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Space X CR6 First stage landing

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Re: Space X CR6 First stage landing

#181

Post by peeters »

justin66 wrote: post #175
will_hughes wrote: post #167

Earlier quoted context omitted.

For the final stage of landing only a single Merlin engine is lit. They're also limited in how much they can control the throttle on it. Even at minimum throttle, it's not possible for it to hover.

Odd responses. I guess I shouldn't have phrased my response in the form of a question. Here's another try: > When near fuel exhaustion, the Merlin engine has a thrust to weight ratio above 1. The rocket will always have a thrust to weight ratio well above 1.

I still don't understand the point of your comment then. Yes, the rocket's (potential) TWR will be above 1 at all points of the flight.

What does that have to do with the comment you're replying to? The Falcon 9 has 9 engines. The combined thrust of all of them has to be greater than the weight of the fully loaded rocket. That doesn't mean a single engine will always have more thrust than the weight of the entire rocket.

Re: Space X CR6 First stage landing

#182

Post by [deleted] »

justin66 wrote: post #175
will_hughes wrote: post #167

Earlier quoted context omitted.

For the final stage of landing only a single Merlin engine is lit. They're also limited in how much they can control the throttle on it. Even at minimum throttle, it's not possible for it to hover.

Odd responses. I guess I shouldn't have phrased my response in the form of a question. Here's another try: > When near fuel exhaustion, the Merlin engine has a thrust to weight ratio above 1. The rocket will always have a thrust to weight ratio well above 1.

[deleted]

Re: Space X CR6 First stage landing

#183

Post by trose »

bane wrote: post #75
staunch wrote: post #57

The best part of their reusable rocket project is how incremental the progress has been. I'm not sure I would have appreciated the difficulty of what they're doing as much without these failures.

Even cooler is how they're pulling off these tests on production flights.

THE best part in my opinion is that they live stream every mission and are very transparent about failures. I think they realize how many geeks and engineers are watching and that we understand that failure !== defeat.

Re: Space X CR6 First stage landing

#184

Post by reneherse »

_Adam wrote: post #26
rebootthesystem wrote: post #22

Non-engineers see this as a failure. Engineers and scientists see this as an awe-inspiring success from which to learn, iterate and try again. I don't fault reporters for exagerated headlined focusing on failure. They don't know any better. That is not what their lives are about and most might be challenged to understand that nothing in that video constitutes failure in the context of evolving a design. In fact, fail…

I don't agree that failure is absolutely necessary. I think success is generally more informative, because it gives you data about something that works end to end. If your rocket blows up on the launch pad, you just learned that you shouldn't overpressure your fuel tank (or w/e). But if your rocket lifts off, goes to space, and lands, you learn thousands of things that work that you can use again.

Consider this: If you're conducting tests and measuring your points of failure over numerous iterations, you eventually find the "threshold" of success. Exactly how much howsit and whatsit you need to produce a desirable outcome. Then you can pile on a margin of safety as needed. Continuous improvement of this sort eventually results in an efficient system or structure along with robust documentation of failure modes which you can then anticipate and accomodate.

Also, there are different ways things can fail, E.G. catastrophically vs gracefully. For example, when your steel bike fails it will generally start creaking and slowly bend, allowing you to come to a stop or even ride home. Your carbon bike bike on the other hand is more prone to snapping or shattering, a catastrophic failure mode with potentially grave results.

Re: Space X CR6 First stage landing

#185

Post by swamp40 »

sfeng wrote: post #87
monk_e_boy wrote: post #71

Earlier quoted context omitted.

How high did it get? Does it burn the whole way down (I assume it uses those little X-wings to 'fly down?) When does it start the descent burn? How fast is it going at this point? How much does it weigh, what sort of forces are we talking about? How hard is landing this puppy in terms of human achievement? Top 10% of tricky things humans have so far achieved? [edit] wouldn't it be easier to hover it a few meters abov…

It burns three times after the second stage detaches. The first is to get the landing zone closer to the takeoff, the second slows it down from 1300 m/s to about 250 m/s, the third slows it to (hopefully) 0 m/s on the landing pad. Here's a diagram: http://media2.s-nbcnews.com/i/newscms/2014_51/812491/141217-... If the 'x-wings' are what I think you're referring to, they're the landing legs. They are shaped like that…

Maybe it needs to hover? There must be something that can be squeezed to throttle it down some more. Call the NASCAR guys with their restrictor plate designs.

Re: Space X CR6 First stage landing

#186

Post by peeters »

Anyone know how fast the engine's gimbal is? The video makes it look like the gimbal lags significantly behind the angle of the rocket, so even when you're rotating one way, you end up burning more toward that angle as the engine slowly gimbals to the other side.

Granted, this is in slow motion. I just would've expected the engine to be gimballing to the other side even before there was a noticeable rotation.

Re: Space X CR6 First stage landing

#187

Post by Lorento »

socialist_coder wrote: post #117

Is there a reason you couldn't have things on the side of the landing pad that "grab" onto it and secure it? It could be as simple as a huge ring of cable that just closes around the top of the rocket, then pulls it tight on all sides- like the guidelines on a tower to keep it stable. Maybe they don't want to do that because they think they can do it without it?

If you want a more intuitive mechanical system, see the Boeing/somebody 1st stage engine recovery plan that uses a heat shield and parachute to land just the engine, not the whole stage body.

Don't forget the barge is also actively controlled to keep it stable. If you have sufficient control systems, you don't need mechanical aids. Just like humans can walk on two legs every day our whole lives using our brains, so we don't need four for "extra safety".

Re: Space X CR6 First stage landing

#188

Post by acadien »

sfeng wrote: post #94
hyperbovine wrote: post #83

Earlier quoted context omitted.

Judging from the ensuing explosion there was still fuel left over.

The RCS thrusters are powered by compressed nitrogen, not the rocket fuel that powers the main engines.

Musk commented himself on twitter something to the effect that the explosion is from the pressure difference of the fuel canister when it is breached. Also the fuel mostly burned at high heat and didn't explode per say.

Re: Space X CR6 First stage landing

#189

Post by NamTaf »

TeMPOraL wrote: post #136
socialist_coder wrote: post #117

Is there a reason you couldn't have things on the side of the landing pad that "grab" onto it and secure it? It could be as simple as a huge ring of cable that just closes around the top of the rocket, then pulls it tight on all sides- like the guidelines on a tower to keep it stable. Maybe they don't want to do that because they think they can do it without it?

> Maybe they don't want to do that because they think they can do it without it? If they master vertical landing without external support equipment, they can pull it off on Mars as well. I think that's their other goal here.

That's certainly the case. It has to be entirely self-contained to the rocket.
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