Rocksat 2010 Final Report Template

RockSat 2010 Final Report

RocketSat VI

The objective of RSVI is to measure large aerosol particle density and charge from 75 to 95 km to characterize the numerical density distribution of these particles and the charge of the particles in the region of the atmosphere above Wallops Flight Facility.

University of Colorado at Boulder Students

Chris Koehler

Kendra Kilbride

Brian Sanders

Zoltan Sternovsky

Colorado Space Grant Consortium

University of Colorado at Boulder

5-7-2010

University of Colorado at Boulder 5-7-2010

RockSat 2010

1.0 Mission Statement

The two main goals of the RocketSat VI project is to measure the amount of meteoric smoke particles in the atmosphere above Virginia, and to determine if the particles have a positive or negative charge. This data will be used to compare to other similar studies to see if the findings are consistent. Additionally, we can use the information to support or refute scientific models of the global shift of the particles during certain seasons. The objectives for the team are to design and implement a supporting payload for the detectors, measure the attitude of the rocket during flight, and retrieve all data when the payload is returned. This mission will allow the team to implement a new flash memory for the RocketSat missions, and will also teach the team about attitude representation.

2.0 Mission Description and Requirements

2.1 Mission Background

Meteors enter the atmosphere and burn up every day, leaving behind several tons of small smoke particles in the upper mesosphere and lower thermosphere [1]. These particles add significantly to the layers of metals already found in the atmosphere, which consists of mostly sodium and iron, but also contain potassium and magnesium. It is unclear what type of metal is left behind from meteoroids, but scientists suspect that they are typically positively charged sodium ions. These ions form larger aerosol particles (diameter > 1 nanometer) when ice collects around the sodium ion. This also causes the particle to descend slightly, so that the particles are concentrated through a range of the atmosphere, approximately 75 km to 95 km.

The meteoritic smoke particles have numerous effects on the upper atmosphere. As previously mentioned, these particles increase the overall metal budget, or amount of metal, in the mesosphere. The concentrations of metals can affect radar waves in the mesosphere [4]. The metal budget is also important to atmospheric scientists because it affect tidal and gravity activities that dictate global circulation [2]. The increasing amount of large particles in the mesosphere also increases the number of solid surfaces on which reactions can occur. Scientists are still investigating the major effects of these particles on the atmosphere.

These sodium ions in the mesosphere are believed to be the positively charged core for ice particles that form in the altitude range from 75 to 95 km in the atmosphere. These ice particles are the result of sub freezing temperatures and an increase in water vapor. As the sodium ions descend in the atmosphere the ice particles continue to gain new layers of ice and the particle grows substantially by the time it reaches 75 km above the surface. The ice particles can reach up to 50 nm in size. The formation of these particles is linked to the increase in global warming effects on the planet. The increased amount of methane causes an increase in the water vapor in the atmosphere, and the increased carbon dioxide causes a reduction of upper atmospheric temperatures. This combination results in a much higher formation rate of these ice particles. However, the ice particles do not form over all locations on Earth. The particles have been measured to be more present in the more polar latitudes of the Earth. Beyond the formation and location, little is known about these particles. In situ measurements of the particles have not been made on more than a handful of occasions.

2.2 Mission Requirements

The requirements for the project were to detect the number large aerosol particles and measure the charge of the particles. Initial design requirements for the system were imposed by the RockSat Program and Wallops Flight Facility. The project level and system level requirements are shown in the following tables. The Subsystem requirements tables are shown in the Appendices.

Project Level Requirements
Requirement / Description / Parent Req.
P1 / The payload shall measure meteoritic smoke particle density / Mission Statement
P2 / The payload shall measure meteoritic smoke particle charge / Mission Statement
P3 / The payload shall be designed to conform to the RockSat 2010 User's Guide as set forth by Wallops Flight Facility / Mission Statement
System Level Requirements
Requirement / Description / Parent Req
S1 / The payload shall be able to detect meteoritic smoke particles / P1
S2 / The payload shall be able to measure charge of meteoritic particles / P2
S3 / The payload shall be able to determine the angle of attack of the detector / P1
S4 / The payload shall convert detector output to a digital signal
S5 / The payload shall store the digital signal
S6 / The payload shall perform in situ measurements from 75-95 km / P1, P2
S6.1 / The system shall record measurements for the entire duration of the flight / S6
S7 / The payload shall not alter the particles during measurement / P1, P2
S8 / The system shall fly on a sounding rocket with an apogee of at least 95 km / P3
S8.1 / The payload shall survive the flight / S8
S8.2 / The payload shall be able to perform with a temperature range of 60-100 degrees F / P1, P2
S9 / The system shall characterize the flight environment / P1, P2
S10 / The system shall make the measured data available after collection / P1, P2
S11 / The system shall be electrically isolated from the rocket / P3
S12 / The system shall be contained in a canister with a diameter of 9.3 inches and a height of 9.5 inches. / P3
S13 / The payload shall not weigh more than 20 lbs / P3
S14 / The system shall have a center of gravity that lies within a 1x1x1 inch envelope of the geometric centroid of the integrated RockSat payload canister / P3

The structural requirements from the system requirements can be seen through P3 and S11-S14. The most important parts of these requirements is that the design must fit inside an aluminum canister provided by RockSat, and that the payload cannot weigh more than 20 lbs. Because the project consists of mostly electronics, and the science instruments are not contained within the canister, it was decided that the RockeSat project would only use half of a canister. The design, coordinated with canister partners (Virginia Tech), would there for be required to use half of the weight. Additionally, requirement S14 had to be coordinated so that the RocketSat assembly had the cg in the middle of the stack, so that when combined with Virginia Tech, the cg would fall into the envelope specified by the requirement.

CDH also had several important system requirements S4, S5, S9-11. WFF required that the payload be electronically isolated from the rocket. A new requirement was that, instead of the electronics having no voltage or current on them before launch, WFF needed to know the status of the payload at all times. Additionally, a command line was made available, which imposed the requirements that the payload could be triggered by the RBF pin and g-switch, and also be turned on and off by the Wallops command line. Payload requirements for the CDH system are that it will store all signals on board and allow them to be retrieved by connecting to the electronics after the payload has been retrieved. The CDH needs sensors to monitor the flight environment, and sensors that will measure the attitude of the rocket.

The Science system requirements are critical to the mission. Requirements S1 and S2 summarize the entire purpose of this system. Additionally, to collect the data for the mission, the measurements must be made in-situ, which is what leads to the requirement for a sounding rocket flight. The science instruments will have to be able to detect the particles but not interfere with the charge. Additionally, the instruments must be able to only detect the large particles, which means they will have to have a way to deflect the smaller particles, including ions and electrons.

2.3 Concept of Operations

The payload will be launched on a Terrier-improved Orion Rocket out of Wallops Flight Facility. The rocket will reach an altitude of approximately 120 km, and then land in the Atlantic Ocean, where it will be retrieved. The payload will be turned on approximately 3 minutes before launch by the command line. The payload will begin sampling all sensors on board. After the rocket launches, all electronics will be latched on, and will continue taking data. No particle detection is expected during burnout, due to the flow that will be going over the detectors. After burnout, the most important area of the ascent will be from 75-95 km. The rocket will land in the ocean, and electronics will continue to run until the payload is retrieved, or until the battery power runs out.

3.0 Payload Design

3.1 Overall System Description

The RocketSat VI system will be utilizing two graphite patch detectors and the electronics boards designed by the RocketSat VI Electrical team. The detectors will be mounted flush with the skin of the rocket for direct exposure to the atmosphere. The detectors will be connected to the electronics using RF cables. All electronics components will be secured in an aluminum canister provided by Wallops Flight Facility (WFF). The system will be recording data for the full battery life (no sequence is used to power down). This is because power down is not required for this mission. Data is stored on board will be read from the electronics memory after the payload is retrieved.

A diagram of the payload integrated into the rocket is shown in the figure below. The detectors are positioned in ports two canisters below the RocketSat canister. There are two cables being used to connect to the detector. Each cable connects to the back of the detector through an SMA connector. The cables will then run up the longerons and into the canister. Because each CVA is enclosed in an aluminum box, a BNC connector will be used to interface with the electronics.

3.2 Detector Design

A modified electrometer called the Colorado Dust Detector will be used to detect these large aerosol particles. This electrometer is also called as a graphite patch detector, due to the large section of graphite located in the middle of the white plastic, as seen in Fig. 2.

Figure 2. Graphite patch detector with aluminum casing

Figure 3. Diagram of Detector

This detector works very similarly to a regular electrometer. When a particle comes into contact with the graphite, the charge is deposited onto the graphite in the form of a current. The current signal is then transferred through the back of the graphite with a wire and is transmitted through a cable to electronics that convert and store the signal. For this type of detector, a higher current corresponds to a greater number of particles impacting the detector. This detector also requires direct exposure to the atmosphere, which means for rocket flights it must be mounted to the skin of the rocket [1].

The detector is designed specifically for larger aerosol particles. To avoid detection of small ions and particles with less mass, there are four magnets in the white plastic around the graphite. These magnets help repel charged particles with a radius less than 1 nm because small particles have less momentum than larger particles due to the smaller mass. Also, smaller particles such as stray ions are not as insulated as meteoritic smoke particles, which have a shell of ice formed around the nucleus of charge [3]. The distance that the charged particles are deflected by is defined by the Larmor radius [1], or gyroradius, equation:

rg=m*vperpq*B (1)

where rg is the radius of the particle, m is the mass of the particle, vperp is the velocity perpendicular to magnetic field, q is the charge of the particle, and B is the magnetic field.

This equation defines the radius of the particles that will be deflected, and is based on the strength of the magnetic field produced by the magnets. The magnetic field is not 100% effective, though, due to the fact that as particles collide in the air, small ions can be deflected with enough speed to penetrate the magnetic field and hit the patch. Also, the formation of the boundary layer around the detector can affect how many particles impact the detector. This issue is accounted for in the data analysis, discussed in the Analysis section.

The flight configuration being used for RocketSat VI has been used for a previous experiment on the MAGIC Sounding Rocket Mission. The detectors were donated to the team by Professor Zoltan Sternovsky of CU Boulder. The detectors were effective for this mission, and the results of the MAGIC mission are discussed in Expected Results.

3.1.1 Boundary Layer Effects on Particle Detection

Due to the supersonic speed of the rocket, there was concern about the data collected being affected by the boundary layer formed on the detectors. This layer would reduce the efficiency of the detectors, therefore providing inaccurate results. A Direct Simulation Monte Carlo (DSMC) code was used to simulate the airflow around the detectors with inputs specifying the altitude and flight conditions. The simulation showed that particles with a diameter greater than 5 nm were not affected by the boundary layers formed on the detectors [1]. To account for the particles with a diameter greater than 1 nm (particles of interest) but less than 5 nm, a relatively small voltage bias of 2V is added into the data collection from the detectors. This voltage bias is important to account for aerosol particles affected by the boundary layer, as well as small ions that may not be deflected by the detectors due to particle collisions.