3 ms·

They don't increase ISP, they increase thrust. This is also something you can do with an ordinary afterburner: Trade ISP for thrust. For space electric propulsi

They don't increase ISP, they increase thrust. This is also something you can do with an ordinary afterburner: Trade ISP for thrust. For space electric propulsion this seems reasonable, since ISP is usually extremely high, but thrust is ridiculously low. It's ok for keeping satellites in orbit, but even a 50% increase means we're not going to send humans anywhere with that any time soon. Additionally, their fusion idea works a bit differently by not directly using the energy created from fusion, which makes the 50% claim seem rather wild. I would wait for a peer reviewed paper or an actual flight test before getting excited about any of this. Small companies promising revolutionary space drives that end up as vaporware are quite common nowadays, because there are lots of simple minded venture capitalists out there who dream of funding the next SpaceX despite having no clue about physics.

jmward01 3y ago
Thanks for the correction! Yeah, thrust != Isp. In this case though, wouldn't this increase the ISP? This type of propulsion gets its energy external to the mass ejected so Isp here, with the energy source not in the factor, should just be based on total propellant mass and the max velocity it is ejected at right? So this -should- increase ISP. I am 100% not a rocket scientist so I am probably way off here. From Wikipedia: 'For engines like cold gas thrusters whose reaction mass is only the fuel they carry, specific impulse is exactly proportional to the effective exhaust gas velocity.' https://en.wikipedia.org/wiki/Specific_impulse https://en.wikipedia.org/wiki/Specific_impulse
- sigmoid10 3y ago
  In the most simple scenario where you inject something inert (literally anything for that matter) into the exhaust stream, you increase its momentum but decrease its velocity. That means higher thrust but at the same time lower ISP. For this fusion enhanced engine here they don't seem to get anything from the fusion process energetically at all, which makes the numbers extra weird. We'll have to wait and see if this whole concept even works.
  - cryptonector 3y ago
    They must be getting heat from the fusion process, thus increasing ISP. Nothing else would make sense here.
    - sigmoid10 3y ago
      No they aren't. It seems their design only really reduces the amount of unpaired electric charges expelled, which otherwise would get pushed back to the cathode because of the plume's total charge density. They don't even use the energy released by fusion itself, because for that you would need to fuse the particles before they reach the exhaust nozzle (which is super hard and also the reason why noone managed to build a real fusion rocket so far). That's why they call it a "fusion-enhanced" instead of "fusion-powered" engine. They talk about it in more detail in another article: https://thedebrief.org/rocketstar-successfully-demonstrates-firestar-nuclear-fusion-enhanced-pulsed-plasma-propulsion-drive/ https://thedebrief.org/rocketstar-successfully-demonstrates-...

jmward01 3y ago

Thanks for the correction! Yeah, thrust != Isp. In this case though, wouldn't this increase the ISP? This type of propulsion gets its energy external to the mass ejected so Isp here, with the energy source not in the factor, should just be based on total propellant mass and the max velocity it is ejected at right? So this -should- increase ISP. I am 100% not a rocket scientist so I am probably way off here. From Wikipedia: 'For engines like cold gas thrusters whose reaction mass is only the fuel they carry, specific impulse is exactly proportional to the effective exhaust gas velocity.' https://en.wikipedia.org/wiki/Specific_impulse https://en.wikipedia.org/wiki/Specific_impulse

sigmoid10 3y ago
In the most simple scenario where you inject something inert (literally anything for that matter) into the exhaust stream, you increase its momentum but decrease its velocity. That means higher thrust but at the same time lower ISP. For this fusion enhanced engine here they don't seem to get anything from the fusion process energetically at all, which makes the numbers extra weird. We'll have to wait and see if this whole concept even works.
- cryptonector 3y ago
  They must be getting heat from the fusion process, thus increasing ISP. Nothing else would make sense here.
  - sigmoid10 3y ago
    No they aren't. It seems their design only really reduces the amount of unpaired electric charges expelled, which otherwise would get pushed back to the cathode because of the plume's total charge density. They don't even use the energy released by fusion itself, because for that you would need to fuse the particles before they reach the exhaust nozzle (which is super hard and also the reason why noone managed to build a real fusion rocket so far). That's why they call it a "fusion-enhanced" instead of "fusion-powered" engine. They talk about it in more detail in another article: https://thedebrief.org/rocketstar-successfully-demonstrates-firestar-nuclear-fusion-enhanced-pulsed-plasma-propulsion-drive/ https://thedebrief.org/rocketstar-successfully-demonstrates-...