[ctack]

"Such an engine design offers a couple of key benefits over most existing propulsion technology. Perhaps most notably, unlike chemical rockets, Vasimr operates on electricity. As it flies through space, therefore, it does not need massive fuel tanks or a huge reservoir of liquid hydrogen and oxygen fuel. Instead, the rocket just needs some solar panels".

Sounds incredible. I wish him the best of luck.

[Gravityloss]

Electric propulsion has existed and been flown for decades.

Many commercial satellites use it for station keeping.

https://en.wikipedia.org/wiki/List_of_spacecraft_with_electr...

[infogulch]

The difference is this one can scale up the power/efficiency ratio on demand.

[binarycoffee]

I guess you mean the power-to-thrust ratio, which indeed scales roughly with the specific impulse.

The thing is, pretty much every plasma propulsion device has the theoretical ability to throttle specific impulse. Gridded ion engines and Hall thrusters can for instance directly throttle specific impulse (Isp) by varying the discharge voltage. Other plasma thrusters can do this by other means like increasing RF heating, varying the magnetic field, etc.

Unfortunately, in real life the actual usable range of Isp always ends up much narrower that initially predicted because of a variety of factors that are difficult to predict theoretically (erosion and ionization efficiency in particular).

AFAIK, due to the shear size and complexity of Vasimr, its thrust has never been directly measured and we know very little about its actual performance. I would therefore wait a little and discard sensationalist articles until real, extensive testing has taken place.

[Gravityloss]

There's basically four inputs to electric propulsion: power source mass efficiency (W/kg), required delta vee (m/s), required acceleration (m/s/s), and exhaust velocity (m/s). (Well there's efficiency too.)

You can approximately minimize total mass with this info. Turns out, your spacecraft will in total be heavier, if you go to higher exhaust velocities. You save on propellant but you need bigger solar arrays. Not worth it.

All this talk about "Mars in x days" assumes a fantastic power plant. It's a little bit like you're starting a car company and showing wheels and saying "my car company enables range and acceleration three times that of Tesla" while you don't have any kind of battery or motor yet.

[nthcolumn]

You would need two of these ion engines side by side, with solar panels say outside those and a bubble cockpit in front center with... :P