(In)visible revolution
Watching historic barge landing of the first stage of Falcon 9 rocket during CRS-8 mission, it was hard not to be excited by all the cheering of SpaceX engineers. Something like this is usually experienced during sport events.
It seemed like a historic moment - excitement was so high that primary mission - delivery of Dragon spacecraft to orbit, was something not really paid much attention to. Rocket landing on a small, movable patch of artificial land far on the sea. That was really exciting. Mastery and precision of vehicle and thrust vector control finally enables recovery and reuse of the 1st stage. Expected results: up to 30% launch cost reduction in the longer run. Economically speaking, SpaceX is still far away from radical reduction of the launch costs.
But after watching re-run of the whole launch, I became aware of another, much more transparent revolution that is also happening in front of our eyes. While watching the video, we have been seeing a concurrent live video feeds in HD quality - from both stages, Dragon trunk, ASDS and a chasing airplane. Having all these video feeds in high quality, available, from mobile, moving remote locations is no small feat. And the real neat thing is: all that communication infrastructure cost probably was very very small percentage of the total cost.
This aspect is important because every other aspect of space economy critically depends upon communications. Telecommunication satellites need high bandwidth. Remote sensing satellites also. Scientific, deep space probes - also. And human space flight? There are continuous live broadcasts of video feeds from the space station. And on every ISS mission, there is a live feed during capture and docking phases of the mission. They clearly have very important educational and entertainment value.
So the need of downlink bandwidth is of growing importance for every space mission. Downlink from Mars orbit is around 250kbit at best of times. From New Horizons we get 2000 bits per second with two meter antenna. From Mars we can get whopping 256kbit per second. So fast that it sometimes surpasses 2G mobile network. At the moon it gets better - LRO had up to 100mbit per second using 40W antenna. And from the ISS? It is quite better. Blazingly fast 30mbit uplink and 300mbit downlink. Sounds nice, until you consider that it is a 100 billion+ facility.
Introduction of laser based communication terminals changes this equation. LADEE has LLCD experiment which demonstrated 622Mbit downlink. EDRS demonstrated 1.8GBit downlink. OPALS was around 400mbps (calculated).
But the real problem with laser based communication in space is pointing. Greater frequency means smaller beam spot size. Thus spacecraft needs increased accuracy of attitude control in order to maintain a stable link. This problem is explained well in this LLCD presentation, where they needed to implement measurement and compensation for microvibrations on the LADEE spacecraft in order to maintain a stable beam pointing.
Problem of downlink bandwidth also affects small satellites in LEO. Remote sensing satellites collect huge amount of data that needs to be cached on-board and downloaded to ground stations during brief passes. Antennae pointing needs to be adjusted quickly due to relative attitude changes between satellite and the ground station.
In radio communications world, an emerging technology is dynamically steerable phased array antenna, which offers electrically/electronically controlled beam steering without any movable parts. Electrically driven pointing is much faster than mechanical pointing. For satellites that translates to reduced stresses and cycles on RCS and momentum wheels. In other words - it increases lifetime of the satellite. There are many contenders in this arena: Kymeta, Phasor, as well as "classic" providers such Harris/Exelis.
Since laser based communication terminals offer much narrower beam, they are also more sensitive to any on-board vibrations or attitude inaccuracies. Thus electrically controlled beam steering would be ideal companion to LCT based communication, enabling also spacecraft-to-spacecraft and spacecraft-to-ground station communication. Wide beam steering capability enables easy switching between ground stations, which is especially important due to weather/cloud sensitivity of laser communication links. Some time ago I was thinking about this idea and found optics vendor Vescent Photonics, which provided just that - electrically controlled laser beam steering. At that time, the primary purpose of the device was adaptable barcode scanning. I got it touch with the vendor asking whether it could be applied for the space applications.
And then I got in the email notification of their two papers: "Laser-based satellite communication systems stabilized by non-mechanical electro-optic scanners. But it gets better: here is the quote from their previous paper coauthored with JPL:
It seemed like a historic moment - excitement was so high that primary mission - delivery of Dragon spacecraft to orbit, was something not really paid much attention to. Rocket landing on a small, movable patch of artificial land far on the sea. That was really exciting. Mastery and precision of vehicle and thrust vector control finally enables recovery and reuse of the 1st stage. Expected results: up to 30% launch cost reduction in the longer run. Economically speaking, SpaceX is still far away from radical reduction of the launch costs.
But after watching re-run of the whole launch, I became aware of another, much more transparent revolution that is also happening in front of our eyes. While watching the video, we have been seeing a concurrent live video feeds in HD quality - from both stages, Dragon trunk, ASDS and a chasing airplane. Having all these video feeds in high quality, available, from mobile, moving remote locations is no small feat. And the real neat thing is: all that communication infrastructure cost probably was very very small percentage of the total cost.
This aspect is important because every other aspect of space economy critically depends upon communications. Telecommunication satellites need high bandwidth. Remote sensing satellites also. Scientific, deep space probes - also. And human space flight? There are continuous live broadcasts of video feeds from the space station. And on every ISS mission, there is a live feed during capture and docking phases of the mission. They clearly have very important educational and entertainment value.
So the need of downlink bandwidth is of growing importance for every space mission. Downlink from Mars orbit is around 250kbit at best of times. From New Horizons we get 2000 bits per second with two meter antenna. From Mars we can get whopping 256kbit per second. So fast that it sometimes surpasses 2G mobile network. At the moon it gets better - LRO had up to 100mbit per second using 40W antenna. And from the ISS? It is quite better. Blazingly fast 30mbit uplink and 300mbit downlink. Sounds nice, until you consider that it is a 100 billion+ facility.
Introduction of laser based communication terminals changes this equation. LADEE has LLCD experiment which demonstrated 622Mbit downlink. EDRS demonstrated 1.8GBit downlink. OPALS was around 400mbps (calculated).
But the real problem with laser based communication in space is pointing. Greater frequency means smaller beam spot size. Thus spacecraft needs increased accuracy of attitude control in order to maintain a stable link. This problem is explained well in this LLCD presentation, where they needed to implement measurement and compensation for microvibrations on the LADEE spacecraft in order to maintain a stable beam pointing.
Problem of downlink bandwidth also affects small satellites in LEO. Remote sensing satellites collect huge amount of data that needs to be cached on-board and downloaded to ground stations during brief passes. Antennae pointing needs to be adjusted quickly due to relative attitude changes between satellite and the ground station.
In radio communications world, an emerging technology is dynamically steerable phased array antenna, which offers electrically/electronically controlled beam steering without any movable parts. Electrically driven pointing is much faster than mechanical pointing. For satellites that translates to reduced stresses and cycles on RCS and momentum wheels. In other words - it increases lifetime of the satellite. There are many contenders in this arena: Kymeta, Phasor, as well as "classic" providers such Harris/Exelis.
Since laser based communication terminals offer much narrower beam, they are also more sensitive to any on-board vibrations or attitude inaccuracies. Thus electrically controlled beam steering would be ideal companion to LCT based communication, enabling also spacecraft-to-spacecraft and spacecraft-to-ground station communication. Wide beam steering capability enables easy switching between ground stations, which is especially important due to weather/cloud sensitivity of laser communication links. Some time ago I was thinking about this idea and found optics vendor Vescent Photonics, which provided just that - electrically controlled laser beam steering. At that time, the primary purpose of the device was adaptable barcode scanning. I got it touch with the vendor asking whether it could be applied for the space applications.
And then I got in the email notification of their two papers: "Laser-based satellite communication systems stabilized by non-mechanical electro-optic scanners. But it gets better: here is the quote from their previous paper coauthored with JPL:
Here we have begun a design for a system that could fit within a few cubic inch volume, require less than 1 watt of power and be able to provide ground station tracking (including orbital motion over wide angles and jitter correction) with a >50 Mbps downlink and no moving parts.What it means is that you can have a Cubesat in LEO with sustainable 50Mbps downlink without any intermediary satellite in GEO. That takes remote sensing applications a step further. That is one high resolution image per second instead od having a new image of any place on earth every few hours...we can have it every minute. Live traffic routing? Check. Instant imaging of every disaster anywhere in the world? Check. Locating and reporting open fire in five minutes? Check. Detecting large number of soldiers on any border? Check. Detecting illegal border crossings? Check. Finding lost airplanes and ships in minutes anywhere in the world? Check. And we haven't even touched astronomy, multispectral, radar and telecommunication applications yet.
Introduction of low-cost laser based communication terminals might prove more significant than reusable rockets.
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