Capella Space

Spotting mobile missile launchers in a timely fashion could allow the US to launch preemptive strikes, a plan known as “Kill Chain”. To tackle the North Korean threat, DIUx began by contracting with Orbital Insight in February 2017. The start-up, which is focused on turning advances in machine learning to satellite imagery, will build tools for the government that can analyze space radar data in real time.

In March 2017, DIUx signed a contract with Capella Space, a new company founded by former government engineers, to develop a constellation of small radar satellites. These will use Synthetic Aperture Radar or SAR, which builds up high-resolution images by making repeated passes over the same spot. Capella expected to launch the first satellite of an expected 30-36 by the end of 2017, but the delay-plagued business of launching satellites took its toll. Capella more than doubled the size of its antenna, which is expected to be able to obtain imagery at a resolution of one meter per pixel. The 36 spacecraft constellation will allow the company to scan any spot on Earth once every hour.

Remote sensing systems, such as radar systems used to detect the presence, position, speed and/or other characteristics of objects, are vital to both civilian and military operations. These systems utilize electromagnetic (EM) waves to detect, track and classify, for example, precipitation and natural/man-made objects. In operation, these systems typically transmit "beams" or signals toward targets, and process reflected return signals (or echoes) for target identification and characterization. Modern radar systems include phased array radar systems which utilize a plurality of selectively-controlled, parallel-processed, antenna elements making up an antenna.

SAR systems have been developed which may utilize, for example, a single transmitting antenna element mounted to a moving platform, such as a spacecraft. The antenna element may be used to form a single beam which is transmitted in pulses, repeatedly illuminating a portion or segment of a target area, and receive reflected signals including amplitude and phase data corresponding to illuminated segment of the target area. As the spacecraft travels relative to the target area, reflected signals from subsequent segments of the target area are obtained over a given period of time. Using this data, image processing algorithms may generate or reconstruct high-resolution images of the entire target area, electronically synthesizing an image which could only be obtained by a larger antenna (i.e. an antenna having a length equal to the velocity of the spacecraft multiplied by the time period).

In synthetic aperture radar (SAR) systems, the motion of the platform hosting the radar transmitter is used to synthesize a much larger antenna aperture, consequently resulting in a higher resolution than is possible with the smaller physical aperture used in typical radar systems. The characteristics or parameters of radar signals that are reflected from a target object can be employed to provide imagery of the target. Because these images are generated from radio frequency (RF) waveforms as opposed to visible light, radar images can typically be obtained in poor weather or when the target is obscured by foliage, fog, or cloud cover.

The performance of typical SAR systems can be characterized by examining an ambiguity function of the transmitted radar signal. The ambiguity function of the radar signal is related to the autocorrelation of the signal as a function of system parameters, time delay, and Doppler frequency shift. Ideally, the ambiguity function can be plotted as a narrow spike centered at the origin, with limited energy content along both the time and Doppler axis. Errors in interpreting the radar signal parameters in the pulsed radar signals, as reflected from the target object or terrain, can result in artifacts and degraded resolution that can affect the processed radar image. Radar signals, including linear frequency modulated (FM) chirp pulse trains employed in SAR systems, may have limited bandwidth and time duration, such that the fundamental radar system performance can be compromised. The critical parameter of time-bandwidth product (TW) for a linear frequency modulated chirp is constrained by radar system design factors, such as ambiguous range, peak pulse power, and coherent bandwidth of the RF electronics.

More than 60% of the costs of any SAR system are related to the receiving of RADAR pulses, the digitisation of the received pulses and the storage and onward transmission of the radar data. This can be further compounded if on-board SAR processing is employed to convert received radar pulses into a SAR image. A high proportion of this cost is associated with producing receivers capable of functioning on a space-borne platform. To reduce the costs of a SAR system the space-borne components of such a system should be limited to the transmission and/or reflection of radar pulses.

Most SAR systems transmit a bandwidth and waveform constrained by the system's ability to receive and digitise it. If the satellite segment is not used for reception then more adventurous waveform and bandwidths can be transmitted. These could potentially provide unique solutions to existing intelligence problems such as ultra high resolution and spectral diversity for building, ground or foliage penetration.

Satellite-based radar systems with aperture synthesis could utilize digital beam formation technologies. For this purpose, parts of the analog reception hardware are replaced by digital components, which will enhance the flexibility of such systems. The objective consists in obtaining radar images with a large capturing range (i.e. a large strip width) and, at the same time, high resolution. Due to the limited transmission power, a need exists for antennas with large aperture surface which are capable of electronically controlling the antenna lobe across a large angular range.

Reflector antennas are typically realized in the constructional designs of a paraboloid, a parabolic cylinder or a corner reflector. A further option according to the current state of the art resides in the use of planar array antennas, notably inter alia also with digital beam formation.

A Rocket Lab Electron malfunctioned during a launch 19 September 2023, resulting in the loss of a Capella Space radar imaging satellite. The Electron lifted off from Rocket Lab's New Zealand launch complex at 2:55 a.m. Eastern, and the rocket's first stage appeared to operate normally, However, onboard video from the rocket was lost right after stage separation, and telemetry showed the vehicle's speed decreasing, suggesting a problem with the upper stage's single Rutherford engine. Rocket Lab declared an anomaly moments later, but did not disclose additional details. The failure is the third for the Electron in a little more than three years, with the previous two involving issues with the upper stage. The rocket was carrying the second Acadia SAR satellite for Capella Space, after the previous Electron launch last month placed the first Acadia satelite into orbit.