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The Solar Polar Orbiter

The Solar Polar Orbiter

The Solar Polar Orbiter (SPO) Technology Reference Study (TRS) examines the feasibility of a mission to obtain true solar polar orbit at an altitude of less than 0.5 AU to perform remote sensing of the Sun and in situ measurements of the surrounding environment.

Solar flare (SOHO/EIT ESA/NASA)

Scientific objectives

The Solar Polar Orbiter has the following scientific objectives:

  • image the global extent and dynamic effects of coronal mass ejections
  • discover the sources, longitudinal structure, rotational curvature and time variability of coronal features
  • link particle and field observations to images of the Sun, corona, and heliosphere at all latitudes
  • determine magnetic structures and convection patterns in polar regions
  • follow the evolution of solar structures over a full solar rotation

Mission Architecture

The Solar Polar Orbiter consists of a single spacecraft, launched on a Soyuz Fregat 2B from Kourou, French Guiana. The spacecraft will utilize a solar sail to lower its orbit to less than 0.5 AU before raising its inclination. After about 4 years the SPO spacecraft will achieve an inclination of approximately 83 degrees in the ecliptic coordinate frame. At this point the sail will be detached in order to perform undisturbed scientific measurements.

The Solar Polar Orbiter trajectory

Solar Sail

The preliminary concept for SPO employs a square solar sail with a total area of approximately 25 000 m². The characteristics of the sail are given in the table below.

Solar Sail Characteristics
Acceleration (mms-2) 0.42
Sail side 1 side (m) ~150
Sail Assembly loading (g/m²) 8
Sail material CP-1
Sail thickness 2 micron

Mass Budget

The preliminary mass budget is given in the table below, outlining the spacecraft and payload masses.

Mass Budget
Payload Mass 44 kg
Spacecraft Dry Mass 250 kg
Launch Mass 540 kg

The Challenges

Boom Deployment for Sail

The SPO Technology Reference Study is intended to identify the technologies required for a mission to a solar polar orbit. The main developments required for such a mission involve the use of a solar sail and are outlined below:

Solar Sail Material: A lightweight material needs to be developed with the required optical properties to reduce system mass and requirements. The optical properties of the sail must also be preserved during the sail phase.

Solar Sail Deployment: The development of a lightweight deployment structure for a very large (~30 000 m²) sail is required.

Lightweight booms: Developments of lightweight booms with a length approaching 100 m are required. Such booms should have a specific mass of less than 100 g/m.

Solar Sail Attitude Control: There are several options for performing attitude control. The options currently under consideration include a gimbaled boom between the sail and spacecraft, moving masses along the boom structure, and tip vanes or thrusters on the booms.

Solar Sail Jettison Mechanism: The sail must be jettisoned upon reaching the final orbit in order to prevent interference with the instruments. This separation must take place with a minimum risk of collision.

Study details

This study was completed in 2004. It was carried out by SRE-PAM with the assistance of the University of Glasgow.

Contact Information

For further information about this study please contact the study manager:

Dr. Peter Falkner
Head of Planetary and Solar System Exploration Studies Section (SRE-PAP)
Advanced Studies and Technology Preparation Division (SRE-PA)
European Space Agency, ESA-ESTEC
Postbus 299, NL-2200 AG Noordwijk, The Netherlands
tel: +31 71 565 5363

Last Update: 1 September 2019
11-Jul-2020 09:32 UT

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