Alumina is a pretty good high temperature, rigid and mm-wave transparent
material. The brittleness is the obvious downside.
During the DARPA-NASA MTLS program (Millimeter-wave Thermal Launch System,
2012-2014), a high temperature ceramic heat exchanger was developed and used
for a low altitude demonstrator. If you are interested in the program, you can
have a look at the (early) results that were presented at the Advanced Space
Propulsion Workshop last year:
- Program overview by K. Parkin (PI of the project)
http://aspw.jpl.nasa.gov/files/ASPW2014%20PRESENTATIONS/WEDNESDAY/Advanced%20Launch%20Systems/Parkin.pdf
<http://aspw.jpl.nasa.gov/files/ASPW2014%20PRESENTATIONS/WEDNESDAY/Advanced%20Launch%20Systems/Parkin.pdf>
- More details on the heat exchanger development (by myself):
http://aspw.jpl.nasa.gov/files/ASPW2014%20PRESENTATIONS/WEDNESDAY/Advanced%20Launch%20Systems/Lambot.pdf
<http://aspw.jpl.nasa.gov/files/ASPW2014%20PRESENTATIONS/WEDNESDAY/Advanced%20Launch%20Systems/Lambot.pdf>
Cheers,
Tom
On Dec 2, 2015, at 10:46 AM, Jonathan Goff <jongoff@xxxxxxxxx> wrote:
Pierce,
Interesting idea. Though making high-temperature, high-strength, microwave
transparent materials doesn't sound super easy either, but an gelled ammonia
engine using microwave absorbing particles does sound intriguing.
~Jon
On Wed, Dec 2, 2015 at 11:17 AM, Pierce Nichols <piercenichols@xxxxxxxxx
<mailto:piercenichols@xxxxxxxxx>> wrote:
Jon,
Solid heat exchangers are a PITA -- they're heavy and their thermal limits
constrain ISP. I wonder if you could do the soot one better and mix ammonia
with nanoparticles of a variety of microwave absorbers (susceptors) to get a
desired temperature.* Then, instead of a heavy heat exchanger, you just need
a microwave-transparent plumbing section.
-p
*The reason you need more than one is each type of susceptor has a
temperature range. Ordinary glass is quite a good susceptor above red heat...
a fact which can be used to melt a glass bottle in your microwave.
On Tue, Dec 1, 2015 at 4:20 PM, Jonathan Goff <jongoff@xxxxxxxxx
<mailto:jongoff@xxxxxxxxx>> wrote:
Doug,
Agreed on the disassociation benefits of Ammonia. The interesting thing Kevin
Parkin was mentioning on his site
(http://parkinresearch.com/microwave-thermal-rockets/
<http://parkinresearch.com/microwave-thermal-rockets/>) was that the soot
produced by methane decomposition at high temperatures is a good microwave
absorber, meaning it might actually enable heating the methane hotter than if
they had to transfer all the heat from the heat exchanger walls...
~Jon
On Tue, Dec 1, 2015 at 5:10 PM, Doug Jones <djones@xxxxxxxx
<mailto:djones@xxxxxxxx>> wrote:
In my opinion, ammonia is the unsung hero of non-combustion rockets. By
decomposing into N2 and H2 (no fouling), the molecular weight drops to 8.5.
lower than anything but helium and hydrogen. Yet at 200K & one bar the
density is 728 kg/m3, and at 2200K the vac Isp can hit about 3900 m/s. That
rho*isp is hard to beat.
Doug Jones
On 12/1/2015 3:43 PM, Jonathan Goff wrote:
On a note somewhat related to stable, high-performance monopropellants,
Kevin Parkin just announced the start of a San Francisco-based startup
to pursue his previous Microwave Thermal Rocket launch technology (which
I think we discussed a bunch on aRocket back in the day). Hard to get
more stable than inert, and even with Methane or Ammonia, the
performance is still very respectable...
~Jon