You have been hired to plan a mission to Mars. Your employer knows very little a

Question

You have been hired to plan a mission to Mars. Your employer knows very little about space travel; he simply wants to be the first individual to send a mission to Mars. He has vast but not unlimited resources. Your first step is to educate him about the realities of space flight and the pros and cons of various options.

A. Give at least one advantage for each option. For example, answer both “what is an advantage of one-way over round trip travel?” and “ What is an advantage of round trip over one way?” Try to be as specific as you can.

(a) One way vs. round trip

(b) Manned vs. unmanned

(c) Hohmann vs. fast transfer

(d) Landing vs. orbiting

B. Your employer says “If you were to send a mission to Mars, what kind would it be? Describe it for me.”

C. After listening to your presentation, your employer says “What I really want to do is to land a spacecraft on Mars and dig down into the surface to find water. Can you tell me how to do this with minimal cost? Also, once I have the water, how might I use that to benefit future Mars missions?” What is your response?

Explanation / Answer

Manned or unmanned

Almost all the missions to mars are unmanned. Mainly, space travel is physically hard on the human body. During liftoff from the Earth astronauts experience very strong forces, and in space they experience microgravity. Even though astronauts might not expect microgravity to be a problem, many astronauts undergo sick at the beginning of a flight and not everyone gets over that feeling as the days pass. Also, in zero-g or free-fall, the human body changes in delicate ways. Astronauts tend to get taller, increases up to three inches. This extra height disappears when they land again. A more severe health threat is that over a wide time period (months and years), bones get weaker. Another risk for humans is the contact to radiation during the trip, and even to some extent while on Mars. These radiations are harmful to human body.

A second problem with sending people to Mars is the cost of travel.

Finally robots and computers can handle more and more tasks and it better than, astronauts. If scientists require grinding a sample of rock and conducting experiments on it, they can construct a robot that lands on the surface of Mars and perform tests, and convey those results back to Earth. This is much easier than flying astronauts to Mars.

Round trip or one way

There are mainly two reasons why we require the mission to return: One is that it would be helpful to have a Mars mission return to Earth with samples of the Martian “soil.” Another reason for a round-trip is to transport people back.

But it is a lot more costly and more complicated to have a round-trip mission rather than simply a one-way mission. A spacecraft on Mars requires fuel to take off and return to Earth. It needs a lot of fuel and a large, costly rocket to send the fuel to Mars for the return trip back to Earth.

Hohmann or fast transfer

Hohmann Transfer Orbit to Mars is the orbit where the spaceship is set just enough “delta-vee” to depart Earth on an eccentric orbit with perihelion at 1AU and aphelion at Mars’ orbit. This is the slow, cheap orbit.

If we enhance it with a larger “delta-vee” from HEO it will move on a larger ellipse, one that crosses the orbit of Mars. The spacecraft on this larger orbit will be moving faster than one on a Hohmann orbit. Moving faster gets you there sooner. So the fast trip was made faster by traveling in an orbit that was bigger than needed. In this case, we get home sooner.

Landing or orbiting

When we launch a spacecraft from Earth, we require speeding it up to more than 7 km/s to get it into orbit around Earth, or more than 11 km/s to escape Earth and head off towards some other planet. A spacecraft returning from Mars will already be moving pretty fast relative to Earth. We could slow it down with rockets, just as we used rockets to speed it up, but that would use a lot of fuel and isn’t really necessary. With care, we can slow the spaceship down and bring it in for a safe landing.

The more air the spaceship moves into, it gets slower, but the friction with the air heat the spaceship. The safest path is therefore the path that brings spacecraft along a shallow dive and gives time to cool down while it is being slowed by friction with the air. If the spacecraft moves into the atmosphere too steeply, and it gets too hot; too shallow and it bounce back out into space.

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