> However, this is not really 'new' tech. https://en.wikipedia.org/wiki/Deep_Space_1 used an early version in 1998.

As discussed in the article, this is a very different kind of ion thruster. That category is quite large. In particular, I believe essentially all ion thrusters flown have been electrostatic ion thrusters, including both Deep Space 1 and the Hall thrusters discussed in the article.

https://en.wikipedia.org/wiki/Ion_thruster#Electrostatic_ion...

In contrast, the VASIMR engine discussed in the article is an electromagnetic ion thruster

https://en.wikipedia.org/wiki/Ion_thruster#Electromagnetic_t...

(Apologies if you didn't intend to suggest the tech isn't that new, and just meant that the low-propellant-usage part isn't that new.)

They all need a propellant and power feed. But, you can use those same feeds for an array of multiple engines. Thus, 'scaling up' has a wide range of options and trade-offs. Vasimr let's you scale power output a lot from the same engine, but so would an array of smaller engines.

With that in mind the specific techniques are important, but the gaps are often overstated.

(IAN a physics major) But to elaborate per my understanding, there are 2 important variables you're playing with in rocket engines:

- Specific impulse / Isp (aka how much thrust you get for a given amount of propellant)

- Maximum Thrust

Due to the rocket equation [1], adding more propellant increases the weight of your vehicle, making it harder to move, requiring more propellant, etc etc. So being efficient with your propellant is very good.

That said, given a requirement against a gravity well (e.g. a planet), there's usually a minimum total thrust required for a given maneuver to be successful (low total thrust = maneuver takes longer = more time for gravity to pull you = more propellant required).

Thus far, we generally have two types of engines. (1) High maximum thrust, lower Isp (chemical rockets) & (2) high Isp, low maximum thrust (ion/electric engines). The two are currently very far apart [2, sort by Specific Impulse decreasing, then look at the Thrust column].

As examples (Isp Vacuum / Thrust Vacuum): NEXT ion thruster 4,100s/0.236N @ 6.9 kW, VASIMR 5,000s/5.7N @ 200 kW, Space Shuttle SRBs 268s/14MN.

The hope with VASIMR is that it provides a middle ground where high Isp is available with enough total thrust to actually be useful for something other than slow orbital adjustments. An example of "something useful" would generally be anything beyond Earth orbit that covers large distances, e.g. flying to Mars.

[1] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

[2] https://en.wikipedia.org/wiki/Comparison_of_orbital_rocket_e...

This is correct but incomplete: Vasimr may have a higher power density (be it power per thruster mass or per thruster volume) than ion thrusters but I am pretty sure it has lower power density than a Hall thruster, while being also much more complex.

The main (and not yet verified) claim of Vasimr compared to existing and proven tech like Hall thrusters is the ability to greatly vary the specific impulse.

That's what the article claims. That you can run in a less efficient mode that produces more total thrust when you're climbing out of a gravity well, then switch to the lower thrust higher efficiency mode for the long haul.

I thought one of the issues with Hall thrusters was that, in engineering-practical terms, getting enough total thrust out of them was impossible. Or would they scale effectively?