Mike:
Nah, I could do that: years of experience must count for something….
Bill
On Tue, Jul 13, 2021 at 4:47 PM Michael Kelly <dmarc-noreply@xxxxxxxxxxxxx>
wrote:
It would be hard to make a nuclear engine that costs more than an RS-25.
Sent from my iPhone
On Jul 13, 2021, at 6:07 PM, William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
Henry V.:
What if the nuclear rocket costs no more than a chemical motor of the same
size? It is always are assumptions that get us….
Bill
On Tue, Jul 13, 2021 at 2:11 PM Henry Vanderbilt <
hvanderbilt@xxxxxxxxxxxxxx> wrote:
What he said. Conventional nuclear-thermal is a dead end. You can match
the transit-time performance at lower overall cost by simply adding more
conventional rocket propellant.
And note that there may well be little or no NTR advantage even if you
ignore the (LARGE) additional development, hardware, and ops costs that
show up the instant you say "nuclear". Not all propellant costs are
equal. Conventional NTR requires pure LH2 propellant or there's no Isp
advantage at all. Putting, say, twice the total propellant mass of 6:1
LOX/LH2 into LEO when & where needed may not cost much more than the NTR's
required mass of LH2 - might possibly cost less - because LOX is hugely
easier to transport (far higher-density thus more compact) and store (far
"warmer" thus far less relative mass of insulation and/or refrigeration
needed.)
As my estimable colleague alludes, solid-core NTR due to materials
temperature limits simply can't reach high enough Isp to justify the poor
thrust-to-weight and TERRIBLE costs. Better to spend available nuke R&D
funding on more advanced technologies that don't require solid-material
heat exchangers, thus have some chance of delivering enough real
performance advantage over chemical rockets to be worth the very high
nuclear overheads.
Henry's evil twin
On 7/13/2021 12:26 PM, Henry Spencer wrote:
On Tue, 13 Jul 2021, roxanna Mason wrote:
Perhaps the realities of long duration human spaceflight have finally
sunk in,i.e. zero g, radiation, one way travel/isolation,etc.
Don't get too excited. These are small, short design studies, which
won't actually build or test *anything*, with no apparent plans for
followup. The purpose is "to establish the basis for future technology
design and development efforts".
It doesn't qualify as serious until the plans include testing hardware.
All this said, nuclear is still not a cake walk with perhaps at best only
half the travel time...
And that, we could do without nuclear -- just add more fuel. Fuel is
cheap, even in LEO.
IMLEO (Initial Mass in LEO) is a dangerously misleading surrogate for
cost, because it assumes that a kilogram of LOX in orbit costs about as
much as a kilogram of nuclear engine in orbit. You could launch many
kilotons of chemical fuel into LEO for what the first nuclear engine will
cost. Especially if you set up a fuel depot and announce that for the next
fifteen years, you'll buy X tons of fuel per year, priced on a sliding
scale (scaling down as volume builds), from the first people who deliver it
to the depot -- no exclusive contracts, no development subsidies, payment
on delivery only.
It's far from clear that plain old NERVA-style solid-core nuclear can
actually improve things enough to be worth the up-front investment; at most
it's a pathfinder for something better. Any serious plan for nuclear
propulsion should include starting real work on a more aggressive Phase Two
at the same time (not just penciling it in for the vague and misty future).
Holding of breath is not recommended. :-(
Henry
