Exam 1

Question 1

Kepler’s Laws

Answer 1

1. orbits are either elliptical or hyperbolic
2. the speed of an orbiting body is fastest at periapsis and slowest at apoapsis
3. the larger an orbit’s major axis, the longer the orbital period

Question 2

In what special position in the Earth’s orbit is the Sun?

Answer 2

The Sun is at the OCCUPIED FOCUS of the Earth’s orbit. The Perihelion and Aphelion are not points IN the orbit, they are points ON the orbit.

Question 3

In an elliptical orbit around the Earth, which point has the maximum energy of position?

Answer 3

The highest EOP is at apogee, because the EOP increases as you get further, like a roller coaster.

Question 4

What causes the seasons on Earth?

Answer 4

The seasons are caused by Earth’s axial tilt. Eccentricity, in this case, doesn’t matter, because the Earth’s orbit is fairly circular.

Question 5

During a journey from Earth to Mercury, how are you moving with respect to the Sun?

Answer 5

You are speeding up with respect to the Sun. During most of the journey, you’re orbiting the Sun, in order to fall from the aphelion of your transfer orbit to the perihelion of your new orbit.

Question 6

If you are orbiting the Sun and you fire your engines to speed up at perihelion, what happens?

Answer 6

Your aphelion increases, and your perihelion stays the same. Whatever point on the orbit you make the change will stay the same, but the opposite point will change.

Question 7

During a launch, which kinds of energy are created by the combustion of fuel?

Answer 7

Heat, energy of position, energy of motion, light, and sound.

Question 8

Which forces are most important in the first few seconds after liftoff?

Answer 8

Thrust and gravity/weight are important at first. Drag doesn’t matter yet, but will matter later on. At first, the ship is moving too slowly for drag to matter.

Question 9

If you’re orbiting the Earth every two hours and you make a maneuver that increases your orbital speed, is your new orbital period longer or shorter than two hours?

Answer 9

Kepler’s Third Law.

It’ll be longer than two hours. You’re moving into a larger orbit, meaning it has a longer orbital period.

If you want to travel faster (shorter orbital period) then you want to slow down and fall into an orbit with a smaller major axis.

Question 10

If you’re traveling in a circular orbit around Earth at 7.8 km/sec, what would happen if you slowed down to 7.7 km/sec?

Answer 10

Normally, you’d fall into a lower and smaller elliptical orbit.

But, because 7.8 km/sec is the MINIMUM speed required to be in the LOWEST POSSIBLE Earth orbit, slowing down would cause you to become suborbital and the perigee of your new orbit would be inside of the planet.

Question 11

If you’re in an elliptical orbit around the Earth at 11 km/sec and you increase your speed to 12 km/sec at perigee, what will happen?

Answer 11

Normally, speeding up would get you into a larger elliptical orbit with higher perigee, but in this case, you’d hit ESCAPE SPEED and go HYPERBOLIC. A hyperbolic orbit has a perigee, but no apogee.

Question 12

At what point during a launch do you experience maximum acceleration?

Answer 12

You experience maximum acceleration just before burnout.

As you go up, you are losing mass (fuel is being burned), so the ship becomes lighter.

Because it is lighter, the engines are able to push it faster, so it makes you feel heavy and you experience the most acceleration.

Once the fuel is all burned out, you feel weightless. The engines shut off and you float.

Question 13

The period of the Earth-to-Mars Hohmann transfer orbit is 16 months. So how long will it take to get to Mars via a Hohmann transfer orbit?

Answer 13

It’ll take 8 months. It wouldn’t take 16 months because that’s the whole Hohmann orbit, so you’d just end up where you started. But if you travel 8 months, that’s half of an orbit, so then you hit aphelion at Mars.

Question 14

If you’re millions of kilometers away from any moon, planet, asteroid, or comet, are you orbiting anything?

Answer 14

Yes. As long as you’re in the solar system, you’re orbiting the Sun. It’s massive and has very strong gravitational influence.

Question 15

For most of the journey from Earth to Jupiter, you measure your velocity with respect to what?

Answer 15

You always use the center of whatever you’re orbiting at your point of reference, so in this case, because you’re in the solar system and not orbiting a planet or moon, you’d measure your velocity with relation to the sun.

Question 16

Benefits of various fuel types:

Answer 16

Kerosene: cheapest

Liquid hydrogen: cleanest

Solid propellant: highest thrust

Hydrazene: no need for ignition

Question 17

Why is it good to launch from Florida?

Answer 17

Earth spins east, so you get help from the spin.

That sends you over the Atlantic Ocean, where you don’t have to worry about flying over inhabited land.

Question 18

What is Pitch?

Answer 18

X-axis rotation. Pointing the nose up or down.

Question 19

What is Roll?

Answer 19

Y-axis rotation. Spinning along the ship’s length.

Question 20

What is Yaw?

Answer 20

Z-axis rotation. Turning nose from side to side.

Question 21

A rocket can only take off if its ___ is greater than the combination of its ____ and its ____.

Answer 21

A rocket can only take off if its thrust is greater than the combination of its weight and its drag.

Question 22

What is special about the Space-X Falcon Heavy?

Answer 22

It could lift as much weight as any rocket since the Apollo program.

It was able to send multiple stages back to Earth for reuse.

It was built by Space-X, a private company.

Question 23

What did the Falcon Heavy eject into space?

Answer 23

The Falcon Heavy ejected a Tesla Roadster. It went into orbit around the Sun, where it will be for billions of years.

Question 24

What is 1 AU from Earth?

Answer 24

The Sun, and sometimes Mars.

Question 25

A planet that is cold for 90% of the year and hot for 10% of the year has ______ and ______.

Answer 25

A planet that is cold for 90% of the year and hot for 10% of the year has a large major axis and high eccentricity.

Question 26

What’s cheapest: landing, going into orbit, or doing a fly-by?

Answer 26

Fly-by.

Going into orbit requires fuel for speeding up or slowing down.

Landing requires a TON of fuel for slowing down.

A fly-by doesn’t require any additional fuel burning.

Question 27

Earth takes 365 days to orbit the Sun. Mercury takes 88 days. Roughly how long is the orbital period of an Earth-to-Mercury Hohmann Orbit?

Answer 27

About 200 days.

A Hohmann orbit is in between orbit A and orbit B, so its orbital period is about midway between those of A and B.

200 is roughly in between 88 and 365.

Question 28

You leave an eastward Earth orbit and are heading to Venus. When you make the maneuver to change orbit and head into a bigger one, what time should it be on Earth below?

Answer 28

Noon.

Leave for Venus at noon, and leave for Mars at midnight.

This is because, if you leave at noon, you can speed away from Earth whilst slowing down with relation to the sun, so this way you can fall into Venus’ orbit.

Question 29

What can a gravity assist maneuver let you do? What was the first gravity assist maneuver?

Answer 29

Slow down, speed up, or change direction.

The first gravity assist maneuver was the Mariner 10 probe, which used Venus to slow down and get closer to the sun in order to reach Mercury.

Question 30

If you’re going from Earth to Mars, why not leave Earth when Mars is at its closest point?

Answer 30

This would require too much energy. First, you’d have to leave Earth, then you’d have to hard stop the orbit around the sun and go straight toward Mars.

It makes more sense to fling the craft away from Earth using slightly more velocity than Earth’s orbital velocity, and then catch Mars at the other side of the Sun at the aphelion of the transfer orbit.

Question 31

Why do we launch vertically from Earth?

Answer 31

It’s not to overcome gravity quickly, because that’s quite the opposite effect.

Instead, it is to get out of the atmospheric drag in the lowest and thickest part of the atmosphere. This makes the drag much less bad.

Question 32

What’s the more expensive way of getting payloads into orbit: reusable rockets or expendable rockets?

Answer 32

Reusable rockets are much more expensive. They have to keep their engines and fuel reserves in order to return, so a lot of their weight is occupied by these things.

In contrast, expendable rockets can lose their engines and fuel, so that leaves a lot of extra space to be occupied by payload.

Question 33

Why was the Space Shuttle unique?

Answer 33

Not because it traveled to the moon – it didn’t.

Not because it landed vertically on Earth – it didn’t.

And not because it hit multiple space stations along its route. Other ships have done this too.

It’s special because it was the only aircraft to take people into orbits using reusable engines.

Question 34

What’s the advantage of multiple stage launch vehicles?

Answer 34

Despite being expensive and hard to reuse, they’re good because they let you go into orbit using conventional fuels. We still don’t know how to hit orbit without multiple staging.

Question 35

What are some benefits of landing a rocket vertically?

Answer 35

It’s cheap to retrieve, unlike an ocean splashdown.

There’s no need for a runway, so you have more options for a landing site.

No need for wings, which are heavy, so you have more room for payload.

Question 36

90% of the mass of a launch vehicle is taken up by the ____

Answer 36

Propellant (fuel + oxidizer).

You need a lot of propellant in order to get sufficient thrust to leave Earth’s gravity.

Question 37

What’s special about the following launch types?

Sea Launch
Pegasus Launch
Delta Clipper
Falcon
Venture Star

Answer 37

Sea Launch launches from the equator.

Pegasus Launch launches horizontally from an airplane.

Delta Clipper lands vertically.

Falcon lands vertically.

Venture Star uses new nozzle design.

Question 38

What two companies are offering space tourism?

Answer 38

Virgin Galactic (owned by Richard Branson)

Blue Origin (owned by Jeff Bezos)

Question 39

What are some advantages of RADAR satellites over photoreconnaissance satellites?

Answer 39

RADAR can penetrate clouds.

RADAR can launch to the east.

RADAR can get images at night.

Question 40

What kind of orbits are used by photoreconnaissance satellites?

Answer 40

Photoreconnaissance satellites follow retrograde orbits, meaning they orbit around Earth to the west, opposite to Earth’s rotation.

They have to launch toward the west, so they require more push to get into orbit. They work best in sun-synchronous orbits, because then they can take pictures at the same time each day.

Question 41

How long is a solar day?

Answer 41

A solar day is 24 hours.

Question 42

How long is Earth’s rotation period?

Answer 42

Earth’s rotation period is 23 hours and 56 minutes.

Question 43

Why are communication satellites usually put into the Clarke Band (geostationary)?

Answer 43

They are very far away and don’t work on the poles because they are equatorial, but because they orbit Earth at the same rate at Earth’s rotation, they are able to appear stationary from Earth.

Question 44

Which country always launches satellites into retrograde orbits?

Answer 44

Israel always launches satellites into retrograde orbits because it usually launches photoreconnaissance satellites which need to be in retrograde orbits.

Question 45

What are Molniya satellites?

Answer 45

They are satellites with high eccentricity and high orbital inclination. Usually used for satellite communication in the Arctic.

Question 46

Where can you see a geostationary satellite?

Answer 46

They’re very high up, so basically anywhere. Just not the poles (Arctic or Antarctic).