Could nuclear propulsion or laser propulsion bring space cost down

[A_M_Swallow]

aquanaut99 the laws of physics are not malleable.  They are what they are.  Humanity needs stored forms of energy in space just as it needs it on Earth.  On Earth chemical stored energy works pretty well.  We are able to do all pretty much everything we need to do with the old ICE and reasonable amounts of fuel.  Space travel on the other hand requires much more energy.  Energy that only nuclear power could provide in a stored form, otherwise the amount of chemical fuel required to do many of the things we need want to do are just astronomical.

In which case you had better find a source of nuclear material on the Moon or Mars or an asteroid.

[IsaacKuo]

There are no clouds in space and night lasts at most 45 minutes in LEO.  So no, there is not a need for nuclear fuel in space.  As a concrete example, the ISS uses solar power and chemical power--no nuclear power necessary.

[MrAnthonyDR]

There are no clouds in space and night lasts at most 45 minutes in LEO.  So no, there is not a need for nuclear fuel in space.  As a concrete example, the ISS uses solar power and chemical power--no nuclear power necessary.

To my understanding this only applies to Space vehicles within a certain range of the Sun. As we start to look long-term at deep space exploration beyond the main asteroid belt, RTGs and Nuclear power are the only feasible option for powering a spaceship (based on current technology).

An asteroid mission, even to a NEO would likely need to include alternate sources of energy to ensure lower costs.

Anthony

[IsaacKuo]

To my understanding this only applies to Space vehicles within a certain range of the Sun. As we start to look long-term at deep space exploration beyond the main asteroid belt, RTGs and Nuclear power are the only feasible option for powering a spaceship (based on current technology).

Current technology is already advanced enough to launch a solar powered Jupiter mission.  This reduced the cost of Juno compared to the more traditional alternative of atomic power.

An asteroid mission, even to a NEO would likely need to include alternate sources of energy to ensure lower costs.

We have also launched solar powered missions to asteroids.  Solar power was used to lower costs, compared to atomic power.

[DarkenedOne]

aquanaut99 the laws of physics are not malleable.  They are what they are.  Humanity needs stored forms of energy in space just as it needs it on Earth.  On Earth chemical stored energy works pretty well.  We are able to do all pretty much everything we need to do with the old ICE and reasonable amounts of fuel.  Space travel on the other hand requires much more energy.  Energy that only nuclear power could provide in a stored form, otherwise the amount of chemical fuel required to do many of the things we need want to do are just astronomical.

In which case you had better find a source of nuclear material on the Moon or Mars or an asteroid.

We have already found relatively high concentrations of uranium on the moon. 

Scientists also believe that many of the heavy elements on the Earth's surface were delivered here by asteroids because Earth was molten in the beginning all of the heavy elements from the initial formation of Earth sunk to the core.

[nec207]

Well The big problem why space exploration is not taking of like the combustion engine or first  flight the Wright brothers  is cost and the same why only 3 countries the US, China and Russia can put people into space.The apollo program ,space shuttle and project constellation proposed by president Bush to get people back to the moon and have a moon base got scrapped  do to cost.And going to Mars would be very very costly like no one has ever seen.



All the cool x- programs that NASA was doing with conjunction with the Air force in the 80's and 90's  and among the VentureStar X-33  got canceled do to lack of money to continue research.



No one really knows if any of the x- programs or x-33 would bring space cost down .It may bring it down some what , but still no where to take of like the combustion engine or first  flight the Wright brothers  .



Has chemical propulsion does not allow for that.


The proposed plan by president Obama to send people to a asteroid by 2025 and mars by 2030 would be like no one has seen in history the cost would be nothing like NASA has ever done.


It is highly unlikely anyone in government would vote on this bill do to the US major recession and high debt.

[nec207]

I still have no reply to my last question if laser propulsion or microwave propulsion could be the next big thing like the combustion engine a cheap way to take people and cargo into space.

Some people say laser propulsion or microwave propulsion will need gigawatts of power for it to work and that is the best engineering problem why laser propulsion or microwave propulsion is scfi.

[KelvinZero]

Secondly heat is the form of energy that is used in all rockets.  Chemical rockets use combustion to generate heat that results in pressure in the combustion chamber.  As the hot propellant expands out the nozzle the thermal energy is converted into the motion of the propellant as it pushes the spacecraft forward.  Nuclear rockets do the same thing just with fission or fusion.  Converting that heat into electricity than into motion is inefficient compared to simply converting heat into motion.  It also requires electrical generation systems.

The problem of getting rid of heat will still be greater for an NTR because it has to expel less propellant and hotter in order to gain any advantage over chemical rockets. It has to gain a significant advantage to make up for the simplicity of going chemical.

I am not sure that you understand the concept behind NTR.  Heat is used directly to propel the vehicle.  It is absorbed and taken away by the propellant.  That is why the tried and tested NTR systems did not require radiators.

Hi DarkenedOne,
I think it is very clear that I did understand that NTR expel propellant and this carries away heat. It expels less than chemical rockets and hotter. Chemical rockets themselves have great issues with heat. What is the confusion?

[nec207]

Secondly heat is the form of energy that is used in all rockets.  Chemical rockets use combustion to generate heat that results in pressure in the combustion chamber.  As the hot propellant expands out the nozzle the thermal energy is converted into the motion of the propellant as it pushes the spacecraft forward.  Nuclear rockets do the same thing just with fission or fusion.  Converting that heat into electricity than into motion is inefficient compared to simply converting heat into motion.  It also requires electrical generation systems.

The problem of getting rid of heat will still be greater for an NTR because it has to expel less propellant and hotter in order to gain any advantage over chemical rockets. It has to gain a significant advantage to make up for the simplicity of going chemical.

I am not sure that you understand the concept behind NTR.  Heat is used directly to propel the vehicle.  It is absorbed and taken away by the propellant.  That is why the tried and tested NTR systems did not require radiators.

Hi DarkenedOne,
I think it is very clear that I did understand that NTR expel propellant and this carries away heat. It expels less than chemical rockets and hotter. Chemical rockets themselves have great issues with heat. What is the confusion?

sorry how does this answer my questions here??

[scienceguy]

If you're talking about answering your questions in the first post of this thread, you asked if nuclear or laser propulsion will bring the costs of space travel down in 50 to 100 years. The answer is that nobody knows! How can anyone know what will happen with technology in 50 to 100 years?

[kkattula]

IF one of the 'alternative' fusion ideas like Focus or Polywell work out then almost certainly space travel will become a lot easier and cheaper. Otherwise, we may get in-space NTR for interplanetary missions, but I very much doubt it would ever be used for launch from Earth.

Microwave and laser propulsion generally depend on heating onboard LH2 for most of the launch. (Air may be used in the early phases of flight). The underlaying assumptions (that I've seen) as to how much the tanks would weigh seem to be overly optimistic.  Applying those same assumptions to tanks for dense chemical propellants such as LOX/RP-1 yield terrific mass ratios. More than good enough for SSTO.

[93143]

I think it is very clear that I did understand that NTR expel propellant and this carries away heat. It expels less than chemical rockets and hotter. Chemical rockets themselves have great issues with heat. What is the confusion?

For starters, NTRs don't run hotter than chemical rockets.  The RS-25 runs at about 3300°C IIRC, which is too hot for a metal wall, but the metal wall is regeneratively cooled.  A solid-core NTR has to stay within the structural limits of its core materials, and I believe the record stands a little past 2800°C for a Russian test.

This is why you need hydrogen or ammonia.  Feed an NTR water, and you get an Isp worse than that of a hydrolox rocket.  Feed it CO₂ and you get an Isp worse than that of a LOX/CO rocket.  It's only worth it if the molecular weight of the working fluid is very low.

[nec207]

If you're talking about answering your questions in the first post of this thread, you asked if nuclear or laser propulsion will bring the costs of space travel down in 50 to 100 years. The answer is that nobody knows! How can anyone know what will happen with technology in 50 to 100 years?

I also ask what are the engineering problems that have to be overcomed before we can start to see if this will bring space cost down or not.

I also got no reply on Microwave propulsion  how that will work and  what are the engineering problems that have to be overcomed .

[Patchouli]

I think it is very clear that I did understand that NTR expel propellant and this carries away heat. It expels less than chemical rockets and hotter. Chemical rockets themselves have great issues with heat. What is the confusion?

For starters, NTRs don't run hotter than chemical rockets.  The RS-25 runs at about 3300°C IIRC, which is too hot for a metal wall, but the metal wall is regeneratively cooled.  A solid-core NTR has to stay within the structural limits of its core materials, and I believe the record stands a little past 2800°C for a Russian test.

This is why you need hydrogen or ammonia.  Feed an NTR water, and you get an Isp worse than that of a hydrolox rocket.  Feed it CO₂ and you get an Isp worse than that of a LOX/CO rocket.  It's only worth it if the molecular weight of the working fluid is very low.

The main advantage of using water or CO2 would be very easy ISRU with very little processing of the propellant.

NTR on a lunar lander could be a big game changer despite the low ISP as it requires very little infrastructure.
http://www.neofuel.com/moonicerocket/

 Mars hopper with NTR engines and CO2 as a propellant could hop to a new location several hundred miles away every few days.

[kkattula]

Microwave works much the same as Nuclear Thermal. Liquid Hydrogen is pumped into a hot chamber where it is heated then expelled through a nozzle.

The difference is the chamber heat comes from energy beamed via microwaves from the ground to a rectenna on the launch vehicle, rather than being generated on board by a nuclear reactor.

The engineering problems would seem to be fairly obvious:

  How to transmit that much power in a tight beam

  How to steer the beam accurately to follow a fast moving target

  What to do when that target moves over the horizon from the launch site

  How to efficiently convert the microwaves back to heat in a lightweight package

  How to avoid frying the rest of the vehicle with stray radiation

  How to transfer the heat to the chamber without melting the rest of the vehicle

 
LH2 being a very low density propellant, the tanks have to be quite large, which like NTR, reduces the Mass Ratio, offsetting the benefits of higher Specific Impulse.

 

[IsaacKuo]

I seem to recall someone demonstrating the use of microwaves to "burn" salt water.  It caused the water to electrolyze, and immediately burn.

Could a microwave powered rocket use this principle to get the Isp of a hydrolox rocket with cheap dense salt water propellant tanks?  Even if it required a multi-stage rocket, each stage could be pretty darn cheap and/or reusable.

Or maybe it could be used for something vaguely similar to a solid rocket booster.  The booster is made of a material transparent to the microwave beam, and the propellant is a block of salt water ice.  The microwaves electrolyze the bottom layer of ice/water, which burns like a hydrolox rocket.  It's dumb, cheap, and simple without the traditional disadvantages of a solid rocket booster.

[strangequark]

I seem to recall someone demonstrating the use of microwaves to "burn" salt water.  It caused the water to electrolyze, and immediately burn.

Could a microwave powered rocket use this principle to get the Isp of a hydrolox rocket with cheap dense salt water propellant tanks?  Even if it required a multi-stage rocket, each stage could be pretty darn cheap and/or reusable.

Or maybe it could be used for something vaguely similar to a solid rocket booster.  The booster is made of a material transparent to the microwave beam, and the propellant is a block of salt water ice.  The microwaves electrolyze the bottom layer of ice/water, which burns like a hydrolox rocket.  It's dumb, cheap, and simple without the traditional disadvantages of a solid rocket booster.

Power limited device, so low thrust, and low Isp too because it's a thermal device. Better off using whatever is powering the microwave generator to power something like a Hall thruster.

[IsaacKuo]

I seem to recall someone demonstrating the use of microwaves to "burn" salt water.  It caused the water to electrolyze, and immediately burn.

Could a microwave powered rocket use this principle to get the Isp of a hydrolox rocket with cheap dense salt water propellant tanks?  Even if it required a multi-stage rocket, each stage could be pretty darn cheap and/or reusable.

Or maybe it could be used for something vaguely similar to a solid rocket booster.  The booster is made of a material transparent to the microwave beam, and the propellant is a block of salt water ice.  The microwaves electrolyze the bottom layer of ice/water, which burns like a hydrolox rocket.  It's dumb, cheap, and simple without the traditional disadvantages of a solid rocket booster.

Power limited device, so low thrust, and low Isp too because it's a thermal device. Better off using whatever is powering the microwave generator to power something like a Hall thruster.

Huh?  The microwave beam is generated on the ground.

[strangequark]

I seem to recall someone demonstrating the use of microwaves to "burn" salt water.  It caused the water to electrolyze, and immediately burn.

Could a microwave powered rocket use this principle to get the Isp of a hydrolox rocket with cheap dense salt water propellant tanks?  Even if it required a multi-stage rocket, each stage could be pretty darn cheap and/or reusable.

Or maybe it could be used for something vaguely similar to a solid rocket booster.  The booster is made of a material transparent to the microwave beam, and the propellant is a block of salt water ice.  The microwaves electrolyze the bottom layer of ice/water, which burns like a hydrolox rocket.  It's dumb, cheap, and simple without the traditional disadvantages of a solid rocket booster.

Power limited device, so low thrust, and low Isp too because it's a thermal device. Better off using whatever is powering the microwave generator to power something like a Hall thruster.

Huh?  The microwave beam is generated on the ground.

Haha, needed to refresh on the original post. I wasn't clear you were talking ground to orbit propulsion. Feel free to ignore my commentary.

[nec207]

I seem to recall someone demonstrating the use of microwaves to "burn" salt water.  It caused the water to electrolyze, and immediately burn.

Could a microwave powered rocket use this principle to get the Isp of a hydrolox rocket with cheap dense salt water propellant tanks?  Even if it required a multi-stage rocket, each stage could be pretty darn cheap and/or reusable.

Or maybe it could be used for something vaguely similar to a solid rocket booster.  The booster is made of a material transparent to the microwave beam, and the propellant is a block of salt water ice.  The microwaves electrolyze the bottom layer of ice/water, which burns like a hydrolox rocket.  It's dumb, cheap, and simple without the traditional disadvantages of a solid rocket booster.

Power limited device, so low thrust, and low Isp too because it's a thermal device. Better off using whatever is powering the microwave generator to power something like a Hall thruster.

Huh?  The microwave beam is generated on the ground.

Haha, needed to refresh on the original post. I wasn't clear you were talking ground to orbit propulsion. Feel free to ignore my commentary.

Well chemical rockets do not work economically as no more than 3 countries can put peopler into space at cost  unbelievable !!!! Also 95% of the rockets weight is just to launch 5% of its mass !!!!

So by reading this thread it is not clear if  nuclear propulsion or laser propulsion or microwaves propulsion would solve these problems.