Answers to questions. Kourou is in Guyane in S America: 5.2N,52.7W. All Arianes are launched from there. I am part of a team who wrote the flight program for the on-board-computer on the Ariane 4 (and 1,2 and 3). This does the navigation, guidance, attitude control etc from a few secs before liftoff to a few minutes after payload release. We also update the program, run a standard set of tests for each launch, and analyse the telemetry after the launch. We have nominal position and velocity in earth-centred inertial coordinates; for the Spot launch from -9s to 1600s. These I converted into the table in my 1 May email. >From Bjorn Gimle (thanks) I deduce that a "trj" file is 4 columns with time(sec) Lat Long Height(km), so I will provide that in the future. Do the number of spaces between columns matter? Are further columns to the right permitted in a trj file? I was (first time for me) at the "Jupiter" control centre about 15km from the launch pad, and saw the launch up to about liftoff+5min, when I suspect it went behind clouds, but possibly the third stage (burning Lox & LH2) is less visible. Payload separation was scheduled at launch+19m 15s = 015101, but the actual time depends on the time of cutoff (typical variation 5 or 10secs) and duration of the reorientation manoevres after stage 3 cutoff, and this depends on the angular rates at cutoff, and this depends critically on many things in the last few seconds before cutoff. Variations of 10 or 20 secs are common. I do not have actual flight details yet. I see that many observers saw the fuel dump(s), and some saw the rocket. There is almost always some unused fuel when orbit is reached. Fuel dumps are done to avoid later explosions of rockets; most rockets do fuel dumps. >From the mission data Lox, LH2 and in-orbit orientation propellant Lox & LH2 dumping (main stage 3 propellants) starts about 5min after cutoff, and in-orbit orientation propellant dumping a few minutes later. Times uncertain by tens of secs as above. Some parts of Spot are covered with shiny orange material. Spot 5 is externally identical to its predecessors, the rocket is identical. Spot will do several small manoevres (I dont have details, we just put it into orbit): so may be a minute or more away from predictions for one or two weeks. The IDEFIX payload (French amateur comms) will remain attached to the rocket stage. For Spot the orbit that our guidance is trying to reach is Apogee=812612.6 Perigee=793913.5 relative to earth radius 6378135m Incl=98.744 Arg of perigee=120.0589 Longitude of ascending node=4.68847 This longitude is relative to the longitude of the launch site (-52.77583) at the time of platform release. Platform release is when the navigation reference is defined = H0-9s = liftoff-13.4s. For most missions the longitude of ascending node has the same value whenever the launch occurs, but for sun-synchronous missions (like this one) the longitude is fixed inertially: so that if the launch is 10min late then the trajectory over the earth is more West, but the orbit has the required RA of ascending node. Although the navigation uses the J2 gravity coefficient (equator bulge) the guided orbit above is calculated from position & velocity but no J2 (I think this is called an "osculating" orbit). The guidance optimises the point at which the rockets reaches the required orbit, so the mission data does not have a required time of equator crossing (or equivalent time). The actual orbit will be slightly different, mostly due to errors in the navigation reference (laser gyros & accelerometers), typically by about 1m/s. Fuel dumps may affect the orbit of the rocket by a similar amount, but not the orbit of the payload. mike.waterman@marconi.com (work) mike.waterman@web-hq.com (home: not checked very often) ----------------------------------------------------------------- Unsubscribe from SeeSat-L by sending a message with 'unsubscribe' in the SUBJECT to SeeSat-L-request@lists.satellite.eu.org http://www.satellite.eu.org/seesat/seesatindex.html
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