Voyager Spacecraft: The Ultimate Power Management Challenge?

2026-07-09T14:00:00Z

The power management issues faced by the Voyager spacecraft make yours look trivial.

It’s not news that power management, in one form or another, is increasingly a priority consideration for nearly all designers. Whether it’s sipping microwatts from a tiny battery or providing megawatts to AI data centers, designers struggle with obtaining and handling power, often followed by concerns about “disposing” of the waste heat.

Despite the challenges these power management scenarios present, they are not unique, one-off cases. Instead, each of them has enough commonality and unit volume to warrant dedicated conferences, forums, publications, industry standards, and consultants focused on addressing them.

However, there are some truly unique cases, especially when it comes to deep-space vehicles with no precedent or examples to follow. Among the most extreme examples are the

Both spacecraft have gone

The paired Voyagers were launched a few months apart after a tightly compressed design, build, and launch schedule. The project’s “rush” and hard deadline were driven by a fortuitous and rare alignment of the major planets, allowing for a “grand tour” that would exploit an upcoming alignment of Jupiter, Saturn, Uranus, Neptune, and Pluto—an event that would occur in the late 1970s and not recur for another 175 years.

What further enabled this “tour” was an insight by a UCLA graduate student in June 1961.

Can you spare some milliwatts?

Each Voyager is powered by a

Despite its low efficiency, the RTG is the only choice that makes sense. The heat that is not converted to electricity is not wasted; it is routed to heat the associated electronics, a critical function in space.

Note that TEGs and RTGs have been used on almost every manned and unmanned spacecraft since the early days, but NASA doesn’t make a big deal about it for obvious, radiation-related reasons.

Both Voyager probes lose about 4 W of power output each year. After almost half a century in space, their available power margins have become very thin, requiring the team to conserve energy by shutting off heaters and instruments while ensuring that the spacecraft don’t get so cold that their fuel lines freeze.

Although many isotopes offer the needed decay, plutonium isotope Pu-238 best satisfies the RTG fuel requirements. It has high radiation output that is primarily due to alpha decay and thus has low shielding needs, a very long half-life of just under 88 years, and a fuel pellet packaged into the size of a marshmallow, fabricated in the form of plutonium dioxide (Figure 4). Depending on the RTG and mission, initial nominal power generation ratings are between 100 and 500 W. Some higher-power units are also made, but there is a significant weight penalty.

There are also battery fabrication issues. Pu-238 is a byproduct of nuclear weapons production and nuclear power operations. Its availability has been a problem, as some of the reactors used to produce it have been shut down for various reasons. Also, you can’t make more than you need and just store the excess, because it inherently and unavoidably decays while sitting “on the shelf.” The output power degradation due to the radioactive decay of Pu-238 is about 0.8% per year.

There’s also thermocouple degradation at about 0.8% per year, depending on the material and the operating conditions. Thermocouples used in RTGs and RTUs contain high-performance thermoelectric materials such as bismuth telluride; lead telluride; tellurides containing antimony, germanium, and silver; and silicon germanium.

What’s the power management challenge here for the Voyager spacecraft?

It’s logical to assume that, given the distance to the Voyagers, the data link rate of about 100 bits/second (yes, bits), their relatively ancient and crude technology, and the round-trip signal delay, there would be little opportunity for ongoing power management. In fact, that’s not the case at all.

I recently saw an announcement from NASA that engineers at the Jet Propulsion Laboratory at California Institute of Technology in Southern California (which manages Voyager and other unmanned spacecraft) had sent commands on April 17 to

The LECP measures low-energy charged particles, including ions, electrons, and cosmic rays originating from our solar system and galaxy. It has operated almost without interruption since the launch of Voyager 1 nearly half a century ago—an impressive record for any sensitive electronic instrument, especially one that has also endured the rigors of space, including extreme cold and radiation.

There’s a major “mindset” difference between managing RTGs and conventional batteries. The number of watts the RTG can deliver is strictly a function of the initial design and the battery’s age, not the power drawn, and it declines with time due to natural decay, irrespective of the load. This contrasts with a conventional chemical battery, where deliverable power is first defined by energy capacity (watt-hours). With RTGs, it’s more of a “use it or lose it” situation.

For system designers using conventional batteries, perhaps with solar-based recharging, the way to extend battery life is to cut back on loads, either via manual direction or dynamic, autonomous load management. For spacecraft and especially Voyager at this point, there are too many operational unknowns. Therefore, the mission controllers must decide how to best allocate the available power—and that available power cannot be throttled back to extend power-source life.

There’s also the time lag in an operating environment where nothing happens quickly. The choice of which instrument to turn off next wasn’t made suddenly. Years ago, the Voyager science and engineering teams sat down together and agreed on the order in which they would shut off parts of the spacecraft while ensuring the mission can continue to conduct its unique science. Of the 10 identical sets of instruments that each spacecraft carries, seven have been shut off so far. For Voyager 1, the LECP was next on that list; the team already shut off the LECP on Voyager 2 in March 2025.

Try to imagine operating the spacecraft, including standard functions such as getting routine data, receiving interrupt updates, issuing directives, and receiving confirmation after a command is issued. Because Voyager 1 is more than 15 billion miles (25 billion kilometers) from Earth, a sequence of commands to shut down the instrument will take over 23 hours just to reach the spacecraft and another three-plus hours before confirmation that the shutdown has been completed can be received.

That’s an almost incomprehensible pace to designers who do power management on a millisecond/microsecond time scale. Adding to the challenge, the communication window is very limited and must be carefully scheduled, as radio dishes are booked with so many users wanting their slice for other projects. There’s no “let’s just do it right now” in this situation, that’s for sure.

If you are interested in the amazing story of the paired Voyagers, check out the book “

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RELATED TOPICS: AEROSPACE/AVIONICS MILITARY AND AEROSPACE POWER MANAGEMENT SPACE APPLICATIONS SPACECRAFT

COMPANIES: NASA

Bill Schweber is an electronics engineer who has written three textbooks on electronic communications systems, as well as hundreds of technical articles, opinion columns, and product features. In past roles, he worked as a technical website manager for multiple EE Times sites and as both Executive Editor and Analog Editor at EDN. At Analog Devices, he was in marketing communications; as a result, he has been on both sides of the technical PR function, presenting company products, stories, and messages to the media and also as the recipient of these. Prior to the marcom role at Analog, Bill was Associate Editor of its respected technical journal, and also worked in its product marketing and applications engineering groups. Before those roles, he was at Instron Corp., doing hands-on analog- and power-circuit design and systems integration for materials-testing machine controls. He has a BSEE from Columbia University and an MSEE from the University of Massachusetts, is a Registered Professional Engineer, and holds an Advanced Class amateur radio license. He has also planned, written, and presented online courses on a variety of engineering topics, including MOSFET basics, ADC selection, and driving LEDs. Follow Bill on LinkedIn

Bill Schweber is an electronics engineer who has written three textbooks on electronic communications systems, as well as hundreds of technical articles, opinion columns, and product features. In past roles, he worked as a technical website manager for multiple EE Times sites and as both Executive Editor and Analog Editor at EDN. At Analog Devices, he was in marketing communications; as a result, he has been on both sides of the technical PR function, presenting company products, stories, and messages to the media and also as the recipient of these. Prior to the marcom role at Analog, Bill was Associate Editor of its respected technical journal, and also worked in its product marketing and applications engineering groups. Before those roles, he was at Instron Corp., doing hands-on analog- and power-circuit design and systems integration for materials-testing machine controls. He has a BSEE from Columbia University and an MSEE from the University of Massachusetts, is a Registered Professional Engineer, and holds an Advanced Class amateur radio license. He has also planned, written, and presented online courses on a variety of engineering topics, including MOSFET basics, ADC selection, and driving LEDs.