Venus as seen in visible light Radar image of Venus
Credit: Calvin J. Hamilton, DOD Credit NASA/JPL
This unit covers some of the probes which were sent from Earth to explore our solar system. We will only cover the probes themselves here (and only a select few) and save the results of their investigation for the next unit.
Don't think for a second that the United States (NASA) is the only kid on the block. Of course you should know that Russia has a very active space program .... and possibly the ESA (European Space Agency). However, China, India, Japan, and several other countries pursued space missions. Just scroll down this page and look at the flags.
Passively observing the universe is one thing, going on a field trip is quite another. Ever since the 60's, we have sent vessels from Earth to various places in our solar system to investigate the unknown. Most probes were unmanned missions. In fact, the farthest any person got from Earth was the moon, but that mission was probably the greatest technological achievement in all of mankind. So let's start there.
After World War II, our country fought another war, ... a cold war with the Soviet Union. Part of that conflict involved a massive buildup of nuclear weapons and methods to deploy them. Space was seen as a strategic foothold in gaining an advantage over the enemy. We knew it, ... and so did the Russians. During this period, both superpowers were engaged in a massive struggle to win the upper hand. It appeared that the Soviet Union was always one step ahead of the US at every turn. For example:
When president Kennedy announced to Congress (on May 25, 1961) the decision to land a man on the moon before the end of the decade, our country had quite an ambitious goal. NASA (National Aeronautics and Space Administration) was conceived to carry out his mission. This was done in three phases:
Mercury Program - Send an American in space (accomplished May 5, 1961,
Astronaut Alan Shepard)
Gemini Program - Prepare for the moon by doing ship rendezvous & space
walking (all in Earth orbit)
Apollo Program - Send a ship to the moon, separate a Lander which goes to
the surface with 2 Astronauts, return and rendezvous with the orbiter, and
return safely to Earth.
Apollo 1 - A fire on the launch pad kills three Astronauts and puts the program behind schedule a few years.
Apollo 8 - Wisconsin native, James Lovell and his crew become the first humans to orbit the moon (December, 1968)
Apollo 11 - Neil Armstrong becomes the first person to walk on the moon (July 20, 1969 on the Sea of Tranquility). He is accompanied by Edwin (Buzz) Aldrin, Jr. We did it!
Apollo 17 - Last manned mission to the moon (Eugene Cernan - December 1972)The space race (and other NASA projects) produced many technological byproducts that we enjoy today. The desktop computer is a common item found in most homes today. The technology that made them a reality came from the need to have small, light weight computers onboard spacecraft. Other items we have as a result of spaceflight technology are smoke detectors, joy sticks, cordless power tools, ceramic braces, and satellite dish TV and radio (to name a few).
Mercury - Messenger has answered several questions about this hot, small, dense planet. Only 45 % of Mercury's surface has been photographed since Mariner 10 flew by in 1973. Since Messenger, we know much more about the structure and magnetic properties of Mercury. Messenger flew by Mercury in 2008 and finally got into orbit around Mercury in 2011. The probe ran out of fuel and crashed into Mercury in 2015.
Since Mariner 10 was the first spacecraft to use this technique, it seems fitting to cover gravity assist here. Astrophysicists have found that spacecraft can either pick up or lose speed by flying by any planet in a carefully designed way. This is a complicated maneuver, but is similar to a way we once gained speed on skateboards (many, many years ago) playing "crack the whip". The energy of a group of skaters was transferred to the last person, ... giving them a great ride. For example, Messenger received gravity assists in flybys with Earth (once), Venus (twice), and Mercury (3 times) before achieving orbit. In this case, Messenger needs to lose a lot of kinetic energy but probes to the outer planets need to pick up speed by the assist.
Venus - The Russians were the only ones who attempted to soft land on Venus, and were eventually successful with Venera 7 (1970) & several other follow-up missions. The US was mostly interested in surveying Venus from orbit. The most successful mission was Magellan. This craft entered Venetian orbit in 1989 and spent 4 years taking images of the surface. Magellan was destroyed in 1994 when it was sent into the thick Venetian atmosphere, but not until it had mapped 98% of the surface of the planet. It did this despite the fact that Venus has a perpetual cloud cover, by using radar.
Echo Location - Bats send out very high pitched sound waves which reflect off obstacles in caves and back to the bat. These reflected waves enable the bat to fly in the dark. Dolphins have the same ability (no, they can not fly in the dark). This is a simple form of echo location called sonar. The same idea can be used when using electromagnetic radiation, in which case, we call it radar. This technique has been used for many years using radio waves to map precipitation in the atmosphere. A radio pulse is sent out and will reflect back to the tower if rain is present. The round trip time tells the meteorologist how far away the storm is. Space probes (like Magellan) used radar to map the surface of cloudy Venus.
Venus as seen in visible light Radar image of Venus
Credit: Calvin J. Hamilton, DOD Credit NASA/JPL
Mars - Mars has been studied from the surface and from orbit by several US spacecraft.
Surface Probes - In 1976, the US parachuted two probes, Viking 1 & Viking 2 to the surface of Mars.
Credit NASA - Viking 2 landing siteThe mission of both probes was to detect any presence of life (past or present) on the planet. It did this by scooping up some Martian soil with a robotic arm and placing it through a series of biological tests for life. It didn't find any evidence of life, ... but biologists now have better tests and better landing sites proposed to resume the search.
Credit NASA (notice the "scoop" marks left by Viking)
Pathfinder returned to the surface of Mars in 1997. It was really an experiment to test a different approach to Martian landings and exploration. Instead of a parachute entry to the surface, Pathfinder deployed airbags which inflated around the craft (like a cocoon), ... allowing it to bounce to the surface. Once landed, the airbags deflated exposing the craft. Pathfinder was also equipped with a small solar-powered rover called Sojourner which was able maneuver across the surface and perform geologic tests on local rocks. Pathfinder set the stage for two more surface probes ....Spirit and Opportunity.
Credit NASA
Sojourner rover
Spirit & Opportunity - The success of Pathfinder was surpassed when twin rovers "bounce" landed on Mars in early 2004. Their mission was to search for evidence of liquid water which may have been on the surface in the past (there is no liquid water there now). These rovers were equipped with compact tools which allowed geologists to drill into and sample microscopically the interior of Martian rocks. They have already declared their findings - Mars did have water on its surface in the distant past! Both rovers are now dead!
Credit NASACuriosity (Mars Science Laboratory) is currently the most advanced Marian rover yet. It landed in 2012 using a new technique. After a parachute slowed the descending probe close to the surface, rockets hovered in a stationary position as a crane lowered the rover to the surface. This car sized probe (still working 2017) is capable of doing complex chemical analysis on surface rocks and is equipped with drills and lasers. It is not powered by solar panels (like all previous Martian rovers), but runs on electricity produced from the heat of radioactive decay. This idea has been used for many years for deep space probes, but is now used on Mars. Curiosity is trying to answer the question: "Could Mars provide an environment (now or in the past) that could support microbial life forms?"
Perseverance - This is the most ambitious rover mission yet. On February 2021, it successfully landed in Jezero crater on Mars. Please watch this amazing video. Its mission is to look for evidence of any ancient bacterial life that may have once existed during the period when Mars was wet and warm (several billion years ago). This is actually just the first step to eventually return pristine rock samples back to Earth for study so please be patient. This lander also carried a small helicopter (more like a drone) called Ingenuity ... way cool.Observing Mars from Orbit - There are currently several probes orbiting Mars, taking high resolution images of the surface and studying the Marian atmosphere. Here are just two: , Odyssey (arrived in 2001), and the Mars Reconnaissance Orbiter (arrived in 2006).
NASA has had its share of successes and also several failures (especially when it comes to Mars). For example, the Mars Polar Lander was lost when an engineer radioed the wrong numbers to the craft as it was preparing its decent, causing it to crash. In fact, only about half the spacecrafts sent to Mars actually carried out their missions successfully. Still want to sign up to go there with SpaceX?
Jupiter - There have been several fly-bys of Jupiter, but the most successful probe to visit Jupiter was Galileo, which spent 14 years orbiting Jupiter and studying the Jovian system. It parachuted a probe into Jupiter, which was able to transmit 58 minutes of data before being crushed by the atmosphere. Galileo was eventually destroyed when it entered Jupiter's atmosphere in 2003. The Juno spacecraft reached Jupiter orbit in 2016 and was expected to end its mission in 2018 when it will disintegrate in the Jovian atmosphere (but was extended by NASA for 3 years).
Saturn - Just as Galileo's mission at Jupiter ends, Cassini begins its mission at Saturn. Part of the mission is to parachute a probe (Huygens) to the surface of Titan, a very interesting moon of Saturn. Cassini arrived at Saturn in 2004. The mission ended in September 2017 when it disintegrated in the atmosphere of Saturn.
Uranus & Neptune - The very little we know about these two planets comes from the only spacecraft to fly-by, Voyager 2 (there are actually two Voyager probes). In fact, Voyager 2 made a "grand tour" of the outer solar system, flying by Jupiter, Saturn, Uranus, and Neptune. Now well over 100 AU from Earth, Voyager 1 has entered interstellar space (out of the solar influence) and is still taking data in one of the most successful missions ever undertaken by NASA. Maybe even more impressive is that we can still receive the signal from Earth. Voyager's power output is equal to a typical porch light bulb.
Pluto/Charon - The New Horizons spacecraft flew past this former planet in 2015.
Near Shoemaker, mission to the asteroid, Eros. This craft actually landed on an asteroid in 2001.
Stardust Mission - In 2002 this craft flew by a comet named Comet Wild 2 and collected debris. It returned a sample of this material to Earth in 2006.
Rosetta Mission - The European Space Agency placed Rosetta in orbit of comet 67P in August 2014. The mission attempted to soft land a probe (Philae) on the comet itself without success and the mission ended when the craft crashed into the comet in 2016.
So, as you can see, we have taken field trips to all the planets, one dwarf planet, an asteroid, and comets. Way cool!!!!
ŠJim Mihal 2004, 2014, 2017, 2020, 2023 - all rights reserved
