Quote from: Kabloona on 01/06/2015 09:42 pmQuote from: Antares on 01/06/2015 09:39 pmThere would have to be a force physically causing the drift. Recalibration would be insufficient without determining where that force is coming from then either eliminating it or determining it can be withstood in flight.That's assuming there was actual physical drift as opposed to signal drift from a bad LVDT or other electronic component in the position feedback system. Also, since the actuator is fueldraulic, a leaky servovalve could also cause drift without external force being applied.Contamination of the servovalve might also be an issue.QuoteMay just need to replace the whole actuator.They have to drain the hydraulic system (you don't want to have oily fluid everywhere), remove the actuator, adding a new one, taking care of contamination (typically these things are handled in lower class clean rooms) and afterwards the system must be flushed to remove entrapped air. Which takes some time. The dark side of hydraulic.
Quote from: Antares on 01/06/2015 09:39 pmThere would have to be a force physically causing the drift. Recalibration would be insufficient without determining where that force is coming from then either eliminating it or determining it can be withstood in flight.That's assuming there was actual physical drift as opposed to signal drift from a bad LVDT or other electronic component in the position feedback system. Also, since the actuator is fueldraulic, a leaky servovalve could also cause drift without external force being applied.
There would have to be a force physically causing the drift. Recalibration would be insufficient without determining where that force is coming from then either eliminating it or determining it can be withstood in flight.
May just need to replace the whole actuator.
Isn't the second stage TVC electric?
JASC’s Thrust Vector Control Actuators are used on the nine first-stage Merlin engines and the single second-stage Merlin engine
Hydraulic actuators are finicky things and can behave in unexpected ways in extreme thermal situations. The 737's rudder actuator problems in the 90's comes to mind...
Quote from: yokem55 on 01/08/2015 01:56 amHydraulic actuators are finicky things and can behave in unexpected ways in extreme thermal situations. The 737's rudder actuator problems in the 90's comes to mind...IIRC its a jackscrew and nut that actuates the rudder and lubrication failure was the cause.
Crossing fingers for the next F9R launch attempt, here there are my updated contribution to the topic.
Quote from: archipeppe68 on 01/07/2015 08:06 amCrossing fingers for the next F9R launch attempt, here there are my updated contribution to the topic.I wanna thanks all the folks who helped me to improve my graphics jobs...CiaoGiuseppeA very nice graphic, but a couple of errors if you want to correct them:1. Your F9 doesn't appear to be thin enough. Have you tried overlaying the F9 graphic from the SpaceX F9 page to check your proportions? http://www.spacex.com/falcon92. The center engine on the first stage is not any bigger than the other, nor does it hang that low. (see the graphic at http://www.spacex.com/falcon9 )3. The cargo Dragon trunk is the same diameter as the F9.4. The first stage has three restarts, not two. http://www.spacex.com/news/2014/12/16/x-marks-spot-falcon-9-attempts-ocean-platform-landing
Crossing fingers for the next F9R launch attempt, here there are my updated contribution to the topic.I wanna thanks all the folks who helped me to improve my graphics jobs...CiaoGiuseppe
Quote from: archipeppe68 on 01/07/2015 08:06 amCrossing fingers for the next F9R launch attempt, here there are my updated contribution to the topic.The fins are deployed at T+5 minutes, not at 6 minutes. Seehttp://forum.nasaspaceflight.com/index.php?topic=35853.495
Quote from: Remes on 01/08/2015 01:13 am[...] The dark side of hydraulic.IIRC it's a fueldraulic system, ie the RP-1 fuel is used as the working fluid.
[...] The dark side of hydraulic.
Add to that the integrated electrical testing that must be completed.
Quote from: Lars-J on 01/07/2015 04:36 pm2. The center engine on the first stage is not any bigger than the other, nor does it hang that low. (see the graphic at http://www.spacex.com/falcon9 )2. The same official drawing in the same web page shows off the central Merlin nozzle sporting among the others, I based my drawings on the same assumption
2. The center engine on the first stage is not any bigger than the other, nor does it hang that low. (see the graphic at http://www.spacex.com/falcon9 )
Can someone shed light on why the alternate dates vary between next day and +3 days? The original attempt on 6th had an alternate on 9th, then the next opportunity is 10th now as planned for the launch currently and then the next alternate is 13th. Is there any orbital dynamics reasons or probably just ISS scheduling?
Quote from: toruonu on 01/09/2015 07:22 amCan someone shed light on why the alternate dates vary between next day and +3 days? The original attempt on 6th had an alternate on 9th, then the next opportunity is 10th now as planned for the launch currently and then the next alternate is 13th. Is there any orbital dynamics reasons or probably just ISS scheduling?Phase angle between the ISS and the Dragon at launch, IIRC.
Quote from: Galactic Penguin SST on 01/09/2015 07:31 amQuote from: toruonu on 01/09/2015 07:22 amCan someone shed light on why the alternate dates vary between next day and +3 days? The original attempt on 6th had an alternate on 9th, then the next opportunity is 10th now as planned for the launch currently and then the next alternate is 13th. Is there any orbital dynamics reasons or probably just ISS scheduling?Phase angle between the ISS and the Dragon at launch, IIRC.As far as I understand it:You try to launch when the ISS moves over your launchpad, but the ISS is almost never exactly above your launchpad. The difference is the phase angle. ISS gets close to the launchpad once every day, but for some days close is not close enough so you lose that day. Normally you get 2 or 3 days in a row and then you have to wait around 2 days for the next opportunity.
Quote from: Shanuson on 01/09/2015 08:59 amAs far as I understand it:You try to launch when the ISS moves over your launchpad, but the ISS is almost never exactly above your launchpad. The difference is the phase angle. ISS gets close to the launchpad once every day, but for some days close is not close enough so you lose that day. Normally you get 2 or 3 days in a row and then you have to wait around 2 days for the next opportunity. Based on the higher inclination of the ISS orbit, there are two times per day, every day, when the orbital plane passes through the launch site. Because of downrange constraints, you can only launch from the Cape on the ascending node (to the northeast, not to the southeast). There may be constraints on the use of the Eastern Test Range, or sun angles or other constraints at ISS, or just needing to stand down to refill propellant supplies (usually takes more than one launch attempt, though), any of which could cause you to miss one or more days, but there is always one valid launch window per day based strictly on the physics of the situation.
As far as I understand it:You try to launch when the ISS moves over your launchpad, but the ISS is almost never exactly above your launchpad. The difference is the phase angle. ISS gets close to the launchpad once every day, but for some days close is not close enough so you lose that day. Normally you get 2 or 3 days in a row and then you have to wait around 2 days for the next opportunity.
Yes clearly the launch pad passes under the orbital plane twice each rotation of the Earth and only one of those presents an opportunity to reach something like a rendezvous orbit. The question is why the location of ISS at the time the launch site passes under its orbital plane makes a difference. Shouldn't rendezvous be relatively simple (low delta-v) regardless of whether ISS were someplace on the opposite side of the globe at that moment, or directly overhead?
