10:00 AM - 10:15 AM
[PEM12-25] The development of a vacuum gauge for observing the upper atmosphere on a sounding rocket
Keywords:Sounding rocket, Vacuum gauge, Upper atmosphere
In the lower thermosphere, the ionized particles tend to move in a different direction from the neutral atmosphere mainly due to the electromagnetic forces. This causes collisions between the ionized and neutral particles, and results in the momentum transfer and the complicated motion of particles in this system. In this region, it is well known that characteristic phenomena related to this particular condition occur but many of those are still unexplained. To understand them, it is necessary to precisely measure physical quantities based on in-situ measurements.
We decide to use a small size, simple mechanics, and reliable vacuum gauge to measure atmospheric pressure in the thermosphere on board a sounding rocket. The atmospheric pressure measured with the vacuum gauge during its flight will be used to estimate information on the neutral atmosphere in the lower thermosphere. In order to obtain information, on the atmospheric flow on the sounding rocket from the vacuum gauge pressure measurements, we need to develop a container for the gauge that can detect the inflow direction of the neutral atmosphere with respect to the rocket frame, i.e., one has a structure that functions a different response depending on the direction in which the inflow arrives.
Information on sounding rocket attitude is necessary to understand the geometrical condition of the atmospheric inflow on the moving platform. The attitude data from the S-520-26 sounding rocket launched from USC in 2012 were used for this purpose. As a result, it was obtained that the atmospheric inflow tends to come from the direction of 30-45 degrees with respect to the rocket axis at altitudes below 200 km during the rocket ascent. Under these conditions, we designed and fabricated a double-cylinder vacuum gauge container that meets the condition described above.
On the other hand, a vacuum gauge that provides the background atmospheric pressure is necessary to discuss the atmospheric pressure measured by the developed vacuum gauge. In general, when atmospheric pressure is measured on a platform with a supersonic velocity such as a rocket, it is difficult to accurately measure the pressure because the translational kinetic energy generated by the speed of the rocket is added to the thermal kinetic energy of the atmospheric particles. In our case, a spherical Patterson probe with a vacuum gauge inside is decided to use so that the energy generated by the rocket motion has no influence on the measurement.
Vacuum gauges with pressure sensors inside two types of containers; a cylindrical and a spherical container, were installed on the S-520-32 sounding rocket, which was launched in August 2022. As a gauge element, we adapted a crystal ion gauge, which operates in the low vacuum region above approximately 4 Pa behaving as a quartz crystal, and in the high vacuum region below behaving as an ion gauge.
The data acquired by the developed ion gauges during the S-520-32 flight were analyzed mainly from a viewpoint of the pressure variation. The pressure gradually decreased with almost constant rate as a function of altitude until it reached about 10-2 Pa at ~80 seconds from the launch. However, the decreasing rate became insignificant with a very gradual slope until 460 seconds. Such a gentle change was probably related to outgas from the inner wall of the ion gauge container. After ~87 seconds, a sinusoidal change in the pressure value was confirmed to exist and is probably caused by the rocket spin. The pressure values measured with the two types of gauges generally showed similar trends after launch. After the nose cone of the rocket was opened at 54 seconds from the launch, the pressure tends to change with a larger amplitude. This change is thought to reflect a larger change in the atmospheric pressure after the nose-cone open. When the pressure reached 3-4 Pa, a sudden change in the measured value was observed, confirming that the vacuum gauge was switched from a crystal gauge to an ion gauge at an altitude of around 100 km.
In the presentation, a result of our analysis of the measured data will be discussed in more detail.
We decide to use a small size, simple mechanics, and reliable vacuum gauge to measure atmospheric pressure in the thermosphere on board a sounding rocket. The atmospheric pressure measured with the vacuum gauge during its flight will be used to estimate information on the neutral atmosphere in the lower thermosphere. In order to obtain information, on the atmospheric flow on the sounding rocket from the vacuum gauge pressure measurements, we need to develop a container for the gauge that can detect the inflow direction of the neutral atmosphere with respect to the rocket frame, i.e., one has a structure that functions a different response depending on the direction in which the inflow arrives.
Information on sounding rocket attitude is necessary to understand the geometrical condition of the atmospheric inflow on the moving platform. The attitude data from the S-520-26 sounding rocket launched from USC in 2012 were used for this purpose. As a result, it was obtained that the atmospheric inflow tends to come from the direction of 30-45 degrees with respect to the rocket axis at altitudes below 200 km during the rocket ascent. Under these conditions, we designed and fabricated a double-cylinder vacuum gauge container that meets the condition described above.
On the other hand, a vacuum gauge that provides the background atmospheric pressure is necessary to discuss the atmospheric pressure measured by the developed vacuum gauge. In general, when atmospheric pressure is measured on a platform with a supersonic velocity such as a rocket, it is difficult to accurately measure the pressure because the translational kinetic energy generated by the speed of the rocket is added to the thermal kinetic energy of the atmospheric particles. In our case, a spherical Patterson probe with a vacuum gauge inside is decided to use so that the energy generated by the rocket motion has no influence on the measurement.
Vacuum gauges with pressure sensors inside two types of containers; a cylindrical and a spherical container, were installed on the S-520-32 sounding rocket, which was launched in August 2022. As a gauge element, we adapted a crystal ion gauge, which operates in the low vacuum region above approximately 4 Pa behaving as a quartz crystal, and in the high vacuum region below behaving as an ion gauge.
The data acquired by the developed ion gauges during the S-520-32 flight were analyzed mainly from a viewpoint of the pressure variation. The pressure gradually decreased with almost constant rate as a function of altitude until it reached about 10-2 Pa at ~80 seconds from the launch. However, the decreasing rate became insignificant with a very gradual slope until 460 seconds. Such a gentle change was probably related to outgas from the inner wall of the ion gauge container. After ~87 seconds, a sinusoidal change in the pressure value was confirmed to exist and is probably caused by the rocket spin. The pressure values measured with the two types of gauges generally showed similar trends after launch. After the nose cone of the rocket was opened at 54 seconds from the launch, the pressure tends to change with a larger amplitude. This change is thought to reflect a larger change in the atmospheric pressure after the nose-cone open. When the pressure reached 3-4 Pa, a sudden change in the measured value was observed, confirming that the vacuum gauge was switched from a crystal gauge to an ion gauge at an altitude of around 100 km.
In the presentation, a result of our analysis of the measured data will be discussed in more detail.