Reply to post: Re: Weight?

Watch: SpaceX Dragon capsule breathes fire during crucial hover test


Re: Weight?

But how much does the whole setup weigh, including the fuel?

According to wiki, SuperDracos have a propellant capacity of 1,388kg, which is an odd way to phrase things - is that for the capsule and 8 engines, or just one pair of engines? And couldn't the engines have different sized fuel tanks? But given the entire (test) capsule is 6,000kg, I'll assume the former: 1,388kg total for the current capsule design.

I'm not sure what the engine weight is after a cursory Google search, but assuming they're typical mid-sized, dense fuel engines then a 100:1 thrust-to-weight ratio is reasonable. That means 8 SuperDracos total about 550kg.

Total: a bit under 2,000kg of the 6,000kg capsule.

And what is the cost of lugging it all up into orbit in the first place?

Define "cost." A manned capsule flight is going to use the full capacity of a Falcon 9 whether the capsule is full of cargo or not, or whether the Falcon 9 has unused payload capacity. That's because the capsule's not going to share the ride. Chances are, though, the capsule isn't going to use the full 13,000kg+ of Falcon 9 payload capacity. So what's 2,000kg of reusable engine and propellants matter?

Would a detachable escape rocket + parachute be more efficient?

Yes, but less flexible. The integral SuperDracos give the Dragon capsule an escape capacity. They also give the Dragon the ability to land on land or barges, or for its derivatives to land on the moon and Mars. 1388kg of 240Isp fuel for a 6,000kg gives the capsule an integral 600m/s delta-V, too, which makes for a lot of orbital maneuvering. The sort not seen since the shuttle was grounded.

The engines also have the advantage of being reusable and proven, which means they have engine data and mechanics who are familiar with each engine. Disposable escape towers can be flight-tested once, and then you need a new escape tower without the track record of the old one.

Finally, a parachute is being included. This means the engines and parachute combination give the capsule options in an emergency, rather than a single shot at safety.

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