SpaceX Falcon 9 : PAZ & Microsat 2a/2b : SLC-4E : Feb 22, 2018 : DISCUSSION

[Space Ghost 1962]

Didn't Elon write that they needed a bigger parachute to slow the fairing down? What do you suppose the "landing" speed of the fairing is? That is, how fast is it moving along its glide slope while Mr. Stevens is trying to catch it? Or just maybe, trying to catch up with it.

Wind speed and direction may be a significant factor here. Turning into the wind is obvious but it assumes the fairing "knows" the direction of the wind.

Inertial guidance systems can "infer" wind speed and direction. (Airlines use it routinely.)

Quite well for where it IS ....but perhaps not so well for 200 meters further down and 600 meters over (or whatever the glide path is).

Gusts show up with minor lag time quite well. (When your on the ground, you can see them when they "lurch" the plane.

When you have a miss like this, its a fine grain control problem of some sort.

One of the easy approaches is to heave over until under then cut the lines and have it dive/drop in, assuming no bounce. Perhaps that's what they were doing ... and it bounced!

I don't want to rube goldberg this[1] but maybe drones that are relaying inferred windspeed/direction back to the fairing control computer might add some accuracy?

Consider how much easier the fielder's job would be if the balls were being told wind speed and were cooperating with the mitt in being caught.

1 - who am I kidding, yes I do.

You're not fooling anyone here - of course you want the "rube". 

[LouScheffer]

I don't want to rube goldberg this[1] but maybe drones that are relaying inferred windspeed/direction back to the fairing control computer might add some accuracy?

1 - who am I kidding, yes I do. 

You can't Rube Goldberg this, it's *already* Rube Goldberg!   We'll just bolt some giant arms and a huge net onto a fast ship and try to catch a fairing falling from a spacecraft.   That's the ticket.  All it needs is the "ACME" label on the fast boat.

This is brilliant on the part of SpaceX.   ULA and Ariane, prim and proper, would die of humiliation if they tried this, and it ever failed.

[denis]

I'm curious: why a sun-synchronous orbit for a RADAR satellite?

It is synchronous on the dawn-dusk boundary, so the solar panels are continuously exposed to sunlight and batteries are not needed to power the radar.

Sun-synchronous is indeed to simplify the spacecraft design in term of solar panel (one fixed panel always on the Sun side) but note that there are still eclipses on such orbit for part of the year (when Sun around winter/summer solstices)

[speedevil]

Quite well for where it IS ....but perhaps not so well for 200 meters further down and 600 meters over (or whatever the glide path is). I don't want to rube goldberg this[1] but maybe drones that are relaying inferred windspeed/direction back to the fairing control computer might add some accuracy?

Consider how much easier the fielder's job would be if the balls were being told wind speed and were cooperating with the mitt in being caught.

1 - who am I kidding, yes I do.

I've commented in the past that a cylindrical shell of a hundred drones five windspeed-seconds out - perhaps with ocean height sensors too, would give you really really good microscale predictions.

[Lar]

I've commented in the past that a cylindrical shell of a hundred drones five windspeed-seconds out - perhaps with ocean height sensors too, would give you really really good microscale predictions.

I reused your idea....

I don't want to rube goldberg this[1] but maybe drones that are relaying inferred windspeed/direction back to the fairing control computer might add some accuracy?

1 - who am I kidding, yes I do. 

You can't Rube Goldberg this, it's *already* Rube Goldberg!   We'll just bolt some giant arms and a huge net onto a fast ship and try to catch a fairing falling from a spacecraft.   That's the ticket.  All it needs is the "ACME" label on the fast boat.

point.

This is brilliant on the part of SpaceX.   ULA and Ariane, prim and proper, would die of humiliation if they tried this, and it ever failed.

I'd argue that SMART midair catching isn't exactly completely dignified. But yeah.

[LouScheffer]

This is brilliant on the part of SpaceX.   ULA and Ariane, prim and proper, would die of humiliation if they tried this, and it ever failed.

I'd argue that SMART midair catching isn't exactly completely dignified. But yeah.

Yeah, but at least SMART involves square-jawed, steely-eyed, military helicopter pilots, saving our valuable space assets for democracy.

The SpaceX approach brings to mind a cigar-chomping, eye-patch wearing, scourge of the seas, looking skyward while frantically zooming around in a seemingly random pattern as he tries to catch the fluttering fairing.  Roughly as dignified as Wile E. Coyote trying to catch a package dropped from a cliff, or a beagle trying to catch a frisbee on a windy day.

Along these lines, I like the idea of SpaceX renaming the ship the "GO fetch".  Conversely, ULA should NOT name their helicopter "get SMART".

[Kabloona]

The SpaceX approach brings to mind a cigar-chomping, eye-patch wearing, scourge of the seas, looking skyward while frantically zooming around in a seemingly random pattern as he tries to catch the fluttering fairing.  Roughly as dignified as Wile E. Coyote trying to catch a package dropped from a cliff, or a beagle trying to catch a frisbee on a windy day.

Which is a big part of the fun of watching SpaceX innovate.

I was at a friend's house recently and saw he had Ashlee Vance's book on the coffee table. I haven't read the book, so I thumbed through and skimmed a few pages. One page that stuck in my mind described how Musk reacted to engineers whose justification for their approach was "we'll do it this way because that's how it's always been done." Those people were quickly and energetically informed by Musk that they should either find a better rationale for their engineering decisions or find another job (probably misquoting the book, but that was the gist of it, IIRC).

[AC in NC]

The SpaceX approach brings to mind a cigar-chomping, eye-patch wearing, scourge of the seas, looking skyward while frantically zooming around in a seemingly random pattern as he tries to catch the fluttering fairing.

Catch a Great White, you say?  Six million dollars?

[John Alan]

Thinking out loud here... 
Seems to me, if the boat had a ILS transmitter on it like THOUSANDS of airports have on their runways...
And they set the angle of the beam up to within the gliding abilities of the inbound "package"...
Aim it thru the net and out over the stern of the boat
They could swing the boat slowly till the 'package' acquires the glideslope on it's 'autopilot' ILS receiver...
It could fly right to them...  Just like a plane flies right to the end of a runway in low visibility conditions...
Just a thought on subtopic... 

On edit... OK, a VOR or NDB to tell the 'package' where the boat is and to fly toward an approach entry... and the afore mentioned ILS setup to then guide it into the net...
Thinking old school instrument approach and landing procedure... (pre GPS days)
Follow the pattern in, as published (or programmed) on the 'Jepp chart'... 

Ok... better edit...
Based on calculations and weather (winds aloft)... SpaceX picks a GPS point at X,Y with a Z altitude and puts that updated value in the fairing ECU during early countdown...
Same point is relayed to the Boat... which dashes there from it's last update point it last had...
Boat takes some stationary  wind readings and then proceeds to a point directly upwind...
The distance is based on winds and glide ability of 'package; in that wind...
Sets it's ILS beam angle to point straight at that GPS X,Y,Z point in the sky...
Rocket launches... blah, blah... fairing deploys...
Fairing glides toward and then spirals down at some D distance over point X,Y
As it gets down close to Z height, it will sense the ILS beam and when the time is right, start following it down...
Fairing glides straight into the wind and straight into the net... (in theory)
SO, no radio emissions/license except a temp ILS like setup using legal frequency not used at an anywhere nearby airport... as approved by the FAA permit...
Yeah... something like that... 

https://en.wikipedia.org/wiki/Instrument_landing_system_glide_path

[TorenAltair]

Perhaps they intentionally let the first 2.0 fairing drop into the water to get a feeling about accuracy, handling, behaviour and all these things. And with all the secrecy SpaceX now apply to their new stuff, they presumably wouldn't announce that. Let the others think you still have to go a far, far way.

[IanThePineapple]

So Elon said about 1-2 hours post-launch that the sats will fly over LA about 22 hours after launch and try to send down "Hello world".

Do we know how this went? Radio silence as it usual with Starlink?

[envy887]

4 objects cataloged in orbit, one lower and elliptical... Did the upper stage fail to completely deorbit?

[speedevil]

4 objects cataloged in orbit, one lower and elliptical... Did the upper stage fail to completely deorbit?

I do wonder if they could be doing more extended coast tests.
Where was the splash zone?

[SmallKing]

4 objects cataloged in orbit, one lower and elliptical... Did the upper stage fail to completely deorbit?

I do wonder if they could be doing more extended coast tests.
Where was the splash zone?

https://forum.nasaspaceflight.com/index.php?topic=44892.msg1788363#msg1788363

[Kabloona]

So Elon said about 1-2 hours post-launch that the sats will fly over LA about 22 hours after launch and try to send down "Hello world".

Do we know how this went? Radio silence as it usual with Starlink?

FWIW, some people on Twitter saying they tried to find a  Tintin signal and couldn't. I assume they tried at the right time and place, but who knows. Couldn't find anyone who said they got a signal.

[meekGee]

I don't want to rube goldberg this[1] but maybe drones that are relaying inferred windspeed/direction back to the fairing control computer might add some accuracy?

1 - who am I kidding, yes I do. 

You can't Rube Goldberg this, it's *already* Rube Goldberg!   We'll just bolt some giant arms and a huge net onto a fast ship and try to catch a fairing falling from a spacecraft.   That's the ticket.  All it needs is the "ACME" label on the fast boat.

This is brilliant on the part of SpaceX.   ULA and Ariane, prim and proper, would die of humiliation if they tried this, and it ever failed.

I don't think the boat is trying to catch the fairing.

I think the computer controlled parachute is trying to drop the fairing onto the boat.

It tells the boat in which direction to go, then overtakes it, and cuts the cord at the right time.

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[Surfdaddy]

My gut feeling is that in many ways the fairing landing into a net by parafoil is a harder problem than landing the 1st stage on a barge.

Having flown both general aviation aircraft and also light hang-glider type ultralights in the past, as your wing loading goes down, you are more subject to buffeting and it's hard to control landing point to the level of precision that you'd need to hit that net. Flying a light General Aviation aircraft, I'm not sure I could always hit that net-sized spot landing with a plane. The more vertically you are descending, the easier it is to hit that spot. But that means a high descent rate. If you are more "flying" a wing then you have more forward velocity and it becomes harder to target a spot. And if you need to flare to reduce decent rate, then that maneuver also adds quite a bit of uncertainty about at what point you are going to hit the exact altitude of the net.

My gut also tells me that the boat, even though highly powered, has a lot of mass so that its agility is limited. The fairing probably has more agility in maneuvering/targeting, but a lot of uncertainty around the precise impact point (in this case, of the net's altitude where they will meet).

It's an interesting problem. The good news is that clearly SpaceX can get the fairing down to sea level with little to no damage. So the final challenge is landing/catching it safely. I do suspect they will solve it and hopefully my suspicions above are wrong - or at least solvable by tuning of software, aerodynamics, etc.

[aero]

I guess they could try to fly the fairing over at some low (very low) altitude then release the chutes at the right time. The fairing would drop predictably into the net. Maybe.

[meekGee]

I guess they could try to fly the fairing over at some low (very low) altitude then release the chutes at the right time. The fairing would drop predictably into the net. Maybe.

Very low, yes.  A near miss. 

This way you need to get less things right, since it doesn't matter how fast you're overtaking the boat. In exchange, you need to cut the cord when the ballistic IIP hits the net.

Sent from my R2 Plus using Tapatalk

[LouScheffer]

I guess they could try to fly the fairing over at some low (very low) altitude then release the chutes at the right time. The fairing would drop predictably into the net. Maybe.

Very low, yes.  A near miss. 

This way you need to get less things right, since it doesn't matter how fast you're overtaking the boat. In exchange, you need to cut the cord when the ballistic IIP hits the net.

Clearly the ship is helping to catch the fairing.  Ships capable of 32 knots are expensive.

The overtaking speed matters a lot.   In the reference frame of the boat, the angle of the incoming fairing is tan^-1(V_sink_fairing /(V_forward_fairing - Vship)).  If the ship can keep up with the fairing, then it appears to descend vertically.  Even if can only half keep up with the fairing, it roughly doubles the angle (from horizontal) and thus doubles the cross sectional area of the net.

I think they will control the fairing all the way into the net.  The tradeoff is the ability to make last minute corrections vs the chance of a last minute gust pushing you off course.   Human parachuters control all the way to the ground without seeming problems, and the air should be even more predictable at sea, and high up like the net.  Plus assuming the ship keeps a course into the wind, the large added constant component reduces the relative size of the gusts.  In addition, with this approach you can stall the parachute for the last second of flight, which reduces impact loads.  This is important for people, and might be a consideration for the fairing.