The SpaceX Thread

[Megalodon]

It sounds like they need extremely good specific impulse.

 

[Kaputnik]

tinyMan[/url]":2alpz0tr]what problems they are trying to solve that required this departure

Mars

 

[Bad Monkey!]

Megalodon[/url]":1zyh73ks]http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/

Holy thrust buckets, Batman! A launcher with 27 million pounds of launch thrust? Where do they plan on launching this monster? Obviously not at Cape Canaveral, which I think is limited to 12 million pounds. Where ever it is, I'll be excited to see it. Just not too close...

 

[Tom the Melaniephile]

Bad Monkey![/url]":1fa16teg]

Megalodon[/url]":1fa16teg]http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/

Holy thrust buckets, Batman! A launcher with 27 million pounds of launch thrust? Where do they plan on launching this monster? Obviously not at Cape Canaveral, which I think is limited to 12 million pounds. Where ever it is, I'll be excited to see it. Just not too close...

Perhaps the Texas site which has been discussed.

 

[Bad Monkey!]

Tom the Melaniephile[/url]":2ins34at]

Bad Monkey![/url]":2ins34at]

Megalodon[/url]":2ins34at]http://www.nasaspaceflight.com/2014/03/spacex-advances-drive-mars-rocket-raptor-power/

Holy thrust buckets, Batman! A launcher with 27 million pounds of launch thrust? Where do they plan on launching this monster? Obviously not at Cape Canaveral, which I think is limited to 12 million pounds. Where ever it is, I'll be excited to see it. Just not too close...

Perhaps the Texas site which has been discussed.

I have my doubts about even that. The Cape restriction is to prevent buildings being damaged in Titusville, 10 miles away. I think they'd have to launch from one of the Marshall Islands sites.

 

[MilleniX]

Just a heads-up that CRS-3 is scheduled for launch next week. For anyone who needed a reminder, that'll include testing propulsive return to a soft water landing.

 

[Tom the Melaniephile]

Nice!

 

[Barmaglot]

Wasn't it supposed to be a soft ground landing? I've seen mentions that they're attaching the landing legs to the rocket this time - wouldn't need those for a splashdown, would they?

 

[Kaputnik]

Fractional baby steps - first test legs deploy even if it only happens relatively long after high speed part of re-entry, re-test re-entry trajectory, re-test touchdown. IE the whole EDL sequence still needs too much proving to test on land where debugging's hampered by more destructive failure modes.

 

[Megalodon]

Bad Monkey![/url]":1blu4hk6]I think they'd have to launch from one of the Marshall Islands sites.

They've essentially closed those down.

 

[MilleniX]

From what I've read, the ground landing had substantial permitting issues to be worked out, and there was too much uncertainty about whether those would be resolved by launch time.

The landing legs are needed precisely to address the problems that they encountered on CRS-2 - aerodynamic spinup beyond their roll-control authority, leading the fuel tanks to centrifuge and thus the engines to flame out. And of course, they'll want to test deployment and instrumentation on the legs as they 'touch down', even if it's not on land.

 

[Barmaglot]

Hmmm, do the legs double as aerodynamic control surfaces as they unfold? I haven't thought about that.

 

[MilleniX]

Not active control surfaces, AFAIK, but they are expected to provide stability. The failure of the previous re-entry test was directly attributed to their absence.

 

[Megalodon]

MilleniX[/url]":aerdvqf6]Not active control surfaces, AFAIK, but they are expected to provide stability. The failure of the previous re-entry test was directly attributed to their absence.

Yeah. I think the main thing they wanted from that flight was reentry. It was a powered reentry which hasn't really been done before.

 

[jbode]

MilleniX[/url]":1epql9sq]
The landing legs are needed precisely to address the problems that they encountered on CRS-2 - aerodynamic spinup beyond their roll-control authority, leading the fuel tanks to centrifuge and thus the engines to flame out.

Don't have a link handy, but my understanding is that the forces were so great that the baffles within the tanks broke and debris clogged the engine.

Either way, this is going to be fun to watch. What's going to be interesting is seeing how the legs affect performance on the way up; they're as aerodynamic as possible when stowed, but they're still going to add some drag and mass (after all, they have to support the weight of the vehicle on landing). Really interested to see what happens at max Q.

 

[Kaputnik]

IIRC the legs weigh as much or less than a Tesla Model S.

 

[Dilbert]

I can't wait to see this! Exciting.

 

[Megalodon]

tinyMan[/url]":3hq2jzhj]I don't know if I would say that SpaceX's current crop of engines are not World Class. The Merlin's are inexpensive, robust, mechanically simple, reliable and offer exceptional power-to-weight ratios. While they aren't the biggest, most powerful or most efficient, they did an amazingly good job of being "good enough" for lots of use cases -- especially for what is essentially a first attempt by a new-to-the-industry player.

That's what I mean when I say right engine for the business model. It was a cheap development path, and it was sized so they could build a small rocket with one of them. It was the right engine for SpaceX to build at the time. I don't want to belittle the accomplishment of building the right engine for the job with how routinely everyone else fucks that up, but no, I don't think it's a particularly good engine on the world stage right now. Even on thrust to weight Russian engines got close >40 years ago with 20 seconds better ISP. I don't think anyone else is scrambling to buy or copy them even with their low cost and I don't think you'd end up with competitive launchers if you got other programs to use them. And I don't think SpaceX or anyone else's larger ambitions can be accomplished with them because they simply don't have the ISP.

What makes this work for SpaceX is that they're good enough at the rest of the engineering problems that they can build economical rockets around entry level engines and it turns out nobody is doing anything today that requires more than that. SpaceX has a fungible unit of propulsion and they size the rocket to the customers. Others have these cold war relics that might as well be alien artifacts and spare no expense building rockets around them. SpaceX's business model is better, but I wouldn't compare Merlin to SSME or RD-180.

Raptor seems like a really elegant synthesis of some of the sophistication of these other engines, implemented with SpaceX expediency. I don't think you'll see anyone else using Merlin, but that seems not out of the question for Raptor.

 

[Kaputnik]

...Why would one compare Merlin with SSME or the 180....

 

[Megalodon]

Sputnik[/url]":1h207svp]...Why would one compare Merlin with SSME or the 180....

They're first stage engines in comparable vehicles. RD-180 in Atlas V and maybe others at some point, RD-171 and RD-191 in more, SSME derived in SLS.

If it's the basis for vehicles in the same payload range there's obviously a comparison to be made. Merlin 1 is clearly punching above its weight by most standards.

 

[Kaputnik]

Yes.. But the engines in terms of pointing at respective strictly-engines profile IE excluding their vehicles.. Apples and oranges. The SS/Orbiter isn't really comparable with F9 and Atlas V.

Never mind, it doesn't matter.

 

[Megalodon]

So apparently Raptor is a gas-gas cycle, AKA full flow staged combustion, which is a distinction I was not previously aware of.

My understanding is:

-In a gas generator engine you use an uneven mixture, a stoichiometric mixture would be too hot. The incompletely burned fuel is vented. Both propellants are injected into the combustion chamber as liquids (liquid-liquid)
-In a staged combustion you still use an uneven mixture to control temperature in the preburner, but it goes to the combustion chamber rather than getting vented. You can fully consume one of the propellants and that gives you more pump power, meaning higher combustion chamber pressure, with the remainder of the other fuel being injected as liquid (gas-liquid). Engines like RD-180 have crazy high preburner pressures to get enough pumping power.
-In a full flow staged combustion cycle, gas-gas, you have two preburners. Both use uneven mixtures, but they're inversely uneven. They have much more mass available for driving turbines so temperatures and pressures can be backed off significantly in the preburners but remain high in the combustion chamber. There's no liquid fuel remaining, it's all been through one of the preburners.

The points people made about Merlin being a very good engine are well taken, it might be the best ever in its size and for a gas generator, but Raptor is clearly a new level of sophistication for SpaceX. I don't think anyone has ever done a production full flow engine.

Sputnik[/url]":gvunuhmj]Yes.. But the engines in terms of pointing at respective strictly-engines profile IE excluding their vehicles.. Apples and oranges.

From an engine perspective I can see your point. Merlin is probably the best gas generator engine anyone's ever done.

 

[tinyMan]

Just contemplating a rocket with 27 Raptors for the first stage and 9 for the "second" stage (is the core booster of a Falcon-Heavy 3-booster configuration a stage?) boggles my mind. That's like 4+ Saturn V's. But only more efficient with the propellant transfer.

 

[Jonathon]

tinyMan[/url]":4fuf6rvs]Just contemplating a rocket with 27 Raptors for the first stage and 9 for the "second" stage (is the core booster of a Falcon-Heavy 3-booster configuration a stage?) boggles my mind. That's like 4+ Saturn V's. But only more efficient with the propellant transfer.

Falcon Heavy is using the Merlin 1D just like the Falcon 9. So not quite that insane.

From what I'm reading, the Mars Colonial Transporter's first stage is currently expected to use 9 Raptors (per booster core-- are they expecting to use more than one like Falcon Heavy?). Which puts it at roughly the same thrust as the first stage of the Saturn V (5x F-1s), but a fair bit more efficient.

 

[Barmaglot]

MilleniX[/url]":eo2ttaoc]Just a heads-up that CRS-3 is scheduled for launch next week. For anyone who needed a reminder, that'll include testing propulsive return to a soft water landing.

Looks like it's been pushed back another two weeks, to March 30

 

[Kaputnik]

Jonathon[/url]":q4pylb0i]

tinyMan[/url]":q4pylb0i]Just contemplating a rocket with 27 Raptors for the first stage and 9 for the "second" stage (is the core booster of a Falcon-Heavy 3-booster configuration a stage?) boggles my mind. That's like 4+ Saturn V's. But only more efficient with the propellant transfer.

Falcon Heavy is using the Merlin 1D just like the Falcon 9. So not quite that insane.

From what I'm reading, the Mars Colonial Transporter's first stage is currently expected to use 9 Raptors (per booster core-- are they expecting to use more than one like Falcon Heavy?). Which puts it at roughly the same thrust as the first stage of the Saturn V (5x F-1s), but a fair bit more efficient.

That notional Markusic drawing with a rocket as good as identical to the MCT HLV also had a three core version.

 

[Megalodon]

Sputnik[/url]":2rvllbqy]That notional Markusic drawing with a rocket as good as identical to the MCT HLV also had a three core version.

Except, that three core version is closer to the thrust of ONE of the new Raptor core now being discussed.

The new Raptor core is similar to the Falcon XX on the right. Imagine the three core version of that.

Somewhat less thrust with 9 Raptors than 6 Merlin 2, but vastly superior ISP.

 

[DonRoberto]

Sputnik[/url]":1tpifozj]Yes.. But the engines in terms of pointing at respective strictly-engines profile IE excluding their vehicles.. Apples and oranges. The SS/Orbiter isn't really comparable with F9 and Atlas V.

Never mind, it doesn't matter.

Don't forget the RD-180 is a derivative of the RD-170 for the Energia launcher for the Soviet space shuttle (Buran). Booster engine, though.

 

[jbode]

Launch is being pushed back again, this time because of range issues. One radar asset was severely damaged in a fire, and several launches are being delayed as a result.

 

[leecbaker]

CRS-3 is launching in a couple of hours- livestream starts in an hour or so from now.

NASA live stream

SpaceX live stream

Mission status and text updates

The really interesting part of today's launch is that they will be deploying legs, and trying to simulate a landing (but over the ocean, not on land):

During tomorrow’s today's CRS-3 launch to station, SpaceX will attempt to recover Falcon 9’s first stage. This test is not a primary mission objective and has a low probability of success (30-40%), but we hope to gather as much data as possible to support future testing. After stage separation, when Dragon is well on its way to the ISS, the first stage will attempt to execute a reentry burn and then a landing burn over the Atlantic Ocean. Falcon 9 is carrying four landing legs, which will deploy partway into the landing burn. Eventually, SpaceX hopes to land the first stage on land. Though success is unlikely with this test, it represents an exciting effort toward someday developing a reusable rocket.

EDIT: Good picture of a rocket leg here

 

[jbode]

Scrubbed. Next attempt is on Friday.

 

[.劉煒]

:/

 

[leecbaker]

It seems like a lot of launches are scrubbed due to leaks of either helium, hydrogen (space shuttle), oxygen, or another fuel. Seems like getting these things right shouldn't be that complicated. Does anybody know why leaks are so common on launch vehicles? Is it the cold temperatures causing pieces to crack?

Surely plumbing isn't that hard .

 

[truth is life]

leecbaker[/url]":mbpkyb4n]It seems like a lot of launches are scrubbed due to leaks of either helium, hydrogen (space shuttle), oxygen, or another fuel. Seems like getting these things right shouldn't be that complicated. Does anybody know why leaks are so common on launch vehicles? Is it the cold temperatures causing pieces to crack?

Surely plumbing isn't that hard .

Cryogenic plumbing is tough, as you suppose. Additionally, hydrogen and helium are both very small, and can leak through extremely tiny holes, while hydrogen exposure makes many metals brittle and fragile (above and beyond the effects of cryogenic cooling).

All in all, it's very tough to keep everything contained.

 

[Megalodon]

SpaceX and ULA were up for the same slot on April 10th and ULA got it because, according to various things I've seen on space sites, people liked their odds of launching first time out better than SpaceX's. SpaceX is still pretty new at this and need to get their process worked out so it's reliable and fast. It is hard but the people involved are smart.

 

[Alamout]

All in all, it's very tough to keep everything contained.

Plus you have to balance your desire to build the perfect plumbing with your desire to conserve mass. Every bit of weight you save is weight you don't need to send to space. As long as it's easier to get a launch window than it is to get a rocket, we'll probably keep erring on the side of "only launch in perfect conditions".

 

[Frennzy]

leecbaker[/url]":1fmol45q]It seems like a lot of launches are scrubbed due to leaks of either helium, hydrogen (space shuttle), oxygen, or another fuel. Seems like getting these things right shouldn't be that complicated. Does anybody know why leaks are so common on launch vehicles? Is it the cold temperatures causing pieces to crack?

Surely plumbing isn't that hard .

Do this. Build yourself a perfect helium balloon that doesn't leak.

Once you do that, come back and tell us how easy it was.

 

[jbode]

Some details on the scrub (from here):

“During Monday’s launch attempt, preflight checks detected that a helium valve in the stage separation pneumatic system was not holding the right pressure. This meant that the stage separation pistons would be reliant on a backup check valve,” noted the company in a release on Wednesday.

“No issue was detected with the backup valve and a flight would likely have been successful, but SpaceX policy is not to launch with any known anomalies.”

Yeah, life's easier for everyone if the primary systems are function properly. Given that they want to try to recover this stage (as well as, you know, accomplish the primary mission), it's in their interest to clear any anomalies before launch, no matter how minor.

 

[Jonathon]

About 35 minutes out from today's launch attempt, and everything's good so far (assuming the weather stays the way it is).

NASA stream here: http://www.nasa.gov/multimedia/nasatv/i ... 1FygeaJ6A1
SpaceX stream here: http://www.spacex.com/webcast/

 

[jbode]

T minus 10 minutes. Looks good so far.