Bill,
I actually disagree with that idea that depots will always be more
expensive than tanking. Sure it's possible to do a depot that costs more
than tanking, but I'd argue that's doing depots wrong.
To me, the point of a properly done depot, is to enable you to offload most
of the mass and expense of the rendezvous, capture, and propellant handling
equipment to a system that gets reused on-orbit multiple times. With a
tanker, you have to launch that hardware every single flight, cutting
directly into how much propellant you can deliver to orbit in one go, and
driving up the cost of the tanker, especially if it's expendable. With some
of the tech we're developing at Altius, I think I could get the mods to
make a Centaur V capable of rendezvousing with a depot, being captured by
it, and being refueled by it to <<$1M marginal cost compared to a stock
Centaur V. A fully reusable tanker at least would allow you to amortize
those pieces of hardware, but you still take the payload hit on every
launch. And because you have to do it on every launch, you're almost
certainly going to end up optimizing for mass more than robustness, which
will likely increase your odds of the occasional unsuccessful refueling
operation.
Depots also provide logistic benefits by decoupling the propellant launches
from the mission, dramatically decreasing the odds of a failed propellant
launch costing you a mission. It makes it easier to leverage international
partners for propellant launch. And if you place it in the right place, you
can potentially even tap into scenarios where propellant would otherwise be
wasted.
I know it's the conventional wisdom, I just think it's wrong. Even if Elon
disagrees.
~Jon
On Fri, Aug 23, 2019 at 9:25 AM William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
Jon:
Confusing depot economics w/ SLS is a red herring: tanking will always be
lower cost than a depot because of amortization and depreciation. SLS has
nothing to do with these facts.
Refueling a fully reusable lunar lander in LLO does make economic sense
because it saves the cost of sending all those expended landing stages to
the lunar surface.
It still appears lower cost in the near term to tank from a resupply
mission than to build a depot; if lunar propellant were to become available
at a lower cost than Earth propellant it might be lower cost in LLO; but
might not. In either case, such propellant is probably better stored near
the mine than in LLO, again, tanking appears more likely than a depot so
long as we are talking about a dozen or fewer landing missions per year.
Bill
On Fri, Aug 23, 2019 at 9:04 AM Jonathan Goff <jongoff@xxxxxxxxx> wrote:
Bill,
The cost per kg of propellant launched on SLS (and a lunar mission is
mostly propellant in LEO) is going to be north of $10-20k/kg ($1-2B per
launch 100,000kg/launch). The cost of launching that propellant on say a
Falcon 9 or Falcon Heavy can be <$2.8k/kg ($50M for 18,000kg). It seems
like there's plenty of room for a depot-based architecture being
dramatically cheaper than keeping SLS. Especially if it's a privately
developed depot.
It's worth noting that NASA is at least on board with depots in lunar
orbit--they're paying Altius (through Orbit Beyond) to work on prototype
cryo transfer couplings and systems for lunar orbit refueling under their
NextSTEP Human Lander System BAA.
~Jon
On Fri, Aug 23, 2019 at 8:56 AM William Claybaugh <wclaybaugh2@xxxxxxxxx>
wrote:
Sorry, but it is entirely about the cost of propellant at the depot.
OMB is unlikely to endorse any scheme that makes space travel more
expensive rather than less and a depot makes propellant more expensive not
less.
Using tankers to refuel reusable assets is—obviously—much less costly
than building a depot; I assume that is why SpaceX has chosen to go with
tanking.
Bill
On Fri, Aug 23, 2019 at 8:16 AM Rand Simberg <simberg@xxxxxxxxxxxxxxx>
wrote:
It's not about the cost of propellant at the depot. It's about the cost
of the SLS, which a depot renders unnecessary (and which will require
multiple launches anyway). If you can refuel from one vehicle to
another, then perhaps one doesn't need a dedicated depot, but the
notion
that we should get anywhere with the launch of a single vehicle from
earth is a relic of Apollo. Even Starship is intended to be refueled.
On 2019-08-23 06:06, 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> 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 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/ [1]
(941) 360-3100 x101 Sarasota
(905) 887-2370 x222 Toronto
Links:
------
[1] http://www.cesaronitech.com/
