Orbcomm OG2 Falcon 9 Satellite Launch • Hacker News Board

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#41

Post by cdash » Mon, Jul 14, 2014, 5:24 PM UTC

mrfusion wrote: post #40

rst wrote: post #37

Earlier quoted context omitted.

It doesn't actually hover over the water. For that, the rocket's thrust would have to exactly balance the weight of the first stage, with the tanks nearly empty, and even a single Merlin engine can't actually throttle down that low. As long as the engine is firing, the rocket is accelerating up, so the actual landing maneuver is something they call a "hoverslam", which is designed to zero out vertical velocity close…

Hmm, but on the grasshopper videos it seems to be hovering in air and descending pretty agiley?

Grasshopper is a testing platform.

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#42

Post by Crito » Mon, Jul 14, 2014, 5:25 PM UTC

mrfusion wrote: post #40

rst wrote: post #37

Earlier quoted context omitted.

It doesn't actually hover over the water. For that, the rocket's thrust would have to exactly balance the weight of the first stage, with the tanks nearly empty, and even a single Merlin engine can't actually throttle down that low. As long as the engine is firing, the rocket is accelerating up, so the actual landing maneuver is something they call a "hoverslam", which is designed to zero out vertical velocity close…

Hmm, but on the grasshopper videos it seems to be hovering in air and descending pretty agiley?

Grasshopper can hover for a while because, at least at that stage in its flight, it is heavier than the returning F9 core. As it burns more and more fuel it becomes lighter and lighter, and I believe that towards the end of Grasshopper flights it is too light to hover.

The landing that Grasshopper has been doing recently, and which the F9 core will do, has been termed a "hover-slam" by SpaceX. Basically it decelerates rapidly, hitting 0m/s right when it also hits the ground. If it did not cut out the engine right at that point, it would begin going back up (until the fuel ran out).

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#43

Post by rst » Mon, Jul 14, 2014, 5:28 PM UTC

mrfusion wrote: post #40

rst wrote: post #37

Earlier quoted context omitted.

It doesn't actually hover over the water. For that, the rocket's thrust would have to exactly balance the weight of the first stage, with the tanks nearly empty, and even a single Merlin engine can't actually throttle down that low. As long as the engine is firing, the rocket is accelerating up, so the actual landing maneuver is something they call a "hoverslam", which is designed to zero out vertical velocity close…

Hmm, but on the grasshopper videos it seems to be hovering in air and descending pretty agiley?

Grasshopper and F9R-1 (their newer test vehicle) are widely believed to fly with extra mass as ballast in order to make them easier to control -- most likely just as extra fuel in the tanks which they don't plan to burn on that flight.

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#44

Post by jerf » Mon, Jul 14, 2014, 5:40 PM UTC

caval wrote: post #12

Watching the camera feed of the launch around the 5 minute mark all I could think was: if the rocket turned around now, it could probably land in New York in another 5 minutes

On a ballistic trajectory, you can reach anywhere on Earth in 40 minutes or less. I've seen cute little diagrams of the relevant times before, but I wasn't able to quickly Google one up.

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#45

Post by lutorm » Mon, Jul 14, 2014, 5:45 PM UTC

pjkundert wrote: post #38

The second stage Falcon engine appears to have suffered some insulation degradation and loss. It develops just above the bell, on the right-hand side of the motor image in the video. After second stage shutdown, a vapor emission is visible just above the site of the degradation (at the very end of the video). Was this a normal venting, or a non-catastrophic failure of the second stage engine? Congratulations, SpaceX,…

I believe those are normal vents. If you look at previous videos like http://youtu.be/RtDbDMRG3q8, there's are whole frost "christmas trees" at several places around the base of the nozzle.

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#46

Post by jccooper » Mon, Jul 14, 2014, 6:10 PM UTC

coder23 wrote: post #2

This is the fourth separate attempt at launching this mission. The first one was more than a month ago. Their biggest problem are helium leaks. Successful launch. We can expect better video footage of the first stage landing.

First was a first stage helium valve, second was weather, third was thrust vector control actuator.

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#47

Post by cstross » Mon, Jul 14, 2014, 6:28 PM UTC

Humph.

I'm choosing to take this personally!

(I was in Orlando at YAPC::NA in June, and drove up to the Cape twice in hope of seeing it launch. Scrubbed both times, and I got bitten to hell by mosquitos before I discovered DEET -- yes, I'm British, we don't have flybown tropical swamps.)

Ah well, maybe next time I visit ...

(Note that on the second visit they'd closed off the beach that enthusiasts usually used to watch launches from. Much muttering among the rocket fans present about SpaceX behaving very oddly -- this was the attempt when they also cancelled the webcast. I wonder what was going on?)

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#48

Post by trothamel » Mon, Jul 14, 2014, 6:30 PM UTC

rst wrote: post #37

vonklaus wrote: post #4

Earlier quoted context omitted.

I wonder if they have tracking planes or a spotter out on the water. After all this bad press and the violent ocean churn from the last attempt, it would be nice to get a money shot of the vehicle hovering over the water.

It doesn't actually hover over the water. For that, the rocket's thrust would have to exactly balance the weight of the first stage, with the tanks nearly empty, and even a single Merlin engine can't actually throttle down that low. As long as the engine is firing, the rocket is accelerating up, so the actual landing maneuver is something they call a "hoverslam", which is designed to zero out vertical velocity close…

From what I remember, during the last landing, Elon announced that the Merlin engine can throttle down a lot farther than people though. (IIRC, it can go down to 30%, rather than the 70% figure bandied about in internet rumors.)

This means it's possible for the Falcon to do a constant velocity descent, rather than having to do a hoverslam.

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#49

Post by ChuckMcM » Mon, Jul 14, 2014, 7:39 PM UTC

cryptoz wrote: post #3

Wow I can't believe this finally launched. So far so good! And of course, the most exciting thing about this is the return attempt of the F9 first stage core. I don't think that'll be covered in the webcast but we'll certainly get video of it later. MECO successful. Edit: r/spacex has good updates regarding the landing attempt [T+27m]: Elon's jet and NASA plane circling a particular area... http://www.reddit.com/r/sp…

Awesome, I noticed they were tracking the landing leg attachment points at liftoff, so perhaps there is a new leg deployment system.

Also the note that 'kaboom' after splashdown suggests that some part of the landing mechanism didn't deal well the transition from flight to sailing. One wonders what the temperature differential is between the landing first stage and the ocean, on the one hand it might be hot (burning retro) on the other it could be sub zero (cryogenic propellant usage).

Questions then are:

1) What was the mechanism that instituted the rapid disassembly of the landing stage.

2) Would that mechanism come into play on a 'ground' based recovery?

3) What is the safe radius for ground recovery in the event of a structural failure?

Re: Orbcomm OG2 Falcon 9 Satellite Launch

#50

Post by toomuchtodo » Mon, Jul 14, 2014, 7:40 PM UTC

trothamel wrote: post #48

rst wrote: post #37

Earlier quoted context omitted.

It doesn't actually hover over the water. For that, the rocket's thrust would have to exactly balance the weight of the first stage, with the tanks nearly empty, and even a single Merlin engine can't actually throttle down that low. As long as the engine is firing, the rocket is accelerating up, so the actual landing maneuver is something they call a "hoverslam", which is designed to zero out vertical velocity close…

From what I remember, during the last landing, Elon announced that the Merlin engine can throttle down a lot farther than people though. (IIRC, it can go down to 30%, rather than the 70% figure bandied about in internet rumors.) This means it's possible for the Falcon to do a constant velocity descent, rather than having to do a hoverslam.

Merlin engines can throttle down to as low as 40%:

https://twitter.com/elonmusk/status/462104679116050432

http://www.reddit.com/r/spacex/comments/24j5dk/merlin_1d_can...