Suborbital Vs. Orbital Expendable Launch Vehicles
A launch vehicle is the device used to transfer humans or cargo along suborbital and orbital trajectories. With the exception of the Space Shuttle, all launch vehicles in use today are disposed of after each launch, and are referred to as expendable launch vehicles (ELVs). ELVs represent an evolution of long-range ballistic missiles first developed by the Germans in WWII. This missile was known as the V-2 rocket (also the A-4 rocket), and was pioneered by German scientist Wernher Von Braun. Following the War, Von Braun and his team of German scientists came to the United States and worked for the Army Ballistic Missile Agency at Redstone Arsenal in Huntsville, Alabama. The team led the U.S. development of the Jupiter and Redstone intermediate range ballistic missiles, which had their heritage with the V-2 rocket. The Jupiter C was used to launch America's first satellite, Explorer I, into space on January 31, 1958. When the Space Race began in 1960, the U.S. Government determined that the fastest way to get to space, and the moon, was by leveraging experience with the Army Ballistic Missile Agency’s missiles. In 1961, a modified Redstone rocket was used to send Alan Shepard on a sub-orbital flight. Eight years later in 1969, the Saturn V, an evolution of the rockets developed at Redstone Arsenal, was used to carry Neil Armstrong, Buzz Aldrin, and Michael Collins to the moon. Today’s U.S. medium and heavy-lift ELVs (e.g., Delta, Atlas) can also trace their origins to the rockets developed at Redstone arsenal, and ultimately to the V-2 rocket. The ELVs in use today that achieve suborbital velocities are known as sounding rockets. Sounding rockets derive their name from the nautical term "to sound," which means to take measurements. This is because sounding rockets do not place payloads in orbit, but rather provide the only means of making in-situ measurements at altitudes between the maximum altitudes for balloons (about 30 miles) and the minimum altitude for satellites (100 miles, although sounding rockets are also launched to altitudes as high as 870 miles). Figure 2 displays the configuration of a typical sounding rocket [ref 1]. Figure 2. Sounding Rocket Configuration (Image provided courtesty of NASA.) The profile for a sounding rocket mission, as displayed in Figure 3, is much different than an orbital launch vehicle mission. The sounding rocket payload follows a parabolic trajectory and is retrieved less than 30 minutes after launch, whereas the orbital payload maintains motion around the Earth for an extended period of time (usually years). Though the flight time on a sounding rocket is short, a significant amount of data is collected. Figure 4 displays the difference between these two trajectories. Sounding rocket missions are much less expensive than orbital launch vehicle missions, partly because the launch system itself is much simpler and requires much less ideal velocity, but also because the payload can often be retrieved, allowing the payload or parts of the payload to be refurbished and flown again [ref 1]. Orbital ELVs, on the other hand, are much larger, more complex, and consequently more expensive than sounding rockets. Because of the high velocities needed to obtain orbit, the mass and volume of orbital expendable launch vehicles consists mostly of propellant. Further, orbital ELVs transport much heavier payloads than sounding rockets (10-100 times), thus requiring the launch vehicle to have even more energy. (In fact, orbital systems incorporate liquid propulsion, as opposed to the solid propulsion systems of sounding rockets, therefore requiring additional hardware; e.g., fuel and oxidizer lines, tanks.) This translates to more complex systems, more support structures, and ultimately much larger vehicles. Figure 5 displays Boeing’s Delta III launch vehicle and how it compares in size to the suborbital Nike-Orion sounding rocket. The associated increase in size and complexity further translates to higher costs. As a comparison, the launch cost for Bristol Aerospace’s Black Brant V is approximately $200,000, and for the larger Black Brant XII approximately $600,000; while the launch costs for orbital expendable launch vehicles is between $12 M (for a Pegasus) and $450 M (for a Titan IV).
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