Solar Panels

[Warped]

Why do some space-probes, like the Dawn have solar panels while others, like New Horizons don't?

 

[Woo482]

I think it's because of the distances from the sun the probe will be at and also the power requirements of the probe, but I might be wrong

 

[garyw]

Out past the orbit of Mars Solar panels become ineffective. New horizons is going to Pluto and beyound so uses an RTG.

 

[Warped]

Then why would a Soyuz have solar panels and not the Space Shuttles? do the Shuttles just use batteries?

 

[jinglesassy]

Shuttle uses fuel cells

 

[Warped]

Shuttle uses fuel cells

How did I forget that? thanks.

 

[statickid]

so many options for powering things in space!

 

[garyw]

Shuttle has three fuel cells. Endeavour and Discovery can also use the Solar Arrays of the ISS via the SSPTS (Station-Shuttle Power Transfer System).

 

[Unstung]

The Orion module will have solar panels.

 

[Andy44]

The X-37 reportedly also has deployable solar panels.

 

[tblaxland]

Out past the orbit of Mars Solar panels become ineffective. New horizons is going to Pluto and beyound so uses an RTG.

To expand on that: insolation drops with the square of the distance from the sun so the size and weight of the solar panels to meet the spacecraft's power requirements must increase in proportion. As far as I understand, spacecraft designers will use solar panels if they can, due to the headaches associated with getting RTGs approved for flight.

For the Shuttle, I estimate you would need about 200sqm of solar panel, although operational constraints and redundancy could easily double that. I wonder how small they could fold those to fit in the payload bay?

 

[T.Neo]

The X-37 reportedly also has deployable solar panels.

That would be a fun thing to see...

The efficiency of solar cells is reaching the level where it is feasible economically and physically to use them at further distances. The upcoming Juno mission will use solar panels for power out to Jupiter.

It is also possible to use a nuclear reactor to provide power.

 

[Spike Spiegel]

Pardon my ignorance, but what's an RTG? (Soooo much alphabet soup. )

 

[Woo482]

a RTG is a Radioisotope thermoelectric generator, this'll explain better than I can: [ame="http://en.wikipedia.org/wiki/Radioisotope_Thermoelectric_Generator"]RTG[/ame]

 

[jedidia]

What exactly is the difference between that and a nuclear reactor?

 

[Urwumpe]

What exactly is the difference between that and a nuclear reactor?

Nuclear reactor works by nuclear fission, a RTG works by nuclear decay. Also a nuclear reactor is more for high power outputs, while a RTG produces little power for a long time.

 

[orb]

And nuclear reactors (even those used for spacecrafts) are larger and heavier than RTGs.

 

[astrosammy]

Before I discovered Orbiter I knew nothing about radiators. So I thought: Hey, that must me solar panels inside the payload bay doors!

 

[jedidia]

Nuclear reactor works by nuclear fission, a RTG works by nuclear decay.

Ah, silly me! I should have noticed the difference between something falling apart on its own and something getting blown appart...

 

[Izack]

There are no reactions in an RTG. It generates electricity with radioactive decay (Seebeck effect).

EDIT: Page turn fail. Question's been answered.