SpaceX Grasshopper 744m test flight [video] | Hacker News Reader

SpaceX Grasshopper 744m test flight [video]

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171 pointsnkoren37 comments

That may have been the coolest cinematography of a real piece of space hardware I've ever seen. One robotically controlled flying camera shooting and flying around a reusable spaceship, both right out of sci-fi.

More often I feel that I'm living in the future.

I didn't read about what it was supposed to do before I watched the video.

Seeing it stop in mid-air then land perfectly... wow. It actually gave me chills. That's some year 2213 shit, here, now. Amazing.

744 meters is just over 2,440 feet, I wonder what they are doing to deal with the spin issue from the Falcon9 flight out of Vandenberg.

Watching this makes me feel the same way I did seeing the DC-X take off and land which is make me feel like "real" science fiction rockets are about to be realized.

Apparently simply having landing legs on the stage (and extending them) will be enough to stabilize the spin problem sufficiently to allow it to be controllable by the RCS et al.

Since you've been likely keeping up with this, has there been any video released on the fate of the return stage? Musk mentioned they would put something out there, but it doesn't seem to have materialized yet.

I realize that Elon speculated that would be the case, but I wasn't neccesarily buying his explanation.

Two things need additional color, one being given the lack of atomosphere at the altitude where the first stage separates (tapes put it at just over 3 minutes into the flight), and two structural integirty of those struts making the atmospheric transition.

So you need to get the retro burn off while you are exo-atmospheric or you risk melting off the important bits when you re-enter. That suggests that you need some sort of RCS to cut rotational dynamics so that you can stage for retro, then re-enter at less than hypersonic velocity. Further you can't do you retro burn until you've allowed the upper stage to clear.

Another interesting bit is that the first stage appears to have cameras, they were showing video from them during the launch, but we've not seen the post separation video. I hope that video surfaces at some point as it could help design something to mitigate the whole roll thing before it got out of hand.

Musk has mentioned posting that video online[1].

[1] http://www.reddit.com/r/spacex/comments/1ne36t/partial_succe...

great resource thanks. Looks like the first test with legs is going to be in FL.

I thought the spin problem was a non issue: they just wanted to see if they could relight the engine when Falcon is falling back to earth at speed. When it's relit they can compensate the spin and take control.

The challenge was that with the stage spinning they couldn't feed fuel to the engines to finish the retro burn. That is an issue. They need to work around that in the next attempt (either by not spinning or by allowing for it with a different fuel feed mechanism)

Increasing tank pressurization would mitigate it, but I suspect it's a lot easier to plan to control the spin.

It is a fascinating problem, you launch with one type of space craft and then you recover with a different craft (in terms of mass distribution, fuel supply, etc). I'd love to hear how the avionics deals with the two systems. especially given that most of the rocket systems I've seen internal descriptions of are very narrowly tuned to be critically damped around their launch parameters. Unlike say aircraft that are dealing with fuel weight management issues and load balancing.

I know Elon said he would release the videos, and I'm sure they will, this is definitly the kind of 'rocket science' that is very intriguing to me.

This is really exciting technology, but as far as I can tell not even SpaceX is sure that it will be practical to include it in a production rocket (https://www.youtube.com/watch?v=IIVCCaYWGpk).

That's not meant as a criticism though -- the fact that they're willing to try anyway already brings them to legendary status in my book.

It doesn't matter to them that they think it might fail. The only reason that SpaceX exists is to colonize Mars, and the only way to do that is with reusable spaceships. The reason they're willing to try it is the same reason they were willing to build non-reusable rockets to start: it's the only way forward.

Elon appears to be pretty confident after they tested booster return on the last Falcon 9 flight. See this tweet:

https://twitter.com/elonmusk/status/384407846349062144

You're pretty much right.

This has no production value. This is great "look at this thing that we can do" video but the reason no one else attempts it is because there is no next step. They didn't just stop at 744 meters for no reason, fuel is the limitation here.

It is impossible(unless you want to build something the size of Saturn V again) to put enough fuel on a launch vehicle to carry a satellite to orbit and then land it back like this.

I don't have the exact data, but as an guesstimate it would take twice as much fuel(fuel + "return fuel") to land the rocket back like this. We also need to put in extra fuel to take the "return fuel" up there in the first place...you get the idea.

Extremely un-economical. I do not see a next step for grasshopper because building another rocket is cheaper than returning the engine back like this.

The idea is not to slowly fly to orbit and back - it is for the stages to fall to earth and then decelerate from terminal velocity to a gentle landing. The reason for these tests is to develop the technology required to do that.

According to Musk, fuel accounts for only 0.3% of the costs of a launch, so a re-usable rocket could achieve significant cost savings even though it would require more fuel.

"I don't have the exact data..."

Well said. You don't. Buy if you can do ticket science on the back of the envelope, imagine what the ACTUAL rocket scientists can do. You think they went "hey, I just came up with this guesstimate that this is going to be impossible, but let's go ahead and blow the money anyway."

I can bullshit rocket science too: you overlook all kinds of stuff. Such as when coming back to Earth they don't need fuel to fight air resistance which will actually do most of the work for them. Bam! No need to double the fuel.

But what do I know. I'm not the one doing it and neither are you.

Well said.

Fuel is cheap compared to the launch vehicle.

Well, rockets are staged. If you only recover the first stage, that's still a big savings. As it happens, the first stage on a space rocket doesn't need to climb very high and doesn't need to move downrange very far; it just has to lift a lot of weight. Having it come back down afterwards is still a huge control problem, but not impossible in terms of physics. You're not that far downrange and have (relatively) little lateral movement to compensate.

A second or third stage could be more tricky, of course.

Since most of the trip back is conducted at terminal velocity, you only need enough fuel to decelerate from that. In addition, you are no longer lifting the 2nd stage and all that fuel any more.

So it would be SUBSTANTIALLY less than 50% probably less than 10% extra fuel. Far far smarter though. Much harder design.

As fantastic as that was I can't help but think that now I want a quadcopter with an HD video camera on it.

Start with a tricopter. They're a lot more fun to fly.

http://www.youtube.com/watch?v=YCPMC_fiSMI

Anyone know what models and price ranges can get to altitudes like that? And how are these controlled - if manually in real-time what kind of connection is needed?

I think this was shot with a DJI S800. The RC link to fly it is usually 2.4GHz. A separate link, often at 5.8GHz, is used to send the camera feed back to the ground to help the pilot or compose the shot, or both.

Good eye ID'ing the distinctive DJI arms on the hexacopter.

The convention seems to be 2.4Ghz for telemetry back the to base-station or radio display - and something lower in the UHF band like 433 or 900Mhz for actual control.

Mainly because Zigbee/802.15.4 radios are readily available in 2.4Ghz and 433Mhz goes a lot further (and through more things) by comparison at 1W.

[/sitting next to 3 hexacopters at the moment]

What kind of transmitter are you using for manual control? I assume you aren't using a ground station all the time...

I only ask because most new 'brand name' (JR, Futaba, Airtronics, Robbe) tramsitters seem to be 2.4Ghz. I know FM radios are still available on 36 and 40 Mhz, among others, but I haven't seen many used for a while with new aircraft.

UHF transmitters can be rigged on a RC transmitter as a module or through the trainer port, depending on the radio. DragonLink and EZUHF appear to work this way. (I haven't used any of these.)

Correct. The EZUHF is my preferred transmitter.

A simple DJI Phantom will easily get to that altitude. Slight modifications would be required - possibly a different receiver and remote control to ensure the range, and an FPV system (camera and transmitter on the copter, and a receiver with a screen or video goggles on the ground). Altogether easily done in under $1000.

Control is real-time, just like any other flying model aircraft or multirotor. For flying at that altitude, I'd use FPV - meaning you'd fly using the camera image to pilot the copter viewed through a screen or even better, video goggles, as opposed to looking at the model from the ground.

Be aware though that at this altitude, you're often in controlled airspace, which is troublesome for model aircraft in most cases.

I may have just started looking at building a tricopter with FPV. This is going to be an expensive hobby, I can feel it. Satisfying, though!

diydrones.com, flitetest.com, /r/multicopter and /r/fpv will help you out :)

This is so cool, it looks CGI. Unbelievable. At first I thought the camera was in a helicopter, but a drone makes more sense (and is even cooler).

Elon Musk is Tom Swift.

Did you notice how the rocket tilted to correctly position itself over the landing strip. Great camera angle.

RLV Grasshopper is well named.

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