File:KSC-05-S-00250 (ksc 080805 mro smrekar1).webm

English: With so much interest in the exploration of Mars, our NASA Direct question board has had quite a response. Are you ready to answer a few of our viewers' questions now? Sure. Let's go. Let's get started. Our first question comes from Patrick, and he's eight years old and he's from Telford. Why is it so important that the rocket has to be launched within just two hours on Aug. 10? What does it mean when you say that Mars is in opposition to Earth? Okay, well, I think I'll answer the opposition part first. Forgive my finger puppets, but, this is the Sun and this is the Earth, and this is Mars.Opposition means that all three are aligned, and Earth and Mars are on the same side of the planet as, the same side of the Sun as each other. So they're right close together. So opposition is the time that they are closest as they go around in their orbits, and it's also the time that we can see them most readily from Earth because the Sun is fully illuminating Mars as we see it, and it's also closest to us, so we can see it very brightly in the sky. And it's a really good time to launch our spacecraft, because it'll mean that the distance it travels from Earth and it, you know, the planets are going to start moving, so it's the time when it makes the trip from Earth to Mars the shortest. What was the first part of the question? The first part was, why is it so important that the rocket has to be launched within just two hours? Okay, so, the two hours has a number of considerations. The main consideration is when it's the best time when the Earth is moving and it'll, when you launch in that time window, it'll send it off on its way to Mars in the shortest distance. We don't have to use a lot of extra fuel to get on our right trajectory towards Mars. But there also are some other considerations. One is that we want to be able to communicate with antenna, large antenna here on the Earth, and be sure that the spacecraft is functioning as we expect it to. So we have to have the spacecraft in view of those antenna. The other aspect is, we want to launch the spacecraft in the right pattern so that the Sun doesn't shine directly into our big cameras, because that would really, cause, you know, it would destroy some of our instruments. We have to make sure the Sun is not shining down the barrel of our cameras. Those are the main factors.