Author Topic: SpaceX Eastern Range Landing Facilities  (Read 179311 times)

Offline old_sellsword

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Re: SpaceX Eastern Range Landing Facilities
« Reply #480 on: 11/30/2017 04:43 PM »
This might be a stupid question, but what's the point of a landing radar since the trajectory is pre-programmed and can't be changed mid-flight from the ground...

They use radar to get more precise altitude readings as they approach the pad.

Is the AFTS re-armed for landings?

No, you can hear the "Stage 1 FTS is safed" callout sometime after MECO.

Offline John Alan

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Re: SpaceX Eastern Range Landing Facilities
« Reply #481 on: 11/30/2017 04:43 PM »
The ground radar gives the Stage much faster (readings per second) altitude above the landing surface for the last 1000' or so... Much more so then the GPS can do...
More reads and more accurate... why it's there and kinda important... to stick the landing...  ;)

Offline octavo

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Re: SpaceX Eastern Range Landing Facilities
« Reply #482 on: 11/30/2017 06:48 PM »
The ground radar gives the Stage much faster (readings per second) altitude above the landing surface for the last 1000' or so... Much more so then the GPS can do...
More reads and more accurate... why it's there and kinda important... to stick the landing...  ;)
Most especially on a pitching drone ship deck.

Offline rpapo

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Re: SpaceX Eastern Range Landing Facilities
« Reply #483 on: 11/30/2017 08:39 PM »
This might be a stupid question, but what's the point of a landing radar since the trajectory is pre-programmed and can't be changed mid-flight from the ground, or is it just the launch trajectory that can't [per Jim}? Is the AFTS re-armed for landings?
One reason: GPS is much less accurate in Z than in X and Y.  And Z really matters in the last few seconds of the landing.
« Last Edit: 11/30/2017 08:39 PM by rpapo »
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Online speedevil

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Re: SpaceX Eastern Range Landing Facilities
« Reply #484 on: 11/30/2017 10:54 PM »
This might be a stupid question, but what's the point of a landing radar since the trajectory is pre-programmed and can't be changed mid-flight from the ground, or is it just the launch trajectory that can't [per Jim}? Is the AFTS re-armed for landings?
One reason: GPS is much less accurate in Z than in X and Y.  And Z really matters in the last few seconds of the landing.

GPS is also so low power it can be almost trivially jammed, perhaps even accidentally.
Something you certainly don't want to happen in the last 50m.

Offline CyndyC

Re: SpaceX Eastern Range Landing Facilities
« Reply #485 on: 11/30/2017 11:53 PM »
Those are some very interesting characteristics & differences between GPS & radar, but my point was no matter how they watch, I didn't think the landing trajectory could be altered once it was programmed. There was a big discussion in an Iridium thread with Jim insisting no changes to a launch could be made from the ground, so I wrongly assumed changes couldn't be made at all, or couldn't be made to landings either. I take it the responses imply there are some "IF/THEN" scenarios built into the programming in the avionics inside the interstage, just nothing from the ground.
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Offline launchwatcher

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Re: SpaceX Eastern Range Landing Facilities
« Reply #486 on: 12/01/2017 12:12 AM »
Those are some very interesting characteristics & differences between GPS & radar, but my point was no matter how they watch, I didn't think the landing trajectory could be altered once it was programmed. There was a big discussion in an Iridium thread with Jim insisting no changes to a launch could be made from the ground, so I wrongly assumed changes couldn't be made at all, or couldn't be made to landings either. I take it the responses imply there are some "IF/THEN" scenarios built into the programming in the avionics inside the interstage, just nothing from the ground.
The planned trajectory is not altered after launch.   Because nothing's perfect, the vehicle can't and won't exactly follow the planned trajectory; instead, it needs to be able to continuously estimate how far away it is from the planned trajectory so it can correct its actual trajectory to approach the planned trajectory. 

Think "solving for [dx, dy, dz, z] = [0,0,0,0]" rather than "if/then".




Offline e of pi

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Re: SpaceX Eastern Range Landing Facilities
« Reply #487 on: 12/01/2017 12:24 AM »
Those are some very interesting characteristics & differences between GPS & radar, but my point was no matter how they watch, I didn't think the landing trajectory could be altered once it was programmed. There was a big discussion in an Iridium thread with Jim insisting no changes to a launch could be made from the ground, so I wrongly assumed changes couldn't be made at all, or couldn't be made to landings either. I take it the responses imply there are some "IF/THEN" scenarios built into the programming in the avionics inside the interstage, just nothing from the ground.
Yeah, the avionics on pretty much any launch vehicle these days are "smart". For instance, IIRC, ULA's avionics on Atlas are smart enough they can take into account wind speeds and change the ascent profile midflight to  reduce angle of attack and resulting aerodynamic stresses, expanding the margin for allowable upper level winds.The computers have sensors, use that to make a model of the state of how they're flying, compare to a given state they want to achieve, and rules about the actions they can take to push the state-as-it-is to the state they want.

Similarly, Falcon on descent needs to account for winds pushing it around in the upper atmosphere, variable atmospheric braking that might result from varying density (due to temperature/humidity/whatever), and then dynamically steer itself with the grid fins to remain on target, not just hold attitude, then pick the right moment before impact to start firing its engine(s) for landing. If the atmosphere slows it down by 1 m/s more or less than expected, then over the last minute or so before landing, the stage's altitude could be plus or minus 60m--more than its own height! You need a closed-loop onboard control system to adjust to that kind of change.

Offline deruch

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Re: SpaceX Eastern Range Landing Facilities
« Reply #488 on: 12/01/2017 01:39 AM »
And SpaceX is using some kind of special heat-resistant cement, I think. And a generous layer of radar-reflective paint.

It doesn't seem it would matter whether or not the concrete itself is heat resistant if it's coated with reflective paint,

I hadn't heard about the heat-resistant cement, but if they are using it, it makes sense because any spalling/degredation of the concrete as it gets hit with the F9 exhaust on landing is going to create a lot of FOD getting blasted everywhere, including potentially back into the vehicle itself or a side core landing on the next pad.
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Offline CyndyC

Re: SpaceX Eastern Range Landing Facilities
« Reply #489 on: 12/01/2017 02:53 AM »
And SpaceX is using some kind of special heat-resistant cement, I think. And a generous layer of radar-reflective paint.

It doesn't seem it would matter whether or not the concrete itself is heat resistant if it's coated with reflective paint,

I hadn't heard about the heat-resistant cement, but if they are using it, it makes sense because any spalling/degredation of the concrete as it gets hit with the F9 exhaust on landing is going to create a lot of FOD getting blasted everywhere, including potentially back into the vehicle itself or a side core landing on the next pad.

Omigosh, silly me, I was thinking only of heat from sunlight (I've had to spend almost all of this year devoted to refurbishing more conventional real estate). What component(s) could possibly make concrete more heat resistant, or perhaps more importantly what component(s) were omitted would be a subject of curiosity for some. The research paper I mentioned discussed tests of 32 different mixes. Cement is only one component of concrete, and the researchers used either white or gray Portland, along with selections from 4 different types of sand and 4 different types of rocks, each pictured on page 4 of the paper. Below is the chemical composition of each cement, and the most obvious answer is to leave out all the iron in gray Portland. Rocks come into play increasingly after abrasion.

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Offline georgegassaway

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Re: SpaceX Eastern Range Landing Facilities
« Reply #490 on: 12/01/2017 03:34 AM »
The planned trajectory is not altered after launch.   Because nothing's perfect, the vehicle can't and won't exactly follow the planned trajectory; instead, it needs to be able to continuously estimate how far away it is from the planned trajectory so it can correct its actual trajectory to approach the planned trajectory. 

Think "solving for [dx, dy, dz, z] = [0,0,0,0]" rather than "if/then".

This video about guidance comes to mind (I know many have seen this before).  "The missile knows where it is at all times. It knows this by knowing where it isn't.....".  Educational and a bit funny.  Intended for explaining guidance for  missiles hitting a target, but also applicable for steering a planned trajectory along the way to the target (some like the Tomahawk may make several planned course changes along the way to the target).



The landing radar is ONBOARD the Falcon.  Think Lunar Module Landing Radar (Radar altitude system mounted on the base of the Descent Stage).  It has been stated by many, on many occasions, that the F9 uses no uplinked ground signals for the landing process (with the caveat that IIRC, SpaceX has not officially said this (?). ). So ground-based radar can be useful for live tracking to see "where it is", or for later analysis, but not to actively assist the booster with the landing.

Dec 11th update - Came across this video recently, by Ryan.  About how the LM Landing Radar was fabricated. And at about 4:50 into it,  "why" it was needed and how it was used for landing. Obviously F9 does not use mid 1960's landing radar, and not exactly the same way (but both need/needed to be extremely accurate the last few hundred feet). But I hope it's of some value for this thread and otherwise.

« Last Edit: 12/11/2017 07:26 AM by georgegassaway »

Online gongora

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Re: SpaceX Eastern Range Landing Facilities
« Reply #491 on: 12/12/2017 10:13 PM »
[Florida Today] NASA talks underway about potential rocket landing site at KSC
Quote
In the future, the rockets may target another local landing site: a proposed pad at Kennedy Space Center that is the subject of early discussions between the Air Force, NASA and Space Florida.

The goal is to lessen the burden landings impose on the Cape’s nearby industrial area, which workers must evacuate for hours during some missions.
...
As outlined in KSC’s master plan, the new landing pad could be built near the northern end of the spaceport’s secure perimeter — north of pad 39B and south of State Road 402 leading to Canaveral National Seashore's Playalinda Beach.
...
It was not immediately clear who would pay for the landing pad and if it would be exclusive to SpaceX or potentially available for other uses.

Online FutureSpaceTourist

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Re: SpaceX Eastern Range Landing Facilities
« Reply #492 on: 12/15/2017 03:02 PM »
Excellent launch and landing!

Anyone else think for a few seconds that the Falcon 9 was WAY off from the landing pad on final approach--  :-\

--until you realized that the second landing pad was now complete?

Congratulations to SpaceX, CCAFS and NASA. Onward with the mission.

For those that missed shot of second pad

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Re: SpaceX Eastern Range Landing Facilities
« Reply #493 on: 12/15/2017 04:47 PM »
Quoting from today's post launch press conference:

FH landing pads.

LZ-2 will be ready.  It's right next to LZ-1.  Center core to ASDS Of Course I Still Love You.
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Online docmordrid

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Re: SpaceX Eastern Range Landing Facilities
« Reply #494 on: 12/15/2017 05:37 PM »
That shot is missing a circular feature north of LZ-1 and LZ-2, visible for a very few frames on the technical webcast. Any ideas? LZ-3 for a triple RTLS?

« Last Edit: 12/15/2017 05:38 PM by docmordrid »
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Offline rpapo

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Re: SpaceX Eastern Range Landing Facilities
« Reply #495 on: 12/15/2017 05:45 PM »
That shot is missing a circular feature north of LZ-1 and LZ-2, visible for a very few frames on the technical webcast. Any ideas? LZ-3 for a triple RTLS?
That should be where the stand the booster gets bolted to is placed.
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