13

The image below, found in this answer shows four "Solar Pressure Vanes" on Mariner 4.

I've never heard of such a thing.

I can imagine that it might have been thought to help favor the spacecraft's direction more towards the Sun than away from it which might at least keeping the low gain antenna from being completely behind the spacecraft relative to Earth in the event of loss of attitude control.

But I wonder, without damping would they just induce crazy though extremely slow oscillations?

Question: What is the principle behind Mariner 4's "Solar Pressure Vanes"? In what case(s) would they be effective?

Mariner's Solar Pressure Vane

The Mariner 4 spacecraft

above x2: Cropped from image in COSMOS Magazine. "The Mariner 4 spacecraft. CREDIT: NASA / JPL"

uhoh
  • 148,791
  • 53
  • 476
  • 1,473
  • If it were a first order system, then it would just oscillate as you suggest. However, at the same angle, a vane moving toward the sun will be struck with a higher relative volocity than a vane moving away from the sun, producing a second order effect, damping the motion.

    Or to put it another way, it's like a shuttlecock.

     –  May 07 '18 at 01:18
  • @JCRM considering the speed of light is 3E+08 m/s and the speed of "tilt" would be a dozen orders of magnitude slower, I'm really looking forward to seeing the calculation that demonstrates this is realistic. Maybe it is, but wow it's hard to imagine it would damp on the scale of even years due to the Doppler effect. Why not post this as an answer and see what happens? – uhoh May 07 '18 at 01:22
  • I was wondering how the vanes would work in a spin-stabilized craft; I'm imagining that gyroscopic precession would make a mess of things. But the internet tells me that Mariners were not spin stabilized, so that's how. – Wayne Conrad May 07 '18 at 01:42
  • @uhoh, it's restorative, proportionate and damped - a perfect passive control. For tiny peturabations that should be fine. Timescales are for engineers. I'd never post speculation as an answer. –  May 07 '18 at 01:57
  • @JCRM Shuttlecocks do not have moving parts, much less star cameras and computers. It's not passive damping "like a shuttlecock". Turn off the computer, will there still be damping? – uhoh May 07 '18 at 02:05
  • 1
    @uhoh, they were a passive system, even though they were adjusted. It is, as you pointed out, unlikely the damping would be in a practical timeframe; and without trim adjustment it is unlikely it would work in the real solar system. –  May 07 '18 at 02:13
  • The vanes are to small/passive and can be made much larger to propel and change orbit not only stabilize. – Muze May 07 '18 at 02:21
  • 4
    Per the comment by @WayneConrad , in the 1990's I came up with a method for using light pressure to keep a spin-stabilized spacecraft in a heliocentric orbit roughly sun-pointed. NASA gave me a little money to analyze it (I got out my coin purse for the award money! ;-) and I found it would work for small satellites, stuff roughly the size of a 12U CubeSat or smaller. But NASA decided they weren't really interested, published a summary of my report in Tech Briefs, and that was the end of it. – Tom Spilker May 07 '18 at 02:38
  • @TomSpilker is this it? https://www.techbriefs.com/component/content/article/1357 or this? https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20110023954.pdf or is there a full report somewhere? – uhoh May 07 '18 at 02:44
  • 2
    @uhoh , both sites refer to the same work. I gave them a full report but I don't think they ever published it. – Tom Spilker May 07 '18 at 03:04
  • 2
    I wonder if they could be made into active system while remaining solid-state. Using materials like e-paper to change reflectivity of the vanes, providing active stabilization. – SF. May 07 '18 at 06:58
  • @SF. that is a really really cool idea! Either 1. Delete your comment and start writing a patent, 2. write a story, or 3. write another answer to the 10,000 year satellite question. You can modify it to include self-point solar warmers (or solar-avoiding radiators) and even self-pointing photovoltaics. – uhoh May 07 '18 at 07:01
  • @TomSpilker it easy to come up with the idea but another to put it in practice. I suggest that the whole idea you have can take different shapes and manipulate the gradients of gravity of Earth. – Muze May 08 '18 at 03:22
  • @Muze , this wasn't for Earth-orbiters, it was for craft in heliocentric orbits, where the gravity gradient is truly tiny. – Tom Spilker May 08 '18 at 03:37
  • @TomSpilker Still a non zero as long as you are in the suns gravity well it can be used as a gradient. I'm not even sure that much gradient is needed to have a dramatic overall effect on the trip. – Muze May 08 '18 at 04:39
  • 1
    FYI, James Webb will have some too ! – Antzi Apr 09 '19 at 05:25
  • @Antzi tell me more? How will JWST manage solar pressure effects to maintain attitude and station keep it's unstable orbit? – uhoh Apr 09 '19 at 06:43

1 Answers1

13

The vanes move to stabilse the spacecraft - although that may only be a first order stabilisation "Compensation for an unbalance in solar radiation pressure is provided by moveable paddles located on the tips of the solar panels"