We're the team at NASA that designed and built the High Definition Earth Viewing (HDEV) payload for the International Space Station (ISS), Ask us anything!

Hello HDEV Team! (Liam here - ISS-Above )

Of course as you know I just can't thank you enough for what you have provided to the world with this capability from the ISS.

Now my question.

What was your biggest surprise or unexpected result from launching this experiment?

We were quite surprised by the public reception to our payload. To date, we've had nearly 50 million views on the Ustream page, and we're glad that people have enjoyed it so far. We're also surprised at the lack of visible bad pixels on the video over time.

Love the HDEV! I leave it on every day and have a folder full of cool screenshots.

Do you guys expect to continue the feed beyond the stated end date later this year provided the cameras are still working well?

Currently HDEV has been extended to 2017. Another payload is scheduled to take our place at that time.

is there a big difference between a camera used on earth and a camera used in space?

For our payload, we used commercially available cameras. The cameras are identical to the cameras that you can buy in the store, so there is no difference in the actual hardware. We removed the baseplate on one of the cameras in order to help it fit inside the HDEV enclosure. In addition, we also removed the internal camera batteries and physically locked the focus on the lenses.

As a part of this study, will you be quantitatively or qualitatively comparing the degradation of video quality over time? If quantitatively, what metric will you use to measure this? Will measurements be observed through a software process?

The goal is to quantitatively measure the pixel damage to the sensors over time. During night passes, when the video is black, we use a custom software program to analyze the video and count dead pixels.

Is this why the cameras are sometimes not rotating?

HDEV features two modes: auto-sequence and manual camera selection. We have the capability to manually select any of the cameras.

How does the signal travel from the camera get back to Earth? (What kind of radio signal can travel that far?) Is there a delay and if so, for how long?

The signal follows a somewhat complicated path. In simple terms the video goes from HDEV to the ground via the Space Station Ku band on the TDRSS satellite system. The downlink signal is received at the White Sands Test Facility, and is then transmitted to the Johnson Space Center for processing and distribution.

how delayed is it by the time we see it?

HDEV video is delayed by about 20 seconds to the end user.

Hindsight being 20/20, is there anything you wish you had done differently when designing and implementing the HDEV payload?

We developed HDEV with given resources and an aggressive timeline. We can apply the lessons we've learned to future space systems. The sun's reflection in the windows is greater than we anticipated; so it would have been good to use a coating on the glass to help reduce the reflections.

Do you have a favorite picture taken from HDEV?

From HDEV's perspective, could you rank the continents in order of attractiveness?

We've found that each of us has a favorite picture, and that beauty is in the eye of the beholder. From our perspective 250 miles above, all the Earth is beautiful.

Sometimes the cameras can't be streamed because of lack of signal, does this always happen at the same point? (e.g. Is it when the ISS is over a certain part of the earth where it is far from any transmitters?) Or is it dependent on other factors, e.g. weather?

The ISS loses signal with the ground for a couple of reasons. As the ISS orbits, it will switch satellites it communicates with depending on which one is on the same side of earth as ISS. During this switch the Ku antenna will swing between antennas, causing a short outage. There are also times in the orbit the solar arrays will back the signal between the antenna and satellite as it tracks the sun, these will be slightly longer outages. There is also an area over the Indian Ocean that does not have continuous satellite coverage. In addition, periodically the systems are shut down briefly for maintenance.

Firstly I'd like to say what a cool idea this is. It makes it so much more enjoyable knowing it's live footage. I have a billion questions but i'll ask just a few.

Firstly how much of a delay in the footage is there?

what type of camera/hardware are you using for this?

and what are you plans for the future? will this keep going? multiple camera angles?

The delay in our video distribution varies depending on certain circumstances, including the time it takes to downlink, process, and distribute the video. Typically, HDEV video is delayed by about 20 seconds. Interestingly, the downlink signal delay is only a couple of seconds. The biggest delay occurs during distribution across the Internet.

What would be the next step in this experiment?

The next step is to analyze the camera performance and make recommendations for future use in space.

1. Can the cameras move?
2. What is the amount of delay observed in the live stream?

I want to thank you guys for this. When I am feeling down or just having a bad day, I go to the live stream and just watch our beautiful earth spin. Damn yes we may be small, yes we may be just a speck of dust in the vast expanse of the universe, but what defines us humans are not those things. Its the pursuit of science despite those things. Thanks for being the frontier of human knowledge.

The camera positions are fixed inside the HDEV enclosure. We don't have any pan or tilt capability.

We're glad you've enjoyed the imagery. We had fun making it happen.

Detailed engineering Q's. What is the window material? (Fused silica?) Does it have broadband AR coating inside and out? Is the internal environment 1 atmosphere N2?

The window material is fused silica. We chose not to use an AR coating in order to guarantee as much image quality as possible. The internal environment is in fact 1 atmosphere N2.

will we be able to see "cities" and lights during night anytime soon?

Each of the cameras do have the ability to take images in low light scenarios such as cities at night or auroras. However, each camera has fixed settings which were optimized on the ground for daylight imagery.

If you would like to see cities at night, you can view some of the time lapse sequences created by the Earth Science and Remote Sensing Group at the Johnson Space Center: http://eol.jsc.nasa.gov/BeyondThePhotography/CrewEarthObservationsVideos/. These are created using sequences of still images stitched together to create videos.

Which components were the high school students from HUNCH involved in designing, and how did you work with them? Was it in person in labs, or virtually?

The HUNCH students designed some of the secondary mounting hardware for the cameras, and some of the thermal isolators inside the HDEV enclosure. We provided them with the designs, and the NASA HUNCH team worked with the high schools to manufacture the components.

Do you receive the stream of the 4 cameras in each moment or do you have to choose one? How much bandwidth are you allowed to use for downstream? What resolution have the image you receive?

Thanks for the emotions HDEV gives to earthlings

Only one camera is downlinked at any given time. The HDEV video encoder is configured to output 720p video at 6Mbps. After we receive the video, it is decoded, then re-encoded for the Internet at 4Mbps.

If something were to happen to the camera, would the ISS crew be able to service it, or would that be the end of the experiment?

HDEV is located on an external platform on ISS, and can't be accessed by the crew for maintenance. We have 4 cameras on HDEV. If any one of the cameras fails, we have the option to take it out of the rotation.

Is there a reason that nadir cam doesn't point exactly to nadir but its FOV is slightly shifted toward East? See http://www.satflare.com/track.asp?q=25544#TimeBar for reference.

The nadir camera is shifted due the fact that the ISS is rolled slightly in the starboard direction. In addition, it is tilted to give us a better view of visiting vehicles docking to Node 2.

Have radiation hits been a problem?

The nadir location of HDEV and the enclosure provide some protection against radiation. Radiation has not been a problem to date.

If you were to have an opportunity to build the next version of HDEV – what new capabilities would you put highest on the priority list?

If we get the chance to build another camera payload, we would like to include more commanding capabilities (viewing angles, camera settings, etc) and use more efficient video compression.

In what manner will the lessons learned from HDEV be applied to future imagery gathering procedures? Have you determined any factors as of yet, related to camera construction or technology that produce better image quality or sensor longevity? Furthermore, does the fact that each camera has a distinctly different FOV make it more difficult to interpret certain data?

Some team members from the HDEV project are involved in current imagery system upgrades, so we are carrying forward the lessons learned as the new systems are being designed and built.

We have not yet determined any factors related to the construction or technology to produce better image quality.

The field of view is not a concern because the pixel analysis is performed during the night pass when the video is all black.

What do you do in terms of compression for the live video? And is there any reason why 720p is the highest resolution?

The video is compressed to 6Mbps. We chose 720p because that is the NASA standard for video distribution.