Very cool that in the same IAmA Musk answers deeply complex questions as chief rocket engineer and, then, answering a side question offers up a potential low level architecture for how to make an internet feed work from earth to mars.
It would be interesting to know what the max capacity is for the human brain to store these kind of multi disciplinary low level details.
The internet response is very vague and not particularly insightful to anyone who has worked on any internet protocol. It's not evidence he's an interdisciplinary mastermind. (It's not evidence he isn't, either.)
> Elon: But, yes, it would make sense to strip the headers out and do a UDP-style feed with extreme compression and a CRC check to confirm the packet is good, then do a batch resend of the CRC-failed packets. Something like that. Earth to Mars is over 22 light-minutes at max distance.
It's meant for people who like rockets, not internet protocols. They're smart enough to look up terms, but inexperienced. I love that he dumbs down terms where needed but goes into detail where he thinks people can understand them.
Could you tell me whether he's suggesting to send a batch of data packets, then wait a 44-minute turn-around time to hear back from Earth which ones failed so the failed ones can be resent? This is almost certainly not the best way to do this, from an info-theory perspective, right? Wouldn't you put the entire batch of data in an error-correctable code that you could ensure had very high likelihood of being fully recovered on Earth? Send-check-failure-resend works when you have a fast but intermittently congested network on Earth, but it seem silly for a connection with such extreme latency.
Forward Error Correction involves sending extra data in the initial transmission so that most errors can be corrected without needing a resend. It sounds like that's what you were attempting to describe in your comment.
Thanks! If FED is standard for deep space and Musk know this (both reasonable), do you have any idea what he might have meant by "then do a batch resend of the CRC-failed packets"? Is it just that guaranteeing zero packet losses has a large overhead (surprising to me), so that the optimal FED protocol in deep space does in fact include a bit of resending?
There is a thing called delay tolerant networking, which is specialized in building interplanetary communication. Vint Cerf is one of the people who initiated that research. Though it fades away quickly now no one cares much about this DTN thing.
I was giving additional examples of the same concept (tolerating long delays) in a different domain (inside a datacenter). You are correct that I was not referring to Vint Cerf's work.
Sorry to be cynical, but perhaps he had some help? He works very hard at PR and at his image, and in the past it has been very well planned and executed.
/r/spaceX lists it as "December", and they cite some SpaceX report (more recent than Musk's July tweet) saying that Falcon Heavy is targeted for "no earlier than the end of 2017".
While that it is true it hides what is going on. Falcon Heavy was delayed because they managed to massively improve F9 and many of the Falcon Heavy contracts are actually now flown on the F9. The last couple flights that did not land were all FH contracts.
So the Falcon Heavy we are gone get now is way, way more powerful and all 3 boosters will land and be reusable. The side boosters are actually reused F9 boosters.
But better late than never.
I am much happier to see a Falcon Heavy launch and not explode on the pad than one do. Not that the existing one won't, Elon has said it himself that it would be a miracle for the thing to make it to orbit.
I’m afraid not. The SpaceX ISRU plan is to extract water from ice and electrolytically split it into hydrogen and oxygen. The hydrogen is combined with CO2 from the Martian atmosphere to produce Methane fuel, while the oxygen is chilled for use in the rockets as well.
On the moon you have water (ice), but no carbon dioxide. You can split the water into hydrogen and oxygen to use as fuel, but the BFR requires methane fuel.
Why use methane? It has a lower ISP than hydrogen but higher energy density, to simplify somewhat, and is easier (possible even) to store on long flights.
The oxygen is there for hydrogen/oxygen engines (and that's most of the weight.) However, Elon's decision to go with methane undercuts this a lot since the ratios you need carbon (a relatively heavy molecule that's scarce on the moon) as well.
Carbon is just one one-thousand of the weight of that regolith, not something you'd want to try anytime soon; certainly switching to hydrogen as the fuel (with oxygen) would be easier.
Well, if the moderators are enforcing "on-topic" questions in an Ask Me Anything, then it seems reddit's transformation into a marketing and brand promotion platform seems complete.
I don't feel that at all. If Musk is having an AMA on a topic, like the BFR, I feel that is better than an open ended AMA, since the signal to noise ratio will be better and I can go there to read about exactly the topic I'm interested in. I'm not particularly interested, for example, in questions about Musk's divorce or dating habits.
Perhaps they need to change the name of these on-topic AMAs, but Musk isn't selling BFR rockets to consumers, generally geeks are interested in SpaceX from a hobby interest point of view, and so the idea of marketing and brand promotion seems a little divorced from reality.
SpaceX isn't going to increase their launch contracts by entertaining AMA questions. My guess is, Musk likes engaging people and talking about the cool shit he's working on.
I think this has less to do about signal to noise and more to do with crowd control.
BFR as a project is out of touch with the current affairs at Tesla and SpaceX which means that there is basically no negative sentiment that can be generated from asking questions about the topic or their answers.
A general AMA however will likely touch about things like the failure to support Autopilot 2.0 hardware on schedule, Model 3 delivery delays, Falcon Heavy delays, and those are just the light stuff.
One does have to wonder why is there an AMA on the only detached and "universally rosie" subject just as Tesla announced layoffs.
While I don't think it was planned, I do have a strong suspicion that the AMA was intentionally focused and the mods were asked to enforce question rules (and looks like more strictly than usual even based on previous Musk AMAs).
How does it make the slightest bit of sense that an AMA on a space forum would be intended as a deflection from firings at a totally different company in a different field? A bunch of space enthusiasts asking about Mars isn’t going to change public perception of Tesla in the slightest. Not everything is a vast PR conspiracy.
You say you have a strong suspicion that it was intentionally focused. Did the fact that it says “about BFR” in the title give it away? Of course it’s focused.
> AMA was intentionally focused and the mods were asked to enforce question rules
I don't think the mods had to be even asked to do it. The AMA was posted in /r/space, and widely advertised in /r/spacex. There was a group effort to get technical BFR questions upvoted from /r/spacex members.
I would guess that even without any outside influence, the mods and most voters did not care about Tesla questions - Tesla only matters to the extent of "does it help finance Mars plans" for them.
Tesla is the #1 automobile brand in owner satisfaction and you think it's important to ask Elon about Autopilot 2.0 software being late in an AMA, which has a limited number of questions.
Gotcha.
Even if the AMA was about Tesla, that probably wouldn't make the list.
The original purist concept yes, absolutely, but a lot of people actually prefer it this way. The world is big enough for both approaches to exist as they offer different things.
Finally, what is wrong with honest informative advertising content on things people to want to know about? Is such a thing inherently bad? If so why?
Many companies used to regularly RIF their bottom 1-2%, but I'm not sure why Tesla's firings has anything to do with r/spacex.
When an AMA is held on Tesla, then I might be interested in that, but I'm interested in more technical details of upcoming SpaceX rockets.
If NASA had an AMA about the Space Shuttle, do you want the thread polluted with questions about NASA's opinion on the F-35? Or on Obamacare? Is NASA "advertising"?
Musk frequently engages people on Twitter. He's obviously a tech-nerd, and loves talking about rockets and mars, it's an obsession. No one would bet their money on an uneconomical plan to colonize Mars. He literally cried on 60 minutes when confronted with Aldrin's support of ULA.
It's a pretty cheap shop to chalk this up to some advertising campaign, rather than personal ego.
No one would bet their money on an uneconomical plan to colonize Mars. He literally cried on 60 minutes when confronted with Aldrin's support of ULA.
He hasnt, he’s betting money on rockets which are useful for highly lucrative activities, while talking aboutna currently far fetched vision of Martian colonization. Apparently though all it takes to disable the critical thinking of many is wanting to believe, and in your case, tears.
The Space industry isn't very profitable unless you get Cost+ government contracts. The margins are terrible. SpaceX's profit margins are either negative, zero, or razor thin.
If Musk wanted high ROI, he wouldn't have bet on SpaceX. He's obviously doing it not because it's easy money, but because he's interested in space as a hobby.
The first think he tried to do with his PayPal money was to buy an ICBM to fly a greenhouse to Mars. Does that sound like something that's a good investment?
I don't think you're convincing very many people that Musk is doing this for advertising purposes. What's next, Musk gives a space talk to middle school students, and you accuse him of trying to recruit cheap future employees?
Yesm yes, you are so smart and all us sheep who don't understand anything.
If you knew even the first thing about the Space industry you would know that these sorts of rockets are super high risk and even now the demand for such rockets is highly questioned even should they manage to build it.
There are really not so many "highly lucrative activities" even if they manage to achieve technical breakthroughs on rocket designed. Also, the rocket and space ship very clearly are designed around Mars, every design choice is informed by that.
If he had wanted to make the most possible profitable rocket to do 'highly lucrative activities' he would have build a different rocket.
Are you proposing that this AMA about SpaceX’s Mars plans is intended as a distraction from some firings at Tesla? That seems rather far fetched and doesn’t really make sense anyway.
Definitely a provocative comment that might not be correct but I don't think it deserved to be down-voted. Just because he's Elon doesn't mean he doesn't play his own manipulation games
It’s been like that for years. IAmA is mostly a PR vehicle for celebrities and they don’t try to hide it. At least this one is fairly sincere and engaging. Look up Woody Harrelson’s attempt to see how badly and hilariously it can go wrong.
> if the moderators are enforcing "on-topic" questions in an Ask Me Anything
Every subreddit has its own moderators, and they set the rules for content in that subreddit. Reddit generally never interferes with the content or moderation of a subreddit, unless it gets into illegal or "bad publicity in national media" territory.
Elon decided to host the AMA in /r/space, so the space enthusiast moderators there get to decide how to run it. If they decide that they want to see Elon answer space questions, and banning Tesla questions helps with that, then it's their subreddit and their choice.
It would be interesting to know what the max capacity is for the human brain to store these kind of multi disciplinary low level details.