Engine Idea

[RocketSquid]

So, I came up with an idea for an engine:

1. Start with liquid hydrogen fuel
2. Heat it up by some means (nuclear, laser, helicon, electrodes)
3. Inject LOX while maintaining heat source
4. Eject super-heated gas for thrust

Theoretically, this should get a reasonable thrust and efficiency, perhaps a bit more than LANTR.

Is this practical? Can anyone get a better estimate of the thrust and ISP?

[Bill Phil]

Exhaust velocity may not be that high. You're increasing the mass, which, given a specific amount of momentum, reduces velocity.

[p1t1o]

9 hours ago, RocketSquid said:

So, I came up with an idea for an engine:

1. Start with liquid hydrogen fuel
2. Heat it up by some means (nuclear, laser, helicon, electrodes)
3. Inject LOX while maintaining heat source
4. Eject super-heated gas for thrust

Theoretically, this should get a reasonable thrust and efficiency, perhaps a bit more than LANTR.

Is this practical? Can anyone get a better estimate of the thrust and ISP?

Umm , this exactly is LANTR (if using nuclear, that is)...

There's some facts + figures here: http://www.projectrho.com/public_html/rocket/enginelist.php#lantr (coincidentally, using KSP mods as illustrations  )

Generally though, by doing this you exchange a lower Isp for a higher thrust, as you are adding reaction mass (O2) to the exhaust. It's not exactly a propulsion solution in-and-of-itself, more of a way to get more utility options from an existing High-Isp solution.

Edited June 6, 2016 by p1t1o

[magnemoe]

37 minutes ago, p1t1o said:

Umm , this exactly is LANTR (if using nuclear, that is)...

There's some facts + figures here: http://www.projectrho.com/public_html/rocket/enginelist.php#lantr (coincidentally, using KSP mods as illustrations  )

Generally though, by doing this you exchange a lower Isp for a higher thrust, as you are adding reaction mass (O2) to the exhaust. It's not exactly a propulsion solution in-and-of-itself, more of a way to get more utility options from an existing High-Isp solution.

Yes, think the idea was to add O2 during the first part of the burn to get fast out out of the van alen belt, benefit is that you trades isp for trust. 

[cantab]

It's still a thermal engine, and the temperature limit will be set by the ability of the materials used to withstand the conditions. The Isp then depends on the temperature and the atomic mass of the exhaust. Shoving all that LOX in kills your atomic mass, you want that light, so overall you might get somewhat more than a hydrolox chemical rocket but not by much and I doubt it would reach the Isp of eg the nuclear lightbulb concept.

[EnderKid2]

That's basically how you give a NERVA an afterburner.

[DDE]

There are at least two mods that produce such an engine, PorkJet's Atomic Age and Nertea's Kerbal Atomics.

Isp is inherently lowered because the oxidizer is heavier than the tiny H2 molecule. To boost efficiency of a hydrogen-based engine without raising core temperature, you should go from H2 to H.

Good luck containing that.