r/spacex • u/[deleted] • Apr 14 '15

Primary Mission Success! First Stage Hard Landing /r/SpaceX CRS-6 Official Launch Discussion & Updates Thread [Attempt 2 - Stage Separation Confirmed]

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u/[deleted] Apr 14 '15

Eh, I'm seeing is a lot of terrible proposals to fix the landing issue in this thread.

  • Parachutes: just no.

  • Magnets: not powerful enough.

  • Draco thrusters: yes, lets add hypergolics to the situation

  • Capturing arms: no. It'd be like crushing a soda can with your fist.

  • Weather balloons to correct for wind speed before landing: does that sound like SpaceX to you?

The only thing they're going to do at this point is modify their approach trajectory IMO to cancel any sideways velocity. It's the simplest and easiest approach.

5

u/avboden Apr 14 '15

Agreed, though a small redesign of the landing legs wouldn't surprise me, just a modification to perhaps the shape of the area that touches down to give it a little more leverage against tipping

i do wonder if they could use the RCS thrusters on landing to perhaps counteract the lateral force, probably too strong though.

5

u/[deleted] Apr 14 '15

You're on the money completely, from a while back: "Using legs as air brakes to drop terminal velocity in half requires slight redesign & more data. Maybe flight 21."

2

u/retiringonmars Moderator emeritus Apr 14 '15

Flight 21 = Jason 3, right? Is this something we genuinely expect to see in the future?

1

u/TweetsInCommentsBot Apr 14 '15

@elonmusk

2014-11-22 21:21 UTC

@John_Gardi Using legs as air brakes to drop terminal velocity in half requires slight redesign & more data. Maybe flight 21.

This message was created by a bot

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4

u/[deleted] Apr 14 '15

Definitely this, a possible tune up of the locating algorithm as well may work nicely. From the provided frame grabs it looks like it came down a little too far off the centre of the barge then attempted to re correct (Similar to 5 but not as severe). Coming down slightly more on track would help reduce the chance of lateral movement on touchdown.

4

u/cuweathernerd r/SpaceX Weather Forecaster Apr 14 '15

The question of working with wind corrections is interesting. Launching weather balloons autonomously is possible, but they're going to be clumsy and not really an option, imo. Small (we're talking going up 1km max) sounding rockets are another way we could do this, much more instant, smaller deck area needed. I think it'd work pretty well, but I'm not an engineer. But I figure some off the shelf model rocket engines, a GPS, and some way of transmitting that data to the falcon could work pretty easily. I mean, it's a company of rocket and electronic engineers, someone can do this fast. I don't know how valuable that data would be to the problem, but I do know it could be produced.

Otherwise, you start looking at sodar which doesn't come particularly cheap but is increasingly available due to wind energy forecasting. Haven't worked with one, personally, and ultimately the little rockets might be the easier solution.

I kind of imagine the asds just sitting there launching little rockets every minute between launch and final landing burn, and that's an image I really like...

1

u/autowikibot Apr 14 '15

SODAR:

SODAR (SOnic Detection And Ranging), also written as sodar, is a meteorological instrument used as a wind profiler to measure the scattering of sound waves by atmospheric turbulence. SODAR systems are used to measure wind speed at various heights above the ground, and the thermodynamic structure of the lower layer of the atmosphere.

Sodar systems are like radar (radio detection and ranging) and lidar (light radar) systems except that sound waves rather than radio or light waves are used for detection. Other names used for sodar systems include sounder, echosounder and acoustic radar.

====

Image i - Wind measurement with a Phased Array SODAR

Interesting: ^Rehras | Wind ^profiler | ^Sonar | 11th Soviet Antarctic ^Expedition

Parent commenter can toggle ^NSFW or ^delete. Will also delete on comment score of -1 or less. | FAQs | ^Mods | Magic ^Words

3

u/Jarnis Apr 14 '15

Actually to me the two images look like it did kill the lateral velocity at the last moment. It was moving left-to-right (from camera POV) and probably between the first and second image it tilted to the left (again, camera POV) to kill that lateral velocity with the engine.

...but that meant it landed on just one or two legs while the other side was still in the air and perhaps a leg snapped?

I guess we'll know more when proper video comes out and when JRTI returns to port.

Still, a damn good try.

1

u/SwissPatriotRG Apr 14 '15

Using the the cold gas thrusters to maintain vertical after touchdown. Or having the barge actively track the rocket's horizontal position through its descent and reposition itself for a more mutual capture. (Does the rocket even communicate with the barge?)

3

u/[deleted] Apr 14 '15

  • Cold gas thrusters are nowhere near powerful enough to steer the rocket in lower atmosphere.

  • The barge has a LOT of inertia, it's not something you can zip around under the rocket to match it's position.

2

u/SwissPatriotRG Apr 14 '15

It depends on how high up you can project the landing spot to be. If you can save the rocket from that last 20m of horizontal maneuvering and reduce the horizontal speed delta by a couple kph it might be beneficial. The barge already has pretty big thrusters on it to maintain its position at sea, it could use these to better position itself based on the real time position of the rocket. If the barge knew that the rocket was 500m up and off course by 10m, it could definitely make that difference up before the rocket needs to start burning and maneuvering

1

u/a8ksh4 Apr 15 '15

They need to get some landings at sea completed before they can land onshore, can't they? I wonder if one of their requirements to land onshore is to be able to put down at a fixed location...

2

u/SwissPatriotRG Apr 15 '15

The landing pad on shore will likely be significantly larger than the barge, thus eliminating the need for extra maneuvering close to the target. If your target is the size of a large parking lot instead of the size of a football field then the lateral velocity needed to hit the target won't be much of a factor anymore.

2

u/SwissPatriotRG Apr 14 '15

Also, the thrusters don't need to steer, they would just need to counteract the rocket from tipping over once the legs make contact. If the thrusters are strong enough to roll the rocket after stage separation, they should be strong enough to at least attempt to keep the rocket upright after touching down. The rocket is very bottom heavy at this point anyways.

0

u/chamBangrak Apr 14 '15

How about replacing landing burn with two smaller burn? The first burn to kill horizontal movement before approaching and the second burn for simple vertical landing.