NASA’s plasma rocket making progress toward a 100-hour firing

Almost everyone recognizes that if humans are truly to go deeper into the Solar System, we need faster and more efficient propulsion systems than conventional chemical rockets. Rocket engines powered by chemical propellants are great for breaking the chains of Earth's gravity, but they consume way too much fuel when used in space and don't offer optimal control of a spacecraft's thrust.

NASA recognizes this, too. So in 2015, the space agency awarded three different contracts for development of advanced propulsion systems. Of these, perhaps the most intriguing is a plasma-based rocket—which runs on Argon fuel, generates a plasma, excites it, and then pushes it out a nozzle at high speed. This solution has the potential to shorten the travel time between Earth and Mars to weeks, rather than months.

But to realize that potential, Houston-based Ad Astra Rocket Company must first demonstrate that its plasma rocket, VASIMR, can fire continuously for a long period of time. The three-year, $9 million contract from NASA required the company to fire its plasma rocket for 100 hours at a power level of 100 kilowatts by 2018.

This week, Ad Astra reported that it remains on target toward that goal. The company completed a successful performance review with NASA after its second year of the contract, and it has now fired the engine for a total of 10 hours while making significant modifications to its large vacuum chamber to handle the thermal load produced by the rocket engine.

I am confused about the concern for the use of nuclear power for space vehicles. For me, it would seem that, in many ways, nuclear power would be more manageable in space than on earth as the power plant can be isolated from human contact. There is so much radiation in space already that the vehicles should be protected. Cooling would seem simpler in space.

It just seems like nuclear power in space opens up a lot of possibilities. I’m ignorant of the additional risks compared to conventional rockets and fuel storage.

Maybe a smart person can explain to me. (I understand how a nuclear reactor works to generate electricity.)

I'm all for study and development of faster space travel engines but...two words:

Acceleration. Deceleration.
Neither of which can the human body handle well at high velocities. So calculating how fast a ship can go against the distance to travel does not yield a usable number as to how long a trip will take.

At super fast speeds, a ship will have to accelerate slowly and will need to decelerate just as slowly at roughly the halfway point. No sense having astronauts pinned up against or splattered all over the bulkeads.

Nothing else comes near the power density of nuclear in space applications. When you SWAP analysis (Space, Weight And Power trade offs) nuclear is head and shoulders above anything else.

Currently, space systems use very low power nuclear sources called “batteries” rather than “reactors” (10’s or 100’s of kilowatts, or even less).

We can however, get ten Megawatts of electricity for ten years (conservatively) out of a power plant the size of two five gallon paint buckets. It would very likely require less cooling than whatever systems it supplies, require no more shielding than space itself, and be an ultra-high reliability system.

Currently, that is only useful for running onboard systems, while propulsion remains the overwhelming energy requirement - to escape the gravity of Earth, or land some where else (requiring tons of chemical fuel).

A few things could change in the coming decades though:

More and bigger facilities could persist longer in space (e.g. more space stations), and they might take on more energy intensive missions (like supporting more life, manufacturing, or processing basic materials and fuel)- which would change the balance of energy requirements more toward long term onboard electricity, and less toward initial liftoff.

ElectroMagnetic (EM) drives could be developed for space propulsion. So far, no showstoppers have cropped up that rule out using just electric energy for propulsion. Although it is very low thrust bench top demonstrators right now, it seems promising that it could be able to scale up to propel spacecraft quickly and efficiently around space (but not liftoff or landing). A little acceleration continuously applied for a few weeks gets a spacecraft up to high speed, then you turn it around and gradually slow down as you approach your destination. EM drives, if they work as theorized, could also enable travel to Mars in a matter of weeks, instead of the current two year journey, without being dependent on infrequent launch windows.

Also, we could move further out, where solar panels become ineffective options for electricity. Beyond the Asteroid belt between Mars and Jupiter, the Sun begins to dim below the useful energy density for solar panels. Also, just like here, we will want constant energy at night, on the dark side of the moon, and in underground facilities or mines. Nuclear power sources won’t be as vulnerably to clouds, dust or storms as solar panels would be on another planet with atmosphere, or to solar flares/EM storms in space.

When we get serious about inhabiting and doing business in space, we need to get serious about nuclear power to support it.

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