Reusable SpaceX Rocket Has Implications For a Return To the Moon (examiner.com)

MarkWhittington writes: While it is unclear what, if any, implications the recent successful landing of the first stage of the Falcon 9 first stage means for the future of space travel, planetary scientist and space commentator Paul Spudis suggested that the feat and the similar one performed earlier by Blue Origin could have some benefit for a return to the moon. In the meantime, a test of the engines in the recovered first stage had mixed results. The engines fired alright, but SpaceX CEO Elon Musk reported, "thrust fluctuations" that might have been caused by "debris ingestion."

Comments

Duh!

[taiwanjohn]

Would dropping the cost of getting payloads to orbit have implications for a return to the moon? Hmm.... let's see... I can't quite tell...

Re:Duh!

[Rei]

Unfortunately, LOX/RP-1 like SpaceX uses now isn't a great fuel for lunar operations. For a small lunar craft, you want something that has very small, light and simple engines, like a monoprop or hypergolic biprop; if your landing craft is bigger, you want something very high ISP. In both cases it's about keeping your mass down because you're so far down the chain on the rocket equation that any small change in mass (esp on the return stage) has a huge impact on the launch mass. Things that LOX/RP-1 excels at, such as thrust, aren't very important in lunar operations. And it would be extremely hard to make RP-1 there because of the shortage of carbon (even hydrogen is unavailable in most locations, but there are some isolated places where it appears to be present in good quantities).

In terms of lunar-manufactured propellants, obviously LOX/LH has gotten a lot of attention. But another interesting one is ALICE - aluminum-ice. Aluminum is an extremely energetic metal - we don't see this side of it often because its surface coating of aluminum oxide is so effective at shielding it. But aluminum can burn not only in oxygen but also carbon dioxide and water (which is why when you weld aluminum you can't use CO2 as a shielding gas). There's only a few other elements out there whose oxides aluminum won't gladly strip the oxygens from at high temperatures - which is why thermite works, and why it can explode fiercely in contact with water. Its affinity for oxygen is so much greater than water's that the two actually make a pretty strong propellant combination - the key is getting past that oxide layer (which has been achieved pretty well in lab scale propellant mixes). The main advantage of ALICE over LOX/LH in lunar operations is not having to deal with leaky, frigid, low density hydrogen.

Unfortunately, while aluminum oxides are incredibly abundant on the moon, ALICE doesn't work where you don't have water ice. You can't just burn a stoichometric ratio of aluminum and oxygen because the hydrogen is actually very important - burned aluminum (aluminum oxide) condenses out at very high temperatures. No gas = no expansion = no thrust**. You need another gas - the lighter the better, and nothing beats hot hydrogen - to take the heat from the aluminum oxide (not just the heat of combustion, but also the heat of condensation). So this rules out most of the moon, only water-rich areas (albeit, those are the places you'd want to set up a colony). Elsewhere, you could use excess oxygen as your heat transfer gas, but at 16 AMU, it's no lightweight. Another possibility would be to outgas helium from regolith, but you'd have to go through a lot of regolith for that much helium.

On Mars it's much easier, as both carbon and hydrogen are abundant. SpaceX rightfully realized that for Mars you either need a very high ISP or a local propellant supply in order to have reasonable launch masses, and have opted for the latter with the Raptor LOX/Methane engine that they're working on. But that's just one of numerous possibilities on the red planet. A more unusual possibility involves the use of the abundant soil perchlorates as an oxidizer with any number of potential fuel species - they're easier to store than LOX and lower energy to produce (albeit lower performance).

** Likewise, when aluminum is added to a hydrocarbon mixture, the optimum ratio of oxygen, hydrocarbon and aluminum is one where the carbon only burns to CO, not CO2 - you want your carbon exhausts in a gaseous form, but your main goal as far as energy release goes is to burn the aluminum; the extra energy you get from carrying additional oxygen to fully burn the carbon is more efficiently spent carrying more stoichiometric mix of aluminum and oxygen for them to burn together.

Re: Duh!

[Anonymous Coward]

And a reusable is only several reuses away from being a proven thing. Hint: getting back a chunk of metal that looks nice enough to display isn't proof of a reusable stage. Reuse something a few times before crowing.

Re:why land on legs?

[Rei]

The rocket launches upright. It's designed to bear loads vertically being imparted through its base. It's not designed to dangle from a cable from its nose. Plus, in terms of "things that can go wrong", grappling onto elevated cables sounds far worse than landing on legs.

From the look of it, the real culprit this time was ice, from all of the fog. That's the leading theory as to why the leg didn't latch. Unfortunately, icing on aerial vehicles in general has killed an awful lot of them over the course of modern history.

Re:why land on legs?

[Rei]

So we're totally going to colonize the universe, but look out for the ice fog!

You mean the stuff that regularly takes down airplanes, despite over a century of experience?

Re:Lessons from SpaceX landing

[Rei]

Huh? Were you thinking of stowing away in the Falcon's first stage?

There are no plans by SpaceX to ever have people land in that manner. Dragon (the part humans actually ride in) has both parachutes both retrorockets, only one of which needs to work, and a degree of "crumple zone" (shock-absorbing legs plus the heat shield and service hardware) in case of partial failures of either of the two.

Perhaps you also missed the fifty or so times that the SpaceX newscasters added the word "experimental" before the word "landing". Would you prefer that like most companies they keep their development work in secret? Or should every company be like them, with, say, car manufacturers releasing footage every time, say, a new experimental safety-critical system ends up with a test car plowing into a fence?