Straight to the quotes file!
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On 16 Jun 2019, at 08:55, Jonathan Goff <jongoff@xxxxxxxxx> wrote:
Craig,
Sounds like an exercise in applied asking for trouble...
~Jon
On Sat, Jun 15, 2019 at 4:53 PM Craig Fink <webegood@xxxxxxxxx> wrote:
Hi Jon,
Filling the Hydrogen Tank could be a two step process to get a coating of
water frost capped with a layer of clear ice to create a disposable Dewar on
the outside of the tank. Fill the Hydrogen tank with LOX, LN2, or some
other cryogenic. Build the frost/ice layer the way you want on the outside
of the tank. Empty the Hydrogen tank and purge with warm but still freezing
Nitrogen, or Helium. Then fill the pre-cooled tank with LH2. Frost capped
with a layer of clear ice might work as a reasonable Dewar. Any air trapped
in the inside of the frost layer will condense creating a vacuum.
--
Craig Fink
WeBeGood@xxxxxxxxx
On Sat, Jun 15, 2019 at 3:07 PM Jonathan Goff <jongoff@xxxxxxxxx> wrote:
Henry,
I wonder if you could do a CO2 purge instead of helium--get something that
will deliberately solidify at those temperatures that you could fill the
air with in higher quantities than just humidity. IIIRC didn't the common
bulkheads on one of the past LOX/LH2 stages use a honeycomb filled with CO2
in the bulkhead with the intent of having the CO2 freeze to one side of the
bulkhead creating vacuum in the honeycomb cutting down on heat flux? This
isn't an analogous situation, since you're talking about the external skin
of a rocket, but I wonder if there's some potential there.
That said, for rockets bigger than amateur rockets, SOFI insulation isn't
*that* hard. Does anyone know if Blue Origin has had big issues with LH2
handling with New Shepard?
I'm not as bullish on LH2 being relevant to most hobbyists as Craig is, but
I'm interested in it for some of the work we're trying to do professionally
at Altius.
~Jon
On Sat, Jun 15, 2019 at 3:28 PM Henry Spencer <hspencer@xxxxxxxxxxxxx>
wrote:
On Wed, 12 Jun 2019, Jamie Morken wrote:
...saturate the surrounding air with ambient temperature water vapour,
using piezo water droplet generators etc, to prevent the ice insulation
layer turning to slush from liquid air condensing, and then immediately
prelaunch, turn off the ambient water vapour generators, and weaken the
insulating layer by venting nitrogen gas around the tank to create a
slush layer of insulation. This could allow for good insulation for the
majority of the pre launch time.
Unfortunately, the vapor pressure of water at (say) 25degC is only about
0.03atm, so 25degC air saturated with water vapor is still mostly air.
(At 100degC, of course, the vapor pressure is 1atm, but circulating hot
steam around your LH2 tank is unappealing!) You'd need to make up the
remaining 0.97atm with helium, which is possible but costly and clumsy.
Most other schemes for removable insulation have the same problem -- they
need a continuous helium purge to make sure air doesn't get under the
insulation. So do some kinds of non-removable insulation, in fact: the
S-II (Saturn V second stage) originally had insulation panels fastened to
it, but helium purging and other little complications added so much hassle
that midway through the program, they switched to spray-on foam. (In
fact, the shuttle ET foam was an improved version of the S-II foam.)
Also, any scheme which removes the insulation at launch will still have a
problem on the way up -- there's enough time for an uninsulated LH2 tank
to see quite substantial boiloff, especially with aerodynamic heating
contributing to the problem. Ideally, removable LH2 insulation should
stay with the stage until just before burn time. Centaur originally did
that... but between the need for structural strength during ascent, and
the mass of the jettison system and the helium purge, the result wasn't
all that lightweight, and Centaur payload went *up* when they switched to
permanently-attached foam.
Henry
