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Falcon 9 Rocket question

Falcon 9 Rocket question

Any physicists out there: If the Falcon 9 rocket was spinning like a top as it was landing, would it's angular momentum make it easier to land upright?

nine_thermidor | 16 januar 2015

I'm not a physicist, but I can tell you the best place to ask about this kind of thing is the Nasa Spaceflight Forums, where people with a wide range of expertise discuss every tiny detail of space missions, and where you can find 3 sub-fora dedicated to SpaceX.
This question belongs in http://forum.nasaspaceflight.com/index.php?board=66.0
It may have been already answered though, so have a lurk first.
Cheers.

Brian H | 17 januar 2015

An early Falcon recovery failed because it was spinning, and forcing the liquid fuel to the walls instead of feeding it to the engines.

Grinnin'.VA | 17 januar 2015

I earned an M.S. in physics as a young man.
Spinning would stabilize the Falcon, but would make a successful landing on a barge much more difficult. Keep in mind that a successful landing ends with the rocket stationary, sitting on the barge. With the rocket spinning as it approached the barge, they would need a mechanism to support it upright on the barge while the spinning is gradually slowed to a stop.

For comparison, NASA's missions taking astronauts to the moon's surface didn't use spinning vehicles to 'land' on the moon.

My interpretation of the Falcon crash is that it wasn't even close to a successful landing. Not only was the rocket spinning, it wasn't close to vertical when it reached the barge. And it arrived traveling much too fast.

Sorry, Elon and SpaceX: This landing attempt wasn't close to successful. I'd you 'stick' such landings. Hopefully, "soon".

EmperorTytus | 17 januar 2015

They've proven they can controlled land several times now. What was left unproved was navigating from space down to a tiny dot in the ocean using x-wing fins and controlled burns. They've now proved they can do that. They're closer than you think, Frownin'.

DTsea | 17 januar 2015

Thays right frownin. Despite coming in too fast they were centered. They say they ran out of hydraulics for the control fins. We will see how it goes next time.

Re spin, that would make attitude changes very difficult- ie too much stability- so, no.

evsisson | 17 januar 2015

The video of the crash showed the cylinder coming down at about a 30-45 degree angle (at first)and with a good burn going on. The vertical component of that thrust was a fraction of what it otherwise would have been, leaving open the possibility that it might have been prefect if it hadn't run out of hydraulic fluid.

Elon didn't comment on anything but the hydraulic fluid, so I think that's all it was.

Grinnin'.VA | 17 januar 2015

@ EmperorTytus | January 17, 2015
@ DTsea | January 17, 2015

They say they ran out of hydraulics for the control fins.

IMO, the booster just plain crashed. No amount of hydraulic fluid could have enabled the control fins to control it given that it was spinning and descending too fast at point of contact with the barge. Note: My opinions have occasionally been proven wrong, but not often.

Re spin, that would make attitude changes very difficult- ie too much stability- so, no.

Absolutely NO. Unless the "control fins" were designed to control a spinning booster. Anyone want to take me up on a $100 bet on this?

evsisson | January 17, 2015

The video of the crash showed the cylinder coming down at about a 30-45 degree angle (at first)and with a good burn going on. The vertical component of that thrust was a fraction of what it otherwise would have been, leaving open the possibility that it might have been prefect if it hadn't run out of hydraulic fluid.

I presume that you think the "control fins" were designed to control a spinning booster. Right?

Elon didn't comment on anything but the hydraulic fluid, so I think that's all it was.

Yes, that's what he said. I'd like to believe he always tells the truth and nothing but the truth. When I saw the video, I was shocked. I had expected something close to a successful landing. What I saw was no such thing. To me, it's a bit disappointing.

rlwrw | 17 januar 2015

evsisson observed correctly.
Because of the angle, the rocket basically tripped over its own landing leg at touchdown, and when the engine pack ripped away from the bottom of the rocket, explosion from the residual fuel "launched" the body of the rocket overboard, never to be seen again.
That explains why there was so little debris spotted on the barge when it was towed back into port.
Even if the rocket had been upright, it looked like it was at the far edge of the landing pad which still could have been an issue.

AtlantaCourier | 17 januar 2015

@Grinnin

IMO, the booster just plain crashed. No amount of hydraulic fluid could have enabled the control fins to control it given that it was spinning and descending too fast at point of contact with the barge.

Are you saying the rocket was spinning when it crashed? It doesn't look that way in the video.

rlwrw | 17 januar 2015

The small, porous fins that unfold at the top of the rocket provide just enough drag in the atmosphere to keep the rocket upright when falling back down, They can be angled to arrest any spin. They can also be configured to provide a minor amount of directional control. The rest is up to the rocket pack subset of engines when fired. Even then, the rocket motors do not have a lot of directional control on their gimbals, and can only make small corrections. When launching spacecraft into orbit, a little correction goes a long way.
The hydraulic system for the fins is an open system, which means that after the fluid runs through the hydraulic motors on the fins, it is exhausted overboard. Hence, loss of fluid.
Elon mentioned that installing a closed hydraulic system would add more weight than they wanted.
Running out of hydraulic fluid prematurely caused the fins to free float or fold back against the rocket (Not sure how SpaceX is doing this.)
In any event, running out of hydraulic fluid caused loss of stability which tilted the rocket farther than the engine could recover when it fired for the final time.

evsisson | 17 januar 2015

@ Grinnin'

"I presume that you think the "control fins" were designed to control a spinning booster. Right?"

No, I assumed the booster was NOT spinning, and I didn't even consider whether the fins could control spin (although I imagine they could be designed to do so). I saw in the video what seemed to be the legs of the booster, and they didn't appear to be moving around the cylinder.

In the video, as the booster first appeared at the top of the frame, it was more upright than it was when it hit the deck. I thought the fins were supposed to control that tilting movement. I feel that if the hydraulic fluid had not run out, the tilting would have been corrected well before it came into view, and the enhanced (downwardly directed) thrust would have slowed it considerably more.

I didn't think the booster was dropping all that fast. I was also wondering if the legs might have had shock absorbers on them, but that's just a guess. Was the video shown in real time? I didn't think to look for a timer. If it was slow motion, then yes, it might have been going too fast, though I don't know why it would have been, since it's already been tested for landing on a solid surface.

I know next to nothing about how the engine was expected to react to such a situation, and I don't have the data I'd need to figure out the answers, so I can't assume that my gut reaction is anything close to the truth.

AtlantaCourier | 17 januar 2015

@ Grinnin'

I presume that you think the "control fins" were designed to control a spinning booster. Right?

In the following video, you can clearly see the fins being used to initiate a spin on the way down and then arresting the spin just before touchdown.

https://www.youtube.com/watch?v=DgLBIdVg3EM

It looks to me like spin control is one of the primary functions of these fins as well as vertical stabilization.

grega | 17 januar 2015

Thanks Atlanta I was going to look for the grasshopper video :)
Yes they control spin.

SpaceX was designing it to use small stabilising rockets originally, but I presume using these has less of a fuel requirement. Losing their use will have had a few significant effects - though I hope SpaceX starts to look at their automatic landing system "plan B" if these cut out again (even if plan B is "don't hit the barge"

Brian H | 17 januar 2015

Grinnin';
Completely out to lunch. The spinning-crash Falcon was a single rocket early design, and this is the F9 composed of 9 cores. It was not spinning, just off-line.

carlgo2 | 18 januar 2015

It was a spectacular video. The ship is pretty sturdy it seems as that rocket looks huge and was coming in fast, yet mostly bounced off. No hydraulic fluid would mess up many things and if that was the problem, along with a tweak or two, then next time maybe!

vgarbutt | 18 januar 2015

The landing attempt was highly successful to my mind. To even get close enough to crash is amazing. The fins actually do most of their work at high speeds when there is enough drag for them to work. They also help keep the top up, and point the rockets against the trajectory so they can slow it down.

BrassGuy | 19 januar 2015

We don't know how high it was when it ran out of fluid. I'd say that if it wasn't within a hundred meters of touchdown, it's orientation in the video is no surprise. It's amazing the thing made it to the platform at all. I expect Elon to dramatically increase the likelihood of a successful landing for the next attempt. He openly gave it a 50% chance last time. Can't wait for the next attempt!

Grinnin'.VA | 19 januar 2015

@ AtlantaCourier | January 17, 2015

@ Grinnin'

I presume that you think the "control fins" were designed to control a spinning booster. Right?

... see the fins being used to initiate a spin on the way down and then arresting the spin just before touchdown.

https://www.youtube.com/watch?v=DgLBIdVg3EM

Great video, which I had not seen before.
I think your interpretation of this is correct.

It looks to me like spin control is one of the primary functions of these fins as well as vertical stabilization.

My understanding of the crash video is subject to nontrivial error caused by the poor quality of the video. I thought I saw it spinning. I know it wasn't close to vertical when it hit. And it wasn't descending on a vertical path. Combining these observations, I concluded that the crash wasn't a near-success.

Certainly, I hope SpaceX is able to do better the next time.
I definitely believe that, with enough effort and practice, they should be able to pull of this astounding feat. And I look forward to celebrating their success in recovering a Falcon booster as it returns to sea level in a real Space Station resupply mission.

Go SpaceX

grega | 19 januar 2015

The previous 2 water landings also had it coming down at an angle. The engines were simultaneously slowing its descent and horizontal velocity, and in the second it became upright.

Brian H | 19 januar 2015

Spin is undesireable. It's a liquid-fueled rocket, and spin forces the fluid away from the engine intakes.

No spin in the video, just excess tilt.

holidayday | 20 januar 2015

Success: Aiming at the landing platform. (If this was unsuccessful, then it would have landed in the absolutely huge ocean around the landing platform.

Not a Success: Safely landing the rocket.

cpmarino | 20 januar 2015

Anyone viewing this is unsuccessful has a significantly distorted understanding of the process. They took a rocket, burning fuel, from space ... steered it from 50 miles up and hit a postage stamp in the middle of the ocean. Frankly, I don't see how they will ever be successful as it was just coming in too fast, fins or no fins. Still, this is an AMAZING achievement, which we all get to witness first hand. Not quite as exciting as landing on the moon, but in the grand scheme of things, significantly more important.

Yes, Elon is a visionary ... a "dreamer" even ... and you have to take a lot of what he says with a grain of salt. However, you have to give him kudos for even trying such a thing and the fact is that Space X can launch resupply missions $200 MILLION less than what UT can do today ... if they can nail the landing and actually re-use these things, it will cost even less.

This is a win, no matter how you choose to measure it. It might take 10 more shots to get it right or prove that it can't be done. Still, you've got to be awed just a little bit, no?

Grinnin'.VA | 20 januar 2015

@ holidayday | January 20, 2015

Success: Aiming at the landing platform.

Not a Success: Safely landing the rocket.

@cpmarino | January 20, 2015

I may be wrong, but IMO the purpose of the Falcon 9 booster aiming "at the landing platform" was to actually land on the barge in a condition allowing SpaceX to reuse the booster. If you disagree, please provide a link to the source of the real purpose.

BTW, I hope and wish for SpaceX to pull off a successful Falcon 9 booster recovery ASAP. Furthermore, I'd guess that they will do exactly that some time this year.

Go SpaceX!

cpmarino | 20 januar 2015

@Grinnin: Yes, clearly, the objective was to land the thing, standing upright, and bring it back home. I do understand that.

Hitting the damned platform was a win, no matter how you wish to measure it, given the odds against such, the incredible complexities involved in doing so and the fact that it's never been done before.

All I'm saying is that you have to see the big picture. Nobody, Elon included, thought they'd do it on the first try. I doubt they'll do it on the second or third either, but, eventually, they will.

So, no, the ultimate goal of landing and re-using was not successful, but, c'mon man, aren't you at least a little impressed that they actually hit the freakin' thing?

I mean, the Wright Brothers are largely credited with the first successful flight ... they were like 6 feet off the ground and "flew" for something like 1 minute and 900 feet ... doesn't diminish the accomplishment and look what it led to. Maybe I get too excited by stuff like this but ... you gotta admire the effort and the balls to even try it in the first place.

Grinnin'.VA | 20 januar 2015

@ cpmarino | January 20, 2015

I said that this attempt failed to meet its goal.

You reacted as if I had made some outrageous claim.

Can we please just wait until SpaceX lands one of their boosters on a barge before we celebrate this astounding accomplishment?

DTsea | 20 januar 2015

Yes frownin, your claim is outrageous.

Spacex made it very clear that the primary objective was to tighten terminal autonomous navigation from a tolerance of miles to a tolerance of feet.

This was successful.

They also said the likelihood of a successful landing on the barge was 50% or less. Obviously they knew that there was more to learn.

What spacex is teaching us, that we have forgotten, is that the path to success is paved with partial failures. We used to know this.

DTsea | 20 januar 2015

And even HITTING the barge is a TREMENDOUS ACHIEVEMENT that deserves celebration.

What have YOU done, Frownin', that compares?

Brian H | 20 januar 2015

cp;
the rocket is not just falling; it reserves about 10% of its original fuel for slowing the descent, in addition to airbraking. The nose vanes help, and aim and stabilize it.

holidayday | 21 januar 2015

Grinnin' " IMO the purpose of the Falcon 9 booster aiming "at the landing platform" was to actually land on the barge in a condition allowing SpaceX to reuse the booster. If you disagree, please provide a link to the source of the real purpose.

Don't disagree. This seems to be saying exactly what I was saying.

Aiming at Landing Platform was a success. This is a much bigger deal that many think it is. It's absolutely incredible that out of the millions of square miles of ocean, the rocket hit the Landing Platform.
Safely landing the rocket was not a success. It came in a bit sideways and a little fast.

BrassGuy | 21 januar 2015

I don't have source info either, but I see the goal is to get closer to being able to reuse the first stage. They did succeed in getting closer to that point. Sure the ultimate goal is a soft landing and to reuse the rocket, but had this been a successful vertical landing, could they have recovered that rocket and brought it back to land and reused it? I doubt it. At the very least their goal was to learn. They did.

This is more like SpaceX has possession and just gained 55 yards in a single play. No TD, but a huge gain. I'd say they are within the last 10 yards. (No, I don't watch much football; but that's my analogy anyway.)

Grinnin'.VA | 21 januar 2015

@ DTsea | January 20, 2015

And even HITTING the barge is a TREMENDOUS ACHIEVEMENT that deserves celebration.

What have YOU done, Frownin', that compares?

Believe what you wish. However, your insults are out of line!

DTsea | 21 januar 2015

I didnt insult you- your tone is frowning not grinning. I answered your question- yes i think your opinion is outrageously disrespectful of the people at SpaceX and their astonishing achievements.

vgarbutt | 21 januar 2015

If the goal is to land it upright and recover it intact, it was a failure. A spectacular one. But the goal was stated as 'trying to land it'. In this they were successfull.

Even more exciting they found out what it was, and can correct it. Of course according to murphys law, that simply allows the next thing in line to bug it up. And so on and so on till murphy is defeated.

The odds went up now to better than 50/50 that the next attempt might land.

I wish they would launch in the day.

EcLectric | 21 januar 2015

@rlwrw,

Nice post. That makes a lot of sense.

Brian H | 21 januar 2015

Elon admits he's guessing, but says the odds of success on the next attempt (currently scheduled for Feb. 8) went up from 50% to 60%. I'd guess about 80%, though!

carlgo2 | 22 januar 2015

What will really be spectacular is when the Falcon Heavy goes into use as there will be multiple large parts to land, hopefully simultaneously and near each other. But, first things first of course.

Grinnin'.VA | 22 januar 2015

@ DTsea | January 21, 2015
i think your opinion is outrageously disrespectful of the people at SpaceX and their astonishing achievements.

In one of my posts I said:

* I'll be pleased to celebrate a successful recovery of a SpaceX booster after they have landed one.
* I hope and expect SpaceX to achieve this astounding feat.

How in hell is that outrageously disrespectful?

Believe what you wish, including a rather derogatory interpretation of my comments.

Brian H | 22 januar 2015

Well, three parts, corresponding to three F9 V1.1 boosters. Two separate/fall away first then land, and the core booster follows. Then later the Dragon capsule lands on its return. The second stage is sacrificed, as it doesn't pay to load it with enough fuel to come back.

DTsea | 22 januar 2015

According to spacex website they intend to land 2nd stage too.

DTsea | 22 januar 2015

Grinnin', (not sure how to punctuate that), i felt your tone was critical and judgmental, and as an engineer i felt like the spacex people didnt deserve that.

Brian H | 22 januar 2015

DT;
Where do they say that? Elon stated the exact opposite in an interview recently.

Brian H | 22 januar 2015

If you're referring to the video, I think that was an early wishful effort, but not likely in the foreseeable future. It doesn't pencil out, no matter how they sharpen it.

Iowa92x | 22 januar 2015

Electrionic gyros, nor spinning, is how it works.

grega | 23 januar 2015

@dtsea
They were going to retrieve the second stage, but they've determined it's not worthwhile.

The MCT/BFR will be specifically designed for full reuse - with learnings they're still making now.

Grinnin'.VA | 23 januar 2015

@ DTsea | January 22, 2015

Grinnin'..., i felt your tone was critical and judgmental, and as an engineer i felt like the spacex people didnt deserve that.

What I read on the forums was an overwhelmingly over-the-top celebration of SpaceX's "success" when they had not IMO come close to succeeding. So I posted my reaction to that in emphatic terms saying what I thought. Then the verbal "rocks and poison arrows" were aimed at me denouncing me as inadequately enthusiastic, or in your post, excessively "critical and judgmental".

Yet you appear to agree with me after I challenged the conventional over-the-top enthusiasm of those who wanted to celebrate SpaceX's "success" in hitting the barge even though it obviously did not succeed in safely landing the booster.

BTW, I seriously doubt that my "critical and judgmental" attitude has caused SpaceX any angst.

Question: Why the thin skinned reaction to criticism?

DTsea | 23 januar 2015

I just didnt like the tone of it. Too many people who arent doing anything to help criticizing from sidelines.

Grinnin'.VA | 24 januar 2015

@ DTsea | January 23, 2015

I just didnt like the tone of it. Too many people who arent doing anything to help criticizing from sidelines.

It seems to me that over-the-top statements by Elon's fans are doing far less to help. IMO, progress is based on a healthy respect for reality, the good and the bad, combined with daring efforts to eliminate problems. So when people heap praise on SpaceX for its "success" in "hitting" a barge, I'm inclined to remind people that the purpose was/is to recover SpaceX boosters for reuse. And of course, from the perspective of the purpose, this latest attempt was a failure, not a success. Whoever doesn't like that, don't blame me: I'm just telling it like it is.

I remain hopeful that SpaceX will succeed in landing the booster on the barge on the next attempt or soon thereafter. Then I'll be pleased to join in the celebration.

Go SpaceX

Brian H | 24 januar 2015

Grinnin';
A translated Scots adage says fools and children shouldn't see work still in progress.

Grinnin'.VA | 25 januar 2015

@ Brian H | January 24, 2015

A translated Scots adage says fools and children shouldn't see work still in progress.

Your clearly implied insult would be humorous, except that you're wasting people's time.
What do you think you gain by posting insults?

carlgo2 | 25 januar 2015

Really. Stop fighting or I will take your rockets away.

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