Yes, Voyager 1 loses power each year—its radioisotope thermoelectric generator (RTG) produces about 4 watts less every year. As of 2024, the spacecraft has roughly 250 watts available, down from 470 watts at launch in 1977. This steady decline forces NASA engineers to shut down non-essential systems to keep the probe alive.
Formula
The power output of Voyager 1’s RTG declines by about 4 watts per year, a rate derived from the half-life of plutonium-238 (87.7 years) and the gradual degradation of the thermocouples that convert heat to electricity. The formula is:
P(t) = P₀ × (0.5)^(t / 87.7)
Where:
- P(t) = power at time t (watts)
- Pâ‚€ = initial power at launch, 470 W
- t = years since launch
In practice, engineers use a simpler linear approximation of about 4 W/year for near-term planning, which matches the exponential curve closely over a few decades.
Worked Example
Using the default values (current power 250 W, 47 years since launch), the linear decay model gives:
- Decay per year: 4 W/year (as stated).
- Power after 10 more years: 250 − (4 × 10) = 210 W.
The exponential formula gives a slightly different value: 470 × (0.5)^(57 / 87.7) ≈ 228 W, because the decay rate slows as the plutonium depletes. The linear model is fine for short-term estimates but overestimates loss over many decades.
Background: The RTG and Why Power Drops
Voyager 1 is powered by three radioisotope thermoelectric generators (RTGs) that convert heat from the natural decay of plutonium-238 into electricity. Unlike solar panels, RTGs work in the deep dark of interstellar space, but they have a finite lifespan. The plutonium fuel decays exponentially—half is gone every 87.7 years—so the heat output drops over time. Additionally, the thermocouples (the devices that turn heat into electricity) degrade due to radiation and thermal cycling, reducing conversion efficiency. The combined effect is a roughly linear power loss of about 4 watts per year in the early decades, slowing slightly as the fuel depletes.
How NASA Manages the Decline
To keep Voyager 1 alive, engineers have had to shut down instruments and heaters. Key steps include:
- In 2019, the cosmic ray subsystem was turned off.
- In 2023, the plasma science instrument was shut down.
- In 2024, engineers turned off the voltage regulator heater to save a few more watts.
Each shutdown extends the mission by months or years. The spacecraft still has five active instruments (as of 2024) that measure magnetic fields, plasma waves, and charged particles. NASA prioritizes keeping the most scientifically valuable instruments running.
When Will Voyager 1 Run Out of Power?
If the current trend continues, Voyager 1 will have too little power to operate any instruments by around 2030. However, exact timing is uncertain because the decay rate changes as the RTG ages. The team expects to have to turn off the last instrument by 2030 or 2031. After that, the spacecraft will continue to coast silently through interstellar space, but no data will be transmitted.
Common Misconceptions
One common myth is that Voyager 1 uses a nuclear reactor. It does not—it uses passive decay, not a fission chain reaction. Another misconception is that the power loss is linear forever; in reality, the exponential decay of plutonium means the rate slows over time. Also, some people think the spacecraft is dead already, but as of 2024 it still sends back data, albeit with reduced capabilities.
Comparisons: Voyager 2 and Other RTG Missions
Voyager 2, launched a few weeks earlier, has a nearly identical RTG and loses power at the same rate. Other missions using RTGs include the Curiosity rover (which uses a smaller RTG that decays slowly) and the New Horizons spacecraft (which flew past Pluto). Each has a different power budget and mission profile. For example, New Horizons has only about 200 watts at launch and will likely run out of power in the late 2030s, but it has fewer instruments to power.
Frequently Asked Questions
How much power does Voyager 1 have left?
As of 2024, Voyager 1 has about 250 watts of electrical power, down from 470 watts at launch. That’s enough to run a few light bulbs, but it’s carefully rationed to keep five science instruments alive.
Why doesn’t Voyager 1 use solar panels?
At Voyager’s distance (over 15 billion miles from the Sun), sunlight is only about 1/1000th as intense as at Earth. Solar panels would need to be enormous and still wouldn’t produce enough power. RTGs provide a steady, reliable source regardless of distance.
Can Voyager 1 be recharged or repaired?
No. Voyager 1 is over 15 billion miles away, and no spacecraft has ever traveled that far. The RTG is not rechargeable, and the thermocouples cannot be replaced. Once the power is gone, it’s gone.
What happens when Voyager 1 runs out of power?
When the power drops below the threshold needed to operate even one instrument, NASA will send a final command to turn off the transmitter. The spacecraft will then drift silently for billions of years, carrying the Golden Record as a message to any future finder.
Is the power loss accelerating or slowing?
It’s slowing slightly because the plutonium decay rate decreases as the remaining fuel decreases. However, the thermocouple degradation continues, so the net effect is roughly linear at about 4 W/year for now.