Hacker News Reader

Comment by thinkcontext | Hacker News Reader

It's necessary because the Starship upper stage is so heavy. With a non reusable upper stage Starship's capacity would be enormous.

View on HN

Is that true? SpaceX [0] gives the capacity as 150t reusable or 250t expendable, which is significant, but not enough to make one "enormous".

If you really got order-of-magnitude gains from an expendable upper stage, it wouldn't be that exciting to have reusable rockets (which are more complex and still only fly one order of magnitude more times) in the first place.

[0] https://www.spacex.com/vehicles/starship/

If the upper stage wasn't designed to be reusable, it'd probably have a lot less structural dry mass - no heat shield, no fins, possibly different geometry (depending on how much volume they wanted). It might also be possible to drop the sea-level Raptor engines and just use the more efficient vacuum Raptors. I don't think you'd get an order-of-magnitude difference, but it'd be significant, especially for higher-energy trajectories than LEO.

I don't understand why they don't make such an upper stage. It would allow them to refine the booster design and catch logistics while also launching payloads.

My guess would be that it would take too much extra design work. Making the current upper stage reusable is necessary for the HLS contract anyways, and they've got a lot of work to do already on refining the heat shield & fin protection, enabling landing, and working on propellant transfer.

They are making an upper stage with no fins or heat shield. It's called HLS. But they don't need it just to launch payloads to orbit. Starship has such a bonkers huge payload capacity already that it's plenty for now. Nobody is asking for more yet. Testing Starship reentry is super important too, so it makes sense to do it on every launch until it's perfected.

Also because of the Lunar Gateway part of the plan. That pretty much just serves to waste fuel and funnel taxpayer money to the companies funding several congressmembers' election campaigns.

Reply on news.ycombinator.com