How Far Will A Pusher Plate Take You?

[Spacescifi]

Say I snapped my fingers and put a fully loaded pusher plate project orion battleship in orbit.

How far could it get in the solar system for a manned round trip return to Earth?

Mars? Saturn? Jupiter?

Objective: Crew must be alive and reasonably healthy when they return.

Specs: Although fully kitted for travel, you will have to bring food on board to last the duration of the trip. Personally I would choose veggies and fruits to grow in zero g.

 

Bonus question: Swap the nukes for anti-iron (ferromagnetic antimatter) bombs. Now how far can you get on a round trip in the solar system back to Earth?

 

Edited March 25, 2020 by Spacescifi

[magnemoe]

Depend on the size of it, the battleship version, I say Saturn  if you spun it up or used tumbling pigeon, that is having an fairly long ship and used the orion engine as an counterweight. Perhaps Uranus for an more advanced run.
Grown food would be salad for taste. Much easier to bring frozen food for an 3-6 year voyage. 

[Bill Phil]

Depends on the specific impulse and mass ratio, as well as the trajectory flown.

For a decent variant a moon of Saturn and back isn't that far fetched, provided the payload isn't too massive or you're willing to sacrifice acceleration.

For an antimatter vehicle, anywhere is possible - provided you have the mass ratio.

[Spacescifi]

38 minutes ago, Bill Phil said:

 

For an antimatter vehicle, anywhere is possible - provided you have the mass ratio.

 

Likely I suppose, given that the antimatter bomb units are the size of this:

 

1 hour ago, magnemoe said:

Depend on the size of it, the battleship version, I say Saturn  if you spun it up or used tumbling pigeon, that is having an fairly long ship and used the orion engine as an counterweight. Perhaps Uranus for an more advanced run.
Grown food would be salad for taste. Much easier to bring frozen food for an 3-6 year voyage. 

 

I guess we must make sure no one eats too much LOL.

Edited March 26, 2020 by Spacescifi

[magnemoe]

13 minutes ago, Spacescifi said:

 

Likely I suppose, given that the antimatter bomb units are the size of this:

 

 

I guess we must make sure no one eats too much LOL.

You would not use bombs with antimatter but constant trust who is much safer and easier. Orion pulsing is simiply because its an limit on how small you can make effective nuclear bombs and they become less efficient if smaller. 
Now for fusion engines most of the current design is also pulsed as its easier but its not nuclear bomb level, rather think shooting an 20-40 mm cannon, because fusion is not self supported it will be an minutes long delay between pulses as it charges up. 
If self sustained fusion if would still just feel like an automatic cannon or stuff like an pile driver. in short many order of magnitude lower. 

[Spacescifi]

2 hours ago, magnemoe said:

You would not use bombs with antimatter but constant trust who is much safer and easier. Orion pulsing is simiply because its an limit on how small you can make effective nuclear bombs and they become less efficient if smaller. 
Now for fusion engines most of the current design is also pulsed as its easier but its not nuclear bomb level, rather think shooting an 20-40 mm cannon, because fusion is not self supported it will be an minutes long delay between pulses as it charges up. 
If self sustained fusion if would still just feel like an automatic cannon or stuff like an pile driver. in short many order of magnitude lower. 

 

It is my opinion based on the information I have seen so far that pusher plates have greater round trip range than AM thermal rockets.

As awesome as antimatter thermal rocketry is, it's weakness is it's reliance on tons of reaction mass.

I can give rocket vessel eight hundred tons of LH and 500 kilograms of antimatter to spare.

Or I could give pusher plate vessel eight hundred tons of lime size AM bombs.

 

Even if both vessels weigh exactly the same, the pusher plate should outlast the rocket easily for travel range.

Since the AM thermal rocket simply lacks the thrust capacity that pusher plate provides.

Since you can only safely blow up so much AM inside a rocket, and you can use more for a pusher plate.

 

AM thermal rockets with airbreathing make decent small SSTO's.

But a legit interplanetary spaceship?

Not so much as far as I can tell. Unless you perhaps have information I have not considered.

[p1t1o]

8 hours ago, Spacescifi said:

 

It is my opinion based on the information I have seen so far that pusher plates have greater round trip range than AM thermal rockets.

As awesome as antimatter thermal rocketry is, it's weakness is it's reliance on tons of reaction mass.

I can give rocket vessel eight hundred tons of LH and 500 kilograms of antimatter to spare.

Or I could give pusher plate vessel eight hundred tons of lime size AM bombs.

 

Even if both vessels weigh exactly the same, the pusher plate should outlast the rocket easily for travel range.

Since the AM thermal rocket simply lacks the thrust capacity that pusher plate provides.

Since you can only safely blow up so much AM inside a rocket, and you can use more for a pusher plate.

 

AM thermal rockets with airbreathing make decent small SSTO's.

But a legit interplanetary spaceship?

Not so much as far as I can tell. Unless you perhaps have information I have not considered.

There is a great deal of handwaving and opinion here, how serious do you want these answers to be? Because even if you just want to reach "hard scifi" levels, there is a huge amount of work to flesh out your ideas - and to see if they actually work. And all this is before we consider how unbelievably difficult anti-iron is to come by.

Edited March 26, 2020 by p1t1o

[kerbiloid]

3 hours ago, p1t1o said:

how unbelievably difficult anti-iron is to come by.

The anti-iron is a common product of the fusion in the antimatter stars.

Just find the antimatter sector of the universe.

[sevenperforce]

15 hours ago, magnemoe said:

You would not use bombs with antimatter but constant trust who is much safer and easier. Orion pulsing is simiply because its an limit on how small you can make effective nuclear bombs and they become less efficient if smaller. 

Exactly.

13 hours ago, Spacescifi said:

It is my opinion based on the information I have seen so far that pusher plates have greater round trip range than AM thermal rockets.

That is not correct.

13 hours ago, Spacescifi said:

As awesome as antimatter thermal rocketry is, it's weakness is it's reliance on tons of reaction mass.

Pusher plates need reaction mass too: a tamper made of tungsten powder that is vaporized into plasma at detonation. In terms of total impulse, an antimatter rocket would use many many times less reaction mass than a pusher-plate rocket. Also less dry mass.

13 hours ago, Spacescifi said:

Even if both vessels weigh exactly the same, the pusher plate should outlast the rocket easily for travel range.

It will not.

13 hours ago, Spacescifi said:

Since the AM thermal rocket simply lacks the thrust capacity that pusher plate provides.

If you want the antimatter rocket to have more thrust, just make it bigger. You can make it as big as you want. It would have thrust equivalent to a pusher-plate design at a fraction of the total weight.

13 hours ago, Spacescifi said:

Since you can only safely blow up so much AM inside a rocket, and you can use more for a pusher plate.

That is a bug, not a feature.

[KSK]

Okay, a couple of thoughts on this.

The Project Rho website, includes figures for a liquid core antimatter engine with a thrust-to-weight ratio of 2 and an ISP of 2000. That seems like a nice middle ground with a decent amount of thrust and respectable ISP. Solid core antimatter-thermal gives you more thrust but less ISP,  gas and plasma core gives you the opposite. 

Lets take that 800 tons of liquid hydrogen and assume a mass ratio of 5 for our spacecraft (for reasons which will become clear), which is powered by that liquid-core AM engine.

So, assuming my maths is correct, that gives us a 200 ton spacecraft (wet mass 1000 tons, dry mass 200 tons, mass ratio 5) with a total delta-V of approximately 31.5 km/s, and a pretty lousy thrust to weight ratio. Can't give you a number since Project Rho doesn't give an estimated engine mass. So you wouldn't be landing on much with this spacecraft but it should be perfectly fine for getting you into orbit around somewhere.

But where?

Well a direct Hohmann transfer to Pluto requires a delta-V of about 11.6 km/s from LEO. So going with the original premise that we're putting this thing in orbit with a snap of our fingers (maybe we can ask Thanos real nicely like ), then it looks perfectly capable of getting us to pretty much anywhere in the Solar System and back, although to keep journey times manageable, maybe aim at Jupiter or Saturn and use a higher energy trajectory.

Now, taking a quick skim through my copy of Project Orion. ( @Spacescifi - if you don't have a copy of this, I think you'd probably enjoy it), the Orion team were envisaging round trips to Saturn in 3 years, requiring a total delta-V of 80km/s (which I assume includes the launch from Earth and possibly the landing back on Earth) and requiring a mass ratio of 5. So a fission Orion spacecraft gives you nearly 3x the delta-V of the above AM rocket and presumably a rather better thrust-to-weight ratio.

Now, it's unclear how much more performance you get from going to antimatter pulse units rather than fission pulse units for your Orion. In practice, I suspect there may not be that much difference in mass between the two. An example Orion pulse unit design (yield 1 kiloton) weighed in at about 140kg including fissionable core, tungsten propellant and everything else. Now that's mostly solid state and so fairly rugged and amenable to being fired out of the back of a spacecraft. The antimatter pulse unit will require a much smaller antimatter core of course,  but it will still need propellant and it will probably need a fairly hefty containment unit to keep that antimatter where it's meant to be whilst it's being shot out of the back of a spacecraft.  

Incidentally, a 10m Orion was planned for trips to Mars. It would have used around 2500 of those 140kg pulse units.

And, as a slight aside, a version of Orion was sketched out which would have been capable of reaching a velocity of 10,000 km/s (so approximately 3% lightspeed). It would have weighed 240 million tons, 90% of which was pulse units, had a pusher plate 150km in diameter, would take 30 years to accelerate to full speed and 150 years to cover the 4 light years to Alpha Centauri. And that was the 'small' version.

This is why I think interstellar flight in KSP2 is rather silly.

 

 

 

Edited March 26, 2020 by KSK

[sevenperforce]

The 1959 Interplanetary Orion had a planned specific impulse of 4,000 s and a propulsion system TWR of 4.8 or thereabouts. That is NOT a high TWR; it's barely higher than the lowly NERVA and it's nowhere near conventional chemical rocket engines that routinely reach TWR of 60-100 or more.

What Project Rho doesn't account for is inert propellant injection into the propellant stream of a plasma-core antimatter rocket.

 

[Bill Phil]

7 minutes ago, sevenperforce said:

The 1959 Interplanetary Orion had a planned specific impulse of 4,000 s and a propulsion system TWR of 4.8 or thereabouts. That is NOT a high TWR; it's barely higher than the lowly NERVA and it's nowhere near conventional chemical rocket engines that routinely reach TWR of 60-100 or more.

What Project Rho doesn't account for is inert propellant injection into the propellant stream of a plasma-core antimatter rocket.

 

Is that Orion TWR for the propulsion system alone or the entire vehicle?

[sevenperforce]

1 hour ago, Bill Phil said:

Is that Orion TWR for the propulsion system alone or the entire vehicle?

Propulsion system alone. 

[KSK]

Oh, I'm sure there's a lot I'm missing with respect to AM propulsion. I only took a fairly cursory look at Project Rho and, whilst that's good, it's only a single source of information.

But to answer the original question - I think that a fully loaded Orion in orbit could go pretty much anywhere in the Solar System. And as an aside to that, antimatter thermal rocketry will get you pretty far too, so I wouldn't dismiss it out of hand in favour of a pusher plate design.

[sevenperforce]

7 hours ago, KSK said:

Oh, I'm sure there's a lot I'm missing with respect to AM propulsion. I only took a fairly cursory look at Project Rho and, whilst that's good, it's only a single source of information.

But to answer the original question - I think that a fully loaded Orion in orbit could go pretty much anywhere in the Solar System. And as an aside to that, antimatter thermal rocketry will get you pretty far too, so I wouldn't dismiss it out of hand in favour of a pusher plate design.

The upper limit on pusher-plate specific impulse is somewhere around 12,000 s. The upper limit on the specific impulse of an antimatter rocket is somewhere around 15,000,000 s.

[wumpus]

On 3/26/2020 at 11:40 AM, kerbiloid said:

The anti-iron is a common product of the fusion in the antimatter stars.

Just find the antimatter sector of the universe.

That should be easy to find, just find a bunch of space glowing due to all the matter/anti-matter annihilation going on (hint: we don't know of any.  We'd expect huge areas if there were galaxies of anti-matter, but there aren't.  You think you'd find small areas of anti-iron, but I've never heard of any.

8 hours ago, sevenperforce said:

The upper limit on pusher-plate specific impulse is somewhere around 12,000 s. The upper limit on the specific impulse of an antimatter rocket is somewhere around 15,000,000 s.

When I first heard of Orion (probably from Carl Sagan's Cosmos), I've always heard an "can achieve .1c" with no explanation of 30000000m/s delta-v. 

Going by the 12,000s assumption, I'm seeing a wet/dry ratio in the googol (>10¹⁰⁰) range.

On 3/26/2020 at 4:43 PM, sevenperforce said:

Propulsion system alone. 

The pusher plate and spring system should account for a large proportion of an Orion.  Well, at least until you load it up with a few googol nukes.

[Pds314]

On 3/27/2020 at 7:18 AM, sevenperforce said:

The upper limit on pusher-plate specific impulse is somewhere around 12,000 s. The upper limit on the specific impulse of an antimatter rocket is somewhere around 15,000,000 s.

Wait why is pusher plate so low? That's only 1000x the exhaust energy of conventional rockets yet nuclear weapons readily get into kt/kg range, i.e. 1 million times the exhaust energy of chemical rockets. 80% of this can be directed in a 22 degree cone using shaped charge nuclear detonations too. So I don't see why it's so low.

Edited April 7, 2020 by Pds314

[wafflemoder]

5 minutes ago, Pds314 said:

Wait why is pusher plate so low? Shaped charge Nuclear explosives can have specific impulses of millions so does the pusher plate ablate too quickly or something?

You're probably thinking of specific energy, which is very high in nuclear devices.

In terms of specific impulse, the explosive casing can limit final velocities, and much of the energy is wasted from cosine losses, as only a fraction of the explosion actually hits the pusher plate.

There was a proposal to launch the nuclear bombs ahead of the craft and use a large sail structure to use around half of the explosion called Medusa, which could achieve specific impulses of 50000 to 100000

[Bill Phil]

33 minutes ago, Pds314 said:

Wait why is pusher plate so low? That's only 1000x the exhaust energy of conventional rockets yet nuclear weapons readily get into kt/kg range, i.e. 1 million times the exhaust energy of chemical rockets. 80% of this can be directed in a 22 degree cone using shaped charge nuclear detonations too. So I don't see why it's so low.

Not because there isn't enough energy, but because the pusher plate is actually very inefficient. It's basically a brute force attempt to harness nuclear energy for propulsion. Making the plate larger to catch more propellant/energy and making the shocks more efficient would improve performance. Indeed a larger Orion ship (probably taking advantage of thermonuclear pulse units as well) could likely get much higher specific impulse than just 12 thousand seconds, but at that point making large vehicles becomes less practical and it's better to use something more like Mini-Mag Orion or Medusa for that performance.

 

[Spacescifi]

14 hours ago, Bill Phil said:

Not because there isn't enough energy, but because the pusher plate is actually very inefficient. It's basically a brute force attempt to harness nuclear energy for propulsion. Making the plate larger to catch more propellant/energy and making the shocks more efficient would improve performance. Indeed a larger Orion ship (probably taking advantage of thermonuclear pulse units as well) could likely get much higher specific impulse than just 12 thousand seconds, but at that point making large vehicles becomes less practical and it's better to use something more like Mini-Mag Orion or Medusa for that performance.

 

 

Call me crazy but I say there IS a way to make an atmospheric launched Medusa using nukes or AM bombs.

Step 1: Make the large catcher net. It's going to be HUGE with tethers.

Step 2: Attach tethers. From the net to the sides of the spaceship.

Step 3: Attach an array of booster rockets to the edges of the net. A

Step 4: Launch the net via the boosters, while the net tugs at the ship which remains on the ground, while fully stretched, the grounded ship launches a a nuclear missile to detonate in an airburst  high above it where the net is hovering.

 

Before the nuclear missile is launched the booster rockets detach and fly away from the net.

Then before the net can fall back to Earth the nuke detonates, and in strange display, the ship on the ground is yanked upward as if by some massive balloon... propelled by NUCLEAR explosions.

 

We could do it... and my details and methods may be off, but this IS an engineering problem we CAN solve.

 

Edited April 8, 2020 by Spacescifi

[kerbiloid]

1 hour ago, Spacescifi said:

but this IS an engineering problem we CAN solve.

Just an umbrella pushed with antimatter blasts. We did it last week.

[Wjolcz]

This isn't scientific at all. It's just a rocketry fanfic.

[kerbiloid]

1 hour ago, Wjolcz said:

This isn't scientific at all. It's just a rocketry fanfic.

It's a rocketry fanscific.

P.S.
But Medusa has one more advantage.

Spoiler

We can use it as parachute.

 

[sevenperforce]

8 hours ago, Spacescifi said:

Step 4: Launch the net via the boosters, while the net tugs at the ship which remains on the ground, while fully stretched, the grounded ship launches a a nuclear missile to detonate in an airburst  high above it where the net is hovering.

That is some true fanfic.

[wafflemoder]

External pulse propulsion systems like orion, medusa, minmag orion, or even epstein-like fusion or antimatter systems aren't very feasible for usage in atmospheric or low orbital flight.

The first issue is that they can't be used on the surface, as the shock wave reflecting off the launch pad would shred the craft. This is already an issue with larger vehicles like the shuttle, and would be far worse with pulse systems.

Medusa can get around this, as it launches explosive ahead of itself, but it will have ridiculously stupid amounts of drag and be aerodynamically unstable, as it's basically launching while keeping a parachute in front of your craft. Having an external pulse propulsion system as a second stage could also potentially get around this issue, as continuous pulse systems like conventional rockets would be less catastrophic.

Using an orion drive or other external pulse drive in the upper atmosphere and low orbit also has its fair share of problems. Each blast would result in a large EMP, knocking out power in a significant area. Detoning nuclear and antimatter weapons in orbit can also create artificial radiation belts, with isn't exactly desirable.

External pulse propulsion is certainly good in space (though there are certainly better options), but don't even think that they can be used anywhere near a planet.