Some options for a minimum solar probe

Solar Power System Design for the Solar Probe+ Mission

“…The proposal for a probe to fly directly into the solar corona, the source of the solar wind, was initially proposed in the mid-1970s. Earlier concepts [3][4][5][6][7][8] for the mission incorporate a Jupiter flyby, to use the "gravitational slingshot" effect to cancel the Earth's orbital angular momentum, allowing the spacecraft to drop nearly directly toward the sun. This results in a mission concept which has a long flight duration before the solar encounter, and is relatively expensive, in part because of the need to incorporate a power supply which can operate both at the low intensity, low temperature environment of Jupiter orbit (about 4% of the solar intensity at Earth orbit), as well as the high intensity high temperature environment near the sun.…”

“…The equilibrium temperature of a surface illuminated by sunlight is achieved when the absorbed incident energy equals the thermally radiated infrared radiation. This can be calculated using the Stefan-Boltzmann equation: αΙ = (ε f +ε r )σT 4 (1) where I is the incident intensity; α, the solar absorptivity (equal to 1 minus the reflectivity); ε, the thermal (IR) emissivity of the front and rear surfaces (assuming that the surface can radiate from both sides); σ, the StefanBoltzmann constant, and T, the temperature. Figure 3 shows the equilibrium temperature of an uncooled flat-plate solar array, assumed to be flat on to the incident sunlight, as a function of the ratio of solar absorption to thermal emissivity (epsilon).…”