# Antigravity and space probes **URL:** \ **Category:** Factual Questions\ **Created:** [February 11, 2005, 2:20pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575 "2005-02-11T14:20:00Z")\ **Posts on this page:** 10\ **Page:** 1
**Author:** ![Fromage\_A\_Trois](https://avatars.discourse-cdn.com/v4/letter/f/a88e57/32.png) [@Fromage\_A\_Trois](https://boards.straightdope.com/u/Fromage_A_Trois)\ **Post date:** [February 11, 2005, 2:20pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/1 "2005-02-11T14:20:00Z")
I have read over the past few years several references to [this phenomenon](http://news.bbc.co.uk/2/hi/science/nature/1332368.stm) that has been observed on several probes drifting in deep space. The gist of it is, Pioneers 10 and 11 and Voyagers 1 and 2 (and it seems other probes) are not quite proceeding as predicted by Einstein’s equations of gravity. Oddly enough I’ve read conflicting reports, some say that the probes are slowing down more than expected, others saying that it’s less than expected. If they’re slowing down less than expected, this might mean the existence of some anti-gravitational force, which would be interesting to investigate. My question is - has anyone ascertained what’s causing this effect? And is it slowing down more or less than expected? Apologies if this has been asked before but I can’t search the threads. ---
**Author:** ![Bosda\_Di\_Chi\_of\_Tricor](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bosda_di_chi_of_tricor/32/16845_2.png) [@Bosda\_Di\_Chi\_of\_Tricor](https://boards.straightdope.com/u/Bosda_Di_Chi_of_Tricor)\ **Post date:** [February 11, 2005, 2:59pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/2 "2005-02-11T14:59:44Z")
giving you a bump ---
**Author:** ![Squink](https://avatars.discourse-cdn.com/v4/letter/s/b5e925/32.png) [@Squink](https://boards.straightdope.com/u/Squink)\ **Post date:** [February 11, 2005, 3:45pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/3 "2005-02-11T15:45:43Z")
The **slowing** of Pioneer 10 and 11 is still unexplained. > [@](#): > > The discrepancy caused by the anomaly amounts to about 248,500 miles (400,000 kilometers), or roughly the distance between Earth and the Moon. That’s how much farther the probes should have traveled in their 34 years, if our understanding of gravity is correct. [The Problem with Gravity: New Mission Would Probe Strange Puzzle](http://www.space.com/scienceastronomy/mystery_monday_041018.html) (Oct 2004) This wikipedia article on [the Pioneer Anomoly](http://en.wikipedia.org/wiki/Pioneer_anomaly) claims that the Galileo and Ulysses spacecraft also experienced the effect. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [February 11, 2005, 3:52pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/4 "2005-02-11T15:52:38Z")
The most recent review of the situation by the Pioneer tracking team is [this paper](http://arxiv.org/PS_cache/gr-qc/pdf/0104/0104064.pdf) (a large pdf). What’s unexplained is a tiny anomolous acceleration towards the Sun, so the spacecraft are slowing down by slightly more than expected. The team themselves admit that they don’t know what the cause is, but suspect it’s mundane; from their conclusion: > [@](#): > > Until more is known, we must admit that the most likely cause of this effect is an unknown systematic. (We ourselves are divided as to whether “gas leaks” or “heat” is this “most likely cause.”) > The arguments for “gas leaks” are: i) All spacecraft experience a gas leakage at some level. ii) There is enough gas available to cause the effect. iii) Gas leaks require no new physics. However, iv) it is unlikely that the two Pioneer spacecraft would have gas leaks at similar rates, over the entire data interval, especially when the valves have been used for so many maneuvres … iv) Most importantly, it would require that these gas leaks be precisely pointed towards the front of the spacecraft so as not to cause a large spin-rate changes. But vi) it could still be true anyway. > The main arguments for “heat” are: i) There is so much heat available that a small amount of the total could cause the effect. ii) In deep space the spacecraft will be in approximate thermal equilibrium. The heat should then be emitted at an approximately constant rate, deviating from a constant only because of the slow exponential decay of the Plutonium heat source. It is hard to resist the notion that this heat somehow must be the origin of the effect. However, iii) there is no solid explanation in hand as to how a specific heat mechanism could work. Further, iv) the decrease in the heat supply over time should be seen by now. In other words, there are at least two energy sources on board that could account for the effect, but nobody can quite nail it on either. You may be interested in [this related Great Debates thread](http://boards.straightdope.com/sdmb/showthread.php?t=247101) from last year. ---
**Author:** ![TwoTrouts](https://avatars.discourse-cdn.com/v4/letter/t/a9adbd/32.png) [@TwoTrouts](https://boards.straightdope.com/u/TwoTrouts)\ **Post date:** [February 11, 2005, 3:58pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/5 "2005-02-11T15:58:00Z")
Interesting phenomenon. [Here](http://citebase.eprints.org/cgi-bin/fulltext?format=application/pdf&identifier=oai%3AarXiv.org%3Agr-qc%2F0107092) is another article attributing the anomalous behavior of the probes to conventional forces (rthermal radiation and gas leaks). Verey similar to the study that **bonzer** linked. ---
**Author:** ![Fromage\_A\_Trois](https://avatars.discourse-cdn.com/v4/letter/f/a88e57/32.png) [@Fromage\_A\_Trois](https://boards.straightdope.com/u/Fromage_A_Trois)\ **Post date:** [February 11, 2005, 4:31pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/6 "2005-02-11T16:31:39Z")
Thanks guys, that’s very helpful! I shall continue to monitor this issue with interest. The links you provided contain a lot of information. ---
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [February 11, 2005, 8:59pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/7 "2005-02-11T20:59:52Z")
Just a total WAG that came to mind, perhaps intersteller space is destructive to normal matter, but large gravity fields, or solar winds or something prevents this. The probes are dematerilizing as they travel further away, and the ‘front’ of the probe is experencing the greatest of this, giving it a net acceleration to the sun. (well it’s better then the heat theory) ---
**Author:** ![CynicalGabe](https://avatars.discourse-cdn.com/v4/letter/c/3e96dc/32.png) [@CynicalGabe](https://boards.straightdope.com/u/CynicalGabe)\ **Post date:** [February 11, 2005, 9:15pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/8 "2005-02-11T21:15:23Z")
I think its Minbari artificial gravity technology. ---
**Author:** ![Enola\_Straight](https://avatars.discourse-cdn.com/v4/letter/e/dec6dc/32.png) [@Enola\_Straight](https://boards.straightdope.com/u/Enola_Straight)\ **Post date:** [February 11, 2005, 9:34pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/9 "2005-02-11T21:34:21Z")
Someone posted a similar thread a while back and I presented a theory of mine: These probes are encountering the Heliopause…the edge of the Sun’s solar wind cannot expand against the prevailing interstellar conditions. Basically, the probes’ tailwind just became a headwind. ---
**Author:** ![bonzer](https://avatars.discourse-cdn.com/v4/letter/b/45deac/32.png) [@bonzer](https://boards.straightdope.com/u/bonzer)\ **Post date:** [February 12, 2005, 12:43pm UTC](https://boards.straightdope.com/t/antigravity-and-space-probes/289575/10 "2005-02-12T12:43:52Z")
> [@Enola Straight](#): > > Basically, the probes’ tailwind just became a headwind. Note that Anderson _et al_, linked to above, include the pressure of the solar wind in their error budget - see section VII, B. Their conservative estimate is that the “tailwind” from it is no more than 1/100th that from solar radiation and less than about a millionth of the unexplained acceleration (equation (54) and Table II).