SpaceX News

[ladajo]

For the links, it may have just been an artifact of being at work. Sometimes the web access there can be flaky, even though it is suppossed to be full access.

They show up fine at home.

[93143]

The Zenit costs even less than the Falcon, but it's old Russian tech and can't compete so far as the efficiency needed to tail land.

The RD-171 is substantially more efficient than the Merlin 1D, by 26-27 seconds (8-10% depending on altitude). Zenit doesn't have the dry mass fraction of Falcon, which is probably more important for this application, but I'm hesitant to admit the use of the term "efficiency" in reference to mass fraction...

[Skipjack]

That is a long way back for stuff to go wrong.
Too bad they don't get the secondary back as well. Another engine and tank cheaper.

Well, if they somehow loose the stage on the way back, they have not lost much compared to an expendable stage. They are planning on bringing back the second stage and they did some experiments with it on the CRS3 mission. The second stage will need some changes though before it is ready for reuse (added TPS, superdracos for landing, legs). According to Elon, they assume another 30% payload loss from reusing the second stage. With all the losses, the F9R will still have the same payload as the Falcon 9 1.0, maybe even a tiny bit more. So I would not call that all that bad.

The Zenit costs even less than the Falcon, but it's old Russian tech and can't compete so far as the efficiency needed to tail land.

The RD-171 is substantially more efficient than the Merlin 1D, by 26-27 seconds (8-10% depending on altitude). Zenit doesn't have the dry mass fraction of Falcon, which is probably more important for this application, but I'm hesitant to admit the use of the term "efficiency" in reference to mass fraction...

Isp is not everything, especially for a first stage engine. The Merlin has the best T/W ratio (almost twice that of the RD-171).

[ladajo]

The Zenit costs even less than the Falcon, but it's old Russian tech and can't compete so far as the efficiency needed to tail land.

The RD-171 is substantially more efficient than the Merlin 1D, by 26-27 seconds (8-10% depending on altitude). Zenit doesn't have the dry mass fraction of Falcon, which is probably more important for this application, but I'm hesitant to admit the use of the term "efficiency" in reference to mass fraction...

Think of it in the aggregate as "System Efficiency". In this case engine burn efficiency and weight all matter in the total system eff. measurement.

[GIThruster]

Think of it in the aggregate as "System Efficiency". In this case engine burn efficiency and weight all matter in the total system eff. measurement.

Exactly right. I wasn't talking about the engine, but the entire launch vehicle and the Zenit is old tech. The only reason Musk can tail land is the aluminum stir welding technique he started with that makes Falcon truly next gen.

But 93143's point is still well made. If he knows why the RD-171 gets better ISP I'd be all ears. If there's room for Merlin to improve 8% Isp, that's all the more reason to hope Musk can deliver on the first truly reusable system.

[Skipjack]

If he knows why the RD-171 gets better ISP I'd be all ears. If there's room for Merlin to improve 8% Isp, that's all the more reason to hope Musk can deliver on the first truly reusable system.

The RD 171 is a staged combustion cycle. The Merlin 1D is a gas generator engine. The difference in Isp between the two is not earth shattering and the Merlin 1D is focusing on cheap manufacturing and durability for reuse rather than efficiency. The RD-170 has more thrust but that is because it is much bigger. Its thrust to weight ratio is much inferior to the T/W of the Merlin 1D (82 versus 150). Also note that Isp is of less importance for the booster stage of a two stage vehicle than T/W and for an RLV reusability and robustness is also important. Isp is more important for the second stage.
Interestingly SpaceX is developing a large staged combustion engine, the Raptor right now that is going to use methane as a fuel. Methane gives a higher Isp and it burns cleaner than RP1.

[ladajo]

Methane. Nice.

Maybe Elon Musk is behind the BLM land grabs to graze his new Rocket Fuel herds...

[Skipjack]

Methane. Nice.

Maybe Elon Musk is behind the BLM land grabs to graze his new Rocket Fuel herds...

I doubt it
Methane is cheap and plentiful though, another advantage over RP1. Finally it is about the same temperature as LOX that has some advantages in tank design.
Lots of benefits, not just the higher Isp.
On the downside, methane is also less dense, which means larger tanks.

[ladajo]

Maybe they can run the existing tanks with mods for higher pressure. Get a little more stuff stuffed in them.

[Skipjack]

Maybe they can run the existing tanks with mods for higher pressure. Get a little more stuff stuffed in them.

Elon once mentioned prechilling the fuel a bit to make it more dense would be possible with the falcon 9, which would increase its capabilities further. The engines are currently also only operating at a limited thrust. They still have some 15% (IIRC) of headroom there as well. I guess that all that combined could make up for the losses for the reuse of the second stage (which will be about 30% that need to be subtracted from the 13.1 tonnes of payload the F9 with first stage reuse has.
Not sure what plans they have for the methane powered rocket (the so called mars colonial transport) and whether any of this will be applicable there as well. It is still too early to tell. They are only just beginning to test components of the new methane engine at Stennis.

[zapkitty]

Above all else, this:

When the F9 line is fully reusable then being able to launch 10 smaller payloads for the price of one current payload will more than make up for the smaller payloads... and then some.

[Skipjack]

Above all else, this:

When the F9 line is fully reusable then being able to launch 10 smaller payloads for the price of one current payload will more than make up for the smaller payloads... and then some.

Well it will take some time for satellite manufacturers to adapt to the payload constraint for cheaper launches, but eventually they will. That said, SpaceX can always fly a Falcon9 that is nearing the end of its lifecycle in expendable mode and get the full 16 (or more if they prechill and run the engines at full power) payload into LEO, same for larger GTO launches (the majority of the commercial launch market). For even larger payloads they will soon have the Falcon Heavy.

[mvanwink5]

Anybody know if the heavy is being designed upfront for reusability?

[GIThruster]

I'm pretty sure everything at SpaceX is designed to be reusable. The Heavy is essentially three Falcon 9 lower stages strapped together with a single upper stage.

[Skipjack]

The two side booster cores of the falcon heavy are, from what we know slightly longer than a F9 first stage (about as long as the first stage and the interstage combined).
There is a lot of speculation about the reusability of the Falcon Heavy. We know that they intent to bring the two side boosters back, which should be a no brainer. The center core is going to be a bigger issue though. For the heaviest payloads it will be cross fed from the two side boosters, so it will still be full, when the side boosters detach and return to the launch site. By the time the center core is empty, it may be too far away from the launch site to return. SpaceX has indicated however that they want to bring all 3 cores back (all three are depicted with landing legs on the SpaceX website). This might only make sense for the version of the Falcon Heavy that does not cross feed(and so has a slightly lower payload).
The FH is still a while away though and SpaceX might decide to change the design by the time they finally get to building it. If one thing is clear about SpaceX, it is that they are not hesitant to update their designs often.