Orbcomm OG2 Falcon 9 Satellite Launch | Hacker News Reader

Orbcomm OG2 Falcon 9 Satellite Launch

spacex.com

100 pointscryptoz58 comments

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/spacex/comments/2aany2/rspacex_orbco...

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.

You mean like this one (from the last launch)?

https://www.youtube.com/watch?v=CjZ33C9JZTM

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 enough to the ground that after they cut off the engine, the legs can take up the difference.

(Weight conditions at launch are obviously very different. In addition to the weight of the second stage and payload, there's also the weight of the first stage fuel -- and the fuel will be most of the weight of any rocket at launch.)

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

Grasshopper is a testing platform.

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).

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.

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...

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?

Like trothamel commented below, the stage isn't designed for tipping over and slamming into the water.

My problem with that theory/scenario is that the stage is designed to land on its legs. When the test vehicles land they have very little angular momentum, presumably these tests would mimic that. And if the momementum was managed, then at engine shut off it would drop vertically into the water, and then fall over as the counter pressure of buouancy was not stabilized by the landing legs.

If you've ever seen loggers drop tree trunks in a river you can imagine what that looks like, it starts out vertical, then reaches point where it displaces enough water that it is essentially floating (but unstably so) and then rotates to horizontal around the point on the trunk that is at the surface of the water.

I totally understand that this isn't an intended landing mode :-).

Thinking about how they manage fuel load, it made me wonder how I would do it, do you hover until you've exhausted all fuel? Or do you just shut off the engine? And at flameout are you out of volatiles or just some volatiles (like LOX)and do you have the 'gas tank' issue that auto mechanics deal with where residual vapors can be explosive.

Would love to sit through the briefings on this stuff.

The problem with your picture is that the empty stage is extremely light for its volume so, unlike a log, it floats very high in the water. Floating upright, most of it is above water and the top of the rocket is high above the water. The full launch vehicle is 220ft tall, and 2/3 of that is the first stage.

> tracking the landing leg attachment points at liftoff

I suspect its more to do with that being where the giant spacex logo is painted on.

Looks like the landing was only partially successful -

Rocket booster reentry, landing burn & leg deploy were good, but lost hull integrity right after splashdown (aka kaboom)

https://twitter.com/elonmusk

It's better to use a permanent link. In two weeks that link to his profile going to be useless. This applies to blog homepages as well.

https://twitter.com/elonmusk/status/488718649515986944

Well, if it disintegrated due to falling over in the waves and colliding with the water it isn’t necessarily unsuccessful, since it is not designed for landing on water (i.e. the rocket disintegrating after landing on water due to being in water is not a failure – what matters is whether, hypothetically, the rocket would have survived, had it landed on land).

Edit: Seems like Musk is making that point himself: https://twitter.com/elonmusk/status/488719729599578112

I think it's hard to say that, yet.

The rocket isn't really made to survive tipping over onto its side in the water. If they "landed" properly (legs deployed, descending at a slow speed when they hit the water), I think one can make an argument for a fully successful landing.

It really depends on how fast they hit the water.

Sure, it depends, we'll have to wait and see what SpaceX decide to release about it. It'll be nice to see video if they have some.

This launch seemed to use a much steeper trajectory. Typically they go downrange much faster than they gain altitude, but today they seemed to go up faster than they were going downrange.

How does this affect the fuel efficiency of the launch? Is this a way to cut down the horizontal velocity so they first stage can return more easily?

Maybe. This time, the satellite load was just 1.1 tonnes (vs. 6 tonnes capacity), so they probably had more room for maneuvering and hence decided to do stage separation closer to the launch site in order to aid with the recovery attempt. Or maybe it's standard procedure on lighter payloads; perhaps it reduces maximum dynamic pressure.

It's a product of a higher target altitude (650km for Orbcomm vs. 330km for an ISS resupply) and wanting to perform a single second-stage burn to achieve the target orbit.

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, on designing such a robust engine!

Video of launch: http://new.livestream.com/spacex/events/2980259/videos/56576...

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.

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?)

Is this the re-usable launch vehicle, i.e. the one that re-enters the atmosphere and lands itself upright?

Essentially yes. They won't be able to reuse this particular vehicle, but it will return and hover over the ocean for them to retrieve. They'll recover it and study the results to make the next one even better. Real reusability is probably at least a year away.

Yes, the first stage has landing legs. They're planning to deploy the landing legs over water and attempt to hover the booster just before it hits the surface.

SpaceX only has one launcher at present, the difference between re-use and expendable use is a matter of how that hardware is used, not how it's built. Every Falcon 9 v1.1 launch to date has made use of the same, fundamentally reusable first stage core. To actually reuse the core requires bolting on some additional hardware (which has flown on 2 flights already) such as landing legs and then flying the stage back to land. In software terms this is like hiding new functionality behind a "feature flag" so that you can let the code bake in production for a while.

I'll admit I do not regularly follow space launches but I am amazed at the various places that they have installed video feeds. Seeing the first stage drop off was incredible.

Cameras are fairly cheap these days, and a video feed would be extremely valuable to figure out what happened in the event that something goes wrong. Telemetry from sensors is also extremely useful, but sometimes you just want to see what happened with your eyes.

What's a first stage drop off?

AKA stage separation.

The first stage must provide a lot of thrust to get into lower gravity, so it's quite heavy with fuel and has 9 engines. After the fuel in that stage is expended, the rocket splits in two, dropping that first stage back to earth. The top half of the rocket contains additional fuel and whatever payload the rocket is delivering (including potentially an additional stage + engine) and is powered with a single engine.

Here's an older video showing the separation:

https://www.youtube.com/watch?v=p4lOJjKGoIY#t=193 (Goto: 3:15 if the link doesn't work)

The first stage that drops off is the one that SpaceX is attempting to recapture. Historically, that stage just lands in the ocean and is either scuttled or must be extensively cleaned and retrofit in order to fly again. SpaceX figures if you leave a bit of extra fuel in the tanks, you can land it vertically at the same site it took off from, and save yourself the time and expense associated with cleaning and retrieving it.

This would be very valuable since the rocket engines are typically the most expensive components of a launch, and the first stage has 9 such engines:

http://i.imgur.com/QzrPePS.png

It isn't higher gravity they're overcoming with the first stage, but rather the much higher atmospheric pressure near the surface. Gravity in orbit is almost identical to gravity at the surface.

Pedantic and completely correct. H/T.

Having done aerospace instrumentation/telemetry (on a much smaller scale for a private airplane manufacturer), there are some things like separation events, nozzle heating patterns etc that can be captured with a single camera which would take many many standalone sensors to capture - that's a lot of money/time saved. The tough part is that video takes a huge amount of the TM bandwidth, so typically you can only send one or maybe two video feeds down, and then you switch between the cameras, as they have done. Actually, realtime video transmission via TM is a very interesting topic, it often uses a specially configured MPEG format. There are a lot of tradeoffs in the parameters that you get to tweak.

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.

Everyone who grew up during the Cold War knows this instinctively!

In case you want to watch it on youtube, https://www.youtube.com/watch?v=lbHnSu-DLR4

Launch webcast: https://www.youtube.com/watch?v=lbHnSu-DLR4

I have nothing at stake in these launches but every one of them makes me nervous, I almost can't watch them. At any moment, boom.

The launch video was beautiful though, the water vaporizing and forming a could around the rocket is awesome, the inside view of the engine was amazing.

Can't wait to see the landing video!

What about the location of the landings? Have they been on target?

They seem to be having consistent results (modulo the landings), so it's almost safe to take a successful launch for granted (at least for people like us who are just watching).

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.

So what happened on the first 3? Crashes?

Here is the video of the previous one. It landed.

https://www.youtube.com/watch?v=CjZ33C9JZTM

Video was barely recognizable before repair.

That was a different mission.

No, aborted before launch.

That makes sense. I feel like a crash would have been bigger news. Lucky I caught the stream when it actually went up!

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

"Speed 7.2km/s...and we have miko" - what's miko referring to in this case?

Other commenter described it as MECO, googled that, found "Main Engine(s) Cut-Off".

MECO. Main Engine Cut-Off.

It's MECO. Main engine cut-off.

Awesome! Are they going to repeat the launch for the west coast?

Their launch manifest (http://www.spacex.com/missions) lists one more launch from Vandenberg in 2014, and a few more in 2015. Eventually, if everything goes according to their plans, they will be doing regular launches from the west coast. (Which site they use is determined by which sort of orbit they are shooting for. They will launch from Vandenberg whenever appropriate. Vandenberg is typically used for high-inclination/polar orbits, or the rare retrograde orbit)

Orbcomm, you say? This is all I can think of: http://upload.wikimedia.org/wikipedia/en/a/a9/U.F.Off_-_The_...

Reply on news.ycombinator.com