The US Military's use of drones has become commonplace, and widely known at this point. Although these vehicles are operated from nearby bases during these attacks, it seems like the latency (time of transmission) would be problematic as far as flying goes. Are these vehicles typically flown 100% by autopilot, where there's very little real-time reaction?
There are multiple ways to fly and control Unmanned Aerial Vehicles (UAV), or drones, for e.g. the Predator.
- Some UAVs (like the Global Hawk) can perform the entire mission (from takeoff to landing) autonomously, negating the need for a pilot.
- Most of the UAVs, like Predator can perform (i.e. fly in) some simple missions (like reconnaissance) autonomously.
- In case a geostationary satellite is used for communication with the UAV, the latency is around 300 ms (The electromagnetic waves have to travel ~70000 km). In case of other delays (like equipment etc.) this will not be greater than 500 ms or around half a second. This is not significant in case of slow moving systems like Predator (they are not dog-fighting, after all) and the 'pilot' can effectively control the aircraft.
- The only situation where this is a problem is when the UAV is taking off/landing and in this case, the control is handed over to local LoS operators.
The Predator is reported to have a 'latency' of around two seconds, which causes problems during takeoff/landing. According to the telegraph,
But the two-second delay between a pilot moving a joystick in Nevada and an aircraft responding in Afghanistan is enough to cause a crash during take-off and landing. Crews in Afghanistan control 'launch and recovery’ through direct contact with antennae on the aircraft. Half an hour after take-off, control of the Reaper is handed to a crew in Nevada; half an hour before landing, it returns to the crews on the ground in Kandahar.
Note that the RAF also does things the same way. According to the report on formation of 'drone' squadron' at RAF Waddington,
Although the personnel will be permanently based at RAF Waddington, some will go to Afghanistan to control the take-off and landing of the drones locally.
The aerodynamic surfaces of a drone are controlled by computers, not by humans. When a human makes a control input this input is broadcast to the UAV, and the computers on the UAV make the appropriate changes to the flight surfaces to carry that input out. It's not direct control of the drone by humans via radio.
Source: Acquaintances who worked on avionic software and hardware development
- Latency matters for anything mechanical that flies !
- On-board equipments are developed to handle sub-second interactions. Any interaction from ground is assumed to take many 100s of milliseconds to reach the flight (anything that flies). Humans operating the flight are trained to be quick and anticipate rather than react !
- To minimize the impact of latency, a series of information keeps flowing thereby converting latency problem into throughput problem. Throughput problems can be handled using multiple beacons / transmitting sources. This does not reduce latency but pre-loads onboard systems with accurate data to anticipate next 500 mS or so.
- To understand the solutions for latency, look for 2 businesses that are latency sensitive - gaming and high frequency trading. To put things in perspective, in HFT, a market event is detected by software and it generates an order and sends it - all under 1 micro-sec. Further latencies in network stack is not measured here but it gives you a sense of what operates here.
A significant number of these devices use "top/level" control. The operator may have a camera to see what is in front of the device but the main screen they are looking at is a top view of the landscape (including height map) of where it is flying. The altitude is set to x meters/yards above ground/sea level. The device maintains height and direction based on this input. As the drone isn't in live action and dodging anything - the delays and adjustments do not impact the route of the machine.
E.g. A 90 degree turn only requires 2 signals. One to initiate the turn and the other back to base to confirm the turn is complete and the drone's current positioning.
You would rarely find a full scale drone needing manual adjustment of anything less than 500 meters. Also the video footage from the drone is usually only uploaded at full quality once it has returned home.