SPACE EXPLORATION MERIT BADGE
This section covers the basic systems required to build any spacecraft and will help you
with two requirements: requirement 5c, design of a planetary probe, and
requirement 7, design of a space station. On this web page you will find
- a bunch of ideas for things to include and show on your design,
- how to get ideas from pictures of other spacecraft.
If you look at a picture or model of a spacecraft you can usually see how it works and what
makes it go. Here's what to look for:
Summary of Spacecraft Systems
Magellan Spacecraft Venus Orbiter Example
- Batteries: what they had on Sputnik, but they run down after a while. Rechargeable
batteries are used as a backup for solar cells, for when the spacecraft passes through
a planet's shadow or during maneuvers, when the panels aren't pointed toward the sun.
- Solar Cells: like on your calculator. These are the method of choice for most satellites
and probes, because space is real sunny and they last forever. They look like big wings
on the satellite, and can put out a few thousand watts. Not so good for deep-space
probes like those that go to Jupiter, which get too far from the sun to be any good.
- Fuel Cells: burn hydrogen & oxygen to produce electricity. Good for manned vehicles
like Apollo or the Space Shuttle, where you have to carry a bunch of oxygen anyway. Not
as good for unmanned probes, since like batteries they will run out .
- Radioisotope Thermoelectric Generators (RTG's): fancy name for itty-bitty nuclear
reactors. Used on unmanned deep-space probes (which get far from the sun), since
they don't need the sun to operate and the nuclear fuel lasts a long long time.
Picture of Pioneer Jupiter probe.
Note the RTG's at the end of the boom arms and the large dish antenna for beaming a
signal from Jupiter, 500 million miles away.
If a satellite or probe can't communicate back its findings then we might as well have
launched a rock. The antennas are easy to spot:
- A large dish (the high-gain antenna) gives a stronger radio signal in one direction like
cupping your hands around your mouth when you holler.
- A short aerial sticking out someplace (the low-gain antenna), which sends the signal in
all directions. The signal is not as strong, but this antenna always works, even when it
isn't pointed at the Earth.
- This is the rocket system the spacecraft uses to move itself. You can often spot the nozzles,
although sometimes (like on the shuttle) they may just be holes in the
side of the fuselage.
- Propulsion: refers to rocket motors used to change the orbit or trajectory of the craft.
Usually can be spotted as large nozzles that look like they could move the whole
- Attitude Control: a system of thrusters that controls which way the craft is pointing.
Usually these are smaller nozzles or clusters of nozzles pointed in many different directions.
Sometimes "reaction wheels" are used: heavy wheels that are turned with a motor. When the
wheel is spun in one direction, the spacecraft, having nothing to hold on to, turns the other
- Passive Cooling: as temperatures on the sun side of a spacecraft can reach 250 F and
up, several methods will be used to help cool the spacecraft:
- rolling it, so the hot side is turned away from the sun to cool off,
- painting it with a heat reflector - white or gold - or covering it with a blanket or shade
- louvers to control the amount of heat that gets radiated from inside the spacecraft.
- Active Heating: electric heaters or sometimes nuclear-powered heaters are used,
especially for deep-space probes like Voyager and Pioneer.
This image of Mariner 10 to Mercury shows the little white parasol
over the electronics to shade them from the Sun, 6 times as intense at Mercury as at
Earth. The long boom arms hold the magnetometers.
- Star trackers and sun sensors are used by the spacecraft to see where it's pointing.
- Once the spacecraft has one point of reference, it only needs one more (sideways to the
first point of reference) to know exactly which way it is facing. Thatís why both a star
tracker AND a sun sensor are used.
Obviously the science instruments on board the spacecraft depend on its science mission.
- Direct sensing instruments: measure the spacecraft's own environment - particle
detectors (for ions and electrons), dust detectors, magnetometers (measure the
planet's magnetic fields) are typical.
- Remote sensing instruments: imaging instruments to take pictures of the planets, radio
astronomy instruments look at radio waves coming from planets & stars, photometers
and spectrometers analyze light to determine chemical make-up of atmospheres.
- Active sensing instruments: radar imagers (synthetic aperture radar or SAR) image the
surface of heavily clouded planets such as Venus. Radar altimeters measure the height
of the terrain allowing us to map Mars and Venus.
Manned Spacecraft Systems
For manned spaceflight like Gemini, Apollo and the Space Shuttle, additional systems will
be found on the spacecraft - to keep the astronauts alive and to bring them home in
What are all the jobs that need to be done for life support? These tasks will be
particularly important for your Space Station design.
- Astronauts Have to Breathe: atmosphere control includes a supply of oxygen and
removing carbon dioxide, both equally important (remember Apollo 13?). Also the
pressure has to be maintained: if the hatch is opened, either everyone better be
wearing a suit or there needs to be an airlock.
- Temperature and humidity control: people won't survive the temperatures that
electronics and mechanics will. With astronauts aboard, the temperature must be
controlled much more tightly. The Shuttle and the Space Station have water cooling and
radiators for controlling temperature.
- Food and Water: food is usually carried along, water supplied by the fuel cells, reacting
hydrogen and oxygen and producing water in the process. On an extended mission like
the Mars expedition, water will need to be recycled and the food grown along the way in
- Waste management: a dirty job but somebody has to do it - elimination or recycling of
solid, liquid and gaseous waste.
- Radiation Protection: without an atmosphere the astronauts are exposed to cosmic and
solar radiation, particularly solar flares. Some shielding to reduce the effects is needed.
Re-entry and Spacecraft Recovery
Consists of two parts, mainly -
- Heat shielding - to protect the astronauts and the vehicle from the extreme heat of
re-entry into the atmosphere.
- Recovery system - parachutes, like on your model rocket, or in the case of the Shuttle
an aerodynamic body that allows for a soft landing.
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Your questions and comments regarding this page are welcome.
You can e-mail Randy Culp for inquiries,
suggestions, new ideas or just to chat.
Updated 26 November 1999