Bill,
RE propellant costs in space, true enough, but missing two larger points:
Propellant available for transfer in space is a tool to enable reuse of
rocket vehicles that cost far more than the propellant. Neglecting the
rocket vehicle cost savings enabled by the costs of making propellant
available makes for an overly narrow analysis.
And propellant costs in space get quite interesting once that propellant
no longer all has to be lifted from Earth. Looked at long-term,
investment now in space propellant storage and transfer is also an
investment in enabling potential future significantly lower space
propellant (and thus lower transport operations) costs. At least once
we get past the initial sherpas-up-Everest economics of lifting all
propellant from Earth, which admittedly taken purely of itself and
lacking the large context can look quite daunting.
As for why key players have done things the way they have over the last
decade or two, well, I daresay there may also have been some politics
involved.
Henry
On 8/23/2019 6:06 AM, William Claybaugh wrote:
Henry:
Propellant at a propellant depot costs the price of that propellant on the ground plus the cost of launching it to LEO plus the pro-rata amortization of the cost of the depot plus the pro-rata depreciation of the depot plus the cost of losses.
Propellant in an upper stage costs the price of propellant on the ground plus the cost of launching it to LEO.
Depots are not getting any traction because the key players—who are at OMB and the Space Council—know these facts.
Bill
On Thu, Aug 22, 2019 at 11:09 PM Henry Vanderbilt <hvanderbilt@xxxxxxxxxxxxxx <mailto:hvanderbilt@xxxxxxxxxxxxxx>> wrote:
I think there does exist some scope to do significant things in
space over the next generation based on known-reaction chemical
rockets. Within the obvious practical chemical rocket limits:
Days to the Moon, months to inner planets and asteroids
(marginal), years to anywhere else (prohibitive). And only if the
current government space morass can be bypassed, because they both
foot-drag on the obvious need for depots, routine reusability and
eventually local propellant sources, and they multiply
already-high costs by a prohibitive factor of ten-to-twenty.
But, that would still be just an initial industrial toehold
off-planet, with at best iffy long-term economic sustainability.
Yes, agreed, in the long run we must get past conventional rockets
to something orders of magnitude more energetic.
Of course the common problem with higher-energy propulsion is that
generating and handling that higher energy without melting takes
too much mass, resulting in what I am inclined to call "the
mousefart thrust problem." The power supply masses far too much
so it takes too long to get up to speed. And intermediate cases,
like nuke thermal rockets, just don't gain enough Isp to make up
for the reactor mass. Yeah, you can get to Mars in four or five
months - but you can do that with chemical rockets also, given
depots and local propellant spent profligately - which would
likely be cheaper overall than developing and fielding the
thermal-rocket reactors.
NSWR is an interesting attempt to combine high energy and high
thrust-to-weight in an onboard nuclear powerplant. Practical?
Who knows. I'll happily watch the tests - via video, from a LONG
way off.
I tend to think that the most promising near-term approaches to
usefully-better-than-chemrocks space transport involve offloading
as much of the high-energy machinery as possible to fixed
power-beaming stations at either end of high-traffic routes. That
way you can just throw mass at gaining the efficiencies needed so
your power generating and beaming machinery doesn't melt. The two
power transmission methods I currently like are laser array, and
neutral particle beam. Lasers you can convert to electricity then
use in electric thrusters, with useful fast-transport performance
at ship-end power-handling-to-mass ratios only (only!) a half
order-of-magnitude better than current SOTA. (It may also be
possible to use laser beams to directly energize reaction mass in
other-than-material containment, but that has a whole lot lower TRL.)
Neutral particle beams I only last spring became aware of as an
option - I gather the ship needs to apply a charge to the
approaching beam, then magsail on it - others can no doubt shed
much more light on the concept (so to speak).
My bottom line though is that self-contained ships that can zoom
around like the Millenium Falcon require several (human)
generations more advanced low-mass power-handling than an external
beam-powered transport net. Subway cars in space, if you will -
far less sexy. But we can build them a whole lot sooner, within
this generation, and we should, IMHO.
(RE your opening question, FWIW, I've never heard of any
NSWR-specific nuclear experiments. As you say, this isn't the
fifties, there is no known funded program, and I would think it'd
be really hard to do a proof-of-concept on that on any likely
discretionary budget.)
Henry
On 8/22/2019 8:01 PM, anthony@xxxxxxxxxxx
<mailto:anthony@xxxxxxxxxxx> wrote:
Have any experiments been conducted using Zubrin’s nuclear
salt-water rocket (NSWR) concept to verify the design or has it
fallen into the ”anything that’s nuclear” black hole?
The cost to even get to the experimental stage wouldn’t be
trivial seeing this isn’t the 50s. I subscribe to the model that
if we are going to accomplish anything *really* significant in
space flight in the next generation, we have to get the known
chemical reaction approach monkey off our back. That’s just my
opinion. The Zubrin citation is only an example BTW.
I’d like to hear some thoughts about this.
Anthony J. Cesaroni
President/CEO
Cesaroni Technology/Cesaroni Aerospace
http://www.cesaronitech.com/
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
