Intergalactic space travel and hydrogen blasting

[teve]

Main Question or Discussion Point

Intergalactic space travel and hydrogen "blasting"

To travel by space ship to Andromeda (2.5 million light years) within a life time (say 50 years) you would have to travel with a much greater Lorentz factor than LHC protons, 50000 versus 7500. The LHC supposedly can melt a metric ton of copper with its 1 nano-gram proton beams. Would the space ship be significantly eroded from intergalactic hydrogen coming at it during its 50 year trip? If so, how much shielding would be needed?

 

[yuiop]

To travel by space ship to Andromeda (2.5 million light years) within a life time (say 50 years) you would have to travel with a much greater Lorentz factor than LHC protons, 50000 versus 7500. The LHC supposedly can melt a metric ton of copper with its 1 nano-gram proton beams. Would the space ship be significantly eroded from intergalactic hydrogen coming at it during its 50 year trip? If so, how much shielding would be needed?

In non technical language the answer is "a lot". Not only is the intergalactic hydrogen a significant problem, but even the background cosmic radiation becomes a hazard. At a high enough Lorentz factor, background radiation coming towards the space ship could be blue shifted to x rays or gamma rays (very difficult to shield against and harmful to most life). Any small asteroids will be difficult to detect in time to avoid them and would be another major hazard. All in all, travelling at a relative speed close to the speed of light would be technically very difficult, very costly on resources and hazardous.

 

[teve]

In non technical language the answer is "a lot".

Thanks. I had a feeling the intergalactic hydrogen alone, though very thin, would still be a significant problem just by roughly comparing it to the LHC. I read intergalactic hydrogen is maybe about 1 atom per cubic meter but maybe its significantly higher inside galaxies.

 

[yuiop]

Thanks. I had a feeling the intergalactic hydrogen alone, though very thin, would still be a significant problem just by roughly comparing it to the LHC. I read intergalactic hydrogen is maybe about 1 atom per cubic meter but maybe its significantly higher inside galaxies.

I thought it would be interesting to do an order of magnitude calculation of the damage done by hydrogen blasting. What I get is that each atom would have a relativistic kinetic energy of 7.5*10^-6 Joules. This equates to about 2000 watts per meter squared on the front of the rocket for a density of one atom per meter cubed. This can be compared to roughly 6000 watts per meter squared for bullets sprayed from an World War 2 MP40 machine gun* over a similar area, but the machine gun bullets would individual have a kinetic energy of about 600 Joules. This is a bit less than I initially imagined for the hydrogen blasting, so ~maybe~ it would not be too impractical to shield against it. I think the impressive LHC results are a result of focusing the beam on a very small area, while in the rocket case, the impacts would be spread randomly over a wider area.

*To put the MP40 sub machine gun results into context, a modern Dillon M134D Gatling gun has bullets with an individual kinetic energy of about 4000 Joules (over 6 times that of the MP40 so much greater penetration) and a power rating of about 180,000 Watts which is over 30 times that of the MP40. Devastating!

 

[teve]

I found that two LHC beams totaling 724 MJ melts one metric ton of copper. I would think that assumes a spread out beam so that all the copper just melts. http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/beam.htm

So in 50 years (about 1.6E+9 sec) at 2000 J per square meter, that's 3.2E+12 J per square meter for the trip. That's about 4400 metric tons (per square meter) of copper shielding melting away. That's still a lot of shielding. I hope my assumptions and calculations are correct.

 

[yuiop]

I found that two LHC beams totaling 724 MJ melts one metric ton of copper. I would think that assumes a spread out beam so that all the copper just melts. http://lhc-machine-outreach.web.cern.ch/lhc-machine-outreach/beam.htm

So in 50 years (about 1.6E+9 sec) at 2000 J per square meter, that's 3.2E+12 J per square meter for the trip. That's about 4400 metric tons (per square meter) of copper shielding melting away. That's still a lot of shielding. I hope my assumptions and calculations are correct.

That should be 3.2E+12 J per square meter per second for the trip, but that is just a typo and your calculation seems about right. I wonder what sort blasting energy the space shuttle has to cope with? I imagine with some sort of insulating material material like that used on the shuttle, not all the energy need be directly absorbed and maybe with some sort of active cooling system that absorbs the heat and radiates the heat away in radiators near the rear of the ship, that a much lighter shielding system could be made ~maybe~. Recall that the background temperature is near absolute zero in space (3 Kelvin? ... really cold anyway :tongue:) and that 2000 Watts is 'only' the output of a typical domestic electric fire.

 

[yuiop]

I just Googled the space shuttle shielding and according to http://www.thermospokenhere.com/wp/tsh/D318___shuttle/shuttle.html [Broken] the space shuttle has to dissipate 69E+12 Joules during the time it re-enters the atmosphere, so it shouldn't be too much of a problem dissipating 3.2E+12 Joules over the 50 year trip of the ship. For details of the shuttle thermal protection system see http://en.wikipedia.org/wiki/Space_Shuttle_thermal_protection_system

 

[teve]

Now I'm curious how this compares to the oncoming background radiation being blue shifted? Assuming a round value of 200GHz for the radiation and relativistic Doppler shift and Lorentz factor of 50000 I think that make the frequency 2E+15 GHz which I think is ultraviolet. But I don't know how intense the radiation is. I would think this could easily be dealt with but I'm curious how it compares to the energy the oncoming hydrogen at 1 atom per cubic meter.

I also read that interstellar hydrogen within a galaxy is about 1 atom per cubic cm. This makes getting out of or into a galaxy a million times worse.

 

[Nabeshin]

See sections two and three of this:

https://docs.google.com/viewer?a=v&pid=explorer&chrome=true&srcid=0BzErwya_uXcsY2Y2OTQ0ZjYtODE2NC00ZmRlLWI1ZDctOTRiZTRmZWNjMzll&hl=en