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The Pioneer anomaly was solved IIRC. The likely culprit was identified as heat being emitted in a particular direction, accelerating the probe due to radiation

The Pioneer anomaly was solved IIRC. The likely culprit was identified as heat being emitted in a particular direction, accelerating the probe due to radiation pressure. https://en.wikipedia.org/wiki/Pioneer_anomaly https://en.wikipedia.org/wiki/Pioneer_anomaly

matt_kantor 11y ago
This is mentioned in the article: > The pioneer probes were nuclear powered through a radioisotope thermoelectric generator (RTG). These RTGs usually give off heat uniformly, but the design of Pioneer meant that some of the radiant heat was reflecting off the probe resulting in a thermal recoil.
akallio9000 11y ago
So if the spacecraft could be stationary, it would pick up 400km/year acceleration via nuclear power?
- clort 11y ago
  No, your maths is wrong.. in fact after 10 years the acceleration had provided a 1km/hr velocity, resulting in a 400km displacement from its projected position.
- david-given 11y ago
  ITM 0.1 km/h/year, and yes. The Pioneer Anomoly is a photon drive: the RTG gets hot, infrared photons get emitted preferentially in a particular direction (because the body of the spacecraft blocks them), and it's a simple reaction drive. Nothing fancy there. You could make it loads more efficient by putting the RTG at the focus of a parabolic reflector. Now all the photons are being emitted in a single direction, which means you get much more thrust. According to this article: https://en.wikipedia.org/wiki/Nuclear_photonic_rocket https://en.wikipedia.org/wiki/Nuclear_photonic_rocket ...a perfectly collimated photonic rocket runs at about 300MW/N. Assuming you're New Horizons, you have a mass of about 500kg and a 4kW RTG, so you'll get a thrust of 0.1mN, which means an acceleration of 5x10^-8 m/s^2. Assuming my arithmetic is correct (a totally unwarranted assumption!), then over a year this adds up to a velocity change of 1.5 m/s.

matt_kantor 11y ago

This is mentioned in the article: > The pioneer probes were nuclear powered through a radioisotope thermoelectric generator (RTG). These RTGs usually give off heat uniformly, but the design of Pioneer meant that some of the radiant heat was reflecting off the probe resulting in a thermal recoil.

akallio9000 11y ago

So if the spacecraft could be stationary, it would pick up 400km/year acceleration via nuclear power?

clort 11y ago
No, your maths is wrong.. in fact after 10 years the acceleration had provided a 1km/hr velocity, resulting in a 400km displacement from its projected position.
david-given 11y ago
ITM 0.1 km/h/year, and yes. The Pioneer Anomoly is a photon drive: the RTG gets hot, infrared photons get emitted preferentially in a particular direction (because the body of the spacecraft blocks them), and it's a simple reaction drive. Nothing fancy there. You could make it loads more efficient by putting the RTG at the focus of a parabolic reflector. Now all the photons are being emitted in a single direction, which means you get much more thrust. According to this article: https://en.wikipedia.org/wiki/Nuclear_photonic_rocket https://en.wikipedia.org/wiki/Nuclear_photonic_rocket ...a perfectly collimated photonic rocket runs at about 300MW/N. Assuming you're New Horizons, you have a mass of about 500kg and a 4kW RTG, so you'll get a thrust of 0.1mN, which means an acceleration of 5x10^-8 m/s^2. Assuming my arithmetic is correct (a totally unwarranted assumption!), then over a year this adds up to a velocity change of 1.5 m/s.