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From Earth to Mercury Help (page 3)

By — McGraw-Hill Professional
Updated on Sep 16, 2011

An Orbital Interlude

After you return to the Valiant , the captain has little to say. “This is the nature of life in outer space,” she says; “you take what you can get. Now settle in and get comfortable. We have to stay in orbit around Mercury for awhile.”

“Why?” you ask. But the captain has already left the room; she has more important business.

The first officer explains. “The captain selected a polar orbit when we made our rendezvous with Mercury. It was relatively easy to get into that sort of orbit. We drifted in and swooped under Mercury’s south pole. The planet’s gravitational field took care of the rest. But now we find ourselves in an orbit that is inclined 90 degrees to the plane in which the planets orbit the Sun.”

“So?” you ask.

“If we shoot out of this polar orbit in the planetary plane right now,” explains the first officer, “we won’t be heading for Venus. But we have to stay in the planetary plane. If we did not shoot out of Mercury orbit in the plane of the planets, we would find ourselves bound for interstellar oblivion. Our fuel would never be sufficient to get us back to the Solar System. Our ship must leave this orbit along essentially the same line from which it approached (Fig. 5-5). This greatly restricts our options.”

Mercury and Venus From Earth To Mercury An Orbital Interlude

Figure 5-5. A ship must leave a polar orbit from Mercury along essentially the same line from which it approached.

“So what do we do?” you ask.

“We wait,” says the first officer, “until Mercury is in the proper position with respect to Venus. Then we will fire our engines, shoot back out from under the south pole, and coast to Venus, where we will enter an equatorial orbit. That will be much less inconvenient to get out of properly.”

“How long do we have to wait here?”

“Eight days.”

“It is a good thing we have broadband Internet access on this ship,” you say.

“Yes,” says the first officer. “But the latency is horrible. We’re several light-minutes away from the hub in Dallas, Texas. I suggest that you watch old videos or listen to old music albums. We have a huge selection. And don’t forget to work your body out for two solid hours a day. Otherwise you will lose calcium from your bones.”

“Won’t the artificial gravity prevent calcium loss from bones?”

“To some extent. But remember that it’s less than one Earth gravity and will increase slowly because the geometry of our trajectory means that we will be en route to Venus for a long time.”

“How long?” you ask.

“You don’t want to know,” says the first officer.

Practice problems of this concept can be found at: Mercury and Venus Practice Problems

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