Space questions. Clear answers.
How it works
How can a rocket burn without air? Why does the ISS not fall to Earth? How does a spacesuit keep someone alive? Each article starts with a direct answer, explains the principle and its context, and provides sources for further reading.
46 questions answered · NASA · ESA · SpaceX
Spacesuits
How does a spacesuit work?
A spacesuit maintains pressure around the body, supplies oxygen, removes carbon dioxide and carries away excess heat. During a spacewalk it takes over some functions of a spacecraft cabin.
Why are spacesuits so bulky?
A spacesuit is bulky because it must maintain pressure, permit movement and protect the body from its surroundings. Structural layers, joints and life-support equipment all add volume.
How does an astronaut stay cool in a spacesuit?
Working produces body heat that a spacesuit must remove. In many EVA suits, water flows through fine tubes in an undergarment.
How long can an astronaut stay in a spacesuit?
Spacesuit endurance depends on oxygen, carbon-dioxide removal, cooling and power. Why is there no single time limit for every spacewalk?
What happens if a spacesuit is punctured?
The outcome depends on which layer is damaged and how rapidly gas escapes. An abrasion of the outer cover does not necessarily cause depressurization.
Life on the ISS
How does the ISS work?
The ISS is a set of connected living and laboratory modules orbiting Earth. Solar arrays supply power, life-support systems maintain a habitable cabin, and cooling removes excess heat.
Where do ISS astronauts get oxygen and water?
The ISS combines supplies delivered from Earth with recycling. Water is also recovered by treating condensed humidity and processing urine.
How do astronauts use the toilet in space?
A space toilet uses airflow to guide waste in the intended direction. In microgravity, urine and solid waste do not simply fall into a bowl.
How do astronauts sleep in space?
On the ISS, astronauts usually sleep in sleeping bags secured inside the living space. In microgravity they do not need a mattress to support their weight.
What happens if the ISS loses pressure?
The crew must determine the leak rate and protect habitable space according to emergency procedures. Closing hatches can isolate a leaking section.
Rockets and propulsion
How can a rocket work in a vacuum?
A rocket produces thrust by ejecting mass in one direction and changing its own motion in the opposite direction. It does not need air to push against.
How does a rocket engine burn without air?
A chemical rocket carries its oxidizer with it. A liquid engine may burn fuel with liquid oxygen, while other engines use different oxidizers.
Why do rockets discard stages?
Empty tanks and unneeded engines would burden the rest of the flight. Separating a spent stage reduces the mass that the remaining rocket must accelerate.
Why does a rocket turn after launch?
Reaching orbit requires more than climbing high. A rocket must acquire substantial sideways speed.
How is a rocket steered in space?
In a vacuum, thrust changes direction rather than ordinary aerodynamic control surfaces. A main engine may swivel, and small control thrusters can rotate the entire spacecraft.
The Moon and Apollo
Why did astronauts stand during the Moon landing?
Apollo's lunar module had no pilot seats. Two astronauts stood at their control stations, supported and restrained by dedicated equipment.
Why did the lunar module look wrapped in foil?
The lunar module's crinkled reflective surfaces were largely thermal protection rather than its load-bearing wall. Multilayer blankets helped limit radiative heat exchange.
How did astronauts launch from the Moon without a launch pad?
The lunar module's descent stage, left on the surface, served as the launch base. The ascent stage separated with its cabin, and its own engine carried the crew into lunar orbit.
Why did the whole lunar module not return to Earth?
Each part of the Apollo spacecraft had a specific job. The descent stage stayed on the Moon, the ascent stage returned the astronauts to the mother spacecraft and was then discarded.
How did the lunar module save Apollo 13?
After a service-module oxygen-tank failure, the lunar module Aquarius provided independent life support and electrical power. Instead of landing on the Moon, it became a temporary lifeboat.
Why did the flag appear to wave on the Moon?
Wind did not move the flag: the Moon lacks an atmosphere capable of producing that wind. Astronauts transferred motion to it while handling the pole.
Why are there no stars in Moon photographs?
Cameras photographing sunlit ground and astronauts used exposures suited to a bright scene. Faint stars generally did not register at those exposures.
How did Moon astronauts communicate with Earth?
Apollo transmitted voice, telemetry and pictures using radio waves. From the surface, communication passed through lunar-module equipment and antennas to ground stations.
What did Apollo leave on the Moon?
The landing sites retain lunar-module descent stages, scientific instruments, discarded equipment and traces of crew activity. Later missions also left lunar rovers.
Returning to Earth
Why does a spacecraft get so hot during re-entry?
A returning spacecraft must shed an enormous amount of kinetic energy. At high speed it forms a shock wave and intensely heats the surrounding gas.
How does a heat shield work?
A heat shield limits how much re-entry heat penetrates a spacecraft. Some materials deliberately decompose and wear away; others insulate effectively and radiate heat outward.
Why is a parachute not enough for returning from space?
A parachute needs an atmosphere and tolerable deployment conditions. It cannot brake in a vacuum, and an ordinary parachute would not survive initial re-entry loads or heating.
Why does atmospheric entry angle matter?
Entry angle determines how quickly a spacecraft reaches denser air and how braking and heating are distributed. An overly steep entry can produce unacceptable acceleration and heat flux.
Orbits
Why does the ISS not fall to Earth?
The ISS is constantly falling toward Earth, but it also moves sideways fast enough to keep missing the surface. This motion is an orbit.
Why do astronauts float if gravity still acts on them?
Astronauts in orbit float because they and their spacecraft fall freely together. The floor therefore does not support them as it does on Earth.
How does a satellite stay in orbit?
A satellite stays in orbit through the combination of velocity and Earth's gravity. Gravity continuously bends its motion, while sideways speed prevents a rapid fall to the surface.
Humans in space
Can artificial gravity be created in space?
A weight-like effect can be created by rotating or accelerating living space. In a rotating station, the floor forces a person to follow a circular path and provides support.
What does weightlessness do to the human body?
Weightlessness changes body-fluid distribution and removes ordinary loading from muscles and bones. Longer stays can therefore reduce muscle strength and bone mass.
Why do astronauts need to exercise?
In orbit, muscles and bones do not support the body as they do when walking and standing on Earth. Without regular loading, their condition deteriorates.
Starship
How does Starship work?
Starship is SpaceX's developing two-stage system: the lower Super Heavy accelerates the upper Starship spacecraft, which continues after separation. Both stages use methane and liquid oxygen.
Why does Starship have so many engines?
A very heavy launcher needs substantial total thrust at liftoff. Super Heavy produces it with many Raptor engines rather than a few gigantic engines.
Why does Starship descend belly-first?
During part of its return, the upper spacecraft presents a large body area to the atmosphere. Aerodynamic drag helps reduce speed.
How can a tower catch a rocket?
The tower does not stop a rocket arriving at full speed. Engines first slow the returning stage, and guidance brings it into a small region beside the catch arms.
Why does Starship need orbital refuelling for a Moon mission?
Starship consumes a large share of its propellant reaching Earth orbit. A subsequent lunar mission requires an additional velocity-change budget.
Satellites and GPS
How does GPS work?
A GPS receiver measures arrival times of satellite radio signals and uses them to infer ranges. Combining measurements determines its position and corrects its own clock error.
What happens to a satellite after its mission ends?
End-of-life plans depend on orbit and spacecraft capabilities. In low Earth orbit, disposal may involve lowering the orbit for atmospheric re-entry.
How do satellites avoid collisions?
Ground tracking systems measure object orbits and predict hazardous close approaches. Operators can plan a small manoeuvre for a controllable satellite to alter encounter timing or position.
Travelling to Mars
How long does it take to reach Mars?
Chemically propelled Mars probes commonly travel for several months; roughly six to nine months is often quoted. It is not a fixed duration.
Why are Mars launches limited to launch windows?
Efficient transfer trajectories require a suitable relative alignment of Earth and Mars. Favourable opportunities recur roughly every 26 months.
How would people return from Mars?
A crewed Mars return requires launch from the surface, travel to Earth and safe entry into its atmosphere. Different proposals may use several spacecraft or one larger system.
Why is landing on Mars so difficult?
Mars has enough atmosphere to heat an arriving spacecraft intensely, but too little for a parachute to slow heavy payloads easily. Landing systems therefore combine several braking methods.