Onboard IMAP Subsystems
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Attitude Control Subsystem
The Attitude Control subsystem aboard the Interstellar Mapping and Acceleration Probe at the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland.
Image Credit: NASA/Johns Hopkins APL/Ed Whitman
A spacecraft's orientation in space in relation to its orbital path. Control System
IMAP’s attitude control system ensures the spacecraft and each instrument are pointed in the right direction when making measurements, as well as maintaining the rate IMAP spins and keeping the correct orbital path. It features a combination of star trackers and Sun sensors, software, and ground tools to estimate and control the spacecraft’s orientation while spinning at four revolutions per minute. It also executes correction maneuvers as needed to keep IMAP pointing, following its designated The curved path, usually elliptical, described by a planet, satellite, spaceship, etc., around a celestial body, such as the Sun; also called orbital path., and spinning correctly. The attitude control software uses its sensor measurements to estimate the attitude and spin rate of IMAP and then issues commands to the propulsion system thrusters to fire and move the spacecraft to precise positions. These commands from the attitude control system to the thrusters are communicated via the spacecraft Avionics system.
Propulsion
IMAP’s propulsion system enables the attitude control system to repoint the spacecraft, adjust its spin rate, correct its trajectory, insert it into orbit, and perform corrective maneuvers as needed to maintain its orbit. It features 12 thrusters, also known as rocket engine assemblies, and three tanks of hydrazine propellant. Because hydrazine is toxic, engineers take great care in filling the propulsion tanks to minimize risks.
Mechanical
The Mechanical subsystem is the physical structure of the IMAP spacecraft frame, or observatory. The IMAP observatory — including the instruments and subsystems — is about 10 feet (3 meters) in diameter, 5 feet (1.5 meters) tall, and weighs about 1,764 pounds (800 kilograms). It includes open bays so instruments have a clear field of view for measurements, and an 8-foot (2.5-meter) boom for the The Magnetometer (MAG) instrument measures the strength and direction of the magnetic field in interplanetary space as the field is carried past the IMAP spacecraft by the solar wind. It consists of two fluxgate magnetometers installed on a boom arm that will deploy post-launch, extending the instruments away from the spacecraft to minimize magnetic interference of spacecraft and instrument electrical systems. instrument’s A device used to measure the intensity and direction of the local magnetic field. sensors. The boom is tucked between the solar array on the Sunward side of the observatory for launch. In orbit, it unfolds with the MAG sensors attached, placing them away from any Any spacecraft generates a magnetic field, and that magnetic field changes with time. This field combines with (interferes with) the interplanetary magnetic field that a magnetometer is trying to observe. Luckily the spacecraft magnetic field gets smaller as you get farther from the main spacecraft. Putting a magnetometer out on a boom reduces the interference and so the magnetometer can get a more accurate measurement of the interplanetary magnetic field. from IMAP’s electrical systems.
Thermal Control
During IMAP’s A measure of the flow of events. in space, IMAP experiences A measure of the average random speeds of the microscopic particles in a substance. extremes from about -250 Abbreviated C. A unit of temperature. Zero degrees Celsius is equal to 273 Kelvin. Also known as centigrade. Water freezes at 0°C and boils at 100°C.Degrees Fahrenheit = Degrees Celsius *(9/5) +32. (-418 Abbreviated F. A unit of temperature. In the Fahrenheit scale, water freezes at 32 °F and boils at 212 °F. Degrees Celsius = (Degrees Fahrenheit - 32)*5/9.) on the bottom deck (which faces away from the Sun) to about 140 °C (284 °F) on the Sun-facing solar arrays located on the top deck. The thermal control system maintains IMAP’s temperature throughout the mission using a combination of external multi-layer insulation (MLI) (thermal blankets that surround the instruments and spacecraft) frame and thermostatically controlled heaters. The internal electronics also generate heat that can be used to keep internal temperatures warmer. To help excess heat radiate out into space, the surface of the bottom deck of the spacecraft is painted black, and small openings are strategically placed in the MLI to vent any gas that launches with IMAP.
Power
IMAP uses a solar array with solar cells mounted to the top deck of the spacecraft to generate power from sunlight during its mission to power the electronics for the instruments and subsystem components. The IMAP solar array converts sunlight into approximately 500 watts of power, which is more than sufficient, as the entire IMAP system consumes less power than five 100-watt incandescent light bulbs used in homes. A lithium-An atom that has become electrically charged by the gain or loss of one or more electrons. battery provides about 150 watts of power for when the solar array is without sunlight during launch. In orbit, IMAP’s spin axis, which comes through the center of the solar arrays, points sunward to provide constant power.
Radio The number of repetitions per unit time of the oscillations of an electromagnetic wave (or other wave). The higher the frequency, the greater the energy of the radiation and the smaller the wavelength. Frequency is measured in Hertz. (RF) Telecommunications
IMAP’s telecommunications system supports all IMAP communications, including those with NASA’s Deep Space Network (DSN), an international array of giant radio antennas that supports spacecraft mission communications. IMAP features fixed antennas on the top and bottom spacecraft decks and an X-band radio for scientists on Earth to communicate with IMAP, as well as allow it to transmit data back to Earth. The spacecraft’s uplink data rate is at 2 kilobits per second, while its downlink data rates measure between 375 and 500 kilobits per second. By comparison, the system’s data rate is at least 1,000 times lower than you would see with your home internet, but instead of a home network that extends about 50 meters, IMAP has to go about 1.6 million kilometers (more than 980,000 miles). Streaming a 4K movie requires as much bandwidth as IMAP needs to return a month’s worth of science data, while downloading a 50-gigabyte video game would take over nine days at IMAP’s downlink data rate.
IMAP also includes a The conditions and activity observed in interplanetary space caused by the Sun’s activity, such as solar flares, solar storms, and coronal mass ejections (CMEs). Severe space weather conditions directed towards Earth can impact infrastructure and technology on Earth, as well as satellites, spacecraft, and astronauts in its trajectory. broadcast, the IMAP Active Link for Real-Time (The IMAP Active Link for Reat-Time (I-ALiRT) system provides a high-cadence stream of near-real time space weather data from the HIT, CoDICE, SWAPI, SWE, and MAG instruments to scientists on Earth via a network of antenna partners located around the globe, including the DSN. This enhanced data stream will assist in improving overall reliability and timing of Earthbound space weather predictions, providing data to forecasters in time for users to take protective action.), to provide near-real-time space weather observations from a subset of the IMAP science instruments to scientists on Earth.
Avionics, Flight Software, and Autonomy
This system provides engineers with the necessary processors and software onboard the spacecraft to control and operate IMAP while in orbit. Additionally, a recorder is onboard to store collected science and engineering data for transmitting back to Earth. The autonomy system is part of the onboard software that allows IMAP to check onboard systems for unexpected conditions. Depending upon the severity of any unexpected measurement, the autonomy system can restore the spacecraft to its nominal operating state or configure it to a safe mode, maintaining the solar arrays pointed at the Sun and the RF telecommunications system in contact with ground mission operations control on Earth. The instructions are pre- programmed and extensively tested prior to launch. The entire avionics system is able to manage all of IMAP’s onboard spacecraft operations while using no more power than a typical 15-watt refrigerator light bulb.
Harness
The harness is comprised of wire bundles connected to all electrical components and instruments to distribute power and signals throughout the IMAP observatory. Since these wire bundles are used with sensitive electronics in the space environment, they have a special wrap of overlapping film or tape that creates inner and outer shields around the wires, reducing the electrical and magnetic interference for the instruments. The connectors have a backshell cover to protect where the wire connects to instruments and system components, as well as prevent the wires from over-bending.
Instruments
Learn more about the IMAP instruments: