NASA Astronomy Picture of the Day

Aug 16, 2023

Arp 93: A Cosmic Embrace

Locked in a cosmic embrace, two large galaxies are merging at the center of this sharp telescopic field of view. The interacting system cataloged as Arp 93 is some 200 million light-years distant toward the constellation Aquarius in planet Earth's sky. Individually the galaxies are identified as NGC 7285 (right) and NGC 7284. Their bright cores are still separated by about 20,000 light-years or so, but a massive tidal stream, a result of their ongoing gravitational interaction, extends over 200,000 light-years toward the bottom of the frame. Interacting galaxies do look peculiar, but are now understood to be common in the Universe. In fact, closer to home, the large spiral Andromeda Galaxy is known to be approaching the Milky Way. Arp 93 may well present an analog of their distant future cosmic embrace.

https://apod.nasa.gov/apod/astropix.html?

Talking with Webb using the Deep Space Network

Aug 15, 2023

NASA’s James Webb Space Telescope is nearly 1 million miles (1.5 million kilometer) away from Earth, orbiting around the Sun-Earth Lagrange point 2. How do we send commands and receive telemetry – the science and engineering data from the observatory – from that far away? We use the DSN (Deep Space Network) to communicate with the observatory. We receive data when we have a contact with Webb using a DSN antenna

Sandy Kwan, the mission interface manager for Webb within the DSN, notes that “each mesmerizing Webb image that has graced our screens would not have been possible without the support of the DSN antennas and personnel, the backbone of interplanetary communication.”

The DSN has three sites around the world, each positioned 120 degrees apart. There are antennas in Goldstone, California; Canberra, Australia; and Madrid, Spain. This allows us to communicate with Webb at any time of day, as the Earth rotates. The DSN is managed by NASA’s Jet Propulsion Laboratory (JPL) in Southern California. Kari Bosley, the lead Webb mission planner at the Space Telescope Science Institute (STScI), walks us through more of this communication process between Webb and the DSN.

“How do we plan contact time with Webb? It’s not as simple as picking up the phone and calling the telescope. In order for Earth to connect with Webb there are a few things that happen prior to scheduling a contact. On average, the Webb mission operations center connects with the observatory at least 2-3 times in a 24-hour period. There are mission planners at STScI where the Mission Operations Center (MOC) is located, mission schedulers at JPL, and of course at the DSN complexes. The mission planners at STScI work together with the mission schedulers at JPL to create contacts with Webb.

“How do we know when we can contact Webb? The Flight Dynamics Facility at NASA’s Goddard Space Flight Center sends the MOC at STScI the view periods in which the observatory is visible from those three different DSN sites. The mission scheduler compares those times to what is available in the scheduling system where other missions are competing for time with their spacecraft. All missions require specific amounts of time to communicate with their spacecraft, and the timing depends on where the spacecraft are in space. There are times when conflicts between multiple missions request the same resource at the same time. When this happens, our mission scheduler at JPL will negotiate with other missions to come to a compromise that satisfies all of the missions. Once all negotiations are complete, schedules are sent to the mission planners up to 6 months in advance. The scheduling for the first 8 weeks is fixed, with no changes allowed unless there is an emergency or important event with a spacecraft. The later periods are subject to continuing negotiations.

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“Each of the DSN complexes has different types of antennas, including 70-meter (230-foot in diameter), 34-meter (111-foot in diameter), and 26-meter (85-foot in diameter) antennas. The DSN complexes use the 34-meter antennas to talk with Webb with the 70-meter antennas as a backup. The DSN supports different radio frequency allocations, such as the S-band and Ka-band frequencies that Webb uses. S-band has a lower bandwidth, and we use that to send commands to the spacecraft (e.g., start recorder playback), to receive engineering telemetry to monitor the health and safety of the observatory, and for ranging. Ranging is the process of determining Webb’s position and trajectory by the delay between when the signal is sent up and when it is received back on the ground.

“We use Ka-band to downlink stored science and engineering data, and some telemetry from the spacecraft. If we used S-band to downlink data, it would take many days to download each day’s data. With Ka-band, it takes much less time, and we can usually complete download all of the stored data in a couple of hours. The high gain antenna on Webb is used for Ka-band downlink and the medium gain antenna is used for S-band uplink and downlink when both antennas are pointed directly at the complex for a contact. Most of our contacts are 2-6 hours in length.

Normally, we request at least 4-hour contacts. Since DSN hosts almost 40 different missions, scheduling is complicated.

“There are times when our contacts are very short and times when they are longer. In each contact, it is important to downlink as much data as we can since the telescope continually makes science observations and acquires more data. When we are not in contact, the telescope continues to autonomously perform science observations. These data are stored on a solid-state recorder and downlinked on our next contact. After the Webb MOC at STScI receives the data and ingests them into the Barbara A. Mikulski Archive for Space Telescope for processing and calibration, the observers will receive the data from their observations.

https://blogs.nasa.gov/webb/2023/08/15/talking-with-webb-using-the-deep-space-network/

https://eyes.nasa.gov/dsn/dsn.html

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XRISM Spacecraft Will Open New Window on the X-ray Cosmos

Aug 15, 2023

The upcoming XRISM (X-ray Imaging and Spectroscopy Mission, pronounced “crism”) spacecraft will study the universe’s hottest regions, largest structures, and objects with the strongest gravity.

Led by JAXA (Japan Aerospace Exploration Agency), XRISM will peer into these cosmic extremes using spectroscopy, the study of how light and matter interact. In this explainer, video producer Sophia Roberts from NASA’s Goddard Space Flight Center walks us through how understanding spectroscopy deepens our knowledge of the universe.

“I think we all get excited for the beautiful images we get from missions like NASA’s James Webb Space Telescope,” Roberts said. “But after taking a deep dive into spectroscopy, I really appreciate the critical context it gives scientists about the story behind those pictures.”

XRISM’s microcalorimeter spectrometer, named Resolve, is a collaboration between JAXA and NASA. It will create spectra, measurements of light’s intensity over a range of energies, for X-rays from 400 to 12,000 electron volts. (For comparison, visible light energies range from about 2 to 3 electron volts.)

To do this, Resolve measures tiny temperature changes created when an X-ray hits its 6-by-6-pixel detector. To measure that minuscule increase and determine the X-ray’s energy, the detector needs to cool down to around minus 460 Fahrenheit (around minus 270 Celsius), just a fraction of a degree above absolute zero. The instrument reaches its operating temperature after a multistage mechanical cooling process inside a refrigerator-sized container of liquid helium.

Resolve will help astronomers learn more about the composition and motion of extremely hot gas within clusters of galaxies, near-light-speed particle jets powered by black holes in active galaxies, and other cosmic mysteries.

The Webb telescope captures similar spectra, but for infrared light. Webb’s spectra have revealed the makeup of gas near active black holes and mapped the movement of this material toward or away from the viewer. Data from XRISM’s Resolve instrument will do the same at higher energies, helping paint a fuller picture of these objects.

XRISM is a collaborative mission between JAXA and NASA, with participation by ESA (European Space Agency). NASA’s contribution includes science participation from the Canadian Space Agency.

https://www.nasa.gov/feature/feature/2023/xrism-spacecraft-will-open-new-window-on-the-x-ray-cosmos

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