Author Topic: BFR landing cradle discussion and updates  (Read 45451 times)

Offline meekGee

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BFR landing cradle discussion and updates
« on: 01/25/2017 02:04 PM »
In the grand reveal of a few months ago, Musk showed the booster landing in a  cradle, co-located with the launch mount.

Some have called this a fantasy. Some think it's feasible and quite clever.

This thread's for you.

Speculation welcome.
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Offline Robotbeat

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Re: BFR landing cradle discussion and updates
« Reply #1 on: 01/25/2017 02:08 PM »
 To start out, Masten Space Systems had this idea before SpaceX did.

They've recently even developed a vehicle which will be used to develop this technology:
http://masten.aero/vehicles-2/xaerob/
« Last Edit: 01/25/2017 02:11 PM by Robotbeat »
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Offline John Alan

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Re: BFR landing cradle discussion and updates
« Reply #2 on: 01/25/2017 02:12 PM »
I speculate SpaceX will come up with an add on lower thruster package they can add to RTLS bound F9 S1's...
The will paint 4 leg pad outlines on the pad and see how well they can hit them...

Assuming that goes well...

I then speculate SpaceX will build a mobile rig they can wheel out to the RTLS pad and build a few lightweight F9 S1's with fin like structures to use in continuing research using RTLS bound stages...

This may all be BS hogwash... but a guy can speculate...  ;)

Offline woods170

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Re: BFR landing cradle discussion and updates
« Reply #3 on: 01/25/2017 02:13 PM »
Let me put it this way. Outright dismissal of the whole concept, by certain members here, without having insight into the technical details of said concept, is premature.

Outright statements, by certain members here, that the whole concept WILL work, without having insight into the technical details of said concept, is equally premature.

Offline meekGee

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Re: BFR landing cradle discussion and updates
« Reply #4 on: 01/25/2017 02:14 PM »
To start out, Masten Space Systems had this idea before SpaceX did.
Noted.  Kistler was showing it too, and I've seen a helicopter pilot load up his MD500 onto a trailer by landing on it.

A cradle is just a vertical runway. Think of an aircraft carrier. You have to nail it just so, or crash.

The concept is not new. The execution in rocketry, and scale - that's new.
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Offline Jim

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Re: BFR landing cradle discussion and updates
« Reply #5 on: 01/25/2017 02:15 PM »
The issue is not a landing cradle.  The issue is a landing cradle that is also a launch mount.

Offline woods170

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Re: BFR landing cradle discussion and updates
« Reply #6 on: 01/25/2017 02:17 PM »
The issue is not a landing cradle.  The issue is a landing cradle that is also a launch mount.
No doubt Jim. But issues only exist to be transformed into non-issues by providing solutions.

Offline meekGee

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Re: BFR landing cradle discussion and updates
« Reply #7 on: 01/25/2017 02:18 PM »

"Hovering is for humans"

If flight control computers could choose a bumper sticker, that'd be it.

When you hover you just give winds and other unknowns more time to influence​ your position.

The best way to increase X-y accuracy is to hit the pad at higher velocity.  Less time for unknown forces to act and unlike a human, a computer doesn't need to hover nearby to estimate the IIP.

The only problem is that a you try to hit the pad at higher decelerations, you increase your Z uncertainty.

The remedy for this is increase Z travel on capture.  Which means a heavier mechanism.

This is the gain of the cradle - you don't have to carry the landing gear with you, you leave it on the ground.  Make it as tall and heavy as you want, to absorb as much residual vertical velocity as you need.

My bet is that we'll see more slam, and less hover, but that because of the increased physical size, it'll look about the same.


Basically, it's a smaller step then showing that they can land an F9.

And they will be able to tune F9 landings further, and also transfer that knowledge to BFR landing modeling.

If they say today that it can be done, they are certainly in a position of authority to do so.

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Offline Robotbeat

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Re: BFR landing cradle discussion and updates
« Reply #8 on: 01/25/2017 02:21 PM »
The issue is not a landing cradle.  The issue is a landing cradle that is also a launch mount.
Isnt that what legs are on a vehicle like Grasshopper or the NGLLC type vehicles?
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Offline Basto

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Re: BFR landing cradle discussion and updates
« Reply #9 on: 01/25/2017 02:24 PM »
A common concern I am seeing repeated about the cradle mount has been lining up the booster in heavy cross winds. Personally I think that this would be a non issue as rockets don't usually launch with heavy wind conditions.

It is often an issue when landing on an ASDS because the landing site is out at sea.

Offline meekGee

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Re: BFR landing cradle discussion and updates
« Reply #10 on: 01/25/2017 02:27 PM »
The issue is not a landing cradle.  The issue is a landing cradle that is also a launch mount.
So if landing in a cradle, in and of itself, is not an issue, then "fantasy" has nothing to do with it.

You have a simple trade off between two feasible solutions:

Co-locate the two, and risk damaging the launch pad if the landing fails, or have two separate facilities and some kind of transporter.

But since a failed landing will certainly damage the landing mount, and this is a reusable vehicle, what value is the launch pad without the landing pad?

If you want redundancy, build two launch/land facilities, so each one will perform both functions, and if one is damaged, you don't care that the other was too.
« Last Edit: 01/25/2017 11:56 PM by meekGee »
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Offline Robotbeat

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Re: BFR landing cradle discussion and updates
« Reply #11 on: 01/25/2017 02:36 PM »
I always kind of thought the landing cradle could be co-located with the launch mount, and the launch mount attaches to the vehicle after landing. It doesn't have to literally be the same mechanism, only has to be concentric.
Chris  Whoever loves correction loves knowledge, but he who hates reproof is stupid.

To the maximum extent practicable, the Federal Government shall plan missions to accommodate the space transportation services capabilities of United States commercial providers. US law http://goo.gl/YZYNt0

Online Jimmy Murdok

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Re: BFR landing cradle discussion and updates
« Reply #12 on: 01/25/2017 02:37 PM »
A common concern I am seeing repeated about the cradle mount has been lining up the booster in heavy cross winds. Personally I think that this would be a non issue as rockets don't usually launch with heavy wind conditions.

It is often an issue when landing on an ASDS because the landing site is out at sea.

You need to add gas (or more powerful) thrusters in the bottom to ensure good alignment. I would forget about this concept on a small ASDS, it's been shown on ground because you require stability.
http://forum.nasaspaceflight.com/index.php?topic=41249.msg1592281#msg1592281

Offline Basto

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Re: BFR landing cradle discussion and updates
« Reply #13 on: 01/25/2017 02:55 PM »
A common concern I am seeing repeated about the cradle mount has been lining up the booster in heavy cross winds. Personally I think that this would be a non issue as rockets don't usually launch with heavy wind conditions.

It is often an issue when landing on an ASDS because the landing site is out at sea.

You need to add gas (or more powerful) thrusters in the bottom to ensure good alignment. I would forget about this concept on a small ASDS, it's been shown on ground because you require stability.
http://forum.nasaspaceflight.com/index.php?topic=41249.msg1592281#msg1592281

I never claimed otherwise. Just pointing out that the argument of cross winds affecting landing precision should be a non issue because you just wouldn't launch under conditions with heavy cross winds.

Offline meekGee

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Re: BFR landing cradle discussion and updates
« Reply #14 on: 01/25/2017 02:59 PM »
A common concern I am seeing repeated about the cradle mount has been lining up the booster in heavy cross winds. Personally I think that this would be a non issue as rockets don't usually launch with heavy wind conditions.

It is often an issue when landing on an ASDS because the landing site is out at sea.

You need to add gas (or more powerful) thrusters in the bottom to ensure good alignment. I would forget about this concept on a small ASDS, it's been shown on ground because you require stability.
http://forum.nasaspaceflight.com/index.php?topic=41249.msg1592281#msg1592281
Definitely not on an ASDS - the barge location is too unpredictable.

I predict either a test site in New Mexico, or a whole new landing pad for this purpose.

If, that is, F9 (being smaller) can achieve the required level of accuracy.

How accurate must it be?

Imagine that there are guide slideways, and the final cone of acceptance has a half angle of about 15 degrees.

Assume the slam is set for 1g.

If the rocket was able to land within 1 m of ground zero, it would only engage the slides about 4 m above ground, at a vertical speed of 9 m/s, and this will move it at a horizontal speed of about 2 m/s.

Not so crazy.
« Last Edit: 01/25/2017 04:21 PM by meekGee »
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Offline meekGee

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Re: BFR landing cradle discussion and updates
« Reply #15 on: 01/25/2017 04:28 PM »
RB - I'm pretty sure there will be a mechanical guidance  structure, a set of rails or what have you, that will take care of final positioning.

There is no way the rocket will settle into hold-downs all on its own.

There will be some features on the rocket, in lieu of legs, that will interface with this centering structure, and as someone observed, they should be located at the height of the empty booster's CG.
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Offline NotOnImpact

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Re: BFR landing cradle discussion and updates
« Reply #16 on: 01/25/2017 06:13 PM »
RB - I'm pretty sure there will be a mechanical guidance  structure, a set of rails or what have you, that will take care of final positioning.

There is no way the rocket will settle into hold-downs all on its own.

There will be some features on the rocket, in lieu of legs, that will interface with this centering structure, and as someone observed, they should be located at the height of the empty booster's CG.

Musk stated in the Mars video that one of the purposes of the three fins on the 1st stage was to provide that last little bit of alignment on the pad for the landing.

Re: BFR landing cradle discussion and updates
« Reply #17 on: 01/25/2017 07:41 PM »
Given the amount of exhaust from all those engines maybe the landing cradle to would have to be hinged so it could fold up against the tower for launch and then lower down at landing? Or would there be a practical way of protecting it? Just mulling that over.

Offline Jdeshetler

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Re: BFR landing cradle discussion and updates
« Reply #18 on: 01/25/2017 07:49 PM »
Drawn on a paper napkin (Stone Age MS Paint) during my lunch break. 

Pure Speculation.

The Cradle Ring and 8 hydro-shafts would need to be massive and blast proof.
« Last Edit: 01/25/2017 07:53 PM by Jdeshetler »

Offline Lars-J

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Re: BFR landing cradle discussion and updates
« Reply #19 on: 01/25/2017 08:54 PM »
Drawn on a paper napkin (Stone Age MS Paint) during my lunch break. 

Pure Speculation.

The Cradle Ring and 8 hydro-shafts would need to be massive and blast proof.

I think you are overthinking it. With base thrusters and canted walls to guide the three base fins into the cradle, I don't see why a moving cradle is necessary.

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