Silane as an ISRU Fuel

[SOXBLOX]

Silane, or SiH₄, is the silicon analog of methane. It is pyrophoric, which, as far as I can see, means it's hypergolic, and has decent thermal properties, according to a paper I read. It could be produced from abundant silicon in the lunar crust, etc.

What do you think? Would it be a good fuel for lunar use?

[Xd the great]

1 hour ago, SOXBLOX said:

Silane, or SiH₄, is the silicon analog of methane. It is pyrophoric, which, as far as I can see, means it's hypergolic, and has decent thermal properties, according to a paper I read. It could be produced from abundant silicon in the lunar crust, etc.

What do you think? Would it be a good fuel for lunar use?

How do you plan on solving Si/SiO₂ deposits in the rocket engine?

[Spica]

I see three issues with silane as a choice of propellant for ISRU on the moon:

1) I assume any engine intended for this role ought to be reusable, and this seems to conflict with the fact that the exhaust of any silane fueled rocket is largely quartz, some of which will be left behind in the engine after shutdown. Solid silicon deposits may also build up in parts of the engine plumbing wherever high temperatures are experienced.  The large amount of solids and liquids in the nozzle will also reduce Isp.

2) Hypersonic quartz smoke in the exhaust will be damaging to any nearby structures on the ground and in orbit.

3) You still need large quantities of hydrogen in order to make large quantities of silane.

I'm not sure how important each of these problems would actually be in reality, but they certainly need to be either solved or shown to be insignificant in order to make silane a useful propellant.

[AngrybobH]

According to the wiki, silane looks to be a little more complicated than just having Si and H. Like catalyzing with a metal halide, is that available on the moon? I'm sure the Si on the moon isn't just pure Si laying around, how many steps and how much energy would be required to produce silane? Compared with just making hydrolox from moon stuff is it more or less energy? Silane also seems dangerous.

[SOXBLOX]

So, it's probably like coking from kerosene, but worse. But would SiO₂ even be solid in this environment? I can't imagine fine sand blowing out of a rocket nozzle...

I'm thinking that its benefits, if any, would be the hypergolic and ISRU aspects. Like @Spica said, you still need hydrogen, which on the Moon can really only be found in ice deposits.

I was wondering if it would have slightly-worse-than-methane performance, but without needing carbon.

IDK about production of silicon from regolith. I'll check in the morning...

[kerbiloid]

Sand ridges will mark the course from the launchpad.

Later they can be used as a launch embankment for horizontal start.

[Guest]

A quick Google turned up a whole bunch of research about this. The answer seems to be a strong "maybe."  They're also looking at silanes for terrestrial use as scramjet fuel.

Quote

Whether or not a lunar-based propulsion system, more particularly, one based on LO₂/LSiH₄, will ever be developed will depend upon many factors that are beyond the scope of this paper. However, the technology to manufacture oxygen and silane on the Moon and also to develop a lunar-based propulsion system based on the bipropellant LO₂/LSiH₄ combination is within our reach. The development of a lunar-based propulsion system can be accomplished within the time frame under consideration, i.e., by the start of the 21st century. All that is required are the need, the will, and the funds.

From http://articles.adsabs.harvard.edu//full/1985lbsa.conf..169R/0000175.000.html

See also:

• https://www.jstage.jst.go.jp/article/tstj/7/ists26/7_ists26_Pa_33/_pdf
• https://www.jstor.org/stable/44682837?seq=1

 

 

 

Edited May 8, 2021 by Guest

[Piscator]

Since the exhaust of some solid rocket motors can be assumed to consist of sizeable amounts of alumina, producing silicon dioxide might actually not be that terrible. At least if the design is kept simple enough. 

That said, if you're trying to process lunar regolith into rocket fuel, you might want to think about some kind of metal + oxidizer solid propellant or even a  metal + LOX hybrid design. The less hydrogen you need, the better.

[kerbiloid]

2 hours ago, SOXBLOX said:

I can't imagine fine sand blowing out of a rocket nozzle...

Look at a 3d printer's nozzle.

***

And fuel tanks made of glass for silane.

[SOXBLOX]

6 hours ago, Brikoleur said:

From http://articles.adsabs.harvard.edu//full/1985lbsa.conf..169R/0000175.000.html

See also:

• https://www.jstage.jst.go.jp/article/tstj/7/ists26/7_ists26_Pa_33/_pdf
• https://www.jstor.org/stable/44682837?seq=1

Thanks! That first one is the one I read on this, a while ago. It was in some book I got from the library...

So, oxygen can come from ilmenite, pyroxene, or olivine. The Rosenberg paper says that an initial amount of hydrochloric acid would be needed, but after that, Earth would only have to supply water. Of course, now we know that the Moon has water. Maybe this could work...

[mikegarrison]

The basic problem is still the hydrogen. That's why people are so desperate to find ice on the moon.

Edited May 8, 2021 by mikegarrison

[kerbiloid]

Also afair, silane produces much greater heat and pressure stress in the engine, so maybe it's for single-use boosters only.

(Let alone the probable glassy remains in the chamber.)

[SpaceFace545]

On 5/8/2021 at 3:15 PM, kerbiloid said:

(Let alone the probable glassy remains in the chamber.)

That could give it a use not as a rocket propellant but as a method for creating a landing pad with rocket exhaust such as FAST landing pads being developed by Masten.

[Xd the great]

On 5/10/2021 at 12:01 PM, SpaceFace545 said:

That could give it a use not as a rocket propellant but as a method for creating a landing pad with rocket exhaust such as FAST landing pads being developed by Masten.

Spoiler

Why do I see a pogo stick of glass under a rocket engine.

Landing on glass is maybe not the best idea...

Edited May 11, 2021 by Xd the great

[kerbiloid]

Landing cones matching the nozzles.