Antimatter.. how good is it for propulsion?

[Guest]

Sounds interesting! Best of luck!

[NSEP]

Im not a rocket scientist, but geussing the antimatter rocket you are describing is called a Beam Core, which uses equal amounts of matter and antimatter to smash them together and generate tremendous amounts of energy. Its one of the most efficient rocket engines on the Atomic Rockets Engine List, so it must be a good, maybe not exactly for surface to orbit travel, but whatever.

Beam core engines have around 100 million m/s of exhaust velocity, which is extremely fast (like 33% the speed of light)

If we throw these numbers in this calculator, a spacecraft with a dry mass of 97000t would need 9t of fuel to get 9278m/s of Delta-V, which is enough for orbit. Thats like roughly 0.01% of the total ship mass being fuel.

[Spacescifi]

11 minutes ago, Dale Christopher said:

Sounds interesting! Best of luck!

 

Thanks. Kerbal players undesrstand better than most that rocket technology alone does not lend itself toward massive scifi spaceship's that come and go as they please.

In fact, I saw one post on the forums that indicated that infrastructure is needed for regular routes. Refueling stations.

One can boldly go where one has never gone before with rockets... but not randomly. It has to all be pre-planned. Or a crew risk being stranded.

A change of plans can happen, but only at the expense of lots of time doing gravity assist.

6 minutes ago, NSEP said:

Im not a rocket scientist, but geussing the antimatter rocket you are describing is called a Beam Core, which uses equal amounts of matter and antimatter to smash them together and generate tremendous amounts of energy. Its one of the most efficient rocket engines on the Atomic Rockets Engine List, so it must be a good, maybe not exactly for surface to orbit travel, but whatever.

Beam core engines have around 100 million m/s of exhaust velocity, which is extremely fast (like 33% the speed of light)

If we throw these numbers in this calculator, a spacecraft with a dry mass of 97000t would need 9t of fuel to get 9278m/s of Delta-V, which is enough for orbit. Thats like roughly 0.01% of the total ship mass being fuel.

 

Interesting. So 3 tons is not enough. Also thanks, so we are burning through tons of antimatter now LOL!

Edited June 15, 2019 by Spacescifi

[farmerben]

Project Orion nuclear propulsion was mentioned.  

It is important to realize that the pusher plate design creates a large plasma ball to generate thrust.  At launch it could use atmospheric fireballs, but it required larger bombs with more plasma in a vacuum.  I think they planned to use lithium, beryllium, and boron to generate as many alpha particles as possible, and then use vaporized tungsten to help thermalize the helium before striking the massive steel plate.

The Medusa concept relied on X-ray propulsion, and therefore could use bombs with less filler.  But that requires many square kilometers of sail to actually work.  

Gamma ray mirrors do not exist, because the wavelength is subatomic.

[Bill Phil]

6 hours ago, farmerben said:

Project Orion nuclear propulsion was mentioned.  

It is important to realize that the pusher plate design creates a large plasma ball to generate thrust.  At launch it could use atmospheric fireballs, but it required larger bombs with more plasma in a vacuum.  I think they planned to use lithium, beryllium, and boron to generate as many alpha particles as possible, and then use vaporized tungsten to help thermalize the helium before striking the massive steel plate.

The Medusa concept relied on X-ray propulsion, and therefore could use bombs with less filler.  But that requires many square kilometers of sail to actually work.  

Gamma ray mirrors do not exist, because the wavelength is subatomic.

My understanding was that Orion would use smaller yield bombs for atmospheric flight (taking advantage of the atmosphere) and use larger yields in vacuum, probably with more propellant as well. From what I’ve seen they planned to use the radiation from the explosion to rapidly vaporize the propellant (tungsten or whatever material) before the whole propulsion unit was blown apart/vaporized.

 

[Cheif Operations Director]

On ‎6‎/‎14‎/‎2019 at 1:15 AM, Nightside said:

Weight is a function of mass and acceleration (mainly gravity). If you have a “gravity neutralizer” then your weight is zero, so any amount of thrust would give you an infinite TWR.

  Hide contents

What I want to know is: how does the gravity get neutralized??? I think the device should work by completely annihilating all mass on the planet, removing its gravitational pull. Useful, but with some functional limitations. 

 

I should know more than I do to answer this but just an idea

What if you have gravity pulling at x m/s toward a thing

Could'nt you pull it at x m/s the other direction

 

Effectivley x m/s - xm/x = 0

Add:

I was stating that outside of the OPs post

[kerbiloid]

9 hours ago, farmerben said:

Project Orion nuclear propulsion was mentioned.  

It is important to realize that the pusher plate design creates a large plasma ball to generate thrust.  At launch it could use atmospheric fireballs, but it required larger bombs with more plasma in a vacuum.  I think they planned to use lithium, beryllium, and boron to generate as many alpha particles as possible, and then use vaporized tungsten to help thermalize the helium before striking the massive steel plate.

Orion didn't use plasma balls for propulsion. The pusher plate was pushed with gaseous tungsten pancakes. The tungsten membrane was vaporized with Xray.

Edited June 16, 2019 by kerbiloid

[farmerben]

I think people are quibbling with my word choices rather than making a substantially different point.  Whether you call it plasma, vapor, or gaseous material is all roughly the same thing, but I believe plasma is the correct word for a body of ionized atoms lacking a stable electron configuration (which is everything in the bomb right after detonation).  

They were trying to create the cleanest dirty bombs they could.  This meant using the minimum amount of plutonium for the core, and using primarily deuterium lithium 6 for higher yields. 

Some pictures label the channel filler as beryllium oxide.  Beryllium can photofission into 2 alphas plus a neutron.  Or Beryllium can absorb alpha particles transmuting into Carbon plus a neutron.  

Beryllium neutron sources are used to "dial a yield".  And to spike the pit with extra neutrons driving the supercriticality factor of the plutonium higher and getting better burnup.   Such a neutron source is undoubtedly included in the nuclear device.  However, the channel filler is way larger than just that.  And the oxygen is detrimental to boosting plutonium burnup.

So clearly the idea is to disintegrate as much beryllium as possible, throwing helium, carbon, and oxygen ions in the desired direction.  

The radiation case and propellant reflect many X-rays and fast neutrons, and serve as mass tampers to slow the expansion of ions inside. Tungsten is not the most powerful choice, but good for this application.  Making the tungsten propellant cap thicker, shields the spacecraft, and makes it so that a much slower denser plasma cloud impacts the spacecraft.  But it wastes a good deal of energy and contributes little to the explosive power.  

 

I've never heard anyone mention putting Boron in a bomb, but I would.  There is dead space between the radiation case and the delivery case.  There is also lots of extra neutron radiation.  Using Boron 10 would scatter, thermalize, and absorb the most neutrons, yielding even more alpha particles and lithium ions.  In other words a bigger more powerful plasma ball, and at the same time protecting the Earth from unnecessary neutron radiation, during atmospheric launch.  

 

 

 

 

 

[kerbiloid]

2 hours ago, farmerben said:

Some pictures label the channel filler as beryllium oxide.  Beryllium can photofission into 2 alphas plus a neutron.  Or Beryllium can absorb alpha particles transmuting into Carbon plus a neutron.  

Beryllium oxide (channel filler), tungsten (propellant), and uranium (radiation case) catch neutrons and keep X-rays inside the case. This btw protects the ship from the radiation.
The filler and the propellant both become plasma, uranium is a mirror.
Lightweight plasma of filler pushes the flat plasma cloud of propellant towards the ship.
The propellant pancake spreads out as a long narrow jet (because originally it was flat) and hits the plate.

A load of protective liquid (oil or water) is spread from synchronized ejector(s) onto the plate surface to soften the hit.
The 150 km/s fast tungsten jet hits the plate and spreads aside.

Carbon and oxygen are too heavy and slow, so unlikely playe any role, at least they aren't mentioned.

Edited June 16, 2019 by kerbiloid

[farmerben]

Uranium makes a more powerful radiation case because even depleted uranium fissions with fast neutrons.  This is used for weapons, but it increases fallout.  So if the idea is to make the cleanest device, then one wouldn't use it.  

There is a minimum size of fissile material they must use.  For more powerful yields they would use the same amount of fissile but more deuterium lithium 6.  The lithium splits into tritium plus an alpha, and then tritium deuterium fusion occurs.  Far less fallout is created.  And it has higher TWR than fission.  

The beryllium will undergo nuclear reactions and be exploding before the blast of the primary even gets to it.   If they just wanted an inert filler that is transparent; water, plastic, or table salt would do that much cheaper.  

I basically agree about all the useful things the tungsten pusher plate does, but this is only going to protect against some of the radiation.  There will still be plenty of all types of radiation hitting the pusher plate.  

Fortunately, steel can eat alpha and beta radiation all day and not care.  Neutrons are partially scattered, but barely slowed down at all by steel.  Water and oil do almost nothing against X-rays, but they would carry away heat.

If the ablative oil has lithium or boron in it, it can trade some of those neutrons for more sweet sweet alphas.  Lithium and boron greases are widely used on steel machinery.  

[natsirt721]

On 6/14/2019 at 12:55 AM, Spacescifi said:

 

Say you had a device to neutralize gravity's pull on a spaceship with the mass of an aircraft carrier (97,000 tons fully loaded).

 

You are using liquid hydrogen as propellant and mixing it with antimatter. You have 3 tons of antimatter on board.

Would your thrust to weight ratio be decent enough to make several take offs and landings? Or just one or two before running out of propellant?

What about fuel to cargo ratio? Would the aircraft cartier mass spaceship be more than 10% fuel tank? 50%? 80%?

 

Granted this works better for take off with grav-neutralization, but I still wanna know.

Alrighty, lets see here.

First off, I don't recommend using antimatter for surface-to-orbit, because of two reasons. One, a single kilogram of antimatter, when annihilated could easily destroy the moon and probably sterilize the Earth too, so if your launch fails you better have a plan to keep that antimatter safe as you plummet back to the ground. Two, antimatter annihilation produces lots of gamma rays, which will basically kill anything living nearby which isn't properly shielded. Not so great to do on a possibly inhabited surface.

Take a look at this 'realistic' antimatter engine for a sense of scale.

But screw that noise, you want an engine, dammit! 

For liftoff, we need a TWR of about 1.2. 97 kilotons with a TWR of 1.2 makes for an thrust of about 1.15e9 Newtons.

Antimatter reactions produce their energy with about 1/3 gamma radiation and 2/3 charged pions. Lets ignore the gamma radiation and focus on the pions, because they're charged so you can move them around with magnets and harvest their energy.  One gram of matter annihilating one gram of antimatter makes 1.8e14 joules of energy, times 2/3 for the pions makes 1.2e14 J. The pions are moving at 0.94c, so we can just blow them out the back of the spacecraft and call it thrust.  Thrust power = 1.2e14 J/g * antimatter mass = Thrust * Exhaust velocity * 0.5. At 1 gram per second our thrust is 8.53e8 N. Not bad for a conventional engine, but that ain't gonna cut it for our ship.  Fortunately, we can increase the thrust by adding LH2 and reducing our exhaust velocity.

This is where the engineering comes in.  We basically pick the exhaust velocity such that we don't use too much antimatter, and we don't need too much LH2

Quote

P_t = 1.2e¹⁷ J/kg * mdot_a = T * V_e * 0.5 = (mdot_LH2 * Ve²) * 0.5

• Pt is thrust power, W
• 1.2e¹⁷ is antimatter power production per gram of antimatter J/kg
• mdot_a is antimatter consumption rate, kg/s
• T is engine thrust, 1.15e9 N
• V_e is effective exhaust velocity, m/s
• mdot_LH2 is LH2 mass flow rate  kg/s

For a Ve of 100,000 m/s, our thrust power is 57.5 TW, which is 4.8e-4 kg of antimatter per second, or about half a gram per second. LH2 consumption rate is 11 tons per second. For one liftoff/touchdown cycle (call it 20kps without aerobraking) you need about 18 kilotons of LH2, or about 20% of your initial mass. You're probably going to want to land in the ocean, because 57 TW is going to pretty much destroy whatever is under the drive when you touchdown. I'll leave it to you to increase your Ve until you get numbers that you like.  And, if you have antigravity, you can crank the thrust way down and get better performance.

Edited June 17, 2019 by natsirt721
flubbed a calculation, fixed it

[Spacescifi]

3 hours ago, natsirt721 said:

Alrighty, lets see here.

First off, I don't recommend using antimatter for surface-to-orbit, because of two reasons. One, a single kilogram of antimatter, when annihilated could easily destroy the moon and probably sterilize the Earth too, so if your launch fails you better have a plan to keep that antimatter safe as you plummet back to the ground. Two, antimatter annihilation produces lots of gamma rays, which will basically kill anything living nearby which isn't properly shielded. Not so great to do on a possibly inhabited surface.

Take a look at this 'realistic' antimatter engine for a sense of scale.

But screw that noise, you want an engine, dammit! 

For liftoff, we need a TWR of about 1.2. 97 kilotons with a TWR of 1.2 makes for an thrust of about 1.15e9 Newtons.

Antimatter reactions produce their energy with about 1/3 gamma radiation and 2/3 charged pions. Lets ignore the gamma radiation and focus on the pions, because they're charged so you can move them around with magnets and harvest their energy.  One gram of matter annihilating one gram of antimatter makes 1.8e14 joules of energy, times 2/3 for the pions makes 1.2e14 J. The pions are moving at 0.94c, so we can just blow them out the back of the spacecraft and call it thrust.  Thrust power = 1.2e14 J/g * antimatter mass = Thrust * Exhaust velocity * 0.5. At 1 gram per second our thrust is 8.53e8 N. Not bad for a conventional engine, but that ain't gonna cut it for our ship.  Fortunately, we can increase the thrust by adding LH2 and reducing our exhaust velocity.

This is where the engineering comes in.  We basically pick the exhaust velocity such that we don't use too much antimatter, and we don't need too much LH2

• Pt is thrust power, W
• 1.2e¹⁷ is antimatter power production per gram of antimatter J/kg
• mdot_a is antimatter consumption rate, kg/s
• T is engine thrust, 1.15e9 N
• V_e is effective exhaust velocity, m/s
• mdot_LH2 is LH2 mass flow rate  kg/s

For a Ve of 100,000 m/s, our thrust power is 57.5 TW, which is 4.8e-4 kg of antimatter per second, or about half a gram per second. LH2 consumption rate is 11 tons per second. For one liftoff/touchdown cycle (call it 20kps without aerobraking) you need about 18 kilotons of LH2, or about 20% of your initial mass. You're probably going to want to land in the ocean, because 57 TW is going to pretty much destroy whatever is under the drive when you touchdown. I'll leave it to you to increase your Ve until you get numbers that you like.  And, if you have antigravity, you can crank the thrust way down and get better performance.

 

Alright... so knowledge is power. In this case, power to write scifi SSTO's that are reasonably safe enough that they are as common as passenger jets.

Based on your calculations, I would just go smaller with my ships (450 ton passenger jet weight sounds reasonable).

Instead of using rockets to reach orbital velocity, I won't bother. I can use jet engines because I already have antigravity to let my SSTO float like a balloon.

The distance to space is only about 200 kilometers.

Contrast that with distance from Texas to Calufornia (2,263.2 kilometers).

A passenger jet flight from Texas to Califonia only takes a few hours (about three).

Thus a trip straight up to space with a weightless passenger jet should take even less time.

Once in space, I will have the SSTO fly around by using a scifi vacuum jet that does the same thing air jets do... with vacuum.

 

EDIT: If I just want my 97,000 ton SSTO, then I must accept the fact that, barring rocket staging, it will take longer to reach space than a smaller SSTO.

Because of all the drag.

Edited June 17, 2019 by Spacescifi

[kerbiloid]

9 hours ago, farmerben said:

Uranium makes a more powerful radiation case because even depleted uranium fissions with fast neutrons.  This is used for weapons, but it increases fallout.  So if the idea is to make the cleanest device, then one wouldn't use it.  

They idea was not to build the cleanest device, but a portable and focused one.
The case made of uranium was an X-ray mirror redistributing the charge power preferably in the channel direction.

The device "was" working almost all its way in vacuum, far from the Earth, and its charges yield anyway was comparable to the reqular nuclear tests.
So, even if it starts from ground, total yield of its first charges would not exceed what they were usually doing daily.

9 hours ago, farmerben said:

There is a minimum size of fissile material they must use. 

A propulsion charge for 10-m wide Orion was of yield ~1 kt and mass 311 lb (140 kg), so comparable to reqular howitzer nukes. 2000...3000 pc per a Martian expedition.

9 hours ago, farmerben said:

For more powerful yields they would use the same amount of fissile but more deuterium lithium 6.  The lithium splits into tritium plus an alpha, and then tritium deuterium fusion occurs.  Far less fallout is created.

In thermonukes ⁶Li-D doesn't react directly: too cold.
It fills the inner space of uranium case. ⁶Li gets splitted by fission neutrons into helium and tritium, then this tritium reacts with deuterium, so usual D+T takes place.

As a result, at least half of the thermonuke yield is generated by fission, and its radioactive outcome depends only on how much great part of uranium case and plutonium pieces has been burnt.
As plutonium is much more dangerous than uranium in sense of radiation toxicity, the thermonuke is "cleaner" because only a minor part of its yield is generated by plutonium.

As a ⁶LiD absorbs 1 neutron and ejects 1 neutron, so the neutron balance is zero.
But as the ejected neutron is significantly faster than the absorbed fission neutron, so ⁶LiD works as neutron accelerator, so its usage would require thicker protection to keep the ship safe.

Pure ⁶Li+D → alphas would be possible at much higher temperature, unachievable for a nuke. They should heat LiD pellets with some energy beams for that.

9 hours ago, farmerben said:

The beryllium will undergo nuclear reactions and be exploding before the blast of the primary even gets to it.   If they just wanted an inert filler that is transparent; water, plastic, or table salt would do that much cheaper.  

A much thinner layer of beryllium surrounding the fission primer survives enough long to let the fission explosion go.
The channel is just to be evaporated with X-rays long before the slow heavy products of the charge explosion approach, exactly like the secondary charge of a thermonuke.

The beryllium is a neutron reflector which protects the ship and reflects the neutrons back to the reaction zone. And it has low atomic mass, so creates high pressure and expands faster.

9 hours ago, farmerben said:

I basically agree about all the useful things the tungsten pusher plate does, but this is only going to protect against some of the radiation.  There will still be plenty of all types of radiation hitting the pusher plate.  

Fortunately, steel can eat alpha and beta radiation all day and not care.  Neutrons are partially scattered, but barely slowed down at all by steel.  Water and oil do almost nothing against X-rays, but they would carry away heat.

Alpha and beta are scattered far away from the ship because the explosion happens in tens meters behind it.
As well, most part of radiation. Those neutrons who are heading at the ship, get reflected by the thick layer of the channel filler.
Photons are partially absorbed by the filler and the propellant, partially by the plate.

The tiny amount of water spreaded onto the plate does nothing with radiation.
It becomes a thin (hydrogen-rich, so lightweight and effective) plasma layer between the plate and the tungsten cloud and amortizes the tungsten hit, protecting the plate itself from the hotter cloud of tungsten plasma.

5 hours ago, natsirt721 said:

One, a single kilogram of antimatter, when annihilated could easily destroy the moon and probably sterilize the Earth too,

E=mc².
2 * 1 * (3*10⁸)² / 4.2*10¹⁵ ~=42 Mt.
The moon should be rather tiny.

Though, the idea is right.

5 hours ago, natsirt721 said:

antimatter annihilation produces lots of gamma rays, which will basically kill anything living nearby which isn't properly shielded.

Annihilation first produces mesons which then produce photons. (Oops, you mention them later).
The mesons can react with surrounding media in different ways, so the distribution of energy between X-ray and gamma should widely vary depending on the charge construction and surrounding conditions.
Also gamma is well absorbed even by air. The gamma danger zone would be deep inside the shockwave and heatwave zone, just in a several kilometer radius.

P.S.
Why at all use antimatter for ascending?
1. Let the heavy ship stay in orbit, use shuttles. They don't need antimatter.
2. If antimatter must be used by definition, make a well-protected power plant using antimatter to enforce the fission. Say, on the Moon. Transfer the power with microwave emitters or lasers.

Edited June 17, 2019 by kerbiloid

[farmerben]

8 hours ago, kerbiloid said:

They idea was not to build the cleanest device, but a portable and focused one.
The case made of uranium was an X-ray mirror redistributing the charge power preferably in the channel direction.

The device "was" working almost all its way in vacuum, far from the Earth, and its charges yield anyway was comparable to the reqular nuclear tests.
So, even if it starts from ground, total yield of its first charges would not exceed what they were usually doing daily.

A propulsion charge for 10-m wide Orion was of yield ~1 kt and mass 311 lb (140 kg), so comparable to reqular howitzer nukes. 2000...3000 pc per a Martian expedition.

In thermonukes ⁶Li-D doesn't react directly: too cold.
It fills the inner space of uranium case. ⁶Li gets splitted by fission neutrons into helium and tritium, then this tritium reacts with deuterium, so usual D+T takes place.

As a result, at least half of the thermonuke yield is generated by fission, and its radioactive outcome depends only on how much great part of uranium case and plutonium pieces has been burnt.
As plutonium is much more dangerous than uranium in sense of radiation toxicity, the thermonuke is "cleaner" because only a minor part of its yield is generated by plutonium.

As a ⁶LiD absorbs 1 neutron and ejects 1 neutron, so the neutron balance is zero.
But as the ejected neutron is significantly faster than the absorbed fission neutron, so ⁶LiD works as neutron accelerator, so its usage would require thicker protection to keep the ship safe.

Pure ⁶Li+D → alphas would be possible at much higher temperature, unachievable for a nuke. They should heat LiD pellets with some energy beams for that.

A much thinner layer of beryllium surrounding the fission primer survives enough long to let the fission explosion go.
The channel is just to be evaporated with X-rays long before the slow heavy products of the charge explosion approach, exactly like the secondary charge of a thermonuke.

The beryllium is a neutron reflector which protects the ship and reflects the neutrons back to the reaction zone. And it has low atomic mass, so creates high pressure and expands faster.

 

I was under the impression that the smallest propulsion device was about 0.1kT.  The bombs must get bigger going up, because the atmospheric fireball is a huge boost.  On paper they looked at what would happen if the ship mass were increased by x10, x100, x1000 and so on.  It gets relatively cleaner because the amount of plutonium remains minimum in all designs, and more fusion is used.  The US puts some fusion boosting on all its weapons, because the fast neutrons give more complete plutonium burnup.  They also use alpha-beryllium neutron generators at the moment of criticality.  Little boy had a device called the urchin.  All other bombs probably had something similar.  The Soviet RBMK reactors have beryllium neutron source rods, which do the opposite of control rods.  And alpha beryllium neutron sources are the things doctors use to make radiation therapies.

I imagine the plutonium works like a HEAT round, that converges on a hollow sphere then forms a plasma spike directed at the filler.  A small percent of the beryllium will have photofissioned, but something close to 30/1,000,000 alpha particles will do the Be9[a,n]C12 reaction.  Then there are more fast neutrons in the plasma cloud just below the tungsten plate.  

If we desired a filler to offer more neutron scattering, then plastic would be better than beryllium oxide.  And it would do a better job converting neutron kinetic energy into hydrogen kinetic energy for normal thrust.  The oxygen is not particularly maximized for anything other than chemically handling other materials before detonation.  If we desired more power from the filler, anything with deuterium in it could be used. 

If fallout is zero concern, then go ahead and use a uranium radiation case.  But if we desire to reduce fallout, then switching the case to any other heavy metal is the first thing we would do.  They all reflect X-rays, and tungsten is nearly as good as uranium at this.  The point of reflecting X-rays is to produce photofission or fusion.  Plutonium, beryllium, and deuterium and tritium can all photofission at wavelengths close to 10^-13m.   Fusion is boosted due to overall heat.  Photofission is a low probability event and reflectors are not perfect.  A better reflector might have multiple coatings on it.  For example a tungsten case plated with pure beryllium, then pure gold.  Each layer of density is an opportunity for coherent reflections

 

[kerbiloid]

21 minutes ago, farmerben said:

The bombs must get bigger going up, because the atmospheric fireball is a huge boost

Max T/W is required on ground, so the closer to the space - the lesser charge is enough. So, they just used same.

21 minutes ago, farmerben said:

They also use alpha-beryllium neutron generators at the moment of criticality. 

Used in the days  of atompunk.

21 minutes ago, farmerben said:

If we desired a filler to offer more neutron scattering, then plastic would be better than beryllium oxide.

Beryllium oxide is 3 g/cm³ dense, denser than most of plastics.
And hydrocarbons including the plastics are mostly (CH₂)_n , so mostly consist of carbon.
Probably they considered beryllium portion of plasma more concentrated in sense of cross-section and atomic mass.

21 minutes ago, farmerben said:

But if we desire to reduce fallout, then switching the case to any other heavy metal is the first thing we would do.  They all reflect X-rays, and tungsten is nearly as good as uranium at this.

But depleted uranium is cheaper than tungsten, and there is a lot of it. And much denser, so a better mirror.

As probably only several first charges burst in low atmosphere, and all of them except the first one, in air, there should be less fallout than from a regular atmospheric nuclear test in 1950s.

21 minutes ago, farmerben said:

The point of reflecting X-rays is to produce photofission or fusion. 

In this case the point is the filler and propellant heating to increase their thermal velocity.

Edited June 17, 2019 by kerbiloid

[farmerben]

5 minutes ago, kerbiloid said:

 

Used in the days  of atompunk.

 

Lol

I'm not buying it.  Beryllium is crazy expensive.  They could have used magnesium oxide or many other things, to get the results you are talking about.  

I would be inclined to use something like lithium borate.  Li2 B4 O7 density 2.4 g/cm^3.  Because I think helium and tritium ions are fantastic propellant, and lithium or boron ions are just as good as beryllium if no nuclear reaction occurs.  But this is for the case of overabundant neutrons.  If there happens to be not enough neutrons for fissile burnup, then beryllium would be used.

The only reason a bomb would not have a beryllium neutron initiator, is if they could get better results putting deuterium and tritium in its place.

[kerbiloid]

30 minutes ago, farmerben said:

I'm not buying it.  Beryllium is crazy expensive.  They could have used magnesium oxide or many other things, to get the results you are talking about.  

I would be inclined to use something like lithium borate.  Li2 B4 O7 density 2.4 g/cm^3.  Because I think helium and tritium ions are fantastic propellant, and lithium or boron ions are just as good as beryllium if no nuclear reaction occurs.  But this is for the case of overabundant neutrons.  If there happens to be not enough neutrons for fissile burnup, then beryllium would be used.

The only reason a bomb would not have a beryllium neutron initiator, is if they could get better results putting deuterium and tritium in its place.

So, you would probably tell this to Freeman Dyson, whose book I'm trying to quote.

[farmerben]

Which book?  I'd like to check it out.

In the clips I've seen Freeman Dyson refuses to disclose the actual bomb designs, but he was arguing in favor of cleaner bombs.   Which is obviously an argument about the case.  He implied there are concepts relevant to dirty bombs and bunker busters.  So the filler is doing something very important.  If it were simply, put a bunch of salt in a rocket bell and squeeze it out, then it would not be a secret.  

The lithium and beryllium cross sections were top secret for a long time.  I believe George Dyson's book helped crack that open, and more information has got out since then.  

The idea of putting Boron 10 in a bomb propellant is entirely my own idea.  I can argue for it from first principles.   B10 + n = Li7 + He4 + 2.79MeV.  It seldom becomes B11 as one might suspect.  This does not boost other reactions, quite the opposite, the function is only to create more hot low density plasma.  This is double the energy these particles will have vs just what they get thermally.  In terms of ISP the lighter the ions, the higher the velocity, the higher the ISP.  Gamma rays and neutrons don't count because they don't generate as much normal thrust as ions do. 

So the first priority is to ensure good fissile burnup using beryllium.    

Second, boost power using lithium and deuterium.

Third, use boron instead of inert fillers because alpha particles are our friends.

 

For the ridiculously sized interstellar version, the case mounts for using lots of pure deuterium.  But keeping it in a chemical compound is easier to store.    

 

 

 

[natsirt721]

Quote

2 * 1 * (3*10⁸)² / 4.2*10¹⁵ ~=42 Mt.

Ah, so it is. I thought animatter had a better energy density than that (truth be told I was paraphrasing a novel and didn't bother to verify, dammit Niven!)

17 hours ago, kerbiloid said:

P.S.
Why at all use antimatter for ascending?
1. Let the heavy ship stay in orbit, use shuttles. They don't need antimatter.

bingo

Edited June 17, 2019 by natsirt721
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[kerbiloid]

7 hours ago, farmerben said:

Which book?  I'd like to check it out.

(Oops,  by George Dyson, he's his son.)

https://www.amazon.co.uk/Project-Orion-Story-Atomic-Spaceship/dp/0805059857

 

[farmerben]

" wikipedia"

 

Quote

Proton-antiproton annihilation[edit]

When a proton encounters its antiparticle (and more generally, if any species of baryon encounters the corresponding antibaryon), the reaction is not as simple as electron-positron annihilation. Unlike an electron, a proton is a composite particle consisting of three "valence quarks" and an indeterminate number of "sea quarks" bound by gluons. Thus, when a proton encounters an antiproton, one of its quarks, usually a constituent valence quark, may annihilate with an antiquark (which more rarely could be a sea quark) to produce a gluon, after which the gluon together with the remaining quarks, antiquarks, and gluons will undergo a complex process of rearrangement (called hadronization or fragmentation) into a number of mesons, (mostly pions and kaons), which will share the total energy and momentum. The newly created mesons are unstable, and unless they encounter and interact with some other material, they will decay in a series of reactions that ultimately produce only gamma rays, electrons, positrons, and neutrinos. This type of reaction will occur between any baryon (particle consisting of three quarks) and any antibaryon consisting of three antiquarks, one of which corresponds to a quark in the baryon. (This reaction is unlikely if at least one among the baryon and anti-baryon is exotic enough that they share no constituent quark flavors.) Antiprotons can and do annihilate with neutrons, and likewise antineutrons can annihilate with protons, as discussed below.

Reactions in which proton-antiproton annihilation produces as many as nine mesons have been observed, while production of thirteen mesons is theoretically possible. The generated mesons leave the site of the annihilation at moderate fractions of the speed of light, and decay with whatever lifetime is appropriate for their type of meson.^[4]

Similar reactions will occur when an antinucleon annihilates within a more complex atomic nucleus, save that the resulting mesons, being strongly interacting, have a significant probability of being absorbed by one of the remaining "spectator" nucleons rather than escaping. Since the absorbed energy can be as much as ~2 GeV, it can in principle exceed the binding energy of even the heaviest nuclei. Thus, when an antiproton annihilates inside a heavy nucleus such as uranium or plutonium, partial or complete disruption of the nucleus can occur, releasing large numbers of fast neutrons.^[5] Such reactions open the possibility for triggering a significant number of secondary fission reactions in a subcritical mass, and may potentially be useful for spacecraft propulsion.^{[citation needed]}

I don't understand how one can ride on gamma rays and neutrinos.  

Perhaps, a large pellet of metal or a can of noble gas could be released for every pulse of antiprotons.  Then more of the energy would heat up ions.  

 

Dribbling out hydrogen seems like a way to potentially miss and waste antimatter.  Or create weird mesons for nanoseconds, then a cloud of gamma rays and neutrinos.  

 

 

 

Edited June 18, 2019 by farmerben

[kerbiloid]

13 hours ago, farmerben said:

I don't understand how one can ride on gamma rays and neutrinos.  

Perhaps, a large pellet of metal or a can of noble gas could be released for every pulse of antiprotons.  Then more of the energy would heat up ions.  

A frozen pellet of substrate propellant with antinuclei frozen into it.
While it's next to absolute zero, the thermal motion is negligible, so probability of the atomic collision is low, and the annihilation runs slowly-slowly, allowing to store the pellets for years.
Once you eject the pellet and warm it with a beam or with the previous pellet heat, the annihilation runs quicker and heats the substrate propellant up to temperature of, say, aneutronic fusion reactions.
So, you get subluminal protons which you can throw back with magnetic field.

***

Also if have a look at the Orion project, how can we improve it?

As the Dyson's book notices, the Orion is not a rocket, t's a flying cannon.
Whatever author means, the main difference is that not the ship throws back some substance at high speed, receiving an impulse in the opposite direction.
Instead, a directional explosion happens behind the ship, pushing it forwards with a focused hit.

Definitely, the most vulnerable part of Orion is the enormous amount of the  nuke charges, which are complicated devices containing a lot of radioactive materials.

What if replace the fission nuke with an aneutronic thermonuke pellet in a strong case with similar tungsten cap?
Probably, it should work not worse than a fission nuke.

But we should ignite the pellet when it's in a hundred meters behind the ship.
So, either ignite it with some beam (photonic or electronic), or make it contain some antimatter.
(In this case the case could also be a superconducting case allowing to keep the pellet frozen.)
Probably, in any case we should heat the case with some beam, either to ignite the high-temperature fusion directly, or to unfreeze the antimatter frozen in the thermonuke substance.

In Orion the tungsten cloud hits the plate to be then reflected back.
But it can also be reflected with strong magnetic field as well.
So, let's replace the plate with electromagnetic mirror, and power it from the same explosion.

***

Then we can get some Orion Plus:

The ship contains pellets of aneutronic fusion propellant (see KSPI-E table for details),

Spoiler

 

like specially "isotoped" boranes, ammonia, hydrocarbons, maybe ⁶LiD.
They are encased in superconducting ceramic cases with a tungsten cap on "inner" end.
They probably should have a thick protective cap on the "outer" end, to prevent their heating before the arriving to the fusion zone. But not tungsten, maybe carbon or so.
Probably they are anyway frozen. At least for superconductivity.
Maybe (not necessary, but desired) they contain minor amount of antimatter frozen into the fusion propellant.

Behind the ship there is an electromagnetic trap/mirror. It's like a hemisphere closed with a cap, much flatter, though concave. Like two layers of "opposite polarity".
Originally it's powered by an auxilliary reactor.

A pellet dispencer throws the pellets one by one along the trap axis.

At "hundred" meters behind the trap the pellet gets into the focus of electron flow directed by the trap.
It gets warmed.
Either an aneutronic fusion runs directly,
or the frozen antimatter gets enough warm to start colliding with surrounding atoms and annihilating, and ignite the aneutronic fusion.

The fusion evaporates and ionizes the tungsten cap and pushes it directly forward, towards the ship.
The fusion products (which are also positive ions) spherically expand, and partially hit the trap, too.

So, the trap receives two flows: positive ions (tungsten, helium, hydrogen nuclei) and electrons (expanding spherically, so just a part of them).
It magnetically reflects the ions, producing the thrust.

The electrons pass through the outer layer of the trap, obviously being accelerated.
They get into the second layer of the trap "with reverse polarity", so they make a 180+° turn along the trap walls, and fly back, being focused at the pellet fusion zone behind the ship, and heating the pellets.

Somewhere in the trap, the particles energy is partially used to power the magnetic trap itself.

Pistons are no longer needed, as they are replaced with the magnetic field "elasticity".

The protective water shower is obviously gone, too. As well as oil grease for the pistons.

***

So, we get Orion and Daedalus 2-in-1, without nukes and pistons.

Also the pellets (especially containing  the antimatter) can be used as ammo for anti-meteorite cannons and for asteroid mining.

Edited June 19, 2019 by kerbiloid

[FreeThinker]

On 6/14/2019 at 7:15 AM, Nightside said:

Weight is a function of mass and acceleration (mainly gravity). If you have a “gravity neutralizer” then your weight is zero, so any amount of thrust would give you an infinite TWR.

  Hide contents

What I want to know is: how does the gravity get neutralized??? I think the device should work by completely annihilating all mass on the planet, removing its gravitational pull. Useful, but with some functional limitations.

 

Well if you try to do that in KSP, physics breaks down and you are unable to apply any force.

On 6/15/2019 at 11:29 PM, NSEP said:

Beam core engines have around 100 million m/s of exhaust velocity, which is extremely fast (like 33% the speed of light)

Actualy new paper shows its actualy about 66% of speed of light as simulations has shown its possible to redirect all charged partices, before they didn't think it was possible.

Edited June 19, 2019 by FreeThinker

[FreeThinker]

18 hours ago, farmerben said:

I don't understand how one can ride on gamma rays and neutrinos. 

Anything with mass or momentum is usefull for propulsion, the trick is to get it in the right direction without getting destroyed

[Starstruck69]

On 6/16/2019 at 9:18 AM, Cheif Operations Director said:

I should know more than I do to answer this but just an idea

What if you have gravity pulling at x m/s toward a thing

Could'nt you pull it at x m/s the other direction

 

Effectivley x m/s - xm/x = 0

Add:

I was stating that outside of the OPs post

Effectively this is a sort of inverse of Newtons law of attraction and i see your point here. All mass will be effected by gravity and the pull of such force is related to the mass and distance between them. 

Mathematically you have a good point but unfortunately Einsteins Special and General relativity (GR)is a tad more complicated when applying to the real world. GR supercedes Newtons work when we talk about gravity.

of course the point you made can be seen in aircraft such as the harrier, that hovers by pushing equally the opposite vector to the pull of gravity and as such v=0m/s. (in theory). In laymans terms we calculate F and apply an equal force to neutralise.

If only it was that simple. See below.

GR:

As we can see from GR the left side talks about the geometric position and the right side the energy/mass relationship. If we took this into account i would think it will be very difficult to know just exactly how much we have to thrust to neutralise the gravitational effect. It would be  a best guess and very approximated to be honest because we need to keep feeding one side to get an answer out of the other. Also this of course presumes we are working in a vaccuum so no drag, friction etc is accounted for here. There are 10 usable equations above that we can substitute in to find what we need. For example, the effect of gravity on say the x axis, or on the y axis, z axis etc etc. It gets tediously complicated, but doable.

As for antimatter/fuel ratio i have absolutely no idea. If somebody calculates though i would be very interested to see it.