# I Near solar mirror for beam propulsion and space solar power

1. Jun 3, 2017

### RobertGC

NASA just announced a solar probe to travel quite close to the Sun, about
3.7 million miles from the solar surface:

Nasa’s hotly anticipated solar mission renamed to honour astrophysicist
Eugene Parker.
Renamed the Parker Solar Probe to honour solar astrophysicist who predicted
high speed solar wind, the spacecraft will attempt to get close to sun’s
surface.
Wednesday 31 May 2017 07.08 EDT
https://www.theguardian.com/science...ticipated-mission-to-the-sun-solar-probe-plus

Spacecraft able to get this close to the Sun could potentially allow beamed
interstellar propulsion. For a spacecraft of any size, you would need huge
amounts of beamed power. Where to get it? If you make the beam be
solar-powered then can just use space-borne mirrors to focus the Suns rays.
But the mirror(s) would have to be impractically large if they were in Earth
orbit.

But what if we placed them close to the Sun? At the distance quoted of 3.7
million miles away from the Sun a mirror 1 km on a side could collect a
terawatt worth of power.

Note this could also be used for space solar power when beamed towards
Earth.

What would be the size of the collector array at Earth to capture most of
the light focused from the 1 km wide mirror located at the Sun, i.e., the
size of the Airy disk at the Earth? How large at Proxima Centauri?

Bob Clark

2. Jun 3, 2017

### sophiecentaur

What temperature would it need to be operating at? Is there any know refractory material that's also a good reflector?
Perhaps a happy medium distance would be better to aim at? Somewhere a bit closer than Mercury, say 4AU.[Edit: that's about 0.3AU]

Last edited: Jun 3, 2017
3. Jun 3, 2017

### RobertGC

An AU is an "astronomical unit". It stands for the distance from the Earth to the Sun. So you want the distance to be a fraction of an AU. By wikipedia, Mercury is at about 46 million km from the Sun. This is about 7.5 times further out than the Parker Solar Probe is supposed to be. The intensity of the solar light will be decreased by the square so will be 56 times weaker than at the location of the Parker probe.

The temperature is cooler though at Mercury at about 430C compared to 1,400C at the Parker probe location.

For a high temperature reflector you could use tungsten.

Bob Clark

4. Jun 3, 2017

### sophiecentaur

Owch. That's what comes from trying to use an iPhone. I missed out the 0.0!!! Sorry and well spotted.