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The little CubeSat as a customer

The small 6U (or 6 cubic units) Dellingr CubeSat, seen here in the lab before launch, carries two magnetometers designed…



The small 6U (or 6 cubic units) Dellingr CubeSat, seen here in the lab before launch, carries two magnetometers designed to measure the Earth’s magnetic field and an instrument called the Ion Neutral Mass Spectrometer , or INMS. INMS was designed to measure both ions and neutral particles in the Earth’s ionosphere, a volatile region in the atmosphere that expands and contracts in response to the electrifying influence of the sun. Credit: NASA

Zipping through the sky 250 miles up is a shoebox-size bundle detectors and electronics called Dellingr. The name of the mythological Norwegian goddess Dellingr is a new spacecraft called CubeSat. These small satellites, measured in standard 10-in-10-in-10-cubic centimeter units, weigh no more than a pound-bearing little resemblance to the larger spacecraft, such as the Hubble telescope NASA is known for. But SmallSats, which covers a wide range of sizes, including CubeSats, is an increasingly valuable tool in the space investigator’s arsenal.

But CubeSats is still in its infant, with mission’s success rates close to 50 percent. So, a team of scientists and engineers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, launched a quest. Their goal? To build a more resistant CubeSat-one that could handle the unavoidable accidents of the flight that do not hold any spacecraft without going hassle. They wanted a small CubeSat as a customer.

It was a different territory for them – an engineering practice of the highest quality. The team was used to build large spacecraft, with process layers, analysis and testing that make them reliable. Changing to CubeSats would require you to customize or, in some cases, create new processes and approaches, change organizational structures while working fast and on a limited budget. But it was an attempt to try, because the lessons they would definitely learn would benefit the entire CubeSat community. They started working in 2014 and after three years of development, Dellingr was ready to take flight.

Dellingr flies over his head and sends valuable scientific and technical data and elaborates on his final tricks. But Delling’s journey has been far removed: the story of launch, subsequent complications and successful fixes is a classic NASA story of perseverance and ingenuity.

Timeline

Aug. 14, 2017: Launch

Dellingr launched a space-X Falcon 9 rocket on NASA’s CRS-12 mission to revive the international space station. It was charged for the next three months until deployment.

Nov. 20, 2017: Distribution from ISS

Soon after EST’s dinner, the Dellingr team saw a live stream from the International Space Station jubling when Dellingr was released from the NanoRacks installer.

Nov. 20, 2017: Seconds later

When Dellingr fled from ISS, the team’s tension immediately turned to distress when they noticed small attachments that knocked out of spacecraft. A magnetometer designed to measure the Earth’s magnetic field, and an antenna already existed, even though it has been programmed for a 30-minute delay period after installation. Something was wrong.

Investigations showed that the spacecraft had unintentionally been in preparation for deployment, triggering of the magnetometer and antenna while still in the installation program and ran down the spacecraft’s power. Dellingr had been thrown into space with a dead battery.



Dellingr launches onboard CRS-12 missions on a Falcon 9 rocket. Credit: NASA / Tony Gray and Sandra Joseph

Fortunately, like most CubeSats, Dellingr does not depend on propulsion to stay in orbit. Although “dead” in the air, the little satellite leaned through space until its solar panels (covering each surface of the spacecraft) recharged the battery sufficiently. Eight hours later, Dellingr made his first pass over his ground station at NASA’s Wallops Flight Facility in Wallops Island, Virginia. Data from spacecraft showed that it was fully functional, had automatically pointed to the sun and had a healthy charge of the battery. Despite the diverting deployment, the spacecraft worked in a perfect way as designed.

Nov. 21 – 30, 2017: Evaporation

In addition to two magnetometers designed to measure the Earth’s magnetic field, Dellingr carries an instrument called Ion Neutral Mass Spectrometer, or INMS, which measures both ions and neutral particles in the atmosphere. The INMS instrument had never been fully validated in space. To show what it could do was an important goal for the mission. But before it could be put on, INMS needed to complete the degassing process, enabling harmful remains from the Earth’s atmosphere to be vaporized by spacecraft. Nothing to do but wait.

Nov. 30, 2017: Lost the Sun

Dellingr determines its orientation in part by finding the sun and tracing its position as it circles around the earth. By November 30th, the team had noticed that Dellingr did not lock on the sun and seemed to fiddle around in space. The spacecraft orientation control system revived its reaction wheels – which spin to lean spacecraft in one way or another – as it tried to correct the course.

But on the ground something did not look right. Dellingr has two sun pointers: a custom built, high precision and a commercially purchased and aviation state (albeit lower resolution) one. Only the custom sun pointer returned wildlife data. The spacecraft was not wobbling-the custom sun pointer malfunction.

Dellingr engineers uploaded the hotfix code to take it offline until they could figure out the root issue. But before they could do that, an even bigger issue arose.

Dec. 16, 2017: Lost of GPS

Less than a month in circulation, Delling’s commercial GPS system suddenly reduced its power, dropped in temperature and stamped to a halt. The GPS system was dead.

The loss of GPS meant that the team could not accurately determine Dellingr’s position – nor could they determine its direction of motion, which was crucial for correct orientation of the INMS instrument. INMS acts as a snowplow, kicks up ions and neutral particles on the front end of the spacecraft as it flies through space. With GPS, they can not be sure that the bucket turns in the right direction.

The team set Dellingr to minimal operation and started working on a plan for continuing without GPS. In mid-January, they had formulated a plan and began to prepare to implement it. But again a new problem arose.



Dellingr’s deployment to space from the International Space Station on November 20, 2017. Credit: NanoRacks

Jan. 27, 2018: Rescue Problems

Spacecraft in orbit breaks are always at risk for what are called occasional events that can distort spacecraft’s electrical signals, such as being fired by a high speed cosmic beam or energetic particle from the sun. To protect against occasional events, Dellingr is designed to complete once a day, full-spacecraft restore to stay healthy. This rescue had already protected spacecraft on several occasions. In addition to the daily reset, Dellingr will be reset if it sees an error. While a temporary recovery would not be worrying, Dellingr’s resettlement started in mid-January, triggering more often than they should. By January 27, Dellingr was restored every 63 seconds. Communication with the ground became impossible.

Jan. 28 – 5 February 2018: Hatching of a Plan

Dellingr was in a state of rescued induced paralysis. On the ground, the track tracked the reset problem to a row of code in a low level driver that involved the communication protocol used to control the response wheels used to orient the spacecraft. They needed to turn the reaction wheels off – but the constant restraints prevented them from completing the commanders to do it.

The team hatched a plan: On a pass over Dellingr’s base station at Wallops Flight Facility, they would send a repeated series of commands to spacecraft at a fast pace, which stuck the computer so that it never got far enough to recover. If they could pin it up for a long time, it would trigger a full power reset – equivalent to disconnecting the computer – buying time to charge the solution and turn off the spacecraft’s reaction wheel. It was a long shot, but still their best bet.

Feb. 6, 2018: Back to Business

On a pass over Wallops on February 6, the team tried the trick and waited 90 minutes for the next passport when they could check the results. Soon after they received an email from the land operator: “We confirm Dellingr back to business.” It worked.

Later that day, the team hit the INMS instrument, and the first real science measurements of the ions in the atmosphere with the new INMS instrument were collected. The Dellingr team had validated the jewel of the INMS instrument, which achieved one of the most important mission goals.

Feb. 10 – 5 March 2018: Reeling the wheels on

To solve the recovery problem, Dellingr engineers had shut down the spacecraft reaction wheel – the primary tool for reorientation. As a result, it could not remain stable and instead spun slowly through its circulation, collecting data only when the INMS instrument was rotated through the front where it could flush particles. After a while, the team realized that the wheels could be used for a minimum of up to 24 hours at a time without causing any reset. They developed a schedule to hit the wheels at the beginning of each week, adjust the orientation and shut them down for the rest. It worked for a while.

March 6, 2018: Spinning Problem

On March 6, it became clear that minimal use of the reaction wheels was not enough: Dellingr had entered an uncontrolled spin. Dellingr: The Small CubeSat As Customer “/>

Data from the Dellingr’s INMS Instrument from May 25, 2018, which shows valid detection of ions in the atmosphere. The Y-axis shows the number of particles detected, and the x-axis shows the measurement time (the chart extends over 1.5 hours). The lines in the plot rise and fall like rolling waves, because Dellingr tumbles through space, shoots particles when it tumbles in the correct orientation and misses them when it is not aligned properly. The forward orientation is called “frame” – when most of the particles are detected – called reverse-facing orientation “anti-ram”. Credit: NASA / Nick Paschalidis

In the next two months, the team worked with software solutions to control the speed of Dellingr’s spin without using the reaction wheels. The technology they settled based on the fact that magnets want to be customized. Earth is a giant magnet, and Dellingr contained three electromagnets that could be turned on and off the spacecraft. Using Delling’s magnetometers as an orientation tool to sense the Earth’s magnetic field and accurate timing when each onboard magnet was turned on, spacecraft could take advantage of the physics to slow down and adapt the spacecraft with its motion direction.

After the third implementation of the de-spin algorithm was uploaded and drove, the spacecraft was stabilized. Dellingr had come into a very slowly controlled spin and rolled like a wheel along its orbit. The INMS instrument is now rotated with a regular, predictable cadence.

The spacecraft in a controlled spin went INMS data from a noisy mess to clear periodic waves of data. After the rotation of the spacecraft was taken into consideration, the results were surprisingly pure, which showed the detection of ionized hydrogen (H +), helium (He +) and oxygen (O +) in the atmosphere.

Valid data from the INMS instrument in ion mode continue to flow. The neutral mode, which is somewhat more complicated, is still offline but is the focus of current efforts.

With a large program download that took several weeks due to CubeSat radio limitations, the team restored full control over the reaction wheels, so that Dellingr retained its orientation with respect to the sun. The solar panels can now be loaded for maximum power generation, as Dellingr slowly rotates about that shaft, collects data. Almost a year after the implementation, and after overcoming a rash of unexpected problems, the team had recovered a lot of Dellingr’s functionality. The operation of the INMS instrument’s neutral mode continues.

Dellingr already works as a testament to the unique challenges of packing big science into a small box. Keeping it alive and running for this long was an important goal. A standard mission’s lifetime for CubeSats has not been validated, and Dellingr’s mission can help create a benchmark. The team successfully achieved a robust spacecraft mission, while maintaining the low price range known for CubeSats. The added value of the assignment extends to others: papers are already published and describe the best practices learned from the assignment, and these lessons have contributed to the successful proposals for three new Goddard CubeSat missions: petitSat, GTOSat and BurstCube.

Exhibition not overlook, keep looking at the sky to follow the story of this little CubeSat as a customer.


Explore further:
NASA begins cashing on Dellingr spacecraft designed to improve the robustness of CubeSat platforms

More information:
Dellingr: Reliability lessons from orbit. digitalcommons.usu.edu/cgi/vie … 062 & context = smallsat

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