[InclinedPlane]

Almost the entirety of the cost of an orbital launch is in manufacturing and operational costs. Cost of fuel is basically just noise. If you can reduce operational turnaround time and operational complexity, even at a cost of payload, then you'll save so much money it'll be worth it in the long term. SpaceX is aiming for a re-assemble, gas up and go workflow. If they can pull it off it might reduce their per flight launch costs by a factor of 10 in the short term and perhaps as much as 100 if they get really good at it (although that's likely several generations of hardware down the line, at best). With that sort of thing on offer a reduction in payload is easily justifiable.

Imagine if somebody replaced your car with a version that had twice the carrying capacity, but would only run for one tank of gas. It wouldn't be a worthwhile trade would it?

[mikeash]

To put it in perspective, the fuel used to launch a Space Shuttle cost in the neighborhood of $1 million, while the cost of the entire launch was somewhere around $500 million to $1 billion.

[wiredfool]

Another perspective is that the Falcon9 carries about as much kerosene as a 747.

[747facts]

I decided to fact check you. 57,285 U.S. gallons in a fully loaded 747. Jet-A is 6.84 lb/US gal. That's about 196 tons. Looks like stage 1 of the Falcon 9 is estimated to use 239 tons of RP-1 and stage 2 49 tons.

http://www.boeing.com/boeing/commercial/747family/pf/pf_400_...

http://www.spacelaunchreport.com/falcon9.html

[simonh]

Cool, so they're well within an order of magnitude of each other.

[mikeash]

That's a good one, although a 747 gets its oxygen for free.

[schiffern]

LOX is literally cheaper than dirt (8¢/lb, or 67¢/gallon).

[DavidSJ]

Yes, but oxygen's pretty easy to come by it turns out.

[InclinedPlane]

For the Falcon 9, it costs about $200k for propellant per launch (Kerosene is cheaper than LH2 and the F9 puts about 1/10th as much mass in orbit) while the price of the launch is about $50 million.

[slacka]

Could and real or kerbal rocket scientists here explain why SpaceX isn't doing something like the curiosity rover landing? Sure there's 3 extra steps, deploy parachute, cut parachute, and evasive maneuver, but the fuel saving would massive.

[JshWright]

I'm not sure the savings would be as massive as you think (and would be offset by other costs).

Parachutes (and associated equipment) are heavy, so you'll burn fuel lifting that extra weight.

Parachutes are complicated, and would be an extra system to develop, test, and validate.

Parachutes are annoying to repack/replace (increasing turnaround time).

Parachutes put odd stresses on large objects when they deploy (increasing the amount of inspection you would have to do after each flight).

All that hassle to reduce the terminal velocity by a couple hundred miles an hour. That's not that big a win for a pretty high cost.

[Florin_Andrei]

> All that hassle to reduce the terminal velocity by a couple hundred miles an hour.

That's the TLDR. The delta-vee from the parachute is not worth the trouble.

[mikeash]

Or put it another way, parachutes are generally less effective than using a system you already have for other purposes. A parachute probably beats a rocket engine if your only task is landing, but when you already have the rocket engine, you're better off using it for landing than building a completely separate landing system.

In short, same basic reason why we use wings and wheels to land airplanes rather than dropping them from a parachute when they reach their destination.

[schiffern]

Not "massive". The empty stage is very light, so a little propellant goes a long way. It's less than 10% of the fuel for the entire descent phase (and the optimal upper stage length goes up to compensate somewhat).

[smackfu]

Well, one reason is that parachutes at this scale aren't that simple. For instance, check out the ones on the Shuttle SRBs: http://en.wikipedia.org/wiki/Space_Shuttle_Solid_Rocket_Boos...

[samstave]

Also, the first stage put up the second and third stage units.

What if you have a payload container that was the size and weight limits of the second and third stage, which was put up into LEO by the first stage. The payload would then be picked up by vehicles already in orbit, and the first stage unit returns to earth.

Assuming that the payloads are simply building materials, to be assembled by bots in orbit....

[rbanffy]

The first sage alone won't take your payload to LEO - you'd still need a second stage. However, orbital tugs with electric engines could take your payload from LEO to other orbits with less reaction mass than a chemical rocket could.

You'd still have to refuel their reaction mass, unless we are talking solar or magnetic sails.

[6ren]

It's also extra weight to lift.