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Space & Astronomy
Stars, Galaxies & Spaceflight
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Which galaxy contains our Solar System?
Gravity, Orbits and Getting There
Orbital mechanics is deeply unintuitive, and almost everything people assume about it is wrong.
About this topic
Space travel is governed by rules that contradict intuition at nearly every point. Astronauts float not because gravity has stopped but because they are falling continuously. Speeding up in orbit can leave you lower rather than faster. Reaching another planet is mostly about waiting for the right moment rather than pointing at the target. These questions cover the mechanics that actually determine how spacecraft move, and why the answers so often run against instinct.
Questions & answers
Gravity, Orbits and Getting There: all 10 questions and answers
Every question in this quiz is listed below with its correct answer and the reasoning behind it. Play first if you would rather not see the answers — or read through as a study sheet.
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1An object in orbit is best described as doing what?
- A Escaping gravity entirely
- B Balanced between two gravitational pulls
- C Held up by centrifugal force
- D Falling continuously, while moving sideways fast enough to miss Correct
Answer: D. Falling continuously, while moving sideways fast enough to miss
Why: Newton illustrated it with a cannon fired hard enough that the ground curves away as fast as the ball drops.
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2Astronauts float aboard a space station because what?
- A The station spins
- B They wear weightless suits
- C They and the station are falling together Correct
- D There is no gravity at that altitude
Answer: C. They and the station are falling together
Why: Gravity at station altitude is roughly 90 per cent of its strength at the surface. What is absent is any support pushing back.
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3Escape velocity is the speed needed to do what?
- A Reach the Moon specifically
- B Leave a body's gravity without further propulsion Correct
- C Enter a stable orbit
- D Break the sound barrier
Answer: B. Leave a body's gravity without further propulsion
Why: Around 11.2 km per second for Earth. A craft with continuous thrust can leave more slowly; the figure assumes a single push.
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4A geostationary satellite orbits at a height where what happens?
- A Its orbital period matches Earth's rotation Correct
- B Gravity becomes zero
- C It is beyond the atmosphere
- D It travels fastest
Answer: A. Its orbital period matches Earth's rotation
Why: About 35,800 km up, so it appears fixed above one point. That is why satellite dishes can be bolted in place.
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5A gravity assist uses a planet to do what?
- A Refuel the spacecraft
- B Slow the planet noticeably
- C Generate electricity
- D Change a spacecraft's speed and direction using its motion Correct
Answer: D. Change a spacecraft's speed and direction using its motion
Why: Energy is borrowed from the planet's orbital motion. The planet loses an utterly negligible amount in exchange.
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6Firing an engine forward while in orbit does what to your altitude?
- A Lowers the orbit
- B Nothing at all
- C Raises the opposite side of the orbit Correct
- D Immediately increases speed only
Answer: C. Raises the opposite side of the orbit
Why: This is why catching up with another spacecraft can require slowing down: a lower orbit has a shorter period.
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7A Hohmann transfer is a route between orbits that is what?
- A Impossible with modern engines
- B Fuel-efficient but slow Correct
- C The fastest possible
- D Only usable near Earth
Answer: B. Fuel-efficient but slow
Why: It is why missions to Mars launch only within particular windows every couple of years, when the geometry lines up.
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8Why does re-entry generate extreme heat?
- A Air ahead of the craft is compressed and heated violently Correct
- B Friction with the heat shield alone
- C Sunlight is focused by the atmosphere
- D Engines fire continuously
Answer: A. Air ahead of the craft is compressed and heated violently
Why: Compression of the air does most of the work rather than friction, which is why blunt shapes survive better than sharp ones.
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9The Lagrange points are locations where what happens?
- A Gravity cancels to nothing
- B Spacecraft can refuel
- C Radio signals are blocked
- D Gravitational forces and orbital motion let an object hold position Correct
Answer: D. Gravitational forces and orbital motion let an object hold position
Why: The James Webb Space Telescope sits at one, roughly 1.5 million km from Earth, keeping the Sun and Earth behind it.
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10Delta-v is a measure of what?
- A Distance travelled
- B Fuel temperature
- C The change in velocity a spacecraft can achieve Correct
- D Its total mass
Answer: C. The change in velocity a spacecraft can achieve
Why: Mission planning is largely a delta-v budget: every manoeuvre costs some, and once it is gone the craft cannot change course.
Frequently asked questions about Gravity, Orbits and Getting There
How many questions are in Gravity, Orbits and Getting There?
Gravity, Orbits and Getting There has 10 questions and takes about 8 minutes to finish. It is rated Hard and sits in our Space & Astronomy category.
How is Gravity, Orbits and Getting There scored?
Each of the 10 correct answers adds 10 XP, up to 100 XP for a clean run. Wrong answers cost you nothing, and your full question-by-question review is shown at the end.
Are the answers to Gravity, Orbits and Getting There explained?
Yes. All 10 questions carry a written explanation of why the correct answer is right, so the quiz works as a study sheet as well as a test.
Can I replay Gravity, Orbits and Getting There?
Yes, as often as you like. The questions and the answer options are reshuffled on each run, and you can use Practice Mistakes afterwards to retry only the ones you missed. No account is needed to play.
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