Space Exploration Stack Exchange is a question and answer site for spacecraft operators, scientists, engineers, and enthusiasts. It only takes a minute to sign up.
Sign up to join this community
Voyager 2 started its journey some 37 years back so all of the gases must have been exhausted, but it's still moving at a speed of 15km/s. I can say that this might be due to no opposing force to slow down the speed. But if some space debris gets in its way, or any of the extra-planetary objects get in its way or comes too close, then how will that change its path?
I think the only the way to change the direction is by gases; are there any gases still present?
But if some space debris comes on its way or any of the extra planetary objects comes on its way then how it changes its path?
Not only won't Voyager 2 change it's path, it can't change it's path.
Suppose you drop your cellphone from the top of a tall building. Your cellphone is going to fall and hit the ground, hard. Your cellphone has no sensors to detect the hazard, no effectors to avoid the hazard, and no hazard avoidance software to develop a plan that uses those non-existent effectors to avoid the hazard.
Now suppose one of those Voyager spacecraft is on a collision trajectory with some Oort cloud object. Just as your cellphone is going to hit the ground, hard, so will that Voyager spacecraft hit that object. The Voyager spacecraft have no way to detect that they are on a collision course because the cameras that took all of those beautiful images were powered off a long time ago. Even if they spacecraft could see the imminent collision, the spacecraft have so little fuel left in them that nothing could be done to avoid that collision. Finally, even if the spacecraft still had powered sensors to detect the collision and powered effectors to avoid the collision, it still couldn't avoid that collision (without help from the Earth) because the computers on those spacecraft and the software on those computers are extremely primitive.
Space is almost completely empty. The voyager probes are exceedingly unlikely to collide with anything (as demonstrated here: What is the possibility of Voyager 1/2 colliding with matter (Asteroids or planetoids) present in space?) larger than a mote of dust. If they did collide with anything at 15 km/s, then it slowing them down would be the least of their worries.
They do have some hydrazine fuel left, which they use to control their orientation (attitude). http://www.space.com/11527-nasa-voyager-spacecraft-leave-solar-system.html
Hydrazine, by the way, is not a gas, but a liquid. The probe thrusters catalytically split the hydrazine to produce gases for thrust.
When Voyager was a shiny new probe just heading out back in 1977 (or Pioneer, Apollo, or really anything else we've sent beyond low earth orbit) it didn't have the ability to avoid hazards. It's trajectory was more-or-less fixed the moment the Titan booster cut it loose.
The fuel it carried was for course corrections - gentle nudges to go past Jupiter at just the right angle to get to Saturn in a few years. Yes, we could consider Jupiter to be a hazard it avoided but moon-size and larger hazards are very predictable - the Titan profile considered all of that.
True hazards, the ones that pop up without planning, come in "dust speck" and "rocks and larger" categories. We have nothing, even today, to detect dust specks coming toward us at spacecraft speeds and rocks would need to be pretty big to notice 24+ hours before collision. You need that much time to collect sensor data, return it to earth, analyze it, predict a collision, program a maneuver to avoid the collision, send it to the spacecraft and fire the thrusters to nudge it out of the way. You can't do this just-in-time without pretty big fuel reserves, but if you see it far enough out you only need 1 Newton in the right direction to avoid it.
Every spacecraft gets hit by dust. If it takes a big particle (say, 1mm) in something critical that component is dead. 1 gram at LEO speeds produces 22,000 joules on impact - this is more than a .50BMG round point-blank, and that round can split a truck engine in half. Rises to 144,000 Joules at Voyager's speed. That's a 30mm cannon round.
if it gets hit by an impossible-to-see-coming apple-sized object, it's space junk.
We should also consider two things: First, the computer on the Voyager probes is an ancient, CPU-less system with a bunch of kilobytes of core memory (actually sheet memory, a type of core memory) and the processing speed of a 8-bit home computer. It would be unable to react autonomously. Second, the distance to earth is a bunch of light-hours, meaning that even if the cameras were powered, we would see any object hours after the probe saw it. A command to avoid the object would then take the same amount of hours to reach the probe. Furthermore, as the baud rate at these distances is very low, the probe can deliver images with a framerate of maybe an image per hour or less. So any object colliding with it would have to be big enough to be seen at least some hours before or the probe wouldn't have time to transfer the image. Won't happen though, there's almost nothing out there.
Yes, the Voyagers can still use their thrusters, and they do so regularly, to keep their high-gain antennas pointed at Earth.
But these thrusters are too small to deliver the large course correction that would be needed to avoid a large object at short notice. They might be able to avoid a planetoid if it's detected from the ground a few months in advance, because then the team can command the spacecraft to do a small course correction that will be enough to avoid the planet a few months later.
