Objectives

  • describe the history of unmanned space flight
  • identify some of the purposes of unmanned space flight
  • describe some of the important unmanned missions that have been successful

In the years before and during World War II, the Germans developed the first rockets. Though often forgotten, the German V-2 rocket (designed by Hermann Oberth and Wernher Von Braun) was the first man-made object to reach Earth’s orbit. Ironically, these two gentlemen were greatly influenced by the American Robert H. Goddard, while Goddard’s work is often ridiculed in his native country.

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Sputnik 1


The German V-2 rocket was developed as a ballistic missile weapon and used against some European cities in the last year of the war. The first official flight of a man-made object into orbit was during a test of the V-2 on October 3, 1942.
 



After the war, Von Braun came to the United States under a secret operation called ‘Operation Paperclip’ in which many German scientists were brought to the USA to continue their work under the supervision of the US military. Von Braun continued development of the V-2 rocket and later was instrumental in the development of the Saturn V rocket that flew Americans to the Moon. He eventually became the director of the Marshall Spaceflight Centre, and is generally regarded as the father of the American Space Program.

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The V-2 was assembled at the launch site, as seen here in Germany, in stages, similar
to the more modern rockets. However it remained as a whole unit during flight and
eventual impact. It was able to carry a warhead of about 1000 pounds.



Did you know?
 

Rockets are still the only real way to reach outer space. Rockets became a serious possibility after the publishing of a 1919 paper called “A Method of Reaching Extreme Altitudes” by Robert H. Goddard. In this paper Goddard described how a de Laval nozzle could be used to propel rockets at the high speeds needed for reaching orbit. The nozzle is an hour-glass shape which compresses the gas as it passes through the small central part. This accelerates the gas to supersonic speeds and provides a large amount of power. NASA named their major research center the Goddard Space Flight Center after him.



Once rockets became more reliable, scientists set themselves to creating a vehicle to remain in outer space for some time. The Soviet-launched Sputnik 1 was the first man-made object to continually orbit the Earth. This was a tremendous moment for everyone on Earth as citizens all over the world could go out to see this little bright dot move across their skies during the night. It was a powerful symbol for the Soviet Union and also a significant motivator for the United States and the space race that followed.



Manned space flight certainly captured the spotlight for journalism shortly after Sputnik and ‘Laika’ on Sputnik 2 (see Module 7, tutorial 2) took orbit, but unmanned space flight continued. It is much simpler and cheaper to send machines into space and beyond Earth than it is get humans to the same level, so unmanned space flight has always been ahead in the adventure of exploration.

 

The Soviets launched several successful Sputnik missions, but the Americans soon began having their own success with the Pioneer program. The early Pioneer probes had many failures, but Pioneer V successfully launched and studied space between Earth and Venus. More notable firsts include:



Mariner 2 (1962): completed the first flyby of a planet, Venus

Mariner 4 (1964): completed the first trip to Mars, returning the first close-up images of another planet.

Mariner 9 (1971): first artificial satellite of Mars.

Pioneer 10 (1972): first satellite to explore beyond the asteroid belt, first satellite to flyby Jupiter, and first satellite to leave the solar system

Mariner 10 (1973): first probe to encounter 2 planets, and the only satellite to obtain close-up photographs of Mercury.

Pioneer 11 (1973): first trip to Saturn

Voyager 1 (1977): furthest functioning satellite to date, longest running NASA mission

Voyager 2 (1977): first trip to Uranus and Neptune


 

Did you know?

Although Pioneer 10 was the first satellite to leave the solar system, it eventually lost contact with Earth. Its last contact with Earth was on January 23, 2003, and it was 12 terametres (12,000,000,000 km) away! Useful data had not been received for about year before that. The lack of signal is thought to be a combination of its distance from Earth and its weakening power source


 

Voyager is perhaps the most exciting unmanned space probe, as it is still moving through space and returning signals to Earth. It currently moves through a region called the heliosheath, where the Sun’s gravitational influence becomes weak enough that the rest of the galaxy’s gravitational influence matches it. It will hence soon be sending back the first direct information about the interstellar medium between stars beyond the limit of our solar system. It is currently about 15 terametres (15,000,000,000 km or about 100AU) from Earth and is traveling at about 17.2 km/s or 3.6 AU per year (recall that 1 AU is the average distance from the Earth to the Sun). It is estimated tht Voyager 1 will continue to function and transmit signals until sometime after the year 2020. At this point it will be about 160 AU from Earth – quite far, but unfortunately still not even close to reaching another star system.


 

Did you know?

All of the satellites that have been sent out of the solar system, Pioneer 10 & 11 and Voyager 1 & 2, have been equipped with information specifically designed for contact with extra-terrestrial life. Pioneer 10 and 11 were equipped with the plaque shown on this page. Voyager 1 and 2 were equipped with a ‘golden record’, the equivalent of a vinyl sound disc, but made of gold to be more durable. On this record NASA put a collection of sound and images from around the world. It will take about 40,000 years for Voyager 1 to reach the vicinity of another star, so it is very likely that it will never be received by another life form.

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An artist's concept of Voyager 1 on its mission.
Voyager continues to broadcast data back to Earth,
making it the longest running NASA mission to date.





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This is a copy of the image placed on the 6” by 9” plaques on Pioneer 10 and 11. It portrays
humans in relative size to the probe. The two circles with the ‘1’s inside them provide a scale
measurement of the image using hydrogen atoms. This scale measurement is also designed to
provide distances using the image at left. This portrays the distances to 14 pulsars (rapidly
spinning stars with specific spin rates) radiating out from the Sun, in the hopes that anyone who
discovers this probe will be able to discover where it came from. Lastly the probe’s course is
portrayed along the bottom as it leaves Earth and moves past Mars and Jupiter before journeying
out of the solar system, showing exactly from which planet it came.


 

Pioneer 10 and 11, and Voyager 1 and 2 have given us most of what we currently know about the outer planets. They discovered many moons around the outer planets that were previously undiscovered and guided the direction of unmanned exploration in this region since then.
 



Many probes have been sent to explore our solar system since these pioneering satellites. A few of these have been flybys, while others have maintained orbit around a celestial body, allowing a more thorough examination. A few have even contained probes that were designed to fly down through the atmosphere of a planet or moon to get even closer to the surface of these other worlds. Several of the more recent satellites are listed below, with their launch date:



Giotta (1985): performed close flyby of Halley’s Comet

Gallileo Spacecraft (1989): first orbiter of Jupiter, sent an atmospheric probe into Jupiter’s atmosphere, also provided much data on Jupiter’s moons.

Ulysses (1990): probe designed to study the Sun, also provided data on the comet Hyakutake. Mission still in progress.

Cassini-Huygens(1997): first orbiter of Saturn, also separated to land on Titan, Saturn’s largest moon. Mission still in progress.

New Horizons (2006): Expected to be the first probe to study Pluto, and several other outlying objects in the solar system. Expected to flyby Pluto in 2015.




More importantly, landers have been sent to a few of the planets and moons in our solar system. These vehicles were designed to land on the surface of a planet or moon and transmit information back from this contact. The direct inspections of the surface of these celestial bodies are incredibly important in providing the information needed for future, possibly manned, landings.



Surveyor 1 to 7 (1966-1968): These probes landed on the Moon to help facilitate the Apollo missions

Lunokhod 1 & 2 (1970, 1973): First successful rover mission, landed on the Moon and explored surface.

Viking 1 and 2 (1975): Satellites orbited Mars, while stationary probes landed on Mars.

Mars Pathfinder (1996): First robotic lander, Sojourner, on a planet, Mars.

Rosetta (2004): performed flyby of Mars and will separate to land on the comet 67P/Churyumov-Gerasimenko to look for evidence of the formation of our solar system

Mars Exploration Rover (2003): Two robotic landers were sent together: Spirit and Opportunity. Both are still functioning on Mars, beyond their expected lifetime, returning a large amount of invaluable data on Mars.

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A panoramic view of the Martian landscape, provided by the Mars lander,
Pathfinder. Sojourner can be seen as it leaves the landing site.



Several challenges continue to confront scientists as they send unmanned missions out into the solar system and beyond. The first challenge is usually attaining enough speed so that the mission does not take too long, while still maintaining accuracy in its flight path. Due to weight, a spacecraft can usually take only a small amount of fuel along for course corrections. It also needs to remain fairly small so the satellite can be accelerated to the desired speed. Gravitational acceleration from planets has been one of the successful solutions to this problem. A spacecraft is directed to do a close orbit of a planet so that the planets gravity works to accelerate the ship, producing a slingshot effect. It can then emerge on the other side of the planet traveling faster.
 



The faster the spacecraft, the more it must slow down when it eventually reaches its destination, especially if it is going to land or enter a stable orbit. An alternative to using fuel to power deceleration rockets has been atmospheric drag. A spacecraft can be equipped with a protective shield so that it can enter the top of a planet's atmosphere and use the friction created with the small amount of atmospheric gas to slow its speed. Because this causes heat, the protective shield is needed.



The science behind spacecraft, manned or unmanned, continues to develop. It is an exciting topic, and will continue to be for many, many years.

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