Space Environment

Fiels and Particles in Interplanetary Space Environment

Fields:

• solar gravitational field (and of other planets)

• solar magnetic fields

Particles:

• the solar wind

• solar electrons and protons

• Galactic cosmic rays

• Interplanetary material (Comets and asteroids, Gas and dust)

What is the definition of Space Weather ?

Space Weather is an umbrella term for either Solar Weather and/or Cosmic Weather. Usually it is Solar Weather → Solar Weather is the dynamical transfer of energy from the Sun to the Earth in the form of solar photons, charged particles, and fields that vary on multiple time and spatial scales

It affects natural planetary environments (ocean, land, atmosphere, near space) and human technologocal systems (space-based & ground based)

How are Sunspots and Solar Flares formed ? How does coronal mass ejections happen?

How does Space Weather impact human technologies ?

• Aviation – HF communication loss; radiation above 7000 m; GNSS position error

• Navigation – GNSS position and timing error

• Communication – D-region absorption; HF loss; HF/UHF/L-band radio signal scintillation

• Satellite operations – LEO orbit error from drag ; GEO spacecraft charging; SEUs and latchup

• Energy production – drill-bit misalignment from magnetometer error in oil/gas drilling

• Power grid – transformer loss from surges

Atmospheric Drag resuting from interaction with space weather affects location knowledge → Attitude perturbations affect pointing precision and gas supply

F_{D}=\frac12\cdot\rho\cdot V^2\cdot C_{D}\cdot A

What different forms of Radiation exist & Hoe do they impact us humans on Earth ?

First Prerequisite: Knowledge on ambient high energy (solar) photon, electron, ion, neutron, and (galactic) cosmic ray environment

Galactic cosmic rays and solar energetic protons penetrate into the troposphere causing radiation in aircraft

Van Allen belts (inner, outer, and new) are generally the regions in which Earthorbiting spacecraft encounter the trapped particles while energetic photons can be encountered in any environment

Interplanetary and outer planets (e.g., Jupiter, Saturn) environments have their own radiation environments composed of the same particles/photons

What different units exist for Radiation ?

• Gray (Gy): SI Unit; amount of radiation that deposits 1 J/kg in a material

• Rad: mount of radiation that deposits 0.01 J/kg of material; 100 Rads =1 Gray

• Dose: amount of radiation energy deposited in a material as a function of time

The Total Dose deposited over the life of the material and the rate at which the radiation is deposited (dose rate)´are two of the most important factors in determining radiation damage

What are some characteristics of Radiation ?

• Human-produced radiation can achieve high energies of 104-108 eV.

• Solar energetic photons (hard X-rays and gamma rays) are generated during powerful solar flares. The energy of photons during solar events can achieve 104-108 eV

• Radiation belts (RB), the regions populated with high-energy charged particle fluxes, are located within the dipole structure region of the magnetic field of the Earth and giant-planets. Particle energies can be as high as 109 eV for protons and 107 eV for electrons for extreme conditions

• Solar energetic particles (SEPs) are generated during coronal mass ejections and in IMF acceleration shocks. The frequency of such events varies with the solar activity cycle: there are more during the maximum and decline of the solar cycle. The energy of protons and nuclei during solar events can achieve 109-1011 eV.

• Galactic cosmic rays can achieve even higher energies - as high as 1021 eV with an abruptly falling energy spectrum.

eV = Measure of amount of kinetic energy gained by a single electron accelerating through an electric potential difference of 1 Volt in vacuum

What are sources of heating and cooling for a spacecraft in space ?

1. Sun, internal, earth, moon, other planets, atmospheric friction, micrometeorites

2. Radiation to cooler environment – deep space, other component

How does the thermal conditions in space differ than on the groun

• No natural air convection source to conduct heat to or from areas of the spacecraft

• Vacuum – extreme, fast temperature variations

Extremes that a spacecraft sees in space

• Sunlight vs eclipse

• Operation extremes

Calculate the Radiation Intensity from the Sun

H_0=\frac{R_{sun}^2}{D^2}\cdot H_{sun}

What are major parameters driving Thermal Control Design on Spacecraft

• the environment in which the spacecraft has to operate

• the total amount of heat dissipated on board the spacecraft

• the distribution of the thermal dissipation inside the spacecraft

• the temperature requirements of the various equipment items

• the configuration of the spacecraft, and its reliability/verification requirements

What is the definition of Space Debris

Space debris is defined as all non-functional, artificial objects, including fragments and elements thereof, in Earth orbit or re-entering into Earth’s atmosphere. Humanmade space debris dominates over the natural meteoroid environment, except around millimetre sizes.

What is the definition of Resident Space Objects?

Resident Space Object (RSO) is a natural or artificial object that orbits another body e.g. Sun Orbiting, Earth Orbiting, Mars Orbiting etc. It is most often used to reference objects that are Earth orbiting. In the case of Earth orbiting the possible orbit classifications for an object are: Low Earth orbit (LEO), Medium Earth orbit (MEO), High Earth orbit (HEO) or Geosynchronous Earth orbit (GEO - 36 000 km above the equator)

Remark: A piece of Space Debris is a Resident Space Object (RSO), BUT Resident Space Object is not automatically a piece of Space Debris

What causes space debris?

• Collision events

• Fragmentation events = break-ups, explosions (linked to onboard batteries or faulty propellants), collisions or anomalous events

• Military tests

• Separation events

• Defunct satellites

What is the Kessler Syndrome and how is it linked to Number of space debris objects

The Kessler syndrome proposed by NASA scientist Donald J. Kessler in 1978, is a scenario in which the density of objects in low Earth orbit (LEO) due to space pollution is high enough that collisions between objects could cause a cascade in which each collision generates space debris that increases the likelihood of further collisions.

Risk due to Re-Entry

Risk due to re-entries determined through analysis of surviving fragments, their dispersion across a ground swath/foorprint, and the resulting casualty risk for the underlying ground population distribution. A 1-in-10 000 probability threshold for the casualty risk of a single uncontrolled reentry is commonly accepted

How to attack the problem of space debris collisions ?

• Method - Mitigation: curtailing or preventing the creation of new debris, designing satellites to withstand impacts by small debris, and implementing operational procedures such as using orbital regimes with less debris, adopting specific spacecraft attitudes, and even manoeuvring to avoid collisions with debris

• Method 2 - Remediation: mainly aims at removing existing pieces of orbital debris through removal of debris

What are Mitigation measures to prevent space debris collisions ?

• Guarantee successful disposal

• Improve orbital clearance

• Avoid in-orbit collisions → Collision avoidance

• Avoid internal break-ups: improve Satellite health monitoring & implement robust passivation techniques to prevent satellites breaking up from within

• Prevent intentional release of space debris e.g. protective covers, lens caps and rocket fairings

• Improve on-ground casualty risk assessment

Strategies for postmission disposal of space debris

Low Earth Orbit: Strategies for postmission deorbiting rely on forces which decelerate the satellite, thereby reducing the orbital altitude and result in a deorbiting scenario.

Strategies fall primarily into 4 categories:

• Propulsion systems

• Drag-augmentation devices

• Electrodynamic tethers

• Solar sails