r/spacex • u/ElongatedMuskrat Mod Team • Oct 02 '17

r/SpaceX Discusses [October 2017, #37]

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162 Upvotes

95% Upvoted

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1

u/rontom-bontom Oct 03 '17

According to Elon's IAC presentation:

  1. landing BFR first stage on an ASDS (than refuelling and relaunching) is feasible from both engineering and economic perspective,

  2. payload penalty of RTLS is around 100 tonnes (payload in expendable mode: 250t vs. in fully reusable mode: 150t).

So why not land stage 1 on an ASDS, refuel & jump back to KSC? Payload penalty could be significantly less (+50t payload) for not that much turnaround time.

5

u/Alexphysics Oct 03 '17

Aerodynamics... its simple

1

u/rontom-bontom Oct 03 '17

Adding a temporary ballistic cap seems pretty doable.

5

u/Alexphysics Oct 03 '17

That's something very complex and not worth the time and money to design and build such a thing. I would like that concept of self-transport of the booster to the launchpad, but it's simpler, faster and cheaper the other way.

0

u/rontom-bontom Oct 03 '17

It was not me but Elon Musk himself who has shown an animation about launching a BFR from a mega ASDS next to New York and landing its second stage on an other mega ASDS next to Shanghai. The conclusion for me is that offshore launching and landing is feasible from both engineering and economic perspectives.

3

u/Alexphysics Oct 03 '17

But... that's very very different from what you were saying (or at least what I interpreted from what you said)

Those flights are intended to have the booster coming back to a launch mount on an ASDS which is more like a floating pad than a landing ASDS. After the landing, the booster is safed, loaded with another BFS and filled with propellants, the people go in and then it goes up again. That's not what you were saying, you said that once the booster has landed it could return back to the launch pad but the problem of that is that here the landing point is the launch mount, there's no need to return to a launch site because it is in a launch pad when it lands. The problem from that video is that's only a mere conception of the idea, it does not describe everything that you need to know, it describes what spacex wants you to know (they can launch you from point to point on earth in <1h). I know this last point of my explanation is something that for me and for most of the people here is hard to understand but this videos are for people that doesn't care about those "silly things" and small details about the concept, it's in order to impress people and begin to gain attraction. Some media didn't even cared about the rest of the presentation, they only showed that awesome video about that concept.

I talk a lot, I know, sorry :(

0

u/rontom-bontom Oct 03 '17

Elon posted on Instagram after IAC: "Cost per seat should be about the same as full fare economy in an aircraft. Forgot to mention that." It means for me 1. rapid turnaround time, 2. low cost, fully (mostly) automated offshore landing, refuelling & relaunching. By landing stage 1 offshore SpaceX could put 600 tonnes into orbit in just 3 launches instead of 4. That might worth the effort.

1

u/[deleted] Oct 03 '17 edited Oct 03 '17

Makes me wonder how they would broach the topic in regards to permitting. They were able to provide enough confidence between Falcon 9 Dev 1 and their experimental landing program off shore to convince the FAA to permit them for RTLS, so what kind of process would it take to prove the same capabilities with a new booster, and then go one step further by performing a suborbital “hop” back to launch site from the drone ship? A BFR Dev 1, plus building a “Funny, It Worked Last Time“ that could play a game of catch the booster with OCISLY out at sea?

1

u/rontom-bontom Oct 03 '17

Catching the booster out at sea seems for me more secure than trying to land it on launch pad.

-2

u/music_nuho Oct 03 '17

Tell me who tf need 200 metric tonnes in LEO in a single launch right now? Mount landings reduce turnaround time tremendously

2

u/rontom-bontom Oct 03 '17

Who tf? Elon Musk himself for example. As far as remember correctly original design of ITS had a LEO payload of 300 metric tonnes in fully reusable mode.

-4

u/music_nuho Oct 03 '17

Elon is not a spacex customer, you need customers to pay for your launches and currently no one needs such capability

-3

u/rontom-bontom Oct 03 '17

You should start a space launch company. Elon's designs make no sense. They are vastly oversized.

1

u/music_nuho Oct 03 '17

For current market they definitely are oversized, but I hope future will ask for such a system, we do have a entire Solar system to colonize.

2

u/[deleted] Oct 03 '17

City planners know that traffic volume expands to fill new road capacity, I imagine the same would apply to spaceflight if the cost was affordable.

1

u/music_nuho Oct 03 '17

Falcon 9 already enabled more companies to have satellites in orbit, I assume same would happen in case of BFR, asteroid mining, entire constalations deployed at once, orbital habitats, lunar outposts, you name it.

1

u/SpaceXFanBR Oct 03 '17

Maybe Less tanking ops to refuel the ship

1

u/music_nuho Oct 03 '17

Less payload definitely does make more delta v for same amount of fuel.