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SpaceX nails triple booster landing after satellite delivery

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Re: SpaceX nails triple booster landing after satellite delivery

#101

Post by gnode »

ravedave5 wrote: post #94
gnode wrote: post #47

Earlier quoted context omitted.

It doesn't necessarily make it harder. There's a burn to slow the booster down for re-entry, and having the side boosters do a lot of the work means more fuel / delta-v can be saved to slow the core booster. The FH is apparently capable of 8,000kg in a reusable GTO launch ( https://en.wikipedia.org/wiki/Falcon_Heavy#Capabilities ), and this satellite was only 6,000kg. So it looks like there would be plenty of fuel av…

It's the same steps but it is harder, the center booster was going faster than any other core that has been recovered. The recovery itself was ~300 miles further out than any other recovery. Swinging a bat at a 10mph ball is the same technology as swinging at a 90mph one. I don't think anyone would say that they were equally as easy.

My point is that it's less a question of technical difficulty / tolerance, but more fuel / delta-v / mass cost.

In the case of a bat swing, to bat the ball faster, your muscles need to be stronger, and the ball and bat need to withstand greater pressures. In the case of a vehicle travelling through space / thin atmosphere, it only needs more fuel to burn to slow it down. Analogously, you don't parallel park a car from 70mph, having travelled somewhere on a highway.

Here's a graph a booster's speed over time, showing the reentry burn: https://i.stack.imgur.com/xFYIh.png ( from https://space.stackexchange.com/questions/20246/what-is-this... )

Re: SpaceX nails triple booster landing after satellite delivery

#103

Post by theoh »

chasd00 wrote: post #95
CarVac wrote: post #70

Earlier quoted context omitted.

I read a paper on this—it's convex because any optimal trajectory will have the engines at full throttle whenever they're on, so they just fill up the parameter space, confident that illegal values will never be required.

can you link to the paper please?

I don't know which paper they mean, but here's a relevant paragraph from one of the papers available from Blackmore's page:

"In this paper, we unify the convex optimization approaches of [1], [2], [17] and extend them to handle thrust pointing constraints. While convexifying the problem with nonconvex thrust pointing constraints, we develop a geometrical insight into the problem that establishes a connection with “normal systems” [18]. A normal linear system is defined in the context of optimal control theory where the system is said to be normal with respect a set of feasible controls if it maximizes the Hamiltonian at a unique point of the set of feasible controls. In the case when the set of feasible controls is convex, a system being normal implies that the Hamiltonian is maximized at an extreme point of the set [18]. Our convexification result has a similar geometric interpretation since it establishes lossless convexification by ensuring that the Hamiltonian is maximized at the extreme points of a projection of the relaxed set of feasible controls. This set is then shown to be contained in the original nonconvex set of feasible controls, thereby estab- lishing that we can obtain optimal solutions of the original nonconvex problem via solving its convex relaxation."

Re: SpaceX nails triple booster landing after satellite delivery

#104

Post by ecpottinger »

bloopernova wrote: post #64
inflatableDodo wrote: post #20

Earlier quoted context omitted.

I'll swap the house numbers with next door. They'll never find it.

I know this is increasingly off-topic for hn, but the mental image of being woken up by loud booster noises, then seeing a huge booster sitting in your now-ruined garden is hilarious to me. We certainly do live in the future.

In the anime "Rocket Girls" they landed in the school's swimming pool.

Re: SpaceX nails triple booster landing after satellite delivery

#105

Post by inflatableDodo »

narrator wrote: post #46

Can we finally stop having sci-fi films in which the whole outcome of the movie is solely determined on some heroic manual flying of a spaceship while simultaneously using manually aimed weapons like it's World War II?

Maybe look closely at the landing on the Hudson river. A good sci-fi plotline for getting out of hairy situations is heroic manual flying that is only made possible due to the automated systems.

Re: SpaceX nails triple booster landing after satellite delivery

#106

Post by goshx »

ambicapter wrote: post #90
goshx wrote: post #67

I was at Kennedy Space Center's Apollo/Saturn V viewing site for this launch and it was amazing. If you ever have the opportunity to be there for a Falcon Heavy launch, do yourself a favor and go. It's quite an experience and totally worth the money.

Yeah, if you have a week of free time. I planned to go this weekend but chickened out at the last second-turned out in my favor since they launched yesterday, four days after the original date.

Yes, there may be delays or they may postpone the launch. I went on Wednesday and decided to stay one more day for yesterday's attempt and I am so glad I did. It was worth it.

Re: SpaceX nails triple booster landing after satellite delivery

#107

Post by misterprime »

mhandley wrote: post #68

Nice video capturing the sonic booms from the booster landings here: https://twitter.com/jefffwilliams/status/1116486329284595717

Yep, shared that with the office and family. That's amazing. It really does feel like the future.

Re: SpaceX nails triple booster landing after satellite delivery

#108

Post by Sniffnoy »

criley2 wrote: post #81
rinchik wrote: post #78

Earlier quoted context omitted.

Same link but this one doesn't report your click to google: https://www.teslarati.com/spacex-falcon-heavy-fairing-recove...

I see multiple requests to ampproject on the official page, so Google is getting data regardless.

So, now without amp, too: https://www.teslarati.com/spacex-falcon-heavy-fairing-recove...

Re: SpaceX nails triple booster landing after satellite delivery

#109

Post by DennisP »

grey-area wrote: post #91
JshWright wrote: post #69

Earlier quoted context omitted.

You'd be hard pressed to fit 32 tons inside Falcon Heavy's fairing. It's far more likely to be volume constrained than mass constrained when flying to LEO.

That could bring satellite costs down a lot though - if launches are cheap and not weight limited a cheap steel frame satellite with heavy solar panels becomes feasible - all the old rules about building to optimise weight and not price go out the window. I wouldn’t be surprised if spacex also enter the satellite building business after mass producing starlink.

And that makes solar power satellites more feasible, especially with the BFR.

Musk has expressed skepticism, famously asking "what's the conversion rate?" The answer is that microwave transmission is 40% efficient with today's technology. This isn't bad considering that average daily sunlight in geosynch is five times higher than on the ground,[1] and you don't need much storage or backup.

The early SPS designs were hugely expensive monolithic beasts, but current designs use lots of identical parts (of several varieties) that self-assemble in orbit, so you get economies of scale with factory production.

A year ago I read the book The Case for Space Solar Power [2], which broke down the costs in detail. With pre-SpaceX launch costs they got 15 cents/kWh, including manufacturing and ground stations. I plugged in the BFR cost Musk was claiming (I think I used $50/lb) and got about 4 cents/kWh.

[1] https://en.wikipedia.org/wiki/Solar_irradiance#Irradiance_on...

[2] https://www.amazon.com/Case-Space-Solar-Power-ebook/dp/B00HN...

Re: SpaceX nails triple booster landing after satellite delivery

#110

Post by Florin_Andrei »

chucksmash wrote: post #99
narrator wrote: post #46

Can we finally stop having sci-fi films in which the whole outcome of the movie is solely determined on some heroic manual flying of a spaceship while simultaneously using manually aimed weapons like it's World War II?

Seems like it'd be tricky to do from a story telling perspective. Totally removes all agency from protagonists. Every fight becomes a deus ex machina - "welp, our targetting subroutines continue to be superior to their maneuvering systems so they died. Hooray us?" Or I guess more probably just a numbers game: "welp, our effective weapons range is larger than theirs, so that's that" with an MCRN exemption clause.

> Every fight becomes a deus ex machina

Sounds like a book by Iain M. Banks.

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