1st stage is using Autogenous (No He, and we all know how much grieve that has given SpaceX)
ULA has no issues with He on Atlas and Delta.
Yet they are switching to autogenous on Vulcan anyway. Just sayin'
Yet they are switching to autogenous on Vulcan anyway. Just sayin'
Because they can. Can't with RP-1.
By autogenous, do you mean using fuel vapor for tank pressurization instead of helium? I assume this potentially saves a fair amount of weight by eliminating the helium tanks?
By autogenous, do you mean using fuel vapor for tank pressurization instead of helium? I assume this potentially saves a fair amount of weight by eliminating the helium tanks?
Yes, autogenous means propellant is pressurized by its own vapour phase. For oxygen/methane the elimination of helium tank mass is offset by the propellant vapours being heavier than helium.
Cost Savings?
Yes, mostly thru elimination of all the hardware involved in a helium pressurization system.
Sorry, I'm responding to one specific SpaceX point because it was already made, but after this we should save details about SpaceX that aren't simply discussed to contrast with ULA's plan for the SpaceX threads.
Looking at the SpaceX landing video as an engineer - I would say more fuel margin could fix this issue. They just have too great a probability of end-game oscillation given GPS error etc on a short duration suicide end burn. If they can slow the rate of descent a bit earlier and get stable higher they can pull this off. Final correction did them in....
Fuel is not free though...anything reserved for landing comes out of the boost phase.
More fuel margin doesn't help them at all unless they can throttle the engine down significantly more deeply. They can not extend the burn time because they can not hover.
Because even at minimum throttle their thrust-weight is greater than 1, if they extend the burn time, they don't get more useable time to settle out any oscillations. Rather, they stop descending and start ascending. That's not good.
Then time to look at the engine controller perhaps... a hover may not be required...perhaps they simply do some squirts to get less oscillation on the final and don't put it all on a successful final burn.
As other posters have pointed out - length of stage and small gear footprint vs height may always be an issue.
Let's stay focused on ULA, there are other threads to discuss SpaceX landing tech.