No Reg units?
The other day, I think, we decided on hamsters (~53 hamsters per Watt) as a measurement of power. There must be a work equivalent we could use here. Power and work, I believe, are gaps in the Reg calculator...
New NASA measurements of the orbit of the half-kilometer asteroid 1999 RQ36 have given space science its most precise measurement of such space rocks' orbit – and revealed a 160km deviation from the orbit predicted by gravity. The drift, which showed up by comparing observations made in 1999, 2005, and September 2011, is due …
Radiation pressure is much stronger than that produced by the solar wind (by about three orders of magnitude).
It's not negligible, however, and is taken into account when predicting the orbit of a GPS satellite to high precision, for example.
Unlike the solar wind, radiation pressure produces an off-axis force vector for a rotating body (in simple terms it gets hot, turns a bit, re-radiates as it cools).
Fuss, fuss pedantry...
Simple radiation pressure is an on-axis force, and it is radially oriented with respect to the primary, because it is just momentum transfer caused by the secondary absorbing or reflecting the outward radiation from the primary (presumed to be uniform). At the sub-micrometre level, radiation pressure from the Sun is strong enough to completely counter gravity, and such particles inevitably leave the Solar System
Yarkovsky effect forces are caused by the fact that part of the surface of a body is hot, while part is not-so-hot, and that those parts are not radially aligned. The hotter parts emit more photons, and so there is a net force. Depending on the speed and direction of rotation (and the size of the body - Yarkovsky effect is strongest in the 10m to 10km range), the object may be either slowed or speeded in its orbit, moving either in or out relative to the Sun.
The forces are small, but their effect is continuous and accumulative.
That's more than 12 grapes!
@AC Hamsters? 53 in a Watt? That's ridiculous! A supercharged AJV8 (Jag 5L) puts out 380kW in standard tune, that's 20.14 MHam.
If you carry the four and divide by the Watts you get 14 hamsters per horse!
The age old question, just how does one measure work? Spreadsheets produced? Time since last visit to El Reg?
Don't blame this slipping satellite... and, yes, is this scary? I am having trouble figuring out if it's meant to be scary.
Are we going to see Bruce Willis sent up on a Space Shuttle with a hundred rolls of metal baking foil, to wrap an asteroid up in reflective material and change its orbit?
Are they sure that it's the Yarmovsky effect? For that, you'd presumably need to know it's absorbance / emitance parameters and it's rotational velocity to confirm that it is indeed due to the Yarmosvsky effect? I'm surprised that we know enough to say with certainty.
If we do the sums and it doesn't make sense, we'd have to attribute it to something else. Since Dark Matter® and Dark Energy® are already taken, perhaps we could call it Dark Magic?
Didn't we have a Reg story a couple a days ago about NASA using SI units ? This is what I get for my suggestion that we should all convert instead to Plank units - I do abjure and forswear and take it all back - I'll be perfectly satisfied if we could all agree to use the Système international d'unités instead of grapes. If I've calculated right, the mass of those 3 grapes should exert a force at the Earth's surface of about 0.14 N, which is what I think Dr Chesley meant....
Henri