Massachusetts Institute of Technology

Kerri Cahoy

Tam Nguyen Thuc Nguyen

Kathleen Michelle Riesing

David O Caplan

Christian Alexander Haughwout

Ryan Wallace Kingsbury

Paul Serra

James R Clark

Meghan K Quadrino

Anantha P Chandrakasan

Ruonan Han

Ezinne Uzo-okoro

Derek C Barnes

Maxim Oleg Khatsenko

Paula Do Vale Pereira

Ondrej Cierny

Hyosang Yoon

Femto-satellites are very small satellites that can be deployed in constellations from a larger mothership satellite for distributed measurement. They are too small to accommodate the GNSS receivers that many satellites use for navigation, but they can be located with an electromagnetic beam from the mothership satellite. The mothership satellite scans this beam across a constellation of femto-satellites. When the beam scans across a particular femto-satellite, the femto-satellite transmits an acknowledgement to the mothership satellite, e.g., by retroreflecting the beam or via a separate radio link. The beam can be modulated with commands for the femto-satellite, such as to make a measurement or transmit previously acquired data, as well with commands for determining the femto-satellite's location, such as a time stamp or beam pointing information. The femto-satellite can determine its location from the information modulated onto the beam or transmit the time stamp to the mothership satellite for localization.

Localizing, waking-up, and estimating direction of femto-satellites

Described is a spacecraft locker configured be deployed in outer space and configured to assemble satellites (e.g., CubeSats) within it and deploy them in outer space. In an embodiment, an unmanned spacecraft includes a housing configured to be deployed in a microgravity environment, the housing having an access point (e.g. a door), a storage area configured to store parts of a satellite, one or more robots movably positioned in the housing, and a controller configured to control at least one of the one or more robots to access parts from the storage area and to assemble the parts on an assembly platform of the housing. The controller may also control deployment of the assembled satellite through the door of the housing to a position in the microgravity environment.

Unmanned spacecraft and method for assembling satellites

A monostatic, beaconless fiber transceiver for free-space optical links infers fine tracking information using receiver optoelectronics and an injected pointing dither (nutation). A MEMS steering mirror fine-points the beams and injects the nutation. While this may disturb fiber coupling and transmit beam pointing, link loss becomes negligible for sufficient SNR. The SNR for links without point-ahead correction is about 35 dB to keep dither loss below 0.1 dB and RMS spatial tracking noise below a tenth of the beam divergence. Since the pointing and tracking bandwidth is much smaller than the receiver communication bandwidth, this SNR is achievable with appropriate filtering. For point-ahead correction, a single-mode fiber transceiver can reach up to about 1 beamwidth of correction, while a few-mode fiber transceiver can reach up to about 1.75 beamwidths due to improved coupling sensitivity at higher point-ahead offsets. Using a double-clad fiber with a secondary detector further reduces the incurred coupling loss.

Integrated track-and-receive system for free-space optical communications

Communication bottlenecks, particularly in the downlink direction, are a common problem for many CubeSat developers. As described herein, a CubeSat module for a CubeSat comprises an optical transmitter to transmit data to a remote terminal, a receiver to acquire an optical beacon from a remote terminal, and a fine-pointing module operably and directly coupleable to a coarse-pointing module of the CubeSat. The fine-pointing module is configured to point the optical transmitter toward the remote terminal with an accuracy range that overlaps with an accuracy range of the coarse-pointing module of the CubeSat so as to establish a communications link between the CubeSat and the remote terminal over a low-Earth-orbit (LEO) distance.

Free-space optical communication module for small satellites

A controllable shape memory alloy (SMA) hinge apparatus comprises multiple SMA elements to effect a first angle of rotation and a second angle of rotation between a first object and a second object. In one example, respective SMA elements are independently activated by Joule heating to rotate the first object and/or the second object. SMA elements undergo a three-dimensional transformation, and a pair of elements may undergo antagonistic transformations so as to provide for a multiple-use bidirectional non-continuous rotary actuator. SMA elements may be trained to achieve different angles of rotations between the objects (e.g., zero degrees and 90 degrees). In some examples, the first object may be a spacecraft (e.g., a satellite) and the second object may be a deployable structure (e.g., a robotic appendage, a deployable solar panel, a deployable aperture, a deployable mirror, a deployable radiator, and at least one actuator to steer an antenna dish).

Shape memory alloy (SMA) hinge apparatus, and systems and methods employing same

A beam steering system for a free-space laser communication system in a satellite includes a laser that emits a laser beam, a liquid lens assembly with at least one liquid lens to change the direction of the laser beam, and an amplifying optic to amplify the change in direction of the laser beam. The beam steering system may be used to steer a laser beam transmitted to another satellite or received from another satellite. In one example, a satellite may include two beam steering systems, disposed at opposing ends of a frame, where each steering system is configured to cover a hemisphere such that together, the steering systems can transmit and/or receive a laser beam over a 4&#x3c0; steradian sphere. The beam steering system may include a transmit feedback system and a reception system to monitor the direction and signal of the transmitted beam and the received beam, respectively.

Liquid-lens based optical steering system for free-space laser communication

Described herein are systems and methods for attitude determination using infrared Earth horizon sensors (EHSs) with Gaussian response characteristics. Attitude information is acquired by detecting Earth's infrared electromagnetic radiation and, subsequently, determining the region obscured by Earth in the sensors' fields of view to compute a nadir vector estimation in the spacecraft's body frame. The method can be applied when two sensors, each with known and distinct pointing directions, detect the horizon, which is defined as having their fields of view partially obscured by Earth. The method can be implemented compactly to provide high-accuracy attitude within small spacecraft, such as CubeSat-based satellites.

Attitude determination using earth horizon sensors

A portable optical ground station can track a satellite with an amateur telescope mounted on a two-axis gimbal. The telescope is aligned with respect to an inertial, Earth-fixed frame using a wide field of view star camera. Star cameras are accurate to the arcsecond level and have the advantage of providing orientation with a single measurement. Using multiple star sensor measurements at different gimbal angles, it is possible to calculate the alignment of the gimbals in the Earth-fixed frame and the alignment of the star sensor in the gimbal frame. Once the alignment is obtained, satellite tracking can be achieved with a known orbit and precise Earth rotation model, such as the International Earth Rotation and Reference System Service (IERS). This alignment procedure can be carried out in less than one hour, making it practical to move and deploy the portable ground station.

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Lexington, MA, United States of America

Kerri Cahoy