Question by illdieskating83: Solar Sail problem physics please help?
given info:
A solar sail allows a spacecraft to use radiation pressure for propulsion, similar to the way wind propels a sailboat. The sails of such spacecraft are made out of enormous reflecting panels. The area of the panels is maximized to catch the largest number of incident photons, thus maximizing the momentum transfer from the incident radiation.
For such spacecraft to work, the force from the radiation pressure exerted by the photons must be greater than the gravitational attraction to the star emitting the photons. The critical parameter is the area density (mass per unit area) of the sail.
Part A asks for the magnitude of the force due to the radiation pressure of the sunlight on the mirror. The answer for this part is (2(Intensity)(area))/speed of light (c).
Part B: Suppose that the mirror described in Part A is initially at rest a distance R away from the sun. What is the critical value of area density for the mirror at which the radiation pressure exactly cancels out the gravitational attraction from the sun?
Express your answer numerically, to two significant figures, in units of kilograms per meter squared.
To solve the second part of this problem you will need to know the following:
-the mass of the sun, M= 2*10^3 kg,
-the intensity of sunlight as a function of the distance R from the sun,
I(R)=3.2*10^25 (1/R^2) (W/m^2),
-the gravitational constant G=6.67*10^-11 (m^3/(kg*s^2) .
I cannot figure out how to find this last part as to where the pressure and area density are coming from what would this answer be? please help
I know that the area density is M/A so i need to figure out the Area that would cancel out the gravitational force and dont know how to do this. Im guessing that F=(2 (I(R))(A))/c which would give unknowns of distance R and the area A.
Best answer:
Answer by billrussell42
I disagree with your premise: “For such spacecraft to work, the force from the radiation pressure exerted by the photons must be greater than the gravitational attraction to the star emitting the photons.”
The spacecraft would start out in orbit around the sun, so the gravitational attraction of the sun is not relevant. It would spiral out to the destination, presumably another planet.
If the spacecraft had to directly oppose the gravity of the sun, it would need more force than a Saturn V rocket, not even remotely possible for a solar sail.
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