Author Topic: SpaceX Eastern Range Landing Facilities  (Read 217106 times)

Offline MichaelBlackbourn

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Re: SpaceX Eastern Range Landing Facilities
« Reply #340 on: 05/04/2016 03:42 AM »
I don't think they will vary the EIS.

There will be only a single landing. No simultaneous landings.

After the first booster has landed the second booster will arrive on a slightly different trajectory and then will land. We are only arguing about how long this delay counts as 'non simultaneous'.

I'm guessing it will be technically impossible to land two boosters at the 'same' time.

Three serial landings.

Offline nadreck

Re: SpaceX Eastern Range Landing Facilities
« Reply #341 on: 05/04/2016 06:23 AM »

I'm guessing it will be technically impossible to land two boosters at the 'same' time.


They are autonomous in landing, why would it be technically impossible? If their margin of error is X meters  and they land on pads with centres > 2X meters apart all is well.  Or do you simply mean that there will always be some number of milliseconds difference in the moment they touch down, in which case, of course that is correct but it seems a moot point in the context of the discussion here.
It is all well and good to quote those things that made it past your confirmation bias that other people wrote, but this is a discussion board damnit! Let us know what you think! And why!

Offline cscott

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Re: SpaceX Eastern Range Landing Facilities
« Reply #342 on: 05/04/2016 12:20 PM »
I think he is referring to range tracking, which we've been told needs to be updated to support simultaneously tracking two targets.  My understanding, however, is that (a) autonomous flight termination equipment will address this limitation (although it was not successfully demonstrated on the CRS-8 launch), and (b) the range recognizes the tracking limitation and is working with SpaceX to address it.  So perhaps the first landings will be serial, but that's not a situation that will persist.  The EIS will eventually be updated.
« Last Edit: 05/04/2016 12:20 PM by cscott »

Offline cscott

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Re: SpaceX Eastern Range Landing Facilities
« Reply #343 on: 05/04/2016 12:22 PM »
As I understand supersonic retropropulsion, when thrusting from a single engine through the center of the shock front, it doesn't actually push the shock front away from the engine, but instead punches through it, and causes a loss of the aerodynamic drag you'd normally gain from the shockwave. For the shock front that would be at the engines (if  they weren't running) to push out ahead of the engines they would need to run the 8 outer engines to push the shockwave ahead of the stage, not the center engine.

Would the exhaust itself on it's own generate a shock front? Since the center engine running is "punching through" the shockwave, rather than pushing it away as running engines along the periphery of the stage would do, shockwave drag should be almost entirely eliminated with only thrust from the engine providing any major reduction in speed. What would this do to the shockwave, does it somehow "collapse" or otherwise cease to exist at that area? Perhaps this is part of why nothing seems to line up with observed audio...
It does seem clear that the situation is not straightforward!  Perhaps some examination of the supersonic retropropulsion video that NASA posted might lend some clues?

Offline CorvusCorax

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Re: SpaceX Eastern Range Landing Facilities
« Reply #344 on: 05/05/2016 11:04 PM »
As I understand supersonic retropropulsion, when thrusting from a single engine through the center of the shock front, it doesn't actually push the shock front away from the engine, but instead punches through it, and causes a loss of the aerodynamic drag you'd normally gain from the shockwave. For the shock front that would be at the engines (if  they weren't running) to push out ahead of the engines they would need to run the 8 outer engines to push the shockwave ahead of the stage, not the center engine.

Would the exhaust itself on it's own generate a shock front? Since the center engine running is "punching through" the shockwave, rather than pushing it away as running engines along the periphery of the stage would do, shockwave drag should be almost entirely eliminated with only thrust from the engine providing any major reduction in speed. What would this do to the shockwave, does it somehow "collapse" or otherwise cease to exist at that area? Perhaps this is part of why nothing seems to line up with observed audio...
It does seem clear that the situation is not straightforward!  Perhaps some examination of the supersonic retropropulsion video that NASA posted might lend some clues?

I don' t have the expertese to interpret that video, however supersonic retropopulsion has been discussed in various other threads.Unfortunately I can't find it, but one of them had a paper to a study on retropropulsion on martian entryand its effect ( link anyone? )

The gist was, your exhaust does in all cases push "into" the airstream and offset the shock front but:

If you run "outer engines" at low throttle,then they create a short but wide pressure zone. This acts like a large blunt heat shield and makes awide angled shock front, resulting in pretty massive drag (acting on the vehicleby the highpressure area in front of it. You have basically a "virtual heat shield" and the drag force is much higher than the effective engine thrust alone.

The opposite happens if you run a center engine at high thrust. This offsets the shock front to the tip of a long narrow exhaust column. But this pointed ness actually reduces drag ( narrow angled shock cone) and your deceleration is caused exclusively by engine thrust force.

However, with a relatively narrow vehicle like the F9, both shockcone shapes should asily clear the bottom of the stage imho, so no  boom caused by engine compartment itself while under thrust

Online DAZ

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Re: SpaceX Eastern Range Landing Facilities
« Reply #345 on: 05/06/2016 02:06 AM »
If anybody’s looking for additional audio recordings approximately 7 seconds into the 360 barge landing video (you can see the shockwave scare up a bird off the deck to the right) you can hear the arriving Sonic Booms.  They are much closer together than the other audio recordings and almost overlapping.  It is difficult to distinguish the 3 individual booms from the recording.

Analyzing where the shock waves are coming from studying the audio recordings may not be possible as the situation is not static.  We can pretty much assume that as the stage is decelerating from high supersonic toward mack 1 that it is producing the classical N-wave.  There is a shockwave being produced of the engine bells, the aft of the stage (now the forward end) and the folded landing legs.  The shockwave is probably all pretty much merge into one perceptible wave.  At the other end of the stage the grid fins and aftershock wave pretty much merge together at the other end.  As the engine starts just above supersonic it could be presumed that it produces a shockwave at this point but as the stage is quickly decelerating below supersonic at that point the production of all high-pressure shockwaves would cease.  No new shockwaves would be produced but the shockwaves that had been produced would continue to radiate away from the vehicle.  It is these shockwaves that we hear in the recordings.  It may not be possible to determine how many shockwaves or where they’re being produced.  As soon as the new ones are being produced they collapse and radiate away from the vehicle with the previous produced shockwaves.

Depending on the distance from the vehicle different shockwaves may be heard.  Directly underneath it there all almost on top of each other.  From a distance of, let’s say, 5 – 8 miles we may hear 3 distinct booms.  From a distance of 15 – 20 miles we may hear only the classical 2 booms.  All of this could be due to observers at different distances having different paths to the returning vehicle and as such can only perceive the shockwaves being generated at the time the vehicle was traveling along those paths.

Offline Lars-J

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Re: SpaceX Eastern Range Landing Facilities
« Reply #346 on: 05/06/2016 06:27 AM »
As I understand supersonic retropropulsion, when thrusting from a single engine through the center of the shock front, it doesn't actually push the shock front away from the engine, but instead punches through it, and causes a loss of the aerodynamic drag you'd normally gain from the shockwave. For the shock front that would be at the engines (if  they weren't running) to push out ahead of the engines they would need to run the 8 outer engines to push the shockwave ahead of the stage, not the center engine.

No, that's a common misconception. That effect - of a single engine doing retro-propulsion and reducing drag - only happens at *LOW* thrust. At high thrust you get the normal effect.

Offline mvpel

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Re: SpaceX Eastern Range Landing Facilities
« Reply #347 on: 05/06/2016 09:27 AM »
I think he is referring to range tracking, which we've been told needs to be updated to support simultaneously tracking two targets.

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Offline biosehnsucht

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Re: SpaceX Eastern Range Landing Facilities
« Reply #348 on: 05/06/2016 09:18 PM »
As I understand supersonic retropropulsion, when thrusting from a single engine through the center of the shock front, it doesn't actually push the shock front away from the engine, but instead punches through it, and causes a loss of the aerodynamic drag you'd normally gain from the shockwave. For the shock front that would be at the engines (if  they weren't running) to push out ahead of the engines they would need to run the 8 outer engines to push the shockwave ahead of the stage, not the center engine.

No, that's a common misconception. That effect - of a single engine doing retro-propulsion and reducing drag - only happens at *LOW* thrust. At high thrust you get the normal effect.

Are you agreeing with the part you bolded, or saying the bolded part is the misconception? I understand that the increase of drag only works at low thrust when using a center engine, at high thrust the flame "punches through" and you actually have less drag from what I understand. Supposedly thrust around the sides instead of from the center though would allow for a much higher thrust while keeping the drag force in addition to the thrust force, vs thrust from the center.

If I've got it wrong, then I'd like to get it right :)

Offline CorvusCorax

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Re: SpaceX Eastern Range Landing Facilities
« Reply #349 on: 05/06/2016 11:06 PM »
you always have a shock front where (air) molecules that move with the speed of the vehicle hit against air molecules flying towards the vehicle at (super)sonic speeds.

If you run engines, you direct high pressure exhaust molecules against the stream. They quickly decelerate though until they reach the same speed as the stage itself, and in front of that you get the usual shock front.

The only thing that changes is the shape of the shock front, and where it occurs.

narrow pointed shape: narrow angled shock cone - low drag (but in case of reentry, a lot of heating as parts of the vehicle can protrude beyond the shock cone and get exposed to the full onslaught themselves (in case of supersonic aircraft for example wings)

blunt shape: wide angled shock cone - high drag (in case of reentry, the whole vehicle fits into the shadow of the shock cone)

now with engines at the rim of the base, you'd more likely create a wide angled "cushion" in front of the stage. Effectively you can create a "blunter" and wider virtual base behind which the vehicle can hide itself from reentry heat (but it still gets the heat of its own exhaust which is usually pretty hot)
that way you also get more deceleration (which harmlessly heats exhaust gas safely away from the actual metal) without necessarily needing too much engine power.

with a center engine on sufficient thrust you make the cone narrower, the virtual shape pointier, and you get less air drag. Instead your engine thrust decelerates the vehicle.

There are some retropropulsion configurations where you can increase the deceleration force by more than your engine thrust force, amplifying your engines. I assume that's what SpaceX does during the reentry burn.

There's also potentially some retropropulsion configurations where the decrease in drag is actually higher than your effective engine thrust, so your retropropulsion actually helps you cut through the atmosphere more streamlined. You decelerate less than you would with no engines at all. This might make sense for some very steep reentries where a vehicle is facing too high G forces and needs to "soften" the atmospheric impact.

The paper link I still didn't find analyzed this in respect to optimizing the entry delta-V achievable with a certain amount of propellant in the thin martian atmosphere and retropropulsive aerobraking (unlike earth there's a real risk of hitting the ground before the atmosphere even slowed you to terminal velocity - which is pretty high itself compared to earth)

I'll search google scholars, maybe i can find a link

Offline CorvusCorax

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Re: SpaceX Eastern Range Landing Facilities
« Reply #350 on: 05/06/2016 11:08 PM »
« Last Edit: 05/06/2016 11:18 PM by Chris Bergin »

Offline IntoTheVoid

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Re: SpaceX Eastern Range Landing Facilities
« Reply #351 on: 05/07/2016 05:02 AM »
There was also this paper which was referenced a while back somewhere here on NSF.

http://www.ssdl.gatech.edu/papers/phdTheses/CordellC-Thesis.pdf

Offline biosehnsucht

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Re: SpaceX Eastern Range Landing Facilities
« Reply #352 on: 05/07/2016 05:59 AM »
you always have a shock front where (air) molecules that move with the speed of the vehicle hit against air molecules flying towards the vehicle at (super)sonic speeds.

...

The paper link I still didn't find analyzed this in respect to optimizing the entry delta-V achievable with a certain amount of propellant in the thin martian atmosphere and retropropulsive aerobraking (unlike earth there's a real risk of hitting the ground before the atmosphere even slowed you to terminal velocity - which is pretty high itself compared to earth)

I'll search google scholars, maybe i can find a link

Thank you for the in depth information. Seems like I was half on the right track, half not, and this cleared up a lot of details I wasn't really sure of.

Online FutureSpaceTourist

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Re: SpaceX Eastern Range Landing Facilities
« Reply #353 on: 05/24/2016 06:58 PM »
Quote
USAF: SpaceX's landing complex at the Cape Canaveral Spaceport is a multi-user facility...not only for Falcon-9. #SpaceCongress2016

https://twitter.com/flspacereport/status/735157372809838592

Offline envy887

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Re: SpaceX Eastern Range Landing Facilities
« Reply #354 on: 05/24/2016 07:06 PM »
Quote
Edward Ellegood ‏@FLSPACErePORT  9m9 minutes ago
SpaceX at #SpaceCongress2016: Initial reuse of Falcon-9 limited to components: engines, landing legs, paddles, etc. Not entire booster.

What is a paddle?

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Re: SpaceX Eastern Range Landing Facilities
« Reply #355 on: 05/24/2016 07:08 PM »
Quote
USAF: SpaceX's landing complex at the Cape Canaveral Spaceport is a multi-user facility...not only for Falcon-9. #SpaceCongress2016

https://twitter.com/flspacereport/status/735157372809838592

Multi-user or multi-vehicle? I think we might need some clarification on that... what other users (companies) would be landing there?
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Offline Kabloona

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Re: SpaceX Eastern Range Landing Facilities
« Reply #356 on: 05/24/2016 07:20 PM »
Quote
Edward Ellegood ‏@FLSPACErePORT  9m9 minutes ago
SpaceX at #SpaceCongress2016: Initial reuse of Falcon-9 limited to components: engines, landing legs, paddles, etc. Not entire booster.

What is a paddle?

Probably meant grid fins.

Offline envy887

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Re: SpaceX Eastern Range Landing Facilities
« Reply #357 on: 05/24/2016 07:24 PM »
Quote
Edward Ellegood ‏@FLSPACErePORT  9m9 minutes ago
SpaceX at #SpaceCongress2016: Initial reuse of Falcon-9 limited to components: engines, landing legs, paddles, etc. Not entire booster.

What is a paddle?

Probably meant grid fins.
That could explain the "patches" and heavy damage on the JCSAT-14 grid fins.

Online FutureSpaceTourist

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Re: SpaceX Eastern Range Landing Facilities
« Reply #358 on: 05/24/2016 07:51 PM »
what other users (companies) would be landing there?

I'm assuming Blue Origin (eventually).
« Last Edit: 05/25/2016 03:25 AM by FutureSpaceTourist »

Online Coastal Ron

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Re: SpaceX Eastern Range Landing Facilities
« Reply #359 on: 05/24/2016 07:56 PM »
Quote
USAF: SpaceX's landing complex at the Cape Canaveral Spaceport is a multi-user facility...not only for Falcon-9. #SpaceCongress2016

https://twitter.com/flspacereport/status/735157372809838592

Multi-user or multi-vehicle? I think we might need some clarification on that... what other users (companies) would be landing there?

I would imagine that statement is pretty standard.  That the entire range supports multiple users, whether they exist today or not.

And it may also mean that what the USAF does won't be customized just for one user.  Which is a good thing, since in this case SpaceX is being a pathfinder for many capabilities, and I'm sure we all hope others will follow.  And when they do, the USAF will be ready to support them too.

My $0.02
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