3 ms·

One extra efficiency to keep in mind: the rocket can be custom-made for each launch to exactly the right size for the payload. If you only have a few standard r

by tlb 9y ago

One extra efficiency to keep in mind: the rocket can be custom-made for each launch to exactly the right size for the payload. If you only have a few standard rocket sizes, launching small payloads is wasteful unless you can bundle them together, which means they have to be on the same orbit (or else carry extra fuel in the satellite to shift orbits). The metal in a rocket isn't the most expensive part (it has to be well under 5% the weight of fuel). The expensive part is fabrication. So reusability is important iff fabrication is expensive. Reusability also requires adding extra launch weight for landing fuel and struts and guidance fins. So it's too early to conclude that reusability is mandatory. For heavy repeated lifts to a standard orbit, maybe. For small lifts to custom orbits, maybe not. It all depends on the costs of fabrication.

Robotbeat 9y ago
There's the rub: 3D printing is actually more expensive for fabrication than conventional manufacturing if you're making dozens of things, and if you're making hundreds, it's painfully obvious that conventional manufacturing is cheaper. 3D printing buys you faster iteration and design freedom. It's also convenient for making a regeneratively cooled rocket engine (which makes reusable launch easier, by the way!). Making a rocket a little bit bigger to enable reuse is not actually that expensive. Costs don't scale linearly with rocket payload, so making it larger has a smaller marginal cost than you might think. Besides, now you ALSO have a larger rocket that you can fly in expendable mode if you need to. So if anything, 3D printing allows you to do reuse, as it allows you to still afford making a small number of vehicles per year with similar per-unit fabrication costs as if you were making a large number. But because each airframe can be used multiple times, you can do just as many flights per year as if you invested in a large conventional tooling capability but at a much lower cost. The near-utter-lack of reusable smallsat launchers is baffling to me. Especially now that reuse is effectively proven.

by tlb 9y ago

Robotbeat 9y ago

There's the rub: 3D printing is actually more expensive for fabrication than conventional manufacturing if you're making dozens of things, and if you're making hundreds, it's painfully obvious that conventional manufacturing is cheaper. 3D printing buys you faster iteration and design freedom. It's also convenient for making a regeneratively cooled rocket engine (which makes reusable launch easier, by the way!). Making a rocket a little bit bigger to enable reuse is not actually that expensive. Costs don't scale linearly with rocket payload, so making it larger has a smaller marginal cost than you might think. Besides, now you ALSO have a larger rocket that you can fly in expendable mode if you need to. So if anything, 3D printing allows you to do reuse, as it allows you to still afford making a small number of vehicles per year with similar per-unit fabrication costs as if you were making a large number. But because each airframe can be used multiple times, you can do just as many flights per year as if you invested in a large conventional tooling capability but at a much lower cost. The near-utter-lack of reusable smallsat launchers is baffling to me. Especially now that reuse is effectively proven.