CIRCE 1, 2

CIRCE [Blue Canyon Technologies]

CIRCE (Coordinated Ionospheric Reconstruction CubeSat Experiment) is a collaborative space mission between the UK Defence Science and Technology Laboratory (Dstl) and the US Naval Research Laboratory (NRL) in developing small satellite ionospheric physics capability.

The overall aim of this collaboration is to build on our strong existing relationship in this area to address emerging priorities through joint research. Key areas of interest are improved space situational awareness, C4 (command, control, communications & computing), space weather and investigating options for affordable space capabilities.

The CIRCE mission objective is to accurately characterize the dynamic ionosphere. The mission is scheduled to launch in 2021, supported by the US DoD Space Test Program, and will be inserted into a circular 555 km ± 10 km orbit with a 90º ±5º inclination by a LauncherOne launch vehicle. CIRCE will exploit multiple sensor measurements across a two-satellite constellation to characterize the short-timescale dynamics in the ionosphere. The constellation consists of two near-identical 6U CubeSat buses, provided by Blue Canyon Technologies (BCT). The satellites will be flown in a 3-axis stable configuration, with the 2U × 1U axis facing the ram direction, and the 3U × 1U axis facing the nadir direction. The two spacecraft will use differential drag to achieve and maintain a lead-trail configuration, with an in-track separation of between 250 and 500 km, allowing for short timescale dynamics to be observed.

Each of the CIRCE CubeSats carries a complement of three UK and two US payloads. These instruments have all been contributed from academic, industrial and government partners across the two nations.

The UK contribution to CIRCE is the In-situ and Remote Ionospheric Sensing (IRIS) suite, complementary to NRL sensors and comprising three highly miniaturised payloads developed for Dstl by University College London (UCL), University of Bath, and Surrey Satellite Technology Ltd (SSTL), drawing on expertise from the University of Surrey. CIRCE will characterise a region of the space environment, the ionosphere, which is important for a range of defence and civil applications and can impact GPS, communications and sensing technology – both in space and on the ground.

Tthree payloads are provided by UK academia and industry:

• University College London’s Mullard Space Science Laboratory (UCL/MSSL) contribute the Ion and Neutral Mass Spectrometer (INMS). The objective is to improve understanding of the variability of atmospheric drag, the chemistry of the thermosphere and the impact of space weather on the upper-atmosphere.
• Surrey Satellite Technology Ltd (SSTL)/University of Surrey contribute the RadMon radiation monitoring payload.
• University of Bath contribute the TOPside ionosphere Computer Assisted Tomography (TOPCAT II), a tri-band GPS receiver that measures signal propagation delay to map the ionosphere.

The US payload consists of two identical instruments on each satellite:

• TRI-TIP (Tiny Ionospheric Photometer): The F-region of the ionosphere, occupying altitudes from ~150 to 500 km, emits several discrete wavelengths of far ultraviolet (FUV) light. Observing these emissions from space based sensors is ideal, as Earth’s lower atmosphere completely absorbs FUV wavelengths, so preventing any background light from the surface interfering with observations. These FUV emissions are known as “nightglow”, and are often used to observe and characterize the ionosphere.