Three reasons actually. First, as the others said, difficulty of bandwidth. We can only receive a faint signal first which leads to a really slow data rate, worse than the old "dial up" connections.
Data rate for Curiosity for instance if communicating directly to Earth varies from 500 to 3200 bits per second so that's a maximum of about 0.4 Kb per second and a minimum of 0.06 Kb per second. See: MSL Rover Information (this may have changed since Spacecraft1o1 did that web page - but it gives a rough idea at least) -
it can upload to the orbiters at a higher data rate when they pass overhead - up to 250 megabits per day (so, that's 31 MB per day) - again according to that website.
They can then then send that back to Earth in their own time at a higher data rate than Curiosity.
Still that 31 MB has to compete with the images taken by the orbiters themselves, as they want to send that back as well, and is not that much if you wanted to stream back movies to Earth.
Also - the data needs to be received by the Deep Sky Network. And the rovers or orbiters have to be positioned so they can transmit to Earth (easier for orbiters than rovers).
You can watch all the data as it is received from the solar system on this website
Deep Space Network Now
Then - the rovers themselves don't have movie capabilities anyway. You need to have a suitable camera before you can take movies, at least if you want it to be a real time movie.
There was a proposal to add an option to Curiosity to add a special stereoscopic movie camera to take high resolution 3D immersive movies or its surroundings. It also had zoom capabilities, was an amazing camera.
But this was descoped. Curiosity can only take stills and its mast cam can't do a gradual zoom in on the field of view.
It still has the original stereoscopic par of cameras - but their dynamic zoom capabilities have been descoped. One of the pair of camera is set to a fixed wide field of view photos, while the other is zoomed right in at the highest zoom setting of the original proposal, and neither of them can change their amount of zoom. So there is no way to take a photograph at any intermediate zoom or to take a stereo pair with both set to the same zoom level.
They did this to save $1.5 million out of the costs of a mission with total cost to NASA of over $1 billion - i.e. a cost saving of about 0.1% - to many at the time it seemed a foolish decision.
You could set it up to take lots of stills one after another, and stitch these together to make a movie - a "time lapse" type movie - but even then - it would take up loads of disk space on the rover and take ages to transmit to Earth - and the scientists have other priorities of things they are more interested to see than a time lapse movie, e.g. to get it to send back images of particular rocks or take photographs to help with navigation.
Then - we have many spacecraft on Mars all wanting to use the very limited bandwidth back to Earth. Typically Curiosity - or the orbiters relaying Curiosity images - will only send images back once a day. So - you plan your images carefully. You won't just stream back HD video for fun even if you had the capability.
So - this will only change if we can find a way to increase the bandwidth for transmissions from Mars.Probably by dedicated satellites around Mars to send data back to Earth - and maybe using lasers rather than radio waves to increase the data rate.
Laser communications test breaks data-rate record
This would do more to increase the amount we can learn from Mars in a shorter period of time than just about any other update. Imagine what it would be like if our Mars orbiters and rovers could stream back high resolution images in seconds, and HD movies in minutes?
With a data rate like that - and imaging capabilities they have we'd know the entire surface of Mars to resolutions well sub meter.
HiRise can take images with resolution as good as 30 - 60 cms (don't have the problems of looking through a thick atmosphere you have for Earth)
HiRISE - Mars Reconnaissance Orbiter
So - in principle we could take photographs of most of the surface of Mars at this resolution or indeed better, with future orbiters. But - that's petabytes of data for a full resolution imaging of the entire surface. Not likely any time soon - instead scientists choose spots of interest and then ask it to zoom in on those only, for the highest resolution images. But it could be done for the entire surface with a fast broadband connection.
Also, we could monitor real time changes of all the areas of interest.
Most of Mars doesn't change - but there are sand features - and features that are little understood that could be caused by dry ice - and other by liquid water even - and these will show changes every day - even over shorter timescales.
And our rovers would then surely be equipped with real time HD video capabilities and would be given more powerful motors also so they could travel kilometers every day. Especially using simulated delayed real time methods, where you build up a model of the landscape around the spacecraft and drive it in that model of the landscape back on Earth and transmit those commands to Mars (similarly to the way it is done in on-line gaming which has similar issues) - we could drive them almost in real time as if they were on the Moon.
It would revolutionize studies of Mars!
Data rate for Curiosity for instance if communicating directly to Earth varies from 500 to 3200 bits per second so that's a maximum of about 0.4 Kb per second and a minimum of 0.06 Kb per second. See: MSL Rover Information (this may have changed since Spacecraft1o1 did that web page - but it gives a rough idea at least) -
it can upload to the orbiters at a higher data rate when they pass overhead - up to 250 megabits per day (so, that's 31 MB per day) - again according to that website.
They can then then send that back to Earth in their own time at a higher data rate than Curiosity.
Still that 31 MB has to compete with the images taken by the orbiters themselves, as they want to send that back as well, and is not that much if you wanted to stream back movies to Earth.
Also - the data needs to be received by the Deep Sky Network. And the rovers or orbiters have to be positioned so they can transmit to Earth (easier for orbiters than rovers).
You can watch all the data as it is received from the solar system on this website
Deep Space Network Now
Then - the rovers themselves don't have movie capabilities anyway. You need to have a suitable camera before you can take movies, at least if you want it to be a real time movie.
There was a proposal to add an option to Curiosity to add a special stereoscopic movie camera to take high resolution 3D immersive movies or its surroundings. It also had zoom capabilities, was an amazing camera.
But this was descoped. Curiosity can only take stills and its mast cam can't do a gradual zoom in on the field of view.
It still has the original stereoscopic par of cameras - but their dynamic zoom capabilities have been descoped. One of the pair of camera is set to a fixed wide field of view photos, while the other is zoomed right in at the highest zoom setting of the original proposal, and neither of them can change their amount of zoom. So there is no way to take a photograph at any intermediate zoom or to take a stereo pair with both set to the same zoom level.
They did this to save $1.5 million out of the costs of a mission with total cost to NASA of over $1 billion - i.e. a cost saving of about 0.1% - to many at the time it seemed a foolish decision.
" MastCam was originally supposed to have a pair of cameras with zoom capability; the descope, which was done to save $1.5 million, changed that to two fixed-focal-length cameras, one at each extreme of the originally planned zoom capabilities of both cameras. The Planetary Society went on record to state that this action appeared to be penny-wise and pound-foolish, and sent a letter(PDF) to Congress to protest it as well as the other instrument descopes. Several of the descoped instruments were later restored, but the MastCam descope stuck."
You could set it up to take lots of stills one after another, and stitch these together to make a movie - a "time lapse" type movie - but even then - it would take up loads of disk space on the rover and take ages to transmit to Earth - and the scientists have other priorities of things they are more interested to see than a time lapse movie, e.g. to get it to send back images of particular rocks or take photographs to help with navigation.
Then - we have many spacecraft on Mars all wanting to use the very limited bandwidth back to Earth. Typically Curiosity - or the orbiters relaying Curiosity images - will only send images back once a day. So - you plan your images carefully. You won't just stream back HD video for fun even if you had the capability.
So - this will only change if we can find a way to increase the bandwidth for transmissions from Mars.Probably by dedicated satellites around Mars to send data back to Earth - and maybe using lasers rather than radio waves to increase the data rate.
This would do more to increase the amount we can learn from Mars in a shorter period of time than just about any other update. Imagine what it would be like if our Mars orbiters and rovers could stream back high resolution images in seconds, and HD movies in minutes?
With a data rate like that - and imaging capabilities they have we'd know the entire surface of Mars to resolutions well sub meter.
HiRise can take images with resolution as good as 30 - 60 cms (don't have the problems of looking through a thick atmosphere you have for Earth)
HiRISE - Mars Reconnaissance Orbiter
So - in principle we could take photographs of most of the surface of Mars at this resolution or indeed better, with future orbiters. But - that's petabytes of data for a full resolution imaging of the entire surface. Not likely any time soon - instead scientists choose spots of interest and then ask it to zoom in on those only, for the highest resolution images. But it could be done for the entire surface with a fast broadband connection.
Also, we could monitor real time changes of all the areas of interest.
Most of Mars doesn't change - but there are sand features - and features that are little understood that could be caused by dry ice - and other by liquid water even - and these will show changes every day - even over shorter timescales.
And our rovers would then surely be equipped with real time HD video capabilities and would be given more powerful motors also so they could travel kilometers every day. Especially using simulated delayed real time methods, where you build up a model of the landscape around the spacecraft and drive it in that model of the landscape back on Earth and transmit those commands to Mars (similarly to the way it is done in on-line gaming which has similar issues) - we could drive them almost in real time as if they were on the Moon.
It would revolutionize studies of Mars!
About the Author
Robert Walker
Writer of articles on Mars and Space issues - Software Developer of Tune Smithy, Bounce Metronome etc.Studied at Wolfson College, Oxford
Lives in Isle of Mull
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