The landing is all based on how much fuel is left after the primary mission is complete: some missions require more fuel to get to their destination orbits, others require less.
This launch was an ISS resupply, which is on the low end of fuel requirements. So the first stage can get all the way back to its launch site.
Other launches are in the middle of the fuel range: they just follow their ballistic path to the barge, and do not have the extra fuel to get turned all the way back around for a return to the launch site.
A few launches are at the very high end: the upcoming Echostar mission has such a high fuel requirement that SpaceX isn't even attempting a landing: they're just dumping the whole stage into the ocean like we've been doing for 60 years.
SpaceX is saying that this upcoming Echostar launch will be their last "expendable launch", ever.
> A few launches are at the very high end: the upcoming Echostar mission has such a high fuel requirement that SpaceX isn't even attempting a landing: they're just dumping the whole stage into the ocean like we've been doing for 60 years... SpaceX is saying that this upcoming Echostar launch will be their last "expendable launch", ever.
Can I infer that they won't be doing launches that require high-end fuel usage? Are they just giving up on those types of use cases, or do they have another solution for those moving forward?
The future plan for SpaceX is to use Falcon Heavy for heavier payloads. When they sold the launch to Echostar I'm not so sure that they knew exactly where the booster-recovery line was for F9 FT. F9 block 5 is expected to be able to launch a bit more with booster recovery.
Something to keep in mind is that for space exploration, all that really matters is achieving low earth orbit (LEO). After that, ion engines/solar sails/space tethers, all manner or propulsion can get us out to further reaches. But it takes dedicated engineering to build craft powerful enough to get through the atmosphere with only a small fraction of mass going to engine and airframe.
The cost of fuel is generally pretty negligible compared to the cost of spacecraft. Even 1,000,000 pounds of kerosene only costs about $500,000 ($3 per gallon at 7 pounds per gallon). I'm having trouble finding current prices on liquid oxygen but it looks like about 15 cents per pound, so a 2.56:1 ox:fuel ratio gives $384,000 for 2,560,000 pounds of oxygen. (500,000 + 384,000)/(1,000,000 + 2,560,000) = 25 cents per pound of fuel+oxidizer (honestly I have to saw wow here, as this is much lower than I expected). If a shuttle launch cost $1 billion, less than $1 million went to fuel at 2017 prices (assuming that more expensive liquid hydrogen and less expensive booster solid fuel roughly match the cost of ox-kerosene). Another way of saying this is that the design tradeoffs of the shuttle cost 100 to 1000 times more than other designs might have (mainly due to reusing the orbiter rather than the first stages). A lot of people knew this in the late 70s and warned about it, but due to political reasons NASA went with the more expensive shuttle system and now here we are.
My guess is that from here on, SpaceX will do incremental launches, using a rocket to carry a stage to LEO and then assemble those stages in orbit into new rockets to go further out, landing the first stages to reuse them. This is scalable all the way out to Mars and further, which is pretty remarkable and obvious in hindsight. It wasn't until I considered how one would land a stage on Mars with such a thin atmosphere that I realized why SpaceX has been so committed to retrorocket landing.
Yes! I saw it at the 36 minute mark on the video. That had me curious. I think it was a trick of perspective, it first looked like some huge chunk of debris that the first stage flew past, but after watching it again, it looks like a little chunk of ice that got blown off of by the cold gas thrusters.
Yes! Wait are you talking about the second stage that was in the right/second monitor? I am.
I thought it was weird that the two pieces stayed with the second stage for at least a second or two, which was literally ~five+ kilometers. Perhaps there was an eddy created by the movement of the rocket or some weird space/vacuum effect I'm not well-versed in?
The second stage debris that you are talking about showed up when the stage stopped accelerating. The debris and stage were moving at the same speed, so it's normal that they drifted apart relatively slowly.
If you look back at old launch videos, you can often see big chunks of ice form by the second stage engine vents during coast, only to be blown off by the vibration as the engine is restarted. I assume this is something similar.
I didn't! I was irritated that I couldn't see anything, so then had a quick scoot to see if the NASA feed would show the on-board view (unlikely!) before coming back again to miss the first stage separation!
The landing through the clouds, on the other hand, I did appreciate. Once my irritation has subsided, anyway!
I recommend watching the Hosted Webcast on one device and the Technical Webcast on another. Either mute the Technical Webcast or have it on lower volume. They're both easily found on YouTube under SpaceX.
I did this for the previous launch, Iridium-1, and was treated to unbroken views live from the first stage on the technical stream, while the hosts narrated and switched views more frequently on their stream.
This is only the second time they've had live video all the way down. Getting that much data back from the thing must be tough. They've been making steady improvements, though, and it's now paying off delightfully.
Rendezvous isn't scheduled until the 22nd, so there will likely still be quite a distance between the ISS and Dragon tomorrow. They will be in trail, while the Earth rotates, so depending on where the ISS passes relative to you there's a possibility the Earth might have rotated enough by the time Dragon comes around to not see it. It's definitely worth keeping a look out though.
