Date: August 28, 2010

Title: An Introduction to Space Exploration


Podcaster: Gordon Houston

Organization: JPL/NASA Solar System Ambassadors Program –

Description: Space exploration is one of the most challenging human endeavors ever undertaken. However, most of us have a limited working knowledge of space exploration, the methods used, and the unique language we hear used by mission controllers. Have you ever wondered what all those terms mean when the Space Shuttle or other exploration missions take off, such as downlink, payload, flybys, gravitational assist, and so on? In this podcast, I will give a brief history of space exploration, explain the process in broad terms, and finally try and define some of the language and terms used during the missions.

Bio: A lifelong observer, Gordon L. Houston holds a Master of Science in Astronomy from Swinburne University and the designation of “Master Observer” through the Astronomical League, completing 10 observing programs. Gordon is a member of the Houston Astronomical Society, The Association for Lunar and Planetary Observers, Astronomical Society of the Pacific, and a George Observatory volunteer, where he is a certified operator of the 36” Gueymard Research Telescope. Gordon teaches an astronomy course at the Blinn College, Schulenberg, Texas campus and is director of the Schaefer Observatory. Finally, he is a Solar System Ambassador for NASA’s Jet Propulsion Laboratory in Pasadena California.

Today’s sponsor: This episode of “365 Days of Astronomy” is sponsored by — no one. We still need sponsors for many days in 2010, so please consider sponsoring a day or two. Just click on the “Donate” button on the lower left side of this webpage, or contact us at


Podcast by Gordon L. Houston, August 28, 2010

Hello and welcome to another edition of the 365 Days of Astronomy podcasts. I am Gordon Houston, Solar System Ambassador for NASA’s Jet Propulsion Laboratory.

Space exploration is one of the most challenging human endeavors ever undertaken. Many of us are interested in space, but most of us have a limited working knowledge of space exploration, the methods used, and the unique language we hear used by mission controllers. In this podcast, I hope to give a brief history of space exploration, explain the process in broad terms, and finally try and define some of the language used during the missions such as downlink, payload, flybys, gravitational assist, and so on.

There are multiple reasons for exploration of the planets. Solar system formation and search for life through astrobiology, are two of the main objectives for any space science mission. The exploration of the solar system began almost immediately upon man’s first entry into space, with the Russian satellite Sputnik in 1957. Just two years later in 1959 the Russians were successful in sending Luna 1 on the first ever flyby of the Moon. That same year, NASA established a long-range plan of space exploration, with the inner solar system as the primarily target of early exploration, as they are the closest targets. So, the Moon, Mars, and Venus have had the most exploratory missions to date.

The outer solar system, consisting of the gas giants Jupiter, Saturn, Uranus & Neptune, has had much less exploration activity. Voyager 2 is the only mission to have had close flyby contact with both Uranus and Neptune in 1986 and 1989 respectively. Jupiter and Saturn have had recent mission contact, including Galileo to Jupiter and a currently active mission, Cassini is investigating the Saturn system. The New Horizons mission is currently in route to Pluto and the Kuiper Belt.

Space exploration has expanded beyond planetary exploration missions. The list of targets to investigate include comets, asteroids, Kuiper Belt objects, and the Sun. Examples of some of these missions are the STARDUST mission, which explored the comet Wild-2, and has an extended mission life, now known as STARDUST-NExT which is exploring the comet Tempel 1. The DAWN mission is preparing to explore the asteroid Vesta. There are so many missions, I encourage you to visit the Jet Propulsion Laboratory’s website, Missions page,

The science objectives of any mission are the very starting point for any mission proposal. Space exploration can include human participation, but robotic spacecraft with various scientific instrument packages have been the primary exploration method. Mission budgetary issues are always a major consideration. The methods of exploration can be by either remote sensing or in situ measurements or both. The type of investigation will influence the instrument package, spacecraft design, and the cost. Remember, exploration of any planet is a multi-mission process.

The two methods of exploration, remote sensing and in situ, are primarily related to use of robotic instruments. Man has used remote sensing since they first observed the stars and as such, the use of telescopes is a remote sensing technique. A more constrained definition of remote sensing is “Remote Sensing involves gathering data and information about the physical “world” by detecting and measuring signals composed of radiation, particles, and fields emanating from objects located beyond the immediate vicinity of the sensor device(s).”

In Situ exploration literally means “in place” or in touch with the medium being explored or measured. So, a simple definition of in situ exploration would be to change the last part of definition of remote sensing to “…..from objects in contact with the sensor devise(s).” An example is the magnetometer on the Cassini mission. It measures Saturn’s magnetic field, with the spacecraft literally inside of, or in touch with the magnetic field.

Space exploration is guided by what is known as Space Mission Architecture. It is generally divided into five main areas. We have already discussed the first main area, the space mission itself, which is defined by the science objectives. It impacts all other facets of the space mission architecture. These four main areas are: 1) The spacecraft, 2) trajectories and orbits, 3) launch vehicles, and 4) the missions operations systems.

The science objectives directly influence the design of the spacecraft. There are two main parts to the spacecraft, which are the “bus” and the “payload.” The “bus” is the skeleton that holds everything together and it provides all the functions, which support the operation of the payload, including electrical power, temperature control, data storage, communications, and spacecraft orientation. Spacecraft orientation is important, to ensure that the instruments are pointing in the right direction to take the science measurements. The “payload” is the part of the spacecraft that performs the exploration, which is the compliment of instruments measuring and interacting with the “subject” defined by the mission science objectives.

Examples of many of these instruments include visual cameras, both narrow and wide field, all types of spectrometers, magnetometers, radar equipment, microwave, particle detectors, and others. It is common for these instruments to be designed for a specific mission and environment. A name is created for these instruments based on the type or purpose from mission to mission, making it somewhat confusing. For example, the Composite Infrared Spectrometer on the Cassini mission is referred to in capital letters as CIRS. Just remember, each instrument reduced to its common denominator is still just a spectrometer or magnetometer, regardless of the specialized application or name.

The next area of mission architecture, trajectories and orbits, is guided by the mission science objectives, the spacecraft, and the payload. We have talked about two broad areas of the method of exploration. It is necessary at this point to point out some of the different techniques used in space exploration. A mission may be designed as a single flyby, an orbiter with multiple flybys or swingbys, and lander. A mission that does a flyby of a target subject is one style of exploration and the least expensive, but you get one opportunity to get the science measurements. An example would be the Voyager missions, which did flybys of the outer planets, with Voyager 2 specifically visiting Uranus and Neptune. Both of these missions have basically reached the edge of the Solar System.

An orbiter mission has the capability of many flybys, usually called swingbys, which provide multiple opportunities for science measurements. Orbiter missions can also launch specialized probes into the subject or send landers that are or become rovers or penetrators. These different methods of delivering science instruments increase the cost of the missions, which is an important concern for any mission. Examples of rovers are the Mars rovers known as Spirit and Opportunity, both of which had exceptionally long mission lives. The new Mars Science Laboratory has a new rover called Curiosity, with a 2011 expected launch date.

The launch vehicles are the method of lifting the spacecraft out of the Earth’s gravity field. Then considerations must be taken for the location of the target or subject of the mission. The mass of the spacecraft and the mass of the launch vehicle and the propellant are the controlling factors as to the size of the launch vehicle. Launch vehicles come in different configurations and depending on the mass, have multiple stages, to ensure a lift off and initial ∆V, which is the change in velocity.

Having enough propellant and enough thrust to propel a spacecraft has been a limiting factor to space exploration. The Cassini mission, which was a 6,000-kilogram spacecraft, was launched by the most powerful rocket available to NASA in 1997, yet this was not enough to propel it to Saturn. The invention of the gravity-assist trajectory enabled the possibility of interplanetary space travel, which is a technique whereby a spacecraft takes angular momentum from a planet’s solar orbit to accelerate or decelerate the spacecraft. Gravity assist was used by Cassini to get to Saturn, but also uses it to help guide the spacecraft to encounter multiple targets such as flybys of different moons of Saturn.

The term “launch window” is a familiar term, which is a direct result of the mass of the spacecraft and the launch vehicle. All the planets are orbiting the Sun and thus in motion relative to the Earth. The launch window is the particular time to launch on a particular day to ensure that the energy produced by the launch vehicle meets or exceeds the energy requirement to get the particular spacecraft to the particular target body. This target body can be an orbiting planet such as Venus, which can be used for a gravity assist. Thus, Venus needs to be in the right location when the spacecraft arrives to perform the gravity assist.

Finally, the last part of the mission architecture is the mission operations. There are teams for controlling the spacecraft from lift off to target. They monitor the health of the spacecraft and communicate commands. The communication terms of downlink and uplink are often heard. Uplink is a command to the spacecraft and downlink is a communication from the spacecraft down to Earth. The science teams monitor and control the craft during the engagement of the target body or subject, including the monitoring of the science data sent. All communications, including commands and data are facilitated by the Deep Space Network or DSN for short. The DSN is a series of three radio dishes spaced 120 degrees apart around the Earth’s globe, in California, Spain, and Australia. This permit constant observation and contact with the mission.

So, I hope of have not been too technical and have provided you with a basic understanding of space exploration. I have only provided a glimpse of whole process involved, but you can probably determine that many teams are necessary to ensure the success of one mission. I encourage you to look further into this fascinating topic.

Finally, I want to say Happy Birthday to my mother, who turns 83 today. This is Gordon Houston, JPL Solar System Ambassador, signing off, Ad Astra, “To the Stars.”

End of podcast:

365 Days of Astronomy
The 365 Days of Astronomy Podcast is produced by the Astrosphere New Media Association. Audio post-production by Preston Gibson. Bandwidth donated by and wizzard media. Web design by Clockwork Active Media Systems. You may reproduce and distribute this audio for non-commercial purposes. Please consider supporting the podcast with a few dollars (or Euros!). Visit us on the web at or email us at Until tomorrow…goodbye.