Ⅰ. Advanced Composition Explorer (ACE) 

Image source - Google
UMD Space Physics Group 

Description 

It is a NASA solar research & space exploration program to study matter composed of high energetic particles in the range of solar wind ions to cosmic ray nuclei from solar, interplanetary medium & the local galaxy. 

It was launched on 25th August 1997 & the duration of the mission was planned to be about 5 years but it elapsed to 23 years, 11 months & 3 days & is still operating. 

It was carried by the rocket Delta II 7920-8 from Cape Canaveral, Brevard County, Florida & stationed in an orbit at a distance of 1.5 mn Km from the Earth.

The perigee & apogee altitude of its orbit from the Sun is 145.7 mn Km & 150.55 mn Km respectively & has a revolutionary period of 1 year. 

It carries six high-resolution sensors & 3 monitoring instruments that sample low-energy solar particles & high-energy galactic particles. It performs measurements under all solar wind flow conditions & solar flares. 

Some of the major measuring instruments of ACE include :

1. Cosmic Ray Isotope Spectrometer 

2. Solar Isotope Spectrometer 

3. Ultra-Low Energy Isotope Spectrometer

4. Electron, Proton & Alpha Particle Monitor 

5. Magnetometer 

ACE allows investigation of a wide range of fundamental problems in four major areas :

1. Elemental & Isotopic composition of matter 

  • Accurately determine the elemental & isotopic composition of source materials from which nuclei are accelerated. 
  • Determine the elemental composition of the Sun's corona.
  • Establish the pattern of isotopic difference between galactic cosmic rays & solar system matter. 
  • Generate a set of solar isotopic abundances. 

2. Origin of elements & subsequent evolutionary processing 

Isotopic differences in meteorites indicate that the solar system wasn't homogeneous when formed. Similarly, the galaxy is neither uniform in space nor constant in time due to continuous stellar nucleosynthesis. ACE measurements are used to : 

  • Search these anomalies between solar & meteoritic matter. 
  • Determine the contribution of solar particles to lunar & meteoritic matter & to planetary atmospheres & magnetospheres. 
  • Determine the dominant nucleosynthetic processes that contribute to the source material of cosmic rays. 

3. Formation of solar corona & acceleration of solar wind 

Solar particles, wind & spectroscopic observations show that the composition of the corona is different from the photosphere. The detailed composition & charge state data provided by ACE are used to : 

  • Study plasma conditions at the source of solar winds & particles. 
  • Study solar wind acceleration processes. 

4. Particle acceleration & transport in nature 

Particle acceleration is present everywhere in nature & understanding it is one of the fundamental problems of space plasma astrophysics. The data provided by ACE is used to : 

  • Measure charge/mass dependant fractionation during solar particle & interplanetary acceleration events.
  • Constrain solar flare & coronal shock models with charge, mass & spectral data. 
  • Test theoretical models for 3He rich flares & solar gamma-ray events. 


II. Aeronomy of Ice in the Mesosphere (AIM)  

Image source - Google | Image by - Hampton University

It is a NASA Atmospheric research satellite to conduct the study of noctilucent clouds (NLC). It is a geocentric, sun-synchronous satellite launched on 25th April 2007 from Stargazer, Vandenberg Runway 12/30, California. 

It was carried by the rocket Pegasus - XL F38. It is the nineteenth Explorer program mission & is a part of NASA's Small Explorer program (SMEX).

The primary goal of the AIM mission is to help understand whether the cloud's ephemeral nature & its variation over time is related to Earth's changing climate. By measuring the thermal, chemical & other properties of the environment we can determine the long-term variations in the mesosphere & its relationship to global climate change. 

It will also investigate the cloud abundances, their distribution in the atmosphere & the size of particles within them. 

AIM satellite is a 200 kg, 1.4 m by 1.1 m spacecraft that is powered by two solar arrays & carries three instruments : 

1. Cloud Imaging & Particle Size (CIPS) 

  • It has four cameras positioned at different angles 
  • Captures multiple views of the clouds 
  • Determines the size of the ice particles that make it
  • Can be used to infer gravity waves in the atmosphere. 

2. The Cosmic Dust Experiment (CDE)  

  • It records the impacts of cosmic dust particles as they enter Earth's upper atmosphere. 
  • Has fourteen polyvinylidene fluoride detectors
  • Emit pulses of charge when impacted by hypervelocity dust particles. 
  • Measurement of value & variability of dust particles 
  • Helps to determine its role in Polar Mesospheric Cloud (PMC) formation. 

3. The Solar Occultation for Ice Experiment (SOFIE)  

  • Uses solar occultation to measure cloud particles, temperature & atmospheric gases involved in cloud formation. 
  • Determines the mixture of chemicals & the environment required to form noctilucent clouds.