Proposed Kilopower Missions
For those in the nuclear engineering field, often the reactor itself seems to be an end in and of itself (I am guilty of this, as well). However, no matter how simple, elegant, unique, or original a concept is, it still is a power source for… something; in this case a NASA mission of some sort. These fall into two broad categories: spacecraft (orbiters or fly-by missions) and landers (either fixed or rovers). Both orbiters and landers have been considered for Kilopower, and we’ll look at some options for each.
What missions have been proposed that this reactor makes possible? Remember, NASA has stacks and stacks of missions that it commissions a one-to-three (usually two) year study on, and stacks them up to wait on certain enabling technologies to come about. Often, this enabling technology is the power supply, and these are the missions that stand out for Kilopower.
Most of these missions did not incorporate a nuclear reactor as part of their power supply options so often the mission changes from what was originally proposed to account for the reactor. In fact, they were all powered by multiple RTGs, as Cassini was (three MMRTGs), which don’t scale well as a general rule. Even if a mission had planned for a reactor, the specific data about this reactor firms up questions that were left in the original design study.
Titan Saturn System Mission (TSSM)
The Titan Saturn System Mission (TSSM) was a design from a 2010 decadal survey design, re-examined by the Collaborative Modeling for Parametric Assessment for Space Systems (COMPASS) in 2014. Originally designed with a 500 W ASRG, a 1 kWe Kilopower reactor was installed instead in the 2014 study. This is a good example of the tradeoffs that are considered when looking at different power supplies: there’s less mass and a shorter trip time for the original, RTG-based electric propulsion spacecraft, but the fission power supply (the reactor) allows for more power for instruments and communications, allowing for real-time, continuous communications at a higher bandwidth while allowing higher-resolution imaging due to the increased power available.
As with the following concepts, this was a mission that was briefly looked at as an option for a mission to use the Kilopower reactor, not a mission designed with the Kilopower reactor in mind from the outset. The short development time of the reactor (I never thought I’d write those words…), combined with the newness of the capability, caught NASA a bit flat-footed in the mission planning area, so not all the implications of this change in power supply have been analyzed.
The mission as designed is impressive: not only is there an orbiter, but a lander (to be designed by ESA, who have already successfully landed on Titan with the Huygens probe), and as a buoyant cherry on top, a balloon for atmospheric study as well.
These low-power missions are where any new in-space power plant will be tested, to ensure a TRL high enough for crewed missions. Because of this, I’m going to be adding mission pages to the website over time, with this being the first, looking at these nuclear-powered probes is the best way to see what could be coming down the pipeline in the near future.
This design is for a flyby of 2060 Chiron, a Centaur-class asteriod. Originally proposed in 2004 as part of a study of radioisotope electric propulsion across the solar system, it was re-examined in 2014 by the COMPASS team.
This is a mission that I’m very interested in, but unfortunately not much has been published on it.
Kuiper Belt Object Orbiter (KBOO)
A close cousin to the Chiron Observer, the KBOO was originally a RPS-powered mission which used an incredible 9 ASRGs, with a total power output of a little over 4 kWe, to examine an as-yet undetermined target in the Kuiper Belt. Having access to nuclear power is a requirement that far into the solar system, and with Kilopower not only is the mission not power-constrained, but is able to increase the amount of bandwidth available for data, and the power will allow for radar surveys of the objects that KBOO will do flybys of.
A predecessor to the Europa Clipper, the JEO was originally designed with 5 MMRTGs (the equivalent of 1 ASRG, 500 We). However, the design could have double the available power, and much higher data return rates and better data collection capabilities, if a 1 kWe reactor was used. This would increase the power plant mass (at 260 kg for the MMRTGs) by an additional 360 kg, but this would also eliminate the need for Pu-238, which remains very difficult to get a hold of.
The Europa Clipper is based on a more economical version of this mission, the Europa Multiple Flyby Mission, and has some of the same hardware.
Human Exploration Missions
While 1 kW of electrical power is certainly smaller than the power requirements for many crewed surface missions, Kilopower has been designed with crewed surface missions in mind. The orientation of the heat pipes has already been tested, and will be tested more thoroughlly at NNSS (when held vertical in a gravity field, the heat pipe acts as a thermosyphon, increasing how much heat the pipes can reject). This reactor could certainly be used for manned space missions as well, but only for what’s known as “hotel load,” not for providing large amounts of electrical power for an electric drive system (we’ll get to that in a couple blog posts). As such, it’s typically seen being used in crewed missions as a modular power unit, with more reactors added as the base grows to keep up with increased power demand.
One of the biggest advantages that Kilopower offers is in terms of in-situ resource utilization, or ISRU. While the power requirements for a large ISRU operation would far exceed the 1 kWe (or even 40 kWe on larger designs) Kilopower offers, it is perfectly positioned in both mass and power to support initial ISRU experimentation. This is a major focus both on the Moon and Mars, with different goals for each location, and different power requirements as well. However, the utility of Kilopower in these settings is significant, and could well enable faster, more efficient ISRU capabilities in a relatively short period of time.
Phase 1 launches before humans ever leave Earth, for ISRU, and will either be solar or fission powered. The trade-off between the systems mass and time required for refueling: more fuel and water can be extracted faster using Kilopower, but it masses more than solar panels (after factoring in the full power production system). Phase 2 is the beginning of crewed missions. In this case, a NASA study showed significant mass savings due to energy storage costs needed for solar power.
With the start of the Artemis program, and the US’s goal of returning astronauts to the Moon, Kilopower offers many advantages, and has been integrated into the Artemis mission planning for the Shackleton crater.
The fundamental advantage on the Moon for fission power systems is the lack of energy storage requirements for the lunar night. The Fission Surface Power program was, in fact, primarily oriented at use with manned Lunar (and later Martian) missions. Kilopower will be able to operate well in these environments, if only offering up to 40 kWe of power (which is where FSP takes over). The study in the Mars section looks at Lunar mission options and requirements as well.