Elon Musk Reddit AMA

[Dkmdlb]

There's lots of good SpaceX info in this Ask Me Anything. I'll post some of the best comments here and let you enjoy discovering some of the other good stuff.

1 -

Yes, the Falcon Heavy center core is seriously hauling a** at stage separation. We can bring it back to the launch site, but the boost back penalty is significant. If we also have to the plane change for geo missions from Cape inclination (28.5 deg) to equatorial, then a downrange platform landing is needed. The Mars transport system will be a completely new architecture. Am hoping to present that towards the end of this year. Good thing we didn't do it sooner, as we have learned a huge amount from Falcon and Dragon. Our spacesuit design is finally coming together and will also be unveiled later this year. We are putting a lot of effort into design esthetics, not just utility. It needs to both look like a 21st century spacesuit and work well. Really difficult to achieve both.

2 -

Goal is 100 metric tons of useful payload to the surface of Mars. This obviously requires a very big spaceship and booster system.

3 - (in answer to a question about how the Falcon first stage will be secured to the barge)

Mostly gravity. The center of gravity is pretty low for the booster, as all the engines and residual propellant is at the bottom.

We are going to weld steel shoes over the landing feet as a precautionary measure.

Link:

http://www.reddit.com/r/IAmA/comments/2rgsan/i_am_elon_musk_ceocto_of_a_rocket_company_ama/

[Bill Phil]

Why care about Aesthetics? it needs to work!!! And well!!! Aesthetics can add unneeded mass.

[Dkmdlb]

Also - some good talk on getting to Mars:

At first, I was thinking we would just scale up Falcon Heavy, but it looks like it probably makes more sense just to have a single monster boost stage.

[dharak1]

100 tons to Mars? This rocket is going to be gigantic. Not just "big" but insanely massive. The Saturn V was 120 tons to just LEO and it weighed in at nearly 3 million tons. A moderate estimate would put this super rocket at over 4 million tons! How would the launch pad even support that and what would that sound like at launch?

[Ziff]

Elon apparently thinks Kerbal Space Program is awesome.

http://www.reddit.com/r/IAmA/comments/2rgsan/i_am_elon_musk_ceocto_of_a_rocket_company_ama/cnfqmsl

[RainDreamer]

Why care about Aesthetics? it needs to work!!! And well!!! Aesthetics can add unneeded mass.

Or stripped away needed mass like shielding...

But I think maybe, because they are a private company, image is important. So that in the eventual competition over space suit market, they got aesthetics as one of their selling point. Kind of like Apple. But that is just me talking. Should ask him that next AMA.

Elon apparently thinks Kerbal Space Program is awesome.

http://www.reddit.com/r/IAmA/comments/2rgsan/i_am_elon_musk_ceocto_of_a_rocket_company_ama/cnfqmsl

http://www.reddit.com/r/IAmA/comments/2rgsan/i_am_elon_musk_ceocto_of_a_rocket_company_ama/cnfr2kl

Funny how on an article on NBC news, the reporter called KSP a simulation software and that Space X is actually using KSP as testing software. I don't think that was serious...was it?

Edited January 6, 2015 by RainDreamer

[Scotius]

100 tons to Mars? This rocket is going to be gigantic. Not just "big" but insanely massive. The Saturn V was 120 tons to just LEO and it weighed in at nearly 3 million tons. A moderate estimate would put this super rocket at over 4 million tons! How would the launch pad even support that and what would that sound like at launch?

Where did you found 3 million tons figure? It was 3 thousands. Still massive, but very doable. And a proof that EVERYTHING will fly, if you add enough boosters

[Cirocco]

100 tons to Mars? This rocket is going to be gigantic. Not just "big" but insanely massive. The Saturn V was 120 tons to just LEO and it weighed in at nearly 3 million tons. A moderate estimate would put this super rocket at over 4 million tons! How would the launch pad even support that and what would that sound like at launch?

3 million kilograms, 3000 tons I believe. Also, to answer your "how" question: I believe the current plan for the mars transfer vehicle includes a few seperate launches and a nuclear engine transfer stage. Solid core if I'm not mistaken.

[dharak1]

Oh yeah sorry. 3 million kilos. Still a huge amount of mass. I was under the impression he meant one launch to get 100 tons to Mars. Must've misunderstood it.

[LordFerret]

One would think at this point that a single 'huge' rocket for such a trip isn't the ticket... if they put any real thought into it, just as many do here in KSP, several launches and dock/build in orbit and then head out.

[Albert VDS]

^Yes, but in KSP we only pay for the rocket and fuel.

[Scotius]

At some point reuseable transfer stage will probably become a necessity. Time will tell if it'll be propelled by nuclear engine(s), VASIMR or something more exotic, like a fusion pulse drive.

[Streetwind]

Reddit estimated that a launcher capable of delivering a 100 ton payload to Mars surface would weigh in the neighborhood of 8000 to 10000 metric tons... or, in other words, slightly heavier than the Eiffel Tower.

I'm not entirely sold that SpaceX will go that route. Such a vehicle would be insane, and while SpaceX has done a lot of crazy stuff, this rocket would lack a purpose outside of Mars transfers, which only happen once every 2-3 years. That's just not cost effective.

[Camacha]

I'm not entirely sold that SpaceX will go that route. Such a vehicle would be insane, and while SpaceX has done a lot of crazy stuff, this rocket would lack a purpose outside of Mars transfers, which only happen once every 2-3 years. That's just not cost effective.

Can I see a calculation that goes along with that claim?

[SeaDog]

One would think at this point that a single 'huge' rocket for such a trip isn't the ticket... if they put any real thought into it, just as many do here in KSP, several launches and dock/build in orbit and then head out.

Well, KSP makes that seem a lot simpler than it actually is. I could possibly see them bringing the stage for interplanetary transfer seperately, but as for the habitable module, it's problably simpler to build a huge friggin rocket than it is to assemble it in orbit. Besides, with the reusability they're planning, they will have to build very large rockets for moderately sized launches anyway. They can then cancel the reusability for this particular launch, and that might easily be cheaper than orbital assembly.

Reddit estimated that a launcher capable of delivering a 100 ton payload to Mars surface would weigh in the neighborhood of 8000 to 10000 metric tons... or, in other words, slightly heavier than the Eiffel Tower.

I'm not entirely sold that SpaceX will go that route. Such a vehicle would be insane, and while SpaceX has done a lot of crazy stuff, this rocket would lack a purpose outside of Mars transfers, which only happen once every 2-3 years. That's just not cost effective.

No, those calculations must be off. I think they're missing some aerobreaking or assuming full reusability will be used for that particular launch, which I don't think is the case. That's the catch here, a launch vehicle capable of sending 100 tons to mars surface would, when full reusability is used, be able to do smaller missions, such as probes to outer planet moons or large space telescopes. I even think a system like that could turn out cost effective for communications satellites to GEO. They are generally growing simply because one big satellite is cheaper to maintain than several small ones, and you can send several per launch.

[AngelLestat]

Goal is 100 metric tons of useful payload to the surface of Mars. This obviously requires a very big spaceship and booster system.

Lol, this mean at least 150 tons to mars. Which it means close to 250 tons to LEO?

I dont understand why we can not just sent small stuffs and dock in orbit.

But never mind.. This guy thinks in big. He will control the space industry in no time.

[Linear]

Why care about Aesthetics? it needs to work!!! And well!!! Aesthetics can add unneeded mass.

They're a company with a brand..?

[Thiel]

Lol, this mean at least 150 tons to mars. Which it means close to 250 tons to LEO?

I dont understand why we can not just sent small stuffs and dock in orbit.

But never mind.. This guy thinks in big. He will control the space industry in no time.

Because it's very hard to do in a structurally sound manner. It took years to construct the ISS and it doesn't have to deal with any sort of heavy acceleration.

[AngelLestat]

I know that there is some assembling and structure difficulties.

But real docking ports are not like KSP, they are strong, and you can make them bigger.

There is not point to sent to orbit different stages in one constructed block.

Of course that a mars ship has a lot on developing cost which makes the launch cost not so important.

But the cost to develope a launch vehicle 2 times bigger than the new SLS.. seems not needed.

[Nibb31]

I know that there is some assembling and structure difficulties.

But real docking ports are not like KSP, they are strong, and you can make them bigger.

Not really. Docking ports have mechanical specifications and limits. And designing a new system is a very long process. Just look at how convoluted the LiDS/NDS/IDA development has been. It started in 1996 with several redesigns and a lot of money spent. You don't just "make them bigger".

[SargeRho]

I know that there is some assembling and structure difficulties.

But real docking ports are not like KSP, they are strong, and you can make them bigger.

That's why ships that are going to dock approach eachother at snail speed. I think KSP's ports are actually *stronger* than real ones.

[Dkmdlb]

Just some rough numbers here. Using the Saturn V as a template, we can make an estimate of the size of the rocket that will send SpaceX to Mars because we know that they plan on using 9 Raptor engines in the first stage, and we know the thrust they anticipate they will get out of the Raptor. Also, let's assume they use a single core instead of 3 identical cores Falcon heavy style.

According to wikipedia, the Saturn V weighed 2,970,000 kg at launch, and the F-1 engines (of which there were 5 on the first stage) could generate 7,740,000 newtons of thrust.

The launch TWR of the Saturn V was 1.3ish.

5 x 7,740,000 newtons / 2,970,000kg / 9.8 m/s^2 = 1.3

Let's see what SpaceX could do with 9 raptor engines producing a launch TWR of 1.3

9 x 8,200,000 newtons / mass of rocket / 9.8 m/s^2 = 1.3

9 x 8,200,000 newtons / 9.8 m/s^2 = 1.3 x mass of rocket

9 x 8,200,000 newtons / 9.8 m/s^2 / 1.3 = mass of rocket

And we get 5,790,000 kg, which is 6,385 tons, for the launch mass. That's in line with what everybody is saying.

Edited January 7, 2015 by Dkmdlb
math is hard

[Elthy]

No idea where you got those data for the Raptor, but in this AMA Musk said this:

Thrust to weight is optimizing for a surprisingly low thrust level, even when accounting for the added mass of plumbing and structure for many engines. Looks like a little over 230 metric tons (~500 klbf) of thrust per engine, but we will have a lot of them

[Dkmdlb]

No idea where you got those data for the Raptor

Wikipedia. Serves me right I guess.

[AngelLestat]

Not really. Docking ports have mechanical specifications and limits. And designing a new system is a very long process. Just look at how convoluted the LiDS/NDS/IDA development has been. It started in 1996 with several redesigns and a lot of money spent. You don't just "make them bigger".

That's why ships that are going to dock approach eachother at snail speed. I think KSP's ports are actually *stronger* than real ones.

Yeah, I acknowledge that a normal docking port for those mass would not be easy to develop.

But people does not need to cross them, we only need stage separators which act as docking port.

Also a docking port may be difficult to develop, but then how much difficult and costly would be to develope and launch a new super heavy rocket?

About KSP docking ports, they may be stronger to brake, but the minimun force and they bend.

Edited January 7, 2015 by AngelLestat