SpaceX Falcon 9 historic landing thread (1st landing attempt & most recent missions)

Discussion in 'The Watering Hole' started by georgegassaway, Dec 11, 2014.

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  1. Jan 6, 2015 #91

    georgegassaway

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  2. Jan 6, 2015 #92

    billspad

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    On a more positive note, the masks might keep them from catching the flu.
     
  3. Jan 7, 2015 #93

    jmattingly13

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    I'm sure some clever engineer has figured out how to fix that issue. Otherwise, I doubt SpaceX would still be considering landing on terra firma.
     
  4. Jan 7, 2015 #94

    jmattingly13

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    A quick look at an aerial photograph should make it pretty obvious where the landing site will be. At least this is the case for the Vandenberg site. Florida Today reports SpaceX is going after LC-13 down at the Cape.
     
  5. Jan 7, 2015 #95

    georgegassaway

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    Here is a graphic that an individual made up, showing the key moments of the flight for both stages and the Dragon spacecraft.

    [​IMG]

    It does leave out one thing, between #3 to #5, the "boostback maneuver" of the first stage. It seems that even with a sea landing (instead of RTLS), they will do a small boostback burn some time before re-entry.
     
    Last edited: Jan 7, 2015
  6. Jan 7, 2015 #96

    georgegassaway

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    This link is useful for maps of various Launch Complexes at Cape Canaveral:

    https://www.google.com/maps/d/viewer?msa=0&mid=z-ozVwwzQAyM.karCGNQfI72E

    LC-13 is the middle of the three LC's in this image, 2nd north of the east-west road. And CCAFS is to the west of it (left edge of map), about 1.5-2 miles away.

    [​IMG]

    [​IMG]

    Closer view:

    [​IMG]

    Now, in the longer term, possibly months from now, SpaceX would have need for TWO landing sites. Falcon-Heavy will have the outer two boosters that they will want to RTLS and lack back at the Cape. It would seem problematic to try to have both land really close to each other, sharing the land at LC-13 (and either coming in simultaneously, or perhaps one set for a higher loft boostback than the other so it lands a little bit later - seconds, not minutes). So I wonder if things go well, if they can get use of some other abandoned LC's such as #12 or #14 if those are available and would be far enough apart for parallel approaches and landings.

    Of course yet again this all assumes that SpaceX is successful in getting precision soft landings, of first stages that have launched an upper stage into space, to be successful to begin with.

    And SpaceX does not HAVE to have Falcon-Heavy's first flights to land the first stage cores safely for re-use, the prices charged are as though they are 100% expendable. But the sooner they can do that with all of the first stage cores, the better. R&D-wise, if they get any first stage core back intact from the first Falcon-Heavy flight, they'd want it to be the center core, which will have a harder task to survive and land safely, than first stages of Falcon-9 CRS-5 type missions. They'd send the ASDS Barge hundreds of miles farther downrange. And if it lands safely, they'll want to inspect the heck out of it to see how well it held up and whatever needs to be done to tweak the design and what kind of maintenance/refurbishment it may require beyond the Falcon-9 stages that land safely.

    - George Gassaway
     
    Last edited: Jan 8, 2015
  7. Jan 7, 2015 #97

    boatgeek

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    Don't forget to keep the marine side costs in perspective here. ROM cost of one of those landing barges built new is $10-20M. Buying a used barge and putting the dynamic positioning plus a landing deck on would probably be half that. Sure, you'll add a little bit for whatever controls SpaceX puts on there, but probably less than a million. You don't need to recover too many multi-million dollar first stages to make a new barge pay off.
     
  8. Jan 7, 2015 #98

    mpitfield

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    That graphic is HUGE...love the simplicity of the graphic makes it look so simple.
     
  9. Jan 7, 2015 #99

    billspad

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    "Autonomous spaceport drone ship" is the SpaceX name for it. During the prelaunch attempt press conference the SpaceX VP was having a hard time saying that without laughing.
     
  10. Jan 7, 2015 #100

    mpitfield

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    I am curious as to how they will be compensating for a platform heaving up and down due to sea swells. Does anyone know if the barge AKA "Autonomous spaceport drone ship" (man that is a mouthful) have anything built into it to compensate for the seas? I am sure the landing legs can take up some slack but they must have relatively a small threshold.
     
  11. Jan 8, 2015 #101

    Peartree

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    I don't know. But you could deal with some of it in the programming. When we learned how to crane supplies aboard heaving ships (I never had to actually do it, we just simulated) the rule was get reasonably close to see just how high the ship is heaving, and when it can almost "climb" up to your load at it's highest point...

    DROP it.

    The cranes have a release button that, for shore loading is never used, but in pitching or rolling seas you get close and then flip the release lever.

    I'm wondering if the first stage has similar programming, Get close, slow velocity to near zero, and then shut everything down and just drop the last x feet.
     
  12. Jan 8, 2015 #102

    georgegassaway

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    A lot of people have wondered about that. Apparently, the barge is simply so big that it will not heave much in swells (and will not roll much either since it is a flat-bottom wide barge as opposed to relatively narrow ships). Also being "stationary" it does not have as much trouble with swells as a ship traveling thru the water at 20 knots (Yes, I know, ocean currents and wind are an issue in keeping stationary. It has propeller-thrusters to hold position but that does mean it'll be getting some amount of wave action in some horizontal vector).

    Of course if they have a storm, it will be affected a lot regardless. And it will probably make 10 knots or so on the trips back, which may be against the prevailing wind. But they seem to have some method for securing it to the deck after landing, before the trip back, to prevent it toppling over or sliding off the deck.

    The Falcon booster lands at about 2 meters per second, it does not hover. I do not know what the landing gear is rated for, if it could take say a 4 m/s impact, if the barge did heave up and down significantly (but it seems that is not an issue). But in any case, it seems that the Falcon is landing at GPS coordinates, and does not "know" anything about what it is landing on.... it's the barge's job to be exactly where it is supposed to be, not for Falcon to find it or adjust for it. Falcon is trying to land at "X" at a specific GPS location in the ocean surface. The Barge needs to have it's center deck "X" at the same GPS location the Falcon is programmed to land at. There have been questions as to whether the barge may have GPS transponders in order to get more landing accuracy..... it seems nobody outside of SpaceX knows for sure.

    If the first flight lands successfully and the stage is say 5 meters off of center of the X, then the chicken or the egg question will be.... WHAT was off by 5 meters, Falcon, or the barge, or maybe both off for example by 2.5 meters in opposing directions.

    BTW - any minor heaving of the deck will be minimized by a dead-center landing.

    - George Gassaway
     
    Last edited: Jan 8, 2015
  13. Jan 8, 2015 #103

    stealth6

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    Hmmmm. I used to live and work at sea, on some pretty big ships, and I can guarantee that a VERY large ship can still heave a great deal in swells. Something as large as say an aircraft carrier could perhaps be pretty stable, but that barge is much tinier than that. Now I do understand that the width of the barge, and the fact that it would not be under way at the time of the landing, minimize the effect, but still. There's no way that that barge would be immune to moving up and down with the swells.

    That said, we had helicopters taking off, landing, loading and unloading, all the time - sometimes in pretty rough seas - so I know it can be done. But I would think a helicopter has a whole lot more hovering and fine control than Elon's rocket. I doubt that rocket will be coming down with anywhere near that amount of finesse.

    The weather thing is what concerns me. How can they be CERTAIN that the weather, and therefore the sea surface, will provide favorable conditions when they start a given mission. Once they launch, they pretty much have to come down when they come down, yes? It's not like they can say, "the seas are a bit rough at the moment, we'll wait it out and come down tomorrow", can they?

    All in all, this whole project is simply amazing. Obviously they've thought all these things through, plus a million other details that I couldn't even dream of, and they've got a plan or a way to address them. Incredible.

    Can't wait to see where this is all going,
    s6
     
  14. Jan 8, 2015 #104

    georgegassaway

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    UPDATE - Launch postponed to Saturday the 10th, at 4:47 AM.

    Whichever mod changed the thread title with the date and time change, thanks.

    - George Gassaway
     
    Last edited: Jan 8, 2015
  15. Jan 8, 2015 #105

    georgegassaway

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    You have some good points. A lot of people brought up much of that (and more) on forums such as nasaspaceflight. However much the barge may heave in swells, it seems that in most cases it won't be much of an issue.

    For worse weather, if SpaceX is "lucky", the weather would be bad enough at the Cape to also delay the launch. Otherwise, if the seas are going to be VERY rough, likely too much to safely land, well, for the NASA launches to resupply ISS, then SpaceX would be stuck with either trying the risky landing or letting the stage splash int the Atlantic. Because their contract is to launch a spacecraft to deliver supplies, on schedule, period. With no provision for delaying because weather may be bad for landing a reusable first stage that did not exist when the contract was signed, for which NASA is not getting a price break on if it successfully lands (in a VERY real sense, NASA is not only paying SpaceX for the CRS-5 mission, but SpaceX is getting a FREE R&D reusable first stage Test launch paid for by NASA, instead of it being a 100% SpaceX test flight).

    Now, perhaps they could ask NASA to allow for a delay, but from what I've read they are being very business-like on this in not letting their reusable program interfere with the primary objective of delivering the goods to ISS. Also consider how many times this upcoming mission has been delayed..... if a storm was brewing in the landing area this Saturday, I do not think Musk would dare ask NASA for yet another delay due to weather that has nothing to do with successfully launching supplies to ISS.

    Of course the shuttle had various weather constraints, such as bad weather at abort sites across the Atlantic (Like Rota Spain), and IIRC seas too rough to recovering SRB's. However, without Googling, IIRC, there was at least one mission that launched with very rough seas, and the SRB's to bob in the ocean for days before they could be recovered. Possibly after that, weather for SRB recovery was also considered more seriously.

    Anyway, once SpaceX has proven that they can safely land the boosters and reliably refly them, SpaceX will be in the driver's seat for writing contracts with future customers which could give SpaceX a lot of leeway for launch delays due to bad weather at sea.

    Now, back to this quote:

    Oh that is not a problem at all. Because once they launch, the stage will be landing....somewhere..... in 9 to 10 minutes. So if the weather was OK at launch time, it should be still OK 10 minutes later...... unless it was an incredibly rapid squall that suddenly developed without any weather specialists being able to forecast it was likely to happen.

    - George Gassaway
     
  16. Jan 8, 2015 #106

    Peartree

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    I've been thinking that landing on a moving deck is probably a small problem in comparison to worrying that the body of the first stage would act like a sail and get blown sideways (perhaps blown over or blown off the deck of the barge) if the winds were more than expected. That thing is BIG and has a lot of area to catch the wind. Without fuel to ballast it and without a gantry structure to support it, I have to think that the wind is going to be a significant factor.

    Of course they have some experience with the Grasshopper and I know that Texas has its share of wind, so maybe they have it all figured out, but if you've ever walked across a parking lot with a poster board or picture frame in a windy day, you've got to wonder...
     
  17. Jan 8, 2015 #107

    pyrobob

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  18. Jan 8, 2015 #108

    georgegassaway

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    As for landing in wind, see message #47: http://www.rocketryforum.com/showth...-4-47-am-EST-(Jan-10th)&p=1396395#post1396395

    At least one of the test landings of F9R v1.1 (successor to "Grasshopper") was in some significant wind, seen by the smoke/dust blown horizontally after landing. And the legspan is very wide and CG very low since the engines are "heavy" and the tankage relatively light.

    Once it land one the barge.... and only now does this come to mind, the propeller-thrusters holding it in place could either be shut down to let it drift of better yet propel it in the direction of the wind to reduce the wind loads. THough that would make it more difficult for crew members to get aboard from another ship within an hour or so after landing.

    Sliding horizontally..... many have wondered about that. There may be an ultimate low tech solution by the edges of the barge having walls sturdy enough to stop it. There is something along the edges but that info is from long-lens "spying" pics taken by SpaceX enthusiasts, and people speculating on forums what they are. Not clear if those are more to help keep people safe, or could stop the stage from sliding off the deck.

    After the ASDS barge was announced, but before there was a pic, and before there were indications that a heaving deck would not be a big problem, there was even more speculation on those issues. One idea I wondered about would be for the deck to have steel grates mounted to it, with the bottoms of the landing leg footpads having multiple prongs that could slide down between the grate openings and spring outwards to hold the feet to the deck. Sort of like steel Velcro. Before someone says the steel grates would be ruined by exhaust heat, the heat exposure would be relatively brief so probably could be sturdy enough not to fragment during landing but the area of the grating that the exhaust blasted would probably need to be replaced for each mission. The grating the feet landed on would not get hot enough to be an issue. So, that was a theoretical passive way to self-secure it to the deck when it lands, but it seems that is not as severe of a problem to use such solutions.

    But the deck is mostly smooth. There are a few pics at certain low angles that show some kind of shallow holes in a regular pattern, but they are widely spaced. Too far apart for the footpads to have a good chance of landing on. Speculation is they may be for tied-downs to help secure it with ropes after landing (Aircraft carrier decks have tie-down holes), or something else.

    There are apparently some automated systems that will help to service the boosters after landing. Don't know to what extent. Then in about an hour after landing, a crew will go onboard and secure it to the deck for the trip back, among other things.

    But for sure there is some level of risk due to high winds, there will be some amount of wind that will be too much to land reliably. And storms at sea that could be a nightmare to try to secure it to the deck and sail back safely. That's something SpaceX will end up having to risk until the reuseable program becomes operational and they write up new contracts (or renegotiate existing ones) to let them postpone launches when the weather will be too unsafe to land and/or come back after landing on te barge.

    One thing I totally speculate on is the use of R/C multicopters (drones) for documentation of the landing. SpaceX have used them for documenting some of the test flights in McGregor Texas, and the first pic of the barge seems to have been by a drone. A pic I posted a few messages back of the barge out at sea, at night, that was probably a drone shot, not a manned copter or airplane (Perhaps also testing how well it can shoot video at night). The technology exists for the drone copters to be totally autonomous. They can have one (or more for different angles) take off 5 minutes before the stage lands, fly to a spot for the desired view angle(s), point at the barge, hover, and stream the video to the barge. After the stage lands, if the drone copters would have enough battery power, they could get closer to the barge and do a fly-around of the "X" where the booster should be sitting, then land. Now, the support ships will be about 5 miles away, so it is also possible that if the R/C gear uses long-range equipment and the video signal can reliably make it to the ships, those could be flown by human pilots. The barge apparently has a number of cameras mounted to it, it would be a surprise if it did not. But the R/C copters would be capable of getting the most impressive footage.

    - George Gassaway
     
    Last edited: Jan 8, 2015
  19. Jan 8, 2015 #109

    boatgeek

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    A lot of questions about sea motions. While it's true that any size ship will move a lot in a storm, they don't have to land in a storm since that would scrub the launch. What I've seen in the papers is that the landing is about 200 miles downrange of the launch site, so the weather should be fairly comparable to the launch site and pretty well known. Broad weather patterns are pretty accurate out to a day or so, and the things that would force you to abort a landing (lightning, high winds/seas, etc.) would likely make you abort the launch, too. Space Shuttle was limited to about 20 knots wind speed at launch (depending on direction, some could go as high as 35 knots). The highest wind speed on an Apollo launch was also about 20 knots, so let's use that as a max for the launch window. If anyone has better info, let me know. 20 knots is right in the middle of Beaufort 5 conditions, which is 6-9 foot seas. As it happens, one of the main marine cargo insurance surveyors uses Beaufort 5 as their boundary for basic checks on accelerations. For a barge this size, they would recommend designing to 0.1g of heave (linear vertical motion) and 5 degrees of pitch and/or roll on a 10-second period. If Wikipedia and my math are right, that's about 3" of amplitude on the heave. Granted, the barge would be out in the Gulf Stream, where waves can be higher, shorter, and steeper, but still this is all straightforward for marine loads. For reference, a typical summer barge cargo transit to Alaska assumes 25-foot waves on 5-7 second periods, giving 0.5-0.75g side accelerations.

    As far as keeping the barge (excuse me, ASDS) on station, I'm assuming from the pictures that the barge has a dynamic positioning system on board. Looking at the pictures, it looks like a Z-drive at each corner of the ASDS. Z-drives are much like outboard motors on a larger scale--they can turn the propeller in any direction. They will not have any trouble keeping the ASDS within a meter or two of the desired position, even if one of the drives fails.

    I didn't get a good look at the pictures, but most anything that has people aboard needs handrails to keep people from falling overboard. I know, they're no fun at all anymore. There are some exceptions for things like helicopter decks, but they'll usually have horizontal nets to catch anyone who falls off the steel. Normally the handrails are 36-42" high, and there's no real reason they couldn't have put in solid steel bulwarks that high to keep the booster in place. You wouldn't want that sliding around on deck, though, or it might tip over the side when it hit the bulwark. Most likely, the shallow holes you saw are container sockets. There are a lot of D-rings that fit in the standard container sockets, and these could easily be used to tie down the booster to hard points on either the fuselage itself or on the landing legs.
     
  20. Jan 8, 2015 #110

    ThirstyBarbarian

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    On a sort of side topic, but still related to SpaceX and propulsive landings, does anyone know when the first unmanned test flights of the Dragon v2 will be? I'm looking forward to seeing Dragon land under power.
     
  21. Jan 8, 2015 #111

    jmattingly13

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    Pad abort at the Cape was supposed to be in November (2014) and inflight abort was supposed to be at Vandy in January (2015). Of course, CRS-5 was originally slated for December, so who knows. For some reason, I thought in-flight abort was supposed to happen before Jason (also at Vandy), but that's slated for March 31, which makes me think that even though Jason will inevitably get pushed back, in-flight abort will happen after that. Then add on the typical SpaceX delays and I wouldn't be surprised to not see Dragon v2 until the second half of 2015.
     
  22. Jan 8, 2015 #112

    ThirstyBarbarian

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    Thanks for the info.
     
  23. Jan 9, 2015 #113

    Raygun

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    George,
    Just a thought here, maybe ( for SpaceX) its good to know from the operations side, that it may be advantageous to have the capability to land in international waters on higher seas, free of landing rights and fees for regular operations on a case basis. Corporations, avoid paying a royalty and fees( unless the return was large enough), and prefer to make their own access to resources free( in this case, spaceports), with no middle man ( they can charge the client for this unique technology access on that point). They believe that in principle anyway,but I guess regulation would be in hot pursuit too... Its fun to speculate, storytelling and all..;).
     
    Last edited: Jan 9, 2015
  24. Jan 10, 2015 #114

    georgegassaway

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    Launch still on for early Saturday morning, at 4:47 AM EST. As I post this, that is about 7.5 hours!

    I think the Commercial Space Act, which was created to basically help companies get into space flight, covers most of those issues.

    http://www.nasa.gov/offices/ogc/commercial/CommercialSpaceActof1998.html

    It would be contrary to the intent of the act for there to be any excessive fees charged.

    SpaceX has obtained a 20-year lease with NASA for Pad 39A, to use it for Falcon-Heavy (which is supposed to fly the last half of this year) and perhaps the Big Darned Rocket (BFR) they plan to build later. In any case, NASA made the pad available for bids by commercial launch providers, and SpaceX won the bid to lease the pad.

    Seems like they are getting pretty good prices for what they are using.

    For the government-related costs of landing BACK at the Cape, other than leasing LC-13 to land at (and not counting what SpaceX will have to spend to prepare the site for their needs), I do not know if there would be any justification for any significant extra "fees" per landing.

    Launches, and space landings, at KSC and the Cape are controlled by the Eastern Test Range, run by the Air Force. I do not know, when a commercial launch vehicle is launched, if there are any special additional fees charged, or not.

    So, I think various reasons for having the landing barge (ASDS) do not include avoiding paying some exhorbitant fee for landing back. And as I say, any fee big enough to cause a company to consider a barge landing to SAVE money, would seem to be contrary to the intent of the Space Commercialization Act.

    Ironically though, SpaceX does have the spectre of paying large fees for landing on a barge! The company Blue Origin has a patent on landing a reuseable rocket on a platform in the ocean. Seems strange that a company could get that concept patented in the last 10-15 years, or whatever date it was, given all the rocket and space and sci-fi ideas throughout history. So, anyway, there may end up being a court battle over this.

    - George Gassaway
     
    Last edited: Jan 10, 2015
  25. Jan 10, 2015 #115

    jmattingly13

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    It seems more reasonable (from an infrastructure point of view) to fly the big birds from their new Brownsville site when that opens up.

    Didn't SpaceX already challenge that in court? I can't seem to remember if that's already happened or not.
     
  26. Jan 10, 2015 #116

    georgegassaway

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    SpaceX has challenged the patent, but it is still in effect.

    "SpaceX Bringing the Right Stuff to Patent Slog with Blue Origin, Expert Says"

    http://spacenews.com/42007spacex-br...-to-patent-slog-with-blue-origin-expert-says/

    A key part of that article that may favor SpaceX in having the patent killed is this:

    "A possible knockout blow for Blue Origin’s patent is a sea-landing system described by Japanese inventor Yoshiyuki Ishijima in a collection of papers, “Re-entry and Terminal Guidance for Vertical-Landing TSTO (Two-Stage to Orbit),” published in 1998 by the American Institute of Aeronautics and Astronautics. In its petition for a so-called inter partes review, SpaceX makes heavy reference to those papers and others published before the 2009 filing date on Blue Origin’s patent application."

    - George Gassaway
     
  27. Jan 10, 2015 #117

    georgegassaway

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    Little over 4 hours to go.

    I ran across SpaceX's court document to invalidate the Blue Origin patent, here:

    http://www.geekwire.com/wp-content/...s_Review_of_US_Patent_8678321_Claims_1_13.pdf

    One of the interesting parts of the filing is a reference to a report on "Test Results of an F/A-18 Automatic Carrier Landing Using Shipboard Relative GPS". This may be the type of method that the Falcon boosters are using to navigate to the landing spot, whether the landing pad on land or at sea on the ASDS Barge.

    - George Gassaway


    http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA417314

    Accession Number : ADA417314

    Title : * Test Results of an F/A-18 Automatic Carrier Landing Using Shipboard Relative Global Positioning System

    Descriptive Note : Rept. for Jan-Apr 2001
    Corporate Author : NAVAL AIR WARFARE CENTER AIRCRAFT DIV PATUXENT RIVER MD
    Personal Author(s) : Sousa, Paul ; Wellons, Lee ; Colby, Glenn ; Waters, Jack ; Weir, John

    PDF Url : http://www.dtic.mil/cgi-bin/GetTRDoc?Location=U2&doc=GetTRDoc.pdf&AD=ADA417314

    Report Date : 05 SEP 2003
    Pagination or Media Count : 34

    Abstract : Under the U.S. Department of Defense's Joint Precision Approach and Landing System program, the Navy is responsible for developing the shipboard coreponent, termed Shipboard Relative Global Positioning System (SRGPS). As part of the SRGPS effort, a test bed was developed to demonstrate air traffic control, navigation, and landing capabilities in the carrier environment. During flight testing from January through April 2001, Global Positioning System (GPS)-based automatic landings were conducted at NAS Patuxent River, Maryland, and aboard the USS THEODORE ROOSEVELT (CVN-7l) using an F/A-18A Hornet test aircraft. This report describes the overall SRGPS test effort. The report also gives an overview of the test bed hardware, as well as results for navigation sensor error, flight technical error, and total system error. The test and analysis results support the feasibility of the GPS-based precision approach and landing system concept.

    Quote from part of the PDF file:

    INTRODUCTION
    1. Joint Precision Approach and Landing System (JPALS) is a revolutionary, next generation, Precision Approach and Landing System (PALS) under development by the Department of Defense (DoD). JPALS includes both the sea-based variant. Shipboard Relative Global Positioning System (SRGPS) - which provides precision navigation and two-way Air Traffic Control (ATC) for sea-based aircraft operations - as well as the local differential systems for providing precision landing capability ashore. The SRGPS will support all ATC functions including takeoff, departure, taxi, marshal (holding), approach, landing, bolter, missed approach, and long-range navigation as shown in figure I. SRGPS will be compatible with Naval Emissions Control requirements and the associated avionics provide complete interoperability with DoD, Allied, and civil navigation systems. In addition to supporting manned aircraft, SRGPS will fully support automatic takeoff, departure, approach, landing, and ATC automation required by future unmanned systems such as the Naval Unmanned Combat Air Vehicle.

    Figure 1: SRGPS Concept

    2. SRGPS shares some basic concepts with local differential Global Positioning Systems (GPSs) used ashore (such as the FAA's Local Area Augmentation System (LAAS)), but with a few important differences. Any local differential DGPS relies on the fact that relative measurements between two GPS receivers in the same local geographic area can be made very accurately. When the solutions of two receivers utilizing the same satellites are compared, common mode errors such as satellite clock, satellite ephemeris (orbit errors), and atmospheric transmission errors, generally cancel out. This comparison of two GPS receiver's measurements of one satellite is termed a single difference. Since one ground system is meant to serve multiple aircraft, a technique was developed where the ground system broadcasts differential corrections to all aircraft. Each aircraft uses only those corrections that correspond to valid satellite measurements in its own receiver. In addition, these corrections would be made to a surveyed point, resulting in not only an accurate relative solution, but also an accurate absolute position (in the GPS coordinate frame, WGS-84). To use this accurate position for navigation, the glidepath (defined by a set of path points) and waypoint data are sent to the aircraft via the data broadcast.

    3. In the SRGPS concept, the "reference station" is installed on a ship instead of a fixed surveyed point in the WGS-84 coordinate frame. The GPS antenna location(s) aboard ship are precisely surveyed in the ship body axis relative to the inertial system locations, the ship's center of motion, and the aircraft touchdown point. This ensures that accurate relative vectors are maintained as the ship translates through the water, pitches, rolls, and yaws around its center of motion. In addition, the center of motion itself may translate up/down (heave), side to side (sway), and fore and aft (surge). Any location away from the center of motion (such as the GPS antenna location, or aircraft touchdown point) will experience additional heave, sway, and surge
    due to the lever arm effect. Despite this motion, a single difference calculation between a ship antenna and aircraft antenna can be made just as accurately as its shore-based counterpart. The primary difference is simply that the differential correction technique is not used, since absolute positioning accuracy is not required.

    4. Instead of a correction, the shipboard GPS transmits whole satellite measurements to the aircraft and the aircraft directly compares aircraft and ship solutions based on a common set of satellites. This method produces an accurate relative vector between the two antenna locations, which are further translated to the ship and aircraft centers of motion and the reference flightpath points. For tailhook equipped aircraft, the hook point is intended to touchdown halfway between the second and third arresting gear wires on the ship. These translations are made through the use of precision Inertial Navigation System (INS) measurements on the ship and the aircraft.

    5. In addition, unlike the shore approach, the ship flightpath is calculated in a dynamic fashion. The approach path is stabilized for ship motion until approximately 10 sec (0.3 nmi) from touchdown. At this point, the aircraft is commanded to follow the touchdown point sway and heave motions during the final portion of the approach. This portion of the approach is termed the Deck Motion Compensation phase. The aircraft is controlled in reference to an approach heading that is based on a filtered cant deck heading to allow for ship turns and yaw motions during the aircraft's approach.

    6. The safe landing area aboard ship is much smaller than runways at major airports. Aircraft landing off centerline by more than 3 m (-10 ft) laterally can result in the aircraft's wingtip being dangerously too close to obstructions on the flight deck. The aircraft's hook path over the end of the landing area, termed the hook to ramp clearance, is only 4.3 m (-14 ft). The most demanding requirement for a shore-based LAAS system is 2 m (-6.5 ft) of vertical navigation system error to accomplish an automatic landing. Aboard ship, 2 m of vertical error would result in an unsafe landing condition. The SRGPS requires 0.4 m (-1.3 ft) vertical error to accomplish a safe
    automatic landing. Figure 2 shows a 1.5 sec time lapse of an aircraft arrestment, showing both the wire locations and the ideal touchdown point.
    NAWCADPAX/RTR-2003/122

    Figure 2: Aircraft Carrier Landing

    7. To meet the requirement for shipboard landings, further refinements to the standard single difference technique were made. A double difference calculation is made where all satellite measurements at both receivers are also compared against a key satellite. The double difference solution is smoothed in a Kalman filter and the resulting solution is termed the float solution. From this float solution, a carrier phase integer ambiguity determination is made using the LAMDA method developed by Teunissen, reference 1.
     
    Last edited: Jan 10, 2015
  28. Jan 10, 2015 #118

    georgegassaway

    georgegassaway

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    Here is a pretty good image of the ASDS barge. Taken from onboard a cruise ship docked behind it (Carnival Fascination).

    [​IMG]
     
  29. Jan 10, 2015 #119

    Jesse

    Jesse

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  30. Jan 10, 2015 #120

    BLKKROW

    BLKKROW

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    T-2:00

    I am up and waiting again, its only 2:45am and will have a long day at work lol.

    T+2:50 MECO

    T+6:00 First and Second Stage Power and Telemetry Nominal
    T+7:00 Stage one engine start up

    Signal is lost on the first stage. Which is to be expected, they stated more details will be available as the recovery team brings back more data.
     
    Last edited: Jan 10, 2015

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