Hello everyone! I’m going to try out a new weekly newsletter format. This time called the “Space Putin Digest”. Props to those of you who get the reference. So, what were the biggest things that happened in space this week?
(1) SpaceX flies and lands Starship for the first time!!
So I kept looking for good in-depth explainers on why Elon/SpaceX decided to switch over from an aluminium-lithium alloy over to steel, and none the popular space YouTube channels or Twitter personalities had great explanations for it. My favorite one was Real Engineering (link), with an ok runner-up of Everyday Astronaut (link). But neither were quite satisfying. So here’s my attempt at doing a more in-depth layman’s explanation of why SpaceX switched to stainless steel and why it matters SO MUCH
First, this isn’t the first time stainless steel has been used in rockets! In the early Atlas rockets days, stainless steel was our best option, however, because the strength to weight ratio (STWR), basically how strong is a metal relative to how much it weighs, and because our rocket engines were pretty rudimentary, the only way to make a reasonable rocket design with stainless steel (SS), was to keep the SS so thin that you had to keep the rocket tanks pressurized or else the rocket would actually collapse on itself, like a balloon (link). And stainless steel was particularly hard to work with at large scale, since it was so soft and sticky that if you tried to “cold-form” (rather than heat up a metal and pour it a mold, instead bend it into shape, and it ends up stronger) it would end up getting stuck on itself and fracturing.
So aluminium-lithium alloys got invented, which had a much better STWR, so we switched to that largely. They were much more expensive, but in the early days of rockets, all that mattered was who could even build a rocket, with cost not being much of a consideration.
Fast forward to 2002 when Elon was starting SpaceX, and the same was basically true then. Rocket cost didn’t really matter, and STWR is still all that mattered so he stuck to that.
But now in 2018, SpaceX has quite a different set of considerations. Their rockets are returning to Earth on quite a regular basis. And the market has gotten much more cost competitive all around, with other big launchers working on reusable rockets and small launchers being cheaper/faster due to their size.
Before, rockets just went up and were done for. Now, your rockets need to be able to (1) get back to earth (2) be refurbished easily and (3) manufactured at scale since the space economy is booming baby.
So let’s talk about why stainless steel kicks butt at these! (1) When you’re bringing a rocket back from space, you’re going fast! Real fast! And right now SpaceX expends a lot of fuel slowing the rocket down before it enters the atmosphere so it doesn’t burn up. SS’s melting point is much much higher than other metals, and so rather than expending fuel, you can use the atmosphere to slow you down and have a pretty minimal heat shield.
(2) SS is super easy to weld! It also is pretty anti-fragile, because it actually heals over cracks naturally rather than encouraging them unlike most alloys and carbon fibre. And, interestingly enough, when it gets cold, unlike most metals which become brittle and fracture, SS actually becomes stronger. This matters because rocket fuel is cold, real real cold.
(3) SS is real damn cheap. We use it in pots! Pans! Cybertrucks! And, quite recently, a company in the UK invented a new lubricant which allows us to “cold-form” steel, i.e. we don’t have to heat it up to get it into shape, even at pretty large scale. So the manufacturing costs are super cheap.
So Elon’s old rockets were expensive, hard to manufacture, hard to refurbish, and the weeney little metal had to be slowed down so it didn’t burn up. SS is everywhere, easy to manufacture, easy to weld, and it’s a big strong boy when it’s got cold rocket fuel or barreling through the atmosphere.
So in the old days when rockets were thrown away, sure you just wanted to optimize your STWR, but in 2020, the calculus is pretty damn different.
P.S. If you’re wondering why SpaceX has gone quiet on the Falcon Heavy (3 Falcon 9s strapped together), it’s mostly because the world of heavy launch has died down. With launch getting so cheap, a lot of companies and the military are hesitant to put up a huge multi-$b satellite up into a high orbit when it’s made obsolete by a constellation of smaller, cheaper satellites in a lower orbit. So SpaceX is just jumping straight to super heavy launches with starship, hoping that when it’s done being developed they can use it for the moon, point to point on earth, mars etc.
P.P.S. And you GOTTA watch the “tin” can fly 150m and down, it’s so cool to see (link)
(2) Space Force awards $7b to ULA + SpaceX
SpaceX and ULA knocked out other competitors like Blue Origin for a shared $7b contract over the next ~5 years. These contracting processes are super competitive and it’s a huge deal for SpaceX and ULA to know they have pretty significant guaranteed revenues coming in from the military (linklink2)
(3)Astra, a bay-area based small launcher misses their launch window because of a boat!
The only Bay Area-based launcher, Astra, had to call off their maiden flight attempt originally because a boat got in the way, and later in the week the weather and winds were too high. They still haven’t announced their next launch window. Always love to see more launchers come online, although, realistically between SpaceX, ULA, Blue Origin, RocketLab, and Arianespace, there’s probably not much room left for more launchers in the market. Space is a big market but it’s not quite that big yet (link)
(4) Demo 2 landing
Remember when SpaceX sent people up to space! Well we decided that we should probably try bringing them back first before we send the next crew, currently targeted for late September! (link)
Ok, hope you enjoyed it! I know this Substack has quite the variance on what gets published but, oh well, you’re along for the ride.