Why does Ed Lu write about ion engines but not about Nerva?

http://www.spaceref.com/news/viewsr.html?pid=9926 talks all about
electric ion engines but doesn't mention nerva type engines. Why?

"Bar Code" wrote:
http://www.spaceref.com/news/viewsr.html?pid=9926 talks all about
electric ion engines but doesn't mention nerva type engines. Why?

The "N-Word" in NERVA is Nuclear. That's why.

Bar Code wrote

http://www.spaceref.com/news/viewsr.html?pid=9926 talks all about
electric ion engines but doesn't mention nerva type engines. Why?

He's concerned with very high Isp engines; Nerva-style nuclear thermal
rockets have Isps only modestly higher than chemical ones. (Note
that in the rocket equation, "modestly higher" can make a substantial
difference in system performance for some applications.)

(Allen Thomson) writes:
He's concerned with very high Isp engines; Nerva-style nuclear thermal
rockets have Isps only modestly higher than chemical ones. (Note
that in the rocket equation, "modestly higher" can make a substantial
difference in system performance for some applications.)

I'm sure we could generate higher ISP with nuclear engines than
Nerva. Materials science has advanced just a bit since then.

Besides, what nuclear thermal engines lack in ISP, they make up for in
high thrust.

Even better would be a dual mode nuclear engine that could produce
high thrust exhaust or electricity. Use the electricity for cruise
mode where something like an ion or plasma engine is more efficient,
but use the high thrust nuclear engine for entering and leaving
the planned planetary orbit (to save time).

Jeff
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jeff findley wrote:

Even better would be a dual mode nuclear engine that could produce
high thrust exhaust or electricity. Use the electricity for cruise
mode where something like an ion or plasma engine is more efficient,
but use the high thrust nuclear engine for entering and leaving
the planned planetary orbit (to save time).

One can also design a nuclear engine that produces some electricity
with the propellant itself. There are large unnecessary entropy
producing steps in a conventional nuclear thermal rocket (for example,
when injecting cooler propellant into a hot thrust chamber); it's possible
to design the engine to instead extract additional work. This would not
require external radiators.

One could use this electrical energy in a kind of arc afterburner
downstream of the reactor, to heat the propellant to above the
temperature limit of the reactor's materials.

Paul

"Bar Code" wrote in message
...
http://www.spaceref.com/news/viewsr.html?pid=9926 talks all about
electric ion engines but doesn't mention nerva type engines. Why?

Umm, because he didn't feel like it? Keep in mind he's writing these leters
on his own time for his own pleasure.