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Several times when I followed a space launch being broadcasted in the internet, they also included live video from the launch vehicle itself. Such as this ESA ATV launch. Now I don't know if this exact video was streamed online during launch, but usually it does look much like that.

High altitude balloon experiments sometimes attempt video (or rather image) live streaming during balloon flight. But the frame rates are very low. Here is an example of such balloon flight experiment. They say it took between 10 and 60 seconds to send a single image.

The huge difference in budget and systems complexity between a space rocket and such balloon is obvious. I would guess it is a high frequency transmitter that makes live video streaming during rocket launches possible.

But what exactly is it aboard a rocket, that allows live video streaming? And since its power requirements are probably higher, how is it powered?

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I wonder how they got the camera displaying the final stage engine there - that would make the rocket unbalanced, no? – uoɥʇʎPʎzɐɹC Jan 7 at 22:18
    
@CrazyPython Evidently then, such an imbalance is not a problem. Simple :) – Kuba Ober Jan 13 at 21:14
up vote 3 down vote accepted

These are custom commercial video systems developed by aerospace companies that specialize in telemetry. For instance, the linked video includes the credit:

The video system was developed by Kayser-Threde GmbH for ESA and DLR and integrated on Ariane by Astrium GmbH. Usage for ATV-4 was financed by DLR and ESA and supported by Arianespace and CNES.

These are two aerospace companies that provide a wide range of telemetry, data capture, video, and other solutions for space flight.

Cameras such as these have been included recently for a variety of reasons. On manned spaceflights, they need to look for safety events, such as falling ice, to know if they need to inspect the spacecraft before return, or if an abort is required. On commercial flights these are included to understand failures better. They are also useful for marketing and publicity, but the bandwidth and cost (not just financial, but space, weight, and power on the craft) have been too high for regular inclusion. Now they are smaller, cheaper, lighter, and require less power to transmit an HD image in real time, so the added data gained from them makes them a worthwhile investment.

More generally speaking, these videos aren't much different than radio video signals used on the earth, with the exception that launches always have continuous antenna dishes pointed at them, even as they rotate around the earth. Creating the video, encoding the data, and sending it via a chosen RF frequency isn't hard, but by the time the launch "ends" the vehicle may be halfway around the world, and well out of sight of the original launch site.

Therefore all data communications are done by first coordinating a set of frequencies that will need to be received on earth, and sent from earth. Then NASA works with other space agencies with receiving and transmission arrays arranged around the earth along the launch path to get time on their arrays. As the space ship moves away from the launch site, they coordinate switchover so it appears seamless to the launch control center, but in reality may have switched several times from one site to another as the spacecraft accelerates.

The live video feed from the moon was done similarly, except the moon travels very slowly, so they didn't have to switch from site to site during the transmission (if I recall, it was all received in Australia and then re-transmitted around the world using other communications channels).

With large receiving dishes, and very powerful radio transmitters on earth (because space, weight, and power are cheap on the ground) you don't need much space, weight, or power for the receivers and transmitters on the rocket. They are powered like any other radio system on the rocket, and probably transmit at a relatively low power mode.

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Transmitting live video is done just like any other wireless data transmission, except that the video encoding must be fault tolerant. The frequency used is chosen so that attenuation through the atmosphere is tolerable, and will not interfere with other communications systems (as decided by the FCC and other regulating bodies). There are various video encoding protocols that are currently used to stream information, both live and on-demand.

Amateur balloon launches certainly could stream live but here are some complications. The general public is restricted in which frequencies can be used and in transmitter power (1500 Watts maximum in most cases). Rocket launches are typically given authority to use frequency bands controlled by the Government. Because the general public is not allowed to use these frequencies there is little interference to be concerned with.

The communication system would be powered like any other, using on board batteries.

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1500W? We're not talking about radio amateurs here. The balloon mentioned above used a 10mW sender for few bucks that everybody is allowed to operate. – asdfex Jan 7 at 21:59
    
There are several unlicensed ISM frequency bands where anyone is allowed to transmit (providing they don't intentionally cause interference), but because these frequencies are unlicensed they are usually noisy. In the US, the FCC limits transmitter power in ISM bands to 1W / 4W EIRP. On the other hand, a Technician Class amatuer radio license gives you permission to transmit up to 1500W on many other frequency bands. Using a higher transmit power increases theoretical channel capacity. – Andrew W. Jan 8 at 17:55

The transmitter of the balloon you mentioned is very low speed, caused by several points: The transmitter uses only 10mW because these modules are cheap and can be bought everywhere. They can be operated from a small battery for hours. The 434MHz band it uses is used in many applications and hence has a lot of interference and noise. It used an omnidirectional antenna because using a directional antenna would mean to include mechanics to move the antenna in the right position. Last but not least the whole assembly has to be very lightweight, few 100g usually, not allowing for larger batteries or antennas.

The transmitter used in rockets (no matter how exactly it works or if it transmits directly to earth or via a relay satellite) can be much larger and use a bit more power. But this power requirement is not as high as you might think: Television satellites located more than 36000km away from your dish have transmitters of about 100W only. Powering such a transmitter from a battery for few hours is no big challenge.

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