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Snapshots of Scientific Enigmas
While our satellites and space probes discover the big mysteries of the Universe, there are areas of the upper atmosphere and near space, up to about 120 miles that satellites can’t access. A satellite in a 120 mile high orbit would decay and reenter in just a few orbits because there is still enough atmosphere at that height to slow the craft quickly, as it is traveling at 18,000 mph.
To investigate these reaches of the upper atmosphere, NASA uses sounding rockets (SRs) to carry instruments to varying heights. Levels of the atmosphere of particular interest are the mesosphere, the ionosphere and the thermosphere. These are shown in the diagram below.
The mesosphere is just above the stratosphere at about 31 miles. It extends to about 50 miles. It is characterized by rapidly dropping temperatures with altitude.
The ionosphere begins at the top of the mesosphere and extends as high as 400 miles. In this region, particles from the Sun knock electrons out of the oxygen atoms producing ions. This creates a layer that reflects radio waves and produces the aurora.
The thermosphere includes part of the ionosphere and extends out to as much as 800 miles. This layer is characterized by increasing temperature with altitude. Obviously, satellites can probe the upper levels of these levels. Instruments are carried into the lower level on quick jaunts in these smaller rockets.
But it isn’t just atmospheric phenomena that NASA’s stable of small rockets provide access to. Some carry sophisticated telescopes for astronomical observations, particularly of objects too close to the Sun for Hubble be able to image.
Also, due to their free fall descent, they provide ideal platforms for microgravity experiments.
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NASA’s Stable of Rockets
The United State’s first (SRs) were German V2s captured at the end of WWII. These provided scientists with their first dip into the upper atmosphere and space. In the second half of the 20th century, a number of SRs were developed. During the Cold War, as military missiles developed and became obsolete in the rush to produce better weapons, NASA began using surplus military rockets as SRs.
That trend continues today, with a significant exception. NASA’s stable of SRs now includes four surplus U.S. Navy rockets—the Terrier, Talos, Taurus and Lynx—and a surplus Army rocket—the Orion. It even includes a British rocket developed especially as an upper stage.
While the Navy’s Terrier is the booster for many of the multi-stage SRs, a good part of the stable is built around a venerable Canadian rocket, one that has been around a long while—the Black Brandt. This rocket forms a part of half NASA’s SR fleet. Most SRs are multi-stage vehicles, some as much as four stages. Two are single stage--the Army surplus Orion and the single stage Black Brandt--used for research of the lower levels of the upper atmosphere such as the ionsphere and the aurora. Payload capability varies from 200 pounds to 1200 pounds. Altitude capabilities vary from about 68 to 1000 miles.
The top of the line in today’s stable is the Black Brandt XII, a four stage rocket with tremendous capabilities. It can loft 1200 pounds to over 300 miles and 300 pounds to about 1000 miles. The XII consists of a Taurus first stage, a Talos second stage, with the Black Brandt forming the third stage. The British Nikha is the upper stage.
Note in the image the first three stages are finned. This is because they are ignited within the sensible atmosphere and so provide stability. The fourth stage is ignited above any significant atmosphere and is spin stabilized.
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A Typical SR Mission
SRs fly missions so varied it is impossible to list them all. There are the purely scientific missions, some aimed at learning more about various aspects of the atmosphere, such as the ionosphere, the aurora, and even weather patterns. Then there are those that support some satellite operations, such as SOHO. These are flown to obtain additional data and even images to add to the data from the satellites.
Some missions are flown strictly in support of university educational programs. This is a significant part of NASA’s SR program—support of university research.
Whatever the mission, they follow a fairly typical mission profile, as illustrated below. The SR is launched at an angle slightly less than 90 degrees, depending on the altitude to be achieved. The fins on the lower stages impart a slow spin to the vehicle to provide stability. Once the final stage burn is complete, small rockets de-spin the upper stage and payload. The payload separates, and stabilization booms deploy to provide in-space stability.
As the payload coasts to apogee (the highest point above Earth) the Automatic Control System (ACS) locks onto a star or the Sun to keep the payload pointing toward the proper object. Previously, instrumentation doors have opened to expose the cameras, detectors or other instruments.
The payload coasts through apogee, continuing to make its measurements. Depending on altitude and launch angle, a payload package can stay at apogee for as much as 300 seconds.
As the payload begins to descend, the doors close and the stabilization booms retract or are ejected. After the package enters the atmosphere, a parachute deploys, to lower it safely to the surface so it can be reused.
So sounding rockets are a highly useful scientific tools, being relatively inexpensive, with, in most cases, reusable payloads, and unique capabilities.
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