In my amateur survey of propulsion technology I can find only three candidates for high speed space travel. They are all three extremely expensive. There is no cheap.

The first is beam propulsion. It is the dream come true for all space advocates because it is non-nuclear and holds the promise of an airliner to space. A microwave launch vehicle could take a payload up through the atmosphere with a much higher Isp than a conventional rocket because pure hydrogen has a much higher exhaust velocity than hydrogen and oxygen- and microwaves can generate much higher temperatures. If an orbital array can beam energy down into the atmosphere to take over from the surface array then a single stage to orbit vehicle becomes possible. Also an outward bound beam propelled spaceship could be launched from the Moon or lunar orbit at very high speeds. But then slowing down at the other end becomes a problem because of the lack of solar energy resources to power a system at the destination to decelerate the spaceship.

The problem with beam propulsion is the technology is not yet mature and a huge infrastructure would be necessary to beam the necessary power.

The second possibility is an atomic engine using Americium 242. This transuranic element has a unique property that makes it fairly easy to use in a fission fragment propulsion system. In this system a rocket similar to conventional engines would have an Isp in the hundreds of thousands and would allow travel anywhere in the solar system. The engineering is fairly straightforward so such engines could be developed fairly quickly. This path seems too good to be true and of course it is.

The problem with Americium that makes it too good to be true is that it is unobtanium; there is very little of the stuff to be had and it would take a huge investment in an entirely new nuclear industry to make it available. And because the exhaust is highly radioactive it could not be used anywhere near the Earth’s magnetosphere so it still relies on chemical rockets to get into deep space.

The third possibility is nuclear pulse. This has the same disadvantage of fission fragment in that it cannot be used anywhere near the Earth’s magnetosphere. It has the added disadvantage that while a fission fragment propulsion system would resemble conventional rocket engines in size a pulse engine would necessarily need to be either an immense parachute type device several miles in diameter or a smaller disc a few hundred feet in diameter massing several thousand tons.

Nuclear pulse is the most practical of the three because of the availability of fissionable material for pulse units. There is a couple hundred tons of plutonium and a couple hundred more of enriched uranium in storage at this time- enough for several hundred deep space missions using pulse propulsion. So unlike beam propulsion and fission fragment- the infrastructure has been built and the material is available.

Nuclear pulse requires the very large or very heavy engine to be either transported beyond Earth orbit or manufactured in space and the Moon seems to be the only place to assemble, test, and launch such missions. The Moon is also the place to build a beam propulsion infrastructure for future fast missions that may utilized nuclear pulse to decelerate spaceships at destinations in the outer system after high speed transits.

So before any missions to Mars or the outer system can be considered a Moon base is IMO a prerequisite.

Bob Clark

The Block One SLS has the same approximate LEO payload capacity as the Side Mount Configuration SDHLV and it is therefore applicable.

Yes. If NASA could get away from this mental block that: Return to the Moon = Constellation program = $100 billion, we could have an affordable lunar base using the SLS.

Bob Clark

“When I weigh the cost benefit of going back to the lunar surface in a limited budget environment, and going to Mars, I would rather take what little money I have upfront and advance the technologies we’re going to need” to do Mars missions, the website quotes Bolden saying.”

What technologies? The only technology that is going to make a Mars mission possible is nuclear propulsion IMO. The only place to assemble, test, and launch a nuclear mission is the Moon. And if a nuclear propulsion system is required then Mars becomes a second best destination compared to the low gravity icy bodies. And the closest one of those is Ceres.

Ceres becomes the logical manned mission after a Moon base to support such a launch. The ARM mission is all smoke and mirrors. Our space program is dead in the water.

In any event, we cannot go to Mars today or in the near future. That is why the current agency is floundering around with silly ideas for stunt missions, like the haul asteroid proposal.

http://www.thayer.dartmouth.edu/~d76205x/research/Shielding/docs/Parker_05.pdf

is one.

The basic idea is to mimic earths magnetic field to provide a radiation shield. There is a long way to go, but at least they have started addressing the problem.

Travel times with chemical rockets are much to long, the use of electric engines such as the VASIMR should significantly decrease travel times and thus the radiation received during travel.

“It made it very simple for me- not difficult. I believe him and am not confusing the facts with any hidden agenda; the DNA damage caused by heavy nuclei and secondary radiation is real.”

And you have the right to believe anyone you want about anything you want

“I have no knowledge of Dr. Parker having any reason to “persuade casual readers that HSF is just too difficult and should be abandoned.” Do you?”

I have the use of his own (in my opinion extremely unprofessional) words:
– Perils of cosmic rays pose severe, perhaps insurmountable, hurdles to human spaceflight to Mars and beyond.
– What are Astronauts getting themselves into?
– It (meaning spaceflight) is not quite as bad as venturing inside a nuclear reactor, but …
– Even so, the required mass would be at least 400 tons—still not feasible
– MARS’S PITIFUL ATMOSPHERE (and the all caps are his).

“It does not read like propaganda to me; it appears to be the truth and everyone else seems to be dancing around it and trying to find some way to deny or ignore it because it is so disruptive to all the other agendas in play.”

If the above does not read like propaganda to you , that is again your privilege.

It is also my privilege to say I find no further use in continuing this discussion.

Does anybody have any info on this?

Long duration missions, as in years, are unavoidable if human beings are going to explore the solar system in person. The present paradigm is to use unshielded chemically propelled spacecraft that do not even have artificial gravity systems. Just the added structural weight of a tether system to generate artificial gravity makes chemical propulsion a much more difficult proposition. Massive shielding completely changes the whole outlook for human travel in deep space.

Shielding massing in the hundreds and thousands of tons requires a massively powerful propulsion system and the only candidate for the last half century and for the foreseeable future is nuclear pulse propulsion. This seems to be impossible for space advocates to accept.

I have yet to read anything in the mainstream media about this. Maybe I am wrong but no one has ever been able to convince me otherwise. They just ignore the cosmic ray gorilla and nay say. The basic argument against massive shielding that requires pulse propulsion is, “radiation is not a big problem.”

Because humans have not been irradiated for years at a time on space missions this seems to be the proof for many people that it will not be a problem. Uh-huh.