in general is bad? And we use it only when we have no better alternatives. Look at V-1 vs. normal jet engine.

Would you weld an anvil to the back of your car, and propel it forward by repeatedly slamming a wrecking ball into the anvil? I'm sure acceleration would be incredible...

[Shpaget]

27 minutes ago, Scotius said:

Look at V-1 vs. normal jet engine

Well, pulse jet has two major advantages over a turbojet. The cost and design/manufacture simplicity.

As for OP, if we had metallic hydrogen, there would be no need for a heavy Orion-type drive. A regular rocket fueled by metallic hydrogen would be capable of SSTO.

I don't see SSTO as viable, until there is the capability that a craft can launch and land multiple times on Earth between refuelings. Until that happens a two stage rocket will always offer better performance.

[kerbiloid]

1 hour ago, Scotius said:

Look at V-1 vs. normal jet engine.

Am looking and seeing that V-1 was successfully pulsed propulsed long before straight jets became a mainstream.

Also Daedalus has discrete thrust, too. it ignites frozen fusion pellets, not hydrogen flow.

[Scotius]

3 hours ago, kerbiloid said:

Am looking and seeing that V-1 was successfully pulsed propulsed long before straight jets became a mainstream.

And we got rid of pulsed jets and switched to normal engines as soon as they became viable.

[kerbiloid]

1 minute ago, Scotius said:

And we got rid of pulsed jets and switched to normal engines as soon as they became viable.

We use both AC/DC in electric engines.

In case of Orion and Daedalus (or as well any other pulsed nuke engine) the discretion is a replacement of this technohorror.

Spoiler

The reaction zone is wisely placed far from the ship on a long thin truss.
Which can get bending and cause additional oscillations and makes the ship maneuverability enough complex due to both elasticity and bad shape from the attitude pov.
But is still solid, so is afraid of contact with really hot reactor zone.

Both Orion and Daedalus just offset the reaction zone behind the vulnerable part of the ship.
They exclude the truss, replacing it with same distance between the ship and the radiation and heat source.
They also don't care about radial forces, so they can just omit bending deformations.

To use the produced energy they either focus it forward (Orion) or place the reaction zone on the very edge of the magnetic nozzle (Daedalus).

Pulsing is a payment for this. A recharge-discharge cycle.

[wumpus]

Belly lander?  Any particular reason?  Or just make a Starship-like rentry a wee bit easier (except you'll need much more powerful landing rockets for your Earth landing).

Non-nuclear bombs?  You get a lower Isp/less energy than current rocket fuels I'm afraid, the chemistry simply works that way*.  The exception would be using fuel-air bombs behind a pusher-plate.  They would have "less Isp/energy" than current air-breather fuels, but that can still be stupendously high (it better be, you'll still need tons of dry mass on any pusher plate).

Nuclear power without a pusher plate?  Not enough thrust to lift off.

5 hours ago, kerbiloid said:

We use both AC/DC in electric engines.

Except they both look wildly different than 20th century "AC" and "DC" engines.  I suppose that old-fashioned electric motors would still make some sense (for AC motors less than 20hp and DC motors where you don't care about longevity or efficiency, and even less power maximums.  As in you won't pay more than a few cents for a modern DC engine controller).  Induction engines work far better if you create the AC on the fly (in a way that looks just like making a DC power supply, except you can also produce current going the other way) and "DC" motors typically have the "DC" provided in exactly the same way (except it goes directly to the magnets instead of creating the magnetic field via induction).

Supposedly you should be able to create a pulsed jet with no moving parts (I'd assume it would only work in a narrow airspeed range), and that could be used in the modern world (and require some extreme supercomputing to develop).  Otherwise I don't foresee pulsed jets being practical (even then it probably wouldn't be all that practical.  Probably too noisy for general aviation, too inefficient for the big boys, and only useful to model aircraft makers who really want a jet engine (which is were I'd expect to see classical pulse jets anyway).

* the difference is power vs. energy.  Bombs deliver a great deal of power** all at once, while convention fuels take awhile to burn (until you add LOX to the mix, that's the reason rockets can explode).  Also bombs have to contain their own oxidizer, which is typically lower in energy density than LOX).

** I doubt my physics teachers would approve of defining power in a way that ignores work, but assume a pusher plate if that makes you happy.

[kerbiloid]

6 minutes ago, wumpus said:

Supposedly you should be able to create a pulsed jet with no moving parts

Probably in future they could do this in some tricky way of magnetic heating and further heat redistribution or so, but currently any normal jet works due to fast rotation of a discrete wheel of blades, lol.

In case of Orion and Daedalus, they can use magnetic field instead of pusher plate, to receive and reflect the plasma hit, so it will be a motionless engine, though still discrete.

Edited August 26, 2019 by kerbiloid

[DDE]

7 minutes ago, wumpus said:

Belly lander?  Any particular reason?

Dual Thrust Axis concepts seek increased stability and lack of need for a crane/elevator.

[kerbiloid]

16 minutes ago, wumpus said:

Belly lander?  Any particular reason?

A "roll-on, roll-off" -type ship.
An aerodynamic assist on aerobraking.
Easy motion along the landed ship.

I simply must mention this pretty excellent video again. I love this ship very much.

Spoiler

 

 

Edited August 26, 2019 by kerbiloid

[Spacescifi]

13 hours ago, Shpaget said:

Well, pulse jet has two major advantages over a turbojet. The cost and design/manufacture simplicity.

As for OP, if we had metallic hydrogen, there would be no need for a heavy Orion-type drive. A regular rocket fueled by metallic hydrogen would be capable of SSTO.

I don't see SSTO as viable, until there is the capability that a craft can launch and land multiple times on Earth between refuelings. Until that happens a two stage rocket will always offer better performance.

 

Thermodynamic limits of material would not allow a metallic hydrogen fueled rocket to to get the 1700 ISP with high thrust. You would have to mix it with another fuel to lower the temperature.

 

Yet you could still use pure metallic hydrogen for bombs as they explode behind the vessel. Thus getting more energetic reactions than you could survive with a rocket engine.

 

As for pulse detonation, bombs can have shaped explosions, so that is one way to direct the blast mostly toward the pusher plate.

Edited August 26, 2019 by Spacescifi

[Shpaget]

39 minutes ago, Spacescifi said:

Thermodynamic limits of material would not allow a metallic hydrogen fueled rocket to to get the 1700 ISP with high thrust. You would have to mix it with another fuel to lower the temperature.

I am not convinced of that, assuming we had metallic hydrogen. Ablative cooling is fairly good at keeping things not too toasty.

I am also not convinced that bombs would give you much more pleasant environment.

Somebody correct my maths if I'm wrong, but even with a perfect shaped charge that concentrates the entirety of the blast forwards towards the pusher plate, you are still wasting half of the energy on the equivalent blast towards the back.

[kerbiloid]

8 hours ago, Shpaget said:

Somebody correct my maths if I'm wrong, but even with a perfect shaped charge that concentrates the entirety of the blast forwards towards the pusher plate, you are still wasting half of the energy on the equivalent blast towards the back.

It's enough to focus forwards a lesser part of energy, to make losses comparable to the usual engine.

Afaik, according to open data, in Orion tests they've focused about 6% of the blast energy.
But as this is an old open data, probably now they can focus more. And even a quarter is close to ideal.

Edited August 27, 2019 by kerbiloid

[sevenperforce]

18 hours ago, Shpaget said:

I am not convinced of that, assuming we had metallic hydrogen. Ablative cooling is fairly good at keeping things not too toasty.

I am also not convinced that bombs would give you much more pleasant environment.

Somebody correct my maths if I'm wrong, but even with a perfect shaped charge that concentrates the entirety of the blast forwards towards the pusher plate, you are still wasting half of the energy on the equivalent blast towards the back.

Even 10-20% of usage blows chemical rockets away.

To the OP -- I have always been a huge fan of dual-thrust-axis SSTOs. I'm partial to the Firefly.

A chemical Orion is a non-starter. Isp is way too low. Generally, blowing something up and using a pusher plate is really inefficient. The only reason it works well with the Orion concept is that the amount of energy is high enough to overcome inefficiencies. Plus, I think you get a boost in atmo thanks to added reaction mass.

[wumpus]

19 hours ago, Spacescifi said:

 

Thermodynamic limits of material would not allow a metallic hydrogen fueled rocket to to get the 1700 ISP with high thrust. You would have to mix it with another fuel to lower the temperature.

Yet you could still use pure metallic hydrogen for bombs as they explode behind the vessel. Thus getting more energetic reactions than you could survive with a rocket engine.

As for pulse detonation, bombs can have shaped explosions, so that is one way to direct the blast mostly toward the pusher plate.

Nuclear thermal rockets were giving Isp (via heating up hydrogen) of 800s in the early 1970s.  I've heard that Isp ~1200s should be viable now for NTRs.  Metalic hydrogen would have the same issues, and could be cut with LOH to get the most thrust for your given metalic hydrogen (at the cost of Isp).  I'd hope that's enough to get you a SSTO.

2 hours ago, sevenperforce said:

A chemical Orion is a non-starter. Isp is way too low. Generally, blowing something up and using a pusher plate is really inefficient. The only reason it works well with the Orion concept is that the amount of energy is high enough to overcome inefficiencies. Plus, I think you get a boost in atmo thanks to added reaction mass.

I wouldn't ignore fuel-air explosions.  It would  be a quick and dirty means of getting an air-breather up.  The real issue is that an air-breathing Orion SSTO isn't just going to LEO, it has to go to basically LTI (not really, but the difference in delta-v between where the magnetosphere ends and escape velocity is pretty small) before firing up the nukes (assuming you can convince people to let you put them on board).  Does LOH even work as a fuel-air bomb?  I'm pretty sure you could get kerosene to go boom, but I've never heard of LOH (probably because chemical Orions would be the only reason you would try it).  You should also be able to spray the LOH in such a way to get a highly effective shaped charge toward the pusher plate.

The two real contenders for "first SSTO" would have to be a space elevator and an Orion.  Once space elevators are built, I can't imagine much R&D wasted on SSTOs (although you might get enough Isp that it would be a non-issue someday).  Of course, space elevators easily require as much unobtanium as any other SSTO, but simply have more return on investment than any competitor.  The Orion could be built by anyone who really wanted to explore space directly and had the political backing to do it.  Metalic hydrogen might squeak in, but I'm guessing early reports were overly optimistic.

[sevenperforce]

3 hours ago, wumpus said:

I wouldn't ignore fuel-air explosions.  It would  be a quick and dirty means of getting an air-breather up.  The real issue is that an air-breathing Orion SSTO isn't just going to LEO, it has to go to basically LTI (not really, but the difference in delta-v between where the magnetosphere ends and escape velocity is pretty small) before firing up the nukes (assuming you can convince people to let you put them on board).  Does LOH even work as a fuel-air bomb?  I'm pretty sure you could get kerosene to go boom, but I've never heard of LOH (probably because chemical Orions would be the only reason you would try it).  You should also be able to spray the LOH in such a way to get a highly effective shaped charge toward the pusher plate.

My suspicion is that once shaped-charge losses became involved, a fuel-air approach would have no better specific impulse than chemicals...or, at the very least, not high enough to make up for the increase in dry mass. You also have to deal with the same problem faced by scramjets: you need sufficient mixing at subsonic, supersonic, and increasingly hypersonic speeds. At Mach 2+, the wake shock behind a vehicle would be so rarified that it would be almost impossible to get enough oxygen for a detonation. You would almost need an intake to allow mixing, at which point we are dealing with a hypersonic pulsejet anyway.

Of course, if you are building an Orion, you will want to shape the pusher plate in such a way as to take advantage of atmospheric reaction mass. And if you have a pusher-plate Orion optimized to use atmospheric reaction mass, then you could at least get a few pulses out of a fuel-air approach before you were going too fast to allow mixing. With either a conventional Orion or a dual-thrust-axis SSTO, you could conceivably use a fuel-air explosion (or several of them) to get the initial kick up and away from the bulk of the atmosphere, at which point you could light up the nukes. Orions need to launch from the poles anyway to avoid causing EMPs, so once you do the first few pulses with chemical fuel you can light up the Orions in-atmo.

If you're using a conventional (VTOL) Orion, you can get almost double efficiency out of the very first pulse because the shockwave reflects off the launch pad, so that would make a chemical "first stage" more viable.

[kerbiloid]

A shockwave moving in a static medium and a gas flow are not the same.
Orion's propulsive action is based on the focused gas (plasma) flow, pushing the plate, not on a shockwave.

An explosion in mid-air would cause a shockwave. Of course it pushes things, too, but mostly it ununiformly compresses them or makes a short by strong kick.

Edited August 27, 2019 by kerbiloid

[sevenperforce]

3 hours ago, kerbiloid said:

A shockwave moving in a static medium and a gas flow are not the same.
Orion's propulsive action is based on the focused gas (plasma) flow, pushing the plate, not on a shockwave.

An explosion in mid-air would cause a shockwave. Of course it pushes things, too, but mostly it ununiformly compresses them or makes a short by strong kick.

With Orion, the distinction is rather unimportant because you are dealing with massively hypersonic particle velocities anyway.

[kerbiloid]

19 minutes ago, sevenperforce said:

With Orion, the distinction is rather unimportant because you are dealing with massively hypersonic particle velocities anyway.

The distinction is not in the hit details, but in that it doesn't cause a shockwave in a static medium which stays motionless behind the shockwave front. It sends a gas/plasma flow in plate direction.

Unlike an explosion in mid-air.
So, Orion is a gas pump, not just an explosion. The explosion is just its energy source.

So, the idea of conventional blasts pushing a craft works only with very small models, like the Orion mockups were.
When a hand-sized model is pushed by a chemical mini-blast, the distance is so smal that the expanding gas cloud and the shockwave are both close to the model.
So, the model is just pushed by an unfocused gas cloud radial flow simultaneously with the shockwave kick.

With real a Orion-sized ship the blast would happen at enough great distance to have the shockwave and the gas cloud separated (when the gas has stopped expanding due to the air pressure), so the shockwave is mostly a trouble.

In vacuum the only shockwave affecting the ship would appear when the gas flow meets the plate.

So, an aerial blast propulsion is unlikely a thing for crafts bigger than an on- table mockup.

(finished editing)

Edited August 27, 2019 by kerbiloid

[DDE]

On 8/26/2019 at 10:56 PM, Spacescifi said:

As for pulse detonation, bombs can have shaped explosions, so that is one way to direct the blast mostly toward the pusher plate.

I'm not sure that it's easy to pull off with metallic H. It would be premature to assume it's metastable and easily formed into an arbitrary shape.

13 hours ago, sevenperforce said:

If you're using a conventional (VTOL) Orion, you can get almost double efficiency out of the very first pulse because the shockwave reflects off the launch pad, so that would make a chemical "first stage" more viable.

If you're using an Orion, the first charge in a "burn" is half-powered because the pusher plate isn't swung down to limit of the absorbers.

[YNM]

What's the advantage of landing with the engine that's supposed to help you land (and no other asistance) facing sideways and not downwards ?

Alright the forum crashed on me just after I realize I miss the two-engine scheme but before I can edit my post.

 

What would be the advantage of having two propulsion system that both have a TWR > 1 ?

Edited August 28, 2019 by YNM

[sevenperforce]

9 hours ago, YNM said:

What's the advantage of landing with the engine that's supposed to help you land (and no other asistance) facing sideways and not downwards ?

There are a few. Dedicated landing engines can be higher-thrust and lower-efficiency than main engines because their burn time is lower (by analogy, the Puff monopropellant engine had the highest vacuum TWR of any non-SRB back when I was playing regularly). They can also be mounted in a way that protects them from debris on landing, which is more complex to accomplish with a main engine. Dual-thrust-axis landing allows for a more stable landing arrangement with fewer catastrophic failure modes and obviates the need for cranes or complex ingress/egress. If you have a main engine which is known for doing nasty things (like Orion or a NSWR), it allows you to avoid firing that "torchship" engine near the surface. It allows you to better optimize that main engine for lower atmospheric pressures.

[YNM]

5 minutes ago, sevenperforce said:

Dedicated landing engines can be higher-thrust and lower-efficiency than main engines because their burn time is lower (by analogy, the Puff monopropellant engine had the highest vacuum TWR of any non-SRB back when I was playing regularly).

When you're powering yourself with explosions it kind of seems moot. Alright apart from not exploding the ground but why not orbit all the way with the takeoff engine ?

6 minutes ago, sevenperforce said:

They can also be mounted in a way that protects them from debris on landing, which is more complex to accomplish with a main engine.

I kind of question this since if anything your exhaust would be clearing up the debrises, and AFAIK rocket engines doesn't suck in anything.

7 minutes ago, sevenperforce said:

Dual-thrust-axis landing allows for a more stable landing arrangement

Unless one of them is something you'd never use near the ground...

8 minutes ago, sevenperforce said:

If you have a main engine which is known for doing nasty things (like Orion or a NSWR), it allows you to avoid firing that "torchship" engine near the surface.

True, but honestly I wouldn't try operating them anywhere inside an atmosphere, unless you couldn't care enough for the inhabitant of the planets, in which case just use it all the way to the ground anyway !

[sevenperforce]

4 hours ago, YNM said:

When you're powering yourself with explosions it kind of seems moot. Alright apart from not exploding the ground but why not orbit all the way with the takeoff engine?

Apart from a LOX-augmented nuclear thermal rocket (LANTR), there really aren't any liquid-propellant engines with enough thrust AND enough specific impulse to get you into orbit. Also, the side-mounted rockets are not inline and so you wouldn't want to use them for acceleration through the atmosphere, anyway. You can put the engines in side-mounted nacelles a la Serenity if you want, but that might be more trouble than it is worth.

You need to have a liquid-propellant thruster system somewhere, after all, because you need translation and attitude control. You also need liquid landing engines because you cannot exactly land using pusher-plate retropropulsion.

4 hours ago, YNM said:

if anything your exhaust would be clearing up the debrises, and AFAIK rocket engines doesn't suck in anything.

Simulations of exhaust reflection off unprepared surfaces indicates severe damage to engine bells in most cases.

4 hours ago, YNM said:

True, but honestly I wouldn't try operating them anywhere inside an atmosphere, unless you couldn't care enough for the inhabitant of the planets, in which case just use it all the way to the ground anyway !

Nuclear pusher-plate launch doesn't really pose a major health risk. As long as it's done far enough away from population centers, with "clean" mostly-fusion nukes, the global increase in cancer risk is very low.

And you can't use it all the way to the ground, after all -- you're going to have to switch to thrusters at some point because pulse propulsion does not play well with landing pads.