12
$\begingroup$

They mentioned on the live stream that this is because of the shaking antennae.

It has also been discussed on here before why this happens: Why does the video feed always fail during Falcon 9 landings?

But that post doesn't give a solution to the problem. It is asking why it happens, someone confirms this and we have confirmation from SpaceX why this happens.

My question is why can't they just hold the antennae away from the ship? Put the antennae on a buoy. Throw the buoy into the water, let it drift away, and then reel it back when the falcon has landed. Cheap and reusable - the SpaceX way!

Improve this question
$\endgroup$
23
  • 9
    $\begingroup$ A) A buoy would be less stable, and the motion of the boat would cause it to rock. B) The buoy would still have to be connected by a wire carrying the feed, so it couldn't be too far away. C) Perhaps most importantly, this is another decently large complication to an already complicated procedure. Engineers prefer to use the KISS principle: Keep It Simple, Stupid. The primary objective is to land a rocket on the ship. The live camera feed is just a little extra. $\endgroup$
    – Phiteros
    Commented Feb 7, 2018 at 5:27
  • $\begingroup$ @Phiteros about the wire, no. That could be done wirelessly. Maybe not exactly WiFi, but an "omni" antenna and a bit of wattage is all that's needed. I'm also still not 100% convinced the "signal cuts out because of vibrations" to begin with, but that's a different issue completely. $\endgroup$
    – uhoh
    Commented Feb 7, 2018 at 5:55
  • 1
    $\begingroup$ @uhoh the problem with wireless is (spacex is claiming and it makes sense) that the antennae shake to much and this disrupts the signal $\endgroup$
    – zoplonix
    Commented Feb 7, 2018 at 6:20
  • 1
    $\begingroup$ This is the comment I'm referring to ->Why would they spend $$$ on a fancy feed that doesn't interrupt, when the primary goal of that video camera is to have a record they can analyse at their leisure? The data is stored on the ASDS for later review. $\endgroup$
    – Hobbes
    Commented Feb 7, 2018 at 9:22
  • 1
    $\begingroup$ No need for buoys. If they really wanted those extra few seconds of live coverage, they could use a wide-beam, (and hence more vibration proof), UHF link to one of the support ships and then fire the video up to a satellite from a stabilised antenna in the usual way. $\endgroup$
    – Martin James
    Commented Feb 7, 2018 at 11:25

3 Answers 3

Reset to default
12
$\begingroup$

For SpaceX there is no drawback to having a brief interruption in the broadcast. The live transmission is for entertainment/PR purposes only, and they're already elbow deep in good PR so don't need any more.

The ASDS stores the video onboard. SpaceX often publishes the landing video later. Even for crash landings, with the stage exploding on the barge, the video recordings remain intact. The video is available for engineering analysis a few hours after the landing, which is soon enough.

There would be a significant cost to making sure the transmission is uninterrupted.

You can't use a buoy. There's a satcom antenna (i.e. a steerable dish) on the ASDS. You'd have to provide a reasonably stable platform for that antenna. So that means a boat or barge.

I've indicated one of the antennas in this image: ASDS satcom (original here) There's another on on the other side of the barge. They're pretty big (I estimate about 1 m diameter).

That boat means another item whose position needs to be controlled to make sure it doesn't crash into the ASDS. It needs an engine, an azimuth drive or two. Now the boat needs to be big enough to hold these.

Now, instead of recovering just the ASDS, the crew has to recover 2 vessels after the landing, doubling the workload. You need to tow the antenna boat, so that means another tug.

With all this, you still have a wireless link between ASDS and antenna boat. Can't use a wire (will get tangled in a propeller). So still a wireless link with a transmitting antenna that will be right underneath a rocket exhaust, and can be interfered with by the landing radar. A crash landing on top of the antenna will still take out the transmission.

So you'll spend a lot for no benefit. This is why SpaceX won't bother improving the live landing feed. Not until large-scale BFR operations become a reality and turnaround time needs to drop below 24h - then SpaceX might benefit from having the landing video available sooner for analysis.

Improve this answer
$\endgroup$
6
$\begingroup$

Come at it from a different angle --

What is the impact to SpaceX when they lose comms?

There is a momentary interruption in the stream. The livestream is impacted mildly. We have no signs there's a greater impact. We have evidence the impact is actually far more mild than what the public sees -- see the video wall over the hosts shoulder, where you can see the ASDS camera feed clearing moments after the landing attempt.

They are also concerned with telemetry as well as video - even more so, likely. However the ASDS has multiple shipping containers of equipment onboard that could very easily contain a ground station to store data during interruptions in the uplink. Also if the vehicle is recovered, they are likely to have onboard storage too.

So ultimately, you may have a solution searching for a problem. SpaceX doesn't seem to have any problems getting sufficient data from landings.

Improve this answer
$\endgroup$
0
2
$\begingroup$

UPDATE: It doesn't get disrupted completely on every landing!

For example here's the SpaceX video from the ANASIS-II Mission.

Pardon the ugly GIF, I don't know how to make a better one...

GIF from ANASIS-II Mission

video cued at 23:19 or T+ 08:22

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.