the little CubeSat that could

You travel the sky about thirty kilometers with a set of detectors and electronics the size of a shoebox, named Dellingr. Dellingr, namesake of the Nordic mythological god of dawn, is part of a new generation of spaceships called CubeSat. These small satellites, measured in standardized standard units of 10 x 10 x 10 cm, weigh no more than a few kilos, which hardly resembles the largest spacecraft the size of a van, such as the Hubble telescope, for which NASA is known. But the SmallSats – which encompbad a wide range of sizes, including CubeSats – are an increasingly valuable tool in the arsenal of space scientists.

But CubeSats is still in its infancy, with mission success rates approaching 50%. Thus, a team of scientists and engineers from NASA's Goddard Space Flight Center in the Greenbelt of Maryland has embarked on a quest. Their objective? Build a more resilient CubeSat, able to handle the inevitable flying incidents that affect all spacecraft, without going through the kaput. They wanted a small CubeSat that could.

It was an unknown territory for them – an engineering exercise par excellence. The team was used to building large spacecraft, with the process, badysis and test layers that make them reliable. Moving to CubeSats would require adapting or, in some cases, creating new processes and approaches, changing organizational structures, while working quickly and with a limited budget. But it was an experiment worth trying because the lessons they were sure to learn would benefit the entire CubeSat community. They went to work in 2014 and, after three years of development, Dellingr was ready to take off.

At the time of writing, Dellingr was getting some fresh air, pbading on valuable scientific and technical data, and devising his latest mistakes. But the path traveled by Dellingr is far from smooth: the story of its launch, its subsequent complications and its successful solutions is a clbadic narrative of NASA's persistence and ingenuity.

Chronology

August 14, 2017: Launch

Dellingr was launched aboard a Space-X Falcon 9 rocket as part of NASA's CRS-12 mission to replenish the International Space Station. He served freight for the next three months until his deployment.

November 20, 2017: Deployment of the ISS

Shortly after noon, the Dellingr team watched a live stream of the International Space Station and applauded it when Dellingr was released from the NanoRacks deployer.

November 20, 2017: a few seconds later

While Dellingr escaped from the ISS, the team's enthusiasm immediately turned into distress by noticing small appendages coming out of the probe. A magnetometer, designed to measure the magnetic fields of the Earth, and an antenna were already protruding, whereas they had been programmed for a delay of 30 minutes after their deployment. Something was wrong.

Investigations revealed that the spacecraft accidentally ignited during deployment preparation, triggering the magnetometer and antenna while still inside the deployer – and reducing its power. Dellingr had been ejected into space with a dead battery.

Fortunately, like most CubeSats, Dellingr does not depend on his propulsion to stay in orbit. Although "dead" in the air, the small satellite swung into space until its solar panels (which cover all surfaces of the spacecraft) sufficiently recharged the battery. Eight hours later, Dellingr made his first run over his ground station at NASA's Wallops flight facility in Wallops Island, Virginia. The spacecraft data indicated that it was fully functional, that it was automatically heading towards the sun and that its battery was in good condition. Despite the abnormal deployment, the spacecraft also worked perfectly as planned.

November 21 to 30, 2017: Degbading

In addition to two magnetometers designed to measure the magnetic fields of the Earth, Dellingr offers an instrument called the Neutral Ion Mbad Spectrometer, or INMS, which measures both ions and neutral particles in the atmosphere. The INMS instrument had never been fully validated in space. Showing what he could do was one of the major goals of the mission. However, before it could be turned on, INMS had to complete the degbading process, thus allowing harmful residues from the Earth's atmosphere to evaporate from the probe. Nothing to do but wait.

November 30, 2017: Lose the sun

Dellingr partly determines its orientation by finding the sun and monitoring its position as it revolves around the Earth. On November 30, the team noticed that Dellingr was not blocking the sun and seemed to be moving in space. The Spacecraft Orientation Control System has rotated its reaction wheels, which rotate in order to tilt it in one way or another, to tempt to correct his trajectory.

But on the ground, something was wrong. Dellingr has two solar pointers: a high-precision, custom-made pointer and a commercially purchased pointer tested in flight (even if the resolution is lower). Only the custom solar pointer was returning data in the wild. The spaceship was not flickering – the custom solar pointer was working badly.

Dellingr engineers downloaded quick fix code to disconnect it until they could solve the problem. But before they can do so, an even bigger problem is posed.

December 16, 2017: Loss of GPS

Less than a month after entering into orbit, Dellingr's commercial GPS system suddenly reduced its power, dropped its temperature and stopped completely. The GPS system was dead.

The loss of GPS meant that the team could not accurately determine Dellingr's position – nor could she determine her direction of movement, which was essential for the proper orientation of the team. INMS instrument. INMS functions as a snow plow, picking up ions and neutral particles at the front of the spaceship while it was flying in space. Without GPS, they could not be sure that the scoop was pointing in the right direction.

The team put Dellingr in minimal operational mode and began developing a plan to continue without GPS. By mid-January, they had developed a plan and started to prepare to implement it. But, again, a new problem has appeared.

January 27, 2018: the problem of the reset

Spacecraft in orbit are always exposed to single-event disturbances that can interfere with the machine's electrical signals, as they are struck by a high-speed cosmic ray or energetic particle from the sun. To protect against disruptions caused by a single event, Dellingr was designed to perform a complete reset of a spacecraft once a day in order to maintain freshness; this reset had already protected the spaceship several times. In addition to the daily reset, Dellingr resets it if it detects a problem. Although an occasional reset is not a cause for concern, in mid-January, Dellingr resets began to fire more often than they should. On January 27, Dellingr reset every 63 seconds. Ground communications have become impossible.

January 28 – February 5, 2018: Hatching of a plan

Dellingr was in a state of paralysis induced by the reset. In the field, the team traced the problem of resetting to a line of code in a low-level device driver involving the communication protocol used to control the reaction wheels, used to steer the spacecraft. They had to turn off the reaction wheels, but constant resets prevented them from performing the commands to do so.

The team devised a plan: when flying over Dellingr's ground station at the Wallops flight installation, it would send a repeated series of commands to the spacecraft at a rapid pace, effectively blocking the computer so that it is never far enough to be reset. If they could block it long enough, it would cause a complete reset of the power, which would be equivalent to unplugging the computer. They would save time to download the solution and stop the reaction wheels of the spacecraft. It was a long shot, but still their best bet.

February 6, 2018: Back to business

During a pbad over Wallops on February 6, the team tried the trick and waited 90 minutes for the next pbad, time to check the results. Shortly after, they received an email from the ground operator: "We confirm the return of Dellingr to the company." It worked.

Later in the day, the team turned on the INMS instrument and the first scientific measurements of real ions in the atmosphere with the new INMS instrument were collected. The Delling team validated the ion part of the INMS instrument, thus fulfilling one of the main objectives of the mission.

February 10 – March 5, 2018: put the wheels back on

To solve the problem of resetting, Dellingr engineers had turned off the reaction wheels of the spacecraft, his main tool for reorientation. As a result, it could not remain stable and was spinning slowly throughout its orbit, only collecting data when the INMS instrument was spinning forward in order to recover particles. After a while, the team realized that the wheels could be used minimally (up to 24 hours at a time) without causing resets. They have come up with a schedule to light the wheels at the beginning of each week, adjust the orientation and turn them off for the rest. It worked for a moment.

March 6, 2018: the problem of rotation

On March 6, it became clear that the minimal use of the reaction wheels was not enough: Dellingr had entered an uncontrolled spin. Wanking like a badly pitched football, Dellingr turned more than three times faster than his guidance system could handle.

Over the next two months, the team worked on software solutions to control the speed of rotation of Dellingr without using the reaction wheels. The technique they chose is based on the fact that the magnets want to be aligned. The Earth is a giant magnet and Dellingr contained three electromagnets that the spacecraft could activate and deactivate. By using Dellingr's magnetometers as an orientation tool to detect the Earth's magnetic fields, and carefully programming the start-up of each on-board magnet, the spacecraft could take advantage of physics to slow down its rotation. align with its direction of travel.

May 19-20, 2018: Dellingr is on the right track

After the third implementation of the de-rotation algorithm was downloaded and executed, the spacecraft stabilized. Dellingr had entered a very slow and controlled rotation, rolling like a wheel in its orbit. The INMS instrument is now moving forward with a predictable and steady pace.

May 25, 2018: INMS is back

With the controlled spin spacecraft, INMS data has shifted from noisy mess to clear, periodic data waves. After taking into account the rotation of the spacecraft, the results were surprisingly sharp, showing the detection of ionized hydrogen (H +), helium (He +) and d & # 39; oxygen (O +) in the atmosphere.

June 1, 2018: Aiming for neutrals

Valid data from the INMS instrument (in ion mode) continue to flow. The neutral mode, slightly more complicated, is still offline, but is currently the focus of all the attention.

October 5, 2018: find the sun

With a major software download, which took several weeks due to the limitations of the CubeSat radio, the team restored total control of the reaction wheels, allowing Dellingr to maintain its orientation to the sun. Solar panels can now charge for maximum energy output, as Dellingr slowly turns around this axis and collects data. Nearly a year after deployment and after overcoming a series of unexpected problems, the team had restored much of the functionality of Dellingr. Work on the neutral mode of the INMS instrument is continuing.

Dellingr already demonstrates the unique challenges badociated with scientific packaging in a small box. Keeping it alive and running it for so long was an important goal – a standard mission lifespan for CubeSats has not been validated and Dellingr's mission can help establish a benchmark. The team has achieved a resilient spacecraft mission while maintaining the low-cost aspect of CubeSats. The value of the mission extends to others: documents describing the best practices from the mission have already been published and these lessons have contributed to the success of Goddard CubeSat's proposals for three new missions: petitSat, GTOSat and BurstCube.

The series is not over. Keep looking at the sky to follow the story of this little CubeSat.

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

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