Why isn't Project Orion the new space race?

Question

With a huge robust ship you could go get an ice-teroid. With effectively unlimited reaction mass, finely balanced trajectories become unnecessary and launch windows a thing of the past.

A pulsed nuclear launch would provoke a political furore, but the military advantage of being first to have a robust ship and substantial reaction mass is incalculable. It would be tremendously enabling from both military and industrial perspectives. In particular it would enable preventing anyone else from acquiring the capability.

So why aren't the superpowers in a frantic scramble to acquire an ice asteroid?

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Stuff I mistakenly thought was obvious:

• Pulsed nuke is only for getting a big heavy ship into orbit and going to get the ice.
• Once you have the ice, heat from a reactor produces steam for a steam thrusters.
• You don't carry all of it on one ship, if you did that you would have to use a ridiculous amount to move. You park stockpiles orbiting planets and LaGrange points.
• You freeze it around ships as ablative armour, radiation shielding and thermal mass, and spin the ship fairly fast to get both gravity and temperature distribution buffered by the ice.
• For sudden high acceleration you could use steam to throw a lump of ice. This would also make a good weapon when others try to become space powers.
• I don't know about further out but between Earth and the sun, UV radiation with platinum catalysts can split water into hydrogen and oxygen. With ready supplies of fresh oxygen you could simply dump excess CO2 until there is industrial demand to reclaim it.

Answer 1

Let's start from the misconceptions in your question:

• "Unlimited reaction mass" - there's no unlimited reaction mass in pulsed nuclear propulsion - you can go as far as your bomb supply lasts, but no further. Specifically, you cannot manufacture nuclear devices on board.
• "Military advantage of getting an ice-teroid" - there's no advantage to be gained by capturing water off-world, military or commercial. The only things that can be done with ice asteroids are exploration/in-situ extraction of water for life support, or hydrogen/oxygen for propulsion. If you want to blast someone with an asteroid, you can do it better and cheaper with nukes. You cannot use the Orion ship to fight terrorists/insurgents/whatever, either.
• "Preventing others from developing the capability" - exactly the opposite is true. Once the blueprints are out there, it's easier to steal them than to develop anew.
• "Superpowers" - as noted in the comments, an old-fashioned and slightly incorrect term.

Otherwise, the question has two parts:

• why nobody seems to be in a race for a very heavy launcher,
• and why Project Orion is mothballed.

There are nice answers to the first part elsewhere on the site, and you have been pointed to Test Ban and Outer Space Treaties. I'm only going to summarize the two main objections:

• a very heavy launcher is uneconomical due to extremely high fixed costs of R&D and infrastructure maintenance and very unfrequent launches (there are no commercial or military payloads that have to be launched to LEO);

• there exist high specific impulse propulsion technologies not requiring the huge dead weight of the pusher plate (like nuclear thermal rockets).

For a high thrust launch solution, we're still bound to think about Environmental Impact Assessments, and while chemical rockets are not fluffy cute animals due to ozone depletion and (for solids) large plumes of not really healthy particulate matter, they are better than injecting radioactive fallout and unburnt plutonium into the stratosphere for (un)timely transport to millions of civvies around the world by jet streams.

An obligatory reference to Winchell Chung's site: Project Rho.

Answer 2

Bringing propellent rich asteroids to the earth moon neighborhood is an interesting idea. There are a number of entities pursuing this.

However most proposals suggest solar powered ion rocket engines for asteroid retrieval rather than a vehicle driven by a series of nuclear blasts against a pusher plate.

The U. S. is thinking of developing a solar powered asteroid retrieval vehicle. It would be part of the Asteroid Redirect Mission (A.R.M.). The A.R.M. vehicle is expected to be modeled after the vehicle described in the Keck Report.

However A.R.M. is not being sold as an enabler for using asteroid resources. The mission is promoted as an intermediate step to Mars (a foolish sales pitch, in my opinion).

Critics will say politicians embrace A.R.M. because it's doable by SLS and they want to justify the SLS pork barrel program that keeps folks employed in certain congressional districts. They further contend that SLS missions to an asteroid in lunar orbit do little to get us closer to Mars. I believe the critics are correct. But what the politicians as well the critics miss is the potential usefulness of the A.R.M. SEP vehicle.

Planetary Resources has made a nice video giving a layman's explanation of Tsiolkovsky's rocket equation and delta V budgets:

Aseroids aren't the only possible source of extra-terrestrial propellent. Paul Spudis is an advocate of using lunar water as a propellent source. There may be large deposits of ice at the lunar poles. Another advocate of lunar propellent is Bill Stone of Shackleton Energy Company.

Extraterrestrial propellant, whether asteroidal or lunar in origin, would require substantial mining and processing infra-structure. This is an extremely expensive barrier. It may be a large enough hurdle that we will never make use of extraterrestrial water.

There are those who argue captured rocks offer no military advantage. It's true kinetic kill weapons would be horrendously expensive. Nuclear bombs could wipe out a city for a small fraction of the cost. But those using this very obvious argument are stuck in 1970's science fiction. There are other possible military uses for space resources than throwing rocks.

What extraterrestrial propellent might offer is routine access to orbital assets in cislunar space. This includes surveillance satellites, GPS, communication satellites and weather sats. Easy access to these would indeed be of incalculable military value.

As suggested I will elaborate on what I mean by routine access. Presently a ship from earth's surface to LEO has a 9 km/s delta V budget. Returning to earth's surface entails enduring the extreme conditions of an 8 km/s re-entry through earth's atmosphere. So far economical reusable vehicles haven't been realized.

In contrast vehicles between earth orbits would have 3 to 4 km/s delta V budgets. Most wouldn't have to endure the high temperatures and dynamic pressures of re-entry. Those ships with LEO destinations might use aerobraking for circularizing at LEO but the aerobraking would be much less extreme than an 8 km/s re-entry.

With the present paradigm the routine is launch, use and discard. With cheaper transportation between orbits it would be possible to upgrade and maintain existing assets rather than letting them die and add to the population of orbital debris. It would also be possible to salvage dead sats.