SpaceX Did It – What It Should Do Next

Congratulations to SpaceX who landed the first stage intact.
Assuming cost is roughly related to stage mass and engine count, reusing the first stage saves 9/10 of the whole rocket cost.
If they can run the stage ten times, that means on average two new engines per flight as opposed to the original ten, meaning five fold savings.

Now there’s a few very interesting questions.

First is the amount of flights they can get per engine. First, I assume it’s going to be a low count, and experimental at that. Once they inspect and test the engines, they can improve them further.

Second is the ultimate development of the refurbishment process that has to be done to the vehicle between flights. If the turnaround takes a month and 200 people of three shifts each, then it doesn’t save much money, and might even be more expensive than just building a new stage.

If it requires one crane operator to drive some support tower there, place a new second stage, place a new payload, place fuel connections. After refueling they need some air traffic control type permission to fly again in a few hours. Then it has the potential to not only save a lot of money, but to place very large masses to orbit in a relatively short time.

I realize such a vision is still quite far off. Even if all the ground operations were somehow solved, just the winds frequently limit the launch and landing quite a lot at the moment.

Second stage

At the moment the second stage resembles the first one, only with one engine. However it is thrown away after use, as it’s hard to recover.

The first stage is easy to recover because it’s not yet very high or fast when it starts the return trip. On the other end of the stack, the Dragon capsule is relatively easy to recover since it’s so small, so you can make it really sturdy, put a lot of heat shield and parachutes (and RCS rockets on it), and it still doesn’t kill the total weight budget. You can also transport it over sea or land if need be.
One way to get around this would be to combine the second stage and the crew vehicle into one system. It is much more complicated to design though. We don’t want something as heavy as the Space Shuttle, and missions likely won’t need as much cross range anyway.

If a large portion of the flights are tanker flights, one might also not need a separate payload stage at all. Fit the second stage with RCS systems etc and transfer the propellant directly from its tanks. This could save costs a lot. The propellant depot would have most of the complexity, including the robot arm etc as it’s not being thrown away on every flight.

BFR – what do they need it for?

Elon Musk’s BFR plan is for about a 200 ton payload to low earth orbit, with 30 larger LOX-methane Raptor engines in the first stage. He plans to launch three, with two being refueling launches, so the Mars stack will be 600 tons upon leaving Earth orbit.

With Falcon 9 rockets and 10 t per flight, one would need 60 flights for a similar mass – surely hard to reach reliably and with a very long schedule – with last week’s technology!
But now, if the rocket can really be made to work reliably and simply in a Refuel And Go Again fashion, it seems feasible.
If, with some development, a single Falcon 9R flies once per week on average, it can place 500 tons per year to orbit, at relatively little cost. A fleet of twelve rockets might do it in a month! On the side, they would also have a myriad of other uses, revolutionizing spacefaring!

Also, if we can routinely get to Earth orbit relatively cheaply, we can start developing asteroid exploitation technology a lot sooner. Asteroids are the easiest source of materials in space since the delta vee and peak thrust needed to get to them and from them to basically anywhere in space is the lowest. I consider the small moons of Mars pretty much equivalent to asteroids in some senses too.
If you don’t need high peak thrust, you can do everything with high efficiency in space propulsion, and not rockets. Think ion engines or electrostatic sails or what ever. The only downside is the long flight time, but if the raw material hauling is done with robots anyway, I don’t see a problem with that. We just have to plan ahead. Sorry, Space Truckers!
Now, my vision is this:
– Falcon 9R and equivalents flying to low earth orbit frequently with little cost per flight, and
– propellants and raw materials brought from asteroids to Earth or Mars orbit or to the various Lagrange points, or even to cycling orbits (between Earth and Mars for example) with slow unmanned vehicles with high efficiency electric propulsion

With these you got yourself suddenly a potential for actually bringing humans to Mars in a relatively sustainable way.

So, Elon, please don’t build the BFR unless you’re sure it’s absolutely needed.

This entry was posted in Architecture, Depot, Design, engines, industry, Launchers, Lunar, RLV:s, Spacecraft, SpaceX, Transportation. Bookmark the permalink.

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